Semireduced bridging ligands containing N-N multiple bond coordination sites. ESR study of binuclear Group 6 metal carbonyl complexes
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Inorganic Chemistry 25 (19): 3442--3448 (1986)

Centrosym. binuclear metal carbonyl complexes of anion radical ligands contg. the azo group -N:N- were studied by using ESR. The ligands employed were 1,2,4,5-tetrazine (tz), 3,6-bis(2-pyridyl)-1,2,4,5-tetrazine (bptz), and azo-2,2'-bipyridine (abpy). The radical complexes studied were: (m-(N1,N4)-tz.-)M(CO)52 (M = Mo, W); (m-bptz.-)M(CO)42, and (m-abpy).-)M(CO)42 (M = Cr, Mo, W). The ESR spectra of abpy species are line rich and insufficiently resolved so that ENDOR spectroscopy was used for (m-abpy.-)Mo(CO)42. In contrast, the tetrazine complexes exhibit a rather simple ESR hyperfine structure because of spin localization at the 4 N centers in the tetrazine ring. The obsd. response of the hyperfine structure on metal coordination is well reproduced by HMO-McLachlan perturbation calcns. of the spin distribution. Double coordination of equiv. metal fragments and spin localization at the tetrazine N centers create exceptionally favorable conditions to detect metal isotope coupling; a survey of these and several related anion radical complexes shows that the small metal isotope splittings are caused by s/p spin polarization originating from the coordinating N p center. on SciFinder(R)
DOI
10.1021/ic00239a025
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