PARAMAGNETIC-RESONANCE AND MAGNETISM OF COPPER(II) COMPLEXES WITH 2-PYRIDYLMETHYL)-1,4,8,11-TETRAAZACYCLOTETRADECANE

EPR (X- and Q-band) and magnetic susceptibility over the temperature r ange 4.2-300 K are reported for a number of dinuclear Cu(II) complexes derived from N,N',N'',N'''-tetrakis(2-pyridylmethyl)-1,4,8,11 -tetraa zacyclotetradecane (tpmc). [Cu2X(tpmc)](C1O(4))(3) . n (X = N-3, F (n = 2CH(3)CN), Cl (n = H2O), Br, I (n = H2O), NO2), where the X anions b ridge two copper ions and the tpmc ligand has the boat coordination mo de, [Cu(2)tpmc] (ClO4)(4) and [Cu(2)X(2)tpmc] (ClO4)(2) (X = N-3, NCS) , where the X anions occupy apical positions and the tpmc ligand has t he chair coordination mode. It is established that the properties of t he complexes are determined by intramolecular exchange interactions oc curring through both the bridging anion X and the tpmc ligand as well as by magnetic dipole-dipole interactions. In the majority of the comp ounds the exchange is weak, e.g. it corresponds to J equals 2.0 cm(-1) for [Cu2N3(tpmc)](ClO4)(3) and 3.4 cm(-1) for [Cu-2(N-3)(2)(tpmc)] (C lO4)(2) . [Cu2OH(tpmc)] (ClO4)(3) . 2H(2)O is an exception in which an tiferromagnetic (AF) exchange of about several tens of wave numbers is operating. The EPR spectrum of this complex is described by the follo wing spin Hamiltonian parameters: g(z) = 2.25, g(y)= 2.05, gx = 2.04, D = 0.06 cm(-1), E = 0.005 cm(-1). Moreover, an extremely strong influ ence of lattice perturbations on the exchange interactions is recogniz ed for this compound: a partial loss of the H2O molecules (coordinated at a greater distance) by a small amount of dinuclear fragments resul ts in a transformation of an AF exchange into a ferromagnetic or a wea k AF one with different values of the anisotropic spin-spin interactio n parameters (for example, D = 0.172 cm(-1), E = 0.015 cm(-1)). The EP R spectra of frozen solutions of all the complexes in NMF are typical for the triplet state, with a distinctly resolved hyperfine structure for the Delta M-S = 1 and Delta M-S = 2 signals, and show very similar values of g factors, hyperfine and fine structure parameters (g(z) = 2.255, A(z) = 0.0087 cm(-1), g(x,y) = 2.052, D = 0.025 cm(-1)), implyi ng the same molecular structure for dinuclear complexes formed in solu tion as a result of the loss of one bridging X by dimers with the boat configuration or two X anions by dimers with the chair configuration.