Synthesis, spectroscopic and structural investigation of two nickel(II) thiocyanate complexes with isonicotinic acid

Two co-crystals of trans-[Ni(NCS)2(H2O)2(isonicH)2] with isonicotinic acid and water molecules (isonicH = isonicotinic acid, i.e., pyridine-4-carboxylic acid) were obtained by reaction of Ni(NO3)2·6H2O, isonicH and KSCN in 1:2:2 molar ratio in aqueous media. One co-crystal [Ni(NCS)2(H2O)2(isonicH)2]2·4(isonicH)·3(H2O) (2), is obtained from reaction which has been performed at room temperature while the other one, [Ni(NCS)2(H2O)2(isonicH)2]·(isonicH)·2(H2O) (1), was obtained by refluxing the reaction mixture for a few hours. The complexes are characterized by IR-spectroscopy and thermal and X-ray crystallographic methods. The compounds crystallize in monoclinic C2/c (1) and P21/c (2) space groups and in both complexes N4O2 nearly perfect octahedron around nickel is established. In both compounds molecules are linked into three-dimensional framework by O–H⋯O, N–H⋯O and O–H⋯S hydrogen bonds. The co-crystallized isonicotinic acid molecules are mutually linked forming C21(7)[R21(4)] (1) and in C(7) (2) hydrogen-bond motifs along b axis. The IR and thermal data correlate with the structures of the complexes in the solid state.