STRUCTURE AND MAGNETIC-PROPERTIES OF 2,2'-BIPYRIMIDINE-(BPYM)-BRIDGEDBINUCLEAR MN-II COMPLEX - [MN-2(H2O)(6)(BPYM)(SO4)(2)]

A binuclear Mn-II complex of the formula [Mn-2(H2O)(6)(bpym) (SO4)(2)] (bpym = 2,2'-bipyrimidine) has been prepared and its structure and ma gnetic properties have been determined by X-ray diffraction, ESR and m agnetic susceptibility measurements. The structure consists of two Mn- II ions bridged by bis-bidentate bpym ligands and coordinated by H2O a nd SO42- groups to make a binuclear neutral [Mn-2(H2O)(6)(bpym)(SO4)(2 )] unit. The coordination geometry around the manganese atom is that o f a highly distorted octahedron: The averaged Mn-II-N distance (2.31 A ngstrom) is longer than those of the Mn-II-O (2.16 Angstrom) of H2O-Mn -II and Mn-II-O (2.069 Angstrom) of SO42--Mn-II. The configuration of coordinated SO42- groups has a disorder with a 6:4 ratio. X-band ESR s pectra of the complex in water shows an isotropic signal with g = 2.00 7 and A = 94 G. Cryomagnetic investigations (4-300 K) reveal a weak an tiferromagnetic spin exchange with J = -9.96 cm(-1) between manganese( II) cations through the bpym bridge.