2,2'-Bipyrimidine-Bridged Homobinuclear Complexes

Abstract

The synthesis and structural and magnetic properties of a series of 2,2'-bipyrimidine- (Bpm-) bridged binuclear complexes L2M(Bpm)ML2 of Mn(II), Co(II), and Ni(II) are reported, where L = F3CC(O)CHC(O)CF3 (hfa), F3CC(O)CHC(O)CH3 (tfa), and F3CC(O)CHC(O)C6H5 (Phtfa). Mass spectroscopic observation of the [ML2(Bpm)] + or [ML2(Bpm) - F]+ ions distinguishes the binuclear complexes from the mononuclear adducts. The complexes all exhibit antiferromagnetic exchange with a maximum in the magnetic susceptibility in the 18-23 K region for the Ni(II) complexes and in the 13-16 K region for the Co(II) complexes with L = tfa and Phtfa. The structure of one of the complexes, (hfa)2Co(Bpm)Co(hfa)2, is reported. It is monoclinic, P21/n, with Z = 2, a = 8.790 (3) Å, b = 17.980 (4) Å, c = 12.490 (6) Å, and β = 102.76 (3)°. The structure was refined to a R value of 4.9%. The two equivalent cobalt atoms are each bound to four hfa oxygens and two cis nitrogens of the Bpm in a slightly distorted octahedral environment. The cobalt atoms are 0.09 Å out of the Bpm plane, which provides favorable overlap of the metal dx2-y2 orbitals with the ligand π system, allowing magnetic exchange to occur. The metal-metal separation is 5.750 (2) Å, the cobalt-oxygen bonds average 2.051 Å, and the cobalt-nitrogen bonds are 2.150 (3) Å. © 1985, American Chemical Society. All rights reserved.