Aluminum Phenylphosphonates: A Fertile Family of Compounds.

Abstract

Six aluminum phenylphosphonates have been synthesized depending upon the synthetic conditions: Al(2)(O(3)PC(6)H(5))(3).2H(2)O (I), Al(2)(O(3)PC(6)H(5))(3) (II), alpha-Al(HO(3)PC(6)H(5))(O(3)PC(6)H(5)).H(2)O (III), beta-Al(HO(3)PC(6)H(5))(O(3)PC(6)H(5)).H(2)O (IV), Al(HO(3)PC(6)H(5))(3).H(2)O (V), and Al(OH)(O(3)PC(6)H(5)) (VI). Thermal analysis, X-ray powder thermodiffractometry, IR spectroscopy, and (27)Al and (31)P MAS NMR data have been obtained to study the structure and thermal stability of these materials. III crystallizes in the orthorhombic system, space group Pbca, with a = 9.7952(1) Å, b = 29.3878(4) Å, c = 9.3537(3) Å, and Z = 8. The structure was solved ab initio, from synchrotron data (lambda approximately 0.4 Å), using direct methods, and refined by Rietveld methods. The final agreement factors were R(wP) = 6.73%, R(P) = 5.24%, and R(F)() = 6.8%. The compound is layered with the aluminum atoms in an octahedral environment of oxygens and two crystallographically independent phosphonate groups, one being protonated. The powder patterns of V and VI have been indexed, and the experimental observations are consistent with layered structures. The unit cell of V contains one octahedral site for Al and three tetrahedral sites for P. Phosphonate I seems to have a three-dimensional tubular structure with aluminum atoms in both octahedral and tetrahedral environments and phosphorus atoms in three different types of sites.