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)]center dot 2H(2)O (1), [Ni(NCS)(2)(isn)(2)center dot H2O)(2)] (2), [Ni(NCS)(2)(isn)(3)center dot H2O)]center dot 2.5H(2)O (3), [Ni(NCS)(2)(isn)(3)center dot H2O)]center dot 3[Ni(NCS)(2)(isn)(4)]center dot 9H(2)O (4), [Ni(NCS)(2)(isn)(4)]center dot 3H(2)O (5), [Ni(NCS)(2)(isn)(4)]center dot 2(isn) (6) and [Ni(NCS)(2)(isn)(4)]center dot 1.25H(2)O (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 R-6(4)(12) and R-6(4)(16) hexamers were found in 1, R-4(2)(8) tetramer and R-2(2)(8) dimer in 2, while very complex hydrogen bonding ring patterns R-4(2)(8), R-2(2)(10), R-4(3)(14) and R-10(6)(24) were observed in 3. In 4, R-6(4)(16) and R-6(6)(20) hexamers were formed as well as typical head-to-head amide-amide hydrogen bond R-2(2)(8) dimers in a combination with two R-4(3)(10) tetramers. R-4(2)(8) cyclic water tetramers linked in zigzag hydrogen bonded chains, carboxamide catemer C(4) chains with the R-8(6)(24) ring and two fused rings R-3(2)(12) and R-2(2)(16) were found in 5. A 2D corrugated sheet network in the (002) planes with a combination of R-4(4)(16), R-6(4)(16), R-6(6)(24) and R-8(6)(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.

Automated summary

In this study, seven nickel(II) thiocyanate complexes were synthesized and their crystal structures and coordination modes were investigated under varying isonicotinamide concentrations. They were characterized by single-crystal X-ray diffraction and DFT calculations, and some complexes were also analyzed using NMR and IR spectroscopy.