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. - Graphical abstract: Based on N-cyclohexylaminomethanediphosphonate (cmdp4-), compounds Zn3(cmdpH)2(H2O)2 (1) and Co3(cmdpH)2(H2O)2 (2) with a double-layer structure and compounds Co2(cmdpH2)2(4,4'-bipy)0.5(H2O) (3) and Mn2(cmdpH2)2(4,4'-bipy)0.5(H2O) (4) with a pillared layered structure are reported in this paper. Dominant antiferromagnetic interactions are found in compounds 2-4 and an interesting spin flop behavior is observed in 2.