The crystal structures of two new intermetallic carbides, Gd13Fe10C13 and a secondary phase, with unusually short iron-iron bonds of 2.36-2.38 �, are reported. Both structures are built from Lu8Te-type layers of Fe-centered Gd tricapped trigonal prisms. Interwoven Fe-C chains prevent direct layer stacking and lead to the formation of the two new structure types, with three Lu8Te-type layers in Gd13Fe10C13 and four layers in the secondary phase. The chains interpenetrate and surround the tricapped trigonal prisms and connect the prism layers via Fe-Fe bonds which measure 2.36-2.38 �, an unusually short iron-iron distance. No carbon atoms bridge these bonds, making them the shortest known unsupported iron-iron bonds. Preliminary theoretical results suggest the presence of an iron-iron multiple bond, and additional experiments are underway to further characterize the bonding in Gd13Fe10C13. Magnetic measurements have revealed Gd13Fe10C13 to be a soft ferromagnet below about 74 K.

Gd13Fe10C13: Unusual iron-iron contacts in a new intermetallic carbide

244th National Meeting (2012)

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