A flexible tris-phosphonate for the design of copper and cobalt coordination polymers: unusual cage array topology and magnetic properties

Abstract

The reaction of the flexible tris-phosphonate precursor benzene-1,3,5-tris(methylenephosphonic acid) (H6btmp) with CuCl2·2H2O in H2O under hydrothermal conditions afforded the complex [Cu3(btmp)(H2O)3.6]·H2O (1·H2O). A similar reaction between 2,4,6-trimethylbenzene-1,3,5-tris(methylenephosphonic acid) (Me3-H6btmp) and Cu(NO3)2·3H2O or Co(NO3)2·6H2O gave the complex [Cu4(Me3-H2btmp)2(H2O)4] (2) or [Co6(Me3-btmp)2(H2O)4] (3), respectively. The cis,trans,trans-conformation of the flexible tris-phosphonate ligands resulted in the formation of 3D networks 1 and 3. Interestingly, the cis,cis,cis-conformation of the Me3-btmp ligand in 2 results in the formation of M4L2-type copper-based metalloprismatic cages, which can serve as building units for subsequent assemblies with phosphonate (P–O) linkages to afford a 2D array of nanocages. The magnetic study indicated that complexes 1·H2O, 2 and 3 all exhibit antiferromagnetic behaviors. Interestingly, results from alternating current (ac) magnetic susceptibility measurements revealed that complex 3 exhibits slow magnetic relaxation behavior at low temperatures.