A comparative study of optical properties and X-ray induced luminescence of octahedral molybdenum and tungsten cluster complexes.

Darya V Evtushok,Natalia R Obedinskaya,Olga A Efremova,Evgeniy I Kretov,Igor N Novozhilov,Yuri V Mironov,Yuri A Vorotnikov,Anatoly R Melnikov,Natalia V Kuratieva,Dmitri V Stass,Natalya A Vorotnikova,Alexey A Ryadun,Konstantin V Kozyr,Michael A Shestopalov

doi:10.1039/c7dt01919j

Abstract

Octahedral metal cluster complexes have high potential for biomedical applications. In order to evaluate the benefits of these moieties for combined CT/X-ray luminescence computed tomography, this paper compares photoluminescence, radiodensity and X-ray induced luminescence properties of eight related octahedral molybdenum and tungsten cluster complexes [{M6I8}L6]n (where M is Mo or W and L is I-, NO3-, OTs- or OH-/H2O). This article demonstrates that despite the fact that molybdenum cluster complexes are better photoluminescence emitters, tungsten cluster complexes, in particular (Bu4N)2[{W6I8}I6], demonstrate significantly higher X-ray induced luminescence due to a combination of relatively good photoluminescence properties and high X-ray attenuation. Additionally, photo-degradation of [{M6I8}(NO3)6]2- was evaluated.

Highlights

X-rays have been widely used in biomedical imaging over the last century, during which bioimaging techniques based on the detection of X-ray attenuation have been evolving to achieve high precision and spatial resolution in Computed Tomography (CT)
The W6Cl12 compound was synthesised by the high temperature reaction of WCl6 with metallic Bi
We have shown that both absorption and emission profiles of the tungsten cluster complexes are somewhat blue shifted in comparison with their molybdenum analogues, which signifies the broader energy gaps for the former, which is likely to be associated with the slightly higher electronegativity of tungsten atoms

Summary

Introduction

A few types of nanomaterials have already been considered as contrast agents for XEOL based bioimaging and as photosensitisers including lanthanide doped inorganic nanoparticles,[8,9,10,11,12] gold nanoparticles[13] and MOFs.[14] The potential of octahedral molybdenum cluster complex (Bu4N)2[{Mo6I8}(OOC-1-adamantane)6] for X-ray excited optical luminescence and X-ray induced PDT has been recently revealed in ref. Paper ment of phosphorescent octahedral molybdenum cluster complexes, all based on the {Mo6I8}4+ cluster core that have high quantum yields[34,35,36,37] and high efficiency in generating singlet oxygen.[38,39,40,41,42,43] our recent studies have shown that materials doped using {Mo6I8}4+ are highly photoluminescent and have low cellular toxicity in the dark, while by a careful selection of a matrix the cellular internalisation and photoinduced toxicity of the materials can be tuned.[18,19,20,21]. In this work we compare optical and XEOL properties of octahedral tungsten complexes: (Bu4N)2[{W6I8}I6] (1) and new complexes (Bu4N)2[{W6I8}(NO3)6] (2), (Bu4N)2[{W6I8}(OTs)6] (OTs− is p-toluenesulfonate) (3) and [{W6I8}(OH)4(H2O)2]·6H2O (4) with those of the corresponding molybdenum analogues: (Bu4N)2[{Mo6I8}I6] (5), (Bu4N)2[{Mo6I8}(NO3)6] (6), (Bu4N)2[{Mo6I8}(OTs)6] (7) and [{Mo6I8}(OH)4(H2O)2]·2H2O (8)

Results and discussion

Synthetic procedures

Conclusions