ESR and ENDOR study of three isomeric bidiazine anion radicals and of their Group 6 metal carbonyl complexes. Coordinative effects on the spin distribution
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Journal of Physical Chemistry 90 (21): 5010--5014 (1986)

Hyperfine coupling consts. and g values were detd. for the anion radicals of 3,3'-bipyridazine (bpdz), 4,4'-bipyrimidine (bpm), and 2,2'-bipyrazine (bpz) and for several of their penta- and tetracarbonylchromium(0), -molybdenum(0), and -tungsten(0) complexes. Analyses of the ESR spectra and assignments of the coupling consts. were accomplished with the help of ENDOR spectroscopy, by relating data of the free anion radicals with those of their various complexes and by using p MO perturbation calcns. of spin densities at the McLachlan level. Large 14N splittings at the a-diimine centers were obsd. for the bpdz and bpz anion radical systems, whereas the thermodynamically most stable bpm.bul. complexes display a rather balanced spin distribution. Calcns. and exptl. results demonstrate a very strong response of the bpdz.bul. ligand toward coordination at the a-diimine N centers. The bis(pentacarbonyltungsten) complexes of bpdz.bul. and bpm.bul. are persistent at ambient temp. and show distinctly higher g value sthan their tetracarbonyltungsten analogs. Inclusion of the previously studied 2,2'-bipyridine and 2,2'-bipyrimidine systems yields a set of structurally very similar yet electronically quite variegated anion radicals of p acceptor ligands. on SciFinder(R)
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