Journal of Fluorine Chemistry 101 (2000) 161±163

Rapid synthesis of hybrid ¯uorides by microwave heating Son Phan Thanh, Fabrice Gaslain, Marc Leblanc, Vincent Maisonneuve* Faculte des Sciences, Laboratoire des Fluorures, UPRES-A 6010, Universite du Maine, Avenue Olivier-Messiaen, 72085 Le Mans, Cedex 9, France Received 9 May 1999; accepted 6 July 1999

Abstract Two new series of organic±inorganic ¯uorides are synthesized by microwave heating. These compounds constitute probably the ®rst new materials obtained by this way. The conditions of synthesis and several structural features of these hybrid materials together with the structure of the ®rst member of the series, [H3N(CH2)6NH3]
AlF5, are reported. It crystallizes in the monoclinic system, space group P21, Ê , b ˆ 5.507(1) A Ê , c ˆ 12.658(2) A Ê , ˆ 103.67(1)8, V ˆ 535(2) A Ê 3, and Z ˆ 2. Its structure with the lattice parameters a ˆ 7.894(2) A consists of vertex-sharing in®nite chains of AlF6 octahedra connected by diprotonated 1.6 diamines. # 2000 Elsevier Science S.A. All rights reserved. Keywords: Microwave synthesis; Hybrid ¯uorides; Structural features

1. Introduction

2. Experimental

Microwave heating was ®rst used for digestion or drying of solid materials. Recently, this technique has been extended to the sintering of ceramics and the promotion of organic or inorganic reactions [1]. Most of the experiments were done to reproduce the synthesis of known compounds, often molecular sieves. Microwave heating allows a shorter time of reaction as compared with the conventional hydrothermal method; the heat transfer, due to microwave absorption, is limited to the solvent and to the starting materials in contrast with the classic method, where heat is transferred from outside to inside. Obviously, this advantage is very convenient for production cost lowering. It seems also possible to get large crystals [2] or the inclusion of chromophores in zeolites [3]. In addition, the crystallinity and the morphology of some materials can be controlled [4]. The following list gathers the majority of these compounds prepared by microwave heating (Hybrid compounds (zeolites): APO-5, APO-11, OMS-1, ZSM-5, VPI-5, cloverite and mineral materials: BaTiO3, PbTiO3, Na5B2P3O13, apatite). Up to now, no work has been devoted to the synthesis of new inorganic or hybrid inorganic±organic materials. In this article, we present the preliminary studies of two new series of hybrid compounds prepared by the microwave route.

The synthesis of hybrid ¯uorides was achieved with a microwave digestion system (MDS-2100, CEM Corporation). This microwave delivers approximately 950 W of microwave energy at a frequency of 2450 MHz at full power. The power may be programmed in percent increments to control the heating rate. The internal pressure or temperature, sensed respectively by a transducer and a ®ber optic probe with a phosphor sensor, can be regulated by monitoring the power. Microwave sample preparation requires to respect a set of safety considerations. The samples were obtained from a stirred mixture of M2O3 (M ˆ Al, Ga) or MCl3 (M ˆ Cr, Fe, V) Ð 1.6, 1.8, 1.9, 1.10, 1.12 diaminohexane/octane/nonane/decane/dodecane Ð HF and ethanol. H3PO4 was added for the ®rst series of compounds. The mixtures were loaded in polytetra¯uoroethylene (PTFE) autoclaves and heated for 2 h at 1908C. The resulting materials were ®ltered, washed with ethanol and dried in air.

* Corresponding author. E-mail address: [email protected] (V. Maisonneuve)

3. Results and discussion The ®rst series (noted A) of hybrid compounds obtained with 1.6, 1.9, 1.10 and 1.12 alkyldiamines appeared as colorless transparent needles. Chemical analysis on several crystals of 1.6 compound by an energy-dispersive-spectroscopy-equipped scanning electron microscope indicates an

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S.P. Thanh et al. / Journal of Fluorine Chemistry 101 (2000) 161±163

Fig. 1. XRD diffractograms of fluoroaluminophosphates (a) and fluoroaluminates (b) templated by the 1.6, 1.8, 1.9, 1.10, 1.12-diaminohexane/octane/ nonane/decane/dodecane. The position of the first intense peak is related to the number of carbon atoms of aliphatic diamines.

inorganic formulation close to Al(PO4)F4. Two diprotonated 1.6 diaminohexane cations must be necessary to balance the four negative charges of the inorganic part; i.e., global formulation is close to [N2CnH2n‡6]2
Al(PO4)F4. The Xray powder (XRD) diffractograms of this new series of ¯uoroaluminophosphates templated with aliphatic diamines are presented in Fig. 1 (left). Each pattern shows a ®rst intense peak at low angle followed by weaker re¯ections. The position of the ®rst peaks moves simultaneously to the low angle with the increasing of the length of carboned chain of the diamine. The series of materials (noted A), prepared by classical hydrothermal experiments with the same starting materials, except the solvent constituted by a mixture of water and ethanol (60/40), gave similar XRD diffractograms and an analogous evolution of the ®rst peak [5]. However, the positions of these ®rst peaks differ. For the 1.6 diamine compounds, the dhkl value decreases from Ê for A series to 11.73 A Ê for A series. Consequently, 13.52 A the structures are probably slightly different. The structure with 1.6 diaminohexane (ULM-13) is known [6]. It is built up from inorganic sheets formulated [Al4(PO4)3(HPO4)F6]5ÿ separated by organic layers consisting of 1.6 diammonium cations and water molecules. One of the amines connects the inorganic layers and is oriented

perpendicularly to the layers. A linear relationship has been established between the length of the chain of the diamine and the interlayer distances, indicating that the organic molecules are always perpendicular to the organic sheets in this ULM-13 series. The structure of 1.6 hybrid compound prepared by microwave synthesis is currently investigated to shed light on the structural differences and the in¯uence of the synthesis with a binary solvent. The second series (noted B) of hybrid compounds using 1.6, 1.8, 1.10 and 1.12 alkyldiamines, prepared without H3PO4, present a lamellar morphology. A very small single crystal was isolated in the sample with the 1.6 diamine. Crystal data were collected on a STOE AED2 4-circle diffractometer. The structural determination [7] has revealed a [H3N(CH2)6NH3]
AlF5 formulation and a monoclinic symmetry (P21). The structure consists of in®nite chains of vertex-sharing AlF6 octahedra (Fig. 2, left). These octahedra are cis-connected along b-axis. The inorganic chains are linked each other by two crystallographically inequivalent amines (Fig. 2, right). The charge balance is achieved by diprotonation of 1.6 diamine. The cohesion between the inorganic and organic parts is ensured by a set of hydrogen bonds. The syntheses using diamines with longer alkyl chains (CnH2n‡4N2 with n ˆ 8, 10, 12) give

Fig. 2. Projections of [H3N(CH2)6NH3]
AlF5 structure in a±b (a) and a±c (b) planes.

S.P. Thanh et al. / Journal of Fluorine Chemistry 101 (2000) 161±163

163

Table 1 Cell parameters of the A series of hybrid materials [D]
MF5

[1.6 diamine]
AlF5 [1.8 diamine]
AlF5 [1.10 diamine]
AlF5 [1.12 diamine]
AlF5 [1.6 diamine]
FeF5 [1.6 diamine]
CrlF5 [1.6 diamine]
VF5 [1.6 diamine]
GaF5

Ê) a (A

Ê) b (A

Ê) c (A

(8)

Ê 3) V (A

7.894(2) 7.897(7) 7.897(2) 7.871(2) 8.030(2) 7.969(2) 7.991(2) 7.994(3)

5.507(1) 5.496(2) 5.474(2) 5.476(2) 5.800(1) 5.692(1) 5.794(1) 5.707(1)

12.658(2) 14.770(4) 17.118(9) 19.366(4) 12.537(3) 12.493(3) 12.503(3) 12.602(4)

103.67(1) 97.71(2) 92.80(2) 90.20(4) 103.50(2) 104.04(2) 103.87(2) 103.65(2)

535(2) 635(3) 739(2) 835(1) 567(3) 549(3) 562(4) 559(3)

powdered products. The XRD patterns of B series show a same aspect and an evolution similar to that of the A series (Fig. 1, right). The re®ned cell parameters of iso-structural [D]
AlF5 (D ˆ 1.8, 1.10, 1.12 alkyldiammonium) are reported in Table 1. The evolution of cell volumes is linear with the number of carbon atoms of alkyled chain. Moreover, the substitution of aluminum by other metallic cations using 1.6 diamine demonstrates the capacity of the structure to accommodate different metal sizes. Owing to the very similar XRD patterns, the structure of the metal-substituted compounds must be isotype to the structure of [1.6 hexanediammonium]
AlF5. The evolution of the cell parameters shows that the structure adapts mainly the metal size by increasing the b parameter (Table 1). The expansion of the MF6 octahedron size induces the elongation of the in®nite chains. These two new series of hybrid ¯uorides prove clearly the advantages of microwave heating: short time of crystallization, low temperature, and, addition, it seems possible to synthesize original phases inaccessible by other routes. Finally, this method, favored by the recent development

of microwave technique, is a powerful tool for the exploration of chemical diagrams. Acknowledgements The authors are grateful to Jean Renaudin for useful discussions. References [1] D. Michael, P. Mingos, Adv. Mater. 5 (1993) 857. [2] I. Girnus, K. Jancke, R. Vetter, J. Richter-Mendau, J. Caro, Zeolites 15 (1995) 33. [3] I. Braun, G. Schulz-Ekloff, M. Bockstette, D. WoÈhrle, Zeolites 19 (1997) 128. [4] S. Park, D. Kim, J. Chang, W.Y. Kim, Catal. Tod. 44 (1998) 301. [5] J. Renaudin, T. Loiseau, F. Taulelle, G. Ferey, in: Fifth European Conference on Solid State Chemistry, Montpellier, 1995. [6] J. Renaudin, G. Ferey, J. Solid State Chem. 120 (1995) 197. [7] S.P. Thanh, J. Renaudin, V. Maisonneuve, Solid State Sci., submitted.