Two new tetranuclear mu(4)-carbonato copper(II) complexes. Syntheses, crystal structure and magnetic behaviour of [(mu(4)-CO3)(mu-Br)(2){CU4-(bapa)(4)}]Br-4 and [(mu(4)-CO3)(mu-Cl)(2){Cu-4(bapma)(4)}]Cl-4 center dot 12H(2)O [bapa equals bis(aminopropyl)amine and bapma equals bis(aminopropyl)methylamine]

The syntheses, by fixation of atmospheric CO2, and the crystal structures of the new tetranuclear mu(4)-CO32- compounds [(mu(4)-CO3)(mu-Br)(2) {Cu-4(bapa)(4)]Br-4 1 and [(mu(4)-CO3)(mu-Cl)(2)(Cu-4(bapma)(4))]Cl-4 . 12H(2)O 2, [bapa and bapma are bis(3-aminopropyl)amine and bis(3-aminopropyl)methylamine respectively] are reported. Crystallographic data for 1 space group C2/c, a = 14.928(5), b = 19.010(3), c = 17.337(4) Angstrom, beta = 92.75(4)degrees, U = 4914(2) Angstrom(3) and Z = 4, for 2 space group P2(1)/n, a = 14.947(6), b = 13.047(4), c = 16.084(5) degrees, beta = 104.75(5)degrees, U = 3033(2) Angstrom(3) and Z = 2. The analogous compound [(mu-CO3)(mu(4)-Cl)(2){Cu-4(bapa)(4)}Cl-4 3 has been also prepared for comparative purposes; 1-3 show very strong antiferromagnetic coupling. According to the molecular structures, the experimental data were fitted to the expression derived from the Hamiltonian H = - 2J(12)S(1) . S-2 - 2J(13) (S-1 . S-2 + S2S4) - 2J(14) (S-1 . S-4 + S-2 . S-4) - 2J(34) S-3 . S-4, which corresponds to a rectangular array of spins. The best fit parameters were for 1-3 respectively: 2J(12) = -275(14), -390(12), -212(8); 2J(34) = -31(4), -26(7), -26(3); 2J(14) = -57(10), -10(12),-72(9); 2J(13) = -8(8), 22(10), -20(7) cm(-1); g = 2.03(1), 2.09(1) and 2.12(1).