Metal diphosphonates with double-layer and pillared layered structures based on N-cyclohexylaminomethanediphosphonate

Based on N-cyclohexylaminomethanediphosphonic acid (cmdpH₄), four new metal diphosphonate compounds with formula M₃(cmdpH)₂(H₂O)₂ M=Zn(1), Co(2)] and M₂(cmdpH₂)₂(4,4′-bipy)_0.5(H₂O) M=Co(3), Mn(4)] have been obtained and structurally determined. Compounds 1 and 2 are isostructural. Within the structure, the M(2)O₆ octahedra are each corner-shared with four PO₃C tetrahedra to form a single layer containing 3- and 7-member rings. Neighboring single layers are pillared by M(1)O₄ tetrahedra, resulting in a novel double-layer structure. The organic moieties of cmdpH³⁻ are grafted on the two sides of the double layer. Compounds 3 and 4 are also isostructural, displaying a pillared layered structure. Within the inorganic layer, the M(1)O₅ tetragonal pyramids and M(2)NO₅ octahedra are each linked by PO₃C tetrahedra through corner-sharing, forming a layer in the ab plane which contains 3- and 10-member rings. These layers are pillared by 4,4′-bipyridine via coordination with the M(2) atoms from the adjacent layers, leading to a three-dimensional open framework structure with channels generated along the a-axis. The organic groups of cmdpH₂²⁻ locate within the channels. Magnetic studies show that antiferromagnetic interactions are dominant in compounds 2-4. Field dependent magnetization reveals a spin flop behavior for 2.