RESUMO
The synthesis, crystal structure, and magnetic properties are reported for the new bimetallic compound Cu(op)(2)MnCl(4), where op = HN(CH(2))(5)NH. The compound, C(10)H(24)N(4)Cl(4)CuMn, crystallizes in the monoclinic space group P2(1)/n. Cell dimensions are as follows: a = 15.316(3) Å, b = 16.608(3) Å, c = 7.141(2) Å, beta = 100.01(5) degrees, Z = 4. The structure consists of well-separated and magnetically equivalent layers which are composed of chloride-bridged Cu(op)(2)MnCl(4) binuclear units connected by rather loose Cu-N-H.Cl-Mn contacts. The MnCl(4) fragment approximates tetrahedral symmetry. The Cu(II) geometry is (4 + 1) square-pyramidal with the apical position occupied by a bridging chloride ligand and the basal ones by the nitrogen atoms from the organic ligands. The shortest interlayer M.M separations, approximately 7 Å, are of the Mn.Cu type. Magnetic susceptibility and single-crystal EPR measurements for the compound have been carried out over the range 4-300 K. At room temperature the chiT product (per MnCu unit) has a value of 4.84 emu.mol(-)(1).K, close to that expected for uncoupled S = (5)/(2) and S = (1)/(2) spins. When the temperature is lowered, chiT remains almost constant until 80-90 K, slightly increases to reach a maximum at approximately 13 K (5.21 emu.mol(-)(1).K), and then rapidly decreases. Comparison between theory and experiment, made with use of both a mean field corrected dimer model and an approximate 2-D model, indicates that Mn(II).Cu(II) exchange is ferromagnetic within the dimers (J(1) approximately 2.6 cm(-)(1)) and antiferromagnetic among dimers, with J values between -0.07 and -0.03 cm(-)(1) (the interaction Hamiltonian is of the form H = -2JS(A).S(B)). Single-crystal EPR spectra recorded along the a, b, and c axes show a large temperature dependence of the g factors: at 4.2 K, g(a) = 2.10, g(b) = 1.96, and g(c) = 2.01. This pattern substantiates the presence of a 2-D magnetic structure with ferromagnetic intradimer exchange and interdimer antiferromagnetic exchange of weaker magnitude. The opposite signs of the interactions are ascribed to the local symmetries of the Cu(II) and Mn(II) ions.
RESUMO
The X-ray structures of the isomorphous Mg2+, Ca2+, Mn2+ and Co2+ complexes of ATP have been determined. The metal ions are wrapped in hexa-coordination by the alpha, beta and gamma phosphate groups of two ATP molecules thus blocking the interaction of the metal ions with the adenine base. A second metal ion which is fully hydrated, M(H2O)2+(6), is engaged in a strong hydrogen bond with the gamma phosphate group of ATP and suggests a possible step in facilitating the cleavage between the beta and gamma phosphates in phosphoryl transfer reactions.
