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Synthesis and crystal structures of [K(18-crown-6)][Rb(18-crown-6)]2Ge9 · 6NH3, [Rb(18-crown-6)]3Ge9 · 9NH3 and [Cs(18-crown-6)]3Ge9 · 6NH3
Inorganica Chimica Acta 359 (2006) 267–272 www.elsevier.com/locate/ica
Synthesis and crystal structures of [K(18-crown-6)][Rb(18-crown-6)]2Ge9 Æ 6NH3, [Rb(18-crown-6)]3Ge9 Æ 9NH3 and [Cs(18-crown-6)]3Ge9 Æ 6NH3 Christof Suchentrunk, Nikolaus Korber
*
Institut fu¨r Anorganische Chemie der Universita¨t Regensburg, Universita¨tsstrasse 31, 93053 Regensburg, Germany Received 27 June 2005; received in revised form 19 September 2005; accepted 28 September 2005 Available online 3 November 2005
Abstract The new compounds [K(C12H24O6)][Rb(C12H24O6)]2Ge9 Æ 6NH3, [Rb(C12H24O6)]3Ge9 Æ 9NH3 and [Cs(C12H24O6)]3Ge9 Æ 6NH3 were prepared by the extraction of binary and ternary phases of the nominal composition K2Rb2Ge9, Rb4Ge9 and K2Cs2Ge9 with liquid ammonia in the presence of 18-crown-6. The resulting crystals were characterized by low temperature X-ray structure analysis. All of them contain the 21 electron cluster Ge9 3 , which is coordinated by alkali metal cations in ion-paired arrangements. The cages were assigned their specific point group symmetry and were compared with hitherto known structures. 2005 Elsevier B.V. All rights reserved. Keywords: Zintl anion; Germanide; Low-temperature crystal structure analysis; Liquid ammonia; Solvate crystal
1. Introduction Among the polygermanide Zintl anions, the Ge9 x (x = 2, 3, 4) anion is most commonly encountered, and the available data have been reviewed by Fa¨ssler [1]. The Ge9 4 anions are found in solid state binary compounds like Cs4Ge9 [2], in ammoniates like K4Ge9 Æ 9NH3 and Rb4Ge9 Æ 5NH3 [3] or with crown ether sequestered counter cations like in [K(C12H26N2O4)]2Rb2Ge9 Æ 2en [4]. The solvate and crown ether compounds were synthesized by the extraction of binary or ternary compounds, which also leads to phases like [K(C12H24O6)]3Cs3[Ge9Ge9] Æ 2en [5] and Cs6[Ge9Ge9] Æ 4NH3[3], both of which contain the [Ge9–Ge9]6 dimer. A 2 1 polymer was identified in the compound 1 ½Ge9 [K(C12H24O6)]2Ge9 Æ en [6]. Finally, the Ge9 3 anion has up to now been described in the compounds [K([2.2.2]-crypt)]3Ge9 Æ 0.5en [7], [K([2.2.2]-crypt)]3Ge9 Æ PPh3 [8], as well as in [K([2.2.2]-crypt)]6(Ge9)2 Æ xen (x = 0.5, 1.5) [9]. The structure of [K([2.2.2]-crypt)]6(Ge9)2 Æ 2.5en [10] was originally
reported by Corbett as containing two crystallographic inequivalent nine-atom germanium cages Ge9 4 and Ge9 2 with C4v and C2v symmetry. According to the Wade Rules [11], the Ge9 4 anion as a 22 electron cluster should adopt a nido-polyhedron with C4v symmetry (mono-capped square antiprism), whereas a Ge9 2 anion as a 20 electron cluster should display D3h point group symmetry (tri-capped trigonal prism). Consequently, a Ge9 3 anion as a 21 electron cluster should adopt distorted variants between C4v and D3h symmetry [7]. However, according to Fa¨ssler [9], there is no strong correlation between the observed cage structures and the number of electrons. Given the limited number of known Ge9 3 structure reports, the characterization of additional nonagermanides in liquid ammonia seemed desirable. In this paper, we report on the new compounds [K(C12H24O6)][Rb(C12H24O6)]2Ge9 Æ 6NH3 (1), [Rb(C12H24O6)]3Ge9 Æ 9NH3 (2) and [Cs(C12H24O6)]3-Ge9 Æ 6NH3 (3). 2. Experimental
*
Corresponding author. Tel.: +0941 9434448; fax: +0941 9431812. E-mail address: [email protected] (N. Korber). 0020-1693/$ - see front matter 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.ica.2005.09.043
All work was done excluding moisture and air in an atmosphere of purified argon. The compounds were
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prepared by the extraction of binary and ternary phases with liquid ammonia in the presence of 18-crown-6. The binary and ternary phases were prepared from stoichiometric mixtures of the elements in sealed silica tubes. For the crystal preparation, we adapted the technique described by Kottke and Stalke [12]. The thermally unstable and moisture sensitive ammoniate crystals were transferred directly from the mother liquor to the diffractometer using an endcapped fluoropolyether oil. 2.1. Synthesis of [K(C12H24O6)][Rb(C12H24O6)]2Ge9 Æ 6NH3 (1) A mixture of 0.4 g (10.2 mmol) K, 0.8 g (10 mmol) Rb and 3.2 g (44.0 mmol) Ge was heated to 650 C (5 C/h), annealed at 650 C for 120 h, and finally cooled to room temperature (5 C/h). About 0.22 g (0.24 mmol) of the resulting ternary phase with the nominal composition K2Rb2Ge9 and 0.13 g (0.49 mmol) of 18-crown-6 (1,4,7,10,13,16-hexaoxacyclooctadecane) were filled into a Schlenk tube and 30 ml of sodium-dried liquid ammonia was added, yielding a brown-yellow solution. The reaction vessel was stored at 40 C for 4 months. After this period, red needle-shaped crystals of 1 were obtained. 2.2. Synthesis of [Rb(C12H24O6)]3Ge9 Æ 9NH3 (2) About 1.1 g (12.8 mmol) Rb and 2.1 g (28.9 mmol) Ge were heated to 650 C (10 C/h), then annealed at 650 C for 120 h and finally cooled down to room temperature (10 C/h). About 0.2 g (0.2 mmol) of the resulting binary phase of the nominal composition Rb4Ge9 and 0.106 g (0.4 mmol) of 18-crown-6 were filled in a Schlenk tube and 30 ml of sodium-dried liquid ammonia was added, yielding a transparent yellow solution. The reaction vessel was stored at 40 C for 12 months. After this period, red plate-like crystals of 2 were obtained. 2.3. Synthesis of [Cs(C12H24O6)]3Ge9 Æ 6NH3 (3) About 0.2 g (5.1 mmol) K, 0.7 g (5.29 mmol) Cs and 1.72 g (23.7 mmol) Ge were heated up to 650 C (10 C/ h), then annealed at 650 C for 120 h and finally cooled down to room temperature (10 C/h). About 0.3 g (0.3 mmol) of the resulting ternary phase of the nominal composition K2Cs2Ge9 and 0.075 g (0.28 mmol) of 18crown-6 were then filled in a Schlenk tube and 30 ml of dried liquid ammonia was added, yielding a light brown solution. The reaction vessel was stored at 40 C for 6 months. After this period, red plate-like crystals of (3) were obtained. 2.4. X-ray data collection and structure refinement The diffraction data were collected with graphite mono˚ ) radiation on a STOE chromated Mo Ka (k = 0.71073 A IPDS (Imaging Plate Diffraction System) at 150 C. The
structures were solved by direct methods (SHELXS-97) [13] and refined on F2 (SHELXL-97) [14]. A DIFABS-type absorption correction was applied with the help of the PLATON program package [15] for structure 1. The absorption correction was done with X-RED [16] and X-Shape [17] for structures 2 and 3. All of the atoms except hydrogen atoms were refined with anisotropic displacement parameters. The hydrogen atoms of the 18-crown-6 molecules were inserted using a riding model. The majority of the hydrogen atoms of the ammonia molecules were located in the difference Fourier map. The selection of the space groups was certified using PLATON [15]. The crystal data and the details of the structure refinements are given in Table 1. 3. Results and discussion 3.1. Description of [K(C12H24O6)][Rb(C12H24O6)]2Ge9 Æ 6NH3 (1) The asymmetric unit of structure 1 consists of one nineatom germanium cage Ge9 3 (Fig. 1), two crystallographic independent rubidium cations Rb+ and one potassium cation K+. Each of the cations is surrounded by one molecule of 18-crown-6. Additionally, six molecules of ammonia of crystallization are present in the asymmetric unit. The rubidium cation Rb(1) caps the basal square Ge(6)– Ge(7)–Ge(8)–Ge(9) of the nonagermanide cage with ˚ (Fig. 2). The distances between 3.6529(9) and 3.8667(9) A distance of the capping cation Rb(1) to the centre of ˚ . The the adjacent basal square has a value of 3.2441(9) A rubidium cation Rb(2) caps the triangular face built by the three germanium atoms Ge(1), Ge(2) and Ge(5) with ˚ . Each of the distances between 3.4833(9) and 3.669(8) A rubidium cations is located above the mean plane of the coordinating crown ether. The potassium cation K(1) is surrounded by 18-crown-6 and two ammonia molecules of crystallization above and below the crown ether plane. This complex shows potassium–oxygen bond lengths be˚ , while the rubidium–oxygen tween 2.750(4) and 2.856(4) A distances in the anionic complex have larger values be˚ as expected. The potastween 2.864(4) and 3.167(4) A ˚. sium–nitrogen bond lengths are 2.878(6) and 2.918(6) A The ammonia molecule containing the nitrogen atom N(1) forms van-der-Waals contacts (van-der-Waals radii: ˚ , O = 1.4 [18,19]) with its hydrogen atoms H = 1.2 A H(1 A) and H(1C) to the oxygen atoms O(11) and O(7) of the adjacent crown-ether with distances of 2.70(8) and ˚ . The corresponding angles are N(1)–H(1A)– 2.6(1) A O(11) 158(7) and N(1)–H(1C)–O(7) 150(8). Similar hydrogen bonds were observed in the ammoniate of 18crown-6 [20]. The structure contains no potassium–germa˚ . The intracage Ge–Ge nium distances smaller than 5 A ˚ bond lengths measure between 2.5002(9) and 2.9078(8) A and are listed in Table 2. The Ge–Ge distances are in accordance with comparable structures like [K([2.2.2]-crypt)]6Ge9Ge9 Æ 0.5en [9]. As a 21 electron cluster, the polyhedron of the Ge9 3 cage should adopt a distorted variant of the
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269
Table 1 Crystal data and structure refinement for compounds 1–3 No.
1
2
3
Empirical Formula Formula weight (g mol1) Temperature (C) ˚) Wavelength (A Crystal system Space group ˚) a (A ˚) b (A ˚) c (A b () ˚ 3) Volume (A Z Dcalc (g cm3) l (mm1) Crystal size (mm3) F(000) H () Limiting indices
[K(C12H24O6)][Rb(C12H24O6)]2Ge9 Æ 6NH3 1758.6 150 0.71073 monoclinic P21/c (no. 14) 13.072(1) 19.035(1) 26.950(2) 90.54(1) 6705(1) 4 6.741 5.5 0.2 · 0.2 · 0.5 3532 2.03–26.12 16 6 h 6 16, 22 6 k 6 22, 33 6 l 6 33 90 729/12 647 (Rint = 0.0574) 94.7% (26.12) 12 647/0/660 0.948 R1 = 0.0393, wR2 = 0.0942 R1 = 0.0647, wR2 = 0.1012 1.885 and 1.228
[Rb(C12H24O6)]3Ge9 Æ 9NH3 1856.0 150 0.71073 orthorhombic P bca (no. 61) 24.031(2) 23.003(5) 25.669(3)
[Cs(C12H24O6)]3Ge9 Æ 6NH3 1947.3 150 0.71073 orthorhombic P bca (no. 61) 22.959(2) 25.711(2) 24.261(2)
14 189(3) 8 1.703 5.8 0.1 · 0.2 · 0.4 7076 2.07–25.94 29 6 h 6 29, 28 6 k 6 28, 31 6 l 6 31 98 168/13 733 (Rint = 0.1238) 99.1% (25.94) 13 733/0/685 1.047 R1 = 0.0797, wR2 = 0.1900 R1 = 0.1056, wR2 = 0.2095 3.932 and 3.436
14 321(2) 8 1.806 5.3 0.1 · 0.2 · 0.4 7560 1.94–25.91 28 6 h 6 28, 31 6 k 6 31, 29 6 l 6 29 180 531/13 843 (Rint = 0.1180) 99.3% (25.91) 13 843/0/655 1.046 R1 = 0.0624, wR2 = 0.1820 R1 = 0.0756, wR2 = 0.1928 4.485 and 2.414
Reflections collected/unique Completeness to theta Data/restraints/parameters Goodness-of-fit R[I > 2r(I)] R indices (all data) Largest difference peak ˚ 3) and hole (e A
point group symmetries C4v or D3h. For the description of this distortion, the diagonal distances Ge(6)–Ge(8) and Ge(7)–Ge(9) at the uncapped face of the cage and the torsion angle Ge(8)–Ge(9)–Ge(6)–Ge(7) have been established as useful criteria [21]. The basal square of the nonagermanide cage is nearly planar with a negative torsion angle Ge(8)–Ge(9)–Ge(6)–Ge(7) of 2.96(3), corresponding to a small deviation from C4v not towards D3h symmetry, but in the opposite direction with an inward facing edge. The diagonal distances of the basal square are Ge(6)– ˚ and Ge(7)–Ge(9) 3.8963(9) A ˚ , leading Ge(8) 3.4353(9) A away from C4v towards C2v symmetry. The heights of the fictional prism within the cage are Ge(6)–Ge(8) 3.4353(9) ˚ (h1), Ge(2)–Ge(3) 2.7759(8) A ˚ (h2) and Ge(4)–Ge(5) A ˚ (h3). The similar prism heights h2 and h3 give 2.7780(8) A
Fig. 1. A nonagermanide cage showing the angle a and the prism heights h discussed below. The atom numbering scheme is identical for compounds 1–3.
rise to a pseudo twofold axis through the centre of the uncapped basal square and the apical atom Ge(1), even if the centre of gravity of the cage is on a common site. 3.2. Description of [Rb(C12H24O6)]3Ge9 Æ 9NH3 (2) The asymmetric unit consists of one nine-atom germanium cage Ge9 3 and three crystallographic independent rubidium cations Rb+, each surrounded by one 18crown-6 ether. Additionally, nine molecules of ammonia of crystallization are present in the asymmetric unit. All of the rubidium cations rise above the mean plane of the crown ether (Fig. 3). The distances between the rubidium cations and the oxygen atoms are between 2.893(3) and ˚ and are comparable with the rubidium–oxygen 3.149(6) A distances in compound 1. The rubidium cation Rb(3) caps the triangular face of the nonagermanide cage built by the three atoms Ge(1), Ge(2) and Ge(5) with distances between 3.600(1) and ˚ . The cation Rb(2) has a long distance contact 3.898(1) A ˚ as well as to the germanium atom Ge(7) with 4.188(1) A with two additional nitrogen atoms of ammonia N(1) ˚ . The cation Rb(1) and N(2) with 3.249(8) and 3.14(1) A displays no rubidium–germanium distances smaller than ˚ , but has contacts to the nitrogen atoms N(3), N(4) 5A and N(5) of ammonia at one side of the crown ether with ˚ , forming a distances measuring from 3.16(1) to 3.43(1) A + [Rb(C12H24O6)(NH3)3] molecular ion complex. The remaining molecules of ammonia have no contacts to
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C. Suchentrunk, N. Korber / Inorganica Chimica Acta 359 (2006) 267–272 Rb Ge K O N H C
O(7) 3
1 N(2)
H(1C)
Rb(2)
K(1)
4 2 7
N(1) H(1A) O(11)
5 6
8
9 Rb(1)
Fig. 2. The coordination of the nonagermanide cage in compound 1 without the hydrogen atoms of 18-crown-6. Thermal ellipsoids at 50% probability level.
specific cations. As can be seen in Table 2, the intracage Ge–Ge bond lengths have values from 2.509(2) to ˚ . The designation of the atoms is identical to that 2.873(2) A of structure 1 (Fig. 1). The uncapped basal square of the cage has a torsion angle Ge(8)–Ge(9)–Ge(6)–Ge(7) of 5.49(6), which is a small deviation towards D3h symmetry. The diagonal distances Ge(6)–Ge(8) and Ge(7)–Ge(9) at the uncapped square of the cage have values of 3.200(2) ˚ , which shows a notable deviation from and 4.046(2) A C4v towards C2v symmetry. The heights of the prism are
˚ (h2) ˚ (h1), Ge(2)–Ge(3) 2.818(1) A Ge(6)–Ge(8) 3.200(2) A ˚ and Ge(4)–Ge(5) 2.873(2) A (h3). The almost similar prism heights h2 and h3 give rise to a pseudo twofold axis and the cage has approximately C2v symmetry. 3.3. Description of [Cs(C12H24O6)]3Ge9 Æ 6NH3 (3) The asymmetric unit contains one nonagermanide cage, three crystallographic independent cesium cations, three molecules of 18-crown-6 and six molecules of ammonia
Table 2 Intracluster Ge–Ge distances in the nonagermanide cages of compounds 1–3 1
2
3
Bond
˚) Distance (A
Bond
˚) Distance (A
Bond
˚) Distance (A
Ge(1)–Ge(2) Ge(1)–Ge(3) Ge(1)–Ge(4) Ge(1)–Ge(5) Ge(2)–Ge(3) Ge(2)–Ge(5) Ge(2)–Ge(6) Ge(2)–Ge(7) Ge(3)–Ge(4) Ge(3)–Ge(7) Ge(3)–Ge(8) Ge(4)–Ge(5) Ge(4)–Ge(8) Ge(4)–Ge(9) Ge(5)–Ge(6) Ge(5)–Ge(9) Ge(6)–Ge(7) Ge(7)–Ge(8) Ge(8)–Ge(9) Ge(6)–Ge(9) Ge(6)–Ge(8) Ge(7)–Ge(9)
2.6148(8) 2.5723(9) 2.5956(9) 2.5842(8) 2.7759(8) 2.8923(8) 2.5918(9) 2.5755(9) 2.9078(8) 2.7247(9) 2.5770(9) 2.7780(8) 2.5897(9) 2.6777(9) 2.6114(9) 2.5569(9) 2.6331(9) 2.5411(9) 2.5002(9) 2.7236(8) 3.4353(9) 3.8963(9)
Ge(1)–Ge(2) Ge(1)–Ge(3) Ge(1)–Ge(4) Ge(1)–Ge(5) Ge(2)–Ge(3) Ge(2)–Ge(5) Ge(2)–Ge(6) Ge(2)–Ge(7) Ge(3)–Ge(4) Ge(3)–Ge(7) Ge(3)–Ge(8) Ge(4)–Ge(5) Ge(4)–Ge(8) Ge(4)–Ge(9) Ge(5)–Ge(6) Ge(5)–Ge(9) Ge(6)–Ge(7) Ge(7)–Ge(8) Ge(8)–Ge(9) Ge(6)–Ge(9) Ge(6)–Ge(8) Ge(7)–Ge(9)
2.615(1) 2.604(1) 2.556(1) 2.599(2) 2.818(1) 2.793(2) 2.688(2) 2.648(1) 2.818(1) 2.595(1) 2.639(2) 2.873(2) 2.592(2) 2.552(2) 2.618(2) 2.659(2) 2.543(2) 2.635(2) 2.643(2) 2.509(2) 3.200(2) 4.046(2)
Ge(1)–Ge(2) Ge(1)–Ge(3) Ge(1)–Ge(4) Ge(1)–Ge(5) Ge(2)–Ge(3) Ge(2)–Ge(5) Ge(2)–Ge(6) Ge(2)–Ge(7) Ge(3)–Ge(4) Ge(3)–Ge(7) Ge(3)–Ge(8) Ge(4)–Ge(5) Ge(4)–Ge(8) Ge(4)–Ge(9) Ge(5)–Ge(6) Ge(5)–Ge(9) Ge(6)–Ge(7) Ge(7)–Ge(8) Ge(8)–Ge(9) Ge(6)–Ge(9) Ge(6)–Ge(8) Ge(7)–Ge(9)
2.577(1) 2.618(1) 2.593(1) 2.563(1) 2.790(1) 2.879(1) 2.590(1) 2.614(1) 2.852(1) 2.630(1) 2.628(1) 2.781(1) 2.593(1) 2.648(1) 2.586(1) 2.596(1) 2.613(2) 2.563(1) 2.543(1) 2.618(2) 3.344(2) 3.941(1)
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271
Rb(3)
Cs(3) Rb(1)
Cs(1)
1 5
N(5)
6
N(3)
5
N(1)
7
8
3
N(4)
3
4 9
1
4
2
7
6
Rb(2)
N(6)
2
8
9
N(3)
N(2)
Rb Ge O N H C
N(2)
Fig. 3. The coordination of the nonagermanide cage in compound 2 without the hydrogen atoms of 18-crown-6. Thermal ellipsoids at 50% probability level.
of crystallization. All of the cesium cations are situated above the mean plane of the crown ethers. The cesium– ˚. oxygen bond lengths range from 2.984(6) to 3.284(6) A The coordination of the nonagermanide cage is comparable to that of compound 2 (Fig. 4) with the exception that the atom Cs(2), comparable to Rb(2), has only one ammonia contact in addition to the germanium anion contact ˚ . The distances of the cesium with a distance of 4.072(2) A cation Cs(3) capping the triangular face of the nonagerma˚ . The nide-cage are between 3.673(1) and 3.880(1) A remaining cesium–nitrogen bond lengths of Cs(1) range ˚ . The intracage germanium disfrom 3.26(1) to 3.387(9) A ˚ and 2.879(1) tances, listed in Table 2, measure 2.563(1) A ˚ A. The atom designation corresponds to that of Fig. 1. The uncapped basal square Ge(8)–Ge(9)–Ge(6)–Ge(7) of the nonagermanide cage has a very small torsion angle of 0.23(4). Consequently, the basal plane can be considered as nearly planar with an inward facing edge. The diagonal distances at the uncapped square Ge(6)–Ge(8) and Ge(7)– ˚ , giving rise to Ge(9) have values of 3.344(2) and 3.941(1) A a deviation towards C2v symmetry. The prism heights have ˚ , Ge(2)–Ge(3) values of Ge(6)–Ge(8) (h1) 3.344(2) A ˚ ˚ (h3). Due to 2.790(1) A (h2) and Ge(4)–Ge(5) 2.781(1) A the similar prism heights h2 and h3, the nonagermanide cage possesses approximately C2v symmetry.
N(1)
Cs Ge O C H N
Cs(2)
Fig. 4. The coordination of the nonagermanide cage in the compound 3 without the hydrogen atoms of 18-crown-6. Thermal ellipsoids at 50% probability level.
3.4. Discussion The results show that the 21 electron cluster Ge9 3 is accessible by extraction of binary and ternary alkali metal germanides with liquid ammonia and 18-crown-6. The use of 18-crown-6 in the synthesis of deltahedral Zintl ions was established by Fa¨ssler [22], who reduced the elements with alkali metals in molten crown ether. The addition of 18-crown-6 to ethylenediamine extracts of either KGe4 or 2 K2Cs2Ge9 leads to the formation of the 1 1 ½Ge9 poly6 mer [6] as well as the dimer [Ge9Ge9] found in [K(18-crown-6)]3Cs3[Ge9Ge9] Æ 2en [5] up to now. In contrast to [2.2.2]-crypt, 18-crown-6 has a weaker complex stability constant and allows for a better observation of alkali metal–anion interactions [23], which show effects on the symmetry of the polyhedra [24]. The abbreviated data concerning the nine-atom germanium cages of compounds 1–3 reported in this paper are summed up in Table 3. All of the three nine-atom germanium cages possess approximately C2v symmetry. The up to now known structures (Table 4) were all isolated with the use of the sequestering agent [2.2.2]-crypt (4,7,13,16,
Table 3 ˚ ), a1 concerns to the basal plane as shown in Fig. 1, a2 and a3 Geometrical parameters of the nine-atom cages (relative prism heights hx scaled to 2.7759 A concern to the similar trigonal planes between the capping atoms Compound
Cage
h1
h2
h3
h/e
Tors. angle
a1 ()
a2 ()
a3 ()
d1/d2
Symmetry
1 2 3
[Ge9]3 [Ge9]3 [Ge9]3
1.24 1.46 1.20
1.00 1.02 1.00
1 1.01 1.01
1.11 1.10 1.11
2.96(3) 5.49(6) 0.23(4)
4 7 0.3
28 22 26
29 26 28
1.13 1.26 1.18
C2v C2v C2v
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Table 4 Geometrical parameters of the nine-atom cages in the literature
References
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[1] T.F. Fa¨ssler, Coordin. Chem. Rev. 215 (2001) 347. [2] V. Queneau, S.C. Sevov, Angew. Chem., Int. Ed. 36 (1997) 1754. [3] C. Suchentrunk, J. Daniels, M. Somer, W. Carrillo-Cabrera, N. Korber, Z. Naturforsch. 60b (2005) 277. [4] R. Hauptmann, T.F. Fa¨ssler, Z. Kristallogr. NCS 218 (2003) 370. [5] R. Hauptmann, T.F. Fa¨ssler, Z. Anorg. Allg. Chem. 629 (2003) 2266. [6] C. Downie, Z. Tang, A.M. Guloy, Angew. Chem., Int. Ed. 39 (2000) 337. [7] T.F. Fa¨ssler, M. Hunziker, Inorg. Chem. 33 (1994) 5380. [8] C. Belin, New J. Chem. 15 (1991) 931. [9] T.F. Fa¨ssler, U. Schu¨tz, Inorg. Chem. 38 (1999) 1866. [10] C.H.E. Belin, J.D. Corbett, A.C. Cisar, J. Am. Chem. Soc. 99 (1977) 7163. [11] K. Wade, Adv. Inorg. Chem. Radiochem. 18 (1976) 1. [12] T. Kottke, D. Stalke, J. Appl. Crystallogr. 26 (1993) 615. [13] G.M. Sheldrick, SHELXS-97, Universita¨t Go¨ttingen, Go¨ttingen, Germany, 1997. [14] G.M. Sheldrick, SHELXL-97, Universita¨t Go¨ttingen, Go¨ttingen, Germany, 1997. [15] A.L. Spek, PLATON, Utrecht University, Utrecht, The Netherlands, 2004. [16] X-RED 1.11, STOE & Cie GmbH, Darmstadt, Germany, 1998. [17] X-Shape 1.03, STOE & Cie GmbH, Darmstadt, Germany, 1998. [18] A. Bondi, J. Phys. Chem. 68 (1964) 441. [19] R.S. Rowland, T. Taylor, J. Phys. Chem. 100 (1996) 7384. [20] C. Suchentrunk, T. Rossmeier, N. Korber, Z. Kristallogr. (2005), in press. [21] N. Korber, A. Fleischmann, J. Chem. Soc., Dalton Trans. (2001) 383. [22] T.F. Fa¨ssler, R. Hoffmann, Chimia 52 (1998) 158. [23] C. Downie, J.-G. Mao, H. Parmar, A.M. Guloy, Inorg. Chem. 43 (2004) 1992. [24] L. Diehl, K. Khodadadeh, D. Kummer, J. Stra¨hle, Chem. Ber. 109 (1976) 3404. [25] T.F. Fa¨ssler, M. Hunziker, M.E. Spahr, Z. Anorg. Allg. Chem. 626 (2000) 692.
4 5 6 7 8
Compound þ
3
½K ½2:2:2crypt3 Ge9 0:5en ½Kþ ½2:2:2crypt3 Ge9 3 PPh3 [K+[2.2.2]crypt]6[Ge9Ge9]6 Æ (en)0.5 [K+[2.2.2]crypt]6[Ge9Ge9]6 Æ (en)1.5 [K+[2.2.2]crypt]6[Ge9Ge9]6 Æ (en)2.5
Literature
Symmetry
[7] [8] [9] [9] [10]
Cs Cs A: C2v B: C2v A: C2v B: C2v A: C2v B: C4v
A and B denote crystallographically non-equivalent anions.
21,24-hexaoxa-l,10-diazabicyclo[8.8.8]-hexacosane). The cages in compounds 4–7 also contain the Ge9 3 anion, which was proven for compound 4 by EPR measurements [25]. In contrast to this, the two cages in compound 8 were originally reported as a 20- and a 22- electron cluster. While the nine-atom germanium cages in structures 4 and 5 have Cs point group symmetry, both of the different Ge9 3 cages A and B in structure 6 and 7 show C2v symmetry, whereas the two cages A and B in compound 8 possess the different symmetries C2v and C4v. 4. Supplementary material CCDC 276039 (1), CCDC 276041 (2) and CCDC 276042 (3) contain the supplementary crystallographic data for this paper. These data can be obtained free of charge via http://www.ccdc.cam.ac.uk/data_request/cif, by emailing [email protected], or by contacting The Cambridge Crystallographic Data Centre, 12, Union Road, Cambridge CB2 1EZ, UK; fax +44 1223 336033.
Synthesis and crystal structures of [K(18-crown-6)][Rb(18-crown-6)]2Ge9 Æ 6NH3, [Rb(18-crown-6)]3Ge9 Æ 9NH3 and [Cs(18-crown-6)]3Ge9 Æ 6NH3 Christof Suchentrunk, Nikolaus Korber
*
Institut fu¨r Anorganische Chemie der Universita¨t Regensburg, Universita¨tsstrasse 31, 93053 Regensburg, Germany Received 27 June 2005; received in revised form 19 September 2005; accepted 28 September 2005 Available online 3 November 2005
Abstract The new compounds [K(C12H24O6)][Rb(C12H24O6)]2Ge9 Æ 6NH3, [Rb(C12H24O6)]3Ge9 Æ 9NH3 and [Cs(C12H24O6)]3Ge9 Æ 6NH3 were prepared by the extraction of binary and ternary phases of the nominal composition K2Rb2Ge9, Rb4Ge9 and K2Cs2Ge9 with liquid ammonia in the presence of 18-crown-6. The resulting crystals were characterized by low temperature X-ray structure analysis. All of them contain the 21 electron cluster Ge9 3 , which is coordinated by alkali metal cations in ion-paired arrangements. The cages were assigned their specific point group symmetry and were compared with hitherto known structures. 2005 Elsevier B.V. All rights reserved. Keywords: Zintl anion; Germanide; Low-temperature crystal structure analysis; Liquid ammonia; Solvate crystal
1. Introduction Among the polygermanide Zintl anions, the Ge9 x (x = 2, 3, 4) anion is most commonly encountered, and the available data have been reviewed by Fa¨ssler [1]. The Ge9 4 anions are found in solid state binary compounds like Cs4Ge9 [2], in ammoniates like K4Ge9 Æ 9NH3 and Rb4Ge9 Æ 5NH3 [3] or with crown ether sequestered counter cations like in [K(C12H26N2O4)]2Rb2Ge9 Æ 2en [4]. The solvate and crown ether compounds were synthesized by the extraction of binary or ternary compounds, which also leads to phases like [K(C12H24O6)]3Cs3[Ge9Ge9] Æ 2en [5] and Cs6[Ge9Ge9] Æ 4NH3[3], both of which contain the [Ge9–Ge9]6 dimer. A 2 1 polymer was identified in the compound 1 ½Ge9 [K(C12H24O6)]2Ge9 Æ en [6]. Finally, the Ge9 3 anion has up to now been described in the compounds [K([2.2.2]-crypt)]3Ge9 Æ 0.5en [7], [K([2.2.2]-crypt)]3Ge9 Æ PPh3 [8], as well as in [K([2.2.2]-crypt)]6(Ge9)2 Æ xen (x = 0.5, 1.5) [9]. The structure of [K([2.2.2]-crypt)]6(Ge9)2 Æ 2.5en [10] was originally
reported by Corbett as containing two crystallographic inequivalent nine-atom germanium cages Ge9 4 and Ge9 2 with C4v and C2v symmetry. According to the Wade Rules [11], the Ge9 4 anion as a 22 electron cluster should adopt a nido-polyhedron with C4v symmetry (mono-capped square antiprism), whereas a Ge9 2 anion as a 20 electron cluster should display D3h point group symmetry (tri-capped trigonal prism). Consequently, a Ge9 3 anion as a 21 electron cluster should adopt distorted variants between C4v and D3h symmetry [7]. However, according to Fa¨ssler [9], there is no strong correlation between the observed cage structures and the number of electrons. Given the limited number of known Ge9 3 structure reports, the characterization of additional nonagermanides in liquid ammonia seemed desirable. In this paper, we report on the new compounds [K(C12H24O6)][Rb(C12H24O6)]2Ge9 Æ 6NH3 (1), [Rb(C12H24O6)]3Ge9 Æ 9NH3 (2) and [Cs(C12H24O6)]3-Ge9 Æ 6NH3 (3). 2. Experimental
*
Corresponding author. Tel.: +0941 9434448; fax: +0941 9431812. E-mail address: [email protected] (N. Korber). 0020-1693/$ - see front matter 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.ica.2005.09.043
All work was done excluding moisture and air in an atmosphere of purified argon. The compounds were
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prepared by the extraction of binary and ternary phases with liquid ammonia in the presence of 18-crown-6. The binary and ternary phases were prepared from stoichiometric mixtures of the elements in sealed silica tubes. For the crystal preparation, we adapted the technique described by Kottke and Stalke [12]. The thermally unstable and moisture sensitive ammoniate crystals were transferred directly from the mother liquor to the diffractometer using an endcapped fluoropolyether oil. 2.1. Synthesis of [K(C12H24O6)][Rb(C12H24O6)]2Ge9 Æ 6NH3 (1) A mixture of 0.4 g (10.2 mmol) K, 0.8 g (10 mmol) Rb and 3.2 g (44.0 mmol) Ge was heated to 650 C (5 C/h), annealed at 650 C for 120 h, and finally cooled to room temperature (5 C/h). About 0.22 g (0.24 mmol) of the resulting ternary phase with the nominal composition K2Rb2Ge9 and 0.13 g (0.49 mmol) of 18-crown-6 (1,4,7,10,13,16-hexaoxacyclooctadecane) were filled into a Schlenk tube and 30 ml of sodium-dried liquid ammonia was added, yielding a brown-yellow solution. The reaction vessel was stored at 40 C for 4 months. After this period, red needle-shaped crystals of 1 were obtained. 2.2. Synthesis of [Rb(C12H24O6)]3Ge9 Æ 9NH3 (2) About 1.1 g (12.8 mmol) Rb and 2.1 g (28.9 mmol) Ge were heated to 650 C (10 C/h), then annealed at 650 C for 120 h and finally cooled down to room temperature (10 C/h). About 0.2 g (0.2 mmol) of the resulting binary phase of the nominal composition Rb4Ge9 and 0.106 g (0.4 mmol) of 18-crown-6 were filled in a Schlenk tube and 30 ml of sodium-dried liquid ammonia was added, yielding a transparent yellow solution. The reaction vessel was stored at 40 C for 12 months. After this period, red plate-like crystals of 2 were obtained. 2.3. Synthesis of [Cs(C12H24O6)]3Ge9 Æ 6NH3 (3) About 0.2 g (5.1 mmol) K, 0.7 g (5.29 mmol) Cs and 1.72 g (23.7 mmol) Ge were heated up to 650 C (10 C/ h), then annealed at 650 C for 120 h and finally cooled down to room temperature (10 C/h). About 0.3 g (0.3 mmol) of the resulting ternary phase of the nominal composition K2Cs2Ge9 and 0.075 g (0.28 mmol) of 18crown-6 were then filled in a Schlenk tube and 30 ml of dried liquid ammonia was added, yielding a light brown solution. The reaction vessel was stored at 40 C for 6 months. After this period, red plate-like crystals of (3) were obtained. 2.4. X-ray data collection and structure refinement The diffraction data were collected with graphite mono˚ ) radiation on a STOE chromated Mo Ka (k = 0.71073 A IPDS (Imaging Plate Diffraction System) at 150 C. The
structures were solved by direct methods (SHELXS-97) [13] and refined on F2 (SHELXL-97) [14]. A DIFABS-type absorption correction was applied with the help of the PLATON program package [15] for structure 1. The absorption correction was done with X-RED [16] and X-Shape [17] for structures 2 and 3. All of the atoms except hydrogen atoms were refined with anisotropic displacement parameters. The hydrogen atoms of the 18-crown-6 molecules were inserted using a riding model. The majority of the hydrogen atoms of the ammonia molecules were located in the difference Fourier map. The selection of the space groups was certified using PLATON [15]. The crystal data and the details of the structure refinements are given in Table 1. 3. Results and discussion 3.1. Description of [K(C12H24O6)][Rb(C12H24O6)]2Ge9 Æ 6NH3 (1) The asymmetric unit of structure 1 consists of one nineatom germanium cage Ge9 3 (Fig. 1), two crystallographic independent rubidium cations Rb+ and one potassium cation K+. Each of the cations is surrounded by one molecule of 18-crown-6. Additionally, six molecules of ammonia of crystallization are present in the asymmetric unit. The rubidium cation Rb(1) caps the basal square Ge(6)– Ge(7)–Ge(8)–Ge(9) of the nonagermanide cage with ˚ (Fig. 2). The distances between 3.6529(9) and 3.8667(9) A distance of the capping cation Rb(1) to the centre of ˚ . The the adjacent basal square has a value of 3.2441(9) A rubidium cation Rb(2) caps the triangular face built by the three germanium atoms Ge(1), Ge(2) and Ge(5) with ˚ . Each of the distances between 3.4833(9) and 3.669(8) A rubidium cations is located above the mean plane of the coordinating crown ether. The potassium cation K(1) is surrounded by 18-crown-6 and two ammonia molecules of crystallization above and below the crown ether plane. This complex shows potassium–oxygen bond lengths be˚ , while the rubidium–oxygen tween 2.750(4) and 2.856(4) A distances in the anionic complex have larger values be˚ as expected. The potastween 2.864(4) and 3.167(4) A ˚. sium–nitrogen bond lengths are 2.878(6) and 2.918(6) A The ammonia molecule containing the nitrogen atom N(1) forms van-der-Waals contacts (van-der-Waals radii: ˚ , O = 1.4 [18,19]) with its hydrogen atoms H = 1.2 A H(1 A) and H(1C) to the oxygen atoms O(11) and O(7) of the adjacent crown-ether with distances of 2.70(8) and ˚ . The corresponding angles are N(1)–H(1A)– 2.6(1) A O(11) 158(7) and N(1)–H(1C)–O(7) 150(8). Similar hydrogen bonds were observed in the ammoniate of 18crown-6 [20]. The structure contains no potassium–germa˚ . The intracage Ge–Ge nium distances smaller than 5 A ˚ bond lengths measure between 2.5002(9) and 2.9078(8) A and are listed in Table 2. The Ge–Ge distances are in accordance with comparable structures like [K([2.2.2]-crypt)]6Ge9Ge9 Æ 0.5en [9]. As a 21 electron cluster, the polyhedron of the Ge9 3 cage should adopt a distorted variant of the
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269
Table 1 Crystal data and structure refinement for compounds 1–3 No.
1
2
3
Empirical Formula Formula weight (g mol1) Temperature (C) ˚) Wavelength (A Crystal system Space group ˚) a (A ˚) b (A ˚) c (A b () ˚ 3) Volume (A Z Dcalc (g cm3) l (mm1) Crystal size (mm3) F(000) H () Limiting indices
[K(C12H24O6)][Rb(C12H24O6)]2Ge9 Æ 6NH3 1758.6 150 0.71073 monoclinic P21/c (no. 14) 13.072(1) 19.035(1) 26.950(2) 90.54(1) 6705(1) 4 6.741 5.5 0.2 · 0.2 · 0.5 3532 2.03–26.12 16 6 h 6 16, 22 6 k 6 22, 33 6 l 6 33 90 729/12 647 (Rint = 0.0574) 94.7% (26.12) 12 647/0/660 0.948 R1 = 0.0393, wR2 = 0.0942 R1 = 0.0647, wR2 = 0.1012 1.885 and 1.228
[Rb(C12H24O6)]3Ge9 Æ 9NH3 1856.0 150 0.71073 orthorhombic P bca (no. 61) 24.031(2) 23.003(5) 25.669(3)
[Cs(C12H24O6)]3Ge9 Æ 6NH3 1947.3 150 0.71073 orthorhombic P bca (no. 61) 22.959(2) 25.711(2) 24.261(2)
14 189(3) 8 1.703 5.8 0.1 · 0.2 · 0.4 7076 2.07–25.94 29 6 h 6 29, 28 6 k 6 28, 31 6 l 6 31 98 168/13 733 (Rint = 0.1238) 99.1% (25.94) 13 733/0/685 1.047 R1 = 0.0797, wR2 = 0.1900 R1 = 0.1056, wR2 = 0.2095 3.932 and 3.436
14 321(2) 8 1.806 5.3 0.1 · 0.2 · 0.4 7560 1.94–25.91 28 6 h 6 28, 31 6 k 6 31, 29 6 l 6 29 180 531/13 843 (Rint = 0.1180) 99.3% (25.91) 13 843/0/655 1.046 R1 = 0.0624, wR2 = 0.1820 R1 = 0.0756, wR2 = 0.1928 4.485 and 2.414
Reflections collected/unique Completeness to theta Data/restraints/parameters Goodness-of-fit R[I > 2r(I)] R indices (all data) Largest difference peak ˚ 3) and hole (e A
point group symmetries C4v or D3h. For the description of this distortion, the diagonal distances Ge(6)–Ge(8) and Ge(7)–Ge(9) at the uncapped face of the cage and the torsion angle Ge(8)–Ge(9)–Ge(6)–Ge(7) have been established as useful criteria [21]. The basal square of the nonagermanide cage is nearly planar with a negative torsion angle Ge(8)–Ge(9)–Ge(6)–Ge(7) of 2.96(3), corresponding to a small deviation from C4v not towards D3h symmetry, but in the opposite direction with an inward facing edge. The diagonal distances of the basal square are Ge(6)– ˚ and Ge(7)–Ge(9) 3.8963(9) A ˚ , leading Ge(8) 3.4353(9) A away from C4v towards C2v symmetry. The heights of the fictional prism within the cage are Ge(6)–Ge(8) 3.4353(9) ˚ (h1), Ge(2)–Ge(3) 2.7759(8) A ˚ (h2) and Ge(4)–Ge(5) A ˚ (h3). The similar prism heights h2 and h3 give 2.7780(8) A
Fig. 1. A nonagermanide cage showing the angle a and the prism heights h discussed below. The atom numbering scheme is identical for compounds 1–3.
rise to a pseudo twofold axis through the centre of the uncapped basal square and the apical atom Ge(1), even if the centre of gravity of the cage is on a common site. 3.2. Description of [Rb(C12H24O6)]3Ge9 Æ 9NH3 (2) The asymmetric unit consists of one nine-atom germanium cage Ge9 3 and three crystallographic independent rubidium cations Rb+, each surrounded by one 18crown-6 ether. Additionally, nine molecules of ammonia of crystallization are present in the asymmetric unit. All of the rubidium cations rise above the mean plane of the crown ether (Fig. 3). The distances between the rubidium cations and the oxygen atoms are between 2.893(3) and ˚ and are comparable with the rubidium–oxygen 3.149(6) A distances in compound 1. The rubidium cation Rb(3) caps the triangular face of the nonagermanide cage built by the three atoms Ge(1), Ge(2) and Ge(5) with distances between 3.600(1) and ˚ . The cation Rb(2) has a long distance contact 3.898(1) A ˚ as well as to the germanium atom Ge(7) with 4.188(1) A with two additional nitrogen atoms of ammonia N(1) ˚ . The cation Rb(1) and N(2) with 3.249(8) and 3.14(1) A displays no rubidium–germanium distances smaller than ˚ , but has contacts to the nitrogen atoms N(3), N(4) 5A and N(5) of ammonia at one side of the crown ether with ˚ , forming a distances measuring from 3.16(1) to 3.43(1) A + [Rb(C12H24O6)(NH3)3] molecular ion complex. The remaining molecules of ammonia have no contacts to
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C. Suchentrunk, N. Korber / Inorganica Chimica Acta 359 (2006) 267–272 Rb Ge K O N H C
O(7) 3
1 N(2)
H(1C)
Rb(2)
K(1)
4 2 7
N(1) H(1A) O(11)
5 6
8
9 Rb(1)
Fig. 2. The coordination of the nonagermanide cage in compound 1 without the hydrogen atoms of 18-crown-6. Thermal ellipsoids at 50% probability level.
specific cations. As can be seen in Table 2, the intracage Ge–Ge bond lengths have values from 2.509(2) to ˚ . The designation of the atoms is identical to that 2.873(2) A of structure 1 (Fig. 1). The uncapped basal square of the cage has a torsion angle Ge(8)–Ge(9)–Ge(6)–Ge(7) of 5.49(6), which is a small deviation towards D3h symmetry. The diagonal distances Ge(6)–Ge(8) and Ge(7)–Ge(9) at the uncapped square of the cage have values of 3.200(2) ˚ , which shows a notable deviation from and 4.046(2) A C4v towards C2v symmetry. The heights of the prism are
˚ (h2) ˚ (h1), Ge(2)–Ge(3) 2.818(1) A Ge(6)–Ge(8) 3.200(2) A ˚ and Ge(4)–Ge(5) 2.873(2) A (h3). The almost similar prism heights h2 and h3 give rise to a pseudo twofold axis and the cage has approximately C2v symmetry. 3.3. Description of [Cs(C12H24O6)]3Ge9 Æ 6NH3 (3) The asymmetric unit contains one nonagermanide cage, three crystallographic independent cesium cations, three molecules of 18-crown-6 and six molecules of ammonia
Table 2 Intracluster Ge–Ge distances in the nonagermanide cages of compounds 1–3 1
2
3
Bond
˚) Distance (A
Bond
˚) Distance (A
Bond
˚) Distance (A
Ge(1)–Ge(2) Ge(1)–Ge(3) Ge(1)–Ge(4) Ge(1)–Ge(5) Ge(2)–Ge(3) Ge(2)–Ge(5) Ge(2)–Ge(6) Ge(2)–Ge(7) Ge(3)–Ge(4) Ge(3)–Ge(7) Ge(3)–Ge(8) Ge(4)–Ge(5) Ge(4)–Ge(8) Ge(4)–Ge(9) Ge(5)–Ge(6) Ge(5)–Ge(9) Ge(6)–Ge(7) Ge(7)–Ge(8) Ge(8)–Ge(9) Ge(6)–Ge(9) Ge(6)–Ge(8) Ge(7)–Ge(9)
2.6148(8) 2.5723(9) 2.5956(9) 2.5842(8) 2.7759(8) 2.8923(8) 2.5918(9) 2.5755(9) 2.9078(8) 2.7247(9) 2.5770(9) 2.7780(8) 2.5897(9) 2.6777(9) 2.6114(9) 2.5569(9) 2.6331(9) 2.5411(9) 2.5002(9) 2.7236(8) 3.4353(9) 3.8963(9)
Ge(1)–Ge(2) Ge(1)–Ge(3) Ge(1)–Ge(4) Ge(1)–Ge(5) Ge(2)–Ge(3) Ge(2)–Ge(5) Ge(2)–Ge(6) Ge(2)–Ge(7) Ge(3)–Ge(4) Ge(3)–Ge(7) Ge(3)–Ge(8) Ge(4)–Ge(5) Ge(4)–Ge(8) Ge(4)–Ge(9) Ge(5)–Ge(6) Ge(5)–Ge(9) Ge(6)–Ge(7) Ge(7)–Ge(8) Ge(8)–Ge(9) Ge(6)–Ge(9) Ge(6)–Ge(8) Ge(7)–Ge(9)
2.615(1) 2.604(1) 2.556(1) 2.599(2) 2.818(1) 2.793(2) 2.688(2) 2.648(1) 2.818(1) 2.595(1) 2.639(2) 2.873(2) 2.592(2) 2.552(2) 2.618(2) 2.659(2) 2.543(2) 2.635(2) 2.643(2) 2.509(2) 3.200(2) 4.046(2)
Ge(1)–Ge(2) Ge(1)–Ge(3) Ge(1)–Ge(4) Ge(1)–Ge(5) Ge(2)–Ge(3) Ge(2)–Ge(5) Ge(2)–Ge(6) Ge(2)–Ge(7) Ge(3)–Ge(4) Ge(3)–Ge(7) Ge(3)–Ge(8) Ge(4)–Ge(5) Ge(4)–Ge(8) Ge(4)–Ge(9) Ge(5)–Ge(6) Ge(5)–Ge(9) Ge(6)–Ge(7) Ge(7)–Ge(8) Ge(8)–Ge(9) Ge(6)–Ge(9) Ge(6)–Ge(8) Ge(7)–Ge(9)
2.577(1) 2.618(1) 2.593(1) 2.563(1) 2.790(1) 2.879(1) 2.590(1) 2.614(1) 2.852(1) 2.630(1) 2.628(1) 2.781(1) 2.593(1) 2.648(1) 2.586(1) 2.596(1) 2.613(2) 2.563(1) 2.543(1) 2.618(2) 3.344(2) 3.941(1)
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271
Rb(3)
Cs(3) Rb(1)
Cs(1)
1 5
N(5)
6
N(3)
5
N(1)
7
8
3
N(4)
3
4 9
1
4
2
7
6
Rb(2)
N(6)
2
8
9
N(3)
N(2)
Rb Ge O N H C
N(2)
Fig. 3. The coordination of the nonagermanide cage in compound 2 without the hydrogen atoms of 18-crown-6. Thermal ellipsoids at 50% probability level.
of crystallization. All of the cesium cations are situated above the mean plane of the crown ethers. The cesium– ˚. oxygen bond lengths range from 2.984(6) to 3.284(6) A The coordination of the nonagermanide cage is comparable to that of compound 2 (Fig. 4) with the exception that the atom Cs(2), comparable to Rb(2), has only one ammonia contact in addition to the germanium anion contact ˚ . The distances of the cesium with a distance of 4.072(2) A cation Cs(3) capping the triangular face of the nonagerma˚ . The nide-cage are between 3.673(1) and 3.880(1) A remaining cesium–nitrogen bond lengths of Cs(1) range ˚ . The intracage germanium disfrom 3.26(1) to 3.387(9) A ˚ and 2.879(1) tances, listed in Table 2, measure 2.563(1) A ˚ A. The atom designation corresponds to that of Fig. 1. The uncapped basal square Ge(8)–Ge(9)–Ge(6)–Ge(7) of the nonagermanide cage has a very small torsion angle of 0.23(4). Consequently, the basal plane can be considered as nearly planar with an inward facing edge. The diagonal distances at the uncapped square Ge(6)–Ge(8) and Ge(7)– ˚ , giving rise to Ge(9) have values of 3.344(2) and 3.941(1) A a deviation towards C2v symmetry. The prism heights have ˚ , Ge(2)–Ge(3) values of Ge(6)–Ge(8) (h1) 3.344(2) A ˚ ˚ (h3). Due to 2.790(1) A (h2) and Ge(4)–Ge(5) 2.781(1) A the similar prism heights h2 and h3, the nonagermanide cage possesses approximately C2v symmetry.
N(1)
Cs Ge O C H N
Cs(2)
Fig. 4. The coordination of the nonagermanide cage in the compound 3 without the hydrogen atoms of 18-crown-6. Thermal ellipsoids at 50% probability level.
3.4. Discussion The results show that the 21 electron cluster Ge9 3 is accessible by extraction of binary and ternary alkali metal germanides with liquid ammonia and 18-crown-6. The use of 18-crown-6 in the synthesis of deltahedral Zintl ions was established by Fa¨ssler [22], who reduced the elements with alkali metals in molten crown ether. The addition of 18-crown-6 to ethylenediamine extracts of either KGe4 or 2 K2Cs2Ge9 leads to the formation of the 1 1 ½Ge9 poly6 mer [6] as well as the dimer [Ge9Ge9] found in [K(18-crown-6)]3Cs3[Ge9Ge9] Æ 2en [5] up to now. In contrast to [2.2.2]-crypt, 18-crown-6 has a weaker complex stability constant and allows for a better observation of alkali metal–anion interactions [23], which show effects on the symmetry of the polyhedra [24]. The abbreviated data concerning the nine-atom germanium cages of compounds 1–3 reported in this paper are summed up in Table 3. All of the three nine-atom germanium cages possess approximately C2v symmetry. The up to now known structures (Table 4) were all isolated with the use of the sequestering agent [2.2.2]-crypt (4,7,13,16,
Table 3 ˚ ), a1 concerns to the basal plane as shown in Fig. 1, a2 and a3 Geometrical parameters of the nine-atom cages (relative prism heights hx scaled to 2.7759 A concern to the similar trigonal planes between the capping atoms Compound
Cage
h1
h2
h3
h/e
Tors. angle
a1 ()
a2 ()
a3 ()
d1/d2
Symmetry
1 2 3
[Ge9]3 [Ge9]3 [Ge9]3
1.24 1.46 1.20
1.00 1.02 1.00
1 1.01 1.01
1.11 1.10 1.11
2.96(3) 5.49(6) 0.23(4)
4 7 0.3
28 22 26
29 26 28
1.13 1.26 1.18
C2v C2v C2v
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Table 4 Geometrical parameters of the nine-atom cages in the literature
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[1] T.F. Fa¨ssler, Coordin. Chem. Rev. 215 (2001) 347. [2] V. Queneau, S.C. Sevov, Angew. Chem., Int. Ed. 36 (1997) 1754. [3] C. Suchentrunk, J. Daniels, M. Somer, W. Carrillo-Cabrera, N. Korber, Z. Naturforsch. 60b (2005) 277. [4] R. Hauptmann, T.F. Fa¨ssler, Z. Kristallogr. NCS 218 (2003) 370. [5] R. Hauptmann, T.F. Fa¨ssler, Z. Anorg. Allg. Chem. 629 (2003) 2266. [6] C. Downie, Z. Tang, A.M. Guloy, Angew. Chem., Int. Ed. 39 (2000) 337. [7] T.F. Fa¨ssler, M. Hunziker, Inorg. Chem. 33 (1994) 5380. [8] C. Belin, New J. Chem. 15 (1991) 931. [9] T.F. Fa¨ssler, U. Schu¨tz, Inorg. Chem. 38 (1999) 1866. [10] C.H.E. Belin, J.D. Corbett, A.C. Cisar, J. Am. Chem. Soc. 99 (1977) 7163. [11] K. Wade, Adv. Inorg. Chem. Radiochem. 18 (1976) 1. [12] T. Kottke, D. Stalke, J. Appl. Crystallogr. 26 (1993) 615. [13] G.M. Sheldrick, SHELXS-97, Universita¨t Go¨ttingen, Go¨ttingen, Germany, 1997. [14] G.M. Sheldrick, SHELXL-97, Universita¨t Go¨ttingen, Go¨ttingen, Germany, 1997. [15] A.L. Spek, PLATON, Utrecht University, Utrecht, The Netherlands, 2004. [16] X-RED 1.11, STOE & Cie GmbH, Darmstadt, Germany, 1998. [17] X-Shape 1.03, STOE & Cie GmbH, Darmstadt, Germany, 1998. [18] A. Bondi, J. Phys. Chem. 68 (1964) 441. [19] R.S. Rowland, T. Taylor, J. Phys. Chem. 100 (1996) 7384. [20] C. Suchentrunk, T. Rossmeier, N. Korber, Z. Kristallogr. (2005), in press. [21] N. Korber, A. Fleischmann, J. Chem. Soc., Dalton Trans. (2001) 383. [22] T.F. Fa¨ssler, R. Hoffmann, Chimia 52 (1998) 158. [23] C. Downie, J.-G. Mao, H. Parmar, A.M. Guloy, Inorg. Chem. 43 (2004) 1992. [24] L. Diehl, K. Khodadadeh, D. Kummer, J. Stra¨hle, Chem. Ber. 109 (1976) 3404. [25] T.F. Fa¨ssler, M. Hunziker, M.E. Spahr, Z. Anorg. Allg. Chem. 626 (2000) 692.
4 5 6 7 8
Compound þ
3
½K ½2:2:2crypt3 Ge9 0:5en ½Kþ ½2:2:2crypt3 Ge9 3 PPh3 [K+[2.2.2]crypt]6[Ge9Ge9]6 Æ (en)0.5 [K+[2.2.2]crypt]6[Ge9Ge9]6 Æ (en)1.5 [K+[2.2.2]crypt]6[Ge9Ge9]6 Æ (en)2.5
Literature
Symmetry
[7] [8] [9] [9] [10]
Cs Cs A: C2v B: C2v A: C2v B: C2v A: C2v B: C4v
A and B denote crystallographically non-equivalent anions.
21,24-hexaoxa-l,10-diazabicyclo[8.8.8]-hexacosane). The cages in compounds 4–7 also contain the Ge9 3 anion, which was proven for compound 4 by EPR measurements [25]. In contrast to this, the two cages in compound 8 were originally reported as a 20- and a 22- electron cluster. While the nine-atom germanium cages in structures 4 and 5 have Cs point group symmetry, both of the different Ge9 3 cages A and B in structure 6 and 7 show C2v symmetry, whereas the two cages A and B in compound 8 possess the different symmetries C2v and C4v. 4. Supplementary material CCDC 276039 (1), CCDC 276041 (2) and CCDC 276042 (3) contain the supplementary crystallographic data for this paper. These data can be obtained free of charge via http://www.ccdc.cam.ac.uk/data_request/cif, by emailing [email protected], or by contacting The Cambridge Crystallographic Data Centre, 12, Union Road, Cambridge CB2 1EZ, UK; fax +44 1223 336033.