Mixed-Spin Binuclear Nickel(II) Complexes in Unsymmetrical Ligand Environments and Related Mononuclear Compounds: Electronic and Molecular Structures in Solution and in the Solid State

Nickel(II) complexes of three new heterodonor ligands (HL1, H2L2, and H3L3) based on 2-aminocyclopent-1-ene-1-dithiocarboxylate have been synthesized, and their crystallographic characterizations are reported. With the pentacoordinating ligands HL1 and H3L3, the products obtained (1 and 2) are both mononuclear square planar compounds in which one of the pyrazolyl arms of ligand HL1 and the bridgehead alkoxy oxygen of H3L3 are staying away from coordination in 1 and 2, respectively. The saturated three carbon alkanyl chain in the ligand H3L3 provides enough flexibility to generate tetrahedral distortion (dihedral angle, 22.7 °) in the planarity of 2. Compound 1 displays paramagnetic line-broadening in its 1H NMR spectrum due to oligomerization in solution. With the unsymmetrical binucleating ligand H2L2, two mixed-spin homodinuclear complexes (3 and 4) have been synthesized using pyrazole and 2mercaptopyridine as ancillary (mu)^2-bridging ligands. Both these complexes have square planar low-spin and spin-triplet nickel(II) centers which display both coordination number and donor set asymmetry in tandem. The compounds have been characterized by 1H NMR, electronic spectroscopy, and electrochemical studies.