Metal-to-metal charge-transfer transitions in Prussian blue hexacyanochromate analogues

Abstract

Time-dependent density functional theory (TD-DFT) calculations are presented for a series of Prussian blue analogues (PBAs) based on hexacyanochromate in order to investigate optical metal-to-metal charge-transfer (MMCT) transitions. PBE0 hybrid DFT calculations at fixed geometry were carried out on binuclear units of (CN)5-MA-NC-CrIII-(CN)5, with MA=VII, VIII, and CrII. The MMCT transitions occurred at 743nm for the VII-CrIII PBA and at 780nm for the VIII-CrIII PBA. The ordering of the transition energy and strength for these analogues agreed with data available in the literature. The transition for the CrII-CrIII MMCT was found to occur at 284nm. This study shows that TD-DFT is a powerful method to study optical properties of PBAs and that the results for the relatively simple binuclear cluster are comparable to solid PBAs, where MMCT transitions are typically the dominant feature in the visible part of the absorption spectrum.