title: Cupric siliconiobate. Synthesis and solid-state studies of a pseudosandwich-type heteropolyanion.
abstract: The Na (+) and [Cu(en) 2(H 2O) 2] (2+) (en = ethylenediamine) salt of a pseudosandwich-type heteropolyniobate forms upon prolonged heating of Cu(NO 3) 2 and hydrated Na 14[(SiOH) 2Si 2Nb 16O 54] in a mixed water-en solution. The structure [ a = 14.992(2) A, b = 25.426(4) A, c = 30.046(4) A, orthorhombic, Pnn2, R1 = 6.04%, based on 25869 unique reflections] consists of two [Na(SiOH) 2Si 2Nb 16O 54] (13-) units linked by six sodium cations, and this sandwich is charge-balanced by five [Cu(en) 2(H 2O) 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 lambda max at 383 nm for the Cu (II) d-d transition and the (29)Si 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 [SiO 4] (4-) and external [SiO 3(OH)] (3-) tetrahedra, respectively. Unlike tungsten-based sandwich-type complexes, the [Na(SiOH) 2Si 2Nb 16O 54] (13-) units are linked exclusively by Na (+) instead of one or more d-electron metals.
authors.affiliation: Sandia National Laboratories, P.O. Box 5800, Albuquerque, New Mexico 87185, USA.
authors.forename: Travis M
authors.initials: TM
authors.lastname: Anderson
authors.forename: Todd M
authors.initials: TM
authors.lastname: Alam
authors.forename: Mark A
authors.initials: MA
authors.lastname: Rodriguez
authors.forename: Joel N
authors.initials: JN
authors.lastname: Bixler
authors.forename: Wenqian
authors.initials: W
authors.lastname: Xu
authors.forename: John B
authors.initials: JB
authors.lastname: Parise
authors.forename: May
authors.initials: M
authors.lastname: Nyman