DINUCLEAR NICKEL(II) COMPLEXES OF A SERIES OF DINUCLEATING MACROCYCLES WITH SIMILAR OR DISSIMILAR COORDINATION SITES - SYNTHESIS, STRUCTURE AND PHYSICOCHEMICAL PROPERTY

The dinucleating macrocycles H-2(L(m,n)) containing two 2,6-di(aminomethyl)-4-methylphenol entities combined through two alkane chains, -(CH2)m- (m=2, 3) and -(CH2)n- (n=2, 3, 4, 5), at the amine nitrogens, form nickel(II) complexes of the general formula [Ni2(L(m,n))(OAC)2] ((m,n)=(2,2), (2,4), (2,5), (3,3)) and [Ni2(L2,3)(OAc)(NCS)(CH3OH)]. [Ni2(L2,2)(OAc)2].10H2O crystallizs in the triclinic system of space group P1BAR with a=9.983(2), b=12.832(2), c=7.932(1) angstrom, alpha=101.29(1), beta=101.08(2), gamma=106.57(2)-degrees, V=921.1(3) angstrom3 and Z=1. The refinement converges with R=5.65 and R(w)=5.89% based on 2308 reflections with \F(o)\ > 3sigma(\F(o)\). The macrocycle adopts a folded conformation and each nickel has a cis-beta octahedral geometry with the N2O2 donor set of the macrocycle and two oxygens of a bidentate acetate group. The Ni-Ni separation bridged by two phenolic oxygens is 3.004 angstrom and the Ni-O-Ni angle is 95.6-degrees. Cryomagnetic properties (4.2-300 K) of the complexes are well reproduced based on the spin Hamiltonian K=-2JS1.S2-D(S(z1)2-S(z2)2) with a positive exchange integral (J=+10.1 to +2.1 cm-1) and a negative zero-field splitting parameter (D=-0.53 to -2.40 cm-1). Each complex shows two reduction waves and two oxidation waves attributable to the metal centers.