Rational Design of Nonlinear Optical Materials Based on 2D Coordination Networks

Zinc(II) and cadmium(II) coordination networks with m-pyridinecarboxylate bridging
ligands, Zn(nicotinate)2, 1, Cd(nicotinate)2, 2, Cd{3-[2-(4-pyridyl)ethenyl]benzoate}2, 3, Zn4{3-[2-(4-pyridyl)ethenyl]benzoate}8·{3-[2-(4-pyridyl)ethenyl]benzoic acid}·(H2O), 4, Zn{4-[2-(3-pyridyl)ethenyl]benzoate}2·H2O, 5, and Zn{5-[2-(3-pyridyl)ethenyl]thiophene-2-carboxylate}2, 6, have been synthesized under hydro(solvo)thermal conditions. With the exception
of 5, these compounds adopt 2D grid structures. The use of unsymmetrical bent m-pyridinecarboxylate ligands leads to the formation of intrinsically acentric 2D grids which
provide an interesting structural motif for the rational synthesis of polar solids. Compounds
1 and 3−5 are non-centrosymmetric and show significant powder second harmonic generation
efficiencies. Compound 2 adopts a centrosymmetric structure due to the presence of a μ2,η3-carboxylate bridge, while compound 6 adopts a centrosymmetric structure due to the presence
of 2-fold interpenetration. The present work illustrates the potential of rational synthesis
of nonlinear-optical-active acentric solids by exploiting the propensity of the formation of
2D coordination networks based on bent linking groups. Crystal data for 1:  tetragonal space
group P43212, a = 7.709(1) Å, b = 7.709(1) Å, c = 20.327 Å, and Z = 8. Crystal data for 2: 
monoclinic space group P21/n, a = 10.055(1) Å, b = 10.219(1) Å, c = 12.733(1) Å, β =
105.169(2)o, and Z = 4. Crystal data for 3:  orthorhombic space group Fdd2, a = 20.622(1)
Å, b = 36.426(1) Å, c = 6.241(1) Å, and Z = 8. Crystal data for 4:  monoclinic space group
Cc, a = 21.875(2) Å, b = 15.158(1) Å, c = 32.863(2) Å, β = 102.997(1), and Z = 4. Crystal
data for 5:  orthorhombic space group P21212, a = 7.625(1) Å, b = 25.430(2) Å, c = 5.863(1)
Å, and Z = 4. Crystal data for 6:  orthorhombic space group Pcca, a = 17.150(2) Å, b =
9.966(1) Å, c = 12.108(2) Å, and Z = 8.