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.