CHANGES IN GEOMETRIES AND SPIN STATES OF THIOLATO-SCHIFF BASE NIN2S2 COMPLEXES CONTAINING N,N'-BIPHENYL BACKBONES

Four new 5-formylpyrazole-based thiolato Schiff base nickel(II) comple xes (1-4) have been synthesized from the corresponding ligands and nic kel(II) acetate. A new 2-mercaptobenzaldehyde Schiff base nickel(II) c omplex (5) has been synthesized by two routes. X-ray structural analys es on three of the complexes showed the following: 1, chemical formula C26H26N6S2Ni, monoclinic, space group P2(1)/n with a = 10.438(2) Angs trom, b = 12.450(3) Angstrom, c = 19.616(3) Angstrom, beta = 94.33(1)d egrees, Z = 4, and R = 0.044 for 3365 reflections; 4, chemical formula C34H26N6S2Ni, monoclinic, space group C2/c with a = 19.242(3) Angstro m, b = 9.757(2) Angstrom, c = 19.691(3) Angstrom, beta = 125.84(1)degr ees, Z = 4, and R = 0.032 for 2206 reflections; 5, chemical formula C2 8H22N2S2Ni, monoclinic, space group C2/c with a = 25.230(4) Angstrom, b = 11.098(2) Angstrom, c = 17.287(8) Angstrom, beta = 98.46(3)degrees , Z = 8, and R = 0.047 for 1912 reflections. The coordination geometry in 1 is distorted tetrahedral while in 4 and 5 it is close to cis-squ are planar despite the influence of the (6,6'-dimethyl)biphenyl group in the tetradentate ligand backbone. The bond distances are as follows . Ni-S: 1, 2.239(1), 2.243(1) Angstrom; 4, 2.185(1) Angstrom; 5, 2.152 (2), 2.184 (2) Angstrom. Ni-N: 1, 1.963(2), 1.968(2) Angstrom; 4, 1.92 7(2); 5, 1.931(5), 1.917(6) Angstrom. The distortions from tetrahedral to planar geometry are manifest in some interesting changes in dihedr al angles and donor atom ''bite'' distances. The magnetic susceptibili ties were measured in the temperature range 4.2-300 K for 1-5. The sus ceptibilities of 1 and 2 could be fitted well to a simple axial spin H amiltonian with S = 1, D = 34 cm(-1) and S = 1, D = 53 cm(-1), respect ively. Complexes 3-5 are diamagnetic and showed only small temperature -independent paramagnetic susceptibilities. Although no temperature-in duced spin changes were observed for solids of 1-4, they all showed a (1)A(lg) reversible arrow T-3(1) equilibrium in chloroform solutions. Each of complexes 1-5 show LF, CT, and intraligand spectral features i n the spectral region 5,000 - 40,000 cm(-1). Bands assigned to the hig h-spin and low-spin forms are observed separately. The thermodynamic p arameters for the high-spin reversible arrow low-spin equilibria in ch loroform solutions were obtained by using the Evans method, variable-t emperature H-1 NMR spectra, and variable-temperature electronic spectr a. Complexes 1-4 exhibit equilibrium constants K-eq (=N-HS/N-LS) in th e range of 0.456-0.080.