Role of anions in preparing silver(i) complexes with a new multidentate ligand: polymorphs, structures and nonlinear optical properties

Abstract

A new multidentate ligand containing pyridyl and pyrazolyl groups, 6-phenyl-4-(4-(1H-pyrazolyl)phenyl)-2,2′-bipyridine (L) was designed and synthesized. By self-assembly of L with silver(I) salts, three new complexes containing disilver(I) metallocycles, namely [TsOAgL]₂ (1), [AgL]₂(ClO₄)₂ (2) and [AgL₂]₂(NO₃)₂[AgLNO₃]₂·(H₂O)₂ (3), were obtained. Polymorph (II) of L was obtained unexpectedly when AgSCN complex was prepared. In complexes 1 and 2, two ligands in a head-to-tail mode bridge two Ag(I) ions via pyridyl and pyrazolyl N atoms to generate binuclear [AgL]₂ unit. While, in complex 3, the asymmetric unit contains two kinds of crystallographically and conformationally independent molecules with completely different structures and coordination environments of Ag(I) ions. The structure of one kind of molecule is similar to that of complex 1. However, the other kind has a uninuclear structure, and the Ag(I) center is coordinated by four pyridyl nitrogen atoms from two ligands. Different anions have shown a great influence on both the molecular structures and the packing structures of the complexes. The nonlinear optical (NLO) properties of L and the complexes were measured through Z-scan technique. The results show that they may be good candidates for non-linear optical materials.