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Article

Cupric Siliconiobate. Synthesis and Solid-State Studies of a Pseudosandwich-Type Heteropolyanion

Supporting Info

Travis M. Anderson^†, Todd M. Alam^†, Mark A. Rodriguez^†, Joel N. Bixler^†, Wenqian Xu^‡, John B. Parise^‡ and May Nyman*^†

Sandia National Laboratories, P.O. Box 5800, Albuquerque, New Mexico 87185, and Department of Chemistry and Geosciences, SUNYStony Brook, Stony Brook, New York 11794

Inorg. Chem., 2008, 47 (17), pp 7834–7839

DOI: 10.1021/ic800860q

Publication Date (Web): August 1, 2008

†

Sandia National Laboratories.

‡

SUNYStony Brook.

* To whom correspondence should be addressed. E-mail: mdnyman@sandia.gov.

Abstract

The Na⁺ and [Cu(en)₂(H₂O)₂]²⁺ (en = ethylenediamine) salt of a pseudosandwich-type heteropolyniobate forms upon prolonged heating of Cu(NO₃)₂ and hydrated Na₁₄[(SiOH)₂Si₂Nb₁₆O₅₄] in a mixed water−en solution. The structure [a = 14.992(2) Å, b = 25.426(4) Å, c = 30.046(4) Å, orthorhombic, Pnn2, R1 = 6.04%, based on 25869 unique reflections] consists of two [Na(SiOH)₂Si₂Nb₁₆O₅₄]¹³⁻ units linked by six sodium cations, and this sandwich is charge-balanced by five [Cu(en)₂(H₂O)₂]²⁺ complexes, seven protons, and three additional sodium atoms (all per a sandwich-type cluster). Diffuse-reflectance UV−vis indicates that there is a λ_max at 383 nm for the Cu^II d−d transition and the ²⁹Si MAS NMR spectrum has two peaks at −78.2 ppm (151 Hz) and −75.5 ppm (257 Hz) for the two pairs of symmetry-equivalent internal [SiO₄]^4– and external [SiO₃(OH)]³⁻ tetrahedra, respectively. Unlike tungsten-based sandwich-type complexes, the [Na(SiOH)₂Si₂Nb₁₆O₅₄]¹³⁻ units are linked exclusively by Na⁺ instead of one or more d-electron metals.