[PbAsSiiPr3]6 - The first structurally characterized compound with chemical bonds between lead and arsenic

Article abstract of DOI:10.1002/zaac.200300387

The compound [PbAsSiiPr₃]₆ (1) could be obtained by the reaction of PbCl₂ with iPr₃SiAs(SiMe₃) ₂ in THF at 0°C. Central structural motif is a hexagonal prism built by six lead and six arsenic atoms. The average Pb-As bond length is 281 pm. The cluster crystallizes in the monoclinic space group C2/c, the lattice constants are: a = 4460.8(9) b = 2296.6(5), c = 2734.4(6) pm, β = 117.57(3)°. The thermogravimetric analysis in vacuum shows the tendecy of 1 to decompose under formation of elementary lead and volatile arsenic compounds.

Full text of DOI:10.1002/zaac.200300387

Kurze Mitteilungen
[PbAsSiiPr3]6 ؊ the First Structurally Characterized Compound with Chemical
Bonds between Lead and Arsenic
Carsten von Hänisch* and Donna Nikolova
Karlsruhe, Forschungszentrum Karlsruhe, Institut für Nanotechnologie
Received October 30th, 2003.
Abstract. The compound [PbAsSiiPr3]6 (1) could be obtained by
the reaction of PbCl2 with iPr3SiAs(SiMe3)2 in THF at 0°C.
Central structural motif is a hexagonal prism built by six lead and
six arsenic atoms. The average PbϪAs bond length is 281 pm. The
cluster crystallizes in the monoclinic space group C2/c, the lattice
constants are: a ϭ 4460.8(9) b ϭ 2296.6(5), c ϭ 2734.4(6) pm,
β ϭ 117.57(3)°. The thermogravimetric analysis in vacuum shows
the tendecy of 1 to decompose under formation of elementary lead
and volatile arsenic compounds.
Keywords: Lead; Arsenic; Cage compounds; Cluster compounds
Parallel to the intensively investigated field of molecular 13/15 com-
pounds [1], several research groups have worked on the synthesis
of cyclic and cage-like compounds built by the elements of group
14 and 15 [2]. In the past few years the interest in both fields has
increasingly focused on the synthesis of compounds which consist
of the heavier main group elements. Recently, the first molecules
with aluminium-bismuth and gallium-bismuth bonds [Me2MBi-
(SiMe3)2]3 (M ϭ Al, Ga) have been obtained from the reactions of
Bi(SiMe3)3 with Me2AlH and Me2GaH [3]. The reaction of
Sn{N(SiMe3)2}2 with H2AsSiiPr3 yields the first tin-arsenic cage
compound [SnAsSiiPr3]6 [4a]. Lead compounds with the heavier
elements of group 15, however, have not been studied much so far.
The crystal structures of such compounds are hardly known. Only
the crystal structures of cyclic lead(II) phosphorus compounds as
well as the carben homologous compound Pb(PRRЈ)2 (R, RЈ ϭ
sterically demanding silyl groups) have been reported to date [5,
6]. Furthermore Schumann and coworkers described the lead(IV)
arsenic compounds As(PbR3)3 (R ϭ Me, Ph) and Ph2AsPbPh3 sev-
eral years ago. However none of these Pb/As compounds have been
structurally characterized by X-ray diffraction methods [7].
Table 1 Crystallographic data of 1. STOE-IPDS2 (Mo-Kα radia-
tion, λ ϭ 0.71073 A). The structure was solved by direct methods
˚
and refined by full-matrix least-squares techniques against F2 (Pb,
As, Si, C refined anisotropically, H atoms were calculated at ideal
positions, the C atoms of one iPr3Si group were calculated with
split positions (isotropically), at these C atoms no H atom positions
were determined) [12].
Formula
C54H126As6Si6Pb6
C2/c
12
Space group
Formula units
Temperature
Lattice constants
200 K
a ϭ 4460.8(9) pm
b ϭ 2296.6(5) pm
c ϭ 2734.4(6) pm
β ϭ 117.57(3)°
3
˚
Volume
density
2° range
Reflections measured
Independent reflections
Ind. reflections with F0 > 4σ(F0)
Parameter
24832(9) A
2.105 g/cm3
4Ϫ45°
29835
13925 (Rint ϭ 0.0649)
9643
948
Besides the Zintl-anions Pb9nϪ (n ϭ 2, 4) [8], the only other known
cluster compounds of lead are those with bridging oxygen or halog-
enide ligands such as [Pb7O2(OSiMe3)10] or [NBu4]8[Pb18I44]
µ(MoKα
)
14.656 mmϪ1
0.0388
R1
wR2 (all data)
Residual electron density
0.0962
1.337 e/A
3
˚
[9].
Furthermore,
the
transition
metal
complexes
[PPh4]2[Pb{Cr(CO)5}3] and [PPh4]2[Pb2{W(CO)5}4], in which the
lead atoms act as ligands are noteworthy [10].
We have succeeded in synthesizing the first lead(II)-arsenic com-
pound by the reaction of the arsenic species iPr3SiAs(SiMe3)2 [11]
with PbCl2. These starting materials react in THF at 0°C to yield
a deeply red solution. Black crystals form during a period of two
days if the solution is kept at 0°C. These crystals are always associ-
ated with small amounts of elementary lead. The crystal structure
analysis shows that the cage compound [PbAsSiiPr3]6 (1) has been
formed in this reaction [12]. 1 crystallizes in the monoclinic space
group C2/c with two independent molecules. These two indepen-
dent molecules differ only slightly. Therefore only one will be dis-
cussed in detail. The central structural motif of 1 is a distorted
Pb6As6 hexagonal prism. This cage is built by two Pb3As3 rings in
chair conformation. In these rings the PbϪAs bonds come to 280.0
pm on average. Between the rings these bonds are approximately
282.0 pm long. These values are slightly longer than the sum of the
covalent radii of lead and arsenic (276 pm). The arsenic atoms in
1 show a distorted tetrahedral surrounding by three lead atoms and
one silyl group. The lead atoms possess no exocyclic ligands and
consequently have only coordination number three. The molecular
structure of
1 is mostly analogous to the tin compounds
[SnESiiPr3]6 (E ϭ P, As) [4].
* Dr. C. von Hänisch, Dipl-Chem. D. Nikolova
Institut für Nanotechnologie, Forschungszentrum Karlsruhe
Postfach 3640
D-76021 Karlsruhe
Telefax: 07247/82-6368
Thermogravimetric analysis of compound 1 in vacuum shows a one
step decomposition in the temperature range from 160 to 190°C
with a poorly distinguishable shoulder at 177°C. The overall mass
loss is 49.9 % (calculated for the formation of pure lead: 52.85 %).
Considering the unavoidable contamination of 1 with elementary
E-Mail: carsten.vonhaenisch@int.fzk.de
Z. Anorg. Allg. Chem. 2004, 630, 345Ϫ346
DOI: 10.1002/zaac.200300387
 2004 WILEY-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim
345

C. v. Hänisch, D. Nikolova
928 (2) [(AsSiiPr3)4ϩ], 771 (2) [As4(SiiPr3)3ϩ], 696 (30) [(AsSiiPr3)3ϩ], 421
(100) [As2Si2(iPr5)ϩ], 379 (100) [As2Si2H(iPr)4ϩ], 337 (100) [As2Si2H2(iPr)3ϩ],
300 (53) [As4ϩ], 157 (100) [iPr3Siϩ].
This work was supported by the Strategiefonds of the Helmholtz
Foundation. We thank Dr. P. Kramkowski for his valuable help with
the manuscript.
References
[1] a) S. Schulz, Coord. Chem. Rev. 2001, 215, 1Ϫ37; b) R. L.
Welle, Coord. Chem. Rev. 1992, 112, 273Ϫ291.
[2] a) D. Hänssgen, R. Jeske, M. Nieger, W. Roos, Z. Anorg. Allg.
Chem. 2000, 626, 687Ϫ691; b) M. Westerhausen, M. M.
Enzelberger, W. Schwarz, J. Organomet. Chem. 1995, 491,
83Ϫ90; c) A. R. Dahl, A. D. Norman, H.Shenav, R. Schaeffer,
J. Am. Chem. Soc. 1975, 6364Ϫ6370.
[3] a) F. Thomas, S. Schulz, M. Nieger, Organometallics, 2002, 21,
2793Ϫ2795; b) S. Schulz, M. Nieger, Angew. Chem. 1999, 111,
1020Ϫ1021; Angew. Chem. Int. Ed. 1999, 38, 967Ϫ968.
[4] a) M. Westerhausen, N. Makropoulos, H. Piotrowski, M.
Warchhold, H. Nöth, J. Organomet. Chem. 2000, 614Ϫ615,
70Ϫ73; b) M. Driess, S. Martin, K. Merz, V. Pintchouk, H.
Pritzkow, H. Grützmacher, M. Kaupp, Angew. Chem. 1997,
109, 1982Ϫ1985; Angew. Chem. Int. Ed. 1997, 36, 1894Ϫ1897.
[5] a) S. C. Goel, M. Y. Chiang, D. J. Rauscher, W. E. Buhro, J.
Am. Chem. Soc. 1993, 115, 160Ϫ169; b) A. H. Cowley, D. M.
Giolando, R. A. Jones, C. M. Nunn, J. M. Power, Polyhedron
1988, 7, 1909Ϫ1910.
[6] M. Driess, R. Janoschek, H. Pritzkow, S. Rell, U. Winkler,
Angew. Chem. 1995, 107, 1746Ϫ1749; Angew. Chem. Int. Ed.
Engl. 1995, 34, 1614Ϫ1617.
[7] a) H. Schumann, Angew. Chem. 1969, 81, 970Ϫ983; Angew.
Chem. Int Ed. Engl. 1969, 8, 937Ϫ950; b) H. Schumann, A.
Roth, O. Stelzer, M. Schmidt, Inorg. Nucl. Chem Lett. 1966,
2, 311Ϫ312; c) H. Schumann, M. Schmidt, Inorg. Nucl. Chem
Lett. 1965, 1, 1Ϫ5.
Figure 1 Molecular structure of 1, selected bond lengths/pm and
angles/°:
As(1)ϪPb(1) 280.6(1), As(1)ϪPb(2) 279.4(1), As(2)ϪPb(2) 280.2(1),
As(2)ϪPb(3) 280.4(1), As(3)ϪPb(1) 279.6(1), As(3)ϪPb(3) 280.2(1),
As(1)ϪPb(2Ј) 283.7(2), As(2)ϪPb(1Ј) 281.7(2), As(3)ϪPb(3Ј) 283.2(2),
As(1)ϪSi(1) 236.0(4), As(2)ϪSi(2) 236.5(3), As(3)ϪSi(3) 236.5(4);
PbϪAsϪPb (four-membered ring): 90.78(5)Ϫ92.69(4), PbϪAsϪPb (six-
membered ring): 139.28(4)Ϫ140.37(5), AsϪPbϪAs (four-membered ring):
83.86(3)Ϫ85.76(5), AsϪPbϪAs (six-membered ring): 99.34(4)Ϫ100.29(4).
lead, this corresponds to a complete loss of the silyl groups and
the arsenic. This is further confirmed by powder X-ray diffraction
measurements on the gray residue obtained, which display only the
reflexes of elementary lead. The tendency of 1 to decompose under
formation of volatile arsenic compounds can be observed also by
EI mass spectrometry. No lead containing fragments can be ob-
served. Instead signals of the decomposition products (AsSiiPr3)4,
(AsSiiPr3)3 and As4 appear in the mass spectra.
[8] J. D. Corbett, Chem. Rev. 1985, 85, 383Ϫ397.
Experimental Section
[9] a) H. Gröger, C. Lode, H. Vollmer, H. Krautscheid, S.
Lebedkin, Z. Anorg. Allg. Chem. 2002, 628, 57Ϫ62; b) Y.-J.
Shi, Y. Xu, X.-T. Chen, Z. Xue, X.-Z. You, Eur, J. Inorg.
Chem. 2002, 3210Ϫ3213; c) H. Krautscheid, F. Vielsack, Z.
Anorg. Allg. Chem. 2000, 626, 3Ϫ5; d) C. S. Weinert, I. A.
Guzei, A. L. Rheingold, L. R. Sita, Organometallics 1998, 17,
498-500; e) H. Krautscheid, F. Vielsack, Angew. Chem. 1995,
107, 2166Ϫ2168; Angew. Chem. Int. Ed. Engl. 1995, 34,
2035Ϫ2037.
[10] a) P. Rutsch, G. Huttner, Angew. Chem. 2000, 112, 2187Ϫ2189;
Angew. Chem. Int. Ed. 2000, 39, 2118Ϫ2120; b) P. Rutsch, G.
Huttner, Angew. Chem. 2000, 112, 3852Ϫ3854; Angew. Chem.
Int. Ed. 2000, 39, 3697Ϫ3699.
All manipulations were performed under rigorous exclusion of oxy-
gen and moisture using a Schlenk line and nitrogen atmosphere.
Solvents were dried and freshly distilled before usage. iPr3SiAs-
(SiMe3)2 was prepared according to literature [11], PbCl2 (98 %)
was obtained from Aldrich and used as received.
1: A solution of 0.16 g iPr3SiAs(SiMe3)2 (0.42 mmol) in 10 ml THF
is added to a suspension of 0.12 g (0.42 mmol) PbCl2 in 15 ml of
THF at 0°C. Subsequently the solution is warmed to room tem-
perature while stirring and then agitated for additional 20 hours
due to low solubility of PbCl2 and heterogeneous character of the
reaction. Thereby a red solution as well as a grey residue of lead
and lead chloride (characterised by powder X-Ray diffraction)
forms. After filtration and cooling of the solution to 0°C, black
crystals of 1 and small amounts of elementary lead are obtained
during a period of two days. Yield: 0.05 g (28 %). Elemental analy-
sis calc. for C54H126As6Si6Pb6 (2636.84): C 24.60, H 4.82; found: C
22.03, H 4.27 %.
[11] C. von Hänisch, P. Scheer, B. Rolli, Eur. J. Inorg. Chem.
2002, 3268Ϫ3271.
[12] CCDC-214659 contains the supplementary crystallographic
data for this paper. These data can be obtained free of charge
via www.ccdc.cam.ac.uk/conts/retrieving.html (or from
Cambridge Crystallographic Data Centre, 12 Union Road,
Cambridge CB21EZ, UK; fax: (ϩ44)1223-336-033; or
deposit@ccdc.cam.ac.uk).
1H-NMR(THF-D8): δ ϭ 1.144 (d, 3JHH ϭ 7.3 Hz, CH(CH3)2, 108H), 1.422
(hep, 3JHH ϭ 7.3 Hz, CH(CH3)2, 18 H); MS (EI, 70 eV, 190°C) m/z (%):
346
 2004 WILEY-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim
zaac.wiley-vch.de
Z. Anorg. Allg. Chem. 2004, 630, 345Ϫ346