engleski

A series of nickel(II) thiocyanate complexes comprising various molar contents of isonicotinamide and water as ligands or co- crystallized moieties – an experimental and computational study

Seven complexes, [Ni(NCS)2(isn)2(H2O)2]·2H2O (1), [Ni(NCS)2(isn)2(H2O)2] (2), [Ni(NCS)2(isn)3(H2O)]·2.5H2O (3), [Ni(NCS)2(isn)3(H2O)]·3[Ni(NCS)2(isn)4]·9H2O (4), [Ni(NCS)2(isn)4]·3H2O (5), [Ni(NCS)2(isn)4]·2(isn) (6) and [Ni(NCS)2(isn)4]·1.25H2O (7), of Ni(II) thiocyanate with isonicotinamide (isn = pyridine- 4-carboxamide) and water as ligands of biological importance were prepared in aqueous solutions through crystal screening by variation of the isonicotinamide concentration. They were characterized by the single-crystal X-ray diffraction method and DFT calculations, while 1–6 were characterized also by NMR and IR spectroscopy and elemental and thermal analyses. In all complexes, the nickel atom is octahedrally coordinated with two thiocyanate N atoms but with different number of isonicotinamide N and water O atoms. The R46(12) and R46(16) hexamers were found in 1, R24(8) tetramer and R22(8) dimer in 2, while very complex hydrogen bonding ring patterns R24(8), R22(10), R34(14) and R610(24) were observed in 3. In 4, R46(16) and R66(20) hexamers were formed as well as typical head-to-head amide– amide hydrogen bond R22(8) dimers in a combination with two R34(10) tetramers. R24(8) cyclic water tetramers linked in zigzag hydrogen bonded chains, carboxamide catemer C(4) chains with the R68(24) ring and two fused rings R23(12) and R22(16) were found in 5. A 2D corrugated sheet network in the (002) planes with a combination of R44(16), R46(16), R66(24) and R68(24) rings were formed in 6. DFT calculations revealed that altered metal complex stoichiometries originate in different ligand affinities towards nickel, isn > SCN− > H2O. Only neutral complexes were investigated so the nickel : thiocyanate ratio was always 1 : 2 while the concentration of isonicotinamide strongly influenced the number of coordinated isn ligands. The final 3D crystal structures emerged as a compromise between the nucleation process, reactant ratios, ligand affinities and intermolecular interactions in the crystal packing.

Nickel(II) complexes

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