Crystal and molecular structures of trinuclear rhodium(III) complexes: <i>trans</i>-μ<sub>3</sub>-oxo-tris[bis(acetato)aquarhodium(III)] perchlorate dihydrate and monohydrate

Głowiak, Tadeusz; Kubiak, Maria; Szymańska-Buzar, Teresa

doi:10.1107/s0567740877006979

Cited by 31 publications

(11 citation statements)

References 6 publications

(5 reference statements)

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“…Closer inspection reveals that each of the more intense set of sidebands contains two poorly resolved peaks, consistent with the presence of three inequivalent Rh positions. 15 The chemical shifts for these three sites, δ iso ) 9401, 9359, and 9354 ppm, are remarkably close to the measured value δ iso ) 9390 ppm for 2 in aqueous solution. 16 Analysis of the spinning sidebands for the resonance at δ iso ) 9401 ppm indicates a CSA characterized by Ω ) 1720 ppm and κ ) -0.64.…”

supporting

confidence: 69%

“…At a spinning rate of 2 kHz (Figure ), two sets of spinning sidebands are clearly resolved with an approximate intensity ratio of 1:2. Closer inspection reveals that each of the more intense set of sidebands contains two poorly resolved peaks, consistent with the presence of three inequivalent Rh positions . The chemical shifts for these three sites, δ iso = 9401, 9359, and 9354 ppm, are remarkably close to the measured value δ iso = 9390 ppm for 2 in aqueous solution .…”

supporting

confidence: 59%

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Observation of Solid-State ¹⁰³Rh NMR by Cross-Polarization

et al. 2006

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Using 103Rh[1H] cross-polarization (CP) methods, we have obtained solid-state 103Rh NMR spectra for diamagnetic Rh(III) compounds. The isotropic chemical shift and chemical shift anisotropy (CSA) are reported for a crystalline form of the dihydroxy-bridged Rh(III) dimer and for a salt of the oxo-centered acetate-bridged Rh(III) trimer, from analysis of conventional CP/MAS spectra. Comparison of the CP kinetics of the dimer with new crystal structure data suggests a strategy for predicting 103Rh CP/MAS properties in solids.

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supporting

confidence: 69%

supporting

confidence: 59%

Observation of Solid-State ¹⁰³Rh NMR by Cross-Polarization

et al. 2006

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“…Crystal Structures. A considerable number of oxo-centered carboxylate-bridged trimers of formula [M 3 (μ 3 -O)(μ-O 2 CR) 6 L 3 ] n + are known, in particular, those of trivalent Cr, Mn, Fe, and Ru cations as well as mixed-valent species that give rise to neutral complexes. − Surprisingly, there are just a few reports of trivalent Co and Rh salts. − In the case of rhodium(III), only two polymorphs of the perchlorate salt of Rh 3 + (R = CH 3 ) have been reported, one a dihydrate (A) and the other a monohydrate (B). In view of the paucity of information and in order to assess the possible influence of these data on water substitution rates, a comparison of these structures is made.…”

Section: Resultsmentioning

confidence: 99%

“…Average deviations from the mean are given in square brackets. b Glowiak et al A = dihydrate. B = monohydrate.…”

Section: Resultsmentioning

confidence: 99%

Substituent Effects in Five Oxo-Centered Trinuclear Rhodium(III) Clusters

2006

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We here report the rates of water substitution by methanol-d(4) for four new oxo-centered trinuclear rhodium(III) clusters with different carboxylate-bridging ligands, [Rh3(mu3-O)(mu-O2CR)6(OH2)3]+ (R = CH2CH3, CH2CH2Cl, CH2Cl, and CHCl2), and [Rh3(mu3-O)(mu-O2CCH3)6(OH2)3]+. By varying the R group alkyl chain, water substitution rates were found to span almost 3 orders of magnitude (k(298K) = 1.2 x 10(-2)-2.3 x 10(-5) s(-1)) and reflect the following trend R = CH2CH3 > CH3 > CH2CH2Cl > CH(2)Cl > CHCl2. Activation parameters for substitution point toward a dissociative activation pathway (DeltaH = 99-115 kJ mol(-1); DeltaS = 48-52 J mol(-1) K(-1)), indicating that there is little association with the incoming methanol molecule during the formation of the transition-state complex. Because the mechanism for substitution in all five trimers has a considerable dissociative character, substitution rates are likely very similar to water exchange rates. These data suggest that the kinetic reactivity of the ligated waters is heavily influenced by the inductive ability of the aliphatic substituents, but yet the mechanism of substitution remains virtually unchanged. Structural data are also reported for the four new rhodium(III) trimer salts as well as 103Rh NMR spectra. We find that 103Rh NMR chemical shifts span more than 200 ppm and mirror the same reactivity trend found for the rates of water substitution (103Rh delta (9406-9620 ppm): R = CH2CH3 < CH3 < CH2CH2Cl < CH2Cl < CHCl2). Taken together, these data suggest a means for estimating water exchange rates for other oxo-centered rhodium(III) trimers from chemical shift data alone.

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“…The acetato complex is obtained by reacting rhodium triehloride with silver acetate (7) confirmed by X-ray diffraction (93). The dihydrate has also been shown to be isomorphous with the corresponding chromium salt (7).…”

Section: H Rhodiummentioning

confidence: 99%