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-[(NH3)2Pt(1-MeU)2Cu(H2O)2](SO4).4.5H2O (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° ± 2°. The parameters from the powder spectra have been verified by a subsequent single-crystal EPR study which yielded the spinHamiltonian 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 α = 179°, X = 33.4°, and γ = 328°. 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

A supramolecular copper(II) compound with double bridging water ligands: synthesis, crystal structure, spectroscopy, thermal analysis, and magnetism

A complex of composition {[{Cu(NDC)(OH2)(tn)(mu-OH2)}(2)]center dot 2H(2)O}(a) (1) and a mononuclear complex salt [Cu(OH2)(2)(tn)(2)](NDC)center dot 3H(2)O (2), where NDC = 2,6-naphthalenedicarboxylate dianion and tn = 1,3-diaminopropane, were simultaneously crystallized from an aqueous solution of the copper(II) naphthalenedicarboxylate-1,3-diaminopropane-methanol system. The crystal and molecular structures of both complexes were determined by single-crystal X-ray diffraction. Compound (1) consists of a supramolecular coordination complex in which the monomeric unit is assembled from a homodinuclear Cu(II) bridged by two water ligands. The Cu(II) centers exhibit distorted octahedral coordination; the equatorial plane is provided by one chelating tn ligand, one NDC2- ligand, one mu-H2O while the axial positions are occupied by H2O and mu-H2O. Strong intra- and/or intermolecular hydrogen bonds, also involving the crystallization water molecules, together with pi-pi stacking interactions, are involved in building up the supramolecule. The solid structure of compound (2) includes three water molecules of crystallization, the counter ion NDC2-, and a Cu(II) cationic complex in which the metal is six-coordinated in an axially elongated octahedron defined by two chelating tn ligands in the equatorial plane and two water ligands in the axial positions. Thermal analyses of (1) show two significant weight losses corresponding to water molecules (lattice and coordinated), followed by the decomposition of the network