Reversible Thermochromism and Stable Resistance Switching Behaviors Based on a Co(III)-Complex-Linked Polyoxoniobate.

Abstract

A 3D Co(III)-complex hybrid polyoxoniobate framework Na10(H2O)36[Co2(phen)2(4,4'-bipy)(Nb6O19)2]·19H2O (1) has been constructed from [Co2(phen)2(4,4'-bipy)(Nb6O19)2]10- dimer units and 2D inorganic Na-O cluster layers. The Co(III) centers are coordinated with {Nb6O19}, 4,4'-bipy and phen simultaneously. The [Co2(phen)2(4,4'-bipy)(Nb6O19)2]10- fragments link the Na-O cluster layers to generate a 3D metal complex-modified hybrid polyoxoniobate framework with π-π interactions between phenanthroline rings. Compound 1 shows reversible thermochromic behavior resulting from electron transfer from {Nb6O19} to 4,4'-bipy and subsequent formation of radical products, which is first observed in polyoxoniobates. Furthermore, the compound exhibits stable nonvolatile storage behavior and rewritable resistive switching with a low switching voltage (1.12 V) and high current on/off ratio (1.18 × 103) along with stable cyclic performance during stability test for 200 cycles. Charge-transfer mechanism has been studied by analyzing the relationship between current and voltage in the process of resistance switching.