Two successive steps of hypercoordination at tin: The gas-phase and solid-state structures of (N,N-dimethylaminoxy)trimethylstannane

Article abstract of DOI:10.1021/om990219q

Me₃SnONMe₂ has been prepared from trimethyltin chloride and O-lithio-N,N-dimethylhydroxylamine and characterized by IR and NMR spectroscopy, mass spectrometry, and elemental analysis. Its gas-phase molecular structure has been determined by electron diffraction augmented by restraints taken from ab initio calculations at the MP2/DZ(P) level of theory. A secondary interaction (Sn?N, 2.731(14) ?) between the tin and nitrogen atoms has been detected and makes MB₃SnONMe₂ the first partially hypercoordinate tin compound studied in the gas phase. A solid-state structure of Me₃SnONMe₂ has been determined by X-ray diffraction of an in situ grown single crystal. In the crystal lattice the coordination sphere of tin is further enlarged by a weak intermolecular Sn?O contact (2.998(10) ?) and a 4+2 coordination geometry is achieved, which can be deduced from that of a distorted trigonal bipyramid with one of the axial substituents replaced by the two weak contacts. Important geometry parameter values are as follows (gas/solid): Sn-O 2.006(3)/2.063(6) ?, O-N 1.468(6)/1.440(9) ?, Sn-C(in plane) 2.148(4)/2.163(14) ?, Sn-C(out of plane) 2.146(3)/ 2.062(9) and 2.185(10) ?, Sn-O-N 102.5(8)/101.5(4)°, O-Sn-C(in plane) 99.6(10)/99.7(4)°, O-Sn-C(out of plane) 108.1(6)/119.6(4)° and 116.6(4)°.

Full text of DOI:10.1021/om990219q

2610
Organometallics 1999, 18, 2610-2614
Tw o Su ccessive Step s of Hyp er coor d in a tion a t Tin :
Th e Ga s-P h a se a n d Solid -Sta te Str u ctu r es of
(N,N-Dim eth yla m in oxy)tr im eth ylsta n n a n e
Norbert W. Mitzel,*,† Udo Losehand,† and Alan Richardson‡
Anorganisch-chemisches Institut, Technische Universita¨t Mu¨nchen, Lichtenbergstrasse 4,
85747 Garching, Germany, and Department of Chemistry, Oregon State University,
Corvallis, Oregon 97331-4003
Received March 29, 1999
Me3SnONMe2 has been prepared from trimethyltin chloride and O-lithio-N,N-dimethyl-
hydroxylamine and characterized by IR and NMR spectroscopy, mass spectrometry, and
elemental analysis. Its gas-phase molecular structure has been determined by electron
diffraction augmented by restraints taken from ab initio calculations at the MP2/DZ(P) level
of theory. A secondary interaction (Sn‚‚‚N, 2.731(14) Å) between the tin and nitrogen atoms
has been detected and makes Me3SnONMe2 the first partially hypercoordinate tin compound
studied in the gas phase. A solid-state structure of Me3SnONMe2 has been determined by
X-ray diffraction of an in situ grown single crystal. In the crystal lattice the coordination
sphere of tin is further enlarged by a weak intermolecular Sn‚‚‚O contact (2.998(10) Å) and
a 4+2 coordination geometry is achieved, which can be deduced from that of a distorted
trigonal bipyramid with one of the axial substituents replaced by the two weak contacts.
Important geometry parameter values are as follows (gas/solid): Sn-O 2.006(3)/2.063(6) Å,
O-N 1.468(6)/1.440(9) Å, Sn-C(in plane) 2.148(4)/2.163(14) Å, Sn-C(out of plane) 2.146(3)/
2.062(9) and 2.185(10) Å, Sn-O-N 102.5(8)/101.5(4)°, O-Sn-C(in plane) 99.6(10)/99.7(4)°,
O-Sn-C(out of plane) 108.1(6)/119.6(4)° and 116.6(4)°.
In tr od u ction
SiON angle of only 79.7(1)° in the crystal, but does not
undergo even weak intermolecular interactions as de-
tected in related systems such as ClH2SiNMe2.9 Theo-
retical treatment of ClH2SiONMe28 and related systems
showed that the Si‚‚‚N attraction cannot be attributed
solely to electrostatic interactions, and a better way to
rationalize the experimental facts is negative hyper-
conjugation between the lone pair at nitrogen and the
antibonding orbitals σ*(Si-Cl). It has also been found
that the strength of the Si‚‚‚N interaction is markedly
dependent on the electronic nature of the substituent
at silicon in anti position relative to the nitrogen atom.
Consequently we became interested in different ac-
ceptor centers, as elements such as tin with a higher
acceptor ability than silicon should show more pro-
nounced effects toward the donor center and hence lead
to stronger â-donor interactions. The larger radius of
tin, however, allows for accommodation of more atoms
in its first coordination sphere, which opens up the
possibility for further intermolecular contacts, as we
report now for the simplest methylated SnON com-
pound, Me3SnONMe2.
Indications for interactions between the atoms E and
N in E-C-N linkages (E ) Si, Ge, Sn; e.g., in Me3-
SnCH2NMe2), also named the R-effect, were concluded,
for example, from measurements of nitrogen basicities1
and rationalized in terms of a “closed type” three-center
bond caused by transitions of σ-electrons of the N atom
participating in the N-C bond into the empty d-orbitals
of the group 14 element.2 Structurally documented
examples for the existence of donor bonds between
geminal p-block donor and acceptor elements include
compounds with B-C-N,3 Al-CdN,4 and Al-N-N5
linkages.
Recently we have established the occurrence of donor
bonds for SiON6 and SiNN7 linkages. The most extreme
case in our hands is ClH2SiONMe2,8 which adopts a
* Corresponding author. E-mail: N.Mitzel@lrz.tum.de.
† Technische Universita¨t Mu¨nchen.
‡ Oregon State University.
(1) (a) Voronkov, M. G.; Feshin, V. P.; Mironov, V. F.; Mikhailyants,
S. A.; Gar, T. K.; Zh. Obshch. Khim. 1971, 41, 2211. (b) Voronkov, M.
G.; Kashik, T. V.; Lukevits, E. Y.; Deriglazova, E. S.; Pestunovich, A.
E.; Moskovich, R. Y. Zh. Obshch. Khim. 1974, 44, 2211.
(2) Rivie`re, P.; Rivie`re-Baudet, M.; Satge´, J . in:, Wilkinson, G. W.;
Stone, F. G. A.; Abel, E. W. Comprehenshive Organometallic Chemistry;
Pergamon Press: Oxford, 1982.
(3) Brauer, D. J .; Bu¨rger, H.; Buchheim-Spiegel, S.; Pawelke, G. Eur.
J . Inorg. Chem. 1999, 255.
(4) Uhl, W.; Schu¨tz, U.; Hiller, W.; Heckel, M. Chem. Ber. 1994, 127,
1587.
Resu lts a n d Discu ssion
Syn th esis. Me3SnONMe2 was prepared from lithi-
ated N,N-dimethylhydroxylamine and trimethylchlo-
rostannane in pentane and was isolated as colorless
(5) Uhl, W.; Hannemann, F. Eur. J . Inorg. Chem. 1999, 201.
(6) (a) Mitzel N. W.; Losehand, U. Angew. Chem., Int. Ed. Engl.
1997, 36, 2807. (b) Losehand, U.; Mitzel, N. W. Inorg. Chem. 1998,
37, 3175.
(8) Mitzel, N. W.; Losehand, U. J . Am. Chem. Soc. 1998, 36, 2807.
(9) Anderson, D. G.; Blake, A. J .; Cradock, S.; Ebsworth, E. A. V.;
Rankin, D. W. H.; Welch, A. J . Angew. Chem., Int. Ed. Engl. 1986, 25,
107.
(7) Mitzel, N. W. Chem. Eur. J . 1998, 4, 692.
10.1021/om990219q CCC: $18.00 © 1999 American Chemical Society
Publication on Web 06/15/1999

Hypercoordination at Tin
Organometallics, Vol. 18, No. 14, 1999 2611
F igu r e 2. Radial distribution and difference curve for the
electron diffraction refinement.
F igu r e 1. Molecular scattering intensity and final differ-
ence curves (vs model) as obtained by electron diffraction
of gaseous Me3SnONMe2.
liquid by fractionation through a series of cold traps in
vacuo. It was characterized by its IR and NMR spectra
(1H, 13C, 15N, 119Sn). The 15N NMR resonance at -252
ppm is shifted more than 40 ppm with respect to the
simplest aminoxyosilane H3SiONMe2 (-210 ppm),6 but
there are no data for aminoxystannanes for a more
direct comparison. The 119Sn NMR resonance is split
into a decet proving the identity of the SnMe3 group.
Ga s-P h a se Str u ctu r e Deter m in a tion . The high
volatility of Me3SnONMe2 allowed the determination of
the molecular structure in the gas-phase by electron
diffraction. The usual limitations in the refinement of
gas-phase structures were overcome by augmenting the
diffraction data by restraints derived from ab initio
optimizations of the geometry (MP2/DZ(P)) in a com-
bined and extended application of Bartell’s method of
predicate values10 and Scha¨fer’s MOCED method,11 also
called SARACEN.13
The molecular framework and atom-numbering scheme
for Me3SnONMe2 are shown in Figure 3A. The math-
ematical model for the least-squares refinement was
defined in Cs symmetry, with seven bond lengths: Sn-
O, Sn-C7, Sn-C6, O-N, N-C, and two C-H distances
for the methyl groups bound to tin and nitrogen. The
differences between the C-H distances within these
groups were fixed to the values obtained from ab initio
calculations at the MP2/DZ(P) level of theory. Angle
parameters were O-Sn-C7, O-Sn-C6, Sn-O-
N, O-N-C, C-N-C, and C-Sn-C and the angles
Sn-C(7)-H, Sn-C(6)-H, and N-C-H as well as
the torsion angles τCSnCH and τCNCH, whereby the
differences in those parameters for the different hydro-
gen atoms were again fixed to calculated values. A total
of 18 parameters were refined under the action of eight
restraints defining the differences of parameters of
similar nature or absolute values in the case of hydrogen-
F igu r e 3. (A) Molecular structure of Me3SnONMe2 in the
gas phase as determined by electron diffraction. The arrows
show the deformation occurring upon incorporation of a free
molecule into the crystal, as indicated by a superposition
of one molecule from the solid state (dashed part). (B)
Aggregation of Me3SnONMe2 in the crystal as determined
by low-temperature X-ray crystallography.
defining parameters. The parameter and restraint
definitions are given in Table 2; the uncertainties are
based on experience of the reliability of those calcula-
tions. A total of 24 amplitudes of vibration were refined
concurrently, representing all amplitudes belonging to
pairs of scatterers with a contribution of more than 5%
of the scattering of the Sn-O pair. Most of these
amplitudes were subject to restraints, either absolute
or ratios between related amplitudes, with the values
taken from a force field computed at the SCF/DZ(P) level
of theory and transformed into amplitudes by means of
(10) Bartell, L. S.; Romenensko D. J .; Wong, T. C. In Molecular
Structure by Diffraction Methods; Specialist Periodical Reports; The
Chemical Society: 1975; Vol. 3, p 72.
(11) Klimkowski, V. J .; Ewbank, J . D.; v. Alsenoy, C.; Scha¨fer, L. J .
Am. Chem. Soc. 1982, 104, 1476.
(12) Blake, A. J .; Brain, P. T.; McNab, H.; Miller, J .; Morrison, C.
A.; Parsons, S.; Rankin, D. W. H.; Robertson, H. E.; Smart, B. A. J .
Phys. Chem. 1996, 100, 12280.
(13) Hedberg, L.; Mills, I. M. ASYM20, ASYM40, Programs for Force
Constants and Normal Coordinate Analysis, Version 3.0; Corvallis and
Reading: U.K., J une 1994. See also: Hedberg, L.; Mills, I. M. J . Mol.
Spectrosc. 1993, 160, 117.

2612 Organometallics, Vol. 18, No. 14, 1999
Mitzel et al.
Ta ble 1. Selected Geom etr ica l P a r a m eter Va lu es
[Å/d eg] for Me3Sn ONMe2
0.088 for the long camera distance and 0.058 for the
short camera distance data.
In the vapor the tin atom of Me3SnONMe2 is partially
hypercoordinate, as is indicated by the pronounced
deviation of its coordination geometry from an ideal
tetrahedral surrounding (Table 1, Figure 3). The
O-Sn-C angles of 99.6(10)° (in-plane angle) and
108.1(6)° (out-of-plane angle) reflect the sterical require-
ment of the approaching nitrogen donor center at a
2.731(14) Å distance to the tin atom. Such a deformation
of the tin coordination is absent in triorganotinoxides,
e.g., [(PhCH2)3Sn]2O,14 due to the inability of the tin
center to form such interactions with geminal donor
atoms. The Sn-O-N angle is 102.5(8)°, which is
significantly compressed with respect to the related tin
alkoxides (or distannoxanes),15 which generally have
Sn-O-C angles much greater than the tetrahedral
angle. In the isopropoxytin fragment Me2CHOSn, which
is isoelectronic to the Me2NOSn unit, the Sn-O-C
angles are in the range of 128° (e.g., range of Sn-O-C
angles in iPrSn(OiPr)3 126.6(5)-129.5(3)°).16
A small Sn-O-N angle similar to that in Me3-
SnONMe2 was found in the closely related compound
cyclohexanonoximatotrimethylstannane (102.7°),17 but
here the tin atom adopts a typical trigonal bipyrami-
dal coordination OC3Sn‚‚‚O due to an intermolecular
Sn‚‚‚O contact. There are no gas-phase structures of
acyclic tin alkoxides,18 which limits the possibility for
further comparison.
The geometry predicted by ab initio calculations
(MP2/DZ(P)) in general is in satisfying agreement with
that refined on the electron scattering intensities (see
Table 1 for comparison). Due to the different nature of
the geometries (ra for the experimental results, re for
the calculated geometry), differences in interatomic
distances have to be expected. Differences in angles are
telling more about the suitability of the theoretical
method applied. The Sn-O-N angle is predicted more
than 3° smaller than found experimentally. This over-
estimation of the strength of the â-donor interaction has
been observed for various Si-O-N systems before19 and
seems to indicate the use of a too small basis set. Similar
deviations occur in the O-Sn-C angles, with the
O-Sn-C(6) angle predicted 3.6° larger than determined
experimentally. However, if three standard deviations
are taken into consideration, the significant deviations
in angles are all less than 1°, showing the calculations
to be of sufficient quality although not perfectly repro-
ducing the experimental facts.
GED
gas-phase
ab initio
MP2/DZ(P)
XRD
solid-state
Sn-O
2.006(3)
2.148(4)
2.146(3)
2.731(14)
1.468(6)
1.452(4)
102.5(8)
99.6(10)
1.983
2.140
2.138
2.661
1.480
1.464
99.4
103.2
108.7
104.9
2.063(6)
2.163(14)
2.062(9)/2.185(10)
2.745(9)
1.440(9)
Sn-C6
Sn-C(7/8)
Sn‚‚‚N
O-N
N-C(4/5)
N-O-Sn
O-Sn-C6
1.423(12)/1.436(11)
101.5(4)
99.7(4)
O-Sn-C(7/8) 108.1(6)
O-N-C 106.5(8)
119.6(4)/116.6(4)
106.6(6)/107.2(6)
Ta ble 2. In d ep en d en t P a r a m eter s a n d Restr a in ts
for th e GED Refin em en t of Me3Sn ONMe2
no.
parameter
value
restraint
p1
p2
p3
p4
p5
p6
p7
p8
Sn-O
2.006(3)
2.146(3)
2.148(4)
1.468(6)
1.452(4)
1.103(4)
1.106(3)
108.1(6)
99.6(10)
102.5(8)
106.5(8)
107.3(18)
109.3(10)
111.2(8)
109.4(12)
108.4(9)
176.4(49)
-176.7(38)
Sn-C7
Sn-C6
O-N
p3 - p2 ) 0.002(5)
p5 - p4 ) -0.016(10)
p7 - p6 ) 0.004(5)
N-C
C-H(N)
C-H(Sn)
OSnC(7)
OSnC(6)
Sn-O-N
O-N-C
C-N-C
C-Sn-C
SnCH(7)
SnCH(6)
NCH
p9
p10
p11
p12
p13
p14
p15
p16
p17
p18
p14 ) 112.0(10)
p15 - p14 ) -1.4(10)
p16 ) 108.8(10)
p17 ) 176.9(50)
p18 ) -177.3(50)
τCSnCH
τCNCH
Ta ble 3. Selected Dista n ces, Am p litu d es, a n d
Am p litu d e Restr a in ts for th e GED Refin em en t of
Me3Sn ONMe2
no.
atom pair
distance
amplitude
restraint
d1
d2
Sn1-O2
Sn1-C6
2.006(3)
2.148(4)
0.053(4)
0.059(4)
u2/u1 )
1.18(12)
u3/u2 )
1.00(10)
d3
Sn1-C7
2.146(3)
0.057(3)
d4
d5
O2-N3
N3-C4
1.468(6)
1.452(4)
0.052(3)
0.055(3)
u5/u4 )
1.03(10)
d6
d7
d8
d9
C4-H9
1.103(4)
2.73(14)
0.085(2)
Sn1‚‚‚N3
O2‚‚‚C6
O2‚‚‚C7
O2‚‚‚C4
C6‚‚‚C7
C7‚‚‚C8
C4‚‚‚C5
Sn1‚‚‚C4
N3‚‚‚C6
N3‚‚‚C7
C6‚‚‚C4
C7‚‚‚C4
C7‚‚‚C5
Sn1‚‚‚H15
N3‚‚‚H9
Sn1‚‚‚H9
Sn1‚‚‚H10
Sn1‚‚‚H11
0.121(13)
0.125(23)
0.116(13)
0.073(7)
0.118(16)
0.137(26)
0.071(12)
0.165(8)
0.108(16)
0.227(46)
0.220(28)
0.236(35)
0.317(58)
0.153(13)
0.110(19)
0.248(48)
0.198(32)
0.177(28)
0.101(20)
0.132(26)
0.121(24)
0.065(13)
0.136(27)
0.135(27)
0.066(13)
0.141(28)
0.117(23)
0.237(47)
0.199(40)
0.255(51)
0.316(63)
0.124(25)
0.101(20)
0.248(50)
0.188(38)
0.181(36)
3.175(23)
3.363(14)
2.340(13)
3.631(17)
3.501(22)
2.338(28)
3.754(13)
4.451(19)
3.488(24)
5.297(23)
4.848(23)
3.913(32)
2.724(17)
2.082(13)
3.614(31)
4.556(21)
4.240(38)
d10
d11
d12
d13
d14
d15
d16
d17
d18
d19
d20
d21
d22
d23
d24
Cr ysta l Str u ctu r e Deter m in a tion . We were suc-
cessful in growing a single crystal of liquid Me3-
SnONMe2 by in situ methods, which allows a compari-
son of the gas-phase and solid-state geometries and thus
to identify phase-related changes. Upon incorporation
of the Me3SnONMe2 molecules into the monoclinic
(14) Glidewell, C.; Liles, D. C. Acta Crystallogr., Sect. B 1979, 35,
1689.
(15) Vilkov, L. V.; Tarasenko, N. A. Zh. Strukt. Khim./ J . Struct.
Chem. (Engl. Transl.) 1969, 10, 1102/979.
(16) Reuter, H.; Schro¨der, D. J . Organomet. Chem. 1993, 455, 83.
(17) Ewings, P. F. R.; Harrison, P. G.; King, T. J .; Phillips, R. C.;
Richardson, J . A. J . Chem. Soc., Dalton Trans. 1975, 1950.
(18) Vogt, J .; Mez-Starck, B.; Vogt, N.; Hutter, W. MOGADOC-A
database for gasphase molecular spectroscopy and structure, Univer-
sita¨t Ulm, 1999: J . Mol. Struct., in press.
the program ASYM40.13 These amplitudes and re-
straints are given in Table 3. The quality of the
refinement can be assessed from the residuals in the
molecular scattering curves (Figure 1) and the radial
distribution curve (Figure 2). The final R factors were
(19) Mitzel, N. W.; Blake, A. J .; Rankin, D. W. H. J . Am. Chem.
Soc. 1997, 119, 4143.

Hypercoordination at Tin
Organometallics, Vol. 18, No. 14, 1999 2613
Ta ble 4. Cor r ela tion Ma tr ix Elem en ts (× 100) w ith
Absolu te Va lu es Gr ea ter th a n 50 for th e
Lea st-Squ a r es Refin em en t of th e Ga s-P h a se
Str u ctu r e of Me3Sn ONMe2
crystal lattice, the coordination geometry at tin changes
substantially due to the formation of an additional
intermolecular Sn‚‚‚O contact of 2.998(10) Å length
(Figure 3B). A trigonal pyramid is made up of the atoms
of the SnC3O unit and is further weakly coordinated:
intramolecularly to the nitrogen center and intermo-
lecularly to the oxygen atom of a neighboring molecule.
It is possible to describe this type of 4+2 coordination
as a trigonal bipyramid, with one axial substituent
replaced by two weak contacts. As the involvement of a
â-donor center is uncommon and most of the sterically
nonovercrowded triorganooxostannanes are aggregated
in chains with the two oxygen atoms occupying the axial
positions of a trigonal bipyramid, this coordination mode
of tin in Me3SnONMe2 is unprecedented. It is also
noteworthy that the primarily coordinate oxygen atom
occupies an equatorial position of the trigonal pyramid,
rather than an axial, as is commonly found in trimeth-
ylstannyl halides20 and other SnC3O2 units. Only for
compounds with chelating ligands have oxygen atoms
been found in axial positions in the trigonal SnC3O2
bipyramids. Note that similar findings of axial site
occupancy by the least electronegative ligands in trigo-
nal bipyramidally coordinated compounds were recently
reported also for tetraoxyphosphoranes21 and pentaco-
ordinate spirophosphoranes.22
p4
p10
p11
p14
u7
u10
p5
-85
p11
p12
p14
p15
p18
u13
u20
-52
54
-63
-58
-59
100
-80
50
100
57
-58
-86
Exp er im en ta l Section
Gen er a l Con sid er a tion s. The experiments were carried
out using a standard Schlenk line or a vacuum line with
greaseless high-vacuum PTFE stopcocks, which is directly
attached to the gas cell in an FTIR spectrometer (Midac
Prospect FTIR). All NMR spectra were recorded at 21 °C on a
J EOL J NM-LA400 spectrometer in sealed tubes with C6D6 as
a solvent directly condensed onto the sample from K/Na alloy.
(N,N-Dim et h yla m in oxy)t r im et h ylst a n n a n e. n-Butyl-
lithium (0.96 g, 15 mmol, 1.6 M in hexane) was added dropwise
to a solution of 1.0 mL of N,N-dimethylhydroxylamine (0.86
g, 15 mmol) in 20 mL of pentane at -30 °C. The mixture was
stirred for 1 h at ambient temperature, and then the solvents
were removed in vacuo. The remaining salt was suspended in
20 mL of diethyl ether, and a solution of freshly sublimed
trimethylchlorostannane (3.0 g, 15 mmol) in 15 mL of diethyl
ether was added dropwise. The mixture was stirred for 1 h.
All volatile products were condensed into a trap (-196 °C),
and (N,N-dimethylaminoxy)trimethylstannane (1.01 g, 4.5
mmol, 30%) was isolated as a colorless liquid (mp ) -85 °C)
by fractionation through a series of cooled traps (-20, -78,
-196 °C) with the product retained in the trap held at -78
°C.
Interestingly only two O-Sn-C angles are widened
by slightly more than 8° as compared to the gas-phase
structure to accommodate the additional Sn‚‚‚O contact.
The third angle O(2)-Sn(1)-C(6) is almost unchanged
as is the Sn(1)-O(2)-N(3) angle; that is, the strength
of the â-donor attraction between tin and nitrogen atoms
is not altered by the change of the coordination geometry
at the tin atom. This bears witness to the importance
of even weak intermolecular contacts between donor
centers and metal atoms for the structural chemistry
of organometallic compounds.
1
1H NMR: δ ) 0.23, 2.50. 13C NMR: δ ) -5.0 (q, J CH ) 30
1
3
Hz), 51.9 (qq, J CH ) 133 Hz, J CNCH ) 6 Hz). 15N{1H} NMR:
δ ) -252. 119Sn NMR: δ ) 106 (dec, J SnH ) 77 Hz). MS(Cl):
2
m/z ) 223 (M+), 163 (M+ - ONMe2). Anal. Calcd Me3SnONMe2
(223.89 g/mol): C 26.82, H 6.75, N 6.23. Found: C 26.44, H
6.62, N 6.19. IR: ν/cm-1 2990 s (ν CH), 2957 s (ν CH), 2865 s
(ν CH), 1142 m, 810 s, 770 s, 539 s.
Con clu sion
Electr on Diffr a ction Exp er im en t. Electron scattering
intensity data for Me3SnONMe2 were recorded on Kodak
Electron Image film using the Oregon State University dif-
fraction apparatus. Temperatures: inlet nozzle 52 °C, sample
34-48 °C. Diffraction experiments on CO2 were performed
concurrently for the purpose of wavelength calibration. Two
data sets from three and four exposures at camera distances
of 746.37 and 300.79 mm were recorded with wavelength
0.048942 Å and data ranges smin ) 2.0 to smax ) 16.4 and smin
) 8.0 to smax ) 36.0. Refinement: trapezoidal weighting
function: s1 ) 4.0, s2 ) 14.0 and s1 ) 10.0, s2 ) 30.8, scale
factors 1.050(10) and 1.130(21). Standard programs catered
for the data reduction and least-squares refinement,23 with the
scattering factors established by Fink and co-workers.24 The
refined molecular parameters, their definition and the applied
restraints, a list with selected interatomic distances including
vibrational amplitudes and applied restraints, and elements
of the correlation matrix are given in Tables 2, 3, and 4.
Cr ysta l Str u ctu r e Deter m in a tion for Me3Sn ONMe2. A
single cylindrical crystal (0.9 mm length, 0.3 mm diameter)
The present ab initio, GED and X-ray diffraction
study on Me3SnONMe2 provides insight into the step-
wise hypercoordination at tin, first through an intramo-
lecular â-donor interaction with the nitrogen center,
then through an intermolecular Sn‚‚‚O contact to give
a total coordination number of six, but in a new type of
coordination geometry. In this case two weak donor-
acceptor interactions can act in combination in a way
that resembles the action of one single donor ligand in
five-coordinate tin compounds, which is not comparable
to the established way of coordination sphere enlarge-
ment in tin chemistry. The large structural distortion
of the SnMe3 group upon formation of the weak Sn‚‚‚O
contact shows how limited our structural information
is, if only a single phase is studied, and how carefully
such results have to be interpreted. Only a combination
of gas-phase and solid-state structural methods allows
us to draw a more complete picture of hypercoordina-
tion.
(23) Mitzel, N. W.; Brain, P. T.; Rankin, D. W. H. ED96, Version
2.0; Edinburgh and Munich, 1998. A program developed on the basis
of formerly described ED programs: Boyd, A. S. F.; Laurenson, G. S.;
Rankin, D. W. H. J . Mol. Struct. 1981, 71, 217.
(24) Ross, A. W.; Fink, M.; Hilderbrandt, R. International Tables
for X-ray Crystallography; Wilson, A. J . C., Ed.; Kluwer Academic
Publishers: Dodrecht, Boston, 1992; Vol. C., p 245.
(20) Davies, A. G. Organotin Chemistry; VCH: Weinheim, 1997.
(21) Timosheva, N. V.; Chandrasekaran, A.; Prakasha, T. K.; Day,
R. O.; Holmes R. R. Inorg. Chem. 1996, 35, 6552.
(22) Koijma, S.; Takagi, R.; Akiba, K.-y. J . Am. Chem. Soc. 1997,
119, 5970.

2614 Organometallics, Vol. 18, No. 14, 1999
Mitzel et al.
was grown in situ by slowly cooling the melt sealed in a
capillary after generation of a suitable seed crystal: crystal
system monoclinic, space group Pn, Z ) 2, a ) 7.354(1) Å, b )
4.545(1) Å, c ) 13.720(1) Å, R ) 90°, â ) 95.55(1)°, γ ) 90°, V
) 456.4(1) Å3 at 163(2) K, cell from 96 reflections (θ-range 19-
24°), 2θmax ) 54°, ω-scan, 1290 independent reflections. Dif-
fractometer: Enraf-Nonius CAD4, Mo KR radiation, graphite
monochromator, Solution: Patterson methods.25 Refinement:
SHELXL97.26 No absorption correction applied. Non-hydrogen
atoms were refined with anisotropic thermal displacement
tions were undertaken at the SCF level using the 3-21G*,28-30
DZ(P)31 basis sets, while the larger basis set was used for
calculations at the MP2 level of theory. Vibrational frequency
calculations were performed from analytic first and second
derivatives up to the SCF/DZ(P) level of theory.
Ack n ow led gm en t. This work was supported by the
Bayerisches Staatsministerium fu¨r Wissenschaft, For-
schung und Kunst (Bayerischer Habilitationsfo¨rderpreis
1996 for N.W.M.), the Deutsche Forschungsgemein-
schaft, the Fonds der Chemischen Industrie, the Leon-
hard-Lorenz-Stiftung, the Leibniz-Rechenzentrum Mu¨n-
chen (computing time), and the National Science Foun-
dation under Grant CHE95-23581. Generous support
from Prof. K. Hedberg (Corvallis) and Prof. H. Schmid-
baur (Garching) is gratefully acknowledged.
parameters; hydrogen atoms were calculated in idealized
2
positions and refined with a riding model. Weight ) 1/[σ2(Fo
)
+ (0.052P)2 + 0.75P], where P ) (max(Fo2,0) + 2Fc2)/3. A total
of 73 parameters, R1 ) 0.0358 for 1283 reflections with Fo
4σ(Fo) and wR2 ) 0.1201 for all data.
>
Ab In itio Ca lcu la tion s. Ab initio molecular orbital calcu-
lations were carried out on an IBM SP2 parallel computer
using the Gaussian 94 program.27 Geometry optimizations
were performed at the SCF and MP2 levels of theory. Calcula-
Su p p or tin g In for m a tion Ava ila ble: Tables with crystal
data, atomic coordinates, and a full set of bond lengths and
angles for the crystal structure determination of Me3SnONMe2.
This material is available free of charge via the Internet at
http://pubs.acs.org.
(25) Sheldrick, G. M.; Dauter, Z.; Wilson, K. S.; Hope, H.; Sieker,
L. C. Acta Crystallogr. Sect. D 1993, 49, 18-23 (Patterson methods in
SHELXS-97).
(26) Sheldrick, G. M. SHELXL-97; Universita¨t Go¨ttingen, 1998. A
computer program for refinement of crystal structures.
OM990219Q
(27) Frisch, M. J .; Trucks, G. W.; Schlegel, H. B.; Gill, P. M. W.;
J ohnson, B. G.; Robb, M. A.; Cheeseman, J . R.; Keith, T.; Petersson,
G. A.; Montgomery, J . A.; Raghavachari, K.; Al-Laham, M. A.;
Zakrzewski, V. G.; Ortiz, J . V.; Foresman, J . B.; Cioslowski, J .;
Stefanov, B. B.; Nanayakkara, A.; Challacombe, M.; Peng, C. Y.; Ayala,
P. Y.; Chen, W.; Wong, M. W.; Andres, J . L.; Replogle, E. S.; Gomperts,
R.; Martin, R. L.; Fox, D. J .; Binkley, J . S.; Defrees, D. J .; Baker, J .;
Stewart, J . P.; Head-Gordon, M.; Gonzalez, C.; Pople J . A. Gaussian
94, Revision C.2; Gaussian, Inc.: Pittsburgh, PA, 1995.
(28) Binkley, J . S.; Pople, J . A.; Hehre W. J . J . Am. Chem. Soc. 1980,
102, 939.
(29) Gordon, M. S.; Binkley, J . S.; Pople, J . A.; Pietro, W. J .; Hehre,
W. J . J . Am. Chem. Soc. 1982, 104, 2797.
(30) Pietro, W. J .; Francl, M. M.; Hehre, W. J .; Defrees, D. J .; Pople,
J . A.; Binkley J . S. J . Am. Chem. Soc. 1982, 104, 5039.
(31) (a) Dunning, T. H. Unpublished work. (b) Dunning, T. H.; Hay,
P. L. In Modern Quantum Chemistry; Plenum: New York, 1976; pp
1-28.