Giant voids in the hydrothermally synthesized microporous square pyramidal-tetrahedral framework vanadium phosphates [HN(CH2CH2) 3NH]K1.35[V5O9(PO4)2] ·xH2O and Cs3[V5O9(PO4) 2]·xH2O

M. Isaque Khan, Linda M. Meyer, Robert C. Haushalter, Allan L. Schweitzer, Jon Zubieta, James L. Dye

Research output: Contribution to journalArticle

257 Scopus citations

Abstract

The use of a novel mixed-valence pentavanadate phosphate cluster as a building block has made possible the low-temperature hydrothermal self-assembly of the new three-dimensional square pyramidal-tetrahedral framework vanadium phosphates [HN(CH2CH2)3 NH]K1.35[V5O9(PO4) 2]·xH2O (1) and Cs3[V5O9(PO4) 2]·xH2O (2), from structurally simple starting materials. These materials possess some of the lowest framework densities and the largest cavities thus far observed in open-framework solid-state materials. The degree of curvature, size, shape, and charge of the mixed valence {V5O9(PO4)2} V(4+/5+) pentameric building block, which resembles a portion of an arc of a circle, favors the formation of very large cavities. Phosphate 1 crystallizes in space group I4̄3m with α -26.247(3) Å and has very large cubic-shaped cavities that display 4̄3m point symmetry, each of which enclose nearly 50 positive charges. These charges are distributed among 12 HN(CH2CH2)3NH2+, 32 K+ cations, and several waters of crystallization. Each cavity, which could contain a sphere of approximately 13.0 Å diameter and which displays an enormous 32-ring at its maximum diameter, communicates via six 16-ring windows to other similar supercages via intervening smaller cavities. Phosphate 2 is built up from the same pentamers as those in 1 but arranged in a different manner in space group Fd3̄m with α = 32.306(4) Å such that one pentamer lies on each of the six faces of a cube. The three-dimensional structure of 2 consists of two types of cavity, larger ones with all six pentamers curved in an outward fashion, with a free diameter along the diagonal of the cubic-shaped cavity of approximately 20 Å and exhibiting a 24-ring diameter, and smaller ones with all six curved to the inside with cavity diagonals of 7.5 A. The large cavities are interconnected to one another in a manner that is topologically identical to the arrangement of the carbon atoms in diamond. The ion exchange and sorption properties of these two phosphates are also to be presented.

Original languageEnglish (US)
Pages (from-to)43-53
Number of pages11
JournalChemistry of Materials
Volume8
Issue number1
StatePublished - Dec 1 1996

ASJC Scopus subject areas

  • Chemistry(all)
  • Chemical Engineering(all)
  • Materials Chemistry

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