Preparation of a covalently pillared α-zirconium phosphite-diphosphonate with a high degree of interlayer porosity

A pillared alpha-zirconium phosphite-diphosphonate with interlayer porosity has been obtained by means of a new synthetic strategy. It is based on the use of mixtures of phosphorous and diphosphonic acid having a cross-section greater than the free area associated with each -POH group in the a-zirconium phosphate layer (0.24 nm(2)). Under these conditions, the six adjacent sites of each diphosphonic group acting as a pillar cannot be occupied, for steric reasons, by other diphosphonic groups. These sites can, however, be occupied by the small phosphite groups, and a pillared compound is thus formed in which there are six small phosphites around each pillar. If the cross-section of the pillar is not uniform, and if its central cross-section is smaller than the terminal parts (i.e, a pillar with bases), interlayer porosity may be created. A suitable diphosphonic acid, 4,4'-(3,3',5,5'-tetramethyl)biphenyl diphosphonic acid, was synthesised and a compound of composition Zr(HPO3)(1.2)(O3P-R-PO3)(0.4) (R = 3,3', 5,5'-tetramethylbiphenyl) obtained. The specific surface area was 405 m(2)/g with negligible mesoporosity, while the micropore volume was 0.16 cm(3)/g with a micropore distribution around 0.5 nm. A structural model of this covalently pillared layered solid is reported and discussed. (C) 1998 Elsevier Science B.V. All rights reserved.