Inorg. Chem. 2003, 42, 8600−8602
Yttrium Polyoxometalates. Synthesis and Characterization of a Carbonate-Encapsulated Sandwich-Type Complex Xikui Fang, Travis M. Anderson, Wade A. Neiwert, and Craig L. Hill* Department of Chemistry, Emory UniVersity, Atlanta, Georgia 30322 Received September 12, 2003
Reaction of A-R-PW9O349- with YCl3 in an aqueous Na2CO3 solution produces a dianion-encapsulated A-type sandwich polyoxometalate, (YOH2)3(CO3)(A-R-PW9O34)211-. The X-ray structure of this complex reveals that three Y(III) ions are sandwiched between two A-R-PW9O349- moieties and that a carbonate dianion is encapsulated in the same plane as the three Y(III) atoms. The oxygen atoms of the CO32- are sitting at the midpoints of the sides of the triangle formed by the three Y(III) ions. 31P and 13C NMR studies confirm that this complex is significantly more stable than the analogous A-type sandwich polyoxometalates containing divalent metals.
The synthesis and characterization of new transition-metalsubstituted (d- and f-block) polyoxometalates (POMs) continues to be a focus of considerable ongoing research.1-7 The highly tunable nature of these compounds, coupled with their chemically robust nature, has led to applications in catalysis, medicine, and molecular magnetism.4,5 The POM of focus, (YOH2)3(CO3)(A-R-PW9O34)211- (1), is related to the wellknown and structurally similar trinuclear A-type sandwich complexes based on divalent d-block metals, [MII3(A-RPW9O34)2]12- (M ) Mn, Fe, Co, Ni, Cu, and Zn).8,9 This structural type was first reported by Knoth, and recently a
Si-based analogue was reported by Herve´.8-10 All of the divalent-metal-containing A-type sandwich complexes are unstable in solution and eventually isomerize into the B-type sandwich structures. However, a number of factors have been shown to significantly influence the stability of the A-type complexes, including pH, ionic strength, and temperature.10-15 The trivalent oxidation state of the yttrium cations renders 1 more stable than the divalent-metal sandwich analogues, and it allows for the unusual stabilization of a carbonate anion, encapsulated within the sandwich-type structure. Reaction of A-R-PW9O349- with Y(III) in an aqueous Na2CO3 solution produces 1 in modest yield (33%) and in high purity.16 The synthesis of 1 requires the presence of CO32-. Francesconi and co-workers have shown that, in the absence of CO32-, the complex [(PY2W10O38)4(W3O14)]30- is formed instead.17
* Author to whom correspondence should be addressed. E-mail:
[email protected]. (1) Pope, M. T. Heteropoly and Isopoly Oxometalates; Springer-Verlag: Berlin, 1983. (2) Pope, M. T.; Mu¨ller, A. Angew. Chem., Int. Ed. Engl. 1991, 30, 3448. (3) Polyoxometalates: from Platonic Solids to Anti-RetroViral ActiVity; Pope, M. T., Mu¨ller, A., Eds.; Kluwer: Dordrecht, The Netherlands, 1994. (4) Topical issue on polyoxometalates: Hill, C. L., Guest Ed. Chem. ReV. 1998, 98, 1-389. (5) (a) Polyoxometalate Chemistry: From Topology Via Self-Assembly to Applications; Pope, M. T., Mu¨ller, A., Eds.; Kluwer: Dordrecht, The Netherlands, 2001. (b) Polyoxometalate Chemistry for NanoComposite Design; Yamase, T., Pope, M. T., Eds.; Nanostructure Science and Technology; Kluwer Academic/Plenum Publishing: New York, 2002. (6) Contant, R.; Herve´, G. ReV. Inorg. Chem. 2002, 22, 63-111. (7) Hill, C. L. In ComprehensiVe Coordination Chemistry II: Transition Metal Groups 3-6; Wedd, A. G., Ed.; Elsevier Science: New York, 2003; Vol. 4, in press. (8) Knoth, W. H.; Domaille, P. J.; Farlee, R. D. Organometallics 1985, 4, 62-68.
(9) Knoth, W. H.; Domaille, P. J.; Harlow, R. L. Inorg. Chem. 1986, 25, 1577-1584. (10) Laronze, N.; Marrot, J.; Herve´, G. Inorg. Chem. 2003, 42, 58575862. (11) Kim, K.-C.; Pope, M. T. J. Am. Chem. Soc. 1999, 121, 8512-8517. (12) Tourne´, C. M.; Tourne´, G. F.; Weakley, T. J. R. J. Chem. Soc., Dalton Trans. 1986, 2237-2242. (13) Tourne´, C. M.; Tourne´, G. F. J. Chem. Soc., Dalton Trans. 1988, 2411-2420. (14) Contant, R. Can. J. Chem. 1987, 65, 568-573. (15) Maksimovskaya, R. I.; Maksimov, G. M. Inorg. Chem. 2001, 40, 1284-1290. (16) Synthesis of 1: A 0.96 g (3.2 mmol) sample of YCl3‚6H2O is dissolved in 40 mL of deionized water, and 4 mL of 1 M Na2CO3 is slowly added to the solution with stirring. The slurry is heated to 80 °C, and then solid Na8H(A-R-PW9O34) (4.06 g, 1.6 mmol) is quickly added with vigorous stirring. The solution is maintained at 80 °C for 30 min and then cooled to room temperature. Any insoluble material present is removed by centrifugation. Solid KCl (6 g) is added to the solution, and a precipitate is formed. The solution is cooled in an ice water slurry to ensure the best yield of the product. The precipitate is filtered and washed twice with 2-mL aliquots of 5 °C water. The crude product is dissolved in a minimal amount (∼15 mL) of hot water and cooled to 5 °C. This procedure is repeated until a pure product is obtained (yield 33%). Diffraction-quality crystals are obtained by redissolving the pure compound in water at room temperature and adding NaClO4. Elemental analyses and spectroscopic data are based on the bulk pure Na+-free sample because yields of the diffraction-quality crystals are quite low. IR (2% in KBr pellet, 1500 to 600 cm-1): 1491 (sh), 1480 (m), 1068 (s), 1014 (m), 943 (s), 916 (s), 830 (sh), 784 (s), and 708 (s). 31P NMR (D2O): -9.55 ppm. 13C NMR (Li+ salt in D2O): 173.76 ppm. Anal. Calcd for K11(YOH2)3(CO3)(A-R-PW9O34)2‚22H2O: C, 0.21; K, 7.59; Na, 0.0; P, 1.09; W, 58.4; and Y, 4.71. Found: C, 0.24; K, 7.56; Na,
