Building Blocks in Pt-Co Carbonyl Clusters
C,21,23 O,21,23 P,25 H,21,23 Pt,26 and Co26 were taken from the
literature. Because of the limitations in the size of molecules handled
by the program, PPh3 was replaced by PH3. This is a standard
methodology.27 Hence, the computed molecule was [Pt2Co(µ-PH2)-
(PH3)2(µ-CO)2(CO)2]. The bond distances and angles are those
reported in the X-ray structure (average values). For the [Co(CO)4]-
anion in the Td, C2V, C3V, and Cs symmetries, all distances were
kept constant and averaged using the X-ray data as well.
Table 1. Crystal Data and Structure Refinement for Compound
[Pt2Co(µ-PPh2)(CO)4(PPh3)2]‚2C6H5CH3 (7‚2PhMe)
chemical formula
fw
T/K
C66H56O4P3Pt2Co
1455.13
233(2)
cryst syst
space group
a/Å
b/Å
triclinic
P1h
11.791(4)
13.471(6)
18.887(9)
106.654(4)
95.844(3)
92.983(4)
2849(2)
1.696
c/Å
R/deg
Results
â/deg
The reaction of [Co(CO)4]- with [Pt2Cl(µ-PPh2)(PPh3)3]28
(1:1 ratio), which was prepared in situ by attack of HCl on
the orthometalated complex [Pt2(µ-PPh2)(µ-o-C6H4PPh2)-
(PPh3)2],16 afforded the deep green cluster [Pt2Co(µ-PPh2)-
(CO)4(PPh3)2], 7 (eq 1).
γ/deg
V/Å3
F(calc)/ g‚cm-3
Z
2
µ/mm-1
5.319
reflns collected/unique
R(int)
10562/10028
0.0361
0.0444
R1 [I > 2σ (I)]a
wR2 [I > 2σ (I)]b
The mass spectrum of 7 does not contain the molecular
peak [M]+, but fragments resulting from stepwise loss of
carbonyl ligands at m/z ) [M - 2CO]+, [M - 3CO]+, [M
- 4CO]+, and [M - Co(CO)4]+. Its IR spectrum (KBr)
presents two high and two low frequency ν(CO) absorption
bands at 2002(vs), 1954 (vs), 1860(s), 1795 (vs) cm-1, which
are indicative of two terminal and two bridging carbonyls,
respectively. The 31P{1H} NMR spectrum shows a doublet
and a triplet, flanked each by satellites due to 1J(P-Pt) and
2J(P-Pt) couplings. The triplet at low field is assigned to
the P atom bridging two equivalent Pt atoms. The doublet
at 41.1 ppm is due to the terminal phosphines, and the pattern
of the satellites is that of a P-Pt-Pt-P chain, similar to
that found in other complexes containing this unit.10 These
data are fully consistent with the structure found in the solid
state.
X-ray Structure of [Pt2Co(µ-PPh2)(CO)4(PPh3)2]‚2PhMe
(7‚2 PhMe). A view of molecule 7 is shown in Figure 1,
and selected bond distances and angles are given in Table
2. The cluster crystallizes with two molecules of toluene.
The metallic core of this molecule is formed by a Pt2Co
triangle, whose intermetallic distances, d(Pt-Co) ) 2.547-
(2) and 2.574(2) Å, and d(Pt-Pt) ) 2.655(1) Å, are in the
range found in other Pt-Co clusters.1,14,29 Each Pt atom bears
a PPh3 ligand, and the P-Pt-Pt-P chain is almost linear.
The Pt-Pt bond is doubly bridged, symmetrically by a PPh2
group and a Co(CO)4 moiety, in such a way that the Pt, Co,
and µ-P atoms are coplanar. The coordination geometry about
the Co atom is defined by two terminal carbonyls and two
asymmetric bridging carbonyls, the latter leaning toward the
Pt atoms. The mean plane of the molecule contains Pt(1),
Pt(2), P(1), P(2), P(3), C(3), and O(3) (Figure 1). Compared
with the coordination sphere about the cobalt center in 4,
that in 7 experiences a tetrahedral distortion with an increase
of the angles between the phosphine P(1) or carbonyl C(3)O-
(3) and the three carbonyls C(10)O(10), C(20)O(20), C(30)O-
(30) or C(1)O(1), C(2)O(2), C(4)O(4), respectively, as shown
0.1040
a R1 ) ∑||Fo| - |Fc||/∑|Fo|. b wR2) {∑[w(Fo2 - Fc )2]/∑[w(Fo )2]}1/2
.
2
2
dissolution in toluene and addition of hexane, 7‚2PhMe (0.120 g,
yield: 73%) crystallized out as green crystals, suitable for X-ray
diffraction. Anal. Calcd for C66H56O4CoP3Pt2 (M ) 1455.21): C,
54.48; H, 3.88. Found: C, 53.80; H, 4.01. IR (KBr) ν(CO): 2002-
(vs), 1954 (vs), 1860(s), 1795 (vs). 31P{1H} NMR: δ 41.1 [d, PPh3,
1
2
3
2J(P-P) 26 Hz, J(P-Pt) 4380 Hz, J(P-Pt) 112 Hz, J(P-P) 87
Hz], 208.5 [t, µ-P, 2J(P-P) 26 Hz, 1J(P-Pt) 2608 Hz]. Mass
spectrum (intensity in %): m/z 1214 [M - 2CO, 20%]+, 1186 [M
- 3CO, 15%]+, 1158 [M - 4CO, 100%]+, 1099 [M - Co(CO)4,
53%]+.
Crystallographic Data Collection and Structure Determina-
tion. Single crystals were mounted on an Enraf-Nonius CAD4
diffractometer equipped with a graphite monochromated Mo KR
radiation source (λ ) 0.71073 Å). Cell dimensions and orientation
matrix for data collection were obtained from least-squares refine-
ment, using the setting angles of 25 centered reflections. The crystal
data are summarized in Table 1. The intensities were collected (θ-
2θ scans) at 233 K; no significant decay was observed in the three
standard reflections measured every hour during data collection.
Data reduction and correction were performed with MolEN.17
Lorentz polarizations and semiempirical absorption corrections (ψ-
scan method)18 were applied to intensities for all data. Scattering
factors and corrections for anomalous dispersion were taken from
the literature.19 The structure was solved with SHELXS-9720 and
refined with SHELXL-97 programs by full matrix least-squares
method, on F 2. All non-hydrogen atoms were refined anisotropi-
cally, while hydrogen atoms were assigned an isotropic thermal
parameter 1.2 times that of the parent atom (1.5 for terminal atoms)
and allowed to ride.
Computational Details. All the EHMO calculations were of the
extended Huckel type (EHMO)21-23 using a modified version of
the Wolfsberg-Helmholz formula.24 The atomic parameters for
(17) MolEN (Molecular Structure Enraf-Nonius); Enraf-Nonius: Delft, The
Netherland, 1990.
(18) North, A. C. T.; Philips, D. C.; Mathews, F. S. Acta Crystallogr.,
Sect. A. 1968, 351.
(19) International Tables for X-ray Crystallography, vol IV; Kynoch
Press: Birmingham, 1974.
(25) Summerville, R. H.; Hoffmann, R. J. Am. Chem. Soc. 1976, 98, 7240.
(26) Macchi, P.; Proserpio, D. M.; Sironi, A. Organometallics 1997, 16,
2101.
(27) Mealli, C. J. Am. Chem. Soc. 1985, 107, 2245.
(28) Archambault, C.; Bender, R.; Braunstein, P.; Bouaoud, S.-E.; Rouag,
D.; Golhen, S.; Ouahab, L. Chem. Commun. 2001, 849.
(29) Bender, R.; Braunstein, P.; Fischer, J.; Ricard, L.; Mitschler, A. New
J. Chem. 1981, 5, 81.
(20) Sheldrick, G. M. SHELXL 97, Program for the Refinement of Crystal
Structures; University of Go¨ttingen: Germany, 1993.
(21) Hoffmann, R.; Lipscomb, W. N. J. Chem. Phys. 1962, 36, 2179.
(22) Hoffmann, R.; Lipscomb, W. N. J. Chem. Phys. 1962, 37, 2872.
(23) Hoffmann, R. J. Chem. Phys. 1963, 39, 1397.
(24) Ammeter, J. H.; Burgi, H. B.; Thibeault, J. C.; Hoffmann, R. J. Am.
Chem. Soc. 1978, 100, 3686.
Inorganic Chemistry, Vol. 41, No. 7, 2002 1741