Layered crystalline calcium phenylphosphonate—synthesis, characterization and n-alkylmonoamine intercalation

Abstract

Layered calcium phosphonate was synthesized by means of the combination of a metallic salt with an aqueous phenylphosphonic acid solution to yield Ca(HO 3PC 6H 5) 2·2H 2O (CaPP1), which gives the corresponding anhydrous compound on heating. A series of n-alkylmonoamines were intercalated into the crystalline lamellar precursor, resulting in compounds with the general formula Ca(HO 3PC 6H 5) 2· xH 2N(CH 2) n CH 3·(2− x)H 2O ( n=0 to 4). Sharp and intense peaks obtained from X-ray diffraction patterns for both hydrated and anhydrous compounds are in agreement with the crystallinity presented. Thermogravimetric data showed mass losses corresponding to the release of two water molecules, in distinct stages between 300 to 520 K, followed by the organic moiety in the 570 to 880 K interval, to form the compound Ca(O 3P) 2. Two distinct DSC peaks corroborated the presence of the water molecules, in contrast to the absence of similar peaks in the anhydrous compound. The carbon:hydrogen molar ratio found for CaPP1 is 1:1 and the infrared spectrum shows the characteristic bands of the phosphonate group. The 31P NMR spectrum presented two distinct peaks for bonded phenylphosphonate groups at 20.0 and 12.4 ppm, due to the non-equivalence of the phosphorus atoms in the crystal. Elemental analyses for the intercalated compounds presented an increase of carbon and hydrogen percentages as the size of the amine chain increased, accompanied by a corresponding decrease of the percentage of nitrogen. The interlayer distance correlates with the number of carbon atoms of the n-alkylamine chains, a correlation which enabled inferring the interlayer distance for an unknown amine.