Structural analysis of cubane-type iron clusters

The generalized cluster type [M4(μ3-Q)4Ln]x contains the cubane-type [M4Q4]z core unit that can approach, but typically deviates from, perfect Td symmetry. The geometric properties of this structure have been analyzed with reference to Td symmetry by a new protocol. Using coordinates of M and Q atoms, expressions have been derived for interatomic separations, bond angles, and volumes of tetrahedral core units (M4, Q4) and the total [M4Q4] core (as a tetracapped M4 tetrahedron). Values for structural parameters have been calculated from observed average values for a given cluster type. Comparison of calculated and observed values measures the extent of deviation of a given parameter from that required in an exact tetrahedral structure. The procedure has been applied to the structures of over 130 clusters containing [Fe4Q4] (Q = S2−, Se2−, Te2−, [NPR3]−, [NR]2−) units, of which synthetic and biological sulfide-bridged clusters constitute the largest subset. General structural features and trends in structural parameters are identified and summarized. An extensive database of structural properties (distances, angles, volumes) has been compiled in Supporting Information.

The geometry of cubane-type [M4(μ3-Q)4]z cluster cores has been analyzed in terms of perfect tetrahedral symmetry and deviations therefrom. This procedure has been applied to ca. 140 clusters with M = Fe, Q = (S, Se, Te, NPR3, NR) and z = 6− to 6+ for the identification of general structural features and trends. An extensive compilation of structural parameters is provided.Figure optionsDownload as PowerPoint slide