A Solid-State NMR, X-ray Diffraction, and Ab Initio Investigation into the Structures of Novel Tantalum Oxyfluoride Clusters Todd M. Alam,* ,† Jacalyn S. Clawson, †,‡ François Bonhomme, † Steven G. Thoma, † Mark A. Rodriguez, † Shaohui Zheng, § and Jochen Autschbach § Department of Electronic and Nanostructured Materials, Department of Geochemistry, Department of Materials Characterization, and Department of Fuels and Energy Transitions, Sandia National Laboratories, Albuquerque, New Mexico 87185, and Department of Chemistry, UniVersity at Buffalo, State UniVersity of New York, Buffalo, New York 14260-3000 ReceiVed July 5, 2007. ReVised Manuscript ReceiVed December 12, 2007 A series of tantalum oxyfluoride materials containing the [Ta 4 F 16 O 4 ] 4- and [Ta 8 F 24 O 12 ] 8- anion clusters have been synthesized and characterized using X-ray diffraction (XRD) and solid-state nuclear magnetic resonance (SSNMR) spectroscopy. The structure of both tantalum oxyfluoride materials display octahedrally bonded tantalum atoms with bridging oxygen and terminal fluoride atoms. The [Ta 4 F 16 O 4 ] 4- cluster is an eight-membered ring, whereas the [Ta 8 F 24 O 12 ] 8- cluster forms a cagelike structure. Solid- state dynamics of these clusters were explored by monitoring the impact of temperature on the one- dimensional (1D) 19 F magic angle spinning (MAS) NMR, 13 C cross-polarization (CP) MAS NMR, and two-dimensional (2D) double quantum (DQ) 19 F MAS NMR spectra. The DQ 19 F NMR correlation experiments allowed the through space connectivity between the different resolved fluorine environments to be determined, thus aiding in the spectral assignment and structural refinement of these materials. Ab initio 19 F NMR chemical shift calculations were used to assist in the interpretation of the 19 F NMR spectra. The influence of scalar relativistic and Ta-F spin–orbit coupling on the 19 F NMR shielding calculation arising from bonding to tantalum atoms is also addressed. Introduction Tantalum oxide is used as a catalyst and promoter in various industrial organic syntheses. 1,2 For these applications controlled pore and open structure compounds are of great value, yet the relative insolubility of tantalum oxide negates many of the typical hydro- or solvothermal synthesis routes for open structure materials. Tantalum does however, readily form a variety of fluorine compounds. 3 Understanding the coordination chemistry of tantalum, along with the develop- ment of open structure tantalum fluoride compounds, may provide a means to create new, industrially relevant tantalum materials. Tantalum oxyfluoride anionic clusters have been previ- ously reported including the [TaF 6 ] - anion, 4 a series of [TaF 7 ] 2- polyhedron anions, 5–7 the [Ta(O 2 )F 5 ] 2- and [TaF 5 O] 2- anions, 8,9 the linear [Ta 2 F 10 O] 2- dimer, 10 and the adamantane-like cage [Ta 4 F 12 O 6 ] 4- anion. 11 These systems demonstrate a progression in the complexity and size of the oxyfluoro-tantalum cluster. Most of these TaF clusters have been characterized using single-crystal X-ray structural determination. In this paper, two novel tantalum oxyfluoride clusters, [Ta 4 F 16 O 4 ] 4- (TAF16) and [Ta 8 F 24 O 12 ] 8- (TAF24), are described (see Figure 1). In these materials the inorganic TaF clusters are counter balanced by organic cations. Two compounds containing the TAF24 cluster are characterized, one sample containing the imidazole countercation (TAF24- IMI) and the other containing the tris(2-aminoethyl)amine countercation (TAF24-TREN). The third compound char- acterized is the TAF16 cluster with a pyridinium counterion (TAF16-PYR). Because the properties of these compounds are closely related to their structure it is important to structurally characterize these materials as fully as possible. For example, the ferroelectric properties are sensitive to the degree of fluorine-oxygen substitution. 3 In this paper, we utilize X-ray diffraction (XRD) and multinuclear ( 19 F, 13 C, 1 H) solid-state nuclear magnetic resonance (SSNMR) spectroscopy to understand the solid-state structure and dynamics of these * To whom correspondence should be addressed. Phone: (505) 844-1225. Fax: (505) 844-2974. E-mail:tmalam@sandia.gov. † Sandia National Laboratories. ‡ Present address: GlaxoSmithKline Plc, King of Prussia, PA 19406. § University at Buffalo, State University of New York. (1) Ushikubo, T. Catal. Today 2000, 57, 331. (2) Lambert, J. B., Tantalum and Tantalum Compounds. In Kirk-Othmer Encyclopedia of Chemical Technology; John Wiley & Sons: New York, 2001. (3) Agulyansky, A. The Chemistry of Tantalum and Niobium Fluoride Compounds, 1st ed.; Elsevier: New York, 2005; p 407. (4) Edwards, A. J.; Jones, G. R. J. Chem. Soc. A: Inorg., Phys., Theor. 1970, 1891. (5) Saada, M. A.; Hémon-Ribaud, A.; Smiri, L. S.; Leblanc, M.; Maisonneuve, V. J. Fluorine Chem. 2005, 126, 1246. (6) Torardi, C. C.; Brixner, L. H.; Blasse, G. J. Solid State Chem. 1987, 67, 21. (7) Goreshnik, E.; Leblanc, M.; Maisonneuve, V. J. Solid State Chem. 2004, 177, 4023. (8) Ruzic-Toros, Z.; Kojic-Prodic, B. Acta Crystallogr., Sect. B 1976, B32, 1096. (9) Furmanova, N. G.; Verin, I. A.; Zanin, I. E.; Zozulin, A. N.; Il’in, E. G. SoV. Phys. Crystallography 1991, 36, 204. (10) Dewan, J. C.; Edwards, A. J.; Calves, J. Y.; Guerchais, J. E. J. Chem. Soc., Dalton Trans. 1977, 978. (11) Sala-Pala, J.; Guerchais, J. E.; Edwards, A. J. Angew. Chem., Int. Ed. 1982, 21, 870. 2205 Chem. Mater. 2008, 20, 2205–2217 10.1021/cm0717763 CCC: $40.75  2008 American Chemical Society Published on Web 02/16/2008