A μ-1,1,1,3,3,3 azide anion inside a trigonal prism of silver centers

Article abstract of DOI:10.1002/(SICI)1521-3773(19981217)37:23<3268::AID-ANIE3268>3.0.CO;2-U

Layers of face- and edge-sharing trigonal Ag₆ prisms, of which half are filled with azide units, are contained in the novel compound AgN₃ · 2AgNO₃ (see structure). Pendant η¹-nitrate groups are attached to both sides of each layer.

Full text of DOI:10.1002/(SICI)1521-3773(19981217)37:23<3268::AID-ANIE3268>3.0.CO;2-U

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[5] B. Hasenknopf, J.-M. Lehn, N. Boumediene, A. Dupont-Gervais, A.
Van Dorsselaer, B. Kneisel, D. Fenske, J. Am. Chem. Soc. 1997, 119,
10956.
[6] O. Mamula, A. von Zelewsky, G. Bernardinelli, Angew. Chem. 1998
110, 301; Angew. Chem. Int. Ed. 1998, 37, 289; C. Provent, S. Hewage,
1,1,3), and tetradentate (m-1,1,3,3; m-
1,1,1,3).[8] Herein we report a novel com-
pound AgN3 ´ 2AgNO3 in which the azide
unit exhibits an unprecedented bridging
hexadentate (m-1,1,1,3,3,3) coordination
mode as an encapsulated species inside a
trigonal prism (Scheme 1).
The layer-type framework in AgN3 ´
2AgNO3 can be regarded as constructed
from a stacking of slant trigonal prisms
Scheme 1. Sche-
matic representa-
tion of the m-
1,1,1,3,3,3 coordi-
nation mode of
the azido ligand in
the Ag6 prisms of
AgN3 ´ 2AgNO3.
Á
G. Brand, G. Bernardinelli, L. J. Charbonniere, A. F. Williams, Angew.
Chem. 1997, 109, 1346; Angew. Chem. Int. Ed. Engl. 1997, 36, 1287.
[7] R. Krämer, J.-M. Lehn, A. De Cian, J. Fischer, Angew. Chem. 1993,
105, 764; Angew. Chem. Int. Ed. Engl. 1993, 32, 703.
[8] [n]mH is used as a short notation for helicates (H) and circular
helicates (cH). [n] indicates the number of metal ions, and m the
helicity (m ˆ 2 for a double helix, m ˆ 3 for a triple helix).
[9] F. W. Cagle, Jr., G. F. Smith, J. Am. Chem. Soc. 1947, 69, 1860.
[10] J. H. Baxendale, P. George, Trans. Faraday Soc. 1950, 46, 736.
[11] F. Basolo, J. C. Hayes, H. M. Neumann, J. Am. Chem. Soc. 1953, 75,
5102.
each composed of silver atoms at its vertices with azide units
imprisoned within half of them (Figure 1). The filled and
[12] The interconversion of glucan polymers between linear triple helix
and macrocycle forms was recently reported: T. M. McIntire, D. A.
Brant, J. Am. Chem. Soc. 1998, 120, 6909.
[13] Self-Organization. The Emergence of Order (Ed.: F. E. Yates),
Plenum, New York, 1987.
A m-1,1,1,3,3,3 Azide Anion inside a Trigonal
Prism of Silver Centers**
Guo-Cong Guo and Thomas C. W. Mak*
Dedicated to Professor George A. Jeffrey
on the occasion of his 83rd birthday
Azide compounds have been known for more than a
century and continue to attract much current interest.[1] The
field has undergone quite spectacular advances in the last
decade for three main reasons: 1) covalent inorganic azides
are potentially better explosives than lead azide, which is used
as a detonator;[2] 2) the m-azido bridging ligand is undoubtedly
one of the most versatile ingredients for the creation of new
materials with different magnetic properties, leading to an
intensive study of magnetostructural correlations in discrete
complexes as well as in polymeric one-, two-, and three-
dimensional systems;[3] 3) azido complexes can serve as
precursors in preparative materials chemistry as a source of
atomic nitrogen.[4] As a sequel to our study on the bonding
interaction between silver(i) atoms and the acetylenediide
Figure 1. Layer-type framework in AgN3 ´ 2AgNO3 built of filled and
empty trigonal prisms viewed along the b direction. The lengths [Š] of the
edges of a prism are shown. For clarity, the nitrate anions have been
omitted, and Ag N bonds are shown only for one of the encapsulated azide
ions. Selected bond lengths [Š] and angles [8]: Ag1 N3i 2.409(1), Ag1 N1
2.503(1), Ag2 N1 2.278(2), Ag2 N3ii 2.351(2), N1 N2 1.239(2), N2 N3
1.174(2); N2-N1-Ag(2) 122.09(15), N2-N1-Ag1 118.21(8), N3-N2-N1
179.4(2), N2-N3-Ag2iii 120.0(2), N2-N3-Ag1iv 119.80(7). Symmetry codes:
i: x, y,z ‡ 1/2; ii:
x
1, y,z ‡ 1/2; iii:
x
1, y,z 1/2; iv: x,y,z
1/2.
anion, C22 [5] we have turned our attention to the isoelectronic
,
cyanide ion CN ,[6] as well as the azide ion N3 , as these species
have been well studied together with N2 in comparative
substrate binding to the FeMo cofactor of nitrogenase.[7]
Up to now the known coordination modes of the azido
ligand in transition metal complexes are terminal monoden-
tate or bridging bidentate (m-1,1; m-1,3), tridentate (m-1,1,1; m-
hollow prisms are stacked on their trigonal faces to form a
zigzag column extending along the c direction. Such prismatic
columns share rectangular faces and edges alternately along
the a direction to generate a grooved slab, with pendant h1-
nitrate anions attached to Ag1 atoms on both sides (Figure 2).
In any filled trigonal prism, the Ag2 atoms and the encapsu-
lated azide unit all lie on the same mirror plane. The azide unit
in AgN3 ´ 2AgNO3 is linear and asymmetrical (N1 N2
1.239(2), N2 N3 1.174(2) Š), which is consistent with its
Raman spectrum. The terminal N atoms of the azide ligand
are each asymmetrically bound to two Ag1 and one Ag2
atoms (Ag1 N1 2.503(1), Ag2 N1 2.278(2), Ag1 N3
2.409(1), Ag2 N3 2.351(2) Š), and the bond angles Ag-N1-
N2 and Ag-N3-N2 lie in the range of 118.2 to 122.18. It is
[*] Prof. T. C. W. Mak, G.-C. Guo
Department of Chemistry, The Chinese University of Hong Kong
Shatin, New Territories, Hong Kong (China)
Fax: (‡86)852-260-35057
E-mail: tcwmak§cuhk.edu.hk
[**] This work was supported by Hong Kong Research Grants Council
Earmarked Grant CUHK 4179/97P and Direct Grant A/C 2060129 of
The Chinese University of Hong Kong.
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Angew. Chem. Int. Ed. 1998, 37, No. 23

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several times with de-ionized water, and temporarily stored in wet form in
the dark. Caution: AgN3 should never be dried or kept for a prolonged
period, and only a small quantity should be used in any chemical reaction.
AgN3 ´ 2AgNO3: Wet AgN3 was added to a concentrated aqueous solution
of AgNO3 (2 mL; about 40%) under stirring until saturated. The excess
amount of AgN3 was filtered off, and the solution was put into a desiccator
charged with P2O5. In the course of two days colorless crystals of AgN3 ´
2AgNO3 were obtained in nearly quantitative yield. The compound is
stable when immersed in its mother liquor; it is hygroscopic and slowly
decomposes in air, and explodes violently when heated.
Crystal structure analysis: A colorless crystal of dimensions 0.15 Â 0.20 Â
0.10 mm3 mounted inside a 0.3 mm Lindemann glass capillary was used for
data collection on a Rigaku RAXIS IIC imaging plate diffractometer using
graphite-monochromated MoKa radiation (l ˆ 0.71073 Š, rotating-anode,
50 kV, 90 mA). Thirty-one oscillation frames were taken in the range of
f ˆ 0 ± 1808 with Df ˆ 5.08 and 8 min exposure per frame. Crystal data for
AgN3 ´ 2AgNO3: Mr ˆ 489.66, orthorhombic, space group Ccm21 (No. 36),
a ˆ 5.871(1), b ˆ 13.351(3), c ˆ 9.397(2) Š, Vˆ 736.6(3) Š3, Tˆ 293 K, Z ˆ
3
1
4, 1calcd ˆ 4.416 gcm
,
F(000) ˆ 896, m(MoKa) ˆ 79.14 cm
, absorption
Figure 2. Crystal structure of AgN3 ´ 2AgNO3 viewed along the a direction.
The solid, cross-hatched and open circles represent Ag, N, and O atoms,
respectively.
corrections applied using ABSCOR, relative transmission factors in the
range 0.445 ± 1.0. A total of 1178 reflections were collected in the 2q range
4.0 ± 52.08 (0 ꢀ h ꢀ 6,
15 ꢀ k ꢀ 16,
11 ꢀ l ꢀ 11), yielding 653 unique
reflections (Rint ˆ 0.0911), 570 of which with I > 2s(I) were considered as
observed, 71 parameters, R(F2) ˆ 0.0733, Rw(F2) ˆ 0.1908, and GOF(F2) ˆ
1.155. The structure was solved by direct methods (SHELXS-86) and
refined by full-matrix anisotropic least squares on F 2 using the Siemens
SHELXTL-93 (PC Version) package of crystallographic software. Data
collected on another selected crystal did not lead to significantly improved
precision of the crystal structure determination. Further details of the
crystal structure investigation can be obtained from the Fachinformations-
zentrum Karlsruhe, D-76344 Eggenstein-Leopoldshafen, Germany (fax:
(‡49)7247-808-666; e-mail: crysdata@fiz-karlsruhe.de), on quoting the
depository number CSD-408802.
worthy of note that the Ag N distances, especially those
involving the Ag2 atom, are significantly shorter than that
found in an early study of AgN3 (2.56 Š).[9] The complete
encapsulation of the azide species inside an Ag6 polyhedron
may be denoted as N3 @Ag6, by analogy to C22 @Ag6,[5a]
[5b]
C22 @Ag7,[5c] C22 @Ag8,[10] and C22 @Ag9 that are found in
a series of complexes of silver acetylide with soluble silver
salts. The coordination mode of the present N3 ion differs
from those of other isoelectronic three-atom groups such as
CN22 , C43 , BN23 , and CBN4 , which were found to exist in
solid-state alkali and alkaline-earth compounds.[11]
Received: June 15, 1998 [Z11988IE]
German version: Angew. Chem. 1998, 110, 3460 ± 3462
It is interesting to compare the Raman spectra of NaN3,
AgN3, and AgN3 ´ 2AgNO3.[12] The azide unit of AgN3 ´ 2Ag-
NO3 exhibits both us and uas stretching vibrations that are
characteristic of a linear and asymmetrical structure. As
expected, uas(N3) in AgN3 ´ 2AgNO3 shifts to a higher wave-
number in comparison with that in AgN3, whereas a decrease
of us(N3) in the sequence NaN3 > AgN3 > AgN3 ´ 2AgNO3
may be reasonably rationalized in terms of increasing
metal !ligand p-back bonding.
Keywords: azides ´ clusters ´ coordination modes ´ N ligands
´ silver
[1] A. M. Golub, H. Kohler, V. V. Skopenko in Chemistry of Pseudoha-
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Two structural models have been considered for binding of
dinitrogen to the FeMo cofactor of nitrogenase:[13] the
substrate either binds externally to a Fe4 rhombus face of a
twisted form of the central Fe6 trigonal prism,[14] or lies
completely within the cavity.[15] The m6 coordination mode of
dinitrogen in the latter model, denoted as N2@Fe6, is
structurally analogous to the N3 @Ag6 unit in AgN3 ´ 2Ag-
NO3, and also somewhat resembles the [C22 @Agn, n ˆ 6 ± 9]
systems that exist in double salts of silver acetylide with
soluble silver salts.[5, 10] The fact that acetylene is one of the
longest established nitrogenase substrates and that C22 , which
has the same set of molecular orbitals as N2, exhibits a strong
tendency of being encaged inside an assembled silver poly-
hedron may be of relevance in understanding the binding and
weakening of N2 in the FeMo cofactor cavity.
Â
Mautner, R. Cortes, L. Lezama, T. Rojo, Angew. Chem. 1996, 108, 96 ±
Â
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5893 ± 5894; c) R. A. Fischer, H. Sussek, A. Miehr, H. Pritzkow, E.
Experimental Section
AgN3 was prepared by mixing aqueous solutions of sodium azide and silver
nitrate at room temperature.[16] The white precipitate was filtered, washed
Angew. Chem. Int. Ed. 1998, 37, No. 23
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3269

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species that would show novel mesogenic behavior. To this
end, we have prepared a number of 2,6-disubstituted pyr-
idines, such as 1 and 3 (Scheme 1), and allowed them to react
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Commun. 1998, 339 ± 340; b) G.-C. Guo, Q.-G. Wang, G.-D. Zhou,
T. C. W. Mak, Angew. Chem. 1998, 110, 652 ± 654; Angew. Chem. Int.
Ed. 1998, 37, 630 ± 632; c) G.-C. Guo, Q.-G. Wang, G.-D. Zhou,
T. C. W. Mak, unpublished results.
[6] G.-C. Guo, T. C. W. Mak, Angew. Chem. 1998, 110, 3296 ± 3299;
Angew. Chem. Int. Ed. 1998, 37, 3183 ± 3186.
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Schrauzer, G. W. Kiefer, P. A. Doemeny, H. Kirsh, J. Am. Chem. Soc.
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RO
RO
N
Cl
N
Pt
Pt
a
Cl
N
RO
OR
OR
OR
RO
1
[8] M. A. S. Goher, F. A. Nautner, Polyhedron, 1995, 14, 1439 ± 1446, and
references therein.
[9] a) J. I. Bryant, R. L. Brooks, J. Chem. Phys. 1971, 54, 5315 ± 5323;
b) C. D. West, Z. Kristallogr. 1936, 85, 421 ± 425.
2
[10] a) G.-D. Zhou, Acta Sinica Peking Univ. 1963, 9, 389. [In Chinese];
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Chemica Sinica 1990, 48, 232 ± 236. [In Chinese].
[11] H.-J. Meyer, Z. Anorg. Allg. Chem. 1991, 594, 113 ± 118, and
references therein.
R
O
R
H
O
N
Cl
Cl
OR
OR
OR
Pt
Pt
[12] Raman spectra of solid samples were measured on a Renishaw Raman
RO
a
Image Microscope System 2000: NaN3: nÄs(N3) 1361 cm 1, nÄas(N3)
Cl
Cl
N
1
N
inactive; AgN3: nÄs(N3) 1338, nÄas(N3) 2070 cm
; AgN3 ´ 2AgNO3:
O
H
RO
OR
uas(N3) 2079, us(N3) 1330 cm 1. The Raman spectrum of NaN3 is
consistent with D1h symmetry of the azide unit. However, the
literature assignment of a linear and symmetrical structure for the
azide unit in AgN3[9] is at variance with the present data, which clearly
indicate a linear and asymmetrical structure in both AgN3 and AgN3 ´
2AgNO3.
R
O
R
3
4
OR
Scheme 1. Synthesis of 2 and 4. a) K2[PtCl4], acetic acid. R ˆ n-C6H13
.
[13] J. B. Howard, D. C. Rees, Chem. Rev. 1996, 96, 2965 ± 2982.
[14] a) I. G. Dance, Aust. J. Chem. 1994, 47, 979 ± 990; b) I. G. Dance,
Chem. Commun. 1998, 523 ± 530.
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792 ± 794; b) K. K. Stavrev, M. C. Zerner, Chem Eur. J. 1996, 2, 83 ± 87.
[16] N. R. Thompson in Comprehensive Inorganic Chemistry Vol. 3 (Eds.:
with potassium tetrachloroplatinate under normal cycloplati-
nation conditions.[5] When we used pyridine 1 we isolated the
expected cycloplatinated product 2, formed by coordination
of the pyridine followed by intramolecular C H activation, in
high yield. However, when we used pyridine 3 we isolated a
very different product. The only product isolated (indeed, the
only product observed in the crude reaction mixture) was that
which forms from the intermolecular activation of a C H
bond, that is, 4. Complex 4 was isolated in reasonable yield
Â
J. C. Bailar, H. J. Emeleus, R. Nyholm, A. F. Trotman-Dickenson),
Pergamon, Oxford, 1973, Chap. 2, Section 2.10, p. 101.
1
and analyzed by H and 13C NMR spectroscopy and single-
crystal X-ray diffraction.
The X-ray crystal structure of 4 shows a number of
interesting features (Figure 1). A crystallographically im-
posed center of symmetry exists between the two platinum
and two chlorine atoms (Cl1) to give a flat rectangle, with the
other two chlorine atoms (Cl2) only 0.082(4) Š out of this
plane. The nitrogen-containing ring is at an angle of 38.62(24)8
to the plane defined by the Pt2Cl2 rectangle. Two extremes for
the bonding of this organic fragment to this rectangle are
illustrated in Scheme 2. The Pt C bond length of 1.951(9) Š is
very similar to the values observed for the Pt0 ± carbene
complex derived from 1,3-dimesitylimidazol-2-ylidene
(1.959(8) and 1.942(8) Š).[6] It is also similar to the length of
1.973(11) Š for the cationic PtIV ± carbene complex
[PtCl2{C(NHMe)(NHC6H4Cl)}(PEt3)2]ClO4,[7] and signifi-
cantly shorter than that in the non-carbene cycloplatinated
species [{PtCl(tBu2PCMe2CH2)}2] (2.062(6) Š)[8] or PtII ± Caryl
single bond lengths of 1.98 ± 2.02 Š in arylplatinum com-
plexes.[9, 10] Two shorter Pt C bonds have been reported: a
bond length of 1.82(6) Š for the platinum ± carbene complex
[{PtCl(tBuCH2COiPr)}2][11] (though given the relatively large
estimated standard deviations associated with this measure-
ment, this value is not significantly different from ours), and a
Inter- versus Intramolecular C H Activation:
Synthesis and Characterization of a Novel
Platinum ± Carbene Complex**
Gareth W. V. Cave, Andrew J. Hallett,
William Errington, and Jonathan P. Rourke*
Cyclometalation is a reaction that has been both widely
used[1, 2] and widely studied.[3, 4] Typically, the coordinating
moiety within a ligand forms a bond to a metal center, and
then intramolecular C H activation takes place to yield a
five- or six-membered chelate ring. In the course of our
studies, we sought to synthesize a number of cycloplatinated
[*] Dr. J. P. Rourke, G. W. V. Cave, A. J. Hallett, Dr. W. Errington
Department of Chemistry
Warwick University
Coventry CV47AL (UK)
Fax: (‡44)1203-524-112
E-mail: j.rourke@warwick.ac.uk
[**] This work was supported by the Engineering and Physical Sciences
Research Council (UK). We thank Johnson Matthey for the loan of
platinum salts.
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Angew. Chem. Int. Ed. 1998, 37, No. 23