Synthesis, characterization and structure of $[Ni(H_2O)_6]_2(Cr_2O_7)_2(hmta)_4·2H_2O$ (hmta=hexamethylenetetramine): a novel metal organic–inorganic hybrid

A metal organic–inorganic hybrid compound $[Ni(H_2O)_6]_2(Cr_2O_7)_2(hmta)_4 2H_2O$ was prepared and characterized by single-crystal X-ray diffraction. The compound crystallizes in the monoclinic space group $P2_1/c$ with a = 7.976(5)A, b= 13.333(3)A, c= 14.070(3)A,\beta = 97.891(3); Z= 4 and R= 0.048. The structure consists of octahedrally coordinated nickel ions with water and discrete units of dichromate ions in which chromium is tetrahedrally coordinated. This inorganic moiety is well separated in the crystal structure from the organic moiety built by ‘‘hmta’’ ligands, resulting in the formation of a novel organic–inorganic framework