SINGLE-CRYSTAL STRUCTURE-ANALYSIS OF NONASIL(PYR), (C4H10N)(4)[SI84B4O176]

Nonasil(pyr) is a member of the nonasil family (structure type code, N ON). Nonasils are characterized by a unique silicate host framework ca pable of enclathrating various types of guest species. Nonasil(pyr) is orthorhombic (space group Cmca) with a(0) = 22.039(4) Angstrom, b(0) = 14.948(3), c(0) = 13.573(2) Angstrom and an idealized unit cell com position of (C4H10N)(4)[Si84B4O176]. The sing le crystal structure ref inement using 1,697 nonequivalent reflexions led to a residual of R(w) = 0.071. Boron ions (B3+) partially but randomly replace the silicon ions (Si4+) in the framework. The negative charge introduced by this r eplacement is compensated by pyrrolidinium cations (C4H10N+). The fram ework consists of three different types of cage-like voids: the small [5(4)6(4)]-and [4(1)5(8)]-cages, which are empty, and the large [5(8)6 (12)]-cages (free volume approximate to 290 Angstrom(3)), which contai n the pyrrolidinium cations. The silicate framework of nonasil(pyr) ha s several unusually short Si-O distances and high Si-O-Si angles, whic h are interpreted as due to static or dynamic disorder. Fourier synthe ses showed that the guest ions are positionally disordered since the s ymmetry of the guest ion (point group symmetry, 2 mm) is incompatible with the symmetry of the [5(8)6(12)]-cage (point group symmetry, 2/m).