Synthesis of phenyl substituted bisphosphonates and crystal structures and characterization of Cd complexes of (dichloromethylene)bisphosphonic acid phenyl and alkyl ester derivatives

Abstract

Two novel phenyl esters and partial phenyl esters of (dicloromethylene)bisphosphonic acid were synthesised. Three new layered Cd complexes of (dichloromethylene)bisphosphonic acidP,P-diphenyl, monophenyl and monoethyl esters were prepared. The complexes, [Cd₃{(Cl₂CP₂O₆Ph)₂(H₃COH)(H₂O)₅}(H₂O)₂]_n (7), [{Cd(Cl₂CP₂O₆Ph₂)(H₂O)₃}(H₂O)]_n (8) and [{Cd_1.5(Cl₂CP₂O₆Et)(H2O)₂}(C₃H₆O)_0.5(H₂O)_4.5]_n (9), were characterized by single crystal X-ray diffraction, IR spectroscopy, solid-state ³¹P- and ¹¹³Cd-CP/MAS NMR and elemental analysis. Also their thermal behaviour was investigated. Compound 7 consists of 1D chains with four independent octahedral Cd atoms joined by two L₁ ligands, L₁ = (Cl₂CP₂O₆Ph)³⁻. The chains are connected into layers by phosphonate O atoms, and the adjacent layers are held together by face-to-face π–π stacking interactions. Compound 8 shows a new type of layered structure for metal bisphosphonates, where the L₂ ligand, L₂ = (Cl₂CP₂O₆Ph₂)²⁻, coordinates tridentately to three Cd²⁺ ions. Each CdO₆ octahedron is connected to three CPO₃ tetrahedra and each tetrahedron to three octahedra leading to a 2-D framework consisting of 12-membered cyclic cores. The layers are held together by edge-to-face CH/π interactions. In compound 9, the asymmetric unit contains two independent Cd²⁺ cations connected by L₃ ligands, L₃ = (Cl₂CP₂O₆Et)^3– and aqua ligands, to form a Cd–bisphosphonate layer. The layers are further interconnected into a 3-D supramolecular network by extensive hydrogen bonds.