Three new coordination polymers with tetranuclear cluster-based 3D framework and bent 1D ribbons generated from ternary copper(II)-triazole-citrate system: Synthesis, structure, and magnetism

Abstract

Three interesting magnetic coordination polymers (CPs) with the same components and different structures, {[Cu4(atr)2(H2O)3(cit)2] 3H2O}n (1), [Cu2(atr)2(H2O)2(cit)]n (2), and {[Cu2(atr)(H2O)3.25(cit)]·H2O}n (3) (atr=4-amino-1,2,4-triazole and cit4−=citrate), were respectively generated by tuning the preparation methods and synthetic conditions. Structural determinations reveal that 1 is a three-dimensional (3D) robust framework with μ3-cit4− and μ-atr aggregated CuII4 subunits extended by μ5-cit4− connectors. By contrast, both 2 and 3 with different molar ratios of atr and aqua exhibit bent one-dimensional (1D) ribbons with dimeric {Cu2(μ-atr)} subunits periodically propagated by flexible μ3-cit4− connectors, which are further assembled into 3D supramolecular networks by classic hydrogen-bonding interactions. The structural difference of the three samples is more significantly governed by the flexible cit4− connector with various binding modes. Magnetically, strong antiferromagnetic interactions with the coupling constant up to −172.2cm−1 are observed within the dimeric subunits of 1–3, and the coupling strength is close related with the specifically spatial orientations of the magnetic orbits and the bridging angle of the spin carriers.