Self-assembly and third-order optical properties of HgI 2 with linear and angular bipyridine ligands

Abstract

Two bis(pyridyl) ligands: N, N′-bis(4-pyridyl)-1,4-benzenedicarboxamide (bpba) and N, N′-bis(3-pyridylformyl)imidazolidine-2-thione (bpit) have been designed and synthesized. Self-assembly of the linear ligand bpba and angular ligand bpit with HgI 2 results in a one-dimensional zigzag polymer {[HgI 2(bpba)] · 1.5CH 3OH} n ( 1) and a binuclear metallamacrocycle [HgI 2(bpit)] 2 · 3H 2O ( 2), respectively. Single crystal X-ray diffraction analyses reveal that in the crystal structure of 1 the linear ligand bpba is in transoid conformation, while in the crystal structure of 2 the angular ligand bpit coordinates with HgI 2 in cisoid conformation, the different geometries of the two ligands attribute to forming the dissimilar frameworks of two HgI 2 adducts. The determination of third-order nonlinear optical (NLO) properties of 1 and 2 in DMF solution shows that adducts 1 and 2 possess strong NLO self-focusing effect. The hyperpolarizability γ values of 1 and 2 are calculated to be 2.10 × 10 −29 and 3.24 × 10 −29 esu, respectively, which are comparable to those of some NLO materials. And the result indicates that the heavier atoms Hg and I together with the polymeric aggregation play an important role in determining their NLO properties.