Inorganic Chemistry Communications 12 (2009) 97–100

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Inorganic Chemistry Communications

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Thermal dehydration of Y(TFA)3(H2O)3: Synthesis and molecular structuresof [Y(l,g1:g1-TFA)3(THF)(H2O)]11 � THF and [Y4(l3-OH)4(l,g1:g1-TFA)6(g1-TFA)(g2-TFA)(THF)3(DMSO)(H2O)] � 6THF (TFA = trifluoroacetate)

Shashank Mishra a,*, Liliane G. Hubert-Pfalzgraf a,1, Stéphane Daniele a,*, Marc Rolland b, Erwann Jeanneau c,Bernadette Jouguet a

a Université Lyon 1, IRCELYON-UMR5256, 2 Avenue A. Einstein, 69626 Villeurbanne, Franceb Université Montpellier II, IEM, CNRS-ENSCM, Place Eugène Bataillon, 34095 Montpellier, Francec Université Lyon 1, Centre de Diffractométrie, 69622 Villeurbanne, France

a r t i c l e i n f o

Article history:Received 27 June 2008Accepted 22 November 2008Available online 3 December 2008

Keywords:YttriumTrifluoroacetatePrecursorDehydrationX-ray structure

1387-7003/$ - see front matter � 2008 Elsevier B.V. Adoi:10.1016/j.inoche.2008.11.021

* Corresponding authors. Tel.: +33 472445329; fax:E-mail address: mishrashashank74@rediffmail.com

1 Deceased.

a b s t r a c t

In order to obtain a better anhydrous precursor for various applications in materials science and catalysis,thermal dehydration reactions of Y(TFA)3(H2O)3 (TFA = trifluoroacetate) (A) were investigated. Thermaltreatment of A at different temperatures under vacuum (5 � 10�2 mm) for several hours failed to givetotally anhydrous yttrium trifluoroacetate (as indicated by IR). Two different complexes, a partially dehy-drated [Y(l,g1:g1-TFA)3(THF)(H2O)]11�THF (1) and a partially hydrolyzed [Y4(l3-OH)4(l,g1:g1-TFA)6(g1-TFA)(g2-TFA)(THF)3(DMSO)(H2O)] � 6THF (2), were obtained with good and moderate yield,respectively, by crystallization of two different thermally treated batches of A from THF (or THF + DMSO)at room temperature. More efficient dehydration of A could be achieved at 200 �C in a furnace, theobtained anhydrous yttrium tris-trifluoroacetate giving Y(TFA)3(THF)2 (3) on crystallization from THF.All the products were characterized by elemental analyses, FT-IR and 1H NMR spectroscopy as well asthermo-gravimetric analysis. In addition, single crystal X-ray structures are reported for 1 and 2, whichshow either a terminal (g1 and g2) or bridging (l,g1:g1) bonding behavior of the TFA ligand.

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Yttrium tris-trifluoroacetate is an important complex, which isextensively used for a range of applications in materials scienceand catalysis, e.g., as a precursor for the elaboration of high Tcsuperconductors (YBa2Cu3O7�x) [1], for getting upconverting phos-phor materials (YF3 and NaYF4) [2] and as a catalyst in variouspolymerization processes (mostly with Al or Zn alkyls) [3]. Anhy-drous yttrium tris-trifluoroacetate is highly desirable for aboveapplications [1–3], but the classical, cost-efficient synthesis of thiscompound by reacting Y2O3 with trifluoroacetic acid in refluxingtoluene proceeds with the formation of water as a by-product toafford the hydrated complex Y(TFA)3(H2O)3 [4]. To replace watermolecules of this complex, ligand exchange reactions with O-and N-donor ligands have been studied previously, which mostlyled to either partially hydrated or hydrolyzed products [5]. In thiscommunication, we report the results obtained on our attempts toremove the water molecules by thermal treatment of Y(TFA)3-(H2O)3 (described as complex A in this article). A partiallydehydrated [Y(l,g1:g1-TFA)3(THF)(H2O)]11 � THF (1), a partiallyhydrolyzed [Y4(l3-OH)4(l,g1:g1-TFA)6(g1-TFA)(g2-TFA)(THF)3-

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+33 472445399.(S. Mishra).

(DMSO)(H2O)] � 6THF (2) and an anhydrous Y(TFA)3(THF)2 (3) wereobtained under different thermal conditions and were character-ized by elemental analyses, FT-IR and 1H NMR spectroscopy, aswell as thermo-gravimetric analysis. In addition, single crystal X-ray structures are reported for 1 and 2. It is worth mentioning herethat although the structural chemistry of lanthanide acetates andhaloacetates is well explored, similar studies on homometallicyttrium complexes remain quite scarce [6,7]. In particular, theanhydrous homometallic yttrium trifluoroacetate complexes areconfined solely to the type Y2(TFA)6(HOC2H4OR)x [R = Me2CH(x = 4), C2H4OMe (x = 2)] [5].

The TGA and DTA curves of A are shown in the SupplementaryInformation (Fig. S1). The first decomposition step (30–110 �C)consists of the loss of two H2O molecules, whereas the second stepconsists of the loss of the remaining water molecules, accompaniedby the decomposition of some organic ligand (total weight lossafter the second step: calculated for 3H2O molecules 11.2%, ob-served 13.9%). Following this, efforts were first made to removeall the water molecules by thermal treatment under vacuum. Theseefforts were unsuccessful, as indicated by IR spectra of thermallytreated samples at different temperatures (Fig. 1), most probablydue to the strong hydrogen bonding between the water moleculesand the TFA ligands. Such an interaction is a common feature for

Fig. 1. FT-IR spectra of Y(TFA)3(H2O)3 (A) after different thermal treatments: (a)without thermal treatment, (b) at 130 �C/5 � 10�2 mm for 3 h, (c) at 165 �C/5 � 10�2 mm for 4 h, and (d) at 200 �C in a furnace for 3 h.

Fig. 2. FT-IR spectra of derivatives 1–3.

98 S. Mishra et al. / Inorganic Chemistry Communications 12 (2009) 97–100

metal complexes with fluorinated ligands (alkoxides or b-diketo-nates) [8]. In order to seek structural characterization on the prod-ucts obtained by thermal treatment of A at different temperatures,efforts were made to crystallize these products from THF. Apartially dehydrated [Y(l,g1:g1-TFA)3(THF)(H2O)]11 � THF (1)and a partially hydrolyzed [Y4(l3-OH)4(l,g1:g1-TFA)6(g1-TFA)-(g2-TFA)(THF)3(DMSO)(H2O)] � 6THF (2) were obtained by crystal-lization from THF (or THF:DMSO mixture) of A thermally treated at80 �C/5 � 10�2 mm for 3 h and 165 �C/5 � 10�2 mm for 4 h, respec-tively (Scheme 1) [9]. The tendency of Y(TFA)3(H2O)3 to loose someof trifluoroacetate ligands as trifluoroacetic acid has been shownpreviously [10]. Finally, more efficient dehydration of A could beachieved at 200 �C in a furnace, although some decompositionwas also observed. The obtained anhydrous yttrium trifluoroace-tate, which is very hygroscopic due to its high Lewis acidity, gaveY(TFA)3(THF)2 (3) on crystallization from THF [9].

The FT-IR spectra of 1–3 account for the presence of trifluoro-acetate ligands in different bonding modes (Fig. 2). Two to threewell-resolved strong absorptions for masCO2 in the 1732–1622 cm�1 region indicate chelating-bridging TFA for 1 and 3,whereas an overlapping of similar absorptions due to differentbonding modes (monodentate, bidentate and bridging) of TFA in2 results in a strong broad absorption centered at 1685 cm�1.Other characteristic strong absorptions of this ligand in the1463–1460 (msCO2), 1208–1150 (mC–F and mC–O) and 868–712 cm�1 regions also characterize the spectra of 1–3. The absorp-tion due to mOH, which appears as one or more broad peaks in the3100–3700 cm–1 region in 1 and 2, is absent in the spectrum of 3.In the 1H NMR spectra of 1–3, the coordinated/solvated THF mol-ecules appear as two triplets at d 1.81–1.89 and 3.66–3.70 ppm forb- and a-hydrogens, respectively, the spectrum of 2 also showsadditional peaks of DMSO (d 2.58) and l3-OH (d 6.05) in the ex-pected integral ratio. Thermo-gravimetric data of 1–3 were col-lected in argon atmosphere in the 20–600 �C temperature range.The TGA curves of these complexes show a three-to-four stage

Y(TFA)3(H2O)3

Y(TFA)3(TH

1/4 Y4(OH)

Y(TFA)3(T

(

(3)

(A)

80 ˚C/5 x 10-2 mm, 3 hrs

165 ˚C/5 x 10-2 mm, 4 hrs

200 ˚C in furnace, 3 hrs

crystallization from THF

crystallization from THF + DMSO

crystallization from THF

Scheme 1. Synth

decomposition process, where the final decomposition tempera-tures as well as total percentage weight loss vary in the 308–320 �C and 63.5–68.9% ranges, respectively (Fig. 3). The decompo-sition pattern for 1–3 is quite similar and can be generalized bysaying that the removal of solvate molecules (H2O, THF or DMSO)takes place in somewhat complex first few steps, as also indicatedby three to five distinct endothermic peaks in the temperaturerange 50–220 �C in DTA curves (Fig. S2). The last step (220–330 �C) mainly involves a gradual decomposition of TFA ligandsas indicated by a strong exothermic peak at 282–311 �C(Fig. S2), though some remaining THF molecules are also lost inthe beginning of this step. The remaining weight of residues of1–3 accounts a little more than the expected for YF3 material(31.1%, 36.5% and 34% versus 24.8%, 28.2% and 25.5% for 1, 2and 3, respectively), indicating an incomplete decomposition dueto the presence of argon atmosphere.

The structure of 1 corresponds to a 1D-polymer [Y(l,g1:g1-O2CCF3)3(THF)(H2O)]11 � THF running along the a-axis of the unitcell (Fig. S3) [11]. The yttrium centres are bridged by four andtwo g1:g1-trifluoroacetate ligands in an alternate manner(Fig. 4). The geometry around the metal can be described as a bi-capped trigonal prismatic [12]. The Y–O (TFA) bond distances,which range from 2.296(5) to 2.347(5) Å, are in agreement withthe body of literature [5]. On the other hand, the Y–O (THF) bonddistance, 2.551(2) Å, is slightly longer than the values (av. 2.43 Å)found in some other yttrium-THF adducts [13], indicating a rela-tively weakly coordinated THF in 1. The four bridging TFA ligandscause a shortening of the Y� � �Y distance [4.548(8) Å] in comparisonto that of 5.089(8) Å, when only two TFA act as bridges. Any Y� � �Finteractions are ruled out since they are larger than 4.5 Å. This is incontrast with yttrium fluoroalkoxides where such interactionsoften occur [8]. One THF molecule per yttrium atom is not coordi-nated to the metal but to the oxygen O1 of the water ligand via an

F)(H2O).THF

4(TFA)8(THF)3(H2O)(DMSO).6THF + TFAH + 7/4 H2O

HF)2 + 3 H2O

+ 2 H2O1)

(2)

esis of 1–3.

Fig. 3. TGA curves of derivatives 1–3.

Fig. 4. Molecular structure of 1 with atom labelling and ellipsoids at 30%probability. H-atoms and solvated THF molecules have been omitted for clarity.Symmetry codes: (i) 1�x, 1�y, 1�z; (ii) �x, 1�y, 1�z. Selected bond lengths (Å) andangles (�): Y1–O1 2.396(2), Y1–O2 2.314(5), Y1–O6 2.296(5), Y1–O8 2.551(2), O1–Y1–O2 71.9(2), O1–Y1–O4 72.3(2), O1–Y1–O8 125.8(7), O1–Y1–O3i 138.9(2),O2–Y1–O4 79.0(2), O1–Y1–O5 139.6(2), O2–Y1–O6 146.4(2), O2–Y1–O7 82.7(2),O2–Y1–O8 138.5(2), O5–Y1–O6 140.4(2), O5–Y1–O8 73.0(1), O6–Y1–O7 95.9(2),O6–Y1–O8 69.2(1), O3i–Y1–O6 81.8(2), O7–Y1–O8 69.4(1), O3i–Y1–O7 141.6(2),O3i–Y1–O8 74.1(1).

Fig. 5. Molecular structure of 2 with atom labelling and ellipsoids at 30%. H-atomsand solvated THF molecules have been omitted for clarity. Selected bond lengths (Å)and angles (�): Y1–O1 2.366(4), Y1–O5 2.344(4), Y1–O17 2.372(5), Y1–O21 2.423(4), Y2–O1 2.386 (4), Y2–O24 2.356 (5), Y3–O22 2.369 (4), Y4–O18 2.462 (4), Y4–O19 2.473 (4), Y1� � �Y2 3.727(1), Y1� � �Y4 3.803(1), O1–Y1–O2 69.0(1), O1–Y1–O574.1(1), O11–Y1–O5 96.0(1), O5–Y1–O10 141.8(1), O17–Y1–O11 141.5(1), O21–Y1–O17 71.4(1), O1–Y2–O24 126.1(1), O20–Y2–O24 75.3(1), O23–Y3–O22 72.3(1),O19–Y4–O18 53.7(1).

S. Mishra et al. / Inorganic Chemistry Communications 12 (2009) 97–100 99

intermolecular H-bond with a O1� � �O9 distance of 2.726(3) Å. Thesame water molecule also forms an intramolecular H-bond withcoordinated THF [O1� � �O8ii = 2.934(3) Å] and four oxygen atomsof neighbouring bridging TFA with O1� � �O6ii and O1� � �O3i dis-tances of 3.098(6) and 3.023(8) Å, respectively. A similar type ofH-bondings involving water and non-coordinate THF moleculeshas been reported for a pentanuclear barium fluoroisopropoxidederivative [14]. The structure of 1 can be related to that ofLn(RCO2)3(H2O)3 (Ln = Ce, R = CCl3 [6b]; Ln = Pr and Er, R = CF2H[7d]), where the metals are bridged by four and two g1:g1-haloac-etate ligands alternatively.

The structure of 2 incorporates a distorted [Y4(l3-OH)4] cubanecore, where l3-OH groups are derived from H2O molecules onY(TFA)3(H2O)3 (Scheme 1) [11]. In addition to l3-OH groups, theconnection between four yttrium atoms is also achieved by oxygenatoms of six l,g1:g1-trifluoroacetate ligands, which are positionedin a symmetric manner across the six faces of Y4 cubane (Fig. 5).The 7th and 8th trifluoroacetate ligands are linked in a mono-

and bi-dentate fashion to Y1 and Y4, respectively. Eight appearsas the preferential coordination number for yttrium trifluoroace-tate compounds [5]. In contrast to 1, the yttrium atoms haveeither a regular (Y2, Y4) or slightly distorted (Y1, Y3) dodecahedralgeometry [12]. The Y–O bond distances vary from 2.265(4) to2.473(4) Å, the order of variation being Y–O (l,g2-TFA, av.2.467 Å) > Y–O (THF, av. 2.435 Å) > Y–O (g1-TFA, 2.372 Å) � Y–O(H2O, 2.369 Å) > Y–O (DMSO, 2.356 Å) � Y–O (l,g1:g1-TFA, av.2.353 Å) > Y–O (l3-OH, av. 2.342 Å). Formation of oxo/hydroxo-bridged tri- or tetranuclear cluster by the hydrolysis of Y-TFA haspreviously been observed [5,10], although a ‘cubane core’ structureis reported for the first time here for a Y-TFA derivative. To ourknowledge, [Co4(l3-OH)4(l-TFA)2(py)8](ClO4)2 is the onlyother example having such structure with TFA as an ancillary li-gand [15].

The above results underline the sensitivity of Y(TFA)3(H2O)3 to-wards thermal dehydration reactions and show that choosing aright process is of vital importance in getting anhydrous yttriumtrifluoroacetate. At present, efforts are underway to explore theutility of the above complexes, especially the anhydrous 3, in get-ting Na–Y heterometallics with correct stoichiometry as singlesource precursors for host matrix of upconverting lanthanide co-doped NaYF4 phosphor materials.

Acknowledgement

SM is grateful to the Centre National de la Recherche Scientifi-que (CNRS) for a post-doctoral fellowship.

Appendix A. Supplementary material

CCDC 689753 and 690550 contain the supplementary crystallo-graphic data for 1 and 2. These data can be obtained free of chargefrom The Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_request/cif. Supplementary data associated withthis article can be found, in the online version, at doi:10.1016/j.inoche.2008.11.021.

100 S. Mishra et al. / Inorganic Chemistry Communications 12 (2009) 97–100

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[9] Synthesis of Y(TFA)3(THF)(H2O) � THF (1): After heating A (0.75 g, 1.55 mmol)at 80 �C/5 � 10�2 mm for 3 h, its crystallization from THF (3 ml) at roomtemperature gave 1 as colourless prism. Yield, 0.63 g (69%). Calcd. forC14H18F9O9Y: C, 28.42; H, 3.04. Found: C, 28.32; H, 2.99%. IR (nujol, cm�1):3669br, 3453br, 1732 s, 1673 s, 1622 s, 1460 s, 1376 s, 1208 s, 1149 s, 1021 m,868 m, 847 m, 799 m, 722 s, 616 m, 524 m, 455 m. 1H NMR (CD2Cl2, ppm): 1.81(t, 8 H, b-H of THF), 3.67 (t, 8 H, a-H of THF). Y4(OH)4(TFA)8(THF)3-(H2O)(DMSO) � 6THF (2): 0.61 g of A (1.26 mmol) was heated at 165 �C/5 �10�2 mm for 4 h and, after cooling it under argon, was dissolved in THF (3 ml).Two drops of DMSO were added to dissolve the slight turbidity present in thesolution. Crystals of 2 grew as colourless block at room temperature over theperiod of two weeks. Yield, 0.25 g (38% w.r.t yttrium). This compound lost twosolvate THF molecules on keeping under vacuum for few minutes. Calcd. forC46H68F24O29SY4: C, 28.61; H, 3.52. Found: C, 28.47; H, 3.46%. IR (nujol, cm�1):3492br, 3434br, 1685 s, 1460 s, 1206 s, 1155 s, 1046 m, 850 m, 806 s, 712 s,603 m, 574 m, 516 m, 451 m, 400 m. 1H NMR (CD3CN, ppm): 1.89 (t, 28H, b-Hof THF), 2.58 (s, 6H, Me2SO), 3.66 (t, 28H, a-H of THF), 6.05 (br, 4H, OH).Y(TFA)3(THF)2 (3): 0.55 g of A (1.14 mmol) was placed in a furnace at 200 �Cfor 3 h, followed by cooling it down under argon. After dissolving it in 5 ml THFand stirring for 1 h, the brown solution obtained was filtered. Crystallizationfrom concentrated THF solution (2 ml) at room temperature gave 3 ascolourless blocks, which were unsuitable for X-ray crystallography. Yield,0.38 g (58%). Calcd. for C14H16F9O8Y: C, 29.37; H, 2.79. Found: C, 28.93; H,2.70%. IR (nujol, cm�1): 1718 s, 1669 s, 1463 s, 1371 m, 1208 s, 1150 s, 1024 m,918 w, 873 w, 850 m, 798 s, 724 s, 613 m, 522 m, 455 m. 1H NMR (CD3CN,ppm): 1.85 (t, 8H, b-H of THF), 3.70 (t, 8H, a-H of THF). Compounds 1–3 aresoluble in polar solvents (THF, acetonitrile), but are insoluble in non-polarhydrocarbons (toluene, ether).

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[11] Crystal data for 1: C14H18F9O9Y, Mr = 590.19, Monoclinic, P21/n, a = 9.524(1) Å,b = 15.110(1) Å, c = 15.378(2) Å, b = 90.326(1)�, V = 2213.1(5) Å3, Z = 4,T = 173 K, l (Mo Ka) = 2.75 mm�1, R[F2 > 2r(F2)] = 0.042, wR(F2) = 0.090 for7145 independent reflections, 324 parameters, 116 restraints, S = 0.81,Dq = �0.84 to 1.11 e Å�3. Crystal data for 2: C54H84F24O31SY4, Mr = 2072.88,Triclinic, P1, a = 12.7444(3) Å, b = 13.5970(3) Å, c = 13.6898(3) Å, a =66.511(1)�, b = 81.876(1)�, c = 69.415(1)�, V = 2036.76(8) Å3, Z = 1, T = 150 K,l (Mo Ka) = 2.98 mm�1, R[F2 > 2r(F2)] = 0.048, wR(F2) = 0.049 for 14485independent reflections, 1029 parameters, 412 restraints, S = 1.16,Dq = �0.85 to 1.71 e Å�3.

[12] C.W. Haigh, Polyhedron 15 (1996) 605.[13] K. Izod, S.T. Liddle, W. Clegg, Inorg. Chem. 43 (2004) 214.[14] H. Vincent, F. Labrize, L.G. Hubert-Pfalzgraf, Polyhedron 13 (1994) 3323.[15] A.N. Belyaev, A.I. Fisher, M.Tu. Goriov, S.A. Simanova, Russ. J. Gen. Chem. 74

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