Novel polymeric metal complexes of calix[4]arene-11,23-diphosphonic acid: synthesis and structure determination

New calixarene derivatives bearing two phosphonic acid groups, 25,27-dimethoxy-26,28-dihydroxycalix[4]arene-11,23-diphosphonic acid 3 and its tetraethyl ester 2 were synthesized. Their X-ray structures confirmed cone conformation of the molecules, more deformed for the ester due to bulky ethyl groups. Complexes [CaH2L(MeOH)2]·4 MeOH (4) and [LnH2L(NO3)(H2O)2]·2 H2O 2 MeOH (Ln=La(III), Pr(III), Nd(III), H4L=26,28-dihydroxy-25,27-dimethoxycalix[4]arene-11,23-diphosphonic acid) were also prepared. Structures of the Ca(II) complex 4 and Nd(III) complex 5 were determined by X-ray analysis. The structural motif of 4 is similar to that found for the free acid 3. The calixarenes are linked by coordination of phosphonates to Ca(II) in a polymeric structure instead of a network of hydrogen bonds in 3. Structure of 5 is different: four calixarene molecules are linked through coordination to Nd(III) in a supramolecular macroring, which forms a pore (approximately 17 Å in diameter) penetrating through the structure.