Crystal structure and mechanism of water exchange on nonaaquatetraoxotrimolybdenum(4+) from x-ray and oxygen-17 NMR studies

Abstract

b) From 2. A solution of 223 mg (0.216 mmol) of 2 in 10 mL of toluene was saturated with CO. The red microcrystalline 3, which precipitated after 8 h, was filtered and vacuum-dried.(c) From Pd(PCy,),. The absorption of CO by a solution containing 434 mg (0.652 mmol) of Pd (PCy,), in 20 mL of toluene was measured with a gas-volumetric apparatus; 0.645 mmol of CO was absorbed. From the solution a red microcrystalline solid precipitated, which was shown to be identical with a sample prepared by method a.X-ray Crystallography. Crystal data and details of measurements for 1 and 2 are reported in Table I. Diffraction intensities were collected at room temperature by the w/28 scan method of an Enraf-Nonius CAD-4 diffractometer with Mo K a radiation (A = 0.71069 A) and reduced to F, values.The structures were solved by Patterson and direct methods and refined by full-matrix least-squares calculations. For all computations the SHELX76 and SHELX86I3*l4 packages of crystallographic programs were used with the analytical scattering factors, corrected for real and imaginary parts of anomalous dispersions, taken from ref 14b. Thermal vibrations were treated anisotropically.In both compounds the H atoms bound to Pd(I1) were found in a final difference map by using a reduced reflection sphere ((sin 8)/A = 0.3) and kept at their observed distances [ 1.57 (2) and 1.46 (2) A, respectively] from Pd. Also, the phenol and pentafluorophenol 0-bound H atoms were directly located and kept at their found positions of 1.18 and 0.89 A, respectively, from 043. All the remaining H atoms were added in calculated positions (C-H = 1.08 A) and refined riding on the corresponding C atoms. Common temperature factors were refined for chemically equivalent H atoms, while the H(hydride) and H(bridging) atoms were treated independently.Final difference Fourier maps showed residual peaks lower than 1 e A-' in both compounds. Final atomic coordinates for 1 and 2 are listed in Tables I1 and 111, while relevant bond distances and angles are reported in Table IV. Absorption correction was made by applying the Walker and Stuartls method after a complete structural model was obtained and all atoms were refined isotropically for 1. For 2 an empirical absorption correction was applied by measuring scans at intervals of IOo around the diffraction vectors of eight selected reflections near x = 90' (transmission range Registry No. 1, 112469-70-2: 2, 119455-96-8; 3 ( n = 3), 95246-51-8; 7 l-lOO%). Pd(PCy,),, 33309-88-5; PhOH, 108-95-2; C,F,OH, 771-61-9: CH,OH, 67-56-1; i-PrOH, 67-63-0. Supplementary Material Available: Hydrogen atom coordinates (Tables S-I and S-II), anisotropic thermal parameters (Tables S-I11 and S-IV), bond distances and angles (Tables S-V and S-VI), and crystal data and intensity collection parameters (Table S-IX) (74 pages); observed and calculated structural factors (Tables S-VI1 and S-VIII) (78 pages). Ordering information is given on any current masthead page. (15) Walker, N.: Stuart, D. Acta Crystallogr., Sect. A 1983, 158. Acid dissociati...

Kinetic Studies of Water Exchange and Substitution by NCS– on the Sulphur-capped Triangular Ion [Μο3(μ3-S)(μ-O)3(ΟΗ2)9]4+

“…The poor quality of the 17 0 NMR data determined for [Μο3(μ3-0)(μ-0)3(0H2)9] 4+ , which is due largely to evidence of weak but significant inner sphere association of pts" [ Table VII (25°C). Values of k z so estimated for Mo3S03(OH) 3+ (~8s _1 ) are of comparable magnitude to, and certainly no larger than, k QH for exchange at a water 'd' site on the same species (45 s -1 ) in keeping with the same dissociative ij mechanism as concluded for Mo304(OH) 3+ (aq) [6,12] and MO3S4(OH) 3+ (aq) [9,11]. The values of ΔΗ*,Η (81 kj mol" 1 ) and (+57JK" 1 mol -1 ), Table III, for the water exchange process are also largely in keeping with such a mechanism.…”

“…Structural data is provided for the first time on the mixed oxo-sulphido aqua ion [Μο3(μ3-5)(μ-0)3(0H2)9] 4+ from a Mo Kedge EXAFS study in 2 Μ HCIO4 solution for comparison with previous X-ray structural data on the ions [Μ03(μ3-0)(μ-0)3(0Η2)9] 4+ [6] and [Μο3(μ3-5)- on the above three species, now allows structurereactivity relationships to be investigated on this family of [Mo3S"04_"(OH2)9] 4+ cluster 10ns.…”

“…The well-characterised family of triangular incomplete-cuboidal aqua clusters [Μο 3 (μ3-Χ)(μ-X)3(OH2)9] 4+ (X=0, S or Se) [1][2][3][4][5][6][7][8][9][10][11][12][13][14] has provided interest regarding kinetic studies of the water ligand substitution process because of the presence at the molybdenum centre of non-equivalent water ligands, Figure 1, which have markedly differing rates of water exchange [6,9,10]. Those labelled'd' (two per Mo), which are approximately trans to the μ2-Χ bridging groups, undergoing exchange roughly 10 5 times faster than those labelled 'c' (one per Mo), which are trans to the μ3-Χ capping group.…”

Self-Assembled Superanions: Ionic Capsules Stabilized by Polynuclear Chromium(III) Aqua Cations

“…[29] Although studies of the hydrolytic polymerisation of Cr 3 and Rh 3 has led to the isolation and solution characterisation of several oligomers, [22,23] attempts to crystallize oligomers with a higher nuclearity than dinuclear species have been unsuccessful. The superanion or ionic capsule approach demonstrates a new general method for the structural characterisation of metal ions present in aqueous systems.…”

Interfacial Kinetics Through the Lens of Solution Chemistry: Hydrolytic Processes at Oxide Mineral Surfaces

“…The differences are profound: Richens et al (14) found no evidence for exchange of the μ 2 -or μ3-οχο bridges in the [Mo304(OH 2 )9] 4+ (aq) complex over two years. In contrast, although all the terminal waters of this complex exchange readily, rates of exchange of those cis-or trans-to the μ-οχο bridges differ by a factor of 10 5 !…”