Self-assembly and third-order optical properties of HgI2 with linear and angular bipyridine ligands

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 HgI2 results in a one-dimensional zigzag polymer {[HgI2(bpba)] · 1.5CH3OH}n (1) and a binuclear metallamacrocycle [HgI2(bpit)]2 · 3H2O (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 HgI2 in cisoid conformation, the different geometries of the two ligands attribute to forming the dissimilar frameworks of two HgI2 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.