Cyanide Complexes Based on {Mo6I8}4+ and {W6I8}4+ Cluster Cores

Luminescent Supramolecular Ionic Frameworks based on Organic Fluorescent Polycations and Polyanionic Phosphorescent Metal Clusters

Emissive ionic supramolecular frameworks are designed by associating tetraphenylethylene-based tetra-cationic units and di-anionic molybdenum or tetra-anionic rhenium octahedral clusters. Obtained structures were characterized by single-crystal X-ray diffraction. The emission properties of the hybrids were investigated as dry powders or in various solvents by one photon and two photon absorption leading to a O2 concentration dependent luminescence color for the Mo based hybrid.

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

Octahedral cluster complexes of molybdenum and tungsten, [M₆X₈Y₆]^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 {W₆Br₈}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[W₆Br₁₄] (TBA⁺ = tetrabutylammonium), in gram quantities, starting from simple substances─W, Br₂, and Bi─in 70% yield. The formation of pentanuclear tungsten cluster complexes was recorded as a byproduct. Compounds with substituted terminal ligands (TBA)₂[W₆Br₈Y₆] (Y = NO₃, Cl, I) were obtained. We also discuss the instability of (TBA)₂[W₆Br₈(NO₃)₆] under light exposure, the optical properties of a series of compounds (TBA)₂[W₆Br₈Y₆] (Y = Cl, Br, I), and the effect of terminal ligands on the chemical shifts in ¹⁸³W NMR spectra in dimethyl sulfoxide-d₆. 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.

Selective Oxidation of Inner Pnictogenide Ligands in Mixed-Ligand Rhenium Cubane-Type Cluster Complexes

Reactivity of new tetrahedral rhenium cluster complexes with pnictogenide inner ligands μ₃-As^3-, μ₃-Sb^3-, and μ₃-Bi^3- has been investigated in reactions with aqueous H₂O₂. It has been found that the oxidation of clusters [{Re₄As₃Q}(CN)₁₂]^7- (Q = S or Se) led to the formation of stable clusters with μ₃-(AsO)^3- ligands. Under the same conditions, the oxidation of [{Re₄As₂S₂}(CN)₁₂]^6- cluster led to substitution of μ₃-As^3- ligands to μ₃-O^2-. The resulting cluster [{Re₄O₂S₂}(CN)₁₂]^4- easily undergoes further oxidation, and even at room temperature, a unique {Re₄} to {Re₃} rearrangement occurs with the formation of the new triangular cluster [{Re₃(μ₃-S)(μ-O)₂(μ-SO₂)}(CN)₉]^5-. Upon heating, this process proceeds faster and the triangular cluster can be isolated as individual compounds. Cluster anions [{Re₄SbSe₃}(CN)₁₂]^5- and [{Re₄BiS₃}(CN)₁₂]^5- reacted with H₂O₂, yielding clusters containing μ₃-O^2- ligands, namely, [{Re₄OSe₃}(CN)₁₂]^4- and [{Re₄OS₃}(CN)₁₂]^4-. This indicates that oxidized forms of μ₃-Sb^3- and μ₃-Bi^3- ligands can be easily substituted.

The role of hydrolysis in biological effects of molybdenum cluster with DMSO ligands

Biological applications of octahedral molybdenum cluster complexes are complicated by their hydrolytic instability, since hydrolysis leads to irreversible changes in the structure and properties of these compounds. On the other hand, if such changes are thoroughly investigated and understood, the hydrolysis process can become an important tool for regulating specific biological effects of the clusters. In this work, we demonstrate how the luminescence and biological properties (cellular uptake, cytotoxicity in the dark and photodynamic effect) of highly unstable cluster complex [{Mo₆I₈}(DMSO)₆](NO₃)₄ change along with the degree of hydrolysis. Particularly, cluster solution preliminarily aged in water demonstrated lower dark and higher photoinduced cytotoxicity and higher cellular uptake in comparison with fresh solution.