Binuclear copper(II) complexes of some sexadentate phthalazine-hydrazone ligands with strong antiferromagnetic exchange

Abstract

Sexadentate phthalazine-hydrazone ligands (N 6), involving pyridine and N-methylimidazole as peripheral donor groups, form binuclear hydroxo-bridged copper(II) complexes which exhibit very strong antiferromagnetic exchange (−2 J=885−1211 cm −1), which is propagated via a superexchange mechanism through the bridging diazine (NN) and hydroxide groups. When the hydroxide bridge in [Cu 2(APHPH)(OH)(H 2O) 2](ClO 4) 2·H 2O (APHP=1,4-dihydrazinophalazine-bis(2-pyridine) acetaldimine) (−2 J=988 cm −1) is replaced by a pyrazolide bridge, a dramatic decrease in exchange is observed (−2 J=521 cm −1) indicating the importance of hydroxide as a dominant superexchange bridge. The complexes are highly colored, exhibiting very intense visible absorptions (16 400–16 700 cm −1) associated with charge transfer transitions. The crystal and molecular structure of [Cu 2(APHPH)(OH)(H 2O) 2](ClO 4) 2·H 2O ( VI) is reported. VI crystallized in the monoclinic system, space group P2 1/ n, with a=8.0110(20), b=24.100(5), c=15.6750(20) Å, β=100.240(20)° and four formula units per unit cell. Refinement by full-matrix least-squares gave final residuals of R=0.076 and R w=0.038. This complex has a hydroxo-bridged suare-pyramidal structure with a CuCu separation of 3.296(2) Å and a CuO(H)Cu angle of 117.8(3)°.