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P. J. ŠAFÁRIK UNIVERSITY IN KOŠICE FACULTY OF SCIENCE Institute of Chemistry Department of Inorganic Chemistry Experimental study of the system Nickel(II) benzoate and 2,2´- bipyridine (Small research project) Tutor: prof. RNDr. Juraj Černák, DrSc. Co-tutor: RNDr. Lenka Krešáková Author: Alvaro Werner 2 Content 1 Introduction 2 Theoretical part 2.1 Nickel(II) as central atom 2.2 Characterization of 2,2´-bipyridine as ligand 2.3 Characterization of benzoato anion as ligand 3 Experimental part 3.1 Materials used 3.2 Syntheses 3.3 Chemical analysis 3.4 IR spectroscopy 4 Results and discussion 5 Conclusions 6 Literature 3 1 INTRODUCTION At present, the compounds of Nickel(II) are subject of many studies in various fields of science. In the field of biology Ni is interesting because many Ni enzymes are in primitives species and they do important functions in diverse metabolic processes, such as energy metabolism and virulence [Alfano, 2020]. Besides, the nickel is a 3d transition metal with many uses in the field of catalysis, e.g. it catalyses the hydrogenation of nitriles and alkalynes a really interesting reaction for the industries [Sharma, 2020]. If we talk about the environment, the nickel could be an interesting element to study because of there are some Ni complexes that can act like a catalyst for water splitting and CO2 reduction [Wang, 2019]. If this study goes further, we could improve the environment, decrease global warming since we could have a source of clean energy. Nickel(II) complexes are also studied in the field of magnetism since it can form quite interesting molecular magnets. One of the combinations with Ni(II) in complexes in the formation of 3d / 4f heterometallic complexes because they allow this ion to exhibit magnetic anisotropy. [Chakraborty, 2019]. Previously Anna Vráblová (née Ščerbová) et al. [Ščerbová, 2015] have prepared and studied nickel benzoate trihydrate. It crystal structure is formed of infinite positively charged chains built up of Ni(II) atoms which are triply bridged by benzoate and aqua ligands. At the same time it is known that bpy coordinates mostly as a chelating bidentate ligand. As a continuation of the work of Vráblová et al. the aim of this project is to investigate the possibilities to prepare complexes by using a combination of benzoate anion and a blocking ligand bpy, to isolate the formed solid products, and to identify them by chemical analyses and IR spectroscopy. 4 In this thesis the following abbreviations are used: bpy / 2,2´ bpy 2,2′-bipyridine bz benzene cinn cinnamato DABPH 2,6-diacetylpyridine-bis(benzoic acid hydrazone) DMGH dmgh dimethylglyoximato en 1,2-diaminoethane, ethylenediamine Et2O ether mal maleato mpcm methyl-3-pyridylcarbamate ppds phenylphosphinediyl)dibenzenesulfonato tcdp tetracyano-2-(dicyanomethylene) propane-1,3-diide(2-) 5 2 THEORETICAL PART 2.1 Nickel(II) as central atom Nickel (Ni) is a transition metal whose atomic number is 28 and is located in group 10 of the periodic table. It also has 5 different isotopes which makes it have a weight around 58.69 u. It has an electronic configuration [Ar] 4s2 3d8. Some important properties of nickel are reflected in the following Table 1. Table 1: Some properties of Nickel [Greenwood, 1984] Property Ni Atomic number 28 Number of isotopes 5 Atomic weight (g/mol) 58.69 Electronic configuration [Ar] 3d8 4s2 Electronegativity 1.8 Metal radius (12 coordinate) (pm) 124 MP/ºC 1455 BP/ºC 2920 ΔHfus(kJ*mol-1) 17.2 (±0.3) ΔHvap(kJ*mol-1) 375 (±17) Density (20ºC) (g*cm-3) 8.908 Electrical resistivity (20ºC) (µohm*cm) 6.84 Nickel is the seventh most abundant transition element and about 10 per cent of the core is Nickel and, in the crust, there is only 80 ppm of Ni. In nature we can find it in elemental form alloyed with iron or in combination with Arsenic, Antimony or Sulphur (e.g.: NiS, NiAs2, NiSbS) [Cotton, 1999]. The nickel has a silver colour, it is quite resistant to air and water at normal temperatures. However, when the air is heated the nickel is pyrophoric if it is very finely divided. Ni is ferromagnetic and slightly electropositive Ni2++ 2 e- → Ni Eº= - 0.24 V We have said that Ni is resistant to air or water under standard conditions but this element tends to react with B, Si, P, S and halogens (although very slow with Fluor). It has low acid resistance and oxidizes easy but it does not happen with HNO3 because passivation occurs [Cotton, 1999]. 6 The main uses of nickel are the coating of metals to protect it from corrosion (Fe, Al, Cu, Steel) and to catalyze reactions. A typical reaction in which Ni in the form of Raney-Ni is used, is the next hydrogenation reaction where the benzene is reduced to cyclohexane [Wade, 2004]. The oxidation states of nickel vary from -1 to 4+, with 2+ being the most common. Oxidation states 0 and 1+ have little interest and oxidation states 3+ and 4+ are rare/very rare, resp. In addition, nickel is an element with a great variety of coordination numbers and with interesting stereochemistries. In the next Table 2 are shown some examples of Nickel compound with various oxidation states and stereochemistries. Table 2: Overview of Nickel compounds in various oxidation states and stereochemistries [Greenwood, 1984; Cotton, 1999]. Oxidation State Coordination Number Stereochemistry Ni -1 4 ? [Ni2(CO)6]20 (d10) 3 Planar [Ni(P(OC6H4-2-Me3)3] 4 Tetrahedral [Ni(CN)4]41 (d9) 4 Tetrahedral [NiBr(PPh3)3] 2 (d8) 3 Trigonal planar [Ni(NPh2)3]- 4 Tetrahedral [NiCl2(PPh3)2] Square planar [Ni(CN)4]25 Trigonal bipyramidal [Ni(PPhMe2)3(CN)2] Square pyramidal [Ni(CN)5]36 Octahedral [Ni(bpy)3]2+ Trigonal prismatic NiAs 7 Pentagonal bipyramidal [Ni(DAPBH)2(H2O)2]2+ 3 (d7) 4 Square planar - 5 Trigonal bipyramidal [NiBr3(PEt3)2] 6 Octahedral [NiF6]34 (d6) 6 Octahedral K2[NiF6] From coordination chemistry point of view the most abundant and important oxidation state 7 of nickel is 2+ (d8) which will be discussed here in more details. Coordination number rarely exceeds 6 and principal stereochemistries are octahedral or square-planar. There are four types of Ni(II) complexes as to their stereochemistry (Figure 1): a) Octahedral: which are paramagnetic due to presence of 2 unpaired electrons in (t2g)6 (eg)2 orbitals. They are green to blue. b) Tetrahedral: which are paramagnetic due to presence of 2 unpaired electrons in e4t24 orbitals. They are green to blue. c) Square planar: in these complexes all electrons in d-orbitals are paired and this means that such complexes are diamagnetic. They are commonly red to yellow. d) Five-Coordinate Nickel (II) Complexes: these can be trigonal bipyramidal or square pyramidal Figure 1: The splitting of the d-orbitals in Ni(II) (d8) for various stereochemistries [Greenwood, 1984] 8 Octahedral complexes: The aqueous complex of Ni(II) contains [Ni(H2O)6]2+ complex cations with octahedral coordination of the Ni(II) atoms and it exhibits bright green color. Normally, for the nickel (II) to form octahedral complexes the ligands must be neutral and Ndonors (like amines) or O-donors (like DMSO). These ligands displace part or all of the water molecules of the previously named complex cation. The complexes with amines are of a purple or blue color because the orbitals are closer, the electronic transition is lower, absorbs low energies and emits large wavelengths [Greenwood, 1984] Figure 2: Absorption spectra of [Ni(H2O)6]2+ (solid curve) and [Ni(en)3]2+ (dashed curve) [Cotton, 1999] In the previous graphics we can see 3 absorption bands which are characteristic for nickel (II) octahedral complexes. These are shown in the next Table 3. Table 3: Approximate bands of Octahedral Nickel (II) Complexes [Cotton, 1999] Spectra of Octahedral Nickel (II) Complexes Approximate band positions (cm-1) Transition [Ni(H2O)6]2+ [Ni(en)3]2+ 3A2g→3T2g 9.000 11.000 3A2g→3T1g (F) 14.000 18.500 3A2g→3T1g (P) 25.000 30.000 If we focus on the orbitals we can see in them that there are 2 unpaired electrons which will make the octahedral complexes paramagnetic and their magnetic moment will be from the range 2.9-3.4 BM depending on the orbital contribution. 9 Tetrahedral Complexes. Moving on to the issue of Ni tetrahedral there are different types: [NiX4]2-, [NiX3L]-, [NiX2L2], and [Ni(L-L)2] where X is halide ligand, L is neutral ligand such as PPh3 and L-L is a bidentate chelate type ligand. The only strictly tetrahedral complexes are [NiX4]2-, the others for different distortions have slight deformations of a real tetrahedron [Cotton, 1999]. These complexes having a symmetry Td and a d8 configuration have an absorption band in the region of the visible light (15000 cm-1). This is the reason why these complexes are bluishgreen. Finally, supposedly the magnetic moment in a real tetrahedral complex of Ni (II) should be 4.2 BM. As we know perfection does not exist and there are always slight distortions or displacements. Therefore, if a complex is regular, it will have an angular momentum between 3.54 BM and if it is irregular 3 - 3.5 BM [Greenwood, 1984]. Planar Complexes (D4h). Often the Ni(II) compounds are square planar due to their d8 configuration and the ligands make the dx2-y2 orbital have a very high energy and being anti-binding orbital and this orbital is empty. It also helps planarity if these ligands are small. Almost all square complexes are diamagnetic with a reddish, yellow or brown colour due to the absorption bands situated between 450-600 cm-1. Most important compound is K2[Ni(CN)4]. Another interesting complex is [Ni(DMGH)2] because it is a compound that in solid state is formed by molecules stacked on top of each other with NiNi interactions of 320 pm and when dissociated, squareplane monomers occur. Five-Coordinate Nickel (II) Complexes. These can have trigonal-bipyramidal (D3h, highspin) or square-pyramidal (C4v, low-spin) geometry. The symmetry cannot be the full D3h because normally there is a tripod ligand such as pp3 (alanyl-pyridoxal-5'-phosphate) and there are, with few exceptions, low-spin like [Ni(Me6tren)Br]+ (diamagnetic). There are low-spin five coordinate Ni(II) complexes with [NiL5]2+ and [NiL3X2] compositions (X = halogen L= phosphine or arsine type ligand). Figure 3: Structure of square pyramidal (left) and trigonal bypiramidal (right) coordination for [Ni(CN)5]3anion 16 Figure 11: Different bonding fashions of Benzoate anion like ligand. The first bonding mode of the benzoate ligand is monodentate there are so many examples but a clear example is LEQKIE. Figure 12: Benzoate anion like monodentate ligand in bis(benzoato)-tetrakis(methanol)-nickel(ii) [Datchuk, 2017] 17 We can see in the Figure 13 how benzoate ligand acts like a monodentate ligand forming a bond with Nickel. Another mode of coordination is a benzoate like a chelate. Its Refcode is BZONNI and it was synthesized by Hursthouse in 1977 [Hursthouse, 1977]. Figure 13: bis (Benzoato-O,O')-bis(quinoline)-nickel(ii) [Hursthouse, 1977] In the next Figure 14 we can see an ionic bonding of benzoate anion. The compound is tris(2-phenylacetohydrazide)-nickel(ii) bis(benzoate) - REXPUI and is depicted without H2O [Koksharova, 2017]. 18 Figure 14: tris(2-phenylacetohydrazide)-nickel(ii) bis(benzoate) without H2O molecules [Koksharova, 2017] The next bonding fashion of the benzoate ligand is when it acts as syn-syn bridge. ABIZUI is its ref-code and the structure is depicted on the next figure 15 [Kounavi, 2010]. Figure 15: Structure of the cationic part of tetrakis(µ2-Benzoato)-bis(1-methyl-4,5-diphenyl-1Himidazole)-dinickel(ii) acetonitrile solvate [Kounavi, 2010]. Syn-anti bridge its really similar like the syn-syn bridge but the main difference is that in the case of syn-syn bridging the metallic atoms are relatively closely placed while in the case of 19 syn-anti bridging the two metallic atoms are placed at much longer distance. In CSD database we could not find any example with Ni and benzoate anion with syn-anti bridging; the reason may be in interplay of the benzoato ligand conformation and some steric requirements. However, we found an example with Zn, cinn and mpcm ligands (Fig. 16) [Zeleňák, 2006]. Figure 16: View on the crystal structure of [Zn(cinn)2(mpcm)]n complex [Zeleňák, 2006] The next compound represents an example in which benzoate anion acts as a tridentate ligand. Its ref-code is DAVYIJ [Gavrilenko, 2005] and you can see the compound without acetonitrile solvate molecule on Fig. 17. Figure 17: View of the structure of bis(µ2-Benzoato-O,O,O')-tetrakis(µ2-benzoato-O,O')- tetrapyridinemanganese-di-nickel [Gavrilenko, 2005] 20 There is reported an another bonding fashion of benzoate anion but without Nickel. This is the anti-anti bridging fashion (see Figure 18) which was rarely reported but it is interesting bonding fashion. Figure 18: Scheme of the theoretically possible anti-anti bridging fashion of benzoate anion with Ni. This anti-anti bonding fashion was observed in complex [Cu2(phen)2(µ-O2CH)2(O2CH)2]n. The structure consists of four independent polymeric chains of [Cu2(phen)2(µ-O2CH)2(O2CH)2] with asymmetric bidentate bridge. The neighbouring Cu atoms are linked by carboxylato group in anti-anti configuration and all Cu(II) ions exhibit distorted square-pyramidal geometry. [Boonmak, 2008] 21 3 EXPERIMENTAL PART 3.1 Materials used We used Filter flask, Büchner funnel, Hirsch funnel, Erlenmeyer flask, beaker and magnetic stirrer with heating. The chemicals were obtained from commercial sources and they are gathered in the next Table 6. Table 6: Chemicals used in experiments. Name Mw(g/mol) Purity(%) Density(g/cm3) State NaOH 39,997 2,13 Solid NiSO4∙6 H2O 262,85 2,07 Solid Benzoic acid 122,12 1,27 2,2´-bpy 156,188 Solid EtOH 4.06 99% 0.78 Liquid Ba2+ 137,327 Liquid Water 18 1 Liquid 3.2 Syntheses Within the experimental part we have done syntheses with four different molar ratios of Ni, benzoate anion and 2,2bipyridine: 11 of Nickel: 2 of benzoate anion: 0 of 2,2bipyridine (1:2:0). Its name will be AW1 21 of Nickel: 2 of benzoate anion: 1 of 2,2bipyridine (1:2:1). Its name will be AW2 31 of Nickel: 2 of benzoate anion: 2 of 2,2bipyridine (1:2:2). Its name will be AW3 41 of Nickel: 2 of benzoate anion: 3 of 2,2bipyridine (1:2:3). Its name will be AW4 We have worked simultaneously with the above mentioned four systems. The experimental work was done in the following steps. 1st step includes the preparation of a 1 M solution of NaOH for the next reactions steps. During the 2nd step we have prepared four solutions, each by dissolving 657 mg of NiSO4∙6 H2O (2,5mmol) in 15 ml of distillate H2O. 22 As the 3rd step we added to each solution 8 ml of prepared 1 M solution of NaOH with the aim to prepare Ni(OH)2 as starting material according to the reactions: 𝑁𝑖𝑆𝑂4+ 2 𝑁𝑎𝑂𝐻 → 𝑁𝑖(𝑂𝐻)2+ 2𝑁𝑎++ 𝑆𝑂4 2− Within the 4th step the formed precipitate was decanted with warm water in order to remove soluble Na2SO4. The presence of SO42anions was checked by addition of Ba2+ ions according to the reaction 𝑆𝑂4 2− + 𝐵𝑎2+ → 𝐵𝑎𝑆𝑂4↓ (𝑤ℎ𝑖𝑡𝑒) It was necessary to do the decantation several times to rinse out the Na2SO4 thoroughly, till the precipitation reaction was negative. 23 As the 5th step we weighted 611 mg of benzoic acid (5 mmol) for all the four systems and dissolved it in 25 ml of EtOH, consequently we added the obtained ethanolic solution into the prepared Ni(OH)2. We have obtained a green precipitate (see the upper photo). The 6th step consists of adding the appropriate amount of solid 2,2´-bpy into the three reaction mixtures, namely 390 mg of 2,2´-bpy (2.5mmol) was used to prepare the ratio 1:2:1 in AW2, 781 mg of 2,2´-bpy (5mmol) was used to prepare the ratio 1:2:2 in AW3, and 1171 mg of 2,2´-bpy (7.5mmol) was used to prepare the ratio 1:2:3 in AW4. After dissolving the added 2,2´- bpy, we have obtained different coloured reaction mixtures (as the following photos describe). As the 7th step we have slowly heated the open beakers with the solutions till the temperature of 60  C during 30 minutes, to reduce the volume of the solution for more rapid crystallization. 24 You can see the colour changes with the amount of 2,2´-bpy we used. 8th step was the final step formed by filtration of the prepared solutions. The obtained solutions were left aside for crystallization. After two-three weeks the products AW1, AW2, AW3 and AW4, respectively occurred, and were collected by filtration and dried on air. The synthetic procedures were repeated twice. In the 1st series we obtained the following results: • The weight of the green microcrystalline powder AW1 was 152 mg (first filtration). The attempts to recrystallize AW1 from EtOH, MeOH or acetone in order to obtain single crystals were unsuccessful. • The weight of the blue powder of AW2 was 103 mg and by further crystallization of the filtrate we obtained 22 mg of crystals after first filtration. • The obtained colour of the solution AW3 (pink) was different from that expected (violet) so this synthesis was repeated (see below). • AW4 separated in the form of pink powder and its weight was 715 mg. 25 In the 2nd series of synthetic experiments we have obtained following results: • We filtrated product AW1 and obtained 45 mg of green microcrystalline powder (first filtration). The inspection of the obtained solid after first filtration under optical microscope indicated that the solid was contaminated by few white crystals of benzoic acid. Green product was cleaned mechanically under microscope and these was used for further analyses as AW1. The same product AW1 separated from the filtrate by further crystallization (second filtration, weight 34 mg). • As the result of synthetic procedure AW2 we have obtained light blue solution from which nice green needles separated (Fig. 18). The first filtration yielded 288 mg of AW2 and the second filtration yielded additional 274 mg of crystals of AW2 (Figure 18). These were used for CHN analysis and X-ray structure analysis. Figure 18: Green single crystals of AW2 From the above described synthetic procedures (solution method, diffusion method) aimed to isolate AW3 and AW4 we have not obtained single crystals. So we have done the syntheses using solvothermal method (in autoclave, Fig. 19) as follows: the reaction mixture was put in the autoclave, sealed, heated slowly to 110 °C and kept at this temperature during 7 days. After that time the autoclaves were slowly cooled to RT, opened and the formed solutions were left aside for crystallization. From the solution of AW3 some crystals separated which, however, were by IR spectrum identified as AW2. In the case of the second solution (AW4) a solid separated which was by IR spectrum identified as AW4 prepared by solution method (see above). 32 RESULTS AND DISCUSSION We have studied four different systems based on Ni(II), benzoate anion and bpy with different molar ratios, namely from 1:2:0 to 1:2:3. We have also investigated the properties of the different complexes that we have synthesized. We have used for syntheses mostly mild solution conditions and in two cases also the autoclave method. As the results of our synthetic experiments we have isolated and identified by CNH analyses and IR spectroscopy three solid products AW1, AW2 and AW4. Their formulas are: AW1 = Ni(C6H5COO)23H2O AW2 = [Ni(C6H5COO)2(bpy)] AW4 = [Ni(bpy)3](C6H5COO)25H2O By comparison with the literature it became clear that AW1 is the simplest complex and its formula is Ni(C6H5COO)2∙3H2O. This complex was already prepared and studied by Vráblová et al. [Ščerbová, 2015]. Product AW2 was prepared in the form of nice crystals of needle shape (see above Fig. 18). These were examined by prof. Falvello from University in Zaragoza and the obtained crystal data are gathered in Table 8. The structure is formed of [Ni(C6H5COO)2(bpy)] complex molecules, in which the Ni(II) atom is hexacoordinated by 2 ligands of benzoate anion and one of 2,2´-bipyridine. All ligands are of chelating type, the benzoate anions have two bonds O-Ni and the 2,2´-bipyridine have two bonds N-Ni (Fig. 24). The bond distances within the coordination sphere of Ni(II) are gathered in Table 9. As can be seen from this Table the Ni-N bonds are from the range 2.029(3)- 2.049(3) Å while the Ni-O bonds are somewhat longer; they are from the range 2.054(2)- 2.157(3) Å. The bite angles within the chelate rings are 79.53(13) for the chelate ring with bpy ligand, while the bite angles within chelate rings with benzoate anion exhibits values of 62.72(9) and 62.64(9) °. These geometric parameters are close to the corresponding values found by Baruah [2007]: Ni-N are from the range of 2.03 – 2.05 Å, N-O are from the range 2.05 – 2.15 Å and the bite angles are 79.48 ⁰ of chelate ring with bpy ligand and within chelate rings with benzoate anion the values are 62,53 and 62,57 ⁰. We were unsuccessful in preparation of the expected product AW3 for molar ration 1 of Ni: 2 of benzoic acid: 2 of bpy. The product obtained from this system was in fact the product AW2. 33 The product AW4 was identified as [Ni(bpy)3](C6H5COO)2∙5H2O and it seems it is a new compound not described in the literature. This represents a good step for the investigation of this type of complex. Unfortunately, we were not able to prepare it in the form of single crystals so here a further effort should be done in the future. 34 Table 8 Comparison of crystal data of [Ni(C6H5COO)2(bpy)] for our sample AW2 and that published one [Baruah, 2007]. Sample AW2 Published [Baruah, 2007] Empirical formula C24 H18 N2 Ni O4 C24 H18 N2 Ni O4 Molar mass [g/mol] 457.11 457.11 Crystal System Monoclinic Monoclinic Space group P 21/n P 21/n a [Å] 7.4309(2) 7.4322(2) b [Å] 16.7209(6) 16.7224(4) c [Å] 17.3510(7) 17.3528(4) α [] 90 90  [] 101.420(4) 101.3810(10) γ [] 90 90 Dimensions [Å3] 2113.20(13) 2114.27(9) Z 4 4 Absorption Coefficient [mm-1] 0.951 0.951 Form, colour, Needle, green Not given Crystal size [mm] 0,498 x 0,09 x 0,082 Not given Temperature [K] 294(2) 296(2) Radiation MoK [Å]  = 0.71073  = 0.71073 Θ range for data collection [] 4,605 – 27,101 not given - 29.09 Index ranges -9 ≤ h ≤ 9, -21 ≤ k ≤ 21, -22 ≤ l ≤ 22 -9 ≤ h ≤ 9, -22 ≤ k ≤ 19, -23 ≤ l ≤ 21 Reflections collected/ unique 14337/14337 GooF (S) 1.034 1.031 Final R indices [I > 2s(I)] R1 = 0.0523, wR2 = 0.1143 R1 = 0.0298 R indices (all data) R1 = 0.1017, wR2 = 0.1229 R1 = 0.0432 Larguest diff. peak and hole [ e Å-3] -0.279 ; 0.547 Not given 35 Table 9. Selected Bond lengths [A] and angles [°] for AW2 Ni(1)-N(1) 2.029(3) Ni(1)-N(2) 2.049(3) Ni(1)-O(4) 2.054(2) Ni(1)-O(1) 2.077(2) Ni(1)-O(2) 2.148(2) Ni(1)-O(3) 2.157(3) N(1)-Ni(1)-N(2) 79.53(13) O(1)-Ni(1)-O(2) 62.64(9) O(4)-Ni(1)-O(3) 62.72(9) Figure 24: Molecular structure of compound AW2. Its formula is [Ni(C6H5COO)2(bpy)] 36 Conclusion The results obtained can be gathered in the following points: 1. Within the theoretical part we have described the coordination chemistry of Ni(II) as central atom along with the properties and bonding possibilities of benzoate anion and bipyridine as ligands. 2. Within the experimental part we have studied the aqueous-ethanolic systems based on Ni(II) carbonate with benzoic acid and bipyridine with different molar ratios 1:2:0, 1:2:1, 1:2:2, 1:2:2. 3. As the results of our synthetic experiments we have prepared three complexes, namely Ni(C6H5COO)23H2O, [Ni(C6H5COO)2(bpy)] and [Ni(bpy)3](C6H5COO)25H2O and we have identified these compounds by chemical analyses and IR spectroscopy. The third compound has not been documented up to now, that is, we have synthesized it for the first time. 4. The complex [Ni(C6H5COO)2(bpy)] was prepared in the single crystal form. It crystal structure is molecular with two chelating benzoate and one chelating bpy ligand coordinated to the Ni atom. 37 6 Literature [1] ALFANO A., Cavazza C. (2020), structure, functions and biosynthesis of nickeldependent enzymes. [2] BARUAH M.A., Karmakar A., Barua B.J. (2007), Ring opening reactions of pyromellitic dianhydride for the synthesis of the first row transition metal dicarboxylate complexes. [3] BOWMAKER G.A., Effendy, S. Marfuah, B. W. Skelton, A. H. White (2005) Inorg. Chim. Acta, 358, 4371. 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