The polarised single-crystal electronic spectra and e.s.r. spectra of bis-(2.2'-bipyridylamine)copper( 11) diperchlorate have been determined. The in-plane g-values correlate with copper-nitrogen directions and suggest a dxa-va ground state for the compressed tetrahedral CUN, 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 C,, and D, symmetries (with a preference for the former) and yield the tentative one-electron orbital sequence dz1-v3 > dxv > d,, > d, z > dvz. Reasons are given for preferring a tetrahedrally distorted square-coplanar description of the stereochemistry of the CUN, chromophore of Cu(bipyam),(CIO,),.A REGULAR tetrahedral stereochemistry is unknown for complexes of the copper(I1) ion,l but a number of complexes are available which involve a compressed tetrahedral stereochemistry. This is best known in the CuC1,2-, and CuBr,2-3 anions, but also occurs in the CuN, chromophore in bis-(aa'-bromodipyrr0methene)copper(I1) and bis-(2,2'-bipyridylamine)copper(11) diperchlorate [hereafter referred to as Cu(bipyam)%-(ClO,),] and in the CuO,N, chromophores of bis-(N-tbutylsalicylaldiminato)copper(II) 6 and bis-(N-isopropylsalicylaldiminato)copper(n) .' In these four complexes a square-coplanar stereochemistry is not possible owing to the steric requirements of the chelate ligands present, consequently these distorted stereochemistries may be alternatively considered as distorted square-coplanar or as distorted tetrahedral. As the N-Cu-N and 0-Cu-0 angles range5 from 137 to 145" in these chelate complexes, these represent a larger angular compression than is present in the C1-Cu-C1 angle of 120" in Cs2CuC1,. The polarised single-crystal electronic spectra of Cs,-CuCI, have been reported 8 and assigned in D,, symmetry with a dxy ground state, to give a one-electron orbital sequence dxy > dxz, dyz > dxt--ya > dzp, an order which reflects the small distortion from a tetrahedral stereochemistry as predicted by crystal-field calculation^.^The crystal structure of Cu(bipyam),(ClO,), has been reported recently5 and shown to involve a distorted CuN, chromophore and to have a unit cell which is ideal for the measurement of the polarised singlecrystal properties. These are now reported.
EXPERIMENTALPre~aration.-Cu(bipyarn),(ClO,), was prepared as reported ; lo single crystals were prepared by slow evaporation of a solution of the complex in 4 : 1 water-ethanol.Physical Methods.-The electronic l1 and e.s.r. spectra were measured as reported previously and the crystal B. J. Hathaway and D. E. Billing, Co-ordination Chem.
