Semilocalized bonding schemes in extended systems; orbital localization in yttrium chloride (Y2Cl3) and interstitial derivatives
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A semilocalized description of bonding in extended metal-metal-bonded systems is described for the prototype title compounds. Beginning with calculated band orbitals, we explicitly construct localized orbitals (Wannier functions) for the metal-metal-bonding orbitals of a M6X12 cluster and the Y2C13 chain compound. Face-localized three-center bond orbitals for a Zr6Cl18 cluster are remarkably similar to the HOMO for a (Zr6Cl12H7)Cl63- cluster in which hydrogens cap seven of eight Zr6 cluster faces. The (Zr6Cl12H7)Cl63- cluster was chosen to model (Th6Br12H7)Bra-a6/2, reported recently by Simon and co-workers. A semilocalized bonding picture for semiconductors with the Gd2Cl3 structure type is constructed, providing clarification of both structure-property relationships and trends in interstitial chemistry of these compounds. For the metal-metal bonding, a scheme with two 4c-2e bonds and one 2c-2e bond per cell is extracted from the band structure. The insertion of hydrogens into the tetrahedral interstices of these chains (to form structures of the (-Y2C13N type) is seen to be plausible and chains formulated as Y4C16H22+ are electronically viable. 1992, American Chemical Society. All rights reserved.
