Kurze Mitteilungen

Monoammoniates of Aluminium Halides:The Crystal Structures of AlBr3 · NH3 and AlI3 · NH3

Herbert Jacobs* and Felix O. Schröder

Dortmund, Fachbereich Chemie der Universität

Received August 17th, 2001.

Abstract. Single crystals of AlBr3 · NH3 and AlI3 · NH3 sufficientin size for X-ray structure determinations were obtained by evapor-ation/sublimation of the respective compound from its melt. Theammoniates were synthesized by the reaction of the pure halidewith NH3 at 278°C and following homogenization by slowly heat-ing the reaction mixture up to the melting points of the ammoni-ates (124°C and 126°C, respectively).The X-ray structure determinations for both monoammoniateswere successfully carried out for the heavy atom positions (no hy-drogen atoms):AlBr3 · NH3: Pbca, Z 5 16, a 5 11.529 (5) A, b 5 12.188 (2) A,c 5 19.701 (4) A

First fundamental investigations on the ammoniates of aluminiumhalides were done by Klemm and co-workers in 1931 [1, 2]. Theseauthors were mainly interested in the number of ammoniates, theirthermal stability and predicted structural features. A first structuredetermination by X-ray methods was done on AlCl3 · NH3 in 1978[3]. Nearly tetrahedral molecules of Al(NH3)Cl3 are linked by hy-drogen bridge bonds N-H···Cl three- dimensionally.

Later on we reported about syntheses and crystal structure deter-minations on AlCl3 · 2NH3 ; [Al(NH3)4Cl2]1 · [AlCl4]2 [4], AlCl3· 3NH3 ; [Al(NH3)4Cl2]1[Al(NH3)2Cl4]2 [5, 6] veryfied by [7] andAlI3 · 7NH3 ; [Al(NH3)6]31 I3 · NH3 [8]. As the ammoniates AlX3

· nNH3 with e.g. X 5 Cl and n 5 1, 2, 3, 5, 6, 7, 14 are spezies ofa solvation series they can serve as models for an understanding ofa stepwise solvation of cations in polar solvents. We have per-formed further experiments [9] to grow single crystals from am-moniates for X-ray structure determinations. Here we report resultsobtained with the monoammoniates of AlBr3 and AlI3.

Syntheses of the Monoammoniates and StructureDetermination

In a vacuum line apparatus gaseous NH3 (99.999 % Messer-Gries-heim) is very slowly condensed on solid AlBr3 and AlI3, respec-tively (both Johnson Mattey GmbH, Karlsruhe 98 % resp. 95 %)cooled down to 278 °C. The molar ratio of AlX3 with X 5 Br, Ito NH3 was chosen gasvolumetrically exactly to 1 : 1. After warm-ing up to room temperature a mixture of the respective aluminiumhalide and higher ammoniates results (X-ray powder data). Thesemixtures then were homogenized by slowly heating them to 132°C.

* Prof. Dr. H. JacobsFachbereich Chemie der UniversitätD-44221 DortmundE-mail: Jacobs@pop.uni-dortmund.de

Z. Anorg. Allg. Chem. 2002, 628, 3272329 WILEY-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002 004422313/02/628/3272329 $ 17.501.50/0 327

AlI3 · NH3: Pbca, Z 5 8, a 5 13.536 (5) A, b 5 8.759 (2) A,c 5 14.348 (4) A

The structures contain tetrahedral molecules Al(NH3)X3 with X 5

Br, I. They are not isotypic. The main difference is given for thecoordination of NH3 by X2 from neighbouring molecules. InAl(NH3)Br3 one of the two crystallographically independent NH3

ligands has 6Br2 and the other 7Br2 as neighbours whereas inAl(NH)3I3 only 5I2 surround the one kind of NH3.

Keywords: Monoammoniates; Aluminium halides; Lewis acid-baseadducts

By this procedure colorless well-crystallized samples were obtainedwith melting points of 124°C for AlBr3 · NH3 and 126°C for AlI3

· NH3. Crystals suited for X-ray structure determinations were ob-tained by evaporation/sublimation of the respective compound ina vacuum line apparatus from its melt. Another way to obtain e.g.AlCl3 · NH3 is the reaction of NH4Cl with AlCl3 at 300°C toNH4AlCl4 in a glass ampoule. NH4AlCl4 is decomposed to AlCl3· NH3 and HCl in a vacuum line apparatus at 200°C. Crystals ofAlCl3 · NH3 grow in the colder part of the glass line. This methodhas the advantage that the amount of the starting compounds iswell defined by weighing. Single crystals of AlBr · NH3 and AlI3 ·NH3 were investigated on an automatic four circle diffractometer(CAD4 DT, Enraf-Nonius). With the program packages SDP(Structure Determination Package, Version 3.30, Enraf-Nonius)[10] and SHELXTL PLUS 4.0 (Siemens) [11] the structures weresolved by interpretation of Patterson syntheses followed bydifferential Fourier analyses. The quality of the crystals waschecked by precession photographs (MoKα). Table 1 contains somecrystallographic and technical data for the structure determinationof both compounds. Results of positional and isotropic displace-ment parameters for AlBr3 · NH3 are given in Table 2 and for AlI3

· NH3 in Table 4. Tables 3 and 5 contain the respective anisotropicdisplacement parameters.

Powder diagrams (Straumanis method, CuKα) showed that themonoammoniates obtained by both methods were single phasesamples.

Discussion of the Structures of AlX3 · NH3 withX 5 Cl, Br, I

All three monoammoniates crystallize in the same space group typeand contain tetrahedral molecules Al(NH3)X3 with X 5 Cl, Br, Ilinked by hydrogen bridge bonds N-H···X. But neither compoundis isotypic with one of the others. The main difference is given bythe coordination of NH3 by X from neighbouring molecules. InAlCl3 · NH3 the NH3 group is surrounded by 6Cl2 from different

H. Jacobs, F. O. Schröder

Table 1 Crystallographic data for the compounds AlBr3 · NH3

and AlI3 · NH3 and for comparison AlCl3 · NH3 [3]

formula Al(NH3)Br3 Al(NH3)I3 Al(NH3)Cl3 [3]color colorless colorless colorlesscrystal size/mm 0.1 x 0.1 x 0.2 0.1 x 0.2 x 0.2T/K 293 293radiation CuKα AgKαcrystal system orthorhombic orthorhombic orthorhombicspace group Pbca Pbca Pbcaa/A 11.529 (5) 13.536 (5) 9.895 (6)b/A 12.188 (2) 8.759 (2) 10.148 (6)c/A 19.701 (4) 14.348 (4) 11.544 (7)V/A3 2768.3 (9) 1701.1 (8) 1159.2Z 16 8 8ρcalc./g · cm23 2.723 3.312 1.73µ/mm21 21.74 5.814θ-range/° 3 # θ # 56 2 # θ # 26scan ω/2 θ ω/2 θh, k, l ± 12, ± 13, 21 ± 13, 21, 22(Fo)2 $ 3σ(Fo)2 835 of 2085 1012 of 2055internal R/% 7.6 7.5refined parameters 91 46R/Rw/% 3.9/4.8 4.3/5.6residual (e A23) 0.98 1.04

Table 2 Positional and isotropic displacement parameters forAlBr3 · NH3; Pbca all atoms in 8c; standard deviations in paren-theses.

atom x y z B/A2

Br(1) 0.1368 (3) 0.2901 (2) 0.2204 (2) 7.10 (7)Br(2) 0.3557 (2) 0.4865 (2) 0.1468 (1) 5.37 (6)Br(3) 0.4386 (2) 0.0889 (2) 0.1947 (1) 6.10 (6)Br(4) 0.3626 (2) 0.2381 (2) 0.3909 (1) 5.51 (6)Br(5) 0.0974 (2) 0.3869 (2) 0.4548 (1) 5.50 (6)Br(6) 0.1264 (2) 0.0871 (2) 0.4873 (1) 6.13 (6)Al(1) 0.2029 (5) 0.4643 (5) 0.2179 (3) 3.2 (1)Al(2) 0.2237 (5) 0.2464 (5) 0.4724 (3) 3.3 (1)N(1) 0.259 (2) 0.498 (2) 0.3076 (8) 4.7 (4)N(2) 0.303 (1) 0.222 (1) 0.0558 (8) 4.6 (4)

Table 3 Anisotropic displacement parameters for AlBr3 · NH3;Uij (x 103 A22) with standard deviations in parentheses

atom U11 U22 U33 U12 U13 U23

Br(1) 110(2) 59(1) 100(2) 231(2) 218(2) 0(1)Br(2) 62(1) 89(2) 53(1) 1(2) 218(1) 219(1)Br(3) 59(1) 90(2) 83(2) 215(2) 220(1) 24(2)Br(4) 64(1) 91(2) 54(1) 22(2) 219(1) 29(1)Br(5) 59(1) 72(1) 78(2) 19(1) 25(1) 14(2)Br(6) 77(2) 61(1) 95(2) 222(2) 26(2) 4(2)Al(1) 43(3) 44(3) 35(3) 26(3) 1(3) 24(3)Al(2) 39(3) 51(3) 35(3) 0(3) 3(3) 7(3)N(1) 60(10) 70(10) 60(10) 12(9) 0(1) 10(10)N(2) 50(10) 70(10) 60(10) 0(10) 23(9) 0(10)

Table 4 Positional and isotropic displacement parameters for AlI3

· NH3; Pbca all atoms in 8c, standard deviations in parentheses.

atom x y z B/A2

I(1) 0.3309 (1) 0.2869 (2) 0.3121 (1) 5.37 (4)I(2) 0.0162 (1) 0.2890 (2) 0.4175 (1) 5.46 (4)I(3) 0.2216 (1) 0.4424 (2) 0.0582 (1) 4.57 (3)Al(1) 0.3693 (4) 0.4089 (7) 0.1585 (4) 3.4 (1)N(1) 0.087 (1) 0.118 (2) 0.184 (1) 5.1 (4)

Z. Anorg. Allg. Chem. 2002, 628, 3272329328

Table 5 Anisotropic displacement parameters for AlI3 · NH3; Uij(x 103 A22) with standard deviations in parentheses.

atom U11 U22 U33 U12 U13 U23

I(1) 62 (1) 104 (1) 38 (1) 11 (1) 8 (1) 15 (1)I(2) 60 (1) 98 (1) 50 (1) 26 (1) 217 (1) 212 (1)I(3) 59 (1) 53 (1) 62 (1) 23 (1) 227 (1) 2 (1)Al(1) 35 (3) 52 (3) 41 (3) 5 (3) 25 (3) 22 (3)N(1) 60 (10) 60 (10) 70 (10) 7 (9) 20 (10) 210 (10)

Table 6 Distances in A, angles in degrees for the molecules AlX3

· NH3 with X 5 Cl, Br, I including hydrogen bridge bonding distan-ces; standard deviations in parentheses

AlCl3 · NH3 [11] AlBr3 · NH3 AlI3 · NH3

Al (1) 2N (1) 1.921 (3) 1.925 (17) 1.957 (19)2X (1) 2.108 (1) 2.257 (6) 2.504 (6)2X (2) 2.110 (1) 2.267 (6) 2.499 (6)

X (3) 2.115 (1) 2.275 (6) 2.481 (6)Al (2) 2N (2) 1.918 (17)

2X (4) 2.271 (7)X (5) 2.275 (6)X (6) 2.263 (7)

N (1) ······ X 3.419 (3) 3.65 (2) 3.77 (2)3.506 (3) 3.66 (2) 3.80 (2)3.541 (2) 3.70 (2) 3.82 (2)3.559 (3) 3.76 (2) 4.02 (2)3.589 (3) 3.93 (2) 4.06 (2)3.674 (3) 4.13 (2)

N (2) ······ X 3.55 (2)3.74 (2)3.85 (2)3.85 (2)3.95 (2)4.05 (2)4.16 (2)

Mean values:] N2Al2X 106.3 106.6 105.0] X2Al2X 112.5 112.2 113.6

tetrahedra in distances of 3.42 # d # 3.67 A. This is shown inFigure 1a). In AlBr3 · NH3 the two crystallographic different mol-ecules are nearly identical as to their bond lengths and angleswithin the tetrahedra 2 see Table 6 2.But one has 6Br2 (two edgesand two vertices, Fig. 1 b1)) around an NH3 ligand, the second has7Br2 (three edges and one vertex). This is given in Fig. 1 b2). ForAlI3 · NH3 the NH3 group has only five I2 (two edges and onevertex) as neighbours. This is given in Fig. 1c). With the help ofFig. 1 it should be possible to imagine the arrangement of the sur-rounding polyhedra of NH3 ligands by X. Table 6 contains somecharacteristic distances and mean values of angles within the AlX3

· NH3 tetrahedra and distances between NH3 ligands and nearestX2 anions from neighbouring molecules. Only in the case of AlCl3· NH3 [3, 12] positions of H-atoms at NH3 could be determined byX-ray methods. The resulting geometry shows a staggered confor-mation for the orientation of the NH3 ligand with respect to thethree Cl2 ions in the same molecule. This conformation was alsopredicted by [12, 13] and the barrier between staggered and eclipsedform was found to be 2.11 kcal/mole for AlCl3 · NH3.

For AlCl3 · NH3 and AlBr3 · NH3 gas phase electron diffractiongave the following distances:

d (Al2Cl) 5 2.100 (5) A, d (Al2N) 5 1.996 (19) A, ] Cl-Al-Cl 5

116,3 (4)° and d (Al-Br) 5 2.26 (1) A and d (Al-N) 5 2.0 A [13,14] in reasonable agreement with the corrosponding data 2 Table6 2 obtained by X-ray structure determination.

Monoammoniates of Aluminium Halides: The Crystal Structures of AlBr3 · NH3 and AlI3 · NH3

Fig. 1 Coordination of NH3 ligands for AlX3 · NH3 with X 5

Cl, Br, I. The Al atoms centre the grey shaded tetrahedra. Thehalide atoms at the vertices of the tetrahedra are not attributed tothe coordination sphere of the N atoms.a) Al(NH3)Cl3by 6Cl2 from six verticesb) Al(NH3)Br3

b1) by 6Br2 from two edges and two verticesb2) by 7Br2 from three edges and one vertexc) Al(NH3)I3 by 5I2 from two edges and one vertexfrom different coordinating tetrahedral molecules. Edges are indi-cated by dotted lines connecting halide ions.

The structures of the three monoammoniates of AlX3 with X 5

Cl, Br, I contain as expected Lewis-acid-base adducts Al(NH3)X3.These molecules exist as well in the gas phase 2 as shown by massspectroscopy by us 2 as in the solid state. Bonding interactions

Z. Anorg. Allg. Chem. 2002, 628, 3272329 329

between the molecules in the solid state in the sense of hydrogenbridge bonds are easily shown by their broad valence vibrationbands of the NH3 groups 2 some 100 cm21 2 in their IR spectra[8, 12]. On the other hand these broad absorptions hint to a rota-tory disorder of the NH3 ligands.

Acknowledgment. We thank the Deutsche Forschungsgemeinschaftand the Fonds der Chemischen Industrie for financial support ofthese investigations.

References

[1] W. Klemm, E. Tanke, Z. Anorg. Allg. Chem. 1931, 200, 343.[2] W. Klemm, E. Clausen, M. Jacobi, Z. Anorg. Allg. Chem.

1931, 200, 367.[3] K. N. Semenenko, E. B. Lobkovskii, V. D. Polyakova, I. I.

Korrobov, O. V. Kravchenko, Koordinatsion. Khim. 1978, 4,1649.

[4] H. Jacobs, B. Nöcker, Z. Anorg. Allg. Chem. 1992, 614, 25.[5] H. Jacobs, B. Nöcker, Z. Anorg. Allg. Chem. 1993, 619, 73.[6] B. Nöcker, H. Jacobs, Z. Kristallogr., Supplement Issue 1991,

3, 215.[7] St. Bremm, G. Meyer, Z. Anorg. Allg. Chem. 2001, 627, 407.[8] D. Peters, J. Bock, H. Jacobs, J. Less-Common Met. 1989,

154, 243.[9] F.-O. Schröder, Dissertation, Univ. Dortmund 1993.

[10] B. A. Frenz, H. Schenk, R. Althof-Hazekamp, H. van Konigs-veld, G. C. Bassi “Computing in Crystallography” Ed.: H.Schenk, 1978 Delft University Press, Delft (NL).

[11] G. M. Sheldrick, SHELXTL PLUS (Release 4.0) for NicoletR3m/V crystallographic systems, Universität Göttingen 1990.

[12] B. Nöcker, Dissertation, Univ. Dortmund 1991.[13] M. Hargittai, I. Hargittai, V. Spiridonov, J. Chem. Soc., Chem.

Comm. 1973, 750.[14] M. Hargittai, I. Hargittai, V. Spiridonov, J. Mol. Struct. 1975,

24, 27.