Crystal Engineering of Nonlinear Optical Materials Based on Interpenetrated Diamondoid Coordination Networks

Zinc(II) and cadmium(II) coordination networks with p-pyridinecarboxylate bridging
ligands, Zn(4-pyridylacrylate)2 (3), [Cd(4-pyridylacrylate)2]·H2O (4), Cd[4-(4-pyridyl)benzoate]2·H2O (5), and [Zn2(μ-OH)(4-pyridylbenzoate)3]·EtOH (6), have been synthesized under hydro(solvo)thermal conditions. Despite very different metal coordination environments, compounds 3, 4, and 6 all adopt 5-fold interpenetrated diamondoid structures, while compound
5 adopts a 7-fold interpenetrated diamondoid structure. The use of unsymmetrical p-pyridinecarboxylate bridging ligands in 3−5 has ensured their acentricity. Compounds 3−5
show significant powder second-harmonic-generation efficiencies. Compound 6, however,
adopts a centrosymmetric structure because of the presence of symmetrical bis[4-(4-pyridyl)benzoate] double bridges. Compounds 4−6 also exhibit open channels that are occupied by
removable included guest molecules. The present work illustrates the potential of rational
synthesis of NLO-active acentric solids based on interpenetrated diamondoid structures.
Crystal data for 3:  monoclinic space group Cc, a = 10.352(1) Å, b = 22.413(2) Å, c = 8.319(1) Å, β = 126.149(1)°, and Z = 4. Crystal data for 4:  monoclinic space group Cc, a = 12.013(1) Å, b = 22.344(1) Å, c = 7.774(1) Å, β = 123.509(1)°, and Z = 4. Crystal data for 5: 
monoclinic space group Ia, a = 22.92(2) Å, b = 28.74(2) Å, c = 23.00(2) Å, β = 94.908(8)°,
and Z = 4. Crystal data for 6:  monoclinic space group P21/n, a = 22.028(1) Å, b = 6.780(1)
Å, c = 24.399(1) Å, β = 105.096(1)°, and Z = 4.