Noncentrosymmetric Organic Solid and Its Zinc Coordination Polymer with Diamonded Network Prepared from an Ionothermal Reaction: Syntheses, Crystal Structures, and Second-Order Nonlinear Optics Properties

An organic ligand 4-(1,2,4-triazol-1-yl) benzoic acid (Htzbc) with a nonlinear optical (NLO) chromophore has been synthesized. Reaction of Zn(NO3)(2) with Htzbc ligand in 1-n-butyl-3-methylimidazolium tetrafluoroborate ionic liquid afforded compound Zn(tzbc)(2) (1). The Htzbc organic solid and 1 crystallize in the acentric Pn and Cc space groups, respectively. The tetrahedral Zn2+ center in 1 coordinates to two triazole nitrogen atoms and two carboxylate oxygen atoms from four tzbc(-) ligands, leading to a noncentrosymmetric 5-fold interpenetrating diamondoid network. Second-harmonic generation (SHG) measurements revealed the Htzbc solid and 1 have SHG activities. The Htzbc compound has a large SHG effect, which is approximately 3 times that of KDP and is type-I phase matchable, while 1 also belongs to phase-matchable class with a SHG response of about 1.2 times that of KDP. The SHG active of the organic solid can be derived from the inherently dipolar Htzbc molecule as well as the optimal relative orientation of the molecular NLO-phores in the crystal packing. The odd number-fold interpenetrated diamondoid network with dipolar NLO chromophoric units based on asymmetrical bridging ligands and metal centers results in the SHG activity of 1. In addition, elemental analysis, IR spectra, powder X-ray diffraction patterns (PXRD), and thermogravimetric analysis of both compounds are described.