Synthesis and structural characterization of new transition metal complexes of a highly luminescent amino-terpyridine ligand

This is a self-archived version of an original article. This version may differ from the original in pagination and typographic details. Author(s): Title: Year: Version: Copyright: Rights: Rights url: Please cite the original version: CC BY-NC-ND 4.0 https://creativecommons.org/licenses/by-nc-nd/4.0/ Synthesis and structural characterization of new transition metal complexes of a highly luminescent amino-terpyridine ligand © 2019 Elsevier Ltd. Accepted version (Final draft) Nath Ghosh, Biswa; Puttreddy, Rakesh; Rissanen, Kari Nath Ghosh, B., Puttreddy, R., & Rissanen, K. (2020). Synthesis and structural characterization of new transition metal complexes of a highly luminescent amino-terpyridine ligand. Polyhedron, 177, Article 114304. https://doi.org/10.1016/j.poly.2019.114304 2020 Journal Pre-proofs Synthesis and structural characterization of new transition metal complexes of a highly luminescent amino-terpyridine ligand Biswa Nath Ghosh, Rakesh Puttreddy, Kari Rissanen PII: S0277-5387(19)30749-1 DOI: https://doi.org/10.1016/j.poly.2019.114304 Reference: POLY 114304 To appear in: Polyhedron Received Date: 16 October 2019 Revised Date: 5 December 2019 Accepted Date: 6 December 2019 Please cite this article as: B. Nath Ghosh, R. Puttreddy, K. Rissanen, Synthesis and structural characterization of new transition metal complexes of a highly luminescent amino-terpyridine ligand, Polyhedron (2019), doi: https:// doi.org/10.1016/j.poly.2019.114304 This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. © 2019 Elsevier Ltd. All rights reserved. Synthesis and structural characterization of new transition metal complexes of a highly luminescent amino-terpyridine ligand Biswa Nath Ghosh,*[a,b] Rakesh Puttreddy[b] and Kari Rissanen[b] aDepartment of Chemistry, National Institute of Technology Silchar, Silchar, Cachar-788010, Assam, Tel: +91-8018123682, E-mail: [email protected] bDepartment of Chemistry, Nano science Center, University of Jyvaskyla, P.O. Box 35, 40014 Jyväskylä, Finland Abstract The synthesis, NMR and UV-Vis spectroscopy measurements and X-ray diffraction analysis of four new metal complexes of the amino terpyridine ligand 4´-[4-(4-aminophenyl)phenyl]- 2,2´:6´,2´´-terpyridine L, namely [FeL2](ClO4)2 (1), [ZnL2](ClO4)2 (2), [CdL2](ClO4)2 (3) and [PtMe3IL] (4), are reported. The X-ray crystal structures of complexes 1-3 are 1:2 metal:ligand structures with tridentate ligands decorated around the octahedral metal centers. In complex 4, with L in a bidentate coordination mode, the Pt(IV) coordinated methyl and iodine groups form a fac-arrangement. The 1H NMR spectrum of 4 shows three 195Pt-1H resonances for the methyl groups incorporating the fac-arrangement, which confirms the bidentate coordination mode of L in solution. The X-ray crystal structure of L shows a transoid conformation of the pyridine ring nitrogen atoms along the interannular bond in the terpyridine core. Ligand L exhibits a bright blue emission in dichloromethane [fluorescence quantum yield (ΦF) = 68%] and its emission maxima shows significant solvatochromism (461 nm in dichloromethane to 533 nm in N,Ndimethylformamide), while its complexes 2 and 3 are only very weakly emissive and 1 and 4 are found to be non-emissive. Keywords: Amino terpyridine • Fluorescent • Trimethylplatinum(IV) • Bidentate Introduction 2,2´:6´,2´´-Terpyridine and its derivatives are well-known in supramolecular chemistry owing to their ability to strongly coordinate transition metal ions [1-4]. In particular, the 4´-functionalized terpyridines and corresponding metal complexes have received considerable attention in areas such as photophysical, electrochemical and catalytic properties [5-9], hydrogelation [10,11], organic light-emitting devices (OLEDs) [12] and mixed-valence chemistry [13,14]. A number of fluorescent compounds that can act as chemsensors for applications in bio-assays and in-vivo imaging purposes are also reported [9,15-23], yet fine tuning of multi-colour fluorescent staining of cell tissues is still a challenging task. Therefore, tuning the fluorophore electronic state for specific cell-staining and fluorophore structural studies remain a hot topic in supramolecular chemistry since any slight structural modifications to the fluorophore brings about unusual fluorescence properties. Our interest in 4´-functionalized amino terpyridines led us to report the following: i) A highly selective fluorescent sensor based on a 4′-(4-N,N-dimethylaminophenyl)-2,2′:6′,2′′-terpyridineZn(II) complex for pyrophosphate detection at physiological pH values in aqueous media [15]. ii) Ligand and anion effects in the self-assembly processes of divalent transition metal complexes of 4′-(4-N,N-dimethylaminophenyl)-2,2′:6′,2′′-terpyridine and 4′-(4-aminophenyl)-2,2′:6′,2′′- terpyridine [11]. iii) The ligand 4′-[4-(4-aminophenyl)phenyl]-2,2′:6′,2′′-terpyridine (L, Scheme 1) as a thermo-irreversible hydrogelator, particularly using Hg(II) salts under acidic conditions [10]. In the current study, we report the synthesis and characterization of four new metal complexes of L, [FeL2](ClO4)2 (1), [ZnL2](ClO4)2 (2), [CdL2](ClO4)2 (3) and [PtMe3IL] (4). The X-ray diffraction analysis shows that L forms a bidentate complex with the platinum(IV) ion, while tridentate complexes are formed with the divalent metal ions (Fe2+, Zn2+ and Cd2+). Further, the crystal structure and photophysical properties of L are also reported. The crystal structure of L shows a transoid conformation of the pyridine ring nitrogen atoms along the interannular bond in the terpyridine domain. A photophysical study shows that L is highly fluorescent in solution (ΦF = 0.68 in dichloromethane) with an emission maximum that shows significant solvatochromism. Although L is strongly fluorescent, its complexes 2 and 3 are only very weakly emissive, while 1 and 4 are found to be non-emissive. Experimental section Materials and methods: All the chemicals and solvents were of analytical reagent grade, purchased commercially and used as received without further purification. The ligand 4´-[4-(4aminophenyl)phenyl]-2,2´:6´,2´´-terpyridine, L, was synthesized following the literature method [10]. The 1H and 13C NMR spectra were recorded on Bruker Avance III HD 300 and DRX 500 spectrometers. The mass spectra were measured on a QSTAR Elite ESI-Q-TOF mass spectrometer equipped with an API 200 Turbo Ion Spray ESI source from AB Sciex (former MDS Sciex). Elemental analyses were performed with an Elementar Analysensysteme GmbH Vario EL. Spectroscopic studies: The UV-Visible absorption spectra were recorded on a Cary 100 Varian UV-Vis spectrophotometer, whereas the emission spectra were obtained with a Cary Eclipse Varian Fluorescence spectrophotometer. Fluorescence quantum yields were measured using quinine sulfate as the standard (ΦF = 0.546 in 0.1 N H2SO4). Fluorescence decays in different solvents were measured using a Time-Correlated Single Photon Counting (TCSPC) system consisting of a Hydra Harp 400 controller and a PDL 800-B driver from PicoQuant GmBH. All the spectroscopic measurements were carried out at room temperature and under ambient conditions. Synthesis of the complex [FeL2](ClO4)2 (1): To a degassed acetonitrile solution (5.0 mL) of Fe(ClO4)2.6H2O (19.9 mg, 0.055 mmol), a solution of L (44.0 mg, 0.109 mmol) in dichloromethane (20.0 mL) was added and the resulting mixture was stirred at room temperature for 3 h. After this, the solvents were evaporated to dryness, the residue was dissolved in a minimum amount of acetonitrile and excess diethyl ether (30.0 mL) was sequentially added dropwise to give purple coloured precipitates of 1. Complex 1 was filtered, washed with diethyl ether and dried under vacuum. Yield 90% (52.0 mg). 1H NMR (300 MHz, CD3CN, 303.15 K) δ/ppm: 9.22 (s, 4H), 8.63 (d, 4H, J 7.8 Hz), 8.37 (dt, 4H, J 1.8, 8.6 Hz), 8.01 (dt, 4H, J 2.0, 8.6 Hz), 7.92 (td, 4H, J 1.5, 7.7 Hz), 7.66 (dt, 4H, J 1.8, 8.6 Hz), 7.20-7.23 (m, 4H), 7.07-7.12 (m, 4H), 6.84 (dt, 4H, J 1.8, 8.5 Hz). MS (ESI-TOF) [FeL2]2+ m/z 428.1361 (calcd. 428.1357). UVVis, λmax (nm) (dichloromethane): 325, 375, 580. Anal. calcd. for C54H40Cl2FeN8O8 (1055.70): C, 61.44; H, 3.82; N, 10.61. Found: C, 61.18; H, 3.92; N, 10.35%. Synthesis of the complex [ZnL2](ClO4)2 (2): To an acetonitrile solution (5.0 mL) of Zn(ClO4)26H2O (24.6 mg, 0.066 mmol), L (53.0 mg 0.132 mmol) dissolved in dichloromethane (15.0 mL) was added and the resulting mixture was stirred at room temperature for 5 h. After this time, the reaction mixture was evaporated to dryness to give a yellow coloured product. The crude reaction mixture was re-dissolved in a minimum amount of acetonitrile and excess diethyl ether (25.0 mL) was added to precipitate complex 2. The precipitates were filtered, washed several times with diethyl ether and vacuum dried. Yield 91% (64.0 mg). Slow diffusion of diisopropyl ether into an acetonitrile solution of 2 gave yellow coloured crystals. 1H NMR (300 MHz, DMSO-d6, 303.15K) δ/ppm: 9.41 (s, 4H), 9.18 (d, 4H, J 8.1 Hz), 8.48 (d, 4H, J 8.2 Hz), 8.29 (t, 4H, J 7.1 Hz), 7.92-7.97 (m, 8H), 7.63 (d, 4H, J 8.6 Hz), 7.48-7.53 (m, 4H), 6.74 (d, 4H, J 8.6 Hz). MS (ESI-TOF) [ZnL2]2+ m/z 432.1354 (calcd. 432.1328). UV-Vis, λmax (nm) (dichloromethane): 325, 385. Anal. calcd. for C54H40Cl2N8O8Zn (1065.23): C, 60.89; H, 3.78; N, 10.52. Found: C, 61.17; H, 3.93; N, 10.24%. Synthesis of [CdL2](ClO4)2 (3): To an acetonitrile solution (6.0 mL) of Cd(ClO4)26H2O (21.4 mg, 0.051 mmol), 41.0 mg (0.102 mmol) of L dissolved in 15.0 mL dichloromethane was added and the reaction mixture was stirred at room temperature for 7 h. The solvents were removed under reduced pressure and the reaction mixture was re-dissolved in a minimum amount of acetonitrile, then excess of diethyl ether (25.0 mL) was added to precipitate 3 as yellow coloured solids. The precipitates were filtered, washed with diethyl ether and dried under vacuum. Yield 98% (56.0 mg). Single crystals suitable for X-ray diffraction analysis were obtained by slowdiffusion of di-isopropyl ether into an acetonitrile solution of 3. 1H NMR (300 MHz, DMSO-d6, 303.15K) δ/ppm: 9.11 (s, 4H), 9.00 (d, 4H, J 6.5 Hz), 8.46 (br s, 4H), 8.21-8.27 (m, 8H), 7.86 (d, 4H, J 8.4 Hz), 7.54-7.63 (m, 8H), 6.72 (dt, 4H, J 1.9, 8.5 Hz). MS (ESI-TOF) [CdL2]2+ m/z 457.1200 (calcd. 457.1206). UV-Vis, λmax (nm) (dichloromethane): 325, 365. Anal. calcd. for C54H40CdCl2N8O8 (1112.26): C, 58.31; H, 3.62; N, 10.07. Found: C, 58.10; H, 3.41; N, 9.82%. Synthesis of [PtMe3IL] (4): A solution of trimethylplatinum iodide (30.0 mg, 0.082 mmol) in chloroform (10.0 mL) was added to L (33.0 mg, 0.082 mmol) in chloroform (10.0 mL), and the reaction mixture was stirred at 50 °C for 6 h. The solvents were evaporated under reduced pressure and excess n-hexane was added to give a pale-yellow precipitate of 4. The solids were filtered, washed several times with n-hexane and dried under vacuum. Yield 79% (58.0 mg). Also, a 1:1 mixture of trimethylplatinum iodide and L in benzene, on standing for a few days, afforded yellow coloured single crystals of the complexes.1H NMR (500 MHz, CD2Cl2, 213.15K) δ/ppm: 9.02 (d, 1H, J 4.9 Hz), 8.72 (d, 1H, J 7.9 Hz), 8.68 (d, 1H, J 4.1 Hz), 8.35 (br s, 1H), 8.31 (d, 1H, J 7.9 Hz), 8.12 (br s, 1H), 8.08 (t, 1H, J 7.7 Hz), 7.79-7.85 (m, 3H), 7.59-7.65 (m, 3H), 7.40-7.44 (m, 3H), 6.71 (d, 2H, J 8.11 Hz), 3.99 (s, 2H), 1.49 (s, 3H, 2JPt-H 73.5 Hz), 0.26 (s, 3H, 2JPt-H 71.5 Hz), 0.15 (s, 3H, 2JPt-H 70.4 Hz). MS (ESI-TOF) [PtMe3L]+ m/z 640.2032 (calcd. 640.2037). UV-Vis, λmax (nm) (dichloromethane): 315, 362. Anal. calcd. for C30H29IN4Pt (767.57): C, 46.94; H, 3.81; N, 7.30. Found: C, 46.65; H, 3.49; N, 7.05%. X-ray crystallography Single crystal X-ray diffraction data for L, 2 and 3 were collected using a dual source Rigaku Super Nova Oxford diffractometer equipped with an Atlas CCD detector using mirrormonochromated Cu-Kα radiation (λ = 1.54184 Å). The data collection and reduction were carried out using the program CrysAlisPro [24]. The data for 4 was collected using a BrukerNonius Kappa CCD diffractometer [25] equipped with an APEX II detector and graphitemonochromatized Mo-Kα (λ = 0.71073 Å) radiation. Collect software was used for data collection [26] and DENZO-SMN for its processing [27]. An absorption correction was applied with the multi-scan SADABS program [28]. All the structures were solved with direct methods (SHELXS) [29] and refined by full-matrix least squares on F2 using the OLEX2 software [30], which utilizes the SHELXL-2015 module [29]. All the hydrogen atoms were calculated to their optimal positions and treated as riding atoms using isotropic displacement parameters either 1.2 or 1.5 larger than the corresponding carrier atoms. Constraints and restraints were used to model disordered structures when necessary. Crystal data for L: CCDC 1901887, C27H20N4, M = 400.47, yellow needle, 0.1567 x 0.053 x 0.0257 mm3, triclinic, space group P-1, a = 9.4598(4) Å, b = 14.2779(6) Å, c = 15.2307(5) Å, α = 96.284(3) °, β = 95.443(3) °, γ = 98.329(4) °, V = 2010.35(14) Å3, Z = 4, Dc = 1.323 g/cm3, F000 = 840, µ= 0.623 mm-1 , T = 123.01(10) K, θmax = 66.75 °, 12197 total reflections, 5681 with Io > 2σ(Io), Rint = 0.0301, 7063 data, 561 parameters, 0 restraints, GooF = 1.027, R = 0.0453 and wR = 0.1188 [Io > 2σ(Io)], R = 0.0573 and wR = 0.1286 (all reflections), 0.211 < d∆ρ < -0.258 e/Å3. Crystal data for 2: CCDC 1901884, C54H40Cl2N8O8Zn, M = 1065.21, yellow plate, 0.1949 x0.1015 x0.0558 mm3, monoclinic, space group P21/c, a = 22.981(2) Å, b = 8.5117(5) Å, c = 27.206(3) Å, α = 90 °, β = 113.061(13) °, γ = 90 °, V = 4896.3(9) Å3, Z = 4, Dc = 1.445 g/cm3, F000 = 2192, µ= 0.676 mm-1 , T = 173.15 K, θmax = 25.25 °, 32557 total reflections, 4302 with Io > 2σ(Io), Rint = 0.0879, 8852 data, 699 parameters, 49 restraints, GooF = 1.053, R = 0.1037 and wR = 0.2888 [Io > 2σ(Io)], R = 0.1916 and wR = 0.3594 (all reflections), 1.186 < d∆ρ < -0.509 e/Å3. Crystal data for 3: CCDC 1901885, C54H40CdCl2N8O8, M = 1112.24, yellow block, 0.2537 x 0.2019 x 0.1658 mm3, monoclinic, space group P21/c, a = 23.6891(16) Å, b = 8.4550(4) Å, c = 27.3090(16) Å, α = 90 °, β = 113.003(7) °, γ = 90 °, V = 5034.8(6) Å3, Z = 4, Dc = 1.467 g/cm3, F000 = 2264, µ= 0.604 mm-1 , T = 123.0(1) K, θmax = 25.25 °, 20514 total reflections, 6829 with Io > 2σ(Io), Rint = 0.0302, 9103 data, 681 parameters, 31 restraints, GooF = 1.058, R = 0.0817 and wR = 0.2312 [Io > 2σ(Io)], R = 0.1025 and wR = 0.2582 (all reflections), 1.759 < d∆ρ < - 0.780 e/Å3. Crystal data for 4: CCDC 1901886, C36H35IN4Pt, M = 845.67, yellow block, 0.22 x 0.17 x 0.17 mm3, monoclinic, space group P21/n, a = 18.8259(18) Å, b = 7.2471(8) Å, c = 23.1917(17) Å, α = 90 °, β = 96.280(5) °, γ = 90 °, V = 3145.1(5) Å3, Z = 4, Dc = 1.786 g/cm3, F000 = 1640, µ= 5.474 mm-1 , T = 123 K, θmax = 25.00 °, 8745 total reflections, 3699 with Io > 2σ(Io), Rint = 0.0793, 5277 data, 352 parameters, 32 restraints, GooF = 1.079, R = 0.0795 and wR = 0.1647 [Io > 2σ(Io)], R = 0.1219 and wR = 0.1862 (all reflections), 2.841 < d∆ρ < -1.245 e/Å3. Results and discussion The ligand L was synthesized by the reaction between 4-aminophenylboronic acid pinacol ester and 4´-(4-bromophenyl)-2,2´:6´,2´´terpyridine by following the literature method [10]. Complexes 1-3 were obtained by the reaction of L (in dichloromethane) with the metal perchlorate hexahydrate salts (in acetonitrile) in a 2:1 molar ratio, while 4 was prepared by the reaction of L with trimethylplatinum(IV) iodide (1:1 molar ratio) in chloroform (Scheme 1). The presence of only one set of signals for the terpyridine core in the room temperature 1H NMR spectra of complexes 1-3 revealed the tridentate metal-coordination mode of L. Unlike 1-3, the 6.66.87.07.27.47.67.88.08.28.48.68.89.0 ppm 6.704 6.720 7.309 7.409 7.425 7.600 7.612 7.632 7.648 7.792 7.808 7.820 7.836 7.851 8.069 8.085 8.100 8.120 8.304 8.319 8.349 8.673 8.681 8.709 8.725 9.013 9.023 2.028 3.034 3.088 2.986 1.233 1.012 1.145 0.985 0.966 1.007 1.000 1.5 ppm 1.415 1.488 1.562 0.3 0.2 ppm 0.079 0.149 0.190 0.220 0.262 0.333 room temperature 1H NMR spectrum of 4 in CD2Cl2 showed severe broadening (see Figure S4 in the supporting information) and thus the 1H NMR spectrum was measured at low temperature (- 60 °C) to get a better resolved spectrum. The 1H NMR spectrum of 4 is closely analogous to the spectra of reported PtIV-terpyridine complexes [23,31,32]. The presence of three platinum-methyl signals with satellites, due to 195Pt-H scalar coupling, revealed the presence of three nonequivalent methyl groups (MeA, MeB and MeC) in complex 4 (Figure 1). The above observation gives an indication that L binds the platinum metal centre in a bidentate fashion. The ESI-MS of the symmetric homoleptic complexes 1-3 show the parent molecular ion, [ML2]2+, while 4 displays the molecular ion peak with the loss of iodide, i.e. [PtMe3L]+ (see Figures S6-S9 in supporting information). Scheme 1 Chemical structure of the ligand L and synthesis of the metal complexes 1-4. PtMe3I CH3CN/DCM M(ClO4)2.6H2O 1: M = Fe 2: M = Zn 3: M = Cd N N N MeB MeA Pt I MeC 4 N N N H2NN N N M N N N NH2 L NH2(ClO4)2 NH2 CHCl3 MeB MeA MeC Fe(II) and Pt(IV), completely quench the fluorescence of L. The quenching of ligand fluorescence upon metal complexation is a common phenomenon, possibly affected by electron transfer or an energy transfer mechanism [45]. The weak fluorescence of the Zn(II) and Cd(II) complexes is due to an ILCT transition from the amine moiety to the metal coordinated terpyridine fragment [9,23,46]. The non-fluorescence nature of the Fe(II)-terpyridine complex is most likely because of a change of the MLCT type singlet excited state, 1MLCT, to the corresponding short lived triplet state, 3MLCT [47]. On the other hand, the fluxional behavior of the terpyridine ligand could play a significant role in the quenching of fluorescence in the Pt(IV) complex. Figure 6 Fluorescence spectra (left) and colour (right) of L in different solvents at room temperature. Table 2 Absorption and emission properties of L in different solvents Solvent λmaxabs (nm)a λmaxem (nm)b ΦFc τF (ns)d Dichloromethane 322 461 0.68 2.93 Tetrahydrofuran 326 474 0.63 2.24 Acetonitrile 328 520 0.10 1.22 N,N-Dimethylformamide 337 533 0.05 - aLowest energy absorption band. bUpon excitation of the lowest energy absorption band. cRelative fluorescence quantum yield. dFluorescence lifetime. 450 525 600 675 0 Fluorescence Intensity Wavelength (nm) Dichloromethane (DCM) Tetrahydrofuran (THF) Acetonitrile (ACN) N,N-dimethylformamide (DMF) abs Conclusions In conclusion, the synthesis and characterization of four new transition metal complexes of the amino terpyridine ligand 4´-[4-(4-aminophenyl)phenyl]-2,2´:6´,2´´-terpyridine L, [FeL2](ClO4)2 (1), [ZnL2](ClO4)2 (2), [CdL2](ClO4)2 (3) and [PtMe3IL] (4), are discussed. Complexes 1-3 were synthesized by the reaction of metal ions with L in a 1:2 ratio, while the reaction of an equimolar mixture of L and PtMe3I resulted the formation of 4. The complexes were characterized by 1H NMR spectroscopy, Mass spectroscopy, CHN analysis and an X-ray single crystal study. The X-ray crystal structure analysis of complexes 2 and 3 shows the tridentate coordination of L to the metal centre, while the structural investigation of 4 confirms the bidentate coordination mode of L. The X-ray crystal structure of L shows a trans-arrangement of the terminal pyridine nitrogen atoms with respect to central pyridine ring in the terpyridine backbone. The photophysical studies show that L is highly fluorescent in non-polar solvents, with an emission maximum that shows a significant bathochromic shift upon increasing the solvent polarity. The fluorescence of L is reduced significantly upon complexation, with the Zn(II) and Cd(II) complexes showing only very weak fluorescence, while complexes 1 and 4 were found to be non-fluorescent. Appendix A. Supplementary data CCDC 1901884-1901887 contain the supplementary crystallographic data for L and complexes 2-4. These data can be obtained free of charge via http://www.ccdc.cam.ac.uk/conts/retrieving.html, or from the Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: (+44) 1223-336-033; or e-mail: [email protected]. Acknowledgments We thank Dr. Elina Kalenius for measurement of the mass spectra. The authors gratefully acknowledge financial support from the Academy of Finland (RP: grant no. 298817) and the University of Jyväskylä. Conflicts of interest There are no conflicts to declare References [1] U. S. Schubert, H. Hofmeier, G. R. Newkome, Modern terpyridine chemistry, WileyVCH, Weinheim, 2006. [2] A. Wild, A. Winter, F. Schlütter, U. S. 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Graphical Abstract Synopsis The synthesis and structural characterization of four new metal complexes of the highly luminescent amino-terpyridine ligand 4′-[4-(4-aminophenyl)phenyl]-2,2′:6′,2′′-terpyridine L, [FeL2](ClO4)2 (1), [ZnL2](ClO4)2 (2), [CdL2](ClO4)2 (3) and [PtMe3IL] (4), are reported. Structural analysis confirms that L forms a bidentate complex with the platinum(IV) ion, while tridentate complexes are formed with the divalent metal ions (Fe2+, Zn2+ and Cd2+). Further, the crystal structure of L shows a transoid conformation of the pyridine ring nitrogen atoms along the interannular bond in the terpyridine domain. A photophysical study shows that L is highly fluorescent in solution (ΦF = 0.68 in dichloromethane) with an emission maximum that shows significant solvatochromism.