MAGNETIC EXCHANGE THROUGH OXALATE BRIDGES - SYNTHESIS AND CHARACTERIZATION OF (MU-OXALATO)DIMETAL(II) COMPLEXES OF MANGANESE, IRON, COBALT,NICKEL, COPPER, AND ZINC

The syntheses and characterization of a series of binuclear mu-oxalato complexes of the general type [(N)(4)M(C2O4)M(N)(4)](2+), where M is Mn-II, Fe-II, Co-II, Ni-II, Cu-II, and Zn-II, are described. The ligan ds (N)(4) represent the tetradentate ligands N,N'-bis(2-pyridylmethyl) -1,2-ethanediamine (bispicen, H18N4),N,N'-bis(2-pyridylmethyl)1,3-prop anediamine (bispictn, C15H2ON4), and s(2-pyridylmethyl)-N,N'-dimethyl- 1,2-ethanediamine (bispicME(2)- en, C16H22N4). The crystal structures of five representative complexes have been determined. The manganese c omplex [(bispicen)Mn(C2O4)Mn(bispicen)l(ClO4)(2) (1a) crystallizes in the noncentrosymmetric orthorhombic space group Pna2(1) with four binu clear formula units in a cell of dimensions a = 21.771 (4), b = 23.650 (5), and c = 7.328 (2) Angstrom. The corresponding Fe(II), Cu(II), an d Zn(II) complexes (2a, 5a, and 6a, respectively) are isomorphous with this manganese complex 1a. The complex picMe(2)en)Mn(C2O4)Mn(bispicMe (2)en)](ClO4)(2)(1c) crystallizes in the centrosymmetric monoclinic sp ace group P2(1)/c With two binuclear formula units in a cell of dimens ions a = 9.218 (2) Angstrom, b = 13.189 (2) Angstrom, c = 17.213 (3) A ngstrom, and beta = 92.780 (10)degrees. The Co complex [(bispicen)Co- (C2O4)Co(bispicen)](ClO4)(2) . H2O (3a) crystallizes in the triclinic space group <P(1)over bar> with one binuclear formula unit in a cell o f dimensions a = 8.832 (2) Angstrom, b = 9.297 (2) Angstrom, c = 13.04 5 (3) Angstrom, alpha = 108.01 (3)degrees, beta = 98.48 (3)degrees, an d gamma = 93.31 (3)degrees. The corresponding Ni(II) analogue, 4a, is isomorphous with this cobalt complex. The copper(II) complex [(bispice n)Cu(C2O4)Cu(bispicen)](ClO4)(2) (5a) is isomorphous with la: a = 21.5 31(4), b = 23.708(5), and c = 7.186(1) Angstrom. The copper(II) comple x (bispicMe(2)en)Cu(C2O4)Cu(bispicMe(2)en)](ClO4)(2) (5c) crystallizes in the centrosymmetric monoclinic space group P2(1)/n with two binucl ear formula units in a cell of dimensions a = 8.089 (2) Angstrom, b = 22.001 (4) Angstrom, c = 12.179 (2) Angstrom, and beta = 107.93 (3)deg rees. The corresponding Co(II), Ni(II), and Zn(II) complexes (3c, 4c, and 6c, respectively) are isomorphous with this copper complex. All fi ve complexes contain six-coordinate metal centers bridged by planar bi s-bidentate oxalate groups. The J-values for these oxalato bridged met al complexes are approximately 2, 6, 10, 33, and 2 cm(-1) for Mn-II, F e-II Co-II, Ni-II, and Cu-II, respectively. This is explained as a res ult of the magnetic interaction between the x(2)-y(2) orbitals on the two metal atoms, and in spite of the difference between the J-values f or these complexes it is shown that the interaction matrix element bet ween these orbitals have approximately the same value for the Mn-II, F e-II, Co-II and Ni-II complexes. The small J-values for the Cu-II comp lexes are caused by the fact that in these cases the x(2)-y(2) orbital s are not the magnetic orbitals.