Peter G. Hodgson

Crystal structure and electronic properties of bis(2,2′-bipyridyl)-nitratocopper(II) nitrate monohydrate

The crystal structure of the title compound [Cu(bipy)2(ONO2)][NO3]·H2O (bipy = 2,2′-bipyridyl) has been redetermined by X-ray analysis in the triclinic space group P with a= 7.488(2), b= 10.017(2), c= 15.061 (2)A, α= 106.183(4), β= 91.335(3), γ= 89.662(3)°, and Z= 2. The six-co-ordinate CuN2N′2OO′ chromophore has a (4 + 1 + 1*) stereochemistry related to the original square-based pyramidal stereochemistry by an asymmetrically co-ordinated nitrate group to give an unsymmetrical bicapped square-pyramidal structure. The single-crystal e.s.r. and polarised electronic spectra are reported and together are shown to offer the possibility of distinguishing this bicapped square-pyramidal structure from that of a (4 + 1 + 1*) distorted square-pyramidal structure or cis-distorted octahedral structure. A structural pathway is suggested to connect these three geometries of the [Cu(bipy)2(OXO)]+(OXO = ONO–, O2CMe–, or O2CH–) cation by a linear combination of the S1a and S2a modes of vibration of the parent tris(chelate)copper(II) complex.

The single-crystal electronic and electron spin resonance spectra of bis-(2,2′-bipyridylamine)copper(II) diperchlorate

The polarised single-crystal electronic spectra and e.s.r. spectra of bis-(2,2′-bipyridylamine)copper(II) diperchlorate have been determined. The in-plane g-values correlate with copper–nitrogen directions and suggest a dx2–y2 ground state for the compressed tetrahedral CuN4 chromophore present. The electronic spectra correlate, in the xy-plane with the bisectors of the copper–nitrogen directions; possible reasons for this 45° misalignment of the in-plane g-values and electronic spectral axes are discussed. The electronic spectra are assigned in both C2v and D2 symmetries (with a preference for the former) and yield the tentative one-electron orbital sequence dx2–y2 > dxy > dxz > dz2 > dyz. Reasons are given for preferring a tetrahedrally distorted square-coplanar description of the stereochemistry of the CuN4 chromophore of Cu(bipyam)2(ClO4)2.

A reinterpretation of the structure of [ Cu(bipy)2 (ONO2] (NO3).H2O — a distorted bicapped square pyramidal copper(II) stereochemistry

Abstract A reexamination of the structure of [ Cu(bipy)2 (ONO2)] (NO3).H2O suggests that it is best described as a distorted bicapped square pyramidal structure.

Single-crystal electronic and electron spin resonance spectra of the two forms of bis(nitrato)bis-(α-picoline)copper(II) and of bis(nitrato)mono(pyrazine)copper(II)

The polarised single-crystal electronic and e.s.r. spectra of the two forms of bis(nitrato)bis-(α-picoline)copper(II) and of bis(nitrato)mono(pyrazine)copper(II) have been measured. The polarised single-crystal spectra of the first two complexes are assigned in an effective symmetry of C2v, and those of the last complex in D2h symmetry. All three complexes yield the same one-electron orbital sequence, namely dx2–y2 > dxy > dz2 > dyz > dxz, but with significant differences in the energies involved which are correlated with the different molecular structures present and in particular with the potential bonding role of the terminal nitrate oxygen atoms positioned off-the-z-axis.

Single-crystal electronic and electron spin resonance spectra of four trigonal bipyramidal copper(II) complexes

The polarised single-crystal electronic and e.s.r. spectra of four complexes of the copper(II) ion involving a trigonal bipyramidal stereochemistry have been measured. The g-factors of each of the complexes correlate with a dz2 ground state and justify a trigonal bipyramidal description of the local molecular stereochemistries. The electronic spectra have been assigned in C2v symmetry and yield one-electron orbital sequences consistent with that predicted by a crystal field model in D3h symmetry, namely dz2 > dx2–y2,dxy > dxz,dyz. The detailed sequence observed for each complex is interpreted in terms of the local bond lengths and bond angles present and an attempt is made to assess the role of π-bonding in the Cu(bipy)22+ cation.

Redetermination of the crystal structure of dipotassium imidobis(trioxosulphate) by neutron diffraction

The crystal structure of the title compound has been redetermined from three-dimensional neutron diffraction data with 511 reflections. Z= 4 in the monoclinic space group C2/c, with cell dimensions a= 1 248.3(6), b= 749.9(4), c= 720.8(3) pm, β= 91.21(2)°. The structure was refined by full-matrix least-squares in the centric space group C2/c to R 0.056. The nitrogen in the anion was found to be on a two-fold axis and surrounded tetrahedrally by two groups and two half hydrogen atoms. Refinement in the non-centric space Cc gave R 0.058, with the nitrogen trigonally surrounded by the trioxosulphates and one hydrogen atom. This model was rejected on the basis of Hamiltons significance test.

Crystal and molecular structure of bis(diethylenetriamine)zinc(II) dibromide monohydrate

The crystal structure of the title compound has been determined from X-ray diffractometer data by Patterson and Fourier methods. Crystals are monoclinic, space group P21/c with a= 1381(1), b= 891·4(4), c= 1428·1 (6) pm, β= 101·23(3)°, and Z= 4. Least-squares refinement of 595 independent observed reflections led to R 0·064. Significant differences in the bonding were found between this structure and the isomorphous copper(II) complex.

A correlation of the copper-nitrogen bond-lengths, infrared spectra and electronic spectra of some axial tetraammines and pentaammines of the copper(II) ion

Abstract A correlation is shown to exist between the energy of the band maxima of the electronic spectra and the square of the frequency of the asymmetric stretching mode of the copper-nitrogen bonds (395–455 cm−1) in a series of Cu(NH3)4X2 and Cu(NH3)5X2 complexes. Where available, the copper-nitrogen bond-lengths also correlate with the square of the frequency of the νCuN mode.

The single-crystal electronic and electron spin resonance spectra of bis-(N-n-propylsalicylaldiminato)copper(II)

The polarised single-crystal electronic and e.s.r. spectra of bis-(N-n-propylsalicylaldiminato)copper(II) have been recorded. The correlation of the single-crystal g-values and the crystallographic data suggests an approximate dx2–y2 ground state for the CuO2N2 chromophore. The electronic spectra have been assigned in D2h effective symmetry and yield an tentative partial one-electron orbital sequence dx2–y2 > dxz > dyz > dz2 with the position of the dxy orbital uncertain, but probably near to the dxz and dyz orbitals. The combined spin–orbit and orbital reduction parameters have been evaluated and suggest significant out-of-the-plane π-bonding and possible some inplane π-bonding. The results are compared with the published data on Cu(N-methylsalicylaldimine)2(the electronic spectra of which are reassigned with a dx2–y2 ground state) and with the less certain data on Cu[(±)-NN-diethyl-α-alanine]2.