American Chemical Society
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A Three-State Model for the Polymorphism in Linear Tricobalt Compounds

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journal contribution
posted on 2006-03-29, 00:00 authored by Dimitrios A. Pantazis, John E. McGrady
The remarkable polymorphism exhibited by the linear tricobalt compounds, Co33-dpa)4Cl2 and Co33-dpa)4Br2, can be explained using a model involving three distinct electronic states. At high temperatures, symmetric and unsymmetric forms arise from the population of doublet (2A) and quartet (4B) states, respectively, the latter containing a localized high-spin CoII center. In the unsymmetric form, a reduction in temperature leads to a spin-crossover to a second quite distinct doublet state, 2B, where, uniquely, the dx2-y2 character on the localized CoII center is distributed between the occupied and vacant manifolds. The variable population of the Co dx2-y2 orbital gives rise to the continuous change in Co−Co and Co−N bond lengths as the temperature is decreased.