The FeIII/FeIIvs Fe22.5Formulation in Mixed-Valent Species [(NC)4Fe(BL)Fe(CN)4]3-, BL = 2,2‘-Bipyrimidine and 3,6-Bis(2-pyridyl)-1,2,4,5-tetrazine. Distance and Size Do Not Always Matter
- 22 June 1999
- journal article
- research article
- Published by American Chemical Society (ACS) in Inorganic Chemistry
- Vol. 38 (14), 3270-3274
- https://doi.org/10.1021/ic990249l
Abstract
Two molecule-bridged bis(tetracyanoiron) complexes [(NC)4Fe(BL)Fe(CN)4]n-, BL = 2,2‘-bipyrimidine (bpym) and 3,6-bis(2-pyridyl)-1,2,4,5-tetrazine (bptz), were studied by EPR, UV/vis/near-IR and IR spectroelectrochemistry (n = 2−5) in aprotic media. Following these results, the Fe22.5 formulation is the correct valence description for the metal centers in the bptz-bridged trianion (Kc = 1014.6 in CH3CN), whereas the localized FeIII/FeII formulation is appropriate for the bpym-bridged system (Kc = 105.4 in CH3CN and 106.4 in CH2Cl2). In contrast to common perception, the larger tetrazine-bridged system with the longer metal−metal distance exhibits much stronger metal−metal coupling than the bpym-bridged analogue, a consequence of the very low lying π* LUMO of tetrazines with high MO coefficients at the coordinating nitrogen centers.Keywords
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