Structural and theoretical study of six dinuclear Co(II), Ni(II), Cu(II), Zn(II), Cd(II) and Hg(II) complexes containing ON-NO donor azodye ligand, 4,4’-(1E,1’E)-(5,5’-(propane- 2,2-diyl)bis(2-hydroxy-5,1-phenylene)bis(diazene-2,1-diyl)dibenzenesulfonic a