Structures and spectroscopy of some adducts of coinage metal(I) cyanides with 'tetrahedral'-unidentate-N-bases

Article abstract of DOI:10.1002/zaac.200600317

Crystallization of copper(I) cyanide from piperidine ('pip') solution yields an adduct of CuCN:pip (3:4) ratio, as established by a single crystal X-ray structure determination, which also shows the complex to have a single-stranded ...Cu(CN)Cu(CN)...Spine (C,N scrambled), one-third of the copper atoms carrying a pair of pip ligands, the others only one. Crystallization of silver(I) cyanide from piperidine ('pip') or cyclohexylamine ('CyNH₂') solutions yields adducts of the unusual AgX : unidentate-N-base (1:2) stoichiometry. The CyNH₂ adduct is, unusually for cyanide complexes of this type, mononuclear with a trigonal planar silver atom, [(NC)Ag(H₂NCy)₂], the AgCN component lying along the intersection of two crystallographic mirror planes which bisect and relate the H₂NCy ligands (Ag-C, N 2.067(3), 2.335(2) A; N-Ag-N, C 80-80(6), 139.60(4)°). In the pip adduct, the immediate silver atom environment is also three-coordinate (Ag-C; N, N 2.080(1); 2.288, 2.443(1) A; N-Ag-N 88-34(4), N-Ag-C 144.47(4), 125.07(4), (E357.₉°) perturbed toward two-coordination, but the silver atom environment geometry is further perturbed from planarity by the parallel approach of an inversion-related molecule (Ag...C′ 2.926(1) A (Ag...Ag′ 3.1842(2)°°) forming a loose, albeit still discrete, dimer. Key features in the IR spectra of the above compounds and of AgCN:pip (1:1) and CuCN:CyNH₂ (2:3) are assigned and discussed in terms of the structures or of proposed structures in the case of the latter two adducts. The structure of [ClAg(pip)₃], adventitiously obtained, is also described (Ag-Cl 2.471(3); Ag-N 2.147(13), 2.188(7) (×2)A; Cl-Ag-N 96.1(3), 98.5(2), N-Ag-N 116.3(2) (×2), 122.1(3)°).

Full text of DOI:10.1002/zaac.200600317

DOI: 10.1002/zaac.200600317
Structures and Spectroscopy of some Adducts of Coinage Metal(I) Cyanides
with ’Tetrahedral’-Unidentate-N-Bases
Graham A. Bowmakera,*, Claudio Pettinarib, Brian W. Skeltonc, Neil Somersc, Nicholas A. Vigara, and
Allan H. Whitec
a Auckland/New Zealand, Department of Chemistry, University of Auckland
b
`
Camerino 62032/Italy, Dipartimento di Scienze Chimiche, Universita degli Studi
c Crawley 6009/Western Australia, School of Biomedical, Biomolecular and Chemical Sciences, Chemistry M313, The University of
Western Australia
Received November 21st, 2006.
˚
Abstract. Crystallization of copper(I) cyanide from piperidine
(‘pip’) solution yields an adduct of CuCN:pip (3:4) ratio, as
established by a single crystal X-ray structure determination,
N, N 2.080(1); 2.288, 2.443(1) A; N-Ag-N 88·34(4), N-Ag-C
144.47(4), 125.07(4), (Σ357.9°) perturbed toward two-coordination,
but the silver atom environment geometry is further perturbed from
planarity by the parallel approach of an inversion-related molecule
which also shows the complex to have
a single-stranded
˚
···Cu(CN)Cu(CN)···spine (C,N scrambled), one-third of the copper
atoms carrying a pair of pip ligands, the others only one. Crystalli-
zation of silver(I) cyanide from piperidine (‘pip’) or cyclohexyla-
mine (‘CyNH2’) solutions yields adducts of the unusual AgX:uni-
dentate-N-base (1:2) stoichiometry. The CyNH2 adduct is, unu-
sually for cyanide complexes of this type, mononuclear with a trigo-
nal planar silver atom, [(NC)Ag(H2NCy)2], the AgCN component
lying along the intersection of two crystallographic mirror planes
which bisect and relate the H2NCy ligands (Ag-C, N 2.067(3),
(Ag···CЈ 2.926(1) A (Ag···AgЈ 3.1842(2)°) forming a loose, albeit
still discrete, dimer. Key features in the IR spectra of the above
compounds and of AgCN:pip (1:1) and CuCN:CyNH2 (2:3) are
assigned and discussed in terms of the structures or of proposed
structures in the case of the latter two adducts. The structure of
[ClAg(pip)3], adventitiously obtained, is also described (Ag-Cl
2.471(3); Ag-N 2.147(13), 2.188(7) (x2) A; Cl-Ag-N 96.1(3),
98.5(2), N-Ag-N 116.3(2) (x2), 122.1(3)°).
˚
˚
2.335(2) A; N-Ag-N, C 80·80(6), 139.60(4)°). In the pip adduct, the
Keywords: Copper; Silver; Cyanides; Crystal structures; Infrared
immediate silver atom environment is also three-coordinate (Ag-C;
spectroscopy
Introduction
is the ‘tetrahedral’ base piperidine, ‘pip’, which, in some of
its complexes with, e.g., the coinage metal(I) (pseudo-)hal-
ides, MX (X ϭ Cl, Br, I, SCN), has yielded some novel
forms. Thus, e.g., silver(I) chloride [5] and thiocyanate [6]
form 1:2 complexes with it of the unusual ‘castellated’ poly-
mer type with pairs of ligands, L (ϭ pip), pendant from the
metal atoms of an ···MXMXMX··· spine, cf. the extended
form obtained with copper(I) thiocyanate with
···CuSCNCuSCNCuSCN··· spine [6]. In view of these un-
usual results we considered it to be of interest to crystallize
copper(I) and silver(I) cyanides from pip solution and
characterize any resulting products structurally and spectro-
scopically; we also record the nature of the complex ob-
tained with silver(I) cyanide from the (also) ‘tetrahedral’
base cyclohexylamine, ‘CyNH2’, and an adventitious prod-
uct from parallel studies, remarkably AgCl:pip (1:3).
In previous contributions we [1Ϫ3] and others [4] have ex-
plored structurally and spectroscopically the form of com-
plexes formed by crystallizing copper(I) and silver(I) cyan-
ides, MCN (M ϭ Cu, Ag) from solutions in or with unid-
entate nitrogen-donor bases, the nitrogen atom being either
tetrahedral (as in :NR3) or trigonal (as in aromatic bases,
notably derivatives of pyridine (‘py’)) in its environment.
Compounds thus delineated so far have been found to be
single-stranded polymers with -M-CN-M-CN-M-spines
(C,N not infrequently scrambled), the metal atom coordi-
nation number being increased to three or four by the coor-
dination of pendant base molecules, L, leading to gross
MCN:L (1:n) ratios having n in the range 1 to 2, not neces-
sarily integral if, e.g., some of the metal atoms in the chain
are three- and some four-coordinate. One important base
whose complexes of this type have not as yet been explored
Experimental Section
The metal(I) cyanide complexes were obtained by crystalli-
zation of the metal(I) cyanide from solution in the base, by
slow cooling and evaporation. On exposure to the atmos-
phere, they lost solvent/ligand more or less rapidly, so that,
generally, melting points are not recorded nor analyses at-
tempted, except as given below:
* Prof. Dr. G.A. Bowmaker
Department of Chemistry
University of Auckland
Private Bag 92019
Auckland/New Zealand
Fax: ϩ64 9 3737422
Email: ga.bowmaker@auckland.ac.nz
Z. Anorg. Allg. Chem. 2007, 633, 415Ϫ421
 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
415

G. A. Bowmaker, C. Pettinari, B. W. Skelton, N. Somers, N. A. Vigar, A. H. White
3
˚
˚
CuCN:cyclohexylamine (2:3): CuCN was dissolved in excess cyclo-
hexylamine in a Schlenk tube under nitrogen. The product was
collected by vacuum filtration and washed with absolute ethanol.
C20H39Cu2N5 (476.66 g molϪ1); C 50.8 (calc. 50.40); H 7.9 (8.25);
N 14.9 (14.69) %.
c ϭ 23.773(2) A, β ϭ 122.718(2)°, V ϭ 2772 A . Dc (Z ϭ 4) ϭ
1.460 g cmϪ3. µMo ϭ 23.1 cmϪ1; specimen: 0.42 x 0.25 x 0.08 mm;
ЈTЈmin/max ϭ 0.66. 2θmax ϭ 68°; N1 ϭ 21036, N ϭ 5446 (Rint
0.030), No ϭ 4305; R ϭ 0.024, Rw ϭ 0.031. Η∆ρmaxΗ ϭ 0.5(1) e A
ϭ
Ϫ3
˚
.
[(NC)Ag(H2NCy)2]. C13H26AgN3, M ϭ 332.2. Orthorhombic,
17
The samples used in the IR spectroscopic studies were prepared in
the above manner and some of them also in situ by adding an excess
of the liquid ligand to solid AgCN or CuCN, removing the excess
liquid, and then preparing the sample as a mull in the normal way.
In the case of AgCN:piperidine (1:2) and AgCN:cyclohexylamine
(1:2), samples were also prepared by direct absorption of ligand
vapour by solid AgCN. A weighed amount of AgCN in a glass
tube was placed in a Schlenk tube containing an excess of the liquid
ligand; the Schlenk tube was then closed, evacuated, and allowed
to stand. The mass of the final products confirmed that uptake of
2 mole of ligand per mole of CuCN had occurred, with the IR
spectra of these products confirming that they were indeed the
same as the compounds crystallized from the liquid ligand synth-
eses. On exposure to the air, or under vacuum, the AgCN com-
plexes lose ligand, and gravimetric studies of this process revealed
the intermediate formation of a complex of 1:1 ratio in the case
of cyclohexylamine, but not piperidine.
space group Cmcm (D , No. 63), a ϭ 6.6875(6), b ϭ 7.8979(7),
2h
c ϭ 26.828(2) A, V ϭ 1417 A . Dc (Z ϭ 4) ϭ 1.557 g cmϪ3. µMo
ϭ
3
˚
˚
14.1 cmϪ1; specimen: 0.65 x 0.20 x 0.03 mm; ЈTЈmin/max ϭ 0.79.
2θmax ϭ 75°; Nt ϭ 14763, N ϭ 2020 (Rint ϭ 0.036), No ϭ 1768;
R ϭ 0.030, Rw ϭ 0.038.
[(NC)Ag(pip)2]2. C22H44Ag2N6, M ϭ 608.4. Triclinic, space group
P1 (Ci , No. 2), a ϭ 7.4929(5), b ϭ 9.2242(7), c ϭ 10.3569(8) A,
α ϭ 86.356(2), β ϭ 70.970(2), γ ϭ 89.186(2)°, V ϭ 675.3 A . Dc
(Z ϭ 1 ‘dimer’) ϭ 1.496 g cmϪ3. µMo ϭ 14.7 cmϪ1; specimen: 0.55
x 0.45 x 0.35 mm; ЈTЈmin/max ϭ 0.75. 2θmax ϭ 75°; Nt ϭ 13587, N ϭ
6833 (Rint ϭ 0.018), No ϭ 6554; R ϭ 0.021, Rw ϭ 0.031.
1
˚
¯
3
˚
[ClAg(pip)3]. C15H33AgClN3, M ϭ 398.8. Monoclinic, space group
2
˚
P21/m (C2h, No. 11), a ϭ 5.509(7), b ϭ 17.063(5), c ϭ 10.204(3) A,
β ϭ 98.614(4)°, V ϭ 948.4 A . Dc (Z ϭ 2) ϭ 1.391 g cmϪ3. µMo
ϭ
3
˚
1.20 cmϪ1; specimen: 0.10 x 0.05 x 0.04 mm; ЈTЈmin/max ϭ 0.76.
2θmax ϭ 52°; Nt ϭ 8541, N ϭ 1756 (Rint ϭ 0.038), No ϭ 1422; R ϭ
0.052, Rw ϭ 0.072.
The normal product of the crystallization of silver(I) chloride from
pip is the 1:2 adduct described above [5]; in an (as yet, unrepro-
duced) unrelated experiment, crystals obtained from a solution of
[(PPh3)2AgCl(imidazole)] in piperidine unexpectedly proved to be
the 1:3 adduct; we take the opportunity to record its structure in
the present context also.
Variata. (x,y,z,Uiso)H were included constrained at estimates after
location of the relevant atoms in difference maps.
Spectroscopy
Infrared spectra were recorded at 4 cmϪ1 resolution room tempera-
ture as Nujol mulls between KBr plates on a Perkin Elmer Spec-
trum 1000 Fourier-transform infrared spectrometer. Far-infrared
spectra were recorded with 2 cmϪ1 resolution at room temperature
as pressed Polythene disks or petroleum jelly mulls between Poly-
thene plates on a Digilab FTS-60 Fourier-transform infrared spec-
trometer employing an FTS-60V vacuum optical bench with a 5
lines/mm wire mesh beam splitter, a mercury lamp source and a
pyroelectric triglycine sulfate detector. Fresh samples of the com-
plexes obtained from the preparative procedures described above
were used for all infrared spectroscopic studies.
Structure determinations
Full spheres of CCD area-detector diffractometer data were meas-
ured (Bruker AXS instrument, ω-scans; monochromatic Mo Kα
˚
radiation, λ ϭ 0.71073 A; T ca. 153 K) yielding Nt(otal) reflections,
merging to N unique (Rint cited) after ‘empirical’/multiscan absorp-
tion correction (proprietary software), No with F > 4σ(F) being
considered ‘observed’ and used in the full-matrix least squares re-
finements, refining anisotropic displacement parameter forms for
the non-hydrogen atoms, also (x,y,z,Uiso)H. Conventional residuals
R, Rw on ΗFΗ are cited at convergence (reflection weights: (σ2(F) ϩ
0.0004F2)Ϫ1); neutral atom complex scattering factors were em-
ployed within the Xtal 3.7 program system [7]. Pertinent results are
given below and in the Figures, the latter showing 50 % probability
displacement amplitude envelopes for the non-hydrogen atoms, hy-
Results and Discussion
Crystal Structures
˚
drogen atoms having arbitrary radii of 0.1 A; N,C components of
the cyanide groups were clearly defined in the silver(I) cyanide com-
plex structures by refinement behaviour, those for the copper(I)
cyanide derivative being modelled as scrambled, with composite
(C/N) form factor.
CuCN:pip (3:4)(ϱΗϱ). In previous studies of a similar nature
concerning adducts of copper(I) cyanide with unidentate
bases [1Ϫ3], adducts of the form ···(CuLl)(CN)(CuLm)-
(CN)(CuLn)(CN)··· have been described as single-stranded
polymers, wherein l, m, n take integral values, 1 or 2, and
CN may be ordered or scrambled end for end. Arrays struc-
turally characterized include l ϭ m ϭ n ··· ϭ 1 throughout
(L ϭ Et2NH, Et3N (aliphatic N), quinoline (aromatic N)),
l ϭ m ϭ n ϭ 2 throughout (L ϭ pyridine), l ϭ 1, m ϭ
2 (alternately) (2- and 4-methylpyridine). CuCN:pip (3:4),
described here is of a new type, still a linear polymer, with
scrambled CN as modelled, with the sequence of ligand
stoichiometries ···11211211···, the chain being propagated
by an inversion centre midway between the pair of copper
atoms bearing one ligand each and a 2-axis through the
Crystallographic data for the structures have been deposited with
the Cambridge Crystallographic Data Centre, CCDC 626492,
611586-611588. Copies can be obtained free of charge on ap-
plication to The Director, CCDC, 12 Union Road, Cambridge
CB2 1EZ, UK (Fax: int. code ϩ (1223)336-033; email for
inquiry:
fileserv@ccdc.cam.ac.uk;
email
for
deposition:
deposit@ccdc.cam.ac.uk).
Crystal/refinement Data
CuCN:pip (3:4)ϱΗϱ)
. C23H44Cu3N7, M ϭ 609.3. Monoclinic,
space group C2/c (C62h, No. 15), a ϭ 26.377(3), b ϭ 5.2533(5),
416
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Adducts of Coinage Metal(I) Cyanides with ’Tetrahedral’-Unidentate-N-Bases
Fig. 2 (a) Projection of a single molecule of [(NC)Ag(H2Ncy)2].
(b) Unit cell contents projected down a.
Fig. 1 (a) A sequence of the polymer strand of CuCN:pip (3:4).
(b) A section of the unit cell contents about x ϭ 0.5, showing the
stacking of adjacent hydrogen-bonded strands up b.
crystallized from a solution of silver(I) cyanide in cyclohex-
ylamine as AgCN:H2NCy (1:2). As well as being one of
the few adducts of silver(I) pseudo-halide:unidentate
N-base (1:2) structurally defined, it is also one of the few
adducts of AgCN:unidentate N-base (1:n) ratio so defined,
and only the second of 1:2 composition. Unlike
AgCN:quinoline(1:2), which is a single-stranded polymer
(···(quin)2Ag(CN/NC)(quin)2Ag···) with four-coordinate
silver atoms, linked by bridging cyanide, here the array, un-
usually, is discrete mononuclear [(NC)Ag(H2NCy)2)]. The
structure is of high symmetry, one quarter of the molecule
comprising the asymmetric unit of the structure; the mol-
ecule conforms to mm2 symmetry (C2v), with the AgCN
array (C,N assignment defined by refinement) lying along
the intersection of the two crystallographic mirror planes,
the NC···CH2 components of the cyclohexylamine also ly-
ing in one of the planes, which bisects the ligand. Ag-C,N
Table 1 Selected structural parameters, CuCN:pip (3:4)(ϱΗϱ)
(For N/C(1,2) read CN composite)
˚
Distances /A
Angles /°
Cu(1)-C(1)
Cu(1)-N(11)
N(1)-C(1)
1.923(2)
2.1838(9)
1.167(2)
N(11)-Cu(1)-C(1)
N(11)-Cu(1)-N(11i)
N(11i)-Cu(1)-C(1)
N(1)-Cu(1)-N(1i)
105.02(5)
93.56(4)
111.89(5)
125.04(6)
Cu(2)-C(2)
Cu(2)-N(21)
Cu(2)-N(1)
C(2)-N(2ii)
1.872(1)
2.146(1)
1.892(2)
1.158(2)
N(21)-Cu(2)-N(1)
N(1)-Cu(2)-C(2)
N(21)-Cu(2)-C(2)
100.08(6)
143.90(6)
116.00(6)
Transformations of the asymmetric unit: i x¯, y, 1/2Ϫz ii x¯, 2Ϫy, z¯
copper atom which carries two ligands (Fig. 1). Differences
in coordination about the copper atoms are in keeping with
expectations contingent upon the change from a three- to
a four-coordinate environment, most notably in respect of
metal-ligand atom distances and angles within the polymer
strand (Table 1). Contacts from the piperidine NH hydro-
gen atoms to the cyanide groups of adjacent polymer
˚
are 2.067(3), 2.335(2), C-N 1.162(5) A, with N-Ag-N,C be-
ing 80.80(6), 139.60(4), Ag-N-C(CyNH2) being 120.9(1)°,
the silver atom environment being trigonal planar (Fig.
2(a)). The molecules pack in sheets about z ϭ 0.25, 0.75,
normal to c (Fig. 2(b)), the amine-H..N(cyanide) distances
˚
related by the unit b translations being 2.71(3) A.
˚
strands are long (H···C/N ca. 2.8 A), but nevertheless ap-
AgCN:pip (1:2)(2). The counterpart adduct with piperi-
dine may, to a first approximation, be considered a mono-
mer also, one [(NC)Ag(pip)2] unit, devoid of crystallo-
graphic symmetry, making up the asymmetric unit of the
structure. Ag-C,N(11,21) are 2.080(1), 2.443(1), 2.2876(9),
pear instrumental in the formation of sheets of stacked
strands about x ϭ 0, 0.5 (Fig. 1(b)).
AgCN:CyNH2 (1:2). The results of the single crystal X-
ray study are consistent with the formulation of the material
Z. Anorg. Allg. Chem. 2007, 415Ϫ421
 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
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417

G. A. Bowmaker, C. Pettinari, B. W. Skelton, N. Somers, N. A. Vigar, A. H. White
Fig. 4 The time dependence of the composition of the solid for-
med during the addition of piperidine from the vapour phase to
solid AgCN (᭹) and during loss of piperidine from an AgCN:pipe-
ridine mixture (᭺) at ambient temperature.
˚
is 2.926(1) A, with little impact on Ag-C-N linearity;
˚
Ag···AgЈ is 3.1842(2) A. The organic rings here, as in all
the present complexes, are typical ‘chair’ arrays. The crystal
packing here is further influenced by stacking of the dimer
up a (Fig. 3(b)), consequent on interaction between the
amine hydrogen atoms and the cyanide nitrogen atoms
˚
(H(11,21)···N(x-1,y,z) 2.49(2), 2.33(3) A. Interestingly,
neither of the preceding pair of complexes complete the
connection to form a linear chain, although donor capa-
bility and steric accommodation do not appear to be im-
pediments to that.
Themogravimetry and Vibrational Spectroscopy
Since the complexes readily lose ligand upon exposure to
air, in most cases it was not possible to check the identity
and homogeneity of the bulk samples prepared for IR spec-
troscopy by the more usual melting point determinations or
elemental analysis. However, the composition of the bulk
samples was established in the case of the AgCN complexes
by gravimetric monitoring of the addition of ligand from
the vapour phase to a known amount of AgCN (see Exper-
Fig. 3 (a) Projection of the structure of [(NC)Ag(pip)2]2, showing
imental Section). The progress of the addition of piperidine
and cyclohexylamine to AgCN with time is shown in Fig-
ures 4 and 5. In both cases the addition of the ligand to the
solid proceeds up to the point where the reaction essentially
ceases, at 2 mol of ligand per mol of AgCN. This corre-
sponds to the composition of the solids obtained in the
crystallization of the adducts from liquid ligand solution
and characterized crystallographically (see above). Figures
4 and 5 show that the kinetics of absorption of the two
ligands are quite different. It has been noted in a previous
study of the rate of absorption of amine ligands by CuCN
that the rate of addition seems to be a sensitive function of
the particular ligand involved [2].
the loose dimer formation.
(b) Projection of the unit cell contents down b.
˚
C-N 1.152(2) A. N-C-Ag is 177.2(1), with C-Ag-N(11,21)
125.07(4), 144.47(4) and N(11)-Ag-N(21) 88.34(4)°. The
pair of Ag-N interactions are thus less symmetrical than in
the AgCyNH2 counterpart, with a two-coordinate tendency
evident. The angle sum about the silver atom is 357.9°,
slightly perturbed from planarity, away from the approach
of an inversion-related molecule, which with (necessarily)
parallel AgCN arrays opposed in direction, may be re-
garded as precursive of dimer formation (Fig. 3(b)). Ag···CЈ
418
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Z. Anorg. Allg. Chem. 2007, 415Ϫ421

Adducts of Coinage Metal(I) Cyanides with ’Tetrahedral’-Unidentate-N-Bases
complexes are generally higher for bridging compared to
terminal CN groups, although there is some overlap in the
case of bridge bonding involving long Ag-C/N bonds [11].
This is illustrated by the result for AgCN:CyNH2 (1:2),
the value of ν(CN) (2104 cmϪ1) lying at the bottom end of
the range previously observed for terminal CN. The higher
value for AgNC:pip (1:2) (2112 cmϪ1) is also in the range
appropriate for terminal CN, in agreement with the crystal
structure, which shows only a weak interaction between the
two monomer units within the dimer found in the crystal
structure (see above). The effect of the weak CN bridge
bonding within the dimer is perhaps evident from the fact
that that the ν(CN) value is higher in this compound, de-
˚
spite the fact that the Ag-C bond is longer (2.080(1) A) than
˚
that in the corresponding piperidine complex (2.067(3) A).
A previous study clearly showed a decrease in ν(CN) with
increasing Ag-C, so the increase observed in the present
case is attributable to the additional weak AgϪC interac-
Fig. 5 The time dependence of the composition of the solid for-
med during the addition of cyclohexylamine from the vapour phase
to solid AgCN (᭹) and during loss of piperidine from an AgCN:
cyclohexylamine mixture (᭺) at ambient temperature.
˚
tion (2.926(1) A). This is quite a different type of interac-
tion to that involved in the linear Ag-CN-Ag bridge bond-
ing, which would be expected to produce a much greater
increase in ν(CN) [11]. No X-ray structural data could be
obtained for the complex AgCN:CyNH2 (1:1) that is
formed following the thermal dissociation of the (1:2) com-
plex, but its IR spectrum (Table 2) clearly shows that it is a
distinct compound. The ν(CN) frequency (2111 cmϪ1) is in
the range that could correspond to terminal CN bonding
with a short Ag-C bond, or to bridge CN bonding with
considerably longer Ag-C/N bonds [11]. The latter possibil-
ity can be ruled out on the basis of the observed value of
the ν(AgC) frequency (see below), and the close similarity
in the ν(CN) values for Ag(CN):pip (1:2) and
AgCN:CyNH2 (1:1) suggests that the structures are simi-
lar, with one of the amine ligands on each silver atom in
the dimer absent in the latter case. This proposed structure
gains some credibility from the fact that it results from a
simple extrapolation of the unsymmetrical binding of the
two amine ligands that is observed in Ag(CN):pip (1:2),
driven by a tendency towards two-coordination of the silver
atom (see above).
The results of gravimetric studies of ligand loss from mix-
tures that initially had a 2:1 ratio of piperidine or cyclohex-
ylamine to AgCN are shown in Figures 4 and 5. In the case
of piperidine, the ligand is lost rapidly until only uncom-
plexed AgCN remains. However, in the case of cyclohexyl-
amine, the rate of ligand loss decreases abruptly at a mole
ratio of 1:1. This indicates the formation of an intermediate
complex of 1:1 ratio, and this was confirmed by IR spec-
troscopy (see below). The behaviour of piperidine is similar
to that observed previously for a number of pyridine bases,
whose AgCN complexes lost pyridine ligand without the
formation of intermediate complexes of lower ligand:
AgCN ratio [3]. The behaviour of cyclohexylamine, how-
ever, is more akin to that of ethylenediamine, which forms
a 1:1 complex with AgCN that is stable w.r.t. loss of ligand
[3]. This indicates that primary amines, such as cyclohexyl-
amine and ethylenediamine, may form complexes of con-
siderably higher stability with AgCN than do secondary or
tertiary amines.
The compound CuCN:pip (3:4) shows two ν(CN) bands
(2121, 2102 cmϪ1) which lie well within the range of fre-
quencies previously observed for Cu-CN-Cu bridge bond-
ing [12]. The observation of two bands is in agreement with
Assignments of selected bands in the IR spectra of the
CuCN and AgCN complexes are given in Table 2. It has
previously been shown that the ν(CN) frequencies in AgCN
Table 2 IR band assignments (wavenumbers/cmϪ1
)
Compound
ν(CN)
ν(NH)
ν(MC/N)
δ(MCN)
δ(NMC)
CuCNa)
CuCN:pip (3:4)
CuCN:CyNH2 (2:3)
CuCN:CyNH2 (1:2?)
2170
2121, 2102
2115
591
558
326
276, 253
299
168
184, 153
179
3294, 3249
3326, 3304, 3280, 3263
3330, 3292, 3281, 3255
2106, 2087
179
AgCNa)
AgCN:pip (1:2)
AgCN:CyNH2 (1:2)
AgCN:CyNH2 (1:1)
2168
2112
2104
2111
480
348
340
346
272
112
3278
3330, 3278
3316, 3266
a) Refs. [2, 3]
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419

G. A. Bowmaker, C. Pettinari, B. W. Skelton, N. Somers, N. A. Vigar, A. H. White
the crystal structure, which shows that there are two CN
bond lengths in the two 1:2 complexes in the present study.
The presence of
ν(AgC) band at 346 cmϪ1 in
groups in the asymmetric unit. The compound
CuCN:CyNH2 (2:3) shows a single ν(CN) band at
2115 cmϪ1, also in the range expected for Cu-CN-Cu bridge
bonding. Together with the 2:3 ratio of this complex, this
suggests a one dimensional chain polymer structure with
alternating three- and four-coordinate copper atoms, anal-
ogous to the previously published structure of CuCN:2-
methylpyridine (2:3) [2]. However, in contrast to the latter
compound, which contains two CN groups in the asymmet-
ric unit and two corresponding ν(CN) bands, the presence
of a single sharp band in CuCN:CyNH2 (2:3) suggests that
it has a smaller asymmetric unit, containing only one CN
group.
a
AgCN:CyNH2 (1:1) supports the loose dimer structure
proposed above for this compound. The far-IR spectra of
the CuCN complexes show some of the bands expected for
the CuCN chains found or proposed in the structures of
these compounds. Ligand bands obscure the regions where
some of the CuCN bands are expected. In all cases a strong
band due to N-Cu-C bending δ(N-Cu-C) was observed in
the range 150-190 cmϪ1. This band is characteristic of the
chain ϪCu-CN-Cu-CN- structure [2], and confirms the
presence of such chains in the structures of the CuCN com-
plexes.
N-H stretching bands ν(NH) were observed for all of the
complexes in the range 3250-3330 cmϪ1 (Table 2). Two
ν(NH) bands are expected for the NH2 group in cyclohexyl-
amine, and this is what is observed in AgCN:CyNH2 (1:2),
where the two cyclohexylamine ligands are crystallograph-
ically equivalent. The structure proposed above for
CuCN:CyNH2 (2:3) has two different cyclohexylamine
molecules in the structure (one on the three-coordinate cop-
per and two on the four-coordinate copper sites) and the
observation of four ν(NH) bands is consistent with this. In
an experiment to determine whether a complex of higher
cyclohexylamine content exists, the IR spectrum of a mull
of CuCN containing excess cyclohexylamine was obtained.
This also showed four ν(NH) bands, but at slightly different
frequencies to those of the 2:3 complex, and the ν(CN)
band, which occurs at 2115 cmϪ1 in the 2:3 complex, splits
into two bands at 2106, 2087 cmϪ1. The same spectrum re-
sulted from a mull of the 2:3 complex with excess cyclohex-
ylamine. This clearly indicates that a complex of higher
cyclohexylamine content does exist, and the ratio is tenta-
tively assigned as 1:2 (Table 2). The ν(CN) values are con-
sistent with a chain structure with bridging CN ligands
similar to that previously determined for CuCN:pyridine
(1:2) [2]. If this is the case, however, the asymmetric unit
must be more complex than that of the pyridine complex,
which comprises just one formula unit.
Coda
Crystal Structure of AgCl:pip (1:3). Recrystallization of sil-
ver(I) chloride from piperidine solution normally results in
the formation of AgCl:pip (1:2)(ϱΗϱ). It was therefore sur-
prising to find that solution of the structure of a tiny crystal
obtained during crystallization of [(Ph3P)2AgCl(imidazole)]
from piperidine, presumably in the presence of some excess
silver(I) chloride, showed it to be AgCl:pip (1:3). Although
not of comparable precision to the above determinations,
and as yet not having been reproducibly obtained by us,
there can be little doubt as to its authenticity, albeit ob-
One ν(NH) band is expected for the N-H group in piperi-
dine. In AgCN:piperidine (1:2) ν(NH) occurs at
3278 cmϪ1. Apparently the two inequivalent piperidine
molecules in the asymmetric unit, with significantly differ-
ent Ag-N bond lengths, are not sufficiently different to give
rise to a difference in the ν(NH) frequencies. This contrasts
with the situation in CuCN:piperidine (3:4), where there
are two different sets of piperidine sites in the structure (two
on the two three-coordinate copper and two on the four-
coordinate copper sites) and the observation of two ν(NH)
bands is consistent with this.
The far-IR spectra of the AgCN complexes show bands
that can be assigned to ν(AgC) of the terminal Ag-CN
groups. These occur in the range 340-350 cmϪ1 (Table 2).
Based on a previously determined correlation between
ν(AgC) and the bond length r(AgC) [2], this range corre-
sponds very well to that expected on the basis of the Ag-C
Fig. 6 (a) Projection of a molecule of [ClAg(pip)3].
(b) Projection of the unit cell contents down a.
420
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 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Z. Anorg. Allg. Chem. 2007, 415Ϫ421

Adducts of Coinage Metal(I) Cyanides with ’Tetrahedral’-Unidentate-N-Bases
tained under unusual/unexpected circumstances, providing
the first evidence of any capability to access any adduct
of AgCl:unidentate-N-base (1:3) ratio. The compound is a
discrete, molecular array (Fig. 6), one half of the molecule,
disposed with the silver and chlorine atoms in a crystallo-
graphic mirror plane (which bisects one of the pip ligands
and relates the other two), comprising the asymmetric unit
of the structure. Ag-Cl, N(11,21) are 2.471(3), 2.147(13),
metrically coordinated L3AgCl species, we find that in, e.g.
[(Ph3P)3AgCl] [10], Ag-Cl are typically ca. 2.54, 2.50, 2.50
for E ϭ P, As, Sb in quasi tetrahedral arrays, indicating that
the Ag-Cl interaction here, despite the planarity of the
AgN3 array, is significant.
References
[1] J. C. Dyason, P. C. Healy, L. M. Engelhardt, C. Pakawatchai,
V. A. Patrick, A. H. White, J. Chem Soc., Dalton Trans.
1985, 839.
[2] G. A. Bowmaker, K. C. Lim, B. W. Skelton, A. H. White, Z.
Naturforsch. 2004, 59b, 1264.
[3] G. A. Bowmaker, Effendy, P. C. Junk, B. W. Skelton, A. H.
White, Z. Naturforsch. 2004, 59b, 1277.
[4] D. T. Cromer, A. C. Larson, R. B. Roof, Acta Crystallogr.
1965, 19, 192.
[5] P. C. Healy, J. D. Kildea, A. H. White, Aust. J. Chem. 1988,
41, 417.
[6] G. A. Bowmaker, Effendy, W. Skelton, N. Somers, A. H.
White, Inorg. Chim. Acta 2005, 358, 4307.
[7] S. R. Hall, D. J. du Boulay, R. Olthof-Hazekamp (eds.), ‘The
Xtal 3.7 System’, University of Western Australia, 2001.
[8] G. A. Bowmaker, Effendy, K. C. Lim, B. W. Skelton, D. Sukar-
ianingsih, A. H. White, Inorg. Chim. Acta 2005, 358, 4342.
[9] U. Zachwieja, H. Jacobs, Z. Anorg. Allg. Chem. 1989, 571, 37.
[10] Effendy, J. D. Kildea, A. H. White, Aust. J. Chem. 1997, 50,
587.
[11] G. A. Bowmaker, Effendy, J. C. Reid, C. E. F. Rickard, B. W.
Skelton, A. H. White, J. Chem. Soc., Dalton Trans. 1998, 2139.
[12] G. A. Bowmaker, R. D. Hart, B. W. Skelton, A. H. White, Z.
Naturforsch. 2004, 59b, 1293.
˚
2.188(7) (x2) A, with Cl-Ag-N(11,21) 96.1(3), 98.5(2), and
N(21)-Ag-N(21Ј,11) 122.1(3), 116.3(2) (x2)°. The angle sum
between the nitrogen atoms about the silver atom being
354.6°, the aspect is, interestingly, of a quasi-trigonal planar
AgN3 array, perturbed by the approach of a chloride ion
(Fig. 6) successive molecules up a stack head-to-tail
(‘head’ ϭ Cl, ‘tail’ ϭ (NH)3), but the (N)H···Cl distance
˚
estimates are greater than 3 A.
Other 1:3 AgX···L complexes, with organic bases L and
X ϭ NO3, have unsymmetrical distributions of the coordin-
ating nitrogen atoms, with a tendency toward quasi-linear
coordination by a more dominant pair, together with nitrate
interactions of various strengths (e.g. [8]). Interestingly, the
most apt comparison with the present is found in the struc-
ture of AgNO3 :NH3 (1:3) [9], crystallizing in hexagonal
¯
¯
space group P62c, with the silver atoms, on sites of 6 symmetry,
stacked on the c axis at separations of (c ϭ 5.840(6)/2 ϭ)
˚
2.920 A, with three exactly trigonal planar coordinated
symmetry related ammonia ligands at 2.281(7) A, rather
˚
longer than the present values which are more typical of
those found in the two-coordinate systems. In other sym-
Z. Anorg. Allg. Chem. 2007, 415Ϫ421
 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
www.zaac.wiley-vch.de
421