Tetravalent metal diphosphonate-phosphite composition in microporous solid crystalline form, with a narrow micropore distribution

A tetravalent metal diphosphonate-phosphite composition definable by the following general formula:

• M(O.sub.3 P--R--PO.sub.3).sub.1-x (HPO.sub.3).sub.2x (I)
• where:
• M is a tetravalent metal;
• x varies from 0.5 to 0.66;
• R is an organic radical of bivalent aromatic type chosen from those definable by the following general formulas:
• ##STR5## where:
• n varies from 0 to 2;
• A is hydrogen or a group of medium steric hindrance chosen from --CH.sub.3, --C.sub.2 H.sub.5, --OH, --CH.sub.2 OH or another group of similar hindrance, with the condition that at least one A is other than hydrogen;
• the composition also being in the form of a crystalline solid having the following characteristics:
• type .alpha. layered structure with the diphosphonic groups positioned to join said layers together by a covalent bond (pillared compounds);
• B.E.T. surface area from 300 to 500 m.sup.2 /g depending on the nature of R in formula (I);
• and
• porosity in the micropore radius range of less than 20 .ANG. (Angstrom), such micropores contributing to the extent of more than 95% of the total area for the most crystalline materials.