Matrix isolation FTIR spectroscopic and density functional theoretical studies of the nickel, copper, and silver carbonyl chlorides

Article abstract of DOI:10.1021/om000911h

The nickel, copper, and silver metal carbonyl chloride molecules have been prepared and isolated in solid argon by cocondensation of the species generated from 1064 nm laser ablation of metal chlorides with carbon monoxide in excess argon at 11 K. On the

Full text of DOI:10.1021/om000911h

Organometallics 2001, 20, 1137-1143
1137
Ma tr ix Isola tion F TIR Sp ectr oscop ic a n d Den sity
F u n ction a l Th eor etica l Stu d ies of th e Nick el, Cop p er ,
a n d Silver Ca r bon yl Ch lor id es
Limin Shao, Luning Zhang, Mingfei Zhou,* and Qizong Qin
Department of Chemistry, Laser Chemistry Institute, Fudan University,
Shanghai, People’s Republic of China
Received October 24, 2000
The nickel, copper, and silver metal carbonyl chloride molecules have been prepared and
isolated in solid argon by cocondensation of the species generated from 1064 nm laser ablation
of metal chlorides with carbon monoxide in excess argon at 11 K. On the basis of isotopic
substitution experiments and density functional theory frequency calculations, infrared
absorptions at 2118.7, 2156.8, and 2184.0 cm-1 are assigned to the C-O stretching vibrations
of the Ni(CO)Cl, Cu(CO)Cl, and Ag(CO)Cl molecules. Density functional calculations
predicted that the M(CO)Cl (M ) Ni, Cu, Ag) molecules are linear; the binding energies
with respect to MCl + CO were estimated to be 37.7, 34.2, and 17.8 kcal/mol, respectively.
In addition, evidence is also presented for the M(CO)Cl2, M(CO)2Cl, and M(CO)2Cl2 (M )
Ni, Cu) molecules.
In tr od u ction
rides have been characterized by infrared and EXAFS
spectroscopy.9 The C-O stretching vibrational frequen-
cies of these species shifted to high frequency of diatomic
carbon monoxide.
Transition-metal carbonyl complexes are cornerstones
of modern coordination chemistry and organometallic
chemistry.1 Many industrial processes such as hydro-
formylation, Fischer-Tropsch synthesis, and acetic acid
synthesis employ CO as the reagent and transition-
metal compounds as heterogeneous or homogeneous
catalysts and involve transition-metal carbonyl inter-
mediates.2 Transition-metal carbonyl halides have re-
ceived attention for more than a century. In 1868,
Schutzenberger succeeded in isolating and identifying
the carbonyl chlorides of platinum with the compositions
Pt(CO)2Cl2, Pt2(CO)4Cl4, and Pt2(CO)3Cl4.3 Subsequently,
carbonyl halides such as Pd(CO)Cl2, Cu(CO)Cl, and
Au(CO)Cl have been prepared and structurally
characterized.4-6
Matrix isolation infrared spectroscopy has proved to
be a highly effective method for characterization of
transition-metal compounds with weakly bound ligands.
The interactions of transition-metal halides such as
difluorides and dichlorides of first-row transition metals
with carbon monoxide in cryogenic matrices have been
studied.7,8 Some novel transition-metal carbonyl chlo-
In this paper, we report a study of combined matrix
isolation FTIR spectroscopy and DFT studies on the
complexes of nickel, copper, and silver chlorides with
carbon monoxide generated from the reaction of laser-
ablated nickel, copper, and silver chlorides with carbon
monoxide molecules in excess argon.
Exp er im en ta l a n d Th eor etica l Meth od s
The experimental setup for pulsed laser ablation and matrix
infrared spectroscopic investigation is similar to that described
previously.10,11 The 1064 nm Nd:YAG laser fundamental
(spectra Physic, DCR 2, 20 Hz repetition rate and 8 ns pulse
width) was focused onto a rotating metal chloride target
through a hole in a CsI window, Typically, 5-10 mJ /pulse laser
power was used. The laser-ablated metal chlorides were
codeposited with CO in excess argon onto a 11 K CsI window
for 1 h at a rate of 2-4 mmol/h. The CsI window was mounted
on a copper holder at the cold end of the cryostat (Air Products
Displex DE202) and maintained by a closed-cycle helium
refrigerator (Air Products Displex IR02W). A Bruker IFS 113v
Fourier transform infrared spectrometer equipped with a
DTGS detector was used to record the IR spectra in the range
of 400-4000 cm-1 with a resolution of 0.5 cm-1. Carbon
monoxide, isotopic 13C16O, and 12C16O + 13C16O mixture
samples were used in different experiments. Annealing experi-
ments were done by warming the sample deposit to the desired
temperature and quickly cooling to 11 K.
* To whom correspondence should be addressed. E-mail:
mfzhou@fudan.edu.cn. Fax: +86-21-65102777.
(1) Cotton, F. A.; Wilkinson, G.; Murillo, C. A.; Bochmann, M.
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10.1021/om000911h CCC: $20.00 © 2001 American Chemical Society
Publication on Web 02/16/2001

1138 Organometallics, Vol. 20, No. 6, 2001
Shao et al.
Ta ble 1. IR Absor p tion (cm -1) fr om Cod ep osition
of La ser -Abla ted NiCl2 w ith CO in Excess Ar gon a t
11 K
Density functional calculations were carried out using the
Gaussian 98 program.12 The three-parameter hybrid functional
according to Becke with additional correlation corrections of
Lee, Yang, and Parr were utilized (B3LYP).13,14 Recent calcula-
tions have shown that this hybrid functional can provide very
reliable predictions of the state energies, structures, and
vibrational frequencies of transition-metal-containing
compounds.15-17 The 6-311+G(d) basis set was used for C, O,
and Cl atoms, the all-electron basis sets of Wachters-Hay as
modified by Gaussian were used for Ni and Cu atoms, and
the Los Alamos ECP plus DZ basis set (LANL2DZ) was used
for the Ag atom.18-20 The geometries were fully optimized,
vibrational frequencies were calculated with analytic second
derivatives, and zero point vibrational energies were derived.
The scaling factors of C-O stretching vibrations were deter-
mined as experimental observed frequency divided by calcu-
lated frequency.
12C16
O
13C16
O
R(12/13)
assignt
2190.2
2149.2
2148.4
2138.2
2126.6
2118.7
2075.0
2051.8
2017.2
1994.4
1965.6
1877.1
525.2
2141.2
2101.8
2101.2
2091.1
2078.5
2069.9
2029.1
2005.4
1970.4
1946.5
1921.3
1837.1
1.0229
1.0226
1.0225
1.0225
1.0231
1.0236
1.0226
1.0231
1.0238
1.0246
1.0230
1.0218
Ni(CO)Cl2
H2O-CO
Ni(CO)2Cl2
CO
Ni(CO)2Cl
Ni(CO)Cl
Ni(CO)2Cl
Ni(CO)4
Ni(CO)3
NiCO
Ni(CO)2
ClCO
58Ni(CO)235Cl2
58Ni35Cl2
58Ni(CO)35Cl2
58Ni(CO)235Cl2
520.9
469.1
434.4
Resu lts
In fr a r ed Sp ectr a . Experiments were done using
NiCl2, CuCl2, CuCl, and AgCl targets. Sample deposition
at 11 K reveals strong CO absorption at 2138.4 cm-1
and ClCO absorptions at 1877.1 and 570.5 cm-1 that
are common for all systems.21 In addition, absorptions
at 2154 and 2149.2 cm-1 due to CO perturbed by HCl
and H2O were always observed in the experiments.22,23
(a ) NiCl2 + CO/Ar . Experiments were done using a
NiCl2 target with different CO concentrations in argon
(0.2% and 0.5%), and the product absorptions are listed
in Table 1. The spectra in the 2200-2060 and 530-410
cm-1 regions with 0.5% CO in Ar which are of particular
interest here are shown in Figure 1. One hour of sample
deposition at 11 K produced strong NiCl2 absorptions
(520.9 cm-1 for 58Ni35Cl2)24 and weak Ni(CO)x absorp-
tions (not shown: NiCO, 1994.4 cm-1; Ni(CO)2, 1965.6
cm-1; Ni(CO)3, 2017.2 cm-1; Ni(CO)4, 2051.8 cm-1).25
The NiCl absorptions were hardly detected. New ab-
sorptions at 2190.2, 2118.7, 2126.6, 2075.0, and 469.1
cm-1 were produced on sample deposition. The 2190.2
(12) Frisch, M. J .; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.;
Robb, M. A.; Cheeseman, J . R.; Zakrzewski, V. G.; Montgomery, J . A.,
J r.; Stratmann, R. E.; Burant, J . C.; Dapprich, S.; Millam, J . M.;
Daniels, A. D.; Kudin, K. N.; Strain, M. C.; Farkas, O.; Tomasi, J .;
Barone, V.; Cossi, M.; Cammi, R.; Mennucci, B.; Pomelli, C.; Adamo,
C.; Clifford, S.; Ochterski, J .; Petersson, G. A.; Ayala, P. Y.; Cui, Q.;
Morokuma, K.; Malick, D. K.; Rabuck, A. D.; Raghavachari, K.;
Foresman, J . B.; Cioslowski, J .; Ortiz, J . V.; Stefanov, B. B.; Liu, G.;
Liashenko, A.; Piskorz, P.; Komaromi, I.; Gomperts, R.; Martin, R. L.;
Fox, D. J .; Keith, T.; Al-Laham, M. A.; Peng, C. Y.; Nanayakkara, A.;
Gonzalez, C.; Challacombe, M.; Gill, P. M. W.; J ohnson, B. G.; Chen,
W.; Wong, M. W.; Andres, J . L.; Head-Gordon, M.; Replogle, E. S.;
Pople, J . A. Gaussian 98, revision A.7; Gaussian, Inc.: Pittsburgh, PA,
1998.
F igu r e 1. Infrared spectra in the 2200-2060 and 530-
410 cm-1 regions from codeposition of laser-ablated NiCl2
and 0.5% CO in argon: (a) 1 h sample deposition at 11 K;
(b) after 25 K annealing; (c) after 30 K annealing.
and 2118.7 cm-1 bands decreased, while the 2126.6 and
2075.0 cm-1 bands increased on annealing. Sample
annealing also produced new absorptions at 2148.4,
525.2, and 434.4 cm-1. In an experiment at lower CO
concentration (0.2%), the 2190.2, 2118.7, and 469.1 cm-1
bands were also observed after sample deposition and
increased on 25 and 30 K annealing. The 2148.4, 2126.6,
and 2075.1 cm-1 bands were only produced on anneal-
ing. Experiments were also done with isotopic-labeled
13CO and mixed 12CO + 13CO samples, and the spectra
are shown in Figure 2.
(b) Cu Cl2 + CO/Ar . The product absorptions from
codeposition of laser-ablated CuCl2 and CO/Ar mixture
are listed in Table 2, and the spectra in the 2210-2120
and 540-410 cm-1 regions are shown in Figure 3. One
hour of sample deposition produced strong CuCl2 and
CuCl absorptions26 and weak Cu(CO)x (x ) 1-3) ab-
(13) Becke, A. D. J . Chem. Phys. 1993, 98, 5648.
(14) Lee, C.; Yang, E.; Parr, R. G. Phys. Rev. B 1988, 37, 785.
(15) Bauschlicher, C. W., J r.; Ricca, A.; Partridge, H.; Langhoff, S.
R. In Recent Advances in Density Functional Theory; Chong, D. P.,
Ed.; World Scientific Publishing: Singapore, 1997; Part II.
(16) Bytheway, I.; Wong, M. W. Chem. Phys. Lett. 1998, 282, 219.
(17) Siegbahn, P. E. M. Electronic Structure Calculations for
Molecules Containing Transition Metals. Adv. Chem. Phys. 1996, 93.
(18) McLean, A. D.; Chandler, G. S. J . Chem. Phys. 1980, 72, 5639.
Krishnan, R.; Binkley, J . S.; Seeger, R.; Pople, J . A. J . Chem. Phys.
1980, 72, 650.
(19) Wachter, J . H. J . Chem. Phys. 1970, 52, 1033. Hay, P. J . J .
Chem. Phys. 1977, 66, 4377.
(20) Hay, P. J .; Wadt, W. R. J . Chem. Phys. 1985, 82, 299.
(21) J acox, M. E.; Milligan, D. E. J . Chem. Phys. 1965, 43, 866.
(22) Andrews, L.; Arlinghaus, R. T.; J ohnson, G. L. J . Chem. Phys.
1983, 78, 6347.
(23) Dubost, H.; Abouaf-Marguin, L. Chem. Phys. Lett. 1972, 17, 269.
(24) Milligan, D. E.; J acox, M. E.; McKinley, J . D. J . Chem. Phys.
1965, 42, 902.
(25) DeKock, R. L. Inorg. Chem. 1971, 10, 1205. Zhou, M. F.;
Andrews, L. J . Am. Chem. Soc. 1998, 120, 11499.

Ni, Cu, and Ag Carbonyl Chlorides
Organometallics, Vol. 20, No. 6, 2001 1139
F igu r e 2. Infrared spectra in the 2200-2060 cm-1 region
from codeposition of laser-ablated NiCl2 and CO in excess
argon: (a) 0.2% 12CO, after 25 K annealing; (b) 0.4% 12CO
+ 0.4% 13CO, after 25 K annealing; (c) 0.5% 13CO, after 25
K annealing.
F igu r e 4. Infrared spectra in the 2210-2060 cm-1 region
from codeposition of laser-ablated CuCl2 and CO in excess
argon: (a) 0.15% 12CO, after 25 K annealing; (b) 0.1% 12CO
+ 0.1% 13CO, 25 K annealing; (c) 0.2% 13CO, after 25 K
annealing.
Ta ble 2. IR Absor p tion (cm -1) fr om Cod ep osition
of La ser -Abla ted Cu Cl2 w ith CO in Excess Ar gon
12C16
O
13C16
O
R(12/13)
assignt
2205.5
2187.1
2165.8
2156.8
2131.6
2010.0
1890.5
513.4
2156.0
1.0230
Cu(CO)Cl2
Cu(CO)2Cl2
Cu(CO)2Cl
Cu(CO)Cl
Cu(CO)2Cl
CuCO
2116.7
2107.3
2084.4
1965.8
1847.0
1.0232
1.0235
1.0226
1.0225
1.0236
Cu(CO)2
63Cu35Cl2
63Cu(CO)35Cl2
63Cu35Cl
459.1
420.6
F igu r e 5. Infrared spectra in the 2210-2120 cm-1 region
from codeposition of laser-ablated CuCl and 0.15% CO in
argon: (a) 1 h sample deposition at 11 K; (b) after 30 K
annealing.
cm-1 region are shown in Figure 5. Codeposition of
laser-ablated CuCl with CO/Ar produced CuCl absorp-
tions and the 2165.8, 2156.8, and 2131.6 cm-1 absorp-
tions with approximately the same intensity as in the
CuCl2 + CO/Ar experiments, but the CuCl2 absorptions
and the 2205.5, 2187.1, and 459.1 cm-1 absorptions
could hardly be observed.
(d ) AgCl + CO/Ar . An AgCl target was also used in
such experiments. The infrared spectra in the CO
stretching vibrational region are presented in Figure 6.
The observed band positions are listed in Table 3.
Except for the Ag(CO)x absorptions,28 one new absorp-
tion at 2184.0 cm-1 was observed; this band increased
on annealing and was shifted to 2134.5 cm-1 with a
13C16O sample (trace d). In the mixed 12CO + 13CO
spectrum (trace c), only pure isotopic counterparts were
presented.
Ca lcu la tion Resu lts. DFT calculations were per-
formed on the potential products observed in present
experiments. The optimized geometric parameters for
M(CO)Cl, M(CO)2Cl, M(CO)Cl2, and M(CO)2Cl2 (M ) Ni,
Cu, Ag) are shown in Figures 7 and 8, respectively. For
comparison, the calculated geometric parameters for
F igu r e 3. Infrared spectra in the 2210-2120 and 530-
410 cm-1 regions from codeposition of laser-ablated CuCl2
and 0.15% CO in argon: (a) 1 h sample deposition at 11 K;
(b) after 30 K annealing.
sorptions (not shown).27 Meanwhile, new absorptions at
2205.5, 2156.8, and 459.1 cm-1 were also observed on
sample deposition. Annealing markedly increased the
2205.5, 2156.8, and 459.1 cm-1 bands and produced
weak new bands at 2187.1, 2165.8, and 2131.6 cm-1
.
Isotopic substitution experiments were also done, and
the spectra are shown in Figure 4.
(c) Cu Cl + CO/Ar . Similar experiments were done
using a CuCl target, and the spectra in the 2210-2120
(26) Martin, T. P.; Schaber, H. J . Chem. Phys. 1980, 73, 3541.
(27) Huber, H.; Kundig, E. P.; Moskovits, M.; Ozin, G. A. J . Am.
Chem. Soc. 1975, 97, 2097.
(28) McIntosh, D.; Ozin, G. A. J . Am. Chem. Soc. 1976, 98, 3167.

1140 Organometallics, Vol. 20, No. 6, 2001
Shao et al.
F igu r e 6. Infrared spectra in the 2200-2070 cm-1 region
from codeposition of laser-ablated AgCl and CO in excess
argon: (a) 0.15% 12CO, 1 h sample deposition at 11 K; (b)
after 30 K annealing; (c) 0.1% 12CO + 0.1% 13CO, after 30
K annealing; (d) 0.5% 13CO, after 30 K annealing.
F igu r e 8. Calculated geometric parameters (bond lengths
in angstroms, bond angles in degrees) of the M(CO)Cl2 and
M(CO)2Cl2 molecules.
Ta ble 3. IR Absor p tion (cm -1) fr om Cod ep osition
of La ser -Abla ted AgCl w ith CO in Excess Ar gon a t
11 K
Ta ble 4. Ca lcu la ted Vibr a tion a l F r equ en cies
(cm -1) a n d In ten sities (k m /m ol, in P a r en th eses) of
th e M(CO)Cl (M ) Ni, Cu , Ag) a n d M(CO)Cl2 (M )
Ni, Cu ) Molecu les
12C16
O
13C16
O
R(12/13)
assignt
ClNiCO
ClCuCO
ClAgCO
Cl2NiCO
Cl2CuCO
2184.0
1958.6
1841.7
2134.5
1951.2
1800.7
1.0232
1.0227
1.0228
Ag(CO)Cl
Ag(CO)3
Ag(CO)2
2174 (713, 2212 (595, 2235 (459, 2248 (291,
σ)
502 (3, σ)
362 (1, π)
345 (53, σ) 345 (40, σ) 244 (26, σ) 329 (1, b2)
71 (15, π)
2262 (260,
a1)
σ)
σ)
a1)
485 (1, σ)
369 (2, π)
341 (15, σ) 451 (120, b2) 427 (82, b2)
273 (2, π)
338 (3, a1)
324 (1, a1)
311 (4, b2)
291 (2, a1)
250 (2, b1)
97 (11, b1)
88 (8, a1)
38 (0, b2)
78 (10, π)
57 (10, π)
277 (5, a1)
236 (1, b1)
104 (8, a1)
52 (0, b2)
51 (11, b1)
Ta ble 5. Ca lcu la ted Vibr a tion a l F r equ en cies
(cm -1) a n d In ten sities (k m /m ol, in P a r en th eses) of
th e M(CO)2Cl a n d M(CO)2Cl2 Molecu les (M ) Ni,
Cu )a
Ni(CO)2Cl
Cu(CO)2Cl
Ni(CO)2Cl2
Cu(CO)2Cl2
2192 (457, a1) 2220 (204, a1) 2250 (0, ag)
2149 (939, b2) 2186 (868, b2) 2219 (778, b1u
2255 (0, ag)
2249 (440, b1u)
)
457 (1, a1)
430 (13, a1)
373 (39, b2)
351 (3, b1)
320 (46, a1)
293 (2, b2)
253 (0, a2)
76 (4, b1)
370 (18, a1)
361 (8, b2)
334 (6, a1)
304 (2, b1)
303 (17, a1)
276 (20, b2)
227 (0, a2)
61 (4, b1)
530 (57, b2u
)
391 (75, b2u)
459 (8, b3u
445 (0, b3g
)
)
356 (0, b3g
342 (7, b2u
288 (0, ag)
272 (1, b1u
265 (2, b3u
210 (0, b2g
192 (0, ag)
)
)
421 (72, b2u
404 (18, b1u
367 (0, ag)
)
)
)
)
)
333 (0, b2g
311 (0, ag)
)
a
Only the highest 10 vibrational frequencies are listed.
F igu r e 7. Calculated geometric parameters (bond lengths
in angstroms, bond angles in degrees) of the M(CO)Cl and
M(CO)2Cl molecules.
shifted to 2141.2 cm-1 with 13CO, and no intermediate
absorption was observed in the mixed 12CO + 13CO
spectrum, indicating that only one CO is involved in this
mode. DFT calculations predicted the Ni(CO)Cl2 mol-
ecule to have a 3A2 ground state with planar C2v
geometry. The NiCl2 unit in Ni(CO)Cl2 is slightly bent
(154.8°), while NiCl2 is linear. The C-O stretching and
antisymmetric NiCl2 stretching modes were predicted
CO, MCl, and MCl2 are also shown in the figures. The
calculated vibrational frequencies and intensities are
listed in Tables 4 and 5.
Discu ssion
Ni(CO)Cl2. DeKock et al. have deposited thermal
evaporated NiCl2 in CO-doped Ar and obtained two new
absorptions at 2189 and 468 cm-1. These two bands
were assigned to the antisymmetric NiCl2 and C-O
stretching vibrations of the Ni(CO)Cl2 molecule.7,8 Simi-
lar absorptions at 2190.2 and 469.1 cm-1 were observed
in our laser ablation experiments. The 2190.2 cm-1 band
at 2248 and 450 cm-1
.
Ni(CO)Cl. Codeposition of laser-ablated NiCl2 with
CO in excess argon produced a new absorption at 2118.7
cm-1. This band shifted to 2069.9 cm-1 with 13CO and
gave a 12C/13C ratio of 1.0236. Although the number of
CO groups involved cannot be determined using a mixed
12CO + 13CO sample due to the strong absorptions of

Ni, Cu, and Ag Carbonyl Chlorides
Organometallics, Vol. 20, No. 6, 2001 1141
Ta ble 6. Sca lin g F a ctor s a n d th e Obser ved a n d
Ca lcu la ted Isotop ic C-O Str etch in g Vibr a tion a l
F r equ en cy Ra tios of th e Obser ved Ca r bon yl
Ch lor id e Molecu les
alterations were observed in the CuCl2 and AgCl experi-
ments, suggesting that the 2148.4 cm-1 band is not due
to the site of H2O-CO. The 2148.4 cm-1 absorption
shifted to 2101.2 cm-1 with 13CO and defines a 12CO/
13CO ratio of 1.0225, indicating a C-O stretching
vibration. This band appeared only on annealing, sug-
gesting more than one CO involvement. In the low-
frequency region, two weak bands at 525.2 and 434.4
cm-1 went together with the 2148.4 cm-1 band, sug-
gesting different modes of the same molecule. The 434.4
cm-1 band can be assigned to an antisymmetric NiCl2
stretching vibration from its isotopic structure. These
three bands are assigned to the Ni(CO)2Cl2 molecule.
The 525.2 cm-1 band is due to in-plane NiCO bending
mode. The two low-frequency modes have been reported
at 522.8 and 428.2 cm-1 in solid CO,9 which are in good
agreement with our argon matrix values. As shown in
Figure 8, the Ni(CO)2Cl2 molecule was calculated to
12CO/13CO
molecule
scaling factor
obsd
calcd
Ni(CO)Cl2
Ni(CO)Cl
Ni(CO)2Cl
0.974
0.975
0.970a
0.966b
0.968
0.975
0.975
0.975a
0.975b
0.972
0.977
1.0229
1.0236
1.0231
1.0226
1.0225
1.0230
1.0235
1.0232
1.0226
1.0231
1.0236
1.0230
1.0234
1.0231
1.0232
1.0236
1.0235
1.0230
1.0231
1.0231
Ni(CO)2Cl2
Cu(CO)Cl2
Cu(CO)Cl
Cu(CO)2Cl
Cu(CO)2Cl2
Ag(CO)Cl
1.0232
a
b
Symmetric mode. Antisymmetric mode.
13CO, one CO unit is most probably involved in this
mode, as the 2118.7 cm-1 band is the major product
absorption observed on sample deposition in all experi-
ments. This band increased on annealing in a lower CO
concentration experiment but decreased on annealing
in a higher CO concentration experiment. We know that
laser ablation of the NiCl2 target produces NiCl2 as well
as NiCl and Ni atoms. The 2118.7 cm-1 band was not
observed either in thermal evaporated NiCl2 + CO/Ar
experiments or in laser-ablated Ni + CO/Ar experi-
ments, suggesting that the 2118.7 cm-1 band is most
probably due to the reaction product of NiCl and CO.
Accordingly, the 2118.7 cm-1 band is assigned to the
C-O stretching vibration of the Ni(CO)Cl molecule. The
assignment is strongly supported by DFT calculations.
As shown in Figure 7, the Ni(CO)Cl molecule was
predicted to have a 2Σ+ ground state with linear
structure. The Ni-Cl, Ni-C, and C-O bond lengths
were calculated to be 2.120, 1.821, and 1.134 Å, respec-
tively. The C-O bond length is 0.006 Å longer than that
of diatomic CO calculated at the same level. The C-O
stretching vibration was predicted at 2174 cm-1; we note
that the vibrational fundamental of diatomic CO was
calculated to be 2212 cm-1 at the same level. As listed
in Table 6, the calculated isotopic frequency ratio is in
excellent agreement with the observed value. The Ni-
Cl stretching vibrational mode was calculated at 503
cm-1 with very low intensity and was not observed in
the experiments.
1
have a Ag ground state with planar D2h symmetry. The
antisymmetric C-O stretching (B1u), in-plane NiCO
bending (b2u), and antisymmetric NiCl2 stretching (b2u
)
vibrational frequencies were predicted at 2219, 530, and
421 cm-1, respectively, with 778:57:72 relative intensi-
ties.
Cu (CO)Cl. The 2156.8 cm-1 band is the major
product absorption in experiments with CuCl2 and CuCl
targets. It shifted to 2107.3 cm-1 with 13CO and gave a
12CO/13CO isotopic ratio of 1.0235. A doublet isotopic
structure was presented in the mixed 12CO + 13CO
spectrum, which indicated one CO involvement. This
band is assigned to the C-O stretching vibration of the
Cu(CO)Cl molecule. As shown in Figure 7, the Cu(CO)-
Cl molecule was predicted to have a 1Σ+ ground state
with linear geometry. The C-O stretching vibration was
calculated at 2112 cm-1, which requires a scaling factor
of 0.975 to fit the observed value. This scaling factor is
the same as that of the Ni(CO)Cl and Ni(CO)Cl2
molecule. The calculated 12CO/13CO isotopic ratio of
1.0236 is about the same as the experimental value. As
listed in Table 4, the CO stretching vibrational mode
was predicted to be the most intense mode of the Cu-
(CO)Cl molecule.
The solid-state Cu(CO)Cl has been prepared by pass-
ing carbon monoxide through the copper chloride solu-
tion, and the crystal structure has been characterized.6
The solid Cu(CO)Cl contains chloride-bridged layers in
which copper is approximately tetrahedrally coordi-
nated; the Cu-C and C-O distances were determined
to be 1.86 and 1.11 Å. These two bond distances of the
isolated Cu(CO)Cl molecule were calculated to be 1.826
and 1.129 Å, close to the solid values.
Cu (CO)Cl2. The 2205.5 and 459.1 cm-1 absorptions
increased together on annealing in CuCl2 + CO/Ar
experiments. These two bands were not observed in
CuCl + CO/Ar experiments, suggesting that these two
bands be due to the reaction product of CuCl2 and CO.
The 459.1 cm-1 band showed no 13CO isotopic shift and
can be assigned to an antisymmetric CuCl2 stretching
vibration. The 2205.5 cm-1 band shifted to 2156.0 cm-1
with 13CO, and no obvious intermediate was observed
in the mixed 12CO + 13CO spectrum; therefore, one CO
is most probably involved in this mode. These two bands
are assigned to the Cu(CO)Cl2 molecule following the
Ni(CO)Cl2 example. DFT calculations predicted that Cu-
Ni(CO)2Cl. Weak bands at 2126.6 and 2075.0 cm-1
increased together on annealing. These two bands
shifted to 2078.5 and 2029.1 cm-1 with 13CO and gave
12CO/13CO isotopic ratios of 1.0231 and 1.0226. The
2075.0 cm-1 band formed triplets at 2075.0, 2042.7, and
2029.1 cm-1 with 12CO + 13CO, indicating that two
equivalent CO groups are involved in this mode. These
two bands are assigned to the symmetric and antisym-
metric C-O stretching vibrations of the Ni(CO)2Cl
molecule. DFT calculations predicted the Ni(CO)2Cl
2
molecule to have a B2 ground state with symmetric and
antisymmetric C-O stretching vibrations at 2192 and
2149 cm-1, which require scaling factors of 0.970 and
0.966 to fit the experimental frequencies.
Ni(CO)2Cl2. The 2148.4 cm-1 band appeared only on
annealing. It was partially overlapped by the H2O-CO
absorption at 2149.2 cm-1 and may be due to alterna-
tions of the site of the H2O-CO. However, no such

1142 Organometallics, Vol. 20, No. 6, 2001
Shao et al.
(CO)Cl2 has a 2A1 ground state with planar C2v geom-
etry. The CO stretching and antisymmetric CuCl2
stretching vibrational modes were predicted at 2262 and
427 cm-1 with 260:82 relative intensities. The 2205.5
cm-1 CO stretching vibrational frequency is the highest
ever reported for the first-row transition-metal mono-
carbonyl dichlorides.7
Ta ble 7. Ca lcu la ted Bin d in g En er gies (De, k ca l/
m ol) of th e ClMCO a n d Cl2MCO Molecu les (M ) Ni,
Cu , Ag) w ith Resp ect to MCl + CO or MCl2 + COa
molecule
calcdb
exptl
Cl2NiCO
ClNiCO
Cl2CuCO
ClCuCO
ClAgCO
NiCO
11.0
37.7
8.7
34.2
17.8
31.6
7.4
38.9
34.8
20.6
Cu (CO)2Cl. The 2165.8 and 2131.6 cm-1 bands
increased together on annealing, suggesting different
vibrational modes of the same molecule. These two
bands were observed in both CuCl2 + CO/Ar and CuCl
+ CO/Ar experiments, and the intensities are about the
same in both experiments, which suggest that one CuCl
unit is most probably involved in this molecule. These
two bands shifted to 2116.7 and 2084.4 cm-1 with 13CO
and gave 12CO/13CO isotopic ratios of 1.0232 and 1.0226.
The isotopic ratio of the upper mode is slightly higher
than that of the lower mode, indicating more C involve-
ment in the upper mode than the lower mode. Both
bands formed triplets at 2165.8, 2154.3, and 2116.7 cm-1
and 2131.6, 2095.4, and 2084.4 cm-1 with 12CO + 13CO,
indicating that two equivalent CO molecules are in-
volved in these two modes. These two bands are as-
signed to the symmetric and antisymmetric C-O stretch-
ing vibrations of the Cu(CO)2Cl molecule. The assignment
is further confirmed by DFT calculations. As shown in
Figure 7, the Cu(CO)2Cl molecule was predicted to have
40.5 ( 5.8c
6-8d
CuCO
NiCO+
CuCO+
AgCO+
41.7 ( 2.5e
35.5 ( 1.6f
21.2 ( 1.2f
a
For comparison, the calculated and experimental binding
energies of monocarbonyl neutral species and cations are also
b
listed. Binding energies are corrected with zero point energy
d
(ZPE), this work. c Reference 35. Reference 36. e Reference 37.
f Reference 38.
synthesized the first isolable silver monocarbonyl com-
plex, Ag(CO)B(OTeF5)4, by reacting the extremely hy-
groscopic compounds AgOTeF5 and AgB(OTeF5)4 with
a CO atmosphere.31 The solid-state IR spectrum of Ag-
(CO)B(OTeF5)4 exhibited a CO stretching vibrational
frequency at 2204 cm-1, 20 cm-1 higher than that of
the Ag(CO)Cl. Recently, the AgCO+ cation has been
formed and identified in solid neon; the C-O stretching
frequency was observed at 2233.1 cm-1 30
.
1
a A1 ground state with C2v symmetry. The symmetric
In our AgCl + CO/Ar experiments, no evidence was
found for the Ag(CO)2Cl molecule. Our DFT calculations
found a stable minimum for the Ag(CO)2Cl molecue;
however, this stable minimum is higher in energy than
Ag(CO)Cl + CO. Silver dicarbonyl, Ag(CO)2, is a stable
molecule and can be formed by reaction of a silver atom
and CO. The dicarbonyl complex Ag(CO)2[B(OTeF5)4] as
a crystalline solid has also been synthesized; this
compound lost one CO under vacuum, leaving Ag(CO)B-
(OTeF5)4.31 This may suggest that Ag(CO)2[B(OTeF5)4]
is also less stable than Ag(CO)B(OTeF5)4.
In the MCl molecules, there is partial positive charge
on the metal center; therefore, the M(CO)Cl molecules
can be viewed as CO binding to a partially charged
metal center, and the bonding mechanism will be very
similar to the MCO+ cations, the bonding mechanism
of which has been well discussed.32-34 Table 7 lists the
binding energies of the carbonyl chlorides calculated at
the B3LYP level. For comparison, the calculated and
experimental binding energies of monocarbonyl neutrals
and cations are also listed. Recent studies have shown
that the B3LYP hybrid functional can provide very
reliable predictions of the binding energies of transition-
metal-containing compounds.15-17 As can be seen from
Table 7, B3LYP calculations predicted the binding
energies of NiCO+, CuCO, CuCO+, and AgCO+ quite
well.35-38 The large difference between calculated and
experimental binding energies of NiCO is due to the dif-
and antisymmetric C-O stretching vibrational modes
were calculated to be 2220 and 2186 cm-1 with 204:868
relative intensities. As listed in Table 6, the calculated
isotopic ratios are in good agreement with the experi-
mental values.
Cu (CO)2Cl2. Weak bands around 2178.1 cm-1 were
only observed in the CuCl2 + CO/Ar experiment on high-
temperature annealing, suggesting that these bands are
due to cluster species. The most intense 2178.1 cm-1
band is probably due to the antisymmetric C-O stretch-
ing vibration of the Cu(CO)2Cl2 molecule. As shown in
Figure 8, this molecule was predicted to have a 2Ag
ground state with planar D2h symmetry, with a strong
antisymmetric C-O stretching vibration at 2249 cm-1
.
Ag(CO)Cl. The 2184.0 cm-1 band is the only new
product absorption in the AgCl + CO/Ar experiments.
This band was observed after sample deposition and
increased on annealing. It shifted to 2134.5 cm-1 with
a
13CO sample. The 12CO/13CO ratio 1.0232 indicates
that it is a carbonyl stretching vibration, and the mixed
12CO + 13CO spectrum confirmed one CO involvement.
This band is assigned to the Ag(CO)Cl molecule. Our
DFT calculations characterized this Ag(CO)Cl molecule
1
with linear geometry and a Σ+ ground state (Figure 7).
The predicted C-O stretching vibrational frequency is
2235 cm-1, and the 12CO/13CO isotopic ratio is 1.0231.
This frequency requires a 0.977 scaling factor.
Silver is probably the only transition metal that failed
to form stable monocarbonyl. Although earlier research-
ers claimed the existence of the silver monocarbonyl in
rare-gas matrices,28 no evidence of the isolated silver
monocarbonyl was found in later experiments.29,30 The
matrix ESR and theoretical studies showed that silver
monocarbonyl is not a stable complex.29 Hurlburt et al.
(31) Hurlburt, P. K.; Anderson, O. P.; Strauss, S. H. J . Am. Chem.
Soc. 1991, 113, 6277. Hurlburt, P. K.; Rack, J . J .; Luck, J . S.; Dec, S.
F.; Webb, J . D.; Anderson, O. P.; Strauss, S. H. J . Am. Chem. Soc.
1994, 116, 10003.
(32) Barnes, L. A.; Rosi, M.; Bauschlicher, C. W., J r. J . Chem. Phys.
1990, 93, 609. Bauschlicher, C. W., J r. J . Chem. Phys. 1986, 84, 260.
(33) Blomberg, M.; Brandemark, U.; J ohansson, J .; Siegbahn, P.;
Wennerberg, J . J . Chem. Phys. 1988, 88, 4324. Mavridis, A.; Harrison,
J . F.; Allison, J . J . Am. Chem. Soc. 1989, 111, 2482.
(34) Veldkamp, A.; Frenking, G. Organometallics 1993, 12, 4613.
Ehlers, A. W.; Ruiz-Morales, Y.; Baerends, E. J .; Ziegler, T. Inorg.
Chem. 1997, 36, 5031.
(29) Kasai, P. H.; J ones, P. M. J . Phys. Chem. 1985, 89, 1147.
(30) Liang, B. Y.; Andrews, L. J . Phys. Chem. A, in press.

Ni, Cu, and Ag Carbonyl Chlorides
Organometallics, Vol. 20, No. 6, 2001 1143
ficult prediction of atomic Ni by DFT calculations. The
binding energies of Ni(CO)Cl, Cu(CO)Cl, and Ag(CO)-
Cl were predicted to be 37.7, 34.2, and 17.8 kcal/mol,
respectively, after zero point energy corrections. These
values are slightly smaller than those of the MCO+
cations. The binding energies of Ni(CO)Cl2 and Cu(CO)-
Cl2 were calculated to be 11.0 and 8.7 kcal/mol, signifi-
cantly lower than those of the Ni(CO)Cl and Cu(CO)Cl
molecules.
M(CO)2Cl2 species appeared on annealing. These mol-
ecules were formed by MCl2 and CO reactions:
NiCl2 (3Σg-) + CO f Ni(CO)Cl2 (3A2)
∆E ) -11.0kcal/mol (6)
CuCl2 (2Πg) + CO f Cu(CO)Cl2 (2A1)
∆E ) -8.7kcal/mol (7)
Thermal evaporation of MCl2 could only produce MCl2
molecules. Because of the easy formation of clusters, it
was difficult to obtain CuCl in a matrix via thermal
evaporation of solid CuCl.39 However, laser ablation of
MCl2 targets produces MCl2 as well as MCl; it is easy
to produce and isolate the MCl in argon using laser
ablation, and the M(CO)Cl species were produced via
reactions 1-3, which were predicted to be exothermic.
In lower CO concentration experiments, the M(CO)Cl
absorptions increased on annealing, suggesting that
reactions 1-3 require negligible activation energy. The
Ni(CO)Cl and Cu(CO)Cl can further react with CO to
form Ni(CO)2Cl and Cu(CO)2Cl, via reactions 4 and 5.
Ni(CO)Cl2 (3A2) + CO f Ni(CO)2Cl2 (1Ag)
∆E ) -13.1kcal/mol (8)
Cu(CO)Cl2 (2A1) + CO f Cu(CO)2Cl2 (2Ag)
∆E ) -5.0kcal/mol (9)
Con clu sion s
Laser-ablated nickel, copper, and silver chlorides
reacted with CO in excess argon to give the monocar-
bonyl chlorides M(CO)Cl (M ) Ni, Cu, Ag) and M(CO)-
Cl2 (M ) Ni, Cu). Through annealing, the dicarbonyl
chlorides M(CO)2Cl and M(CO)2Cl2 (M ) Ni, Cu) were
produced and identified.
DFT calculations have been performed for all prod-
ucts. The excellent agreement between experimental
results with the frequencies and isotopic frequency
ratios from density functional calculations support the
vibrational assignments and the identification of these
metal carbonyl chloride complexes. As listed in Table
6, the scaling factors for the C-O stretching vibrational
modes are within the range 0.968-0.977. The M(CO)Cl
molecules (M ) Ni, Cu, Ag) were predicted to have
linear structures, and the binding energies with respect
to MCl + CO were estimated to be 37.7, 34.2, and 17.8
kcal/mol, respectively. These simple transition-metal
carbonyl chloride complexes could serve as model com-
pounds for this class of complexes.
NiCl (2Σ+) + CO f Ni(CO)Cl (2Σ+)
∆E ) -37.7 kcal/mol (1)
CuCl (1Σ+) + CO f Cu(CO)Cl (1Σ+)
∆E ) -34.2 kcal/mol (2)
AgCl (1Σ+) + CO f Ag(CO)Cl (1Σ+)
∆E ) -17.8 kcal/mol (3)
Ni(CO)Cl (2Σ+) + CO f Ni(CO)2Cl (2B2)
∆E ) -18.6 kcal/mol (4)
Cu(CO)Cl (1Σ+) + CO f Cu(CO)2Cl (1A1)
∆E ) -2.7 kcal/mol (5)
In the NiCl2 + CO and CuCl2 + CO reactions, the
M(CO)Cl2 species were produced on deposition and the
Ack n ow led gm en t. We gratefully acknowledge sup-
port from the NSFC (Grant No. 20003003) and the
Chinese NKBRSF and Mr. J . Dong and H. Lu for some
experimental work.
(35) Sunderlin, L. S.; Wang, D.; Squires, R. R. J . Am. Chem. Soc.
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