Electronic spectra and electronic structures of [Zr6Cl12Z]Cl6n- (Z = Be, B, Fe) clusters
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Octahedral metal clusters of the type M6X18-1 (X = halogen; n - 2-4) are well-known for M = Nb or Ta. More recently, a diverse zirconium-based cluster chemistry has emerged in which analogous zirconium clusters are stabilized by the encapsulation of a wide variety of interstitial elements. Despite extensive synthetic work and reports of several electronic structure calculations, no spectroscopic measurements of these have been reported. The electronic spectra of Zr6Cl18Z-1 clusters (n = 2-6; Z = Be, B, Fe) have been recorded both in the solid state (by diffuse reflectance) and in acetonitrile solution. Main-group-centered clusters are typically dark orange or red to black, while transition-metal-centered clusters are typically green, blue, or purple. Main-group-centered clusters exhibit strong bands in the near-IR region (800-1200 nm), while transition-metal-centered clusters have, so far, exhibited their longest wavelength band in the visible region (~630 nm). Because of the chemical versatility that interstitial variation allows, spectral features that have otherwise been ambiguously assigned can now be assigned convincingly. In particular, unsettled aspects of the extensively studied niobium and tantalum systems become much clearer when comparison with the zirconium clusters is made. Extended Hückel calculations are shown to provide correct orbital energy orderings, though absolute transition energies are only in fair agreement with experiment. © 1992, American Chemical Society. All rights reserved.
author list (cited authors)
Bond, M. R., & Hughbanks, T.