Influence of steric hindrance of organic ligand on the structure of Keggin-based coordination polymer

Five Keggin-based 3D coordination polymers, namely, [Cu-3(pz)(3)( PW12O40)] (pz) pyrazine) ( 1), [Cu-3(2,3-Me(2)pz)(3)-( PW12O40)] (2,3-Me(2)pz)2,3-dimethylpyrazine) (2), [Cu-2(2,5-Me(2)pz)(1.5)(2,5-HMe(2)pz)(PW12O40)] (2,5-Me(2)pz = 2,5-dimethylpyrazine) ( 3), [Cu-3(2,3-Me(2)pz)(3)(PMo12O40)] (4), and [Ag-3(pz)(3)(PW12O40)]center dot 0.5H(2)O (5), were synthesized and structurally characterized. Crystal data are as follows: trigonal, space group R3c, a = 18.4070(14) angstrom, c = 22.544(3) angstrom, gamma = 120, and Z = 6 for 1; orthorhombic, space group Pccn, a = 16.599( 2) angstrom, b = 20.470( 3) angstrom, c = 14.3757(18) angstrom, and Z = 4 for 2; triclinic, space group P1, a = 10.667( 2) angstrom, b = 11.147(2) angstrom, c = 20.207(4) angstrom, R = 90.983(4)degrees, beta = 108.128(3)degrees, gamma = 92.150(4)degrees, and Z = 2 for 3; orthorhombic, space group Pccn, a = 16.450(3) angstrom, b = 20.170(4) angstrom, c = 14.244(3) angstrom, and Z = 4 for 4; and rhombohedral, space group R 32, a) 18.2047(13) angstrom, c = 23.637(3) angstrom, gamma = 120, and Z = 6 for 5. Their structural differences were investigated using crystal structure analysis, revealing that the influence of steric hindrance of organic ligand on the structures of Keggin-based coordination polymers is realized through changing the number of metal-organic units surrounding the POM anion.