Hydrothermal synthesis and crystal structure study of two novel 3-D mellitates {Nd2[C6(COO)6] (H2O)6} and {Ho2[C6(COO)6](H2O)6}

Two novel 3-D coordination compounds, Nd-2[C-6(COO)(6)](H2O)(6) (1) and Ho-2[C-6(COO)(6)](H2O)(6) (2), were hydrothermally synthesized from mellitic acid and neodymium perchlorate (or holmium perchlorate) in the alkaline aqueous solution and characterized with elemental analysis, TG, IR spectrum, and single crystal X-ray diffraction. The two compounds were isostructural and crystallized in the orthorhombic system, space group Pnnm, with a=1.3531 (4) nm, b=0.6687 (2) nm, c=1.0224(3) nm, V=0.92523(5) nm(3), Z=4, D=2.630 g/cm(3), F(000)=696.0, Goof=1.052. Final R indices [I >2 Sigma(I)]: R-1=0.0195, wR(2)=0.0382 for 1; a=1.3411(2) nm, b=0.6586(1) nm, c=1.0116(2) nm, V=0.8935(3) nm(3), Z=4, D=2.877 g/cm(3), F(000)=724.0, Goof=1.061. Final R indices [I >2 Sigma(I)]: R-1=0.0200, wR(2)=0.0479 for 2. In the two compounds I and 2, the mellitic acid ligand, in which all the carboxylate groups were deprotonated, had only one kind of coordination mode to bridge metal ions to form four-connected three-dimensional diamondiod networks.