The water exchange process on [(CO)(3)Re(H(2)O)(3)](+) (1) was kinetically investigated by (17)O NMR. The acidity dependence of the observed rate constant k(obs) was analyzed with a two pathways model in which k(ex) (k(ex)(298) = (6.3 +/- 0.1) x 10(-3) s(-1)) and k(OH) (k(OH)(298)= 27 +/- 1 s(-1)) denote the water exchange rate constants on 1 and on the monohydroxo species [(CO)(3)Re(I)(H(2)O)(2)(OH)], respectively. The kinetic contribution of the basic form was proved to be significant only at [H(+)] < 3 x 10(-3) M. Above this limiting [H(+)] concentration, kinetic investigations can be unambiguously conducted on the triaqua cation (1). The variable temperature study has led to the determination of the activation parameters Delta H(++)(ex) = 90 +/- 3 kJ mol(-1), Delta S(++)(ex) = +14 +/- 10 J K(-1) mol(-1), the latter being indicative of a dissociative activation mode for the water exchange process. To support this assumption, water substitution reaction on 1 has been followed by (17)O/(1)H/(13)C/(19)F NMR with ligands of various nucleophilicities (TFA, Br(-), CH(3)CN, Hbipy(+), Hphen(+), DMS, TU). With unidentate ligands, except Br(-), the mono-, bi-, and tricomplexes were formed by water substitution. With bidentate ligands, bipy and phen, the chelate complexes [(CO)(3)Re(H(2)O)(bipy)]CF(3)SO(3) (2) and [(CO)(3)Re(H(2)O)(phen)](NO(3))(0.5)(CF(3)SO(3))(0.5).H(2)O (3) were isolated and X-ray characterized. For each ligand, the calculated interchange rate constants k'(i) (2.9 x 10(-3) (TFA) < k'(I) < 41.5 x 10(-3) (TU) s(-1)) were found in the same order as the water exchange rate constant k(ex), the S-donor ligands being slightly more reactive. This result is indicative of I(d) mechanism for water exchange and complex formation, since larger variations of k'(i) are expected for an associatively activated mechanism.

The influence of three dicarboxylate anions, oxalate, (C2O4)2-, glutarate, (H6C5O4)2-, and pimelate, (H10C7O4)2-, on the self-condensation process of the [Mo2S2O2]2+ dithiocation has been investigated. [Mo8S8O8(OH)8(C2O4)]2- ([Mo8-ox]2-), [Mo10S10O10(OH)10(H6C5O4)]2- ([Mo10-glu]2-), and [Mo12S12O12(OH)12(H10C7O4)]2- ([Mo12-pim]2-) have been prepared and characterized in aqueous solution by 1H NMR and electrospray mass spectroscopy and in the solid state by elemental analyses, X-ray crystallography, and infrared spectroscopy. The molecular arrangement of [Mo8-ox]2-, [Mo10-glu]2-, and [Mo12-pim]2- exhibits the same type of topology derived from the neutral cyclic {Mo2 n S2 n O2 n (OH)2 n } backbone. {Mo2 n S2 n O2 n (OH)2 n } inorganic rings encapsulate the organic guest with direct covalent interactions between Mo centers and carboxylate groups. Excess of glutarate does not change the molecular arrangement of the anion but modifies the solid-state arrangement of [Mo10-glu]2-. Rb4(C5H6O4)[Mo10S10O10(OH)10(H6C5O4)]·5H2O (Rb4glu[Mo10-glu]·5H2O) has been crystallized and structurally characterized by X-ray diffraction. The structure of Rb4glu[Mo10-glu]·5H2O contains the same decameric molecular anion as that found in Cs2[Mo10-glu]·20H2O with an additional glutarate capping the molecular wheel. The supramolecular interactions developed in Rb4glu[Mo10-glu]·5H2O are ensured by hydrogen bonds involving the hydroxo bridges of the inorganic ring and the carboxylate groups of the additional glutarate. Negative-ion electrospray mass spectroscopy (ESMS) has been performed on aqueous solution containing the {Mo2S2O2} building block and the templating agent at pH 4.5. The anions [Mo8-ox]2-, [Mo10-glu]2-, and [Mo12-pim]2- were clearly identified by their parent peaks observed in the ESMS spectra. Experimental m/z ratios are fully consistent with the corresponding X-ray diffraction results. The templated anionic Mo2 n rings have been characterized by 1H NMR spectroscopy in aqueous solution and in acetonitrile-d 3. The 1H NMR spectra of [Mo8-ox]2-, [Mo10-glu]2-, and [Mo12-pim]2- as Li+ salts in CD3CN unambiguously contain the resonances of the hydroxo bridges belonging to the ring and those of the inner CH2 groups of the alkyl chain in [Mo10-glu]2- and [Mo12-pim]2-. Variable-temperature 1H NMR spectra recorded in CD3CN revealed the fluxionality of [Mo10-glu]2- and [Mo12-pim]2- in contrast to the rigidity of [Mo8-ox]2-. At low temperature (T = 226 K), the motion of the guest, i.e., the central template in Mo10 and Mo12 rings, becomes slow enough on the NMR time scale to postulate the presence of conformational isomers in solution.

The complex formation in water between the stable tricarbonyltriaqua fac-[(CO)(3)Re(H(2)O)(3)](+) (1) complex and N- and S-donor ligands has been studied by high-pressure (1)H NMR. Rate and equilibrium constants for the formation of [(CO)(3)Re(Pyz)(H(2)O)(2)](+), [(CO)(3)(H(2)O)(2)Re(mu-Pyz)Re(H(2)O)(2)(CO)(3)](2+), [(CO)(3)Re(THT)(H(2)O)(2)](+), and [(CO)(3)Re(DMS)(n)()(H(2)O)(3-n)](+) (n = 1-3) (Pyz = pyrazine, THT = tetrahydrothiophene, DMS = dimethyl sulfide) have been determined and are in accord with previous results (Salignac, B.; Grundler, P. V.; Cayemittes, S.; Frey, U.; Scopelliti, R.; Merbach, A. E.; Hedinger, R.; Hegetschweiler, K.; Alberto, R.; Prinz, U.; Raabe, G.; Kölle, U.; Hall, S. Inorg. Chem. 2003, 42, 3516). The calculated interchange rate constant k(1)' (Eigen-Wilkins mechanism) increases from the hard O- and N-donors to the soft S-donors, as exemplified by the following series: TFA (trifluoroacetate) (k(1)' = 2.9 x 10(-3) s(-1)) < Br(-) < CH(3)CN < Pyz < THT < DMS < TU (thiourea) (k(1)' = 41.5 x 10(-3) s(-1)). On the other hand, values remain close to that of water exchange k(ex) on 1 (k(ex) = 6.3 x 10(-3) s(-1)). Thus, an I(d) mechanism was assigned, suggesting however the possibility of a slight deviation toward an associatively activated mechanism with the S-donor ligands. Activation volumes determined by high-pressure NMR, for Pyz as Delta V(++)(f,1) = +5.4 +/- 1.5, Delta V(++)(r,1) = +7.9 +/- 1.2 cm(3) mol(-)(1), for THT as Delta V(++)(f,1) = -6.6 +/- 1, Delta V(++)(r,1) = -6.2 +/- 1 cm(3) mol(-1), and for DMS as Delta V(++)(f,1) = -12 +/- 1, Delta V(++)(r,1) = -10 +/- 2 cm(3) mol(-1) revealed the ambivalent character of 1 toward water substitution. Hence, these findings are interpreted as a gradual changeover of the reaction mechanism from a dissociatively activated one (I(d)), with the hard O- and N-donor ligands, to an associatively activated one (I(a)), with the soft S-donor ligands.

No abstract

No abstract

5À heteropolyoxothio anions 1 (X P) and 2 (X As). Both 1 and 2 were isolated in the solid state in good yield as mixed cesium ± sodium salts and were characterized unambiguously by elemental analysis, IR and 31 P NMR spectroscopy, and single-crystal X-ray structural analysis. 31 P NMR also gave evidence of the successive replacement of arsenate by phosphate groups in 2. The apparent exchange constants that were calculated were in agreement with a nearly pure statistical exchange between arsenate and phosphate groups. The substitution of the phosphate by acetate ligands in 1 was also examined.31 P NMR spectra agreed with the successive formation of the mono-, di-and triacetato complexes. The very good agreement between the calculated and experimental distribution of substituted compounds confirmed the 31 P NMR assignments and the proposed exchange scheme.

No abstract

No abstract