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Two polymeric malonato-bridged manganese(II) complexes of formula [Mn(mal)(H(2)O)(2)](n)() (1) and [Mn(2)(mal)(2)(4,4'-bipy)(H(2)O)(2)](n)() (2) have been synthesized and characterized (mal = malonate dianion; 4,4'-bipy = 4,4'-bipyridine). The crystal structure of complex 1 was already known. Complex 2 crystallizes in monoclinic space group P2(1)/n, Z = 2, with unit cell parameters of a = 7.2974(10) A, b = 18.7715(10) A, c = 7.514(3) A, and beta = 91.743(12) degrees. The structure determination reveals that the complex [Mn(2)(mal)(2)(4,4'-bipy)(H(2)O)(2)](n)() (2) is a 3D network being composed of Mn-malonate sheets which are pillared by bidentate 4,4'-bipy spacer forming small voids. The Mn-Mn distances through Mn-mu-(O3-C8-O4)-Mn, Mn-mu(O1-C6-O2)-Mn, and Mn-mu-4,4'-bipy-Mn bridges are 5.561, 5.410, and 11.723 A, respectively. The magnetic behaviors of complexes 1 and 2 in the temperature range 300-2 K are very close, corresponding to a weak antiferromagnetic coupling. The magnetic pathways of complex 1 are through two Mn-O-C-O-Mn with anti-anti conformation and two Mn-O-C-O-Mn with syn-anti conformations and in complex 2 through all Mn-O-C-O-Mn with syn-anti conformations. Both syn-anti and anti-anti conformations create weak antiferromagnetic coupling, and the susceptibility data are fitted by the expansion series of Lines and the Curély formula for an S = 5/2 antiferromagnetic quadratic layer, based on the exchange Hamiltonian H = -Sigma(nn)()JS(i)()S(j)(). The best fit is given by the superexchange parameters J = -0.32 cm(-)(1) and g = 2.00 for complex 1 and J = -0.14 cm(-)(1), J(inter) = -0.031 cm(-)(1), and g = 2.00 for complex 2. Finally, in both the complexes there is a magnetic pathway Mn-O-C-C-C-O-Mn, and this pathway through the three carbon atoms of the malonato-bridging ligand could be considered negligible.

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Three new nickel(II) dinuclear azide-bridged compounds, (µ ,3-3) 2[ ( )2]2( 6)2 (1), (Mi,3-N3)2[Ni(l,3-pn)2]2-[B(C6H5)4]2 (2), and (Mi,3-N3)2[Ni(l,2-pn)]2(PF6)2 (3), have been synthesized and characterized (en = ethylenediamine; 1,3-pn = 1,3-diaminopropane; 1,2-pn = 1,2-diaminopropane). The crystal structures of 1 and 2 have been solved. Complex 1 crystallizes in the monoclinic system, space group C2/c, with fw = 731.79, a = 15.252(3) Á, b = 17.872(3) A, c = 12.102(2) A, ß = 126.76(2)°, V= 2643(1) A3, Z = 4, R = 0.053, and Rw = 0.057. Complex 2 crystallizes in the monoclinic system, space group P2\/n, with fw = 1136.4, a = 9.997(2) k, b = 20.838(3) A, c = 14.269(3) A, ß = 96.76(2)°, V= 2952(2) k\Z = 2,R = 0.052, and Rw = 0.052. In both complexes the nickel atom is placed in a distorted octahedral environment. The magnetic properties of these compounds have been studied by means of susceptibility measurements vs temperature. The xm vs T plots for 1-3 show the typical shapes for antiferromagnetically coupled nickel(II) dinuclear complexes. By using the spin Hamiltonian -JSiS2, J values for 1-3 were calculated to be -4.6, -114.5, and -77.2 cm-1, respectively. Extended Hückel calculations on the two structurally characterized complexes, compared with two other analogous complexes previously reported in the literature, indicate that the dihedral angle between the N-Ni-N plane and the plane formed by the two N3-bridging ligands is the main factor which dominates the magnetic coupling: the smaller the dihedral angle, the stronger the antiferromagnetic coupling.