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Highly hydrated cations: Deficiency, mobility and coordination of water in crystalline nonahydrated scandium(III), yttrium(III) and lanthanoid(III) trifluoromethanesulfonate
Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för fysikalisk kemi, oorganisk kemi och strukturkemi.
Vise andre og tillknytning
2005 (engelsk)Inngår i: Chemistry - A European Journal, ISSN 0947-6539, E-ISSN 1521-3765, Vol. 11, nr 14, s. 4065-4077Artikkel i tidsskrift (Fagfellevurdert) Published
Abstract [en]

Trivalent lanthanide-like metal ions coordinate nine water oxygen atoms, which form a tricapped trigonal prism in a large number of crystalline hydrates. Water deficiency, randomly distributed over the capping positions, was found for the smallest metal ions in the isomorphous nonahydrated trifluoromethanesulfonates, [M(H2O)(n)]CF3SO3)(3), in which M=Sc-III, Lu-III, Yb-III, Tm-III or Er-III. The hydration number n increases (n=8.0(1), 8.4(1), 8.7(1), 8.8(1) and 8.96(5), respectively) with increasing ionic size. Deuterium (H-2) solid-state NMR spectroscopy revealed fast positional exchange between the coordinated capping and prism water molecules; this exchange started at temperatures higher than about 280 K for lutetium(m) and below 268 K for scandium(m). Similar positional exchange for the fully nonahydrated yttrium(m) and lanthanum(m) compounds started at higher temperatures, over about 330 and 360 K, respectively. An exchange mechanism is proposed that can exchange equatorial and capping water molecules within the restrictions of the crystal lattice, even for fully hydrated lanthanoid(III) ions. Phase transitions occurred for all the water-deficient compounds at; 185 K. The hydrated scandium(III) trifluoromethanesulfonate transforms reversibly (Delta H degrees= -0.80(1) kJ mol(-1) on cooling) to a trigonal unit cell that is almost nine times larger, with the scandium ion surrounded by seven fully occupied and two partly occupied oxygen atom positions in a distorted capped trigonal prism. The hydrogen bonding to the trifluoromethanesulfonate anions stabilises the trigonal prism of water ligands, even for the crowded hydration sphere of the smallest metal ions in the series. Implications for the Lewis acid catalytic activity of the hydrated scandium(III) and lanthanoid(III) trifluoromethanesulfonates for organic syntheses performed in aqueous media are discussed.

sted, utgiver, år, opplag, sider
2005. Vol. 11, nr 14, s. 4065-4077
Emneord [en]
MOLECULAR-DYNAMICS SIMULATION, X-RAY-DIFFRACTION, LANTHANIDE IONS LN(3+), TRIVALENT METAL-IONS, M = LA, AQUEOUS-SOLUTION, DIMETHYL-SULFOXIDE, MAGNETIC-RESONANCE, COMPLEXES, PERCHLORATE
HSV kategori
Identifikatorer
URN: urn:nbn:se:su:diva-23683DOI: 10.1002/chem.200401339OAI: oai:DiVA.org:su-23683DiVA, id: diva2:193977
Tilgjengelig fra: 2005-04-07 Laget: 2005-04-07 Sist oppdatert: 2018-01-13bibliografisk kontrollert
Inngår i avhandling
1. Structural and Spectroscopic Studies of Solvated Metal Ions
Åpne denne publikasjonen i ny fane eller vindu >>Structural and Spectroscopic Studies of Solvated Metal Ions
2005 (engelsk)Doktoravhandling, med artikler (Annet vitenskapelig)
Abstract [en]

Crystallographic and spectroscopic studies have been performed of structures, coordination and chemical bonding for series of trivalent metal ions solvated by two oxygen-coordinating solvents, water and dimethyl sulfoxide (DMSO). The hydrated scandium(III) and lanthanoid(III) ions, La to Lu, are surrounded by tricapped trigonal prisms of aqua ligands in the isomorphous series of trifluoromethanesulfonates, [M(H2O)n](CF3SO3)3. For the smallest ions, M = Er, Tm, Yb, Lu, Sc, the hydration numbers decrease, n = 8.96(5), 8.8(1), 8.7(1), 8.5(1), 8.0(1), respectively, with decreasing size of the ion. The crystal structures at ambient temperature indicate randomly distributed vacancies of the capping oxygen atoms, and 2H solid-state NMR of the diamagnetic [M(H2O)n](CF3SO3)3, M = Sc, Lu, Y and La compounds revealed increasing mobility of the water ligands in the coordination sphere with increasing temperature, also for the fully nonahydrated LaIII and YIII ions. The stretching force constants of the Ln-O bonds, evaluated from vibrational spectroscopy, increased from 0.81 to 1.16 N cm-1 for the Ln-6O trigonal prism in a smooth correlation with the bond distances from La to Lu. For the capping Ln-3O bonds the increase from 0.49 to 0.65 N cm-1 reflects the increased ligand-ligand repulsion with decreasing ion size. This is also the reason for the water deficiency of the Er, Tm, Yb, Lu and Sc salts, and for [Sc(H2O)8.0](CF3SO3)3 the repulsion induced a phase transition at about 185 K that, by low temperature crystallography, was found to distort the coordination of water molecules toward a monocapped trigonal prism around the scandium(III) ion.

All crystal structures of the octakis(dimethyl sulfoxide)lanthanoid(III) iodides comprise discrete [Ln(dmso)8]3+ complexes surrounded by iodide ions. The lanthanum(III) and praseodymium(III) compounds crystallize in the orthorhombic space group Pbca with more efficient packing than for the heavier and smaller ions in the lanthanoid series, which crystallize in the monoclinic space group P21/n. The group 13 metal ions, aluminium(III), gallium(III), indium(III), thallium(III), and also scandium(III) of group 3, form crystalline hexakis(dimethyl sulfoxide) solvates in the space group R 3, with octahedral MO6 coordination entities, which are increasingly compressed along one threefold axis for increasing ionic size. EXAFS measurements on the solvated ions display similar M-O bond distances in dimethyl sulfoxide solution as in the solid solvates. For all the solid dimethyl sulfoxide solvates the strength and nature of the metal-oxygen bond has been evaluated by normal coordinate analysis of vibrational spectra, and correlated with the S-O stretching vibrational mode.

Distortions from regular octahedral six coordination are discussed for the hydrated isoelectronic soft mercury(II) and thallium(III) ions in the solid bisaquamercury(II) and trisaquatallium(III) trifluoromethanesulfonates, in terms of pseudo Jahn-Teller effects (PJTE). Mercury(II), generally more strongly influenced by PJTE distortions, displays a 2 + 4 Hg-O coordination forming chains that are held together in sheets by hydrogen bonds and in layers by van der Waals interactions, which explain the fragile structure of the crystals.

sted, utgiver, år, opplag, sider
Stockholm: Institutionen för fysikalisk kemi, oorganisk kemi och strukturkemi, 2005. s. 94
Emneord
Coordination, Solvation, X-ray diffraction, EXAFS, IR, Raman, Normal coordinate analysis, trivalent metal ions, dmso, triflate, hydration
HSV kategori
Identifikatorer
urn:nbn:se:su:diva-446 (URN)91-7155-013-5 (ISBN)
Disputas
2005-04-29, Magnélisalen, Kemiska övningslaboratoriet, Svante Arrhenius väg 12 A, Stockholm, 13:00
Opponent
Veileder
Tilgjengelig fra: 2005-04-07 Laget: 2005-04-07bibliografisk kontrollert

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