Metallomacrocycle or coordination polymer: Spacer-directed self-assembly of transition-metal complexes based on flexible bis(benzotriazole) ligands

Abstract

Three structurally related flexible bis(benzotriazole) ligands, 1,2-bis(benzotriazol-1-yl)ethane (L¹1), 1,5-bis(benzotriazol-1-yl)-3-oxapentane (L²2) and 1,8-bis(benzotriazol-1-yl)-3,6-dioxaoctane (L³3), have been synthesized. They were reacted with AgNO₃ and CuCl₂·2H₂O at room temperature, resulting in the formation of six novel complexes: {[AgL¹1(NO₃)(CH₃CN)]}_n (1), [Ag₂(L²2)₃](NO₃)₂ (2), {[Ag₂(L³3)₂(NO₃)₂]}_n (3), {[CuL¹1Cl₂]}_n (4), [Cu₂(L²2)₂Cl₄] (5), and [Cu₂(L³3)₂Cl₄(DMF)₂] (6). All complexes have been characterized by X-ray diffraction analysis. In 1 and 4, they exhibit similar coordination modes in which each ligand links two metal ions to form a 1D non-linear coordination polymeric chain. In 2, two Ag^I centers are close coupled by Ag⋯Ag interaction and three bridging ligands to form a dinuclear cation. The structure of 3 reveals the dinuclear cluster units, formed by two ligands and two Ag^I ions, are linked by anions to self-assemble a 1D chain. Complex 5 is an isolated dinuclear structure, in which ligands and bridging chloro ligands act as the organic clips to bridge two Cu^II centres. But in 6, a pair of ligands takes on the conformation to connect two metal ions to form bimetallic a macrocyclic architecture. These results unequivocally indicate that the influence of flexible ligand spacers, which bring structural varieties for the same metal ion, is the key factor governing the molecular architectures. Moreover, the thermal stability of 1–3 and 4–6 in the solid state has also been compared.