Improved Synthesis of (TBA)₂[W₆Br₁₄] Paving the Way to Further Study of Bromide Cluster Complexes

Abstract

Octahedral cluster complexes of molybdenum and tungsten, [M 6 X 8 Y 6 ] n− (M = Mo, W; X, Y = Cl, Br, I), are promising active components in various fields, including biomedicine and solar energy. Cluster complexes draw considerable attention due to their X-ray opacity, red/near-IR luminescence, and ability to convert triplet molecular oxygen to active singlet oxygen under UV and visible irradiation. Among the octahedral cluster complexes of molybdenum and tungsten, compounds with a {W 6 Br 8 } 4+ core are the least studied. There are only a few examples of compounds with substituted terminal ligands, and their properties are not well understood. Among other things, this is due to more labor-intensive and expensive methods for obtaining the starting compounds in comparison with molybdenum counterparts. In this paper, we describe the synthesis of an octahedral cluster complex, (TBA) 2 [W 6 Br 14 ] (TBA + = tetrabutylammonium), in gram quantities, starting from simple substances�W, Br 2 , and Bi�in 70% yield. The formation of pentanuclear tungsten cluster complexes was recorded as a byproduct. Compounds with substituted terminal ligands (TBA) 2 [W 6 Br 8 Y 6 ] (Y = NO 3 , Cl, I) were obtained. We also discuss the instability of (TBA) 2 [W 6 Br 8 (NO 3 ) 6 ] under light exposure, the optical properties of a series of compounds (TBA) 2 [W 6 Br 8 Y 6 ] (Y = Cl, Br, I), and the effect of terminal ligands on the chemical shifts in 183 W NMR spectra in dimethyl sulfoxide-d 6 . The presented approach to the synthesis of one of the main precursors of various bromide cluster complexes on a gram scale can stimulate the study of their properties and development of new functional materials based on them.