Photoactive Materials Based on Molybdenum Cluster Sulfides

Coordination Chemistry deals with the synthesis and study of the physicochemical properties of metal complexes. Cluster Chemistry is a subfield of Coordination Chemistry, which focuses on the functionalization of complexes in which two or more metal atoms are directly bonded. Over the past few years, Cluster Chemistry has attracted a growing interest among scientists from diverse areas, mainly due to the fascinating properties of these compounds. A historical evolution of the term cluster, as well as an outline of the role of coordinated ligands and structural types in the final properties of metal clusters are provided in Chapter 1. This PhD Thesis is devoted to the synthesis, characterization and applications of two families of group VI metal clusters containing dithiolene or diimine ligands, as detailed in Chapter 2. The synthetic approaches employed for the preparation of a series of dinuclear M2Q2S2 cluster chalcogenides (M = Mo, W; Q = O, or S) bearing bifunctional dithiolene ligands are described in Chapter 3. These metal clusters present great potential for the design of heterometallic systems. Chapter 4 is concerned with the preparation of an extensive family of mixed-ligand diimine-halide (or diimine-dithiolene) trinuclear molybdenum sulfides based on the Mo3S7 core. A great number of bipyridine and phenanthroline derivatives have been coordinated to these Mo3S7 units. The most important feature of the resulting cluster complexes of formula Mo3S7X4(diimine), where X = Cl, or Br, is their crystallization as [Mo3S7X4(diimine)·X]- aggregates, in which the sulfur axial atoms participate in non-bonding interactions with halide anions. The physicochemical properties of both series of metal clusters mentioned above are explored in Chapters 5 and 6. The luminescence properties of bis(dithiolene) M2Q2S2 clusters (M = Mo, W; Q = O, or S), together with those of Mo3S7 clusters functionalized with imidazophenanthroline ligands are detailed in Chapter 5. These diimine Mo3S7 complexes exhibit luminescent anion sensing behavior. The optical limiting capabilities of both series of compounds, namely M2Q2S2- and Mo3S7-based clusters, are also described in Chapter 5 with the aim of finding correlations between molecular structures and third-order nonlinear optical functions. Chapter 6 examines the electro- and photocatalytic activity of diimine Mo3S7 clusters immobilized on TiO2 nanoparticles toward the hydrogen evolution reaction. This study has been stimulated by the analogy between the structure of Mo3S7 and the catalytic active sites of MoS2 nanoparticles. The electrochemical properties of these TiO2 electrodes are assessed in two different media, that is, aqueous perchloric acid and sulfide-sulfite mixtures. The role of the diimine ligands in the adsorption process is also described in this Chapter. All experimental procedures employed in this work, together with the characterization of all compounds are presented in Chapter 7. Finally, the general conclusions of this PhD Thesis are provided in Chapter 8.</p

Synthesis and optical power limiting properties of heteroleptic Mo3S7 clusters

Substitution of the halide ligands in (Bu4N)2[Mo3S7X6] (X = Cl, Br) by diimine ligands, such as 4,4′-dimethyl-2,2′-bipyridine (dmbpy), 2,2′-bipyridine (bpy) and 1,10-phenanthroline (phen), affords the neutral heteroleptic clusters Mo3S7Cl4(dmbpy) (1), Mo3S7Br4(dmbpy) (2), Mo3S7Br4(bpy) (3), and Mo3S7Br4(phen) (4). Further substitution of the halide ligands in Mo3S7Br4(diimine) clusters by dmit (1,3-dithiole-2-thione-4,5-dithiolate) allows the preparation of the mixed diimine–dithiolene neutral cluster complexes Mo3S7(dnbpy)(dmit)2 (5, dnbpy = 4,4′-dinonyl-2,2′-bipyridine), Mo3S7(dcmbpy)(dmit)2 (6, dcmbpy = 4,4′-dimethoxycarbonyl-2,2′-bipyridine), and Mo3S7(dcbpy)(dmit)2 (7, dcbpy = 2,2′-bipyridine-4,4′-dicarboxylic acid). The optical limiting properties of complexes 1–7 have been assessed by the open-aperture Z-scan technique at 570 nm, employing a nanosecond optical parametric oscillator. In order to investigate the effect of increasing the π-system, complexes 1–4, with the general formula Mo3S7X4(diimine), (X = Cl, Br), were compared to clusters 5–7, containing the dmit ligand. The influence of the metal content on the optical power limiting properties was also investigated by comparing the trinuclear series of complexes prepared herein with the bis(dithiolene) dinuclear cluster (Et4N)2[Mo2O2S2(BPyDTS2)2], which has been recently prepared by our group. All trinuclear clusters 1–7 are efficient optical limiters (σeff > σ0) with the threshold limiting fluence F15% decreasing on proceeding from dinuclear to trinuclear clusters and, generally, on extending the π-system.Financial support from the Spanish Ministerio de Economia y Competitividad (MINECO) (Grant CTQ2011-23157), UJI (research project P1.1B2013-19) and Generalitat Valenciana (Prometeo/2014/022 and ACOMP/2014/274) is gratefully acknowledged. The authors also thank Serveis Centrals d ’ Instrumentació Cientifica (SCIC), within Universitat Jaume, I for providing them with materials characterization facilities. D. R. thanks the Spanish Ministerio de Economía y Competividad for a predoctoral fellowship. M. G. H. thanks the Australian Research Council for support. M. S. acknowl- edges the NCN grant DEC-2013/10/A/ST4/0011

First heteroleptic Mo3S7 clusters containing non-innocent phenanthroline ligands

Reaction of the thiobromide [Mo3S7Br6]2− cluster anion with 5,6-dimethyl-1,10-phenanthroline (Me2Phen) in solution leads to the substitution of two bromide ligands and the subsequent formation of a new mixed-ligand neutral complex [Mo3S7Br4(Me2Phen)] (I). Reaction of [Mo3S7Br6]2− with 5,6-dimethyl-1,10-phenanthroline in CH2Cl2 followed by treatment of I with Na(Dtc) · 3H2O (Dtc = diethyldithiocarbamate) results in the new mixed-ligand cluster complex [Mo3S7(Dtc)2(Me2Phen)]2+ (IIa). Slow evaporation of the CHCl3 solution of the complex in the presence of PF 6 − gives crystals of {[Mo3S7(Dtc)2(Me2Phen)]Br}PF6 · 3CHCl3 (II) characterized by X-ray structural analysis. Close contacts S...S result in the formation of cationic dimers {[Mo3S7(Dtc)2(Me2Phen)]2}4+ which form infinite chains through additional Sax...Br contacts. All compounds were characterized by IR, elemental analysis and ESI-MS. Synthesized complexes represent the first examples of heteroleptic Mo3S7 clusters containing phenanthroline ligands

Heteroleptic Phenanthroline Complexes of Trinuclear Molybdenum Clusters with Luminescent Properties

Neutral Mo3(μ3-S)(μ-S2)3X3(diimine) (X = Cl–, Br–) heteroleptic cluster complexes containing the 1,10-phenanthroline ligands 1H-imidazo[4,5-f][1,10]phenanthroline-2-[3,4-bis(dodecyloxy)phenyl] (IPDOP), 4,7-diphenyl-1,10-phenanthroline (BPhen), and 3,4,7,8-tetramethyl-1,10-phenanthroline (tmphen) were prepared in high yields by straightforward ligand-substitution reactions starting from the [Mo3(μ3-S)(μ-S2)3X6]2– cluster anion. The complexes Mo3S7X4(BPhen) [X = Br– (for 3) and Cl– (for 4)] and Mo3S7X4(tmpphen) [X = Br– (for 5) and Cl– (for 6)] crystallized as tetra-n-butylammonium salts of anionic aggregates (3–6·X)–, in which neutral Mo3S7X3(diiimine)3 cluster molecules participate in non-valence interactions between the axial sulfur atoms, Sax, and a halide anion. The complexes Mo3S7Br4(IPDOP) (1) and Mo3S7Cl4(IPDOP) (2) are luminescent when excited at 330 nm and have maximum emission intensities around 450 nm in DMF and around 435 nm in dichloromethane. The maximum fluorescence quantum yield and the maximum emission lifetime were achieved for complex 2 in DMF(φF = 0.15 and τ = 7.5 ns, respectively). The most important property of complexes 1 and 2 is the shift of their emission spectra in the presence of proton-abstractor anions, such as F–, OH–, and AcO–. When these anions are added to solutions of complexes 1 or 2 in DMF or dichloromethane, the maximum emission wavelength shifts by approximately 90 nm to higher wavelengths

Dithiolene dimetallic molybdenum(V) complexes displaying intraligand charge transfer (ILCT) emission

Bifunctional dithiolene ligands have been coordinated to the MoV(O)(μ-S2)MoV(O) unit to afford [Mo2O2(μ-S)2(BPyDTS2)2]2− (12−) (BPyDTS2 (2-bis-(2-pyridyl)methylene-1,3-dithiolene) dianions. Reaction of the 12− molybdenum dimer with pentacarbonylchlorothenium(I) affords a tetrametallic complex of formula [Mo2O2(μ-S)2(BPyDTS2)2{Re(CO)3Cl}2]2− (22−). The monomeric (CH3)2Sn(BPyDTS2) (3) tin complex has also been prepared for comparative purposes. In the structure of (Et4N)2[1], the two metal atoms are in a square pyramidal coordination environment defined by two bridging sulfur atoms, one terminal oxygen atom and the two sulfur atoms of the bifunctional dithiolene ligand. This arrangement leaves two nitrogen atoms on each side which coordinate to two Re atoms in the 22− tetrametallic complex. Compound 3 has a distorted tetrahedral structure defined by two carbon atoms of the methyl groups and two sulfur atoms of the dithiolene ligand. The luminescence properties of all three complexes in acetonitrile have been investigated. Detailed studies supported on quantum mechanical calculations revealed that complex 12− shows photoluminescence in the 600–800 nm region with a maximum wavelength of 628 nm and an emission quantum yield of 0.092, associated with an intraligand charge transfer (ILCT) transition. Coordination of two Re(CO)3Cl fragments to 12− to afford 22− does not affect the emission spectrum and shape although it decreases the quantum yield, approximately by a factor of 4.6. Compound 3 exhibits a similar emission spectrum to those of the complexes 12− and 22− in good agreement with the ILCT assignment. The quantum yield of 3 lies between that of the 12− and 22− complexes