Homoleptic selenium cyanides: Attempted preparation of Se(CN)4 and redetermination of the crystal structure of Se(CN)2

Article abstract of DOI:10.1021/ic801011g

The preparation of Se(CN)₄ was attempted by the reaction of SeF₄ with Me₃SiCN at low temperatures. However, selenium tetracyanide could not be detected by NMR spectroscopy; instead, the decomposition product Se(CN)₂

Full text of DOI:10.1021/ic801011g

Inorg. Chem. 2008, 47, 7025-7028
Homoleptic Selenium Cyanides: Attempted Preparation of Se(CN)4 and
Redetermination of the Crystal Structure of Se(CN)2
Thomas M. Klapo¨tke,* Burkhard Krumm, and Matthias Scherr
Department of Chemistry and Biochemistry, Ludwig-Maximilian UniVersity of Munich,
Butenandtstr. 5-13(D), D-81377 Munich, Germany
Received April 28, 2008
The preparation of Se(CN)4 was attempted by the reaction of SeF4 with Me3SiCN at low temperatures. However,
selenium tetracyanide could not be detected by NMR spectroscopy; instead, the decomposition product Se(CN)2
was isolated and its crystal structure was redetermined. In the structure of Se(CN)2, layers are present with secondary
Se · · · N interactions. The structure of Se(CN)4 and its reductive decomposition reaction has been calculated at the
MP2 level of theory.
Introduction
logue, O(CN)2, probably only exists as an intermediate.6
Among other chalcogen compounds, selenium dicyanide was
discussed recently in the course of the σ-hole concept, and
the positive potential on the outer surface of the selenium
atom was investigated, explaining noncovalent interactions
with neighboring molecules.7
To the best of our knowledge, the only known homoleptic
pseudohalogenides of selenium and tellurium in the +IV
oxidation state are the binary tetraazides Te(N3)4 and
Se(N3)4,1 as well as the tellurium(IV) tetracyanide Te(CN)4.2
A number of reports, dealing with low-valent chalcogen
dicyanides in the oxidation state +II, E(CN)2 (E ) S, Se,
Te) exist,3 and crystal structures have been elucidated more
Experimental Section
4
4d,5
General Procedures. All manipulation of air- and moisture-
sensitive materials were performed under an inert atmosphere of
dry argon using flame-dried glass vessels or oven-dried plastic
equipment and Schlenk techniques.8 The selenium tetrafluoride was
handled in PFA vessels (perfluoralkoxy-copolymer) due to the
extreme sensitivity toward glass. For all NMR measurements of
those compounds, a 4 mm PFA tube was used, which was placed
into a standard 5 mm NMR glass tube. The solvent dichloromethane
was dried by standard methods and freshly distilled prior to use.
The compounds SeF4 (Galaxy Chemicals) and trimethylsilyl cyanide
(Sigma Aldrich) were used as received. Raman spectra were
recorded on a PerkinElmer 2000 NIR FT spectrometer fitted with
a Nd:YAG laser (1064 nm) as neat solids. NMR spectra were
recorded on a JEOL Eclipse 400 instrument, and chemical shifts
were determined with respect to external Me4Si (13C, 100.5 MHz),
MeNO2 (14N, 28.9 MHz), and Me2Se (77Se, 76.3 MHz).
than 40 years ago for S(CN)2 and Se(CN)2
and more
recently for Te(CN)2.2b The dicyanide of the lightest homo-
* To whom correspondence should be addressed. E-mail: tmk@cup.uni-
muenchen.de.
(1) (a) Klapo¨tke, T. M.; Krumm, B.; Scherr, M.; Haiges, R.; Christe, K. O.
Angew. Chem., Int. Ed. 2007, 46, 8686. (b) Klapo¨tke, T. M.; Krumm,
B.; Mayer, P.; Schwab, I. Angew. Chem., Int. Ed. 2003, 42, 5843. (c)
Haiges, R.; Boatz, J. A.; Vij, A.; Gerken, M.; Schneider, S.; Schroer,
T.; Christe, K. O. Angew. Chem., Int. Ed. 2003, 42, 5847.
(2) (a) Lentz, D.; Szwak, M. Angew. Chem., Int. Ed. 2005, 44, 5079. (b)
Klapo¨tke, T. M.; Krumm, B.; Galvez-Ruiz, J. C.; No¨th, H.; Schwab,
I. Eur. J. Inorg. Chem. 2004, 24, 4764.
(3) (a) Cataldo, F. Polyhedron 2000, 19, 681. (b) Jonkers, G.; De Lange,
C. A.; Noodleman, L.; Baerends, E. J. Mol. Phys. 1982, 46, 609. (c)
Jonkers, G.; Mooyman, R.; De Lange, C. A. Mol. Phys. 1981, 43,
655. (d) Austad, T.; Esperas, S. Acta Chem. Scand. 1974, A28, 892.
(e) Pierce, L.; Nelson, R.; Thomas, C. J. Chem. Phys. 1965, 43, 3423.
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1964, 704. (g) Aksnes, O.; Foss, O. Acta Chem. Scand. 1954, 8, 1787.
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58B, 2377. (j) Birckenbach, L.; Kellermann, K. Ber. Dtsch. Chem.
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10.1021/ic801011g CCC: $40.75  2008 American Chemical Society
Inorganic Chemistry, Vol. 47, No. 15, 2008 7025
Published on Web 07/09/2008

Klapo¨tke et al.
X-ray Crystallography. For Se(CN)2,9 an Oxford Xcalibur3
diffractometer with a CCD area detector was employed for data
collection using Mo KR radiation (λ ) 0.71073 Å). The structure
was solved using direct methods (SIR9710) and refined by full-
matrix least-squares on F2 (SHELXL11). All non-hydrogen atoms
were refined anisotropically. ORTEP plots are shown with thermal
ellipsoids at the 50% probability level.
Scheme 1. Reaction of SeF4 with Me3SiCN
Table 1. Comparison of Observed and Calculated Raman Frequencies
[cm-1] for Se(CN)2 (2); Raman Intensities in Parentheses are Relative
Intensities for the Experimental Intensities and are Given in Units of Å4
amu-1 for the Calculated Intensities; ip ) in phase, oop ) out of phase
Caution! The proposed selenium tetracyanide is expected to be
potentially hazardous. For safety precautions please see ref 1a.
Attempted Preparation of Se(CN)4. A solution of SeF4 (274
mg, 1.77 mmol) in CH2Cl2 (1 mL) was treated with Me3SiCN (710
mg, 7.16 mmol) at -50 °C. Upon dropwise addition of Me3SiCN,
a fizzling noise was noticeable. After 15 min stirring, a sample for
NMR spectroscopy was prepared and the spectrum was recorded
at -30 °C. In the 77Se NMR spectrum, no evidence was found for
1, only the resonance for one of the decomposition products
Se(CN)2 (2) was found. 2: 13C NMR (CH2Cl2, -30 °C) δ 92.8.
77Se NMR (CH2Cl2, -30 °C) δ 292. Raman: ν ) 2327 (86), 2310
mode description
calculated
observed
CNstretch, ip
CNstretch, oop
CSeCstretch, oop
CSeCstretch, ip
CSeCbend/scissors
CSeCwag
CSeCtwist
SeCNwag
SeCNtwist
2283 (125)
2270 (59)
540 (6)
522 (2)
441 (3)
2327 (86)
2310 (24)
550 (12)
534 (5)
443 (7)
359 (2)
344 (2)
327 (0.4)
288 (0.2)
105 (8)
112 (24)
reductive decomposition to selenium(II) dicyanide (2) and
cyanogen occurred, which could both be subsequently
identified (Scheme 1).
(24), 550 (12), 534 (5), 443 (7), 359 (2), 112 (24) cm-1
.
Computational Details. The calculations were carried out using
the program package G03W12 at the MP2 level of theory13 using
a cc-pVTZ14 for carbon and nitrogen and a MWB-28-ECP for
selenium15 with a (14s10p2d1f)/[3s3p2d1f] basis set.16
On the basis of 77Se NMR spectra, which were recorded
after the reaction mixture was stirred for 15 min at -50 °C,
no evidence for the formation of 1 was obtained. Instead, a
single resonance at δ ) 292 (CH2Cl2) was observed, which
was assigned to Se(CN)2 (2). The previously reported
chemical shift of δ ) 0.29 is definitely incorrect, as well as
the reported chemical shift for Se2(CN)2 (δ ) 0.45); both
values must be multiplied by the factor 1000, because these
values are reported in parts per thousand, and not in parts
per million, as stated.17
Results and Discussion
The reaction of SeF4 with 4 equiv of Me3SiCN in
dichloromethane as solvent at low temperatures did not yield
the desired product, selenium(IV) tetracyanide (1). Instead,
In the 19F NMR spectrum of the reaction mixture,
resonances corresponding to traces of SeF4 and SeOF2
(impurity in the sample of SeF4 used for synthesis), in
addition to the major resonance corresponding to Me3SiF,
could be detected. After removal of all volatile materials,
the formation of Se(CN)2 was also established by Raman
spectroscopy of the pale-yellow residue (Table 1). The
second decomposition product, cyanogen (CN)2, was identi-
fied by 13C NMR spectroscopy (δ ) 96.3 in CH2Cl2) by
comparison with an authentic sample (δ ) 95.2 in C6D6). A
broad resonance at δ ) -115 (CH2Cl2) is found in the 14N
NMR spectrum, which is assigned to cyanogen (authentic
sample of cyanogen: δ ) -111 in C6D6; Me3SiCN: δ )
-88 in CDCl3). The reported converted value of δ ) -8017
assigned for Se(CN)2 could not be confirmed.
The calculated structure (MP2/cc-pVTZ, Table 2) of 1
adopts a pseudo trigonal-bipyramidal arrangement with the
free valence electron pair occupying one equatorial position
and is shown in Figure 1.
The reductive decomposition of 1 (Scheme 1) yields an
energy difference for 2 and one molecule of cyanogen of
∆E ) -300.4 kJ mol-1. The calculation supports our
experimental findings for the instability of 1. Compared to
the value for the analogous tellurium compound (∆E )
-161.1 kJ mol-1), which was shown to be feasible at low
temperatures,2 the reductive decomposition is considerably
more favored in the case of 1.
(9) Crystallographic data for 2: C2N2Se, Mw ) 130.99, orthorhombic, space
group Pbca, a ) 8.632(5) Å, b ) 6.847(5) Å, c ) 12.8151(7) Å, V
) 757.4(7) Å3, Z ) 8, Fcalcd ) 2.297 g cm-3, µ ) 9.688 mm-1, θ
range 4.0-26.0°, T ) 200 K, reflns collected 2804 (Rint ) 0.0459),
Final R1 (2σ data) ) 0.0334, wR2 (all data) ) 0.0949.
(10) Altomare, A.; Cascarano, G.; Giacovazzo, C.; Guagliardi, A.; Moliterni,
A. G. G.; Burla, M. C.; Polidori, G.; Camalli, M.; Spagna, R. SIR97;
1997.
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Germany, 1997.
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Stefanov, B. B.; Liu, G.; Liashenko, A.; Piskorz, P.; Komaromi, I.;
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Nanayakkara, A.; Challacombe, M.; Gill, P. M. W.; Johnson, B.; Chen,
W.; Wong, M. W.; Gonzalez, C.; Pople, J. A. , Gaussian 2003
(ReVisison A.1); Gaussian Inc.: Pittsburgh, PA, 2003.
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1994, 100, 7410. (c) Kendall, R. A.; Dunning, T. H., Jr.; Harrison,
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7026 Inorganic Chemistry, Vol. 47, No. 15, 2008

Homoleptic Selenium Cyanides
Table 2. Computational Results for 1 and 2
Se(CN)2
Se(CN)4
point group
el. state
C2V
C2V
1A1
1A′
-E/a.u.
194.610124
0
40.82
1.842
379.814761
0
78.92
equatorial 1.854
ax. 2.066
NIMAG
zpe/kJ mol-1
d(SesC)/Å
d(CsN)/Å
<(CSeC)/°
1.176
94.9
equatorial 1.178
ax. 1.180
eq-eq 102.5
ax-ax 167.1
ax-eq 86.0
The same tendency regarding tellurium compounds being
more stable than selenium compounds with the same
substituents was observed previously for the analogous binary
azide species Te(N3)4 and Se(N3)4 and their anions.1
Because there are some ambiguities and contradictions
between the previously reported structural characterizations,
that is, different space group, atom distances and angles, we
redetermined the crystal structure of 2. Single crystals were
grown by slow evaporation of a dichloromethane solution
at ambient temperature. The compound crystallized in the
space group Pbca with 8 molecules in the unit cell and is
shown in Figure 2. Prior crystal structures of this compound
Se(CN)2 (2) have been published in 1963 by Hazell4d and
in 1966 by Linke and Lemmer.5 Whereas the first report
suggested the wrong space group (Cmca), in the second one
the space group Pbca was determined, which we can confirm.
In accordance to the previously reported findings, single
molecules of 2 are present, which are linked via secondary
Se · · · N interactions (Se1 · · · N1 2.813(9) and Se1 · · · N2
2.835(7) Å), and are significantly below the sum of the
selenium-nitrogen van der Waals radii (vdWr SeN 3.45
Å18).
Figure 2. Molecular structure of 2; selected bond lengths (Å) and angles
(deg): Se1-C1 1.862(7), Se1-C2 1.870(7), C1-N1 1.138(8), C2-N2
1.131(8), Se1-C1-N1 179.2(7), Se1-C2-N2 176.3(6), C1-Se1-C2
91.3(3), Se1 · · ·N1(i)/Se1(iV)· · ·N1 2.813(9), Se1 · · ·N2(ii)/Se1(iii)· · ·N2
2.835(7), with i ) 0.5 - x, -0.5 + y, z; ii ) 1.5 - x, -0.5 + y, z; iii )
1.5 - x, 0.5 + y, z; iV ) 0.5 - x, 0.5 + y, z.
These interactions are somewhat comparable to the previ-
ously reported interactions of 2.81/2.74 Å5 but significantly
longer than the earlier reported value of 2.35(10) Å.4d
A
theoretical report explained those relatively strong intermo-
lecular interactions with the σ-hole concept.7 Regions of
positive electrostatic potential on the outer surface of the
Figure 3. View of the layered structure of 2; only selected atoms are labeled
for clarity.
selenium atom, resulting from the strong electron-withdraw-
ing cyano groups, interact with the lone-pairs of the nitrogen
atom of a neighboring cyano group creating intermolecular
contacts. The Se-C distances are 1.862(7) (Se1-C1)/
1.870(7) Å (Se1-C2) and comparable to the reported
distance of 1.86(10) Å4d as well as the calculated value (1.86
Å)17 but considerably shorter than the afterward reported
values of 2.08/2.01 Å.5 The C-N distances (C1-N1
1.138(8)/C2-N2 1.131(8) Å) lie in-between the published
values (1.42(15) Å,4d 1.07/1.27 Å,5 calcd: 1.16 Å17) and are
comparable to the distances in the analogous tellurium
dicyanide (1.131(7)/1.149(7) Å2b). The Se-C-N angles are
close to linearity (Se1-C1-N1 179.2(7)°, Se1-C2-N2
Figure 1. Calculated structure of 1 (C2V) at the MP2/cc-pVTZ level of
theory; selected bond lengths (Å) and angles (deg): Se-Ceq 1.854, Ceq-Neq
1.178, Se-Cax 2.066, Cax-Nax 1.180, Ceq-Se-Ceq 102.50, Cax-Se-Cax
167.17, Se-Ceq-Neq 177.20, Se-Cax-Nax 170.60.
(18) Bondi, A. J. Phys. Chem. 1964, 68, 441.
Inorganic Chemistry, Vol. 47, No. 15, 2008 7027

Klapo¨tke et al.
176.3(6)°) and partly in good agreement with the published
values (177(6)°,4d 168/155°,5 calcd: 175°17). Again signifi-
cantly different is the C-Se-C angle (91.3(3)°), which is
the smallest compared to the other published results
(119(6)°,4d 99°,5 calcd: 97°17); however, the angle is widened
compared to the analogous Te(CN)2 (85.4°2b). Taking the
secondary Se · · · N interactions into account, the geometry
around the selenium atom can be described as distorted
square-planar with an N1(i)· · ·Se1 · · ·N2(ii) angle of 114.6(2)°
and the two lone-pairs of the selenium atom located above
and beneath that plane, respectively. This results in slightly
curled layers along the c axis with a distance of ap-
proximately 3.9 Å between those layers (Figure 3).
As a result of the different Se-C distances, Linke and
Lemmer4a concluded that a selenocyan cyanide, NC- +SeCN,
is formed, which they also suggested for the dicyanide of
the lighter homologue, S(CN)2. Our findings, with two nearly
equal Se-C distances, are in strong contrast to such an ionic
species, and we therefore conclude that two covalent Se-C
bonds are present in 2. The same situation with two covalent
bonds is also likely to be present in the structure of S(CN)2,
because the S-C values published by Emerson are also
nearly equal (1.736(15)/1.718(18) Å4b), in contrast to the
values of Linke and Lemmer (1.87/2.07 Å4a).
Acknowledgment. Financial support of this work by the
University of Munich, the Fonds der Chemischen Industrie,
and the Deutsche Forschungsgemeinschaft (KL 636/10-1)
is gratefully acknowledged.
Supporting Information Available: CIF file for 2. This material
is available free of charge via the Internet at http://pubs.acs.org.
IC801011G
7028 Inorganic Chemistry, Vol. 47, No. 15, 2008