New binuclear Mn-II and Fe-II complexes supported by 1,4,8-triazacycloundecane

Two new binuclear metal complexes supported by 1,4,8-triazacycloundecane (tacud) are reported. [Fe-2(tacud)(2)(mu-Cl)(2)Cl-2] (1) and [Mn-2(tacud)(2)(mu-Cl)(2)Cl-2] (2) are isomorphs consisting of bis(mu-chloro) bridged metal centers along with terminal chloro groups and tacud ligands. Both compounds 1 and 2 crystallize in the P (1) over bar space group. For 1, a = 7.7321(12) angstrom, b = 7.8896(12) angstrom, c = 11.4945(17) angstrom, alpha = 107.832(2)degrees, beta = 107.827(2)degrees, gamma = 92.642(2)degrees, V = 627.85(17) angstrom(3) and Z = 1. For 2, a = 7.7607(12) angstrom, b = 7.9068(12) angstrom, c = 11.6111(18) angstrom, alpha = 108.201(2)degrees, beta = 108.041(2)degrees, gamma = 92.118(3)degrees, V = 636.47(17) angstrom(3) and Z = 1. Variable-temperature and variable-field magnetic susceptibility studies on 1 indicate the presence of weak ferromagnetic interactions between the high-spin iron(II) centers in the dimer (J = + 1.6 cm(-1)) and the crystalline field anisotropy of the ferrous ion (D = -2.8, E = -0.1 cm(-1)). Variable temperature magnetic susceptometry studies on 2 indicate that weak antiferromagnetic coupling exists between the manganese(II) centers (J = -1.8 cm(-1)). Compounds 1 and 2 retain their dinuclearity in weakly coordinating or low polarity solvents, while both become mononuclear in solvents such as methanol.