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

A 3D Co(III)-complex hybrid polyoxoniobate framework Na 10 (H 2 O) 36 [Co 2 (phen) 2 (4,4'-bipy)(Nb 6 O 19 ) 2 ]·19H 2 O ( 1 ) has been constructed from [Co 2 (phen) 2 (4,4'-bipy)(Nb 6 O 19 ) 2 ] 10- dimer units and 2D inorganic Na-O cluster layers. The Co(III) centers are coordinated with {Nb 6 O 19 }, 4,4'-bipy and phen simultaneously. The [Co 2 (phen) 2 (4,4'-bipy)(Nb 6 O 19 ) 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 {Nb 6 O 19 } 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 × 10 3 ) 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.