Abstract

4-(α-Diazobenzyl)-2,2'-bipyridine 2, diazodi{4-(2,2'-bipyridyl)}methane 3, and 1,3-benzenediyl{4-(4'-methyl-2,2'-bipyridyl)diazomethane} 4 were prepared as new types of spin sources/magnetic couplers. The molecular structures of bipyridine ligands, 2, 3, 4, and [Cu(hfac)₂·2] were revealed by X-ray analyses. Photolysis of 2, 3, 4, and their complexes with Cu(hfac)₂ in MTHF frozen solutions at cryogenic temperature was followed by UV–Vis and EPR spectroscopy. UV–Vis and EPR spectra after photolysis showed strong two absorptions; at 508 and 471 nm for 2, and 511 and 476 nm for 3, and characteristic sets of EPR signals due to the triplet states; |D/hc| = 0.418, and 0.436 cm⁻¹ and |E/hc| = 0.021 and 0.022 cm⁻¹ for 2 and 3, respectively. Diazo compound 4 after photolysis also showed absorptions at 506 and 471 nm and EPR signals characteristic of a quintet. Their complexes with Cu(hfac)₂ showed a red shift of 3–14 nm in the visible spectra and gave EPR spectra characteristic of the high-spin complexes under similar conditions. Magnetic susceptibility measurements on a SQUID magnetometer were carried out using a sample similar to the one employed in the UV–Vis and EPR studies. The field dependence of magnetization in frozen solution suggested that the ground-state spin multiplicities of the photoproducts of 2, 3, and 4 were triplet, triplet, and quintet, respectively. Similarly, those of their complexes with Cu(hfac)₂ were quartet, quintet, and septet, respectively.