Molybdenum Iodides – from Obscurity to Bright Luminescence

Abstract

This review is dedicated to the chemistry of Mo iodides. These compounds have a humble origin, and for a long time their chemistry has been almost completely neglected. Although important work on mononuclear and dinuclear Mo iodide complexes was done in 1980-1990s, the situation has dramatically changed within the last decade. The finding that the IntroductionThe iodides of transition metals attract much less attention than their chloride and bromide analogues, even though a book dealing exclusively with metal iodides was published half a century ago. [1] This is partly explainable by general lack of current or proposed practical use for this class of compounds. A notable exception offer the volatile iodides of Ti, Zr, and Hf, and of a few other metals, that can be used in the iodide process of van Arkel and de Boer. [2] Among the group 6 metals, this process can be applied for preparation of high purity chromium, which [a] Nikolaev His research interests focus on the coordination chemistry of 4d and 5d transition metals. Maxim Mikhaylov was born in Novosibirsk, (Russia). In 2009-2013 he completed his Ph. D. at the Laboratory of cluster and supramolecular compounds in the Nikolaev Institute of Inorganic Chemistry (NIIC) under suporevision of Prof. Dr. M. N. Sokolov. Now he is a researcher working in the Laboratory of synthesis of cooridnation compounds at NIIC. His research interests include synthesis of novel clusters and cluster complexes for the development of new materials.

Hexasubstituted Iodide Tungsten Cluster Complexes with Azide and Isothiocyanate Ligands

“…In general, all emission spectra for the tungsten clusters prolonged to the blue region for ≈ 50 nm, which leads to a more orange color of emission in comparison with the molybdenum ones , , . Interestingly, the emission profiles of iodide tungsten clusters, as well as of molybdenum ones, are independent of apical ligands indicating strong core‐centered nature of luminescence, which correlates well with the literature , , . On the other hand, the excitation spectra of all investigated compounds in solutions, including (Bu 4 N) 2 [{Mo 6 I 8 }(OTs) 6 ], are almost identical, with a maximum at ≈ 350 nm (Figure , Figure S5).…”

“…The substitution of apical iodide ligands leads to a small hypsochromic shift of absorption and to significant changes in the spectrum shape. This effect, although a more pronounced one, has been repeatedly demonstrated for molybdenum complexes and is probably associated with a significant contribution of apical ligands to the HOMO , , , , , . In general, from the obtained spectra it can be concluded that (i) the initial complex (Bu 4 N) 2 [{W 6 I 8 }I 6 ] has higher absorption in the visible region and (ii) the isothiocyanate and azide complexes have similar absorption profiles, but the extinction coefficient of 2 is slightly lower.…”

“…The E g values of 1 and 2 are close and equal to ≈ 2.5 eV, while for (Bu 4 N) 2 [{W 6 I 8 }I 6 ] this value is ≈ 2.4 eV, which correlates with higher absorption of the latter in the visible region. At the same time, according to the published data, iodide molybdenum complexes demonstrate E g values from 2.1 to 2.3 eV,, which indicates that their absorption is even more prolonged to the red region of spectra in comparison with tungsten clusters.…”

“…Nowadays octahedral tungsten and molybdenum cluster complexes with the general formula [{M 6 X 8 }L 6 ] n (M – Mo or W; X – halogen; L – neutral or anionic ligands) are very attractive compounds mainly due to their superb luminescent properties. Namely, UV or visible light (250–550 nm) excitation leads to a bright emission of the clusters in a wide wavelength range of 550–900 nm with high quantum yields (up to 0.82) and lifetimes (up to ≈ 400 µs) . Bright emission is essential for the creation of various optical devices (luminescent solar concentrators, lasers, optical waveguides, etc.…”

“…Bright emission is essential for the creation of various optical devices (luminescent solar concentrators, lasers, optical waveguides, etc. ), which explains much attention of the researchers to this class of compounds . Moreover, the ability of the clusters to photosensitize the process of singlet oxygen generation expands the area of possible applications from wastewater treatment to photodynamic therapy,, which determines the importance of further development of cluster chemistry.…”