Near neighbour ligand hyperfine splittings in the e.p.r. spectra of copper(II) complexes

X-band e.p.r. spectra from mixed ligand complexes Cu(btc)-(Hy), Cu(TPA)(Hy) and Cu(Sal)(TPA), have been derived from the spectra of suitable reaction mixtures in CHCl₃ at 25° C (Sal⁻ = salicyladehydate, TPA⁻ = thiopicolineanilide, Hy⁻ = 8-hydroxyquinolinate and btc⁻ =N-benzoyl-N′N′-diethylcarbamide). A digital data acquisition instrument and a personal computer were used for this purpose. The¹⁴N hyperfine splittings observed in these complexes have shown that the observed increase in spin density on the coordinating atoms of one ligand, at the expense of that on the other, is unlikely to be associated with the covalent bonding involving metal d _x ²− _y ²-orbital. Covalent bonding involving metal 4s-orbital component of the unpaired electron orbital has been suggested to be responsible for the observed changes in electron delocalization. This work was carried out during the visit of Drs Z. R. Baratova and P. M. Solozhenkin to India in 1991.