X-ray diffraction, spectral and magnetic studies of the nickel(II) thiocyanate complexes with tridentate 2,6-dithiocarboxamidopyridine SNS and 2,6-dicarboxamidopyridine ONO ligands: Influence of donor atoms on the coordination geometry of nickel

Abstract

The systematic investigation of electronic effects on the coordination geometry of nickel(II) thiocyanate complexes with the tridentate N, N, N′, N′-tetraethylpyridine-2,6-dithiocarboxamide (S-dept) and N, N, N′, N′-tetraethylpyridine-2,6-dicarboxamide (O-deap) ligands shows a significant change in the geometry of the metallic site. Their complexes conform to composition [Ni 2(μ-NCS) 2(S-dept) 2(NCS) 2] ( 1), [Ni(NCS) 2(O-deap)(CH 3CN)] · CH 3CN ( 2) and [Ni(NCS) 2(O-deap)(C 2H 5OH)] ( 3), respectively. X-ray crystallographic studies were done for 1– 3. In the crystal lattice, complex 1 exists as a centrosymmetric dimer in which the dinuclear core is bridged by two N-bonded thiocyanate groups. The near octahedral geometry of the nickel atom is achieved through the two bridging N atoms of the thiocyanate groups, three SNS donor atoms of the ligand S-dept and through the terminal nitrogen atom of a non-bridging thiocyanate moiety. To the best of our knowledge, complex 1 presents the first example in literature with the highest asymmetry in N-bridging thiocyanato ligands. Ni ion is coordinated to ONO donor set of atoms of O-deap and two N-bonded NCS terminal groups. The sixth coordination site is completed by the N atom of an acetonitrile molecule. The coordination around Ni atom in 3 is also distorted octahedral. The change in the sixth coordination position from acetonitrile in 2 to ethanol in 3 has a profound influence in the overall topology of the metal–ligand complex. The complex interplay of weak interactions in stabilizing the 3-dimensional lattice of these molecules is well demonstrated.