Synthesis and Characterization of Octa- and Hexanuclear Polyoxomolybdate Wheels:  Role of the Inorganic Template and of the Counterion

Abstract

Eight new compounds based on [O3PCH2PO3]4- ligands and {MoV2O4} dimeric units have been synthesized and structurally characterized. Octanuclear wheels encapsulating various guests have been isolated with different counterions. With NH4+, a single wheel was obtained, as expected, with the planar CO32- guest, (NH4)12[(MoV2O4)4(O3PCH2PO3)4(CO3)2].24H2O (1a), while with the pyramidal SO32- guest, only the syn isomer (NH4)12[(MoV2O4)4(O3PCH2PO3)4(SO3)2].26H2O (2a) was characterized. The corresponding anti isomer was obtained with Na+ as counterions, Na12[(MoV2O4)4(O3PCH2PO3)4(SO3)2]39H2O (2b), and with mixed Na+ and NH4(+) counterions, Na+(NH4)11[(MoV2O4)4(O3PCH2PO3)4(SO3)2].13H2O (2d). With [O3PCH2PO3]4- extra ligands, the octanuclear wheel Li12(NH4)2[(MoV2O4)4(O3PCH2PO3)4(HO3PCH2PO3)2].31H2O (4a) was isolated with Li+ and NH4+ counterions and Li14[(MoV2O4)4(O3PCH2PO3)4(HO3PCH2PO3)2].34H2O (4c) as a pure Li+ salt. A new rectangular anion, formed by connecting two MoV dimers and two MoVI octahedra via methylenediphosphonato ligands with NH4+ as counterions, (NH4)10[(MoV2O4)2(MoVIO3)2(O3PCH2PO3)2(HO3PCH2PO3)2].15H2)O (3a), and Li9(NH4)2Cl[(MoV2O4)2(MoVIO3)2(O3PCH2PO3)2]. 22H2O (3d) as a mixed NH4+ and Li+ salt have also been synthesized. The structural characterization of the compounds, combined with a study of their behavior in solution, investigated by 31P NMR, has allowed a discussion on the influence of the counterions on the structure of the anions and their stability. Density functional theory calculations carried out on both isomers of the [(MoV2O4)4(O3PCH2PO3)4(SO3)2]12- anion (2), either assumed isolated or embedded in a continuum solvent model, suggest that the anti form is favored by approximately 2 kcal mol(-1). Explicit insertion of two solvated counterions in the molecular cavity reverses this energy difference and reduces it to less than 1 kcal mol(-1), therefore accounting for the observed structural versatility.

Hydrogen-Bonding in Two Pyridinium Salts of [Mo2O4Cl4(μ2-dmsH)]3−Complex (dmsH− = a Half-Neutralized Form of 2,2-Dimethylsuccinic Acid)

“…Our goal was realized by the reaction system of a mononuclear molybdenum(V) starting material, (PyH) 5 [MoOCl 4 (H 2 O)] 3 Cl 2 , and 1,3,5-benzenetricarboxylic acid. In the presence of a weak base, pyridine, a dinuclear anionic complex (PyH) 4 2− stand for anionic forms of the acid with one or two ionized functions, respectively) were prepared [9]. Only the ionized functions of the acid were seen to participate in bonding interactions with the metal atoms.…”

“…The COOH group is hydrogen-bonded to the non-coordinated oxygen of the mal 2− ligand of an adjacent complex (Figure 10b) (Figure 10c). Although the stoichiometry of another example, (PyH) 4 [Mo 2 O 4 Cl 4 (μ 2 -btcH 2 )]Cl, is highly reminiscent of that of compound 2, the ligand, the anion of 1,3,5-benzentricarboxylic acid, possesses two non-ionized COOH functions and a different connectivity pattern is displayed [9]. Both of its COOH functions form hydrogen bonds with chloride counteranions and infinite chains are formed ( Figure 10d).…”

“…The singly metal−metal bonded {Mo 2 (μ 2 -O) 2 , pervades the chemistry of molybdenum(V) [1][2][3][4]. Its ability to retain its structural integrity upon coordination of various ligands to its peripheral sites makes it a suitable candidate for the construction of metal-organic frameworks.…”

Characterization of tetra, dodeca and tetradeca MoV polyoxometalate wheels structured by etidronate ligands

“…Focusing on polyoxomolybdate systems where all the molybdenum centers are reduced in their V oxidation state, a large number of species have been isolated both in organic or aqueous media. In all cases, these polyanions contain the dinuclear dicationic [ 8À has been obtained in presence of methyl arsenate, [6] while ellipsoidal octanuclear clusters have been isolated when the synthetic process is performed in presence of sulfite or carbonate [7]. A larger complex, a dodecanuclear wheel which adopts a cyclohexane-like ring in a chair conformation has been obtained in absence of any additional coordinating groups.…”

En route to {Mo2O2(μ2-O)2}2+ species: Isolation and structural characterization of a novel methoxide-bridged Mo(V) complex

“…The roles of many factors such as temperature, solvent, pH, nature of counter ions and concentration have to be considered. The reduction of Mo(VI) starting material, typically ammonium »heptamolybdate« or Na 2 MoO 4 , with a reducing agent such as hydrazine leads either to mixed-valent Mo(V/VI) or fully-reduced Mo(V) clusters [4], which are based on a well-known structural fragment, a dinuclear, metal-metal bonded {Mo 2 O 2 (l 2 -O) 2 } 2+ core [5]. The formation of the Mo(V) clusters may be envisioned as a stepwise condensation of dinuclear {Mo 2 O 2 (l 2 -O) 2 } 2+ fragments, enabled by the ability of oxygen donor atoms to participate in bridging interactions with two, three or even four metal atoms.…”