This critical review surveys the 3d substituted magnetic polyoxotungstate (POT) molecular compounds reported these last ten years, illustrating the huge variety of topologies that these systems can adopt. Both purely inorganic and organic/inorganic species have been considered, and the cited compounds have been classified according to their nuclearity, i.e., the number of magnetic 3d centres embedded in the POT matrix, which can be as high as 48. This review highlights the synthetic conditions, the solubility and the stability in solution of these species. The magnetic, catalytic and electrocatalytic properties of these complexes are also summarized.

This review provides a thorough overview of composites with molecular catalysts (polyoxometalates, or organometallic or coordination complexes) immobilised into MOFs via non-covalent interactions.

For the very first time, sulfonium polyoxometalate (POM) assemblies are shown to develop efficient solid-state photochromism in ambient conditions. The optical properties of the already known Rb(0.75)(NH(4))(5.25)[(Mo(3)O(8))(2)O(O(3)PC(CH(2)S(CH(3))(2))OPO(3))(2)]·8H(2)O (1) and a new material (Me(3)S)(4)[Mo(8)O(26)] (2) under UV excitation are investigated by diffuse reflectance spectroscopy, revealing that the color change effect is highly tunable playing with the nature of the POM. A mechanism involving the photoreduction of Mo(6+) cations associated with electron transfers from the sulfonium cations toward the POMs is proposed.

Polyoxometalates covalently linked to one or two spiropyran entities have been isolated. These organic-inorganic hybrids exhibit multi-electrochromic and photochromic properties.

The presence of alkylammonium groups covalently grafted on bisphosphonato ligands induces photochromic properties to ligand-coordinated polyoxomolybdate systems. Such intrinsically photoactive polyanions can be used for the preparation of materials combining photochromic polyoxometalates and functional countercations.

Synthetic routes to a penta(4-pyridyl)cyclopentadienyl ligand are explored. The most successful route uses a palladium-catalysed pentapyridation of di(tert-butyl)phosphinoferrocene by using a procedure developed by Hartwig. The same method allows the synthesis of cyclopentadiene ligands substituted with 4-benzaldehydes or 4-phenylthiols. The pyridine ligands are formally five-connected nodes that may be linked by linear coordination metals to give closed spherical complexes of composition [(metal)(30)(ligand)(12)] as shown by molecular modelling. Experiment shows that the ligand complexes copper(I) and silver(I) with the expected 1:2.5 stoichiometry, and the (1)H NMR spectrum of the resulting product shows the ligands to be equivalent. NMR diffusion and light-scattering measurements support the formation of a species with a hydrodynamic radius of the order of 15 A, in agreement with the modelling studies. The resulting complex would be topologically identical to the C(60) fullerene structure.

Abstract:The photophysical properties of a Keggin-type polyoxometalate (POM) covalently bounded to a benzospiropyran (BSPR) unit have been investigated. These studies reveal that (i) both closed and open forms are emissive with distinct spectral features (λem, (closed form) = 530 nm, λem, (open form) = 670 nm); (ii) the fluorescence of the BSPR unit of the POM-based hybrid is considerably enhanced compared to BSPR reference compounds. While the fluorescence excitation energy of the BSPR reference compounds (370 nm) is close to the intense absorption responsible of the photochromic character (350 nm), the fluorescence excitation of the hybrid is shifted to lower energy (400 nm), facilitating the population of the emissive state. Combined NOESY NMR and theoretical calculations of the closed form of hybrid give an intimate understanding of the structural conformation adopted by the hybrid and show that the nitro-aryl moieties of the BSPR is folded toward the POM, which should affect the electronic properties of the BSPR.Photo-responsive molecules and materials are currently receiving considerable attention regarding their potentiality for the development of advanced photonic devices in various applications such as information storage, optical switches, protection, smart labelling and super-resolution microscopy. [1] Particularly, the elaboration of molecular systems combining photo-switching and fluorescence properties constitute a promising research field because of the high sensitivity, resolution, contrast and fast response times of the fluorescence. Furthermore, the emergence of single-molecule fluorescence spectroscopy opens the route to high memory density nanodevices, in which a single molecule would work as one bit of memory, [2] and thus strongly supports the molecular approach. Until now, the development of molecular systems displaying photo-modulated emissive properties has mostly relied on the association of luminescent and photochromic components in a molecular assembly. [3] In these systems, the transformation of the photochromic component is exploited to modulate the emission intensity of the luminescent component on the basis of electron and/or energy transfer. [4] However, molecular systems displaying tuneable fluorescence features, i.e. having different emission energies, according to the form of the photochromic unit, have been scarcely reported in the literature. [5] The coexistence of photochromic and fluorescence properties, in a single photoactive unit, is rarely achieved since in case of fast internal conversion only one photophysical property (photochromic vs fluorescence) is observed. Furthermore the ns timescale of fluorescence [6] is considerably slower than the fs to ps timescale of the ring opening/closure dynamics occurring in the photochromic events. [7] POMs are nanosized molecular oxo cluster that are currently receiving considerable attention because of their wide range of properties and their potential applications in various fields such as analytical chemistry, medicine and ...

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