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)-H-. (4), Cd[4-(4-pyridyl)benzoate](2)(H2O)-H-. (5), and [Zn-2(mu -OH)(4-pyridylbenzoate)(3)](EtOH)-Et-. (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) Angstrom, = 22.413(2) Angstrom, c = 8.319(1) Angstrom, beta = 126.149(1)degrees, and Z = 4. Crystal data for 4: monoclinic space group Cc, a = 12.013(1) Angstrom, b = 22.344(1) Angstrom, c = 7.774(1) Angstrom, beta = 123.509(1)degrees, and Z = 4. Crystal. data for 5: monoclinic space group Ia, a = 22.92(2) Angstrom, b = 28.74(2) Angstrom, c = 23.00(2) Angstrom, beta = 94.908(8)degrees, and Z = 4. Crystal data for 6: monoclinic space group P2(1)/n, a = 22.028(1) Angstrom, b = 6.780(1) Angstrom, c = 24.399(1) Angstrom, beta = 105.096(1)degrees, and Z = 4.