Versatile coordination behaviour of an asymmetric half-salen ligand bearing a dansyl fluorophore

Versatile coordination behaviour of an asymmetric half-salen ligand bearing a dansyl fluorophore María J. Romero, a Rosa Pedrido,* a,b Ana M. González-Noya, a,b Marcelino Maneiro, b M. Isabel Fernández-García, b Guillermo Zaragoza, c Manuel R. Bermejo* a a Departamento de Química Inorgánica, Centro Singular de Investigación en Química Biolóxica e Materiais Moleculares (CIQUS), Universidade de Santiago de Compostela, Santiago de Compostela, Galicia, E-15782, Spain b Departamento de Química Inorgánica, Facultade de Ciencias, Universidade de Santiago de Compostela, Lugo, Galicia, E-27002, Spain c Unidade de Difracción de Raios X, Edificio CACTUS, Universidade de Santiago de Compostela, Campus Sur, Santiago de Compostela, Galicia, E-15782, Spain Page 3 of 56 Dalton Transactions Graphical abstract The versatility in coordination of the asymmetric half-salen ligand bearing a dansyl fluorophore [H 2 L] has been probed after the isolation of its luminescent complexes, which display a great structural diversity. Page 4 of 56Dalton Transactions Abstract The coordinative chemistry of the tridentate half-salen ligand 5-(dimethylamino)-N-(2hydroxybenzylidene)amino)phenyl)naphthalene-1-sulfonamide (H 2 L, 1) has been studied by means of an electrochemical method. All of the complexes have been characterised using analytical and spectroscopic techniques. Ligand 1 and two nickel (6 and 7), copper (9), zinc (12) and cadmium (14) metal complexes have been studied by crystallography. Complexes 6 and 7 are octahedral and tetrahedral nickel(II) complexes, respectively, and both contain an [L] 2– molecule that behaves in an [N 2 O] tridentate manner. Nickel(II) completes its coordination kernel with three water molecules in complex 6, whereas in complex 7 the nickel ion is further bound to a molecule of dansylamine arising from a hydrolysis process. The copper(II) complex 9 is a monomeric compound that contains a bideprotonated ligand thread and a dimethylsulfoxide molecule coordinated through the sulfur atom. The zinc complex 12 is an unusual pentanuclear cluster compound whose structure consists of four anionic ligand units and two hydroxo anions bound to five zinc(II) centres. The appearance of the hydroxo anions in this complex provides new evidence for water reduction electrochemically promoted by zinc metal under mild conditions. The cadmium complex 14 is a dimeric compound that comprises two molecules of the anionic ligand and two dimethylsulfoxide molecules. The great structural variety exhibited by all these complexes demonstrates that the introduction of asymmetry in a salen skeleton by incorporating a dansyl pendant increases the versatility of the resulting ligand on coordination. All complexes are luminescent in solution at room temperature in acetonitrile solutions. Page 5 of 56 Dalton Transactions Introduction Polydentate ligands containing [N,O] donor atoms have been commonly used to form polynuclear complexes, 1 which may have interesting structures and occasionally exhibit novel properties. In particular, N,N'-bis(salicylidene)ethylenediamine (salen) derived ligands show a rich coordination chemistry with a wide variety of metal ions and are considered to be amongst the most useful imine ligands for the assembly of polynuclear compounds. 2 Furthermore, salen-derived complexes have attracted a great deal of interest due to their use as catalysts 3,4 and also their potential as models to mimic the binding sites in metalloenzymes. 5 Thus, for example, our group has employed salen Schiff base ligands to assemble polynuclear complexes that could model the behaviour of the Photosystem II, 6 the peroxidase or the catalase enzymes. 7 The majority of work has been focused on the study of symmetrical salen ligands and the non-symmetrical derivatives have received less attention, despite the fact that structural asymmetry is believed to allow better control over the catalytic properties of the ligated metal. The asymmetry in salen derivatives is normally achieved by the introduction of different substituents on the diamine or salicylaldehyde precursors. An alternative to this strategy involves the design of the so-called half-salen ligands, i.e. those obtained after condensation of salicyladehyde with different monoamines. We used the above approach to design a half-salen ligand derived from salicyladehyde and the dansyl-functionalized amine N-(2-aminophenyl)-5-(dimethylamino)-1naphthalenesulfonamide. This new ligand provides a tridentate [N 2 O] donor set and coordination number asymmetry in tandem. The incorporation of the dansyl fluorophore in the ligand (present in many fluorescent sensors and labels, 8 as well as in larger supramolecular structures, 9,10 and characterised by high emission quantum yields) will allow us to gain simultaneous control of the steric crowding around the metal centre and to achieve asymmetry in the coordination environment – a characteristic that could give rise to novel catalytic and photophysical properties. The results obtained are discussed below. Results and discussion Synthesis of the ligand The [N 2 O] tridentate ligand H 2 L 1 was obtained by condensation of salicylaldehyde and N-(2-aminophenyl)-5-(dimethylamino)-1-naphthalenesulfonamide following the Page 6 of 56Dalton Transactions previously described methodology 11 (Scheme 1). Recrystallization of 1 from chloroform yielded crystals the structure of which was determined by X-ray diffraction. NH 2 NH 2 S OO Cl N NH 2 NH S OO N - HCl NEt 3 - H 2 O CHCl 3 N NH S OO N OH Salicylaldehyde + H2L CHCl 3 ADs Scheme 1. Synthesis of the ligand H 2 L 1. Synthesis of the complexes Neutral metal complexes from the ligand H 2 L 1 were obtained by an electrochemical methodology. 12 Oxidation of the metal anode in an acetonitrile solution containing 1 and a small amount of tetraethylammonium perchlorate as supporting electrolyte, gave rise to electrochemical efficiency values close to 0.5 mol·F –1 for M(II) complexes (M = Mn, Fe, Co, Ni, Cu, Zn, Cd, Sn and Pb) and a value of 1.0 mol·F –1 for the Ag(I) complex. These values are in good agreement with reaction mechanisms involving two and one electrons per coordinated metal, respectively. The case of zinc warrants special attention because the electrochemical synthesis afforded a trinuclear oxo-zinc cluster, the formation of which also involves the reduction of a coordinated water molecule during the synthesis. 11 Analytical and spectroscopic data The electrochemical methodology allowed us to obtain neutral compounds with formulae M(L)·nH 2 O for divalent metal ions (M = Mn, Fe, Co, Ni, Cu, Sn and Pb; n = 3, 4) and Ag 2 (L)·3H 2 O for the silver(I) complex. The zinc and cadmium complexes have the formulae [Zn(H 2 O) 6 ][Zn 3 (L) 3 (µ 3 -O)] 11 and Cd 2 (L) 2 ·4H 2 O, respectively. Page 7 of 56 Dalton Transactions All of these complexes were obtained in good yield and with high purity. The compounds show air and thermal stability and melt above 300 ºC without decomposition. The molar conductivity values are consistent with non-electrolytic compounds. 13 Mass spectrometry and IR spectroscopy The formation of the ligand H 2 L 1 and its derived metal complexes was confirmed by ESI+ and infrared spectra (see Experimental section). The existence of peaks corresponding to the species [ML + H] + in the mass spectra of the complexes confirms the coordination of 1 to the different metal ions. Moreover, the spectrum of the Ag(I) complex exhibits a peak assignable to [M 2 L + 2H] + , which is consistent with the dinuclear stoichiometry proposed for this compound. The spectrum of the dimeric complex [Cd 2 (L) 2 ·4H 2 O] displays the signal corresponding to the species [M 2 L 2 + H] + , implying that its nature (see below) is retained in solution. The band at 3221 cm –1 assignable to the ν(OH) + ν(NH) vibrational mode present in the ligand is not observed in the spectra of the metal complexes, which may indicate that the ligand coordinates to the metal ions in its dianionic form through the deprotonated phenol oxygen and sulfonamide nitrogen atoms. The general displacement of the ν(C=N + C–N) bands to lower frequencies confirms the coordination of the imine and sulfonamide nitrogen atoms to the metal centres. The presence of ν(OH) bands at around 3440 cm –1 confirms the hydrate nature suggested by the analytical data for all the complexes. Page 8 of 56Dalton Transactions ppm 6.57.07.58.08.59.09.510.010.511.011.512.0 N NH S OO N OH H 2 H 6 H 5 H 4 H 3 H 1 H 8 H 7 H 11 H 13 H 10 H 9 H 14 H 12 H 15 H 16 H 17 H 18 H 1 H 5 H 6 H 4 H 1 H 3 + H 4 H 5 H 2 H 7 + H 8 H 9 + H 10 H 11 + H 12 + H 13 H 14 + H 15 H 16 + H 17 H 5 H 5 H 5 H 4 H 4 H 3 H 3 H 4 H 3 H 3 H 6 H 6 H 6 H 6 + H 7 H 8 H 9 + H 10 H 11 + H 13 H 15 H 12 + H 14 + H 16 H 17 H 17 H 17 H 7 + H 8 H 10 + H 13 + H 15 H 12 H 14 + H 16 H 9 + H 11 H 12 + H 14 H 7 + H 8 H 16 H 13 + H 10 + H 15 H 9 + H 11 H 7 + H 8 + H 9 H 16 + H 17 H 12 + H 15 H 10 H 11 + H 13 (a) (b) (c) (d) (e) H 14 ppm 6.57.07.58.08.59.09.510.010.511.011.512.0 N NH S OO N OH H 2 H 6 H 5 H 4 H 3 H 1 H 8 H 7 H 11 H 13 H 10 H 9 H 14 H 12 H 15 H 16 H 17 H 18 N NH S OO N OH H 2 H 6 H 5 H 4 H 3 H 1 H 8 H 7 H 11 H 13 H 10 H 9 H 14 H 12 H 15 H 16 H 17 H 18 H 1 H 5 H 6 H 4 H 1 H 3 + H 4 H 5 H 2 H 7 + H 8 H 9 + H 10 H 11 + H 12 + H 13 H 14 + H 15 H 16 + H 17 H 5 H 5 H 5 H 4 H 4 H 3 H 3 H 4 H 3 H 3 H 6 H 6 H 6 H 6 + H 7 H 8 H 9 + H 10 H 11 + H 13 H 15 H 12 + H 14 + H 16 H 17 H 17 H 17 H 7 + H 8 H 10 + H 13 + H 15 H 12 H 14 + H 16 H 9 + H 11 H 12 + H 14 H 7 + H 8 H 16 H 13 + H 10 + H 15 H 9 + H 11 H 7 + H 8 + H 9 H 16 + H 17 H 12 + H 15 H 10 H 11 + H 13 (a) (b) (c) (d) (e) H 14 Figure 1. Overlapped 1 H NMR spectra for the ligand H 2 L (a) and the complexes Ag 2 (L)·3H 2 O (10) (b), [Zn(H 2 O) 6 ][Zn 3 (L) 3 (µ 3 -O)] (11) (c), Cd 2 (L) 2 ·4H 2 O (13) (d) and Pb(L)·4H 2 O (16) (e) registered in DMSO-d 6 . NMR studies The 1 H NMR spectra of the free ligand 1 and its silver (10), zinc (11), cadmium (14), tin (15) and lead (16) complexes were recorded in DMSO-d 6 at room temperature. These compounds were stable in DMSO with the exception of the tin complex (15), which decomposed in solution. Assignments were made by means of 2D COSY experiments. Page 9 of 56 Dalton Transactions Comparison of the spectra of the ligand 1 and its diamagnetic complexes (Figure 1) leads us to highlight the following aspects: (i) The signals corresponding to the phenol OH (H1) and sulfonamide NH (H2) protons (in the free ligand at 11.7 ppm and 10.1 ppm, respectively) are absent from the spectra of the Zn(II), Cd(II) and Pb(II) complexes, thus confirming the dianionic character of the ligand in these complexes. In the case of the Ag(I) complex a broad signal at around 11 ppm, corresponding to the proton H1, is observed and this can be attributed to demetallation of this compound during the NMR experiment; (ii) The imine proton signal (H5) is shifted downfield in all complexes as a result of the coordination to the metal centres through the imine nitrogen; (iii) The dansyl aromatic and phenyldiamine ring protons are affected to the greatest extent by coordination, depending on the different arrangement adopted by the rings in the metal complexes. Figure 2. 113 Cd NMR spectra for the complex [Cd 2 (L) 2 ·4H 2 O] (13) (a) and 207 Pb NMR spectra for the complex Pb(L)·4H 2 O (16) (b) in DMSO-d 6 . In order to obtain further information about the coordination environments of the silver, cadmium, tin and lead complexes in solution we recorded their 109 Ag, 113 Cd, 119 Sn and 207 Pb NMR spectra in DMSO-d 6 at room temperature. Unfortunately, the low solubility of the silver compound in DMSO-d 6 (and other deuterated solvents) and the instability of the tin complex meant that a signal was not obtained in the spectra of either compound. Page 10 of 56Dalton Transactions The chemical shift value obtained for the cadmium complex 13 [74.9 ppm, Figure 2(a)] in DMSO-d 6 solution is consistent with an [N 2 O 4 ] hexacoordinated environment for each metal ion, as observed in the solid state. It is well established that an increase in the coordination number usually results in a more shielded nucleus. 14 Taking this into account, the assignment for compound 13 is supported by comparison with the signal at 38 ppm in the [N 3 O 4 ] cadmium complex Cd(H 2 daps)(H 2 O) 2 reported by us 15 and the values found in other [N 3 O 4 ] and [N 2 O 5 ] heptacoordinated compounds. 16,17 Besides, a nitrogen donor atom produces a weaker shielding effect compared with an oxygen atom. 16,18 This fact is illustrated for those compounds that have an [N 4 O 2 ] kernel, for which more shielded values have been reported (e.g. 51 ppm). 19 Very few 207 Pb NMR studies have been reported in the literature for hexaand heptacoordinated Pb(II)/Pb(IV) complexes containing nitrogen and oxygen donor atoms in the metal ion coordination sphere. 15,20,21 The signal at –625 ppm in the lead complex Pb(L)·4.5H 2 O (16) [Figure 2(b)] indicates a more shielded nucleus than in the case of the previously reported hydrazone complex [Pb(Hdaphs)(CH 3 COO)], which has an [N 2 O 4 ] kernel (–490.0 ppm). 15 On the other hand, we found literature 207 Pb NMR chemical shifts for Pb(II) complexes with environments corresponding to [N 2 O 4 ] (–520, –772 ppm) 20 and [N 2 O 5 ] (–1100 ppm) 21a donor systems. The differences between chemical shifts in these hexacoordinated compounds could be explained in terms of the coordination geometries adopted, 14 which depend on the nature of the ligand and also on the existence of a stereochemically active lone pair in the lead atom. Considering this approach, we tentatively propose a hexacoordinated environment around the Pb(II) ion that involves the [N 2 O] kernel of the dianionic ligand and three oxygen atoms from DMSO molecules. Structural characterization The structure of the ligand H 2 L (1) (see SI) and nickel(II), copper(II), zinc(II) and cadmium(II) complexes could be determined by X-ray diffraction. [Ni(L)(H 2 O) 3 ]·H 2 O·(CH 2 CH 3 ) 2 O (6) and [Ni(L)(ADs)] (7) Recrystallization of the powdery nickel complex 5 from an acetonitrile/diethyl ether mixture afforded single crystals of [Ni(L)(H 2 O) 3 ]·H 2 O·(CH 2 CH 3 ) 2 O (6) and [Ni(L)(ADs)] (7). The quality of the data for 7 did not allow refinement to a satisfactory level, although we trust the gross structural features. Compounds 6 and 7 (Figures 3 and Page 11 of 56 Dalton Transactions Scheme 2. Proposed mechanism for the formation of 11 and 12. The mechanism proposed for the formation of complexes 11 and 12 would initially involve a common redox route in the electrochemical cell (Scheme 2). In the first stage, the zinc anode undergoes an oxidation to generate Zn 2+ ions, while the sulfonamide N–H and phenoxo O–H bonds from the ligand H 2 L are reduced to give the bideprotonated [L] 2– and hydrogen gas. The coordination of two bideprotonated ligands to two Zn(II) ions would result in the dimeric compound Zn 2 (L) 2 (Figure S2) with µ 2 -phenoxo bridges between the two metal centres (I). 32 The particular coordinative preferences of Zn(II) would provide a suitable kernel for coordination of one additional water molecule from the medium to one of the metal centres, thus one of the zinc(II) ions achieves a pentacoordinated environment (II). At this point the dimer could undergo two different processes: (a) two consecutive reduction processes 33 to afford an O 2– anion that would complete the pentacoordinated environment of a third metal centre in the main product ([Zn 3 (L) 3 (µ 3 -O)] 2– ) 11 (Scheme S1), or (b) a secondary route in which the water molecules of two close dimers (a ‘double dimer’) would be 1e – reduced each to hydroxo groups. Since the electrochemical oxidation of the Zn plate would continue in the cell, [Zn(H 2 O) 6 ] 2+ Page 18 of 56Dalton Transactions ions would be released into the medium and, given that the ‘double dimer’ also posseses four oxygen donor atoms that are susceptible to coordination, it would be feasible for the incorporation of a fifth metal centre, thus generating the pentanuclear cluster 12. Figure 8. Crystal structure of the cadmium(II) complex [Cd 2 (L) 2 ((CH 3 ) 2 SO) 4 ]·(CH 3 ) 2 CO (14). [Cd 2 (L) 2 ((CH 3 ) 2 SO) 4 ]·(CH 3 ) 2 CO (14) Recrystallization of solid 13 from an acetonitrile/dmso mixture afforded yellow crystals of [Cd 2 (L) 2 ((CH 3 ) 2 SO) 4 ]·(CH 3 ) 2 CO (14). This complex is a cadmium(II) dimer comprising two molecules of tridentate ligand coordinated in an anionic mode to two Cd(II) ions (Figure 8), with the coordination sphere of each metal centre completed with two dimethylsulfoxide molecules. Additionally, the complex is solvated with one acetone molecule. This compound shows an [N 2 O 4 ] distorted octahedral coordination geometry for each Cd(II) with the equatorial plane defined by one molecule of [L 2– ] through the imine and sulfonamide nitrogen atoms (N1, N2) and the phenol oxygen Page 19 of 56 Dalton Transactions atom (O1). The fourth equatorial site is filled by one phenol oxygen atom from a neighbouring ligand, which behaves as a µ 2 -oxo-bridge between the two metal atoms. The axial positions are occupied by two dmso molecules coordinated through the oxygen atom (O4, O5). The establishment of µ 2 -oxo bridges affords a four-membered metallacycle constituted by the two cadmium(II) ions and the phenol oxygen atoms [Cd1–O1–Cd1'–O1']. The intermetallic Cd···Cd distance (3.5 Å) is longer than the sum of van der Waals radii corresponding to the cadmium atoms (3.2 Å), 31,35 indicating that intermetallic interactions are not present. The bond distances Cd1–N1 [2.322(4) Å], Cd1–N2 [2.271(4) Å], Cd1–O1 [2.310(3) Å] and Cd1–O1' [2.215(3) Å] are consistent with the values found in other dimeric cadmium(II) complexes derived from [N 2 O] donor ligands. 34 The different bond distance values of the equatorial bonds (Cd1–O1 and Cd1– O1') point to the asymmetry of the two µ 2 -oxo bridges (see Table 2). Thus, the shorter distances are observed for the metal ion bound to the phenol oxygen atom of the neighbouring ligand. The axial bonds Cd1–O4 [2.350(4) Å] and Cd1–O5 [2.371(4) Å] have values within the expected range. It is worth mentioning that the phenol and the phenyldiamine rings in complex 14 do not adopt a coplanar arrangement –in contrast to the previously discussed complexes 6 and 9. However, the spatial orientation of the dansyl group is comparable to that adopted in complexes 6 and 9, since it features a dihedral angle of 70.31(12)º with the phenyldiamine ring. Page 20 of 56Dalton Transactions Figure 9. Overlapped fluorescence emission spectra recorded in acetonitrile for the ligand H 2 L 1 and its metal complexes (1 × 10 –5 −3 × 10 –6 M). Uv-Vis and luminescence emission studies The Uv-Vis absorption spectra of the ligand H 2 L and its metal complexes were measured in acetonitrile. All of the spectra exhibit intense bands in the near UV region (ε = 10 4 −10 5 mol –1 dm 3 cm –1 ), indicating highly π-conjugated systems (Figure S6). Additionally, the spectrum of the ligand shows a single broad charge transfer band at 342 nm assignable to n→π∗ transitions. The absorption spectra corresponding to the metal complexes display several bands within the range 300–430 nm, which could be attributed to the ligand-to-metal charge transfer (LMCT) transitions; these bands are generally red-shifted with respect to those in the free ligand. With the aim of evaluating the effects caused by the different metal ions on the photophysical properties of the ligand, we recorded the fluorescence emission spectra of all complexes in acetonitrile at room temperature (Figure 9). The spectrum of H 2 L 1 exhibits a single broad emission band at 525 nm (excitation at 350 nm) for which the calculated fluorescence quantum yield was Φ = 7 × 10 –4 (Table 4). All of the metal complexes derived from H 2 L show fluorescence emission characterised by a single band (Figure 9) that may be attributed to the fluorescence from the intraligand (IL) excited Page 21 of 56 Dalton Transactions state. This band is slightly blue-shifted in the spectra of the iron(II) (3), nickel(II) (5), copper(II) (8) and zinc(II) (11) complexes, probably due to the effect of coordination of the dansylamide moiety in a deprotonated mode. 35 In contrast, the emission band corresponding to the manganese complex 2 experienced a strong red-shift to higher wavelengths (Table 4), while cobalt(II) and silver(I) showed only minor red-shifts. The coordination of the ligand H 2 L 1 to the different metal ions gives rise to an enhancement in the fluorescence emission in the cases of nickel(II) (5), silver(I) (10), zinc(II) (11), tin(II) (15) and lead(II) (16) complexes, as indicated by their quantum yields. The lowest quantum yield is shown by the cobalt(II) complex 4, although in this case the fluorescence is not completely quenched and a weak emission can still be observed. Conclusions The results obtained in this work provide evidence for the versatility of the asymmetric half-salen ligand H 2 L on coordination, as demonstrated by the great structural variety exhibits by the reported complexes (mononuclear [Ni(II) and Cu(II)], dinuclear [Cd(II)] or higher nuclearity [Zn(II)] species). As expected, the presence of the dansyl fluorophore in this asymmetric ligand makes all metal complexes to be luminescent. And most interesting, high nuclearity Zn(II) complexes were obtained as result of a water reduction process in the electrochemical cell mediated by zinc(II) ions under mild conditions. Experimental Materials All solvents, o-phenylenediamine, triethylamine, dansyl chloride, salicylaldehyde and tetraethylammonium perchlorate are commercially available and were used without further purification. Metals (Ega Chemie) were used as ca. 2 × 2 cm 2 plates, except manganese, which was employed as a platelet. Physical measurements Elemental analysis (C, H, N and S) was performed on a FISONS EA 1108 analyzer. 1 H and 13 C NMR spectra were recorded on a Varian Mercury 300 spectrometer and multinuclear 109 Ag, 113 Cd, 119 Sn and 207 Pb NMR spectra were recorded on a Bruker Page 22 of 56Dalton Transactions AMX-500 spectrometer. All the spectra were registered using DMSO-d 6 as deuterated solvent and the chemical shifts are expressed relative to tetramethylsilane ( 1 H and 13 C NMR), 0.1 M Cd(ClO 4 ) 2 ( 113 Cd NMR) and neat tetramethyllead using a saturated solution of PbPh 4 in CDCl 3 (–178 ppm) as external reference ( 207 Pb NMR). Infrared spectra were measured as KBr pellets on a BRUKER IFS-66V spectrophotometer in the range 4000–100 cm –1 . Electrospray ionisation (ESI) mass spectra were registered on an API4000 Applied Biosystems mass spectrometer with Triple Quadrupole analyser. Matrix Assisted Laser Desorption Ionisation Time of Flight (MALDI-TOF) mass spectra were registered on a Bruker Autoflex spectrometer using DCTB as matrix. Room temperature magnetic susceptibilities were measured using a Digital Measurement system MSB-MKI, calibrated using mercury tetrakis(isothiocyanato) cobalt(II). Conductivity of 10 –3 M solutions in acetone was measured using a Crison micro CM 2200 conductivimeter. UV-Vis absorption spectra were recorded in acetonitrile at room temperature using a Hewlett Packard 8452A spectrophotometer in a concentration range 8 × 10 –6 −8 × 10 –5 M. Steady-state emission and excitation spectra were recorded with a Jovin Yvon-Spex Fluoromax-2 fluorimeter. Quantum yields were determined using quinine sulfate dihydrate in 1.0 N H 2 SO 4 (Φ F = 0.546) as a fluorescence standard. 36 Ligand synthesis The ligand H 2 L (1) was prepared following the reported procedure (see SI). 11 Recrystallization of 1 from chloroform yielded crystals that were studied by X-ray diffraction (see SI). Synthesis of the complexes The neutral complexes were prepared by an electrochemical synthesis widely used by us 12 following a general procedure: the ligand H 2 L was dissolved in acetonitrile containing ca. 10 mg of tetraethylammonium perchlorate as supporting electrolyte. The solution was electrolysed using a platinum wire as the cathode and a metal plate as the anode. The cell can be summarised as: Pt(–)|H 2 L + CH 3 CN|M(+), where M = Mn, Fe, Co, Ni, Cu, Ag, Zn, Cd, Sn and Pb. The suspension obtained was filtered and the resulting solids were washed with diethyl ether and dried in vacuo. In the case of the Page 23 of 56 Dalton Transactions soluble complexes, the solution was concentrated to ca. 5 mL and the metal complex was precipitated by the addition of diethyl ether. Caution! Although problems were not encountered in our experiments, all perchlorate compounds are potentially explosive and should be handled in small quantities and with great care. Mn(L)·3H 2 O (2): Yield 0.11 g, 88%; m.p. >300 ºC; E.A. (Found: C, 54.3; H, 5.1; N, 7.5; S, 5.7; C 25 H 27 MnN 3 O 6 S required: C, 54.3; H, 4.9; N, 7.6; S, 5.8); ESI-MS (m/z): 498.0 [ML] + ; 997.1 [M 2 L 2 ] + ; IR (KBr, cm –1 ): ν(OH) + ν(NH) 3430, ν(C=N) + ν(C–N) 1608, 1561, ν(SO 2 ) as 1335, ν(SO 2 ) s 1153; µ(BM): 5.0; Λ M = 20.1 µS cm –1 ; UV/Vis (CH 3 CN, λ max ): 266, 338 (sh), 397 (sh) nm. Fe(L)·3H 2 O (3): Yield 0.11 g, 89%; m.p. >300 ºC; E.A. (Found: C, 53.8; H, 4.9; N, 7.6; S, 5.6; C 25 FeH 27 N 3 O 6 S required: C, 53.9; H, 4.9; N, 7.5; S, 5.7); ESI-MS (m/z): 498.9 [ML] + , 1015.0 [M 2 L 2 + 18] + ; IR (KBr, cm –1 ): ν(OH) + ν(NH) 3447, ν(C=N) + ν(C–N) 1606, 1570, ν(SO 2 ) as 1342, ν(SO 2 ) s 1148; µ(BM): 4.8; Λ M = 25.6 µS cm –1 ; UV/Vis (CH 3 CN, λ max ): 242, 296, 340, 400 (sh) nm. Co(L)·3H 2 O (4): Yield 0.13, 87%; m.p. >300 ºC; E.A. (Found: C, 55.0; H, 4.9; N, 7.8; S, 5.6; C 25 CoH 27 N 3 O 6 S required: C, 54.8; H, 4.7; N, 7.7; S, 5.9); ESI-MS (m/z): 502.0 [ML] + ; 1005.1 [M 2 L 2 ] + ; IR (KBr, cm –1 ): ν(OH) + ν(NH) 3441, ν(C=N) + ν(C–N) 1609, 1542, ν(SO 2 ) as 1303, ν(SO 2 ) s 1151; µ(BM): 3.7; Λ M = 29.2 µS cm –1 ; UV/Vis (CH 3 CN, λ max ): 248, 340, 420 (sh) nm. Ni(L)·3H 2 O (5): Yield 0.11 g, 88%; m.p. >300 ºC; E.A. (Found: C, 54.4; H, 5.2; N, 7.6; S, 5.5; C 25 H 27 N 3 NiO 6 S required: C, 53.9; H, 4.9; N, 7.6; S, 5.8); ESI-MS (m/z): 501.0 [ML] + ; 1003.1 [M 2 L 2 ] + ; IR (KBr, cm –1 ): ν(OH) + ν(NH) 3448, ν(C=N) + ν(C–N) 1610, 1561, ν(SO 2 ) as 1341, ν(SO 2 ) s 1152; µ(BM): 3.5; Λ M = 28.7 µS cm –1 ; UV/Vis (CH 3 CN, λ max ): 246, 304, 338, 416 nm. Recrystallization of the powdery solid from an acetonitrile/diethyl ether mixture afforded simultaneously single crystals of the complexes [Ni(L)(H 2 O) 3 ]·H 2 O·(CH 2 CH 3 ) 2 O (6) (yellow) and [Ni(L)(ADs)] (7) (red), which were studied crystallographically. The quality of the data for 7 did not allow refinement to a satisfactory level. Cu(L)·4H 2 O (8): Yield 0.11 g, 85%; m.p. >300 ºC; E.A. (Found: C, 51.9; H, 4.8; N, 7.3; S, 5.2; C 25 CuH 29 N 3 O 7 S required: C, 51.8; H, 5.0; N, 7.3; S, 5.5); ESI-MS (m/z): 507.1 [ML + H] + , 1015.1 [M 2 L 2 + H] + ; IR (KBr, cm –1 ): ν(OH) + ν(NH) 3449, ν(C=N) Page 24 of 56Dalton Transactions + ν(C–N) 1609, 1572, ν(SO 2 ) as 1327, ν(SO 2 ) s 1150; µ(BM): 1.8; Λ M = 18.4 µS cm –1 ; UV/Vis (CH 3 CN, λ max ): 244 (sh), 292, 414 nm. Recrystallization of the complex from a chloroform/dimethylsulfoxide mixture yielded green crystals of the compound [Cu(L)((CH 3 ) 2 SO)]·CHCl 3 (9), which was studied by X-ray diffraction. Ag 2 (L)·3H 2 O (10): Yield 0.14 g, 87%; m.p. >300 ºC; E.A. (Found: C, 42.2; H, 3.9; N, 5.9; S, 4.4; Ag 2 C 25 H 27 N 3 O 6 S required: C, 42.1; H, 3.8; N, 5.9; S, 4.5); ESI-MS (m/z) 551.2 [ML + H] + ; 659.0 [M 2 L + 2H] + ; 1 H NMR (DMSO-d 6 , ppm): δ 10.99 (s broad, OH), 8.73 (s, 1H), 8.67 (d, J = 8.6 Hz, 1H), 8.28 (d, J = 8.5 Hz, 1H), 8.23–8.10 (m, 2H), 7.58–7.48 (m, 2H), 7.43–7.30 (m, 2H), 7.15 (d, J = 8.1 Hz, 1H), 7.10 (d, J = 6.9 Hz, 1H), 6.96 (d, J = 7.4 Hz, 2H), 6.91–6.83 (m, 1H), 6.70–6.57 (m, 1H), 2.76 (s, 6H) ppm; IR (KBr, cm –1 ): ν(OH) + ν(NH) 3450, ν(C=N) + ν(C–N) 1618, 1561, ν(SO 2 ) as 1341, ν(SO 2 ) s 1144; Λ M = 52.0 µS cm –1 ; UV/Vis (CH 3 CN, λ max ): 260, 334 nm. [Zn(H 2 O) 6 ][Zn 3 (L) 3 (µ 3 -O)] (11): This complex was recently reported by us, 11 as both powdery (11) and crystalline ([Zn(H 2 O) 6 ][Zn 3 (L) 3 (O)]·2CH 3 CN·3H 2 O (11·2CH 3 CN·3H 2 O) forms, as final evidence of a water reduction process electrochemically performed by zinc metal under mild conditions. In one of the vials containing the mother liquors we found one single crystal of the side product [Zn 5 (L) 4 (µ 3 -OH) 2 ]·5CH 3 CN (12), with the green crystals of 11·2CH 3 CN·3H 2 O being the main product (vide supra). Cd 2 (L) 2 ·4H 2 O (13): Yield 0.21 g, 80%; m.p. >300 ºC; E.A. (Found: C, 50.7; H, 4.4; N, 7.2; S, 5.1; C 50 Cd 2 H 50 N 6 O 10 S 2 required: C, 50.7; H, 4.2; N, 7.1; S, 5.4); ESI-MS (m/z) 557.0 [ML] + ; 1112.1 [M 2 L 2 ] + ; 1 H NMR (DMSO-d 6 , ppm): δ 8.67 (d, J = 8.4 Hz, 1H), 8.55 (s, 1H), 8.30 (d, J = 8.4 Hz, 1H), 8.15 (d, J = 7.1 Hz, 1H), 7.50 (dd, J 1 = 7.9 Hz, J 2 = 7.2 Hz, 1H), 7.42 (d, J = 7.7 Hz, 1H), 7.36–7.25 (m, 2H), 7.16 (d, J = 7.4 Hz, 1H), 7.10 (t, J = 7.5 Hz, 1H), 6.98 (d, J = 8.0 Hz, 1H), 6.80 (t, J = 7.1 Hz, 1H), 6.69 (t, J = 7.2 Hz, 1H), 6.64–6.47 (m, 1H), 6.47–6.29 (m, 1H), 2.80 (s, 6H) ppm. 113 Cd NMR: δ 74.9 ppm; IR (KBr, cm –1 ): ν(OH) + ν(NH) 3449, ν(C=N) + ν(C–N) 1609, 1561, ν(SO 2 ) as 1335, ν(SO 2 ) s 1154; Λ M = 19.3 µS cm –1 ; UV/Vis (CH 3 CN, λ max ): 235, 258, 344, 420 (sh) nm. Recrystallization of compound 13 from an acetone/dimethylsulfoxide mixture yielded yellow crystals of the complex [Cd 2 (L) 2 ((CH 3 ) 2 SO) 4 ]·(CH 3 ) 2 CO 14. Sn(L)·3H 2 O (15): Yield 0.11 g, 78%; m.p. >300 ºC; E.A. (Found: C, 48.6; H, 4.3; N, 6.8; S, 5.2; C 25 H 27 N 3 O 6 SSn required: C, 48.7; H, 4.4; N, 6.8; S, 5.2); ESI-MS (m/z) 562.3 [ML] + ; 1120.4 [M 2 L 2 ] + ; IR (KBr, cm –1 ): ν(OH) + ν(NH) 3449, ν(C=N) + ν(C–N) Page 25 of 56 Dalton Transactions 1611, 1572, ν(SO 2 ) as 1337, ν(SO 2 ) s 1165; Λ M = 55.7 µS cm –1 ; UV/Vis (CH 3 CN, λ max ): 235, 260, 344 nm. Pb(L)·3H 2 O (16): Yield 0.15 g, 94%; m.p. >300 ºC; E.A. (Found: C, 42.7; H, 3.9; N, 5.7; S, 4.4; C 25 H 27 N 3 O 6 PbS required: C, 42.6; H, 3.9; N, 5.9; S, 4.5); ESI-MS (m/z) 652.1 [ML] + ; 1301.0 [M 2 L 2 ] + ; 1 H NMR (DMSO-d 6 , ppm): δ 8.70 (s, 1H), 8.64 (d, J = 8.7 Hz, 1H), 8.32 (d, J = 8.3 Hz, 1H), 8.09 (d, J = 7.2 Hz, 1H), 7.55–7.43 (m, 3H), 7.37– 7.28 (m, 1H), 7.21 (t, J = 6.8 Hz, 2H), 6.97–6.87 (m, 1H), 6.83 (d, J = 7.89 Hz, 1H), 6.71 (t, J = 7.5 Hz, 1H), 6.59 (d, J = 8.4 Hz, 1H), 6.47 (t, J = 7.1 Hz, 1H), 2.81 (s, 6H) ppm. 207 Pb NMR: δ –624.8 ppm; IR (KBr, cm –1 ): ν(OH) + ν(NH) 3447, ν(C=N) + ν(C– N) 1599, 1563, ν(SO 2 ) as 1341, ν(SO 2 ) s 1152; Λ M = 8.7 µS cm –1 ; UV/Vis (CH 3 CN, λ max ): 248, 254, 304, 334, 426 nm. X-ray crystallographic studies Data for 8 and 14 were collected on a Bruker Smart CCD-1000 diffractometer at room temperature and a Bruker APPEX 2 diffractometer was used for 12, both using graphite-monochromated Mo-Kα radiation (λ = 0.71073 Å) from a fine-focus sealed tube source (at 100 K). The computations and reduction were carried out using BRUKER SAINT 37 software, except for 12 where APEX2 was used. In all cases an empirical absorption correction was applied using SADABS. 38 Crystal data for 1 and 6 were collected on an Enraf Nonius TurboCAD4 Diffractometer using graphite-monochromated Cu-Kα radiation (λ = 1.5418 Å) from an Enraf Nonius FR590 source at room temperature. The cell refinement and data reduction were carried out with CAD-4 39 Software. In this case a PSI-SCAN 40 correction type was applied. Compounds 6, 8, 12 and 14 were solved by DIRDIF96, 41 while SIR-97 42 was employed for 1 with refinement by full-matrix least-squares techniques against F 2 using SHELXL97. 43 Positional and anisotropic atomic displacement parameters were refined for all heteroatoms. The hydrogen atom positions were included in the model by electronic density and were refined isotropically [Uiso(H) = 1.2 Ueq(Atom)] or were geometrically calculated and refined using a riding model (isotropic thermal parameters 1.2–1.5 times those of their carrier atoms). The criteria for a satisfactory complete analysis were the ratios of ‘rms’ shift to a standard deviation of less than 0.001 and no significant features in the final difference maps. The DMSO molecules coordinated to the metal ions in crystals 9 and Page 26 of 56Dalton Transactions 14 exhibit disorder in the carbon and sulfur atoms with occupancy factors of 0.62 and 0.38, respectively. The chloroform solvate molecule in 9 also features disorder in the chloro and the hydrogen atoms with occupancy factors of 0.62 and 0.38, respectively. Molecular graphics were obtained with DIAMOND 44 and ORTEP. 45 A summary of the crystal data, experimental details and refinement results are listed in Table 1. Significant bond distances and angles are summarized in Tables 2 and 3. CCDC 877814, 877815, 877816, 877817 and 877819 contain the supplementary crystallographic data for this paper. These data can be obtained free of charge from the Cambridge Crystallographic Data Centre via ww.ccdc.cam.ac.uk/data_request.cif. Acknowledgements Financial support from the Xunta de Galicia (10PXIB262132PR) and the Spanish Ministerio de Ciencia e Innovación and ERDF(EU) (CTQ2010-19191) is acknowledged. Page 27 of 56 Dalton Transactions 21 (a) A. Morsali, J. Abedini, J. Coord. Chem., 2004, 57, 1629; (b) A. Chaudhary, M. Agarwal and R. V. Singh, Appl. Organometal. Chem., 2006, 20, 295. 22 (a) L. Carbonaro, M. Isola, V. Liuzzo, F. Marchetti, F. Balzano, C. S. Pomelli, A. Raffaelli, Eur. J. Inorg. Chem., 2001, 353; (b) F. Luo, J.-M. Zheng, M. Kurmoo, Inorg. Chem., 2007, 46, 8448; (c) S. Lin, M.-X. Yang, S.-X. Liu, Polyhedron, 2007, 26, 4793. 23 (a) I. Castillo, J. M. Fernández-González, J. L. Gárate-Morales, J. Mol. Struct. 2003, 657, 25; (b) L. Zhang, L. Liu, D. Jia, G. Xu, K. Yu, Inorg. Chem. Commun. 2004, 7, 1306; (c) P. Barbazán, R. Carballo, E. M. Vázquez-López, Cryst. Eng. Comm., 2007, 9, 668. 24 A. W. Addison, T. N. Rao, J. Reedijk, J. Van Rijn, G. C. Verschoor, J. Chem. Soc., Dalton Trans., 1984, 1349. 25 (a) J. Sanmartín, M. R. Bermejo, A. M. García-Deibe, A. L. Llamas-Saiz, Chem. Commun. 2000, 795; (b) J. Sanmartín, M. R. Bermejo, A. M. García-Deibe, I. M. Rivas, A. R. Fernández, J. Chem. Soc., Dalton Trans., 2000, 4174. 26 A. S. Burlov, Y. V. Koshchienko, K. A. Lyssenko, I. S. Vasilchenko, Y. E. Alexeev, I. G. Borodkina, M. Y. Antipin, A. D. Garnovskii, J. Coord. Chem., 2008, 61, 85. 27 (a) M. Mikuriya, N. Tsuru, S. Ikemi, S. Ikenoue, Chem. Lett., 1998, 879; (b) G. Xu, L. Liu, L. Zhang, G. Liu, D. Jia, J. Lang, Struct. Chem., 2005, 16, 431; (c) B. Jacques, C. Dro, S. Bellemin-Laponnaz, H. Wadepohl, L. H. Gade, Angew. Chem. Int. Ed., 2008, 47, 4546. 28 A. Bondi, J. Phys. Chem., 1964, 68441. 29 J. E. Huheey, E. A. Keiter, R. L. Keiter, Inorganic Chemistry: Principles of Structure and Reactivity, 4 a Ed., Harper Collins College Publisher, New York, 1993. 30 (a) J. Wang, Z. Lin, Y.-C. Ou, N.-L. Yang, Y.-H. Zhang, M.-L. Tong, Inorg. Chem., 2008, 47, 190; (b) K.-Z. Shao, Y.-H. Zhao, X. L. Wang, Y.-Q. Lan, D. J. Wang, Z.-M. Su, R.-S. Wang, Inorg. Chem., 2009, 48, 10. 31 The evolution of Zn 2 (L) 2 to cluster 11 was followed by 1 H NMR (See reference 11). 32 M. Döring, M. Ciesielski, O. Walter and H. Görls, Eur. J. Inorg. Chem., 2002, 1615. 33 M. Hernick and C. A. Fierke, Archieves of Biochemistry and Biophysics, 2005, 433, 71. Page 34 of 56Dalton Transactions 34 (a) S. S. Tandon, S. Chander, L. K. Thompson, J. N. Bridson, V. Mckee, Inorg. Chim. Acta, 1994, 219, 55; (b) A. Majumder, G. M. Rosair, A. Mallick, N. Chattopadhyay, S. Mitra, Polyhedron, 2006, 25, 1753; (c) W.-X. Cai, Q.-W. Zhang, H. Su, Y.-L. Feng, Acta Cryst., 2006, E62, m1572; (d) N. R. Filipović, A. Bacchi, M. Lazić, G. Pelizzi, S. Radulović, D. M. Sladić, T. R. Todorović, K. K. Andelković, Inorg. Chem. Commun., 2008, 11, 47. 35 T. Koike, T. Watanabe, S. Aoki, E. Kimura, M. Shiro, J. Am. Chem. Soc., 1996, 118, 12696. 36 (a) W. H. Melhuish, J. Phys. Chem., 1961, 65, 229; (b) J. N. Demas, G. A. Crosby, J. Phys. Chem., 1971, 75, 991. 37 SAINT, Siemens Area detector integration software, Bruker AXS Inc., Madison, WI, USA, 2003. 38 G. M. Sheldrick, SADABS, Program for Scaling and Correction of Area Detector Data, University of Göttingen, Germany, 1996. 39 CAD-4 Software: Enraf-Nonius, 1989. CAD-4 Software (or CAD-4 EXPRESS). Enraf-Nonius, Delft, The Netherlands. 40 PSISCANS: A. C. T. North, D. C. Phillips and F. S. Mathews, Acta. Cryst., 1968, A24, 351. 41 DIRDIF99: P. T. Beurskens, G. Beurskens, R. de Gelder, S. García-Granda, R.O. Gould, R. Israel, J. M. M. Smits, 1999. The DIRDIF-99 program system, Technical Report of the Crystallography Laboratory, University of Nijmegen, The Netherlands. 42 A. Altomare, C. Cascarano, C. Giacovazzo, A. Guagliardi, A. G. G. Moliterni, M. C. Burla, G. Polidori, M. Camalli and R. Spagna, SIR97. University of Bari, Italy, 1997. 43 G. M. Sheldrick, Acta Cryst., 2008, A64, 112. 44 K. Brandenburg, DIAMOND, ver. 3.2; Crystal Impact GbR: Bonn, Germany, 2009. Page 35 of 56 Dalton Transactions Graphical abstract The versatility in coordination of the asymmetric half-salen ligand bearing a dansyl fluorophore [H 2 L] has been probed after the isolation of its luminescent complexes, which display a great structural diversity. Page 36 of 56Dalton Transactions 1 Versatile coordination behaviour of an asymmetric half-salen ligand bearing a dansyl fluorophore María J. Romero, a Rosa Pedrido,* a,b Ana M. González-Noya, a,b Marcelino Maneiro, b M. Isabel Fernández-García, b Guillermo Zaragoza, c Manuel R. Bermejo* a a Departamento de Química Inorgánica, Centro Singular de Investigación en Química Biolóxica e Materiais Moleculares (CIQUS), Universidade de Santiago de Compostela, Santiago de Compostela, Galicia, E-15782, Spain b Departamento de Química Inorgánica, Facultade de Ciencias, Universidade de Santiago de Compostela, Lugo, Galicia, E-27002, Spain c Unidade de Difracción de Raios X, Edificio CACTUS, Universidade de Santiago de Compostela, Campus Sur, Santiago de Compostela, Galicia, E-15782, Spain Supporting information Experimental Materials All solvents, o-phenylenediamine, dansyl chloride, triethylamine, salicylaldehyde and tetraethylammonium perchlorate are commercially available and were used without further purification. Metals (Ega Chemie) was used as ca. 2x2 cm 2 plate. Physical Measurements Elemental analysis of C, H, N and S were performed on a FISONS EA 1108 analyzer. 1 H and 13 C NMR spectra were recorded on a Varian Mercury 300 spectrometer, using CDCl3 and DMSO-d 6 as solvents. Chemical shifts are expressed relative to tetramethylsilane. Infrared spectra were measured as KBr pellets on a BRUKER IFS66V spectrophotometer in the range 4000-100 cm -1 . Electronic impact (EI) mass spectrum was recorded on a HP 5988A cuadrupolar mass spectrometer. Electrospray ionisation (ESI) mass spectrum was recorded on an API4000 Applied Biosystems mass spectrometer with Triple Cuadrupole analyser. Matrix Assisted Laser Desorption Ionisation Time of Flight (MALDI-TOF) mass spectra were registered in a Bruker Autoflex spectrometer using DCTB as matrix. Room temperature magnetic Page 37 of 56 Dalton Transactions 2 susceptibilities were measured using a Digital Measurement system MSB-MKI, calibrated using mercury tetrakis(isothiocyanato) cobalt(II). Conductivity of a 10 -3 M solution in acetone was measured in a Crison micro CM 2200 conductivimeter. UV-Vis absorption spectra were registered in acetonitrile at room temperature using a Hewlett Packard 8452A spectrophotometer in a concentration range 8x10 -5 − 8x10 -6 M. Synthesis of N-(2-aminophenyl)-5-(dimethylamino)-1-naphtalenesulfonamide (ADs): To a solution of o-phenylenediamine (1.2 g, 11.1 mmol) and dansyl chloride (3 g, 11.1 mmol) in 120 ml of chloroform was added triethylamine (1.56 ml, 11.1 mmol). The mixture was refluxed for 8 hours and monitored by TLC. After the reaction was complete, the organic layer was washed with water (2x100 mL), dried over anhydrous sodium sulphate and the resulting solution was concentrated to reduced volume. The solid formed was collected by filtration, washed with diethyl ether and dried in vacuo, yielding 3.3 g of a pale yellow product. Yield 90%; m.p. 169-171ºC; E. A. (Found: C, 63.4; H, 5.4; N, 12.2; S, 9.1; C 18 H 19 N 3 O 2 S required: C, 63.3; H, 5.6; N, 12.3; S, 9.4); EI-MS (m/z) 341.2 ([M] + , 51); 1 H NMR (DMSO-d 6 , ppm): δ 8.53 (d, 1H, J= 8.5 Hz), 8.37 (d, 1H, J= 8.6 Hz), 8.06 (d, 1H, J= 7.2 Hz), 7.59 (t, 1H, J = 8.1 Hz), 7.41 (t, 1H, J= 7.9 Hz), 7.21 (d, 1H, J= 7.5 Hz), 6.95 (t, 1H, J= 7.6 Hz), 6.65 (d, 1H, J = 8.0 Hz), 6.46 (s, 1H), 6.35 (t, 1H, J= 7.5 Hz), 6.23 (d, 1H, J = 7.6 Hz), 4.95 (s, 2H), 2.91 (s, 6H); IR (KBr, cm -1 ): ν(NH 2 )+ν(NH) 3434, 3349, ν(SO 2 ) as 1320, ν(SO 2 ) s 1148. Synthesis of E-5-(dimethylamino)-N-(2-(2-salicylideneamino)phenyl)naphtalene-1sulfonamide (H 2 L 1): A solution of the amine ADs (1.15 g, 3.4 mmol) and salicylaldehyde (0.36 mL, 3.4 mmol) in 120 mL of chloroform was refluxed with a Dean-Stark trap for 7 hours. The reaction mixture was concentrated to ca. 20 mL, filtered and concentrated to dryness under reduced pressure. The oily product obtained was solidified under vacuum providing a yellow solid. Yield 80%; m.p. 136-138 ºC; E. A. (Found: C, 66.9; H, 5.2 ; N, 9.3; S, 7.1; C 25 H 23 N 3 O 3 S required: C, 67.3; H, 5.2; N, 9.4; S, 7.2); ESI-MS (m/z) 446.1 ([H 2 L+H] + ); 1 H NMR (DMSO-d 6 , ppm): δ 11.72 (s, 1H), 10.11 (s, 1H), 8.30 (d, 1H, J= 8.4 Hz), 8.21 (d, 1H, J= 8.6 Hz), 8.09 (s, 1H), 7.99 (dd, 1H, J 1 = 7.3 Hz, J 2 = 1.0 Hz), 7.49-7.38 (m, 2H), 7.36-7.29 (m, 2H), 7.26-7.12 (m, 3H), 7.07-6.93 (m, 2H), 6.92-6.84 (m, 2H), 2.73 (s, 6H); 13 C NMR (DMSO-d 6 , ppm): δ 164.79 (HC=N), 160.32 (C ar ), 151.01 (C ar ), 141.11 (C ar ), 133.87 (CH ar ), 133.72 (C ar ), 132.75 (CH ar ), 130.62 (CH ar ), 130.12 (CH ar ), 130.04 (C ar ), 129.22 (C ar ), 129.17 (C ar ), Page 38 of 56Dalton Transactions 3 128.65 (CH ar ), 127.37 (CH ar ), 125.83 (CH ar ), 122.61 (CH ar ), 121.96 (CH ar ), 119.14 (CH ar ), 118.90 (CH ar ), 118.61 (C ar ), 118.05 (CH ar ), 117.00 (CH ar ), 114.83 (CH ar ), 45.18 (CH 3 ); IR (KBr, cm -1 ): ν(OH)+ν(NH) 3221, ν(C=N)+ν(C-N) 1616, 1567, ν(SO 2 ) as 1338, ν(SO 2 ) s 1164. UV/Vis (CH 3 CN, λ max ): 260, 342 nm. Electrochemical synthesis of [Zn(H 2 O) 6 ][Zn 3 (L) 3 (µ 3 -O)] 11: 1 A solution of the ligand H 2 L (0.1 g, 0.22 mmol) containing tetraethylammonium perchlorate as supporting electrolyte, a platinum wire as cathode and a zinc plate as anode, was electrolysed in degassed acetonitrile (80 mL) for 1 h 12 min. The reaction was carried out at 10 mA (15 V) under argon atmosphere. The resulting yellow solution was concentrated under reduced pressure and diethyl ether was added until the precipitation was completed. The solid formed was filtered, washed with diethyl ether and dried in vacuo, providing 0.082 g of a yellow product (see Scheme S1). *Caution! Perchlorate salts are potentially explosive and should be handled with care. Yield 64%; m.p.>300ºC; E. A. (Found: C, 52.3; H, 4.6; N, 7.5; S, 5.4; C 75 H 75 N 9 O 16 S 3 Zn 4 required: C, 52.4; H, 4.4; N, 7.3; S, 5.6); MALDI-TOF MS (m/z) 1017.1 [Zn 2 L 2 +H] + , 1037.1 [Zn 2 L 2 (O)+3H] + , 1546.1 [Zn 3 L 3 (O)+3H] + , 1628.0 [[Zn(H 2 O)][Zn 3 L 3 (O)]+2H] + , 1646.0 [[Zn(H 2 O) 2 ][Zn 3 L 3 (O)]+2H] + ; 1 H NMR (DMSO-d 6 , ppm): δ 8.75 (s, 1H), 8.67 (d, J = 8.6 Hz, 1H), 8.29 (d, J = 8.4 Hz, 1H), 8.05 (d, J = 7.2 Hz, 1H), 7.54-7.46 (m, 2H), 7.41 (d, J = 7.9 Hz, 1H), 7.35 (d, J = 7.7 Hz, 1H), 7.21 (t, J = 7.6 Hz, 1H), 7.13 (d, J = 7.5 Hz, 1H), 7.09 (d, J = 8.1 Hz, 1H), 6.85 (t, J = 7.7 Hz, 1H), 6.73 (t, J = 7.7 Hz, 1H), 6.67 (d, J = 8.6 Hz, 1H), 6.49 (t, J = 7.3 Hz, 1H), 2.78 (s, 6H) ppm; IR (KBr, cm -1 ): ν(OH)+ν(NH) 3433, ν(C=N)+ν(C-N) 1612, 1576, ν(SO 2 ) as 1317, ν(SO 2 ) s 1153; Λ M (Acetone, 10 -3 M)= 106 µS cm -1 mol -1 ; UV/Vis (CH 3 CN, λ max ): 246, 296, 320 sh, 350 sh, 414 nm. Slow evaporation from mother liquors afforded single crystals of 11·3CH 3 CN·H 2 O 1 (see Figure S1) and one crystal of [Zn 5 (L) 4 (µ 3 -OH) 2 ]·5CH 3 CN 12, both being crystallographically characterized. Electrochemical synthesis of [Zn 2 (L) 2 ]: 1 The ligand H 2 L (0.045 g, 0.10 mmol) was dissolved in degassed dry acetonitrile (40 mL) containing tetraethylammonium perchlorate as supporting electrolyte. The solution was electrolysed for 32 min at 10 mA (15 V) under argon employing a platinum wire as cathode and a zinc plate as anode. After the reaction was finished, the solvent was completely removed by bubbling argon Page 39 of 56 Dalton Transactions 4 through the yellow solution. The crude oil obtained was dissolved in 3 mL of hexane and filtered through a syringe filter. The resulting solution was concentrated as described above, providing 0.043 g of a yellow solid which was dried under vacuum. *Caution! Perchlorate salts are potentially explosive and should be handled with care. Yield 85%; E. A. (Found: C, 58.9; H, 4.1; N, 8.2; S, 6.4; C 50 H 42 N 6 O 6 S 2 Zn 2 required: C, 59.0; H, 4.2; N, 8.2; S, 6.3); MALDI-TOF MS (m/z) 1017.1 [Zn 2 L 2 +H] + (see Figure S2); IR (KBr, cm -1 ): ν(NH) 3449, ν(C=N)+ν(C-N) 1609, 1561, ν(SO 2 ) as 1335, ν(SO 2 ) s 1154. The 1 H NMR spectrum of [Zn 2 (L) 2 ] showed a mixture of signals corresponding to complex 11 as main compound and signals of lower intensity assignable to complex [Zn 2 (L) 2 ]. This result indicates that the dimer is not stable in solution and rapidly evolves to compound 11. Crystal structure of H 2 L 1 In an attempt to gain a deeper understanding of the coordination behaviour of this ligand towards different metal ions, we determined its structure by X-ray diffraction. The unit cell of the ligand H 2 L 1 contains two independent conformers, both of which have an E conformation around the imine bond (Figure S3). The phenol and dansyl aromatic groups are almost parallel in both isomers [C1–C6/C14–C23 11.04(7)º; C26– C31/C39–C48 5.86(8)º], adopting a close arrangement that could be attributed to the establishment of weak ‘face to face’ π-stacking interactions (centroid-centroid distance of ca. 3.9 Å, Figure S4). Furthermore, the phenol group is oriented towards the imine nitrogen atoms N1/N4 because of the establishment of intramolecular hydrogen bonds. The dihedral angles between the phenol and phenylene rings C1–C6/C8–C13 [44.68(10)º] and C26–C31/C33–C38 [51.57(9)º] indicate that the sulfonamide NH group of each conformer is not coplanar with the corresponding phenol oxygen and imine nitrogen atoms. Additionally, each conformer establishes two intermolecular hydrogen bonds, with a close different conformer (i.e. I···II, II···I) engaging the sulfonamide NH group and the phenol oxygen atom (Table S3), as shown in Figure S5. In addition, three weak ‘edge to face’ π-stacking interactions are also observed between different ligand strands: one involving dansyl rings and two engaging phenol and phenylene aromatic systems. All of these interactions induce an almost perpendicular orientation between the two enantiomers, as revealed by the angle between the dansyl rings C14–C23/C39–C48 [76.40(5)º]. Page 40 of 56Dalton Transactions 5 The imine, phenol, dansyl and sulphonamide bond distances are in the range expected for these groups and do not warrant further comment (Table S2). Table S1 Crystal data and structure refinement for the ligand H 2 L 1 H 2 L Empirical formula C 25 H 23 N 3 O 3 S Crystal size [mm] 0.48 × 0.20 × 0.08 Formula weight 445.52 Crystal system Triclinic Space group P-1 a [Å] 11.5395(18) b [Å] 14.248(3) c [Å] 14.5284(17) α [º] 75.654(13) β [º] 78.072(8) γ [º] 77.710(19) Volume [Å 3 ] 2231.1(6) Temperature [K] 293(2) Z 4 µ [mm –1 ] 1.553 Reflections collected 9254 Independent reflections [Rint] 8886 [0.068] R 1, wR2 [I>2σ(I)] 0.0510, 0.1338 R 1, wR2 (all data) 0.1078, 0.1566 Table S2 Main bond distances [Å] and angles [º] for the ligand H 2 L 1 H 2 L O1–C1 1.362(3) O4–C26 1.364(3) C7–N1 1.287(3) C32–N4 1.278(3) C13–N2 1.427(3) C38–N5 1.438(3) N2–S1 1.637(2) N5–S2 1.630(2) S1–C14 1.775(3) S2–C39 1.781(3) C19–N3 1.416(4) C44–N6 1.418(4) O1–C1–C6 121.0(2) O4–C26–C31 120.9(2) C7–N1–C8 116.8(2) C32–N4–C33 118.7(2) C13–N2–S1 118.98(17) C38–N5–S2 119.35(17) N2–S1–C14 106.45(11) N5–S2–C39 105.95(11) C19–N3–C25 115.7(2) C44–N6–C50 115.7(3) C13–N2–S1–C14 60.1(2) C38–N5–S2–C39 –68.4(2) Page 41 of 56 Dalton Transactions 6 Table S3 Hydrogen bond parameters [Å] for 1, 6 and 12 Parameter D – H···A/Å D – H/Å H···A/Å ∠ ∠∠ ∠ DHA/º Ligand H 2 L 1 O4—H4O···N4 0.873(18) 1.84(2) 2.629(3) 150(3) O1—H1O···N1 0.890(18) 1.86(2) 2.652(3) 148(3) N2—H2N···O4 i 0.851(17) 2.129(19) 2.951(3) 162(3) N5—H5N···O1 i 0.828(17) 2.130(18) 2.931(3) 163(3) [Ni(L)·3H 2 O]·H 2 O·(CH 2 CH 3 ) 2 O 6 O4—H4A···O1 ii 0.822(18) 2.059(19) 2.875(3) 172(3) O4—H4B···O3 0.79(3) 1.99(3) 2.681(3) 145(4) O5—H5B···N3 i ii 0.92(4) 1.90(4) 2.817(3) 176(3) O5—H5A···O8 0.821(14) 2.168(14) 2.977(4) 169(3) O6—H6B···O1 ii 0.795(18) 2.11(2) 2.843(3) 152(3) O6—H6A···O7 i v 0.817(18) 2.02(2) 2.812(3) 163(4) O8—H8A···O2 0.813(19) 2.15(2) 2.952(3) 170(5) O8—H8B···O3 v 0.814(19) 2.52(3) 3.233(3) 147(5) [Zn 5 (SAlDs) 4 ( µ µµ µ 3 - OH) 2 ]·5CH 3 CN 12 O13 H13O O2 0.77(4) 2.08(4) 2.659(4) 133(4) O14 H14O O9 0.784(19) 2.03(3) 2.696(4) 143(4) Symmetry transformations: (i) 1-x,-y, 1-z (ii) 2-x, 2-y, 1-z; (iii) 1+x, y, z ; (iv) x, 1+y, z ; (v) 2-x, 1-y, 2-z N N O O O N N N N N SO O NH NOH NH N OH 2 Zn 2 Zn 2+(aq) + 4 e - N N OO N N R 2H 2 CH 3 CN (aq) 22 H H Zn [Zn(H 2 O) 6 ] 2+ + 2 e - 1 e - N N OO N N H R R H 2 L N N O O O N N N N H 1/2 H 2 1 e - - R R R R R R = 2RR II III IV N N OO N N R R I H 2 O Zn 2+ L 21/2 H 2 Scheme S1. Proposed mechanism for the formation of 11. 1 Page 42 of 56Dalton Transactions 7 Figure S1. Crystal structure of the zinc(II) complex [Zn(H 2 O) 6 ][Zn 3 (L) 3 (µ 3 - O)]·3CH 3 CN·H 2 O 11. 1 Figure S2. Maldi-TOF mass spectrum of dimer Zn 2 (L) 2 precursor of the complexes 11 and 12. 1 Page 43 of 56 Dalton Transactions Figure 3 253x118mm (96 x 96 DPI) Page 50 of 56Dalton Transactions Figure 4 435x265mm (72 x 72 DPI) Page 51 of 56 Dalton Transactions Figure 5 243x122mm (96 x 96 DPI) Page 52 of 56Dalton Transactions Figure 6 Page 53 of 56 Dalton Transactions Figure 6 Page 54 of 56Dalton Transactions Figure 8 Page 55 of 56 Dalton Transactions Figure 9 213x206mm (72 x 72 DPI) Page 56 of 56Dalton Transactions