Detection and measurement of noncoincidence between the principal axes of the g-matrix and zero-field splitting tensor using multifrequency powder EPR spectroscopy: application to cis-[(NH(3))(2)Pt(1-MeU)(2)Cu(H(2)O)(2)](SO(4)) x 4.5H(2)O (1-MeU = monoanion of 1-methyluracil).

Multifrequency continuous wave EPR spectra (4-34 GHz) on a powder of the title compound are consistent with a spin-triplet state. This arises from interaction between centrosymmetrically related pairs of copper(II) ions in the solid. The spectra at all frequencies have been simulated with a single set of spin-Hamiltonian parameters. The results show that there is noncoincidence between the principal axes of the g-matrices on each copper center and those of the zero-field splitting (D) tensor. This noncoincidence is a single rotation of 33 degrees +/- 2 degrees. The parameters from the powder spectra have been verified by a subsequent single-crystal EPR study which yielded the spin-Hamiltonian parameters g(XX) = 2.074, g(YY) = 2.093, g(ZZ) = 2.385, D(XX) = +/-0.0228 cm(-1), D(YY) = +/-0.0211 cm(-1), D(ZZ) = -/+0.0439 cm(-1) with Euler angles of alpha = 179 degrees, chi = 33.4 degrees, and gamma = 328 degrees. Analysis of the zero-field splitting tensor in terms of exchange indicates that the interaction between the pairs of copper(II) ions is almost entirely dipolar in origin. This study shows that multifrequency EPR spectroscopy on powders, coupled with spectrum simulation, can detect and measure noncoincidence between the principal axes of the g-matrix and zero-field splitting tensor, and does not necessarily require the presence of metal hyperfine interactions.

Formation of Polymeric Network Arrays by Complexes of Manganese(II) or Cobalt(II) with Alkane Chain Linked Bis(amide) Ligands of Biological Relevance.

Bis(amides) of the type CH(3)CONH(CH(2))(n)()NHCOCH(3) (n = 2, 4, or 6) react with a range of manganese(II) and cobalt(II) salts to produce polymeric "framework" arrays, five of which have been studied by X-ray crystallography. Hexamethylenebis(acetamide) (HMBA) forms the compound [Co(HMBA)(3)](CoCl(4)).2EtOH in which the HMBA molecules bridge the metal centers, binding octahedrally via the oxygen atoms of the amide groups and forming cationic arrays of large rhomboidal "boxes" containing tetrahedral CoCl(4)(2-) ions. The butylenebis(acetamide) (BBA) complex [Co(BBA)(3)]Br(2) forms a sheet cationic network, but in this case, the counteranions are simple bromide ions. The ethylenebis(acetamide) (EBA) complex [Co(EBA)(2)(H(2)O)(2)]Br(2) comprises trans-octahedral [Co(O-amide)(4)(H(2)O)(2)](2+) units interlinked by the bridging action of the EBA ligands to form sheet arrays, with simple bromide counterions. From the reaction of HMBA with manganese(II) bromide two crystalline forms were obtained, [Mn(HMBA)(3)](MnBr(4)).2EtOH, with a structure similar to [Co(HMBA)(3)](CoCl(4)).2EtOH, and a solvent-free form, [Mn(HMBA)(3)](MnBr(4)), comprising a cationic sheet array. The preparations of several other transition-metal complexes with these ligands are reported together with relevant spectroscopic data.