Crystal and molecular structure of creatininium tetrachlorocuprate(II)

Abstract: The polarized X-ray absorption cross section of the ls → 3d transition in a square planar CuCl2−4 complex has been measured with respect to rotation about an axis normal to the CuCl4 The cross section exhibits four-fold periodicity about this axis, indicating that the transition is primarily due to coupling with the electric quadrupole component of the radiation The vibronically allowed dipole transition is approximately one-third as the quadrupolar cross section These observations are in agreement with SCF Xα multiple-scattered wave calculations, and may have implications for the intepretation of other X-ray absorption spectra The half-filled d orbital is shown to have the angular characteristics of dx2−y2

Abstract: To elucidate the origin of the shoulder structure which is known to appear about half-way up the Cu K-edge in the X-ray absorption spectra of Cu(II) compounds, polarized X-ray absorption spectra were measured on the single crystal of (creatinium)2CuCl4 by using synchrotron radiation. The transition responsible for the shoulder structure was found to be exclusively polarized in the direction normal to the molecular plane of the CuCl42− ion. The polarization dependence of other structures in the XANES spectra was also examined and compared with the results of ab initio SCF CI calculation. It is shown that the structure half-way up the Cu K-edge is due to the shake-down accompanying the 1s-4p= excitation, arising from the ligand-to-metal charge transfer induced by the core-hole creation. Structures attributable to the shake-down accompanying the 1s-4pσ and 1s-5p=, σ excitations were also found.

Abstract: Attack by reactive oxygen species leads to a decay in phycoerythrin fluorescence emission. This phenomenon provides a versatile new assay for small molecules and macromolecules that can function as protective compounds. With 1-2 x 10(-8) M phycoerythrin, under conditions where peroxyl radical generation is rate-limiting, the fluorescence decay follows apparent zero-order kinetics. On reaction with HO., generated with the ascorbate-Cu2+ system, the fluorescence decays with apparent first-order kinetics. Examination of the major components of human urine in this assay confirms that at physiological concentrations, urate protects against both types of oxygen radicals. A novel finding is that creatinine protects efficiently by a chelation mechanism against radical damage in the ascorbate-Cu2+ system at creatinine, ascorbate, and Cu2+ concentrations comparable to those in normal urine. Urate and creatinine provide complementary modes of protection against reactive oxygen species in the urinary tract.

Abstract: The synthesis, crystal structure and properties of the compound [Cu4(dpk·CH3O)2Cl6]n (dpk·CH3OH = unimethylated diol of di-2-pyridyl ketone) (1), the first example of a copper(II) polymer having a tetrameric repeating unit with S = 2 ground state is reported. The synthesis of compound 1 has been achieved via the reaction of CuCl2 with dpk in methanol. The base-catalyzed addition results in the formation of a unimethylated diol which may deprotonated. Crystal structure data: [C12H11N2O2Cl3Cu2], Mr = 448.68; triclinic; space group P1; a = 7.800(1) (A); b = 8.946(1) (A); c = 13.383(1) (A); α = 118.964(3)°; β = 92.693(3)°; γ = 66.824(3)°; Z = 2. Variable temperature magnetic susceptibility measurements indicate the presence of a ferromagnetic behavior with antiferromagnetic coupling below 15 K. The best fit parameters obtained from this model are J1 = 71.32 cm-1, J2 = 1.43 cm-1, J3 = 0.07 cm-1, J4 = 0 (fixed), zJ = −0.553 cm-1, and g = 2.1 (fixed). The energy levels obtained from the fitting procedure show ...

Abstract: This review summarizes the data for over five hundred and fifty six-, seven- and eight-coordinate Cu(II) coordination compounds. The six-coordinate derivatives are mostly distorted tetragonal (elongation along a single C 4 axis). The seven-coordinate derivatives are only penta-gonal-bipyramidal with different degrees of distortion and the eight-coordinate complexes are dodecahedral. The most common ligands are O- and N-donors. There is a trend for the Cu-L distance to increase with covalent radius of the coordinated atom and also increasing coordination number. In general, Cu(II) compounds “prefer” a monoclinic class and are blue or green. Several relationships were found and discussed. The data are compared and discussed with those of four- and five-coordinate Cu(II) compounds.

Abstract: The x‐ray form factors for a bonded hydrogen in the hydrogen molecule have been calculated for a spherical approximation to the bonded atom. These factors may be better suited for the least‐squares refinement of x‐ray diffraction data from organic molecular crystals than those for the isolated hydrogen atom. It has been shown that within the spherical approximation for the bonded hydrogens in H2, a least‐squares refinement of the atomic positions will result in a bond length (Re value) short of neutron diffraction or spectroscopic values. The spherical atoms are optimally positioned 0.07 A off each proton into the bond. A nonspherical density for the bonded hydrogen atom in the hydrogen molecule has also been defined and the corresponding complex scattering factors have been calculated. The electronic density for the hydrogen molecule in these calculations was based on a modified form of the Kolos—Roothaan wavefunction for H2. Scattering calculations were made tractable by expansion of a plane wave in spheroidal wavefunctions.

Abstract: The crystal structure of the yellow compound (NH4)2CuCl4 has been determined by x‐ray diffraction studies. The compound crystallizes in the orthorhombic space group Cmca with a=15.46 A, b=7.20 A, and c=7.20 A. The structure contains discrete, planar CuCl4= ions with Cu–Cl distances of 2.30 and 2.33 A. These ions are then bonded together by longer Cu–Cl bonds of 2.79 A to form infinite two‐dimensional sheets. The yellow compounds (CH3NH3)2CuCl4 and (C2H5NH3)2CuCl4 probably have closely related structures.