Directed Self‐Assembly, Symmetry Breaking, and Electronic Modulation of Metal Oxide Clusters by Pyramidal Heteroanions

Abstract

Mixed valence/metal polyoxometalate (POM) clusters are one of the most interesting host species because they show the ability to incorporate a wide range of heteroatoms of various charges and geometries. We report herein the incorporation of pyramidal EO heteroanions (E=PH, S, Se, Te) that are responsible not only for directing the templated assembly of a family of mixed-metal POMs but also for the symmetry-breaking of the traditional Dawson architecture and modulation of the electronic characteristics of the cluster's shell. The isolated family of POMs consists of four members: (Me NH ) Na [Mo V O (HPO )]⋅MeOH⋅5 H O (1), (NH ) [Mo V O (SO )]⋅12 H O (2), K [Mo V O (SeO )] ⋅31 H O (3), and (Me NH ) Na[Mo V O (TeO )]⋅15 H O (4), and were characterized by X-ray structural analysis, electrospray ionization mass spectrometry (ESI-MS), thermogravimetric analysis (TGA), UV/Vis, FTIR, elemental analysis, flame atomic absorption spectroscopy (FAAS), and inductively coupled plasma optical emission spectroscopy (ICP-OES). Cyclic voltammetry (CV) and electron paramagnetic resonance (EPR) spectroscopic studies in concert with density functional theoretical (DFT) calculations have been used to elucidate the effect of the heteroatom on the electronic properties of the cluster.

Hydrothermal Reactions of [CoIII(C2O4)(NH3)4]+ and Polyoxomolybdates: Depolymerization of Polyoxomolybdates and in Situ Reduction of Cobalt

“…After the filtration of the undissolved [Bu 4 N] 2 ­[Mo 6 O 19 ], from the remaining red solutions, 2 an orthomolybdatewas isolated as the final product after 20 days. Isolation of products of different nuclearity, i.e., mono-, hexa-, hepta-, and octamolybdates, from the examined reaction mixtures, is in accordance with the existence of equilibrium established between different polyoxomolybdate species in the studied pH range ,, and the ease of their mutual transformations. Also, the ease of conversion between [Mo 8 O 26 ] 4– and Lindquist anion [Mo 6 O 19 ] 2– confirmed the lability of these species in solution as the consequence of the existence of different isomeric forms …”

“…The first-row transition metal complexes containing redox active ligands (e.g., C 2 O 4 2– , SO 3 2– ) can be used both as the counterions or as a source of ligands. Their usage represents an alternative way to direct the assembly process toward the formation of different structures and influences the electronic properties of the polyoxometalates. − …”

“…We have also successfully applied for the first time liquid-assisted ball milling followed by vapor-assisted aging for the synthesis of POMo-s. This mechanochemical approach has enabled us to identify reaction intermediates, a coordination polymer {NaMo 7 O 24 } n , and a heptamolybdate {Mo 7 Besides, a series of ionic compounds containing a polyoxomolybdate anion and a complex cation showed a good performance for epoxidation of olefins as well as for oxidation of sulfides. 10 liquid helium temperature.…”

“…The influence of pH on the formation of different polyoxomolybdate species in solution has been intensively explored since 1970. 19 The development of the synthetic methods, as well as detection (in particularly in situ) methods, 7 have enabled better understanding of and have given more insight into those pH influenced self-assembling processes. Also, one of the intriguing questions is the effect of the used counterions on the aggregation of POMo units during crystallization.…”

When Identification of the Reduction Sites in Mixed Molybdenum/Tungsten Keggin-Type Polyoxometalate Hybrids Turns Out Tricky

“…As molecular metal oxides, polyoxometalates (POMs) have astonishing redox properties, which are highly tunable according to their molecular structure, the nature of the metal addenda, 1 − 4 the heteroatom, 5 the countercations, 6 , 7 etc. These redox properties have been harnessed in several fields of applications, ranging from (opto)electronic devices 8 − 10 to molecular batteries.…”