Influence of Steric Hindrance of Organic Ligand on the Structure of Keggin-Based Coordination Polymer

Five Keggin-based 3D coordination polymers, namely, [Cu3(pz)3(PW12O40)] (pz = pyrazine) (1), [Cu3(2,3-Me2pz)3(PW12O40)] (2,3-Me2pz = 2,3-dimethylpyrazine) (2), [Cu2(2,5-Me2pz)1.5(2,5-HMe2pz)(PW12O40)] (2,5-Me2pz = 2,5-dimethylpyrazine) (3), [Cu3(2,3-Me2pz)3(PMo12O40)] (4), and [Ag3(pz)3(PW12O40)]·0.5H2O (5), were synthesized and
structurally characterized. Crystal data are as follows:  trigonal, space group R3̄c, a = 18.4070(14) Å, c =
22.544(3) Å, γ = 120°, and Z = 6 for 1; orthorhombic, space group Pccn, a = 16.599(2) Å, b = 20.470(3) Å,
c = 14.3757(18) Å, and Z = 4 for 2; triclinic, space group P1̄, a = 10.667(2) Å, b = 11.147(2) Å, c = 20.207(4)
Å, α = 90.983(4)°, β = 108.128(3)°, γ = 92.150(4)°, and Z = 2 for 3; orthorhombic, space group Pccn, a =
16.450(3) Å, b = 20.170(4) Å, c = 14.244(3) Å, and Z = 4 for 4; and rhombohedral, space group R32, a =
18.2047(13) Å, c = 23.637(3) Å, γ = 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.