SYNTHESIS AND STRUCTURE OF TETRACOORDINATED NICKEL(II) COMPLEXES OF DEPROTONATED CHELATED AMINOAZA LIGANDS - X-RAY CRYSTAL-STRUCTURE OF BIS[1-ISOPROPYL-3-METHYL-4-(4-METHYLPHENYLAZO)-5-(4-METHOXYPHENYLAMIDATO)PYRAZOLE] NICKEL(II)

Tetracoordinate nickel(II) complexes NiL2 derived from the deprotonated forms of aminoazoligands HL were prepared and investigated by spectroscopy and magnetic susceptibility measurements. The magnetic moments, which lie in the 3.1-3.6 B.M. range correspond to the occurrence both in solution and in the solid state of the high spin (S = 1) form and a tetrahedral configuration at the metal centre. The u.v. spectra exhibit three ligand field bands at 1020-1280 nm characteristic of high spin nickel(II) complexes. The large isotropic chemical shifts found in the H-1 n.m.r. spectra are consistent with partial delocalization of unpaired electron spin density to the ligand HOMO. The X-ray single crystal structure of NiL24[L4 = 1-isopropyl-3-methyl-4-(4-methylphenylazo)-5-(4-methoxyphenylamino)pyrazole] reveals that the metal is coordinated by four nitrogen atoms in tetrahedral configuration with an angle of 90-degrees between the N(1)NiN(2) and N(6)NiN(7) planes belonging to the different almost planar metallocycles. The rates of R reversible S interconversion of the tetrahedral configuration for NiL24 and NiL25 [L5 = 1-isopropyl-3-methyl-4-phenylazo-d5-5-(4-methoxyphenylamino)pyrazole] are slow on the n.m.r. timescale. In contrast to NiL21-Ni26,NiL27, which contains coordinated NH-groups instead of NAr-groups, is planar.