Mapping the unpaired electron density in [Pt(bipy)L2]- (bipy = 2,2′-bipyridine; L = Cl-, CN-, 13CN-):: A combined EPR-ENDOR-theoretical study

The X-band EPR and electron-nuclear double resonance (ENDOR) spectra of the formally d(9), 17-electron radical anions [Pt(bipy)L(2)](-) (bipy = 2,2'-bipyridine; L = Cl(-), CN(-), (13)CN(-)) are reported. The (195)Pt (I = 1/2, 34%) anisotropic hyperfine matrices are analysed in terms of both 5d and 6p contributions to the singly occupied molecular orbitals (SOMOs). For L = Cl(-) there is 5.0% 5d(yz) and 7.6% 6p(z) character, for L = CN(-) there is < 1% 5d(yz) and 13.1% 6p(z). The bulk of the unpaired electron density is delocalised about the bipy pi* system and ENDOR spectra reveal the superhyperfine couplings to the (1)H, (14)N and (13)C (L = (13)CN(-)) nuclei. The unpaired electron densities in the (14)N 2p(z) orbitals contributing to the pi* systems are calculated to be 12% and 4% for L = Cl(-) and CN(-), respectively. The cyanide pi-orbitals make little contribution to the SOMO for [Pt(bipy)(CN)(2)](-). There is a good agreement with density functional theory (DFT) MO calculations oil the radical anions. DFT calculations also show the atomic orbital compositions of the lowest unoccupied (LU) MO of [Pt(bipy)L(2)] and the SOMO of [Pt(bipy)L(2)](-) to be virtually identical.