Structure dependent charge transfer in bipyrimidinium–octacyanotungstate ion pairs

Anion-cation interactions in a series of salts with substituted Hphen, Hbpy and H2bpy cations and [W(CN)8]4- anion: polymer with "super-short" N-H⋯N hydrogen bridges containing exclusively anions and H. Dalton Trans 2021;50:17981-17987. [PMID: 34842868 DOI: 10.1039/d1dt03224k]

The 10 ion-pairs of [W(CN)₈]^4- with substituted Hphen and H_nbpyⁿ⁺ (where phen = 1,10-phenantroline, bpy = 2,2'-bipyridine, n = 1 or 2) were isolated and the spectroscopic properties of these salts are discussed. Three salts with dimethyl-substituted H_nbpyⁿ⁺ cation were structurally characterized. In the structure of the salt with H₂bpy, one of the cyanido ligands of the anion is in the CNH form. This situation is very unique, as well as the formation of two water double bridges by water molecules in [W(CN)₈]^4-. The formulas of other compounds were determined based on the IR spectra, thermogravimetry, and elemental analyses. The ion-pair formation was accompanied not only by anion-cation charge-transfer bands in the visible part of the electronic spectra, but also low-energy bands above 1000 nm were found and are related to the thermal electron transfer; the amount of the paramagnetic W^V was determined by EPR measurement. The thermal excitation of electrons may indicate the possibility of using these compounds as semiconductors. Finally, the improved method of K₄[W(CN)₈]·2H₂O synthesis is also described.