Metal-metal interactions in platinum(II)/gold(I) or platinum(II)/silver(I) salts containing planar cations and linear anions

Article abstract of DOI:10.1021/ic048333a

The salts [Pt{C(NHMe)₂}₄][Au(CN)₂] ₂, [Pt{C(NHMe)₂}₄][Ag₂(CN) ₃][Ag(CN)₂], [Pt(en)₂][Au(CN)₂] ₂, [Pt(en)₂][Ag(CN)₂]₂, and [Pt(bipy)₂][Au(CN)₂]₂ have been prepared by mixing solutions of salts containing the appropriate cation with solutions of K[Au(CN)₂] or K[Ag(CN)₂]. Because the platinum atom in the cation is sterically protected, the structures of [Pt{C(NHMe)₂} ₄][Au(CN)₂]₂ and [Pt{C(NHMe)₂} ₄][Ag₂(CN)₃][Ag(CN)₂] reveal no close metal-metal interactions. Colorless crystals of [Pt(en) ₂][Au(CN)₂]₂ and [Pt(en)₂][Ag(CN) ₂]₂ are isostructural and involve extended chains of alternating cations and anions that run parallel to the crystallographic a axis, along with isolated anions. In the chains, the metal-metal separations are relatively short: Pt...Au, 3.1799(3) A; Pt...Ag, 3.1949(2) A. In [Pt(bipy)₂][Au(CN)₂]₂, each cation has axial interactions with the anions through close Pt...Au contacts [3.1735(6) A]. In addition, the anions are weakly linked through Au...Au contacts of 3.5978(9) A. Unlike the previously reported Pt/Au complex [Pt(NH₃)₄][Au(CN)₂]₂·1. 5H₂O, which is luminescent, none of the salts reported here luminesce.

Full text of DOI:10.1021/ic048333a

Inorg. Chem. 2005, 44, 3466−3472
Metal
−Metal Interactions in Platinum(II)/Gold(I) or Platinum(II)/Silver(I)
Salts Containing Planar Cations and Linear Anions
Jay R. Stork, Daniel Rios, David Pham, Vincent Bicocca, Marilyn M. Olmstead, and Alan L. Balch*
Department of Chemistry, UniVersity of California, DaVis, California 95616
Received November 24, 2004
The salts [Pt{C(NHMe)2}4][Au(CN)2]2, [Pt{C(NHMe)2}4][Ag2(CN)3][Ag(CN)2], [Pt(en)2][Au(CN)2]2, [Pt(en)2][Ag(CN)2]2,
and [Pt(bipy)2][Au(CN)2]2 have been prepared by mixing solutions of salts containing the appropriate cation with
solutions of K[Au(CN)2] or K[Ag(CN)2]. Because the platinum atom in the cation is sterically protected, the structures
of [Pt{C(NHMe)2}4][Au(CN)2]2 and [Pt{C(NHMe)2}4][Ag2(CN)3][Ag(CN)2] reveal no close metal−metal interactions.
Colorless crystals of [Pt(en)2][Au(CN)2]2 and [Pt(en)2][Ag(CN)2]2 are isostructural and involve extended chains of
alternating cations and anions that run parallel to the crystallographic a axis, along with isolated anions. In the
chains, the metal−metal separations are relatively short: Pt‚‚‚Au, 3.1799(3) Å; Pt‚‚‚Ag, 3.1949(2) Å. In [Pt(bipy)2]-
[Au(CN)2]2, each cation has axial interactions with the anions through close Pt‚‚‚Au contacts [3.1735(6) Å]. In
addition, the anions are weakly linked through Au‚‚‚Au contacts of 3.5978(9) Å. Unlike the previously reported
Pt/Au complex [Pt(NH3)4][Au(CN)2]2‚1.5H2O, which is luminescent, none of the salts reported here luminesce.
Introduction
were designed to bring the two metals into close proximity.6
The framework outlined in structure 1 shows a motif that is
Interactions between closed-shell d10 metal centers, espe-
cially with gold(I), have attracted considerable experimental
and theoretical attention.1,2 Such interactions are necessarily
weak and readily perturbed by local environmental effects.
Similarly, the pseudo-closed-shell d8 ions such as platinum-
(II) also show a proclivity to interact through weak Pt‚‚‚Pt
interactions. Such interactions are seen in dimeric complexes
such as Pt2(P2O5H2)4]4-;3 in the extended chain structures
present in a variety of salts of [Pt(CN)4]2-;4 and in double
salts such as Magnus’ green salt, [Pt(NH3)4][PtCl4].5
particularly well designed to allow the two metal centers to
be placed in close proximity.7-11 This motif provides for a
planar, four-coordinate environment for the d8 metal (M) and
a linear, two-coordinate environment for the d10 metal (M′).
In addition, a number of other bridging ligand arrangements
have been utilized to bring the two metal centers together.12-15
A number of heterobinuclear complexes that combine a
d8 metal center with a d10 metal center also have been
prepared. Most such complexes use bridging ligands that
* To whom correspondence should be addressed. E-mail: albalch@
ucdavis.edu.
(1) Pyykko¨, P. Angew. Chem., Int. Ed. 2004, 43, 4412.
(2) Schmidbaur, H. Gold: Progress in Chemistry, Biochemistry and
Technology; Wiley: New York, 1999.
(3) Roundhill, D. M.; Gray, H. B.; Che, C.-M. Acc. Chem. Res. 1989, 22,
55.
(4) Williams, J. M.; Schultz, A. J.; Underhill, A. E.; Carneiro, K. In
Extended Linear Chain Compounds; Miller, J. S., Ed.; Plenum Press:
New York, 1982; Vol 1, p 73.
(5) Caseri, W. R.; Chanzy, H. D.; Feldman, K.; Fontana, M.; Smith, P.;
Tervoort, T. A.; Goossens, J. G. P.; Meijer, E. W.; Schenning, A. P.
H. J.; Dolbyna, I. P.; Debije, M. G.; de Haas, M. P.; Warman, J. M.;
van de Craats, A. M.; Friend, R. H.; Sirringhaus, H.; Stutzmann, N.
AdV. Mater. 2003, 15, 125.
In this paper, we explore an alternate strategy for the
formation of situations in which a d8 metal center and a d10
(6) Crespo, O.; Laguna, A.; Ferna´ndez, E. J.; Lo´pez-de-Luzuriaga, J. M.;
Jones, P. G.; Teichert, M.; Monge, M.; Pyykko¨, P.; Runeberg, N.;
Schu¨tz, M.; Werner, H.-J. Inorg. Chem. 2000, 39, 4786-4792.
(7) Xia, B.-H.; Zhang, H.-X.; Che, C.-M.; Leung, K.-H.; Phillips, D. L.;
Zhu, N.; Zhou, Z.-Y. J. Am. Chem. Soc. 2003, 125, 10362.
(8) Balch, A. L.; Catalano, V. J.; Olmstead, M. M. Inorg. Chem. 1990,
29, 585.
(9) Balch, A. L.; Catalano, V. J.; Olmstead, M. M. J. Am. Chem. Soc.
1990, 110, 2010.
(10) McNair, R. J.; Nilsson, P. V.; Pignolet, L. H. Inorg. Chem. 1985, 24,
1935.
3466 Inorganic Chemistry, Vol. 44, No. 10, 2005
10.1021/ic048333a CCC: $30.25
© 2005 American Chemical Society
Published on Web 04/21/2005

Metal-Metal Interactions in Pt(II)/Au(I) or Ag(I) Salts
metal center might be combined. Here, we use simple ionic
interactions to bring the two components together by
examining the reactions of cationic d8 platinum(II) complexes
with anionic d10 gold(I) and silver(I) complexes, [Au(CN)2]-
and [Ag(CN)2]-. As long as ligand exchange reactions can
be avoided, this procedure should form salts of the type
[PtL4][M(CN)2]. Yet will the products have the metal centers
close together, or will they be widely separated?
An additional complication to this strategy arises from the
ability of the [Au(CN)2]- and [Ag(CN)2]- ions to self-
associate through aurophilic or argentophilic interactions.
Such interactions arise from a combination of relativistic and
correlation effects1 and generally result in metal-metal
separations that are less than ∼3.5 Å.16 The expected
separation based on the van der Waals radii of the ion is
3.4 Å.17 Whereas the majority of crystal structures of salts
containing [Au(CN)2]- and [Ag(CN)2]- show the linear
anions surrounded by cations,18 a number of examples are
known where these anions self-associate, even though
Coulombic repulsion needs to be overcome to allow such
self-association. Cases where self-association of [Au(CN)2]-
is observed crystallographically include examples where the
cation is a polypyridinium ion,19 a transition metal com-
plex,20-23 or a secondary ammonium ion.24 In many of these
examples, hydrogen bonding of the nitrogen atoms of the
anions with N-H functionalities on the cations occurs along
with self-association. Argentophilic interactions between
[Ag(CN)2]- ions unsupported by additional ligands occur in
Tl[Ag(CN)2].25
Figure 1. View of [Pt{C(NHMe)2}4][Au(CN)2]2 with 50% thermal
contours. This view shows the hydrogen bonded contacts of one cation
with neighboring anions. Selected interatomic distances (Å): Au-C1,
1.985(8); Au-C2, 2.000(8); N1-C1, 1.1155(11); N2-C2, 1.125(11); Pt-
C3, 2.060(8); Pt-C4, 2.048(8); C3-N3, 1.316(10); C3-N4, 1.337(9); C4-
N5, 1.333(10); C4-N6, 1.337(9). Selected interatomic angles (deg): C1-
Au-C2, 177.7(3), Au-C1-N1, 178.4(7); Au-C2-N2, 177.6(8); C3-Pt-
C4, 88.4(3); C3-Pt-C4A, 91.6(3), N3-C3-N4, 117.7(7); N5-C4-N6,
116.9(7).
lographic characterization of new salts that have a variety
of Pt‚‚‚Au, Au‚‚‚Au, and hydrogen-bonding interactions
between the ionic components.
Recently, this laboratory reported that the reaction of
[Pt(NH3)4]Cl2 and K[M(CN)2] produced luminescent crystals
of [Pt(NH3)4][M(CN)2]2. In this solid, the ions formed
columns with continuous ‚‚‚Au‚‚‚Pt‚‚‚Au‚‚‚Au‚‚‚Pt‚‚‚Au‚‚‚
chains that were cross-linked through additional Au‚‚‚Au
interactions.26 Here, we report the synthesis and crystal-
Results
[Pt{C(NHMe)2}4][Au(CN)2]2. Colorless crystals of
[Pt{C(NHMe)2}4][Au(CN)2]2 were obtained by mixing a
solution of [Pt{C(NHMe)2}4](PF6)2 in methanol with a
solution of K[Au(CN)2] in water. The infrared spectrum of
these crystals shows ν(CN) at 2143 cm-1 and bands at 3289
and 3343 cm-1 due to the N-H groups.
(11) Balch, A. L.; Catalano, V. J.; Noll, B. C.; Olmstead, M. M. J. Am.
Chem. Soc. 1990, 112, 7558.
(12) Canales, S.; Crespo, O.; Gimeno, M. C.; Jones, P. G.; Laguna, A.;
Mendizabal, F. Organometallics 2001, 20, 4812.
(13) Canales, F.; Gimeno, M. C.; Laguna, A.; Jones, P. G. Organometallics
1996, 15, 3412.
(14) Albinati, A.; Lehner, H.; Venanzi, L. M.; Wolfer, M. Inorg. Chem.
1987, 26, 3933.
(15) Ferna´ndez, E. J.; Gil, M.; Olmos, M. E.; Crespo, O.; Laguna, A.; Jones,
P. G. Inorg. Chem. 2001, 40, 3018.
(16) Jones, P. G. Gold Bull. 1986, 19, 46; 1983, 16, 114; 1981, 14, 159;
1981, 14, 102.
(17) Bondi, J. Phys. Chem. 1964, 68, 441.
(18) Liau, R.-Y.; Ehlich, H.; Schier, A.; Schmidbaur, H. Z. Naturforsch.
2002, 57b, 1085.
(19) Cramer, R. E.; Smith, D. W.; VanDoorne, W. Inorg. Chem. 1998, 37,
5895.
(20) Shorrock, C. J.; Xue, B.-Y.; Kim, P. B.; Batchelor, R. J.; Patrick, B.
O.; Leznoff, D. B. Inorg. Chem. 2002, 41, 6743.
(21) Leznoff, D. B.: Xue, B.-Y.; Batchelor, R. J.; Einstein, F. W. B.;
Patrick, B. O. Inorg. Chem. 2001, 40, 6026.
The asymmetric unit of [Pt{C(NHMe)2}4][Au(CN)2]2, as
determined by an X-ray crystal structure, consists of an anion
in a general position and one-half of a cation with its
platinum atom residing on a crystallographic center of
symmetry. Figure 1 shows a drawing of one cation and
neighboring anions with their dimensions given in the figure
caption. The structure of the cation is similar to that reported
earlier for [Pt{C(NHMe)2}4](PF6)2.27 The positioning of the
carbene ligands nearly perpendicular to the PtC4 plane
provides steric shielding of the platinum ion. Consequently,
there is no direct Pt‚‚‚Au interaction in this salt. The closest
contact between the platinum and gold centers is 5.136 Å.
The closest contact between [Pt{C(NHMe)2}4]2+ and
[Au(CN)2]- involves hydrogen bonds between the N-H
groups of the carbene ligands and the cyano groups of the
anions. These contacts connect a single cation to four
different anions in its vicinity as seen in Figure 1, although
to conserve space only two of these are shown in the drawing.
(22) Leznoff, D. B.: Xue, B.-Y.; Patrick, B. O.; Sanchez, V.; Thompson,
R. C. Chem. Commun. 2001, 259.
(23) Leznoff, D. B.: Xue, B.-Y.; Stevens, C. L.; Storr, A.; Thompson, R.
C.; Patrick, B. O.; Polyhedron 2001, 20, 1247.
(24) Stender, M.; Olmstead, M. M.; Balch, A. L.; Rios, D.; Attar, S. Dalton
Trans. 2003, 4282.
(25) Omary, M. A.; Webb, T. R,; Assefa, Z.; Shankle, G. E.; Patterson, H.
H. Inorg. Chem. 1998, 37, 1380.
(26) Stender, M.; White-Morris, R. L.; Olmstead, M. M.; Balch, A. L. Inorg.
Chem. 2003, 42, 4504.
(27) Goldberg, S. Z.; Eisenberg, R.; Miller, J. S. Inorg. Chem. 1977, 16,
1502.
Inorganic Chemistry, Vol. 44, No. 10, 2005 3467

Stork et al.
Figure 3. View of the extended chain of alternating cations and anions in
crystalline [Pt(en)2][Au(CN)2]2 with 50% thermal contours. Selected
interatomic distances (Å): Pt1‚‚‚Au1, 3.1799(3); Pt1-N1, 2.061(4); Pt1-
N2, 2.048(4); Au1-C3, 1.990(5), Au2-C4, 1.986(5). Selected interatomic
angles for [Pt(en)2][Au(CN)2]2 (deg): N1-Pt1-N2, 82.99(15); N1-Pt1-
N2A, 97.01(15). Crystals of [Pt(en)2][Ag(CN)2]2 have a similar structure.
Selected interatomic distances for [Pt(en)2][Ag(CN)2]2 (Å): Pt1‚‚‚Ag1,
3.1950(2); Pt1-N1, 2.060(2); Pt1-N2, 2.049(2); Ag1-C3, 2.070(3); Ag-
C4, 2.067(3) Å. Selected interatomic angles (deg): N1-Pt1-N2, 82.99-
(9); N1-Pt1-N2A, 97.01(9).
Figure 2. View of [Pt{C(NHMe)2}4][Ag2(CN)3][Ag(CN)2] with 50%
thermal contours. This view shows the hydrogen-bonded contacts of
one cation with the two types of neighboring anions. Selected inter-
atomic distances (Å): Ag1-N/CA, 2.070(4); Ag1-C2, 2.051(5); N/CA-
N/CB, 1.154(9); N2-C2, 1.150(6); Pt-C8, 2.043(4); Pt-C9, 2.048(5).
Selected interatomic angles (deg): N/CA-Ag-C2, 177.7(6); Ag-N/CA-
N/CB, 177.7(6); Ag1-C2-N2, 176.0(5); C8-Pt-C9, 88.98(17).
No luminescence has been detected from [Pt{C(NHMe)2}4]-
[Ag2(CN)3][Ag(CN)2].
Not only are there no direct Pt‚‚‚Au interactions in
[Pt{C(NHMe)2}4][Au(CN)2]2, but the anions are also widely
separated so that there are no short Au‚‚‚Au contacts in this
salt either.
Samples of [Pt{C(NHMe)2}4][Au(CN)2]2 are not lumines-
cent at room temperature and at 77 K.
[Pt{C(NHMe)2}4][Ag2(CN)3][Ag(CN)2]. Colorless crys-
tals of [Pt{C(NHMe)2}4][Ag2(CN)3][Ag(CN)2] were obtained
in a fashion similar to the procedure used to make
[Pt{C(NHMe)2}4][Au(CN)2]2. However, the product differs
in that two different anions, [Ag(CN)2]- and [Ag2(CN)3]-,
are present. Figure 2 shows a drawing of the cation and the
adjacent anions that are hydrogen bonded to the N-H groups
of the cation. The two different anions are nearly linear, as
expected. The bridging cyano group in [Ag2(CN)3]- is
disordered, as it is in [(dien)Cu(NC)Ag(CN)}]2[Ag2(CN)3]-
[Ag(CN)2].28 The [Ag2(CN)3]- ion is hydrogen bonded to
the N-H groups of a pair of the carbene ligands, and the
[Ag(CN)2]- ion is hydrogen bonded to the N-H group of
one ligand.
[Pt(en)2][Au(CN)2]2. Mixing a solution of [Pt(en)2]Cl2 in
water with an aqueous solution of K[Au(CN)2] produced
colorless crystals of [Pt(en)2][Au(CN)2]2. The infrared spec-
trum of these crystals shows ν(CN) at 2136 and 2144 cm-1
and bands at 3109, 3211, 3248, and 3292 cm-1 due to the
N-H groups.
The structure of [Pt(en)2][Au(CN)2]2 has been determined
by single-crystal crystallography. The asymmetric unit
consists of one-half of a cation and two separate half-anions.
The platinum and gold atoms all reside on centers of
symmetry. Figure 3 shows the extended chains of alternating
cations and anions (involving anion 1) that run parallel to
the crystallographic a axis. Within these chains, the Pt‚‚‚Au
distance is 3.1799(3) Å. The anion is shifted from an eclipsed
orientation with regard to the N-Pt-N bonds in the cation
so that the C3-Au1-C3A unit is turned by 16.2(2)° away
from the N1-Pt1-N1A unit.
The cations have a planar geometry that is entirely
consistent with prior structural data on related salts.29 The
anions are strictly linear because of the crystallographic
symmetry. In addition to the anion that makes up the
extended chains, there is another anion (anion 2) that is not
involved in any Pt‚‚‚Au or Au‚‚‚Au interactions. The relative
As in [Pt{C(NHMe)2}4][Au(CN)2]2, the steric constraints
of the cation preclude any direct Pt‚‚‚Ag interactions in
[Pt{C(NHMe)2}4][Ag2(CN)3][Ag(CN)2]. The anions are also
widely separated. Consequently there are no direct Ag‚‚‚Ag
interactions in this salt.
(28) Cernak, J.; Chomic, J.; Massa, W. Acta Crystallogr. C: Cryst. Struct.
Commun. 2002, 58, m490.
(29) Sato, S.; Haruki, M.; Kurita, S. Acta Crystallogr. C: Struct. Cryst.
Struct. Commmun. 1990, 46, 1107.
3468 Inorganic Chemistry, Vol. 44, No. 10, 2005

Metal-Metal Interactions in Pt(II)/Au(I) or Ag(I) Salts
Figure 4. Drawing of the unit cell for [Pt(en)2][Au(CN)2]2 with 50%
thermal contours. The unit cell for [Pt(en)2][Ag(CN)2]2 is similar.
locations of these components are given in Figure 4, which
shows the unit cell of the salt. Anion 2 is located on the
center of the a axis edges of the cell. Consequently, the
separation of the gold atoms in adjacent pairs of anion 2 is
long, 6.3598(6) Å. Anion 2 forms hydrogen bonds between
the nitrogen atoms and protons on N2 of two different
cations. This interaction allows anion 2 to span two different
chains that run parallel to the crystallographic a axis.
Samples of [Pt(en)2][Au(CN)2]2 are nonluminescent at
room temperature and at 77 K.
[Pt(en)2][Ag(CN)2]2. Colorless crystals of [Pt(en)2]-
[Ag(CN)2]2, which were obtained by mixing aqueous solu-
tions of [Pt(en)2]Cl2 and K[Ag(CN)2], are isostructural with
[Pt(en)2][Au(CN)2]2. Thus, the structural features are similar
to those of [Pt(en)2][Au(CN)2]2. Selected bond distances and
angles are given in the caption to Figure 3. Within the stacks
of alternating cations and anions in [Pt(en)2][Ag(CN)2]2, the
Pt‚‚‚Ag separation [3.1949(2) Å] is slightly longer than the
Pt‚‚‚Au separation [3.1799(3) Å] in [Pt(en)2][Au(CN)2]2. The
Ag-C separations in [Pt(en)2][Ag(CN)2]2 are longer than the
Au-C separations in [Pt(en)2][Au(CN)2]2. These observa-
tions are consistent with recent reports indicating that Ag(I)
is larger than Au(I).30
Figure 5. View of the structure of [Pt(bipy)2][Au(CN)2]2 with 50% thermal
contours which shows the interactions of two of the anions with the cation.
Selected interatomic distances: Pt1‚‚‚Au1, 3.1735(6); Au1‚‚‚Au1A,
3.5978(9); Pt1-N1, 2.026(7) Å; Pt1-N2, 2.044(8); Au1-C11, 1.988(10),
Au1-C12, 1.980(10) Å. Selected interatomic angles for [Pt(en)2][Au(CN)2]2;
N1-Pt1-N2, 79.3(3); N1-Pt1-N2A, 100.7(3).
each other, or twisted, where the two pyridine rings are
rotated about the central C-C bond in opposite directions.
These ligand distortions allow the ortho protons on adjacent
ligands to avoid direct contact. As is evident in Figure 5,
the bipy ligands in the cation are not planar but are bowed.
The [Pt(bipy)2]2+ ions in [Pt(bipy)2](7,7,8,8-tetracyanoquino-
dimethane monoanion)2,31 in [Pt(bipy)2](7,7,8,8-tetracyano-
quinodimethane monoanion dimer),32 and in [Pt(bipy)2]-
(F3CSO3)233 all have the centrosymmetric bowing that is seen
in [Pt(bipy)2][Au(CN)2]2. This type of distortion allows the
platinum atom to retain its usual planar coordination by the
four nitrogen atoms of the ligands. In contrast, in [Pt(bipy)2]-
(NO3)2‚H2O, the pyridine rings in each ligand are twisted
by 7.5°, and the two ligands are arranged so that the dihedral
angle between the least-squares planes of the two bipy
ligands is 24.0(3)°.34 As a consequence, the platinum atom
in this salt has a slight distortion toward tetrahedral coordina-
tion.
Like [Pt(en)2][Au(CN)2]2, [Pt(en)2][Ag(CN)2]2 is not lu-
minescent.
[Pt(bipy)2][Au(CN)2]2. Yellow crystals of [Pt(bipy)2]-
[Au(CN)2]2 were produced by mixing a solution of
K[Au(CN)2] in acetonitrile with a solution of [Pt(bipy)2]-
(BF4)2 in acetonitrile. The infrared spectrum of these crystals
shows ν(CN) at 2137 cm-1.
Figure 6 shows a view of the structure that reveals that
the anions also weakly interact to form an extended, bent
chain. The Au‚‚‚Au separation is rather long, 3.5978(9) Å,
but it is significant to note that the cyano groups are bent
away from each other so that the gold atoms represent the
closest contacts between the anions. The C11-Au1-C12
angle involved in this bending is 171.3(4) Å.
No luminescence has been observed from [Pt(bipy)2]-
[Au(CN)2]2. The absorption spectrum of [Pt(bipy)2]-
[Au(CN)2]2 in a potassium bromide pellet shows maxima at
320 and 400 nm. Similar features at 320 and 400 nm are
The asymmetric unit consists of one-half of a cation in a
special position with the platinum atom located at a center
of symmetry and an entire anion in a general position. A
drawing of the entire [Pt(bipy)2][Au(CN)2]2 unit is shown
in Figure 5. The cation has the expected four-coordinate
geometry with the addition of axial interactions with the
anions through Pt‚‚‚Au contacts. The Pt‚‚‚Au distance is
3.1735(6) Å.
(31) Endres, H.; Keller, H. J.; Moroni, W.; Nothe, D.; Dong, V. Acta
Crystallogr. B: Struct. Crystallogr. Cryst. Chem. 1978, 34, 1823.
(32) Dong, V.; Endres, H.; Keller, H. J.; Moroni, W.; Nothe, D. Acta
Crystallogr. B: Struct. Crystallogr. Cryst. Chem. 1977, 33, 2428.
(33) Fedolova, T. N.; Minacheva, L. Kh.; Kuznetsova, G. N. Russ. J. Inorg.
Chem. 2003, 48, 417.
The [Pt(bipy)2]2+ ion can display two types of distor-
tions: bowed, where the two pyridine rings are bent toward
(30) Bayler, A.; Schier, A.; Bowmaker, G. A.; Schmidbaur, H. J. Am. Chem.
Soc. 1996, 118, 7006. Tripathi, U. M.; Bauer, A.; Schmidbaur, H. J.
Chem. Soc., Dalton Trans. 1997, 2865.
(34) Hazell, A.; Simonsen, O.; Wernberg, O. Acta Crystallogr. 1986, C42,
1707.
Inorganic Chemistry, Vol. 44, No. 10, 2005 3469

Stork et al.
rangement previously observed in [Pt(NH3)4][Au(CN)2]2‚
1.5(H2O), where both Pt‚‚‚Au and Au‚‚‚Au contacts are
found. In [Pt(NH3)4][Au(CN)2]2‚1.5(H2O), each platinum
atom is surrounded by two anions with Pt‚‚‚Au separations
[3.2804(4) and 3.2794(4) Å] that are somewhat longer than
the Pt‚‚‚Au separation in [Pt(en)2][Au(CN)2]2. The [Au(CN)2]-
[Pt(NH3)4][Au(CN)2] units in [Pt(NH3)4][Au(CN)2]2‚1.5(H2O)
are arranged into chains through close Au‚‚‚Au contacts
[3.2902(5) and 3.3312(5) Å]. Additionally, cross-linking of
these chains occurs through further aurophilic interactions
with an Au‚‚‚Au separation of 3.1902(4) Å. The fact that
[Pt(en)2][Au(CN)2]2 is nonluminescent reinforces our earlier
conclusion that the luminescence of [Pt(NH3)4][Au(CN)2]2‚
1.5(H2O) arises from the close aurophilic interactions
between the anions in this solid. It is also interesting to note
that both [PtAu(µ-{bis(dicyclohexylphosphino)methane}2-
(CN)2]+ and [PtAu{µ-bis(diphenylphosphino)methane}2-
(CN)2]+, with shorter Pt‚‚‚Au separations, are luminescent.7,34
The structure of [Pt(bipy)2][Au(CN)2]2 consists of a
Au‚‚‚Pt‚‚‚Au unit formed from a cation surrounded by two
anions with a Pt‚‚‚Au separation of 3.1735(6) Å. This
distance is similar to the Pt‚‚‚Au separation in [Pt(en)2]-
[Au(CN)2]2. The Au‚‚‚Pt‚‚‚Au units are connected by ad-
ditional Au‚‚‚Au interactions [3.5978(9) Å] that are consid-
erably longer than those found in [Pt(NH3)4][Au(CN)2]2‚
1.5(H2O).
To put the present work into a larger context, there are
several d8 platinum(II) salts in which planar cations and
anions combine to form extended chains with significant
Pt‚‚‚Pt interactions. The best and longest-known is Magnus’
green salt, [Pt(NH3)4][PtCl4], which forms columns of
alternating cations and anions with a Pt‚‚‚Pt separation of
3.25 Å.5,40 A number of variations on this structural motif
are known in which the substituents on the amine or the
ligands in the anion vary.41 The double salts of the type
[Pt(CNR)4][Pt(CN)4] also form columns in which anions and
cations alternate and the platinum centers are brought into
close proximity.42 A number of these are vapochromic, that
is, they change color when exposed to the vapors of volatile
organic compounds. Examples in which ionic d8 metal
complexes associate via Coulombic interactions with other
metal complexes with different electronic configurations are
less common. There is one other example of a mixed-metal
complex formed through interactions between d8 and d10 ions.
The salt Ag2[Pt(O2C2O2)2]‚2H2O has two silver ions posi-
tioned above and below the platinum atom of the anion with
a Pt‚‚‚Ag separation of 2.943(1) Å.43 This Pt‚‚‚Ag separation
Figure 6. View of the extended structure of [Pt(bipy)2][Au(CN)2]2 with
50% thermal contours including the interactions of adjacent anions. The
Au1‚‚‚Au1B distance is 3.5978(9) Å.
seen in the absorption spectrum of [Pt(bipy)2](BF4)2. Thus,
the Pt‚‚‚Au contacts do not produce a detectable alteration
the spectrum of the platinum cation.
Infrared Spectra. The infrared spectra of the new salts
are reported in the Experimental Section. All show sharp
bands for ν(CN) that exhibit only modest variations from
compound to compound. For [Pt{C(NHMe)2}4][Au(CN)2]2,
ν(CN) occurs at 2143 cm-1, whereas KAu(CN)2 has ν(CN)
at 2141 cm-1.35 Despite the presence of two different anions,
[Pt{C(NHMe)2}4][Ag2(CN)3][Ag(CN)2] exhibits only a single
ν(CN) at 2136 cm-1. For comparison, KAg(CN)2 has ν(CN)
at 2140 cm-1.36 The two different anions in [Pt(en)2]-
[Au(CN)2]2 and in [Pt(en)2][Ag(CN)2]2 produce two different
ν(CN) values in each salt: 2136, 2144 cm-1 for [Pt(en)2]-
[Au(CN)2]2 and 2126, 2134 cm-1 for [Pt(en)2][Ag(CN)2]2.
For [Pt(bipy)2][Au(CN)2]2, ν(CN) occurs at 2137 cm-1.
Discussion
The five new salts prepared here show a range of metal-
metal interactions. In [Pt{C(NHMe)2}4][Au(CN)2]2 and
Pt{C(NHMe)2}4][Ag2(CN)3][Ag(CN)2], there are no close
metal-metal interactions between any of the components.
The lack of interaction of the platinum atom in the cation
with the gold atoms is clearly a result of the presence of
four bulky carbene ligands that deny access to the platinum
atom.
In [Pt(en)2][Au(CN)2]2, linear chains of alternating cations
and anions form with a Pt‚‚‚Au distance of 3.1799(3) Å.
This separation is somewhat longer than the Pt‚‚‚Au separa-
tions in discrete binuclear complexes such as [PtAu(µ-{bis-
(dicyclohexylphosphino)methane}2(CN)2]+ [Pt‚‚‚Au, 2.954-
(1) Å],7 [PtAu{µ-bis(diphenylphosphino)methane}2(CN)2]+
[Pt‚‚‚Au, 3.045(2) Å],37 and [PtAu{µ-bis(diphenylphosphino)-
methane}2(CtCPh)2]+ [Pt‚‚‚Au, 2.910(1) Å]38 that have the
ligand-bridged structure 1. However, the Pt‚‚‚Au separation
in [Pt(en)2][Au(CN)2]2 is shorter than the sum of the van
der Waals radii for these metal ions, which is 3.47 Å.39 The
linear chains of alternating gold and platinum atoms in
[Pt(en)2][Au(CN)2]2 contrasts with the more complex ar-
(40) Atoji, M.; Richardson, J. W.; Rundle, R. E. J. Am. Chem. Soc. 1957,
79, 3017.
(41) Bremi, J.; Brovelli, D.; Caseri, W.; Ha¨hner, G.; Smith, P.; Tervoort,
T. Chem. Mater. 1999, 11, 977. Cradwick, M. E.; Hall, D.; Phillips,
R. K. Acta Crystallogr. 1971, B27, 480. Casas, J. S.; Parajo´, Y.;
Romero, Y.; Sa´nchez-Gonza´lez, A.; Sordo, J.; Va´zquez-Lo´pez, E. M.
Z. Anorg. Allg. Chem. 2004, 630, 980.
(35) Chadwick, B. M.; Frankiss, S. G. J. Mol. Struct. 1976, 31, 1.
(36) Chadwick, B. M.; Frankiss, S. G. J. Mol. Struct. 1968, 2, 281.
(37) Yip, H.-K.; Che, C.-M.; Peng, S.-M. J. Chem. Soc., Chem. Commun.
1991, 1626.
(38) Yip, H.-K.; Lin, H. M.; Wang, Y.; Che, C.-M.; J. Chem. Soc., Dalton
Trans 1993, 2939.
(42) Grate J. W.; Moore L. K.; Janzen D. E.; Veltkamp, D. J.; Kaganove,
S.; Drew, S. M.; Mann, K. R. Chem. Mater. 2002, 14, 1058. Buss C.
E.; Anderson, C. E.; Pomije, M. K.; Lutz, C. M.; Britton, D.; Mann,
K. R. J. Am. Chem. Soc. 1998, 120, 7783. Daws C. A.; Exstrom C.
L.; Sowa J. R.; Mann, K. R. Chem. Mater. 1997, 9, 363.
(43) Yamaguchi, T.; Yamazaki, F.; Ito, T. J. Chem. Soc., Dalton, Trans.
1999, 273.
(39) Bondi, A. J. Phys. Chem. 1964, 68, 441.
3470 Inorganic Chemistry, Vol. 44, No. 10, 2005

Metal-Metal Interactions in Pt(II)/Au(I) or Ag(I) Salts
Table 1. Crystallographic Data for Salts of [AuI(CN)2]- and [AgI(CN)2]-
[Pt{C(NHMe)2}4]
[Pt{C(NHMe)2}4]
[Au(CN)2]2
[Ag2(CN)3][Ag(CN)2]
[Pt(en)2][Au(CN)2]2
[Pt(en)2][Ag(CN)2]2
[Pt(bipy)2][Au(CN)2]2
color/habit
formula
fw
crystal system
space group
a, Å
colorless needle
C16H32Au2N12Pt
981.56
monoclinic
P21/n
8.919(5)
15.424(7)
10.074(5)
90
107.047(15)
90
colorless needle
C8H16Ag2N8Pt
635.12
triclinic
P1h
6.3899(4)
6.9793(5)
8.9383(6)
89.0260(10)
79.6310(10)
73.7160(10)
376.15(4)
1
colorless needle
C8H16Au2N8Pt
813.31
triclinic
P1h
6.3598(6)
6.9603(7)
9.0333(9)
88.311(2)
79.576(2)
74.306(2)
378.53(6)
1
colorless needle
C8H16Ag2N8Pt
635.12
triclinic
P1h
6.3599(4)
6.9793(5)
8.9383(6)
89.0260(10)
79.6310(10)
73.7160(10)
376.15(4)
1
yellow plate
C24H16Au2N8Pt
1005.47
triclinic
P1h
7.0515(13)
9.2481(14)
9.2728(18)
75.077(2)
77.247(5)
79.743(6)
565.16(17)
1
b, Å
c, Å
R, deg
â, deg
γ, deg
V, Å3
1325.0(11)
2
Z
T, °C
90(2)
90(2)
90(2)
90(2)
90(2)
λ, Å
0.71073
2.460
16.338
0.052
0.140
0.71073
2.804
11.851
0.015
0.039
0.71073
3.568
28.547
0.021
0.050
0.71073
2.804
11.851
0.015
0.039
0.71073
2.954
19.152
0.035
0.092
F, g/cm3
µ, mm-1
R1a (obsd data)
wR2a (all data,
F2 refinement)
2
2
a R1 ) (∑||Fo| - |Fc||)/(∑|Fo|); wR2 ) (∑[w(F -F 2)2])/(∑[w(F )2]).
x
o
c
o
Preparation of Compounds. (i) [Pt{C(NHMe)2}4][Au(CN)2]2.
A filtered solution of 10 mg (0.018 mmol) of [Pt{C(NHMe)2}4]-
(PF6)2 in 1.0 mL of methanol was added dropwise to a solution of
10 mg (0.035 mmol) of potassium dicyanoaurate in 1.0 mL of water.
The colorless reaction mixture was transferred to a 5-mm-diameter
tube and left undisturbed. After 3 days of slow evaporation of the
solvent, colorless needles of the product that were suitable of X-ray
analysis formed. After removal from the mother liquor, 8 mg (48%
yield) of the colorless product was obtained. Infrared spectrum
(cm-1): 527 m, 640 sh, 674 sh, 700 m, 980 w, 1032 sh, 1129 w,
1189 m, 1308 m, 1361 m, 1454 m, 1524 sh, 1576 sh, 2143 sh
[ν(CN)], 2941 w, 3289 vs [ν(N-H)], 3343 vs [ν(N-H)].
(ii) [Pt{C(NHMe)2}4][Ag2(CN)3][Ag(CN)2]. A filtered solution
of 100 mg (0.16 mmol) of [Pt{C(NHMe)2}4](PF6)2 in 1.0 mL of
methanol was added dropwise to a solution of 100 mg (0.50 mmol)
of potassium dicyanoargentate in 0.5 mL of water in a 5-mm-
diameter tube. The colorless reaction mixture was left undisturbed.
After 4 days of slow evaporation of the solvent, a few colorless
plates of the product formed. They were removed from the mother
liquor to yield 3.2 mg (3%) of product. These crystals were suitable
for collection of X-ray diffraction data. Infrared spectrum (cm-1):
532 m, 675 sh, 740 w, 980 w, 1032 sh, 1129 w, 1189 m, 1309 m,
1362 m, 1452 m, 1527 sh, 1577 sh, 2136 m [ν(CN)], 2939 w,
3286 vs [ν(N-H)], 3310 vs [ν(N-H)].
(iii) [Pt(en)2][Au(CN)2]2. A solution of 121 mg (0.420 mmol)
of K[Au(CN)2] in 2 mL of water was added to a solution of 80 mg
(0.21 mmol) of [Pt(en)2]Cl2 in 2 mL of water. Colorless needles
suitable for X-ray crystallography precipitated over the course of
2 days. The precipitate was collected and washed successively with
water, ethanol, and ether to yield 102 mg (60%) of the product.
Infrared spectrum (cm-1): 757 m, 821 m, 899 w, 1020 w,
1589 sh, 1127 m, 1152 sh, 1275 w, 1304 sh, 1322 m, 1367 sh,
1446 sh, 1454 sh, 1589 sh, 1610 sh, 2136 sh [ν(CN)], 2144 vs
[ν(CN)], 3109 vs [ν(N-H)], 3211 m [ν(N-H)], 3248 vs
[ν(N-H)], 3292 vs [ν(N-H)]
is shorter than the Pt‚‚‚Ag separation in [Pt(en)2][Ag(CN)2]2.
A similar structural unit is found in Tl2[Pt(CN)4], which
involves the interaction of a d8 complex with two closed-
shell s2 ions.44 The complex has a pseudo-octahedral structure
with two equivalent thallium ions positioned above and
below the planar anion with a short Pt‚‚‚Tl separation of
3.140 (1) Å. The nature of the Pt‚‚‚Tl bonding in this
complex has been examined in a series of computational
studies.45,46
The interactions between the metal centers in the salts
considered here are likely to result from a combination of
Coulombic and metallophillic interactions. For example, in
Tl2[Pt(CN)4], computations have indicated that the Pt‚‚‚Tl
bonding consists of an ionic component that accounts for
87% of the attraction and a covalent, metallophillic interac-
tion that accounts for the remaining 13% of the bonding
interaction.43 Additionally, theoretical studies have shown
that interaction of the thallium ion with the adjacent nitrile
groups of neighboring complexes diminishes the strength of
the Pt‚‚‚Tl bond.44 In [Cu(1,1′-bis(2-pyridal)octamethyl-
ferrocene)][CuCl2], the Cu‚‚‚Cu contact is short, 2.810 Å,47
but calculations show that the attraction comes entirely from
Coulombic factors and not from metallophilic interactions.48
Further computational studies are needed to sort out the
varying contributions from Coulombic and metallophilic
interactions in the new salts reported here.
Experimental Section
Materials. Samples of [Pt(en)2]Cl2, K[Au(CN)2], and K[Ag-
(CN)2] were obtained from Strem Chemicals and used as received.
[Pt{C(NHMe)2}4](PF6)2 was prepared as described previously.49
[Pt(bipy)2](BF4)2 was prepared by a known route.50
(44) Nagle, J. K.; Balch, A. L.; Olmstead, M. M. J. Am. Chem. Soc. 1988,
110, 319.
(iv) [Pt(en)2][Ag(CN)2]2. A solution of 87 mg (0.44 mmol) of
(45) Ziegler, T.; Nagle, J. K.; Snijders, J. G.; Baerends, E. J. J. Am. Chem.
Soc. 1989, 111, 5631.
K[Ag(CN)2] in 1.5 mL of water was added to a solution of 83 mg
(46) Dolg, M.; Pyykko¨, P.; Runeberg, N. Inorg. Chem. 1996, 35, 7450.
(47) Siemeling, U.; Vorfeld, U.; Neumann, B.; Stammer, H.-G. Chem.
Commun. 1997, 1723.
(49) Miller, J. S.; Balch, A. L. Inorg. Chem. 1972, 11, 2069.
(50) Brown, A. R.; Guo, Z.; Mosselmans, F. W. J.; Parsons, S.; Schro¨der,
M.; Yellowlees, L. J. J. Am. Chem. Soc. 1998, 120, 8805.
(48) Poblet, J.-M.; Be´nard, M. Chem. Commun. 1998, 1179.
Inorganic Chemistry, Vol. 44, No. 10, 2005 3471

Stork et al.
(0.22 mmol) of [Pt(en)2]Cl2 in 1 mL of water. Colorless needles
suitable for crystallography formed upon standing overnight. The
crystals were collected by filtration and washed successively with
water, ethanol, and ether to yield 102 mg (88%) of the product.
Infrared spectrum (cm-1): 759 m, 830 m, 898 m, 1031 w,
1053 sh, 1133 w, 1157 sh, 1235 w, 1277 w, 1307 m, 1324 m,
1369 m, 1447 sh, 1456 sh, 1592 sh, 1617 m, 2126 sh [ν(CN)],
2134 sh [ν(CN)], 3082 vs [ν(N-H)], 3242 vs [ν(N-H)], 3288 vs
[ν(N-H)]
(v) [Pt(bipy)2][Au(CN)2]2. A solution of 30 mg (0.10 mmol) of
K[Au(CN)2] in 2 mL of acetonitrile was added dropwise to a
solution of 34 mg (0.050 mmol) of [Pt(bipy)2](BF4)2 in 6 mL of
acetonitrile. A yellow precipitate immediately formed. The pre-
cipitate was collected by filtration and washed with acetonitrile to
yield 45 mg (90%) of yellow platelets. X-ray diffraction quality
plates were grown by layering a slurry of the reaction mixture over
dimethyl sulfoxide. Yellow plates of the product slowly formed in
this mixture. Infrared spectrum (cm-1): 720 sh, 772 sh, 816 w,
1036-1129 vs br, 1155 m, 1162 m, 1428 m, 1450 sh, 1499 w,
1609 sh, 2137 sh [ν(CN)], 3029 m, 3048 m, 3060 m, 3098 w,
3119 w
a hydrocarbon oil on the microscope slide. Suitable crystals were
mounted on glass fibers with silicone grease and placed in the cold
dinitrogen stream of a Bruker SMART CCD with graphite-
monochromated Mo KR radiation at 90(2) K. No decay was
observed in 50 duplicate frames at the end of each data collection.
Crystal data are given in Table 1.
The structures were solved by direct methods and refined using
all data (based on F2) using the software of SHELXTL 5.1. A
semiempirical method utilizing equivalents was employed to correct
for absorption.51 Hydrogen atoms were added geometrically and
refined with a riding model.
Acknowledgment. We thank the Petroleum Research
Fund (Grant 37056-AC) for support. The Bruker SMART
1000 diffractometer was funded in part by NSF Instrumenta-
tion Grant CHE-9808259.
Supporting Information Available: X-ray crystallographic file
in CIF format for [Pt{C(NHMe)2}4][Au(CN)2]2, [Pt{C(NHMe)2}4]-
[Ag2(CN)3][Ag(CN)2], [Pt(en)2][Au(CN)2]2, [Pt(en)2][Ag(CN)2]2,
and [Pt(bipy)2][Au(CN)2]2. This material is available free of charge
via the Internet at http://pubs.acs.org.
Physical Measurements. Infrared spectra were recorded as
pressed KBr pellets on a Matteson Galaxie Series FTIR 3000
spectrometer. Electronic absorption spectra were recorded using a
Hewlett-Packard 8450A diode array spectrophotometer.
X-ray Crystallography and Data Collection. The crystals were
removed from the glass tubes in which they were grown together
with a small amount of mother liquor and immediately coated with
IC048333A
(51) Sheldrick, G. M. SADABS 2.10; Bruker AXS Inc.: Madison, WI,
2004.The semiempirical method used is based on a method of Blessing,
R. H. Acta Crystallogr. 1995, A51, 33.
3472 Inorganic Chemistry, Vol. 44, No. 10, 2005