R. J. Dudley

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.

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.

The single-crystal electronic properties and stereochemistry of tri-potassium penta(nitro/nitrito)cuprate(II)

The polarised single-crystal electronic and e.s.r. spectra of K3Cu(NO2)5 have been determined and are shown to be consistent with the stereochemistry of the two non-equivalent copper(II) environments present namely, a seven-co-ordinate [CU(NO2)3(ONO)2]3– and a cis-distorted six-co-ordinate [CU(NO2)2(ONO)2(ONO)]3– species. The i.r. spectrum is shown to be compatable with the presence of nitro- and unidentate and bidentate nitrito-ligands, but cannot distinguish the two types of nitrito-co-ordination. A structural pathway is suggested between the seven-co-ordinate and cis-distorted species.

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.