Skip to main content
NCBI home page
ACS Omega logoLink to ACS Omega
. 2023 Jul 6;8(28):25392–25400. doi: 10.1021/acsomega.3c02849

Unraveling the Major Differences between the Trinuclear Cyclopentadienylmetal Carbonyl Chemistry of Cobalt and That of Nickel—A Theoretical Study

Yuexia Lin †, Hongyan Wang †,*, R Bruce King ‡,*
PMCID: PMC10357559  PMID: 37483223

Abstract

graphic file with name ao3c02849_0009.jpg

The geometries and energetics of the trinuclear cyclopentadienylmetal carbonyls Cp3M3(CO)n (Cp = η5-C5H5); M = Co, Ni; n = 3, 2, 1, 0) have been investigated by density functional theory. The cobalt and nickel systems are found to be rather different owing to the different electronic configurations of the metal atoms. For cobalt, the small calculated energy separation of 5.0 kcal/mol between the two lowest-energy singlet Cp3Co3(μ3-CO)(μ-CO)2 and Cp3Co3(μ-CO)3 tricarbonyl structures accounts for the experimental results of both isomers as stable species that can be isolated and structurally characterized by X-ray crystallography. The corresponding Cp3Ni3(CO)3 species in the nickel system are predicted not to be viable owing to exothermic CO dissociation to give the experimentally observed very stable Cp3Ni3(μ-CO)2, which is found to be the lowest-energy isomer by a substantial margin of ∼25 kcal/mol. In all of the low-energy Cp3M3(CO)n (n = 2, 1) structures, including that of the experimentally known triplet spin state Cp3Co3(μ3-CO)2, all of the carbonyl groups are face-bridging or face-semi-bridging μ3-CO groups bonded to all three metal atoms of the M3 triangle. In the lowest-energy carbonyl-free Cp3M3 (M = Co, Ni) structures, agostic C–H–M interactions are found using hydrogens of the Cp rings. In addition, the lowest-energy Cp3Ni3 is the only structure among all of the low-energy Cp3M3(CO)n (M = Co, Ni; n = 3, 2, 1, 0) structures in which each Cp ring is a bridging rather than terminal ligand.

1. Introduction

The chemistry of binary metal carbonyls dates back to the 1890 discovery of Ni(CO)4 by Mond et al.1 Shortly thereafter, the first binary iron carbonyl Fe(CO)5 and its photolysis product Fe2(CO)9 were discovered by the same research group.2 A third iron carbonyl of stoichiometry [Fe(CO)4]n was first synthesized by Dewar and Jones3 and shown to be the trimeric Fe3(CO)12 by Hieber and Becker4 in 1930 using cryoscopy in Fe(CO)5. The trimeric nature of Fe3(CO)12, showing a central Fe3 triangle with ten terminal CO groups and two bridging CO groups, was confirmed by X-ray diffraction in 1966 by Wei and Dahl after considerable disorder problems.5,6 More accurate geometrical parameters for Fe3(CO)12 were determined by Cotton and Troup in 1974 using improved X-ray crystallographic methods.7

The seminal discovery of ferrocene, Cp2Fe (Cp = η5-C5H5), in 19518,9 was soon followed by the discovery of a series of cyclopentadienyl metal carbonyl derivatives. The pentahapto coordination of the Cp ring to the metal atom in such species involves a donation of three electron pairs from the cyclopentadienide anion to the metal atom through one σ-type interaction and two orthogonal π-type interactions. For example, the anions CpM(CO)3– (M = Cr, Mo, W)10,11 are analogues of the corresponding metal hexacarbonyls M(CO)6. Similarly, the neutral mononuclear cyclopentadienylmetal carbonyls CpMn(CO)3 and CpCo(CO)2 can be considered as analogues of Cr(CO)6 and Fe(CO)5, respectively. In such comparisons of neutral cyclopentadienyl metal carbonyl derivatives with neutral binary metal carbonyl derivatives, the central metal in the cyclopentadienylmetal carbonyl lies one position to the right in the Periodic Table relative to the central metal atom in the corresponding binary metal carbonyl.

The three cyclopentadienylcobalt carbonyl derivatives analogous to the three known binary iron carbonyls Fe(CO)5, Fe2(CO)9, and Fe3(CO)12 are CpCo(CO)2, Cp2Co2(CO)3, and Cp3Co3(CO)3, respectively. A second binuclear cyclopentadienylcobalt carbonyl, namely, Cp2Co2(CO)2 with a formal Co=Co double bond,12 is also known analogous to an iron carbonyl, Fe2(CO)8. A second rather unstable triplet state Cp3Co3(CO)2 is known that would be the analogue of the unknown Fe3(CO)11.13 Finally, a tetranuclear cyclopentadienylcobalt carbonyl, Cp4Co4(CO)2, is known analogous to an iron carbonyl Fe4(CO)14. However, neither Fe2(CO)8 nor Fe4(CO)14 has been synthesized as stable species under ambient conditions.14 They have only been observed in low-temperature matrices.

The mononuclear cyclopentadienylcobalt dicarbonyl, CpCo(CO)2, is readily obtained by the reaction of Co2(CO)8 with cyclopentadiene15 or, less conveniently, by the reaction of cobaltocene, Cp2Co, with carbon monoxide under pressure.16 The binuclear Cp2Co2(CO)3 is an initial photolysis product of CpCo(CO)2 in a hydrocarbon solvent under mild conditions.17 However, it readily converts to the trinuclear Cp3Co3(CO)3 upon extended photolysis as initially reported by one of the current authors (RBK) in 1966.18 In addition, Cp2Co2(CO)3 readily loses a CO group to form the unsaturated Cp2Co2(CO)2 with a central Co=Co formal double bond.12,19 The tetranuclear derivative Cp4Co4(CO)2 is obtained by the pyrolysis of Cp3Co3(CO)3 at 130 °C in vacuum with liberation of 1 equiv of CpCo(CO)2. The rather unstable triplet state trinuclear Cp3Co3(CO)2 is obtained from the reaction of CpCo(CO)2 with 2 equiv of CpCo(C2H4)2 in a hexane solution.13

The trinuclear Cp3Co3(CO)3 is of interest because of its structural flexibility observed experimentally.20 The major isomer obtained from the photolysis of CpCo(CO)2 in toluene was shown by X-ray crystallography to have structure F (for face-bridging) (Figure 1) with one μ3-CO group bridging the Co3 triangle and the remaining μ-CO groups bridging different Co–Co edges.21 However, smaller quantities of a second isomer were isolated and shown to have structure B (for edge-bridging) with each edge of the central Co3 triangle bridged by a μ-CO group.22 The isomer T having one terminal CO group and two bridging groups has not been isolated as a stable species but is suggested to be present in solutions of isomer F based on the solution infrared spectrum of isomer F. No evidence is found for the existence of the all-terminal isomer all-term in the Cp3Co3(CO)3 system. However, the all-terminal isomer has been isolated for the analogous iridium species Cp3Ir3(CO)3 from the thermal decomposition of CpIr(CO)H2 and structurally characterized by X-ray diffraction.23

Figure 1.

Figure 1

Open in a new tab

Four structures considered for the Cp3M3(CO)3 derivatives using the designations of Robbin et al.20

Extending the analogy between cyclopentadienylmetal carbonyls and binary metal carbonyls to nickel has the binuclear cyclopentadienylnickel carbonyl Cp2Ni2(CO)2, obtained from Cp2Ni and Ni(CO)4,24 as an analogue of the well-known Co2(CO)8. However, the trinuclear cyclopentadienylnickel carbonyl Cp3Ni3(CO)2 appears to be a thermodynamic sink in cyclopentadienylnickel carbonyl chemistry. This, at least initially, was very surprising since Cp3Ni3(CO)2 does not have a closed shell diamagnetic configuration but instead is a paramagnetic molecule with a single unpaired electron corresponding to a 19-electron configuration for one of the nickel atoms but delocalized over the central Ni3 triangle. Diamagnetic heterometallic derivatives of the type (CpCo)(CpNi)2(μ-CO)2, including species with methyl-substituted Cp rings, in which all three metal atoms have the favored 18-electron configuration, have been synthesized and characterized structurally by Dahl and co-workers.25,26 The cobalt carbonyl analogue of Cp3Ni3(CO)2, namely, Co3(CO)10, is not known as a stable paramagnetic molecule. However, the corresponding Co3(CO)10– anion is obtained as its lithium salt27 by the reaction of LiCo(CO)4 with Co2(CO)8.

One objective of the current paper is to use modern density functional theory (DFT) methods to explore the energetic relationships between the four Cp3Co3(CO)3 isomers in Figure 1 including the experimentally observed F and B isomers isolated as stable species and characterized structurally by X-ray crystallography. In addition, the experimentally available species Cp3Co3(CO)3 and Cp3Ni3(CO)2 both have central nearly equilateral M3 triangles with the edges corresponding to formal single metal–metal bonds. Decarbonylation of such species might be expected to provide novel species having central M3 triangles with formal double or even triple bonds along the M–M edges. This paper reports DFT studies to explore such possibilities. In addition to predictions of formal M=M double bonds and M≡M triple bonds in unsaturated Cp3M3(CO)n (M=Co, Ni; n = 2, 1, 0) species, unusual structures are predicted for the carbonyl-free Cp3Ni3 having agostic Ni–H–C interactions to Cp rings as well as Cp rings bridging Ni–Ni edges of the Ni3 triangle.

2. Theoretical Methods

DFT methods include electron correlation effects, which have been used extensively to model organometallic compounds.28−34 Among the many DFT methods, the Minnesota 2006 local functional (M06-L) is shown to be a good quality and relatively fast local density functional for a computational tool in organometallic chemistry and catalysis.35 Three DFT methods with different exchange-correlation (XC) energy functional, M06-L method,36 as well as the B3LYP37,38 and BP8639,40 methods were used to study the structures of Cp3M3(CO)n (M = Co, Ni, n = 0–3) isomers in this paper. The geometries of all structures were fully optimized with double-ζ plus polarization (DZP) basis sets. For cobalt and nickel, the loosely contracted DZP basis set used the Wachters’ primitive sets augmented by two sets of p functions and one set of d functions and contracted following Hood et al. and designated as (14s11p6d/10s8p3d).41,42 The vibrational frequencies were determined at the same levels by evaluating analytically the second derivatives of the energy with respect to the nuclear coordinates. Because the numerical integration procedures used in existing DFT methods have significant limitations, we do not in general follow the imaginary eigenvector in search of another minimum when the predicted imaginary vibrational frequency is less than 50i cm–1. In such cases, there is a minimum of energy identical to or close to that of the stationary point in question.43−45

All of the final optimized structures reported in this paper have only real vibrational frequencies unless otherwise indicated. The corresponding infrared intensities were evaluated analytically as well. All calculations were carried out in Gaussian 09 with tight optimizations and the ultrafine integration grid (99,590).46 Only the stationary point geometries of the energetically low-lying species in the Cp3M3(CO)n (M = Co, Ni; n = 3, 2, 1, 0) systems predicted by M06-L are shown in Figures 2−6, with all listed interatomic distances given in Å. The results from the other two DFT methods are listed in the Supporting Information. For the vibrational frequencies, only the ν(CO) frequencies by BP86 are discussed. Comprehensive tables of the harmonic vibrational frequencies by BP86 are given in the Supporting Information.

Figure 2.

Figure 2

Open in a new tab

Four lowest-energy Cp3Co3(CO)3 structures. The two experimentally known structures are indicated in red.

Figure 6.

Figure 6

Open in a new tab

Two lowest-energy Cp3Co3 structures and the two lowest-energy Cp3Ni3 structures indicating the shortest distances between Cp ring hydrogen atoms and metal atoms.

3. Results and Discussion

3.1. Molecular Structures

3.1.1. Cp3Co3(CO)3 and Cp3Ni3(CO)3

The search for the stable isomers of Cp3Co3(CO)3 and Cp3Ni3(CO)3 used the four types of starting structures depicted in Figure 1. Only type B and F structures were found among the low-energy structures (Figure 2 and Table 1), consistent with the experimental structures determined by X-ray crystallography as well as infrared spectroelectrochemistry and electron paramagnetic resonance (EPR) spectroscopy.7 The lowest-energy Cp3Co3(CO)3 structure is the singlet structure Co3-1S, with one face-bridging and two edge-bridging CO groups corresponding to isomer F in Figure 1. The Co–Co bond lengths of the edges with one face-bridging CO and one edge-bridging CO in Co3-1S are 2.44 Å. The Co–Co bond length of the edge without a bridging CO group is only slightly longer at 2.48 Å. These predicted Co–Co edge lengths in Co3-1S are very close to the experimental values determined by X-ray crystallography (Table 1).21 The triplet structure Co3-2T, lying only 1.4 kcal/mol in energy above Co3-1S, has a similar Cp3Co3(μ3-CO)(μ-CO)2 configuration.

Table 1. Four Lowest-Energy Cp3Co3(CO)3 Structures.
structure ΔE, kcal/mol ⟨S2⟩ Co–Co distances, Å carbonyl configuration ν(CO), cm–1
          BP86
Co3-1S 0.0   2.438, 2.443, 2.479 μ3-CO + 2 μ-CO 1708, 1802, 1839
Expt     2.438, 2.457, 2.519   1701, 1801, 1843
Co3-2T 1.4 2.12 2.378, 2.457, 2.519 μ3-CO + 2 μ-CO 1750, 1771, 1827
Co3-3S 5.0   3 × 2.395 3 μ-CO 1808, 1808, 1848
Expt     2.396, 2.408, 2.408   1784, 1784, 1839
Co3-4T 11.1 2.11 2.416, 2.425, 2.494 3 μ-CO 1806, 1819, 1858
Open in a new tab

The next Cp3Co3(CO)3 structures in terms of relative energy, namely, Co3-3S and Co3-4T, lying 5.0 and 11.1 kcal/mol above Co3-1S, respectively, approach idealized C3v symmetry with each edge bridged by a CO group (Figure 2 and Table 1). The predicted Co–Co edge lengths of 2.395 Å in Co3-3S are essentially identical to the experimental values of 2.396, 2.408, and 2.408 Å determined by X-ray crystallography.22 Structures Co3-3S and Co3-4T thus correspond to isomer B in Figure 1. The closeness in energy of Co3-1S and Co3-3S is consistent with the degree of structural flexibility in this trinuclear system observed experimentally.20 Each of the three cobalt atoms in the singlet structures Co3-1S and Co3-3S has the favored 18-electron configuration by receiving five electrons from a neutral Cp group, two electrons from the two Co–Co bonds to adjacent cobalt atoms, and two electrons from a CO group. In the Cp3Co3(CO)3 derivatives, the edge-bridging ν(CO) frequencies range from 1806 to 1858 cm–1, whereas the face-bridging ν(CO) frequencies are significantly lower ranging from 1701 to 1750 cm–1 in accord with expectation.

Two doublet Cp3Ni3(CO)3 structures were found of similar energies (Figure 3 and Table 2). The lower-energy structure Ni3-1D is a type B (Figure 1) triply edge-bridged Cp3Ni3(μ-CO)3 structure similar to the experimentally known structure Co3-3S for Cp3Co3(CO)3. Lying only 1.5 kcal/mol in energy above Ni3-1D is a type F structure Ni3-2D analogous to the experimentally known structure Co3-1S with one face-bridging CO group and two edge-bridging CO groups. The quartet Cp3Ni3(CO)3 structures Ni3-3Q and Ni3-4Q corresponding to the doublet structures Ni3-1D and Ni3-2D, respectively, are also low-energy structures lying 4.8 and 8.7 kcal/mol above Ni3-1D. Since all three cobalt atoms in the singlet Cp3Co3(CO)3 structures have the favored 18-electron configuration, the corresponding Cp3Ni3(CO)3 structures must have 19-electron configurations for the electron-richer nickel atoms.

Figure 3.

Figure 3

Open in a new tab

Four lowest-energy Cp3Ni3(CO)3 structures.

Table 2. Four Lowest-Energy Cp3Ni3(CO)3 Structures.
structure ΔE, kcal/mol ⟨S2⟩ Ni–Ni distances, Å carbonyl configuration ν(CO), cm–1
          BP86
Ni3-1D 0.0 0.78 2.552, 2.649, 2.506 μ3-CO + 2 μ-CO 1815, 1828, 1862
Ni3-2D 1.5 0.79 2.358, 2.627, 2.847 CO + 2 μ-CO 1730, 1838, 1870
Ni3-3Q 4.8 3.85 3 × 2.512 3 μ-CO 1840, 1840, 1872
Ni3-4Q 8.7 3.86 2.510, 2.515, 2.608 μ3-CO + 2 μ-CO 1760, 1839, 1860
Open in a new tab

3.1.2. Cp3Co3(CO)2 and Cp3Ni3(CO)2

The optimized Cp3Co3(CO)2 and Cp3Ni3(CO)2 structures have a central M3 triangle bridged by a μ3-CO group on each side of the triangular face to give structures with a central M3C2 trigonal bipyramid having the metal atoms in equatorial positions and the CO carbon atoms in axial positions (Figure 4 and Table 3). The doublet Cp3Ni3(μ3-CO)2 structure Ni2-1D is known experimentally as a remarkably stable species for a paramagnetic cyclopentadienylmetal carbonyl.24 In accord with this remarkable stability, Ni2-1D lies a large 25.7 kcal/mol in energy below its quartet spin state isomer Ni2-2Q. The predicted 2.39 Å Ni–Ni distances with WBI values of 0.23 in the central equilateral Ni3 triangle of Ni2-1D are essentially identical to the experimental values of 2.39 Å as determined by X-ray crystallography.25 The spin density of the one unpaired electron in the doublet Ni2-1D is distributed equally among the three nickel atoms at 0.27 on each nickel atom reflecting its C3v symmetry. In the high-energy quartet Cp3Ni3(μ3-CO)2 isomer Ni2-2Q, the central Ni3 triangle undergoes a Jahn–Teller distortion to give a slightly distorted isosceles triangle with two long Ni–Ni distances of 2.43 and 2.44 Å and one short Ni–Ni distance of 2.31 Å corresponding to WBI values of 0.32, 0.32, and 0.25, respectively.

Figure 4.

Figure 4

Open in a new tab

Two lowest-energy Cp3Co3(CO)2 structures and the two lowest-energy Cp3Ni3(CO)2 structures. The experimentally known Cp3Ni3(CO)2 structure is indicated in red.

Table 3. Lowest-Energy Cp3M3(CO)2 (M = Co, Ni) Structures.
structure ΔE, kcal/mol ⟨S2⟩ M–M distances, Å carbonyl configuration ν(CO), cm–1
          BP86
Co2-1T 0.0 2.11 2.336, 2.358, 2.406 2 μ3-CO 1713, 1736
Expt     3 × 2.370   1710
Co2-2S 4.0   2.208, 2.385, 2.414 2 μ3-CO 1719, 1743
Ni2-1D 0.0 0.78 2.387, 2.390, 2.391 2 μ3-CO 1748, 1774
Expt     3 × 2.389   1750
Ni2-2Q 25.7 3.85 2.312, 2.433, 2.445 2 μ3-CO 1759, 1796
Open in a new tab

For the cobalt derivative Cp3Co3(μ3-CO)2, the energy difference between the singlet and triplet structures is relatively small with the singlet structure Co2-2S lying 4.0 kcal/mol above Co2-1T (Figure 4 and Table 3). The lower energy of the triplet spin-state Cp3Co3(μ3-CO)2 isomer is consistent with its synthesis as a triplet state rather unstable molecule from CpCo(CO)2 and CpCo(C2H4)2 that has been structurally characterized by X-ray crystallography.13 Our calculations show that the central Co3 triangles in both Co2-1T and Co2-2S are distorted with much greater distortion in the singlet structure Co2-2S. Thus, in the triplet structure Co2-1T, the calculated Co–Co distances are 2.336, 2.358, and 2.406 Å with corresponding WBI values of 0.32, 0.33, and 0.41, respectively, corresponding to formal single bonds. A single Co–Co distance of 2.370 Å was found experimentally for all three Co–Co bonds in the Cp3Co3(μ3-CO)2 structure Co2-1T by X-ray crystallography13 corresponding exactly to the mean of the three calculated values.

The singlet Cp3Co3(μ3-CO)2 structure Co2-2S has one short Co=Co distance of 2.208 Å with a WBI of 0.54 that can be considered as a formal double bond as well as longer Co–Co distances of 2.385 and 2.414 Å with WBIs of 0.38 and 0.37 that can be considered as formal single bonds. Thus, loss of a bridging carbonyl group from the singlet tricarbonyl Cp3Co3(μ3-CO)(μ-CO)2 structure Co3-1S with 18-electron configurations for all three cobalt atoms to give the singlet dicarbonyl Co2-2S is balanced by increasing the bond order of one of the edges of the central Co3 triangle from single to double as reflected in one Co=Co edge becoming ∼0.2 Å shorter than the other two Co–Co edges. This allows each of the cobalt atoms in the dicarbonyl Co2-2S to retain the favored 18-electron configuration for a singlet spin-state structure.

The triplet structure Co2-1T has a spin density of 1.91 for the triplet spin state concentrated on one of the cobalt atoms with the other two cobalt atoms bearing essentially zero spin density. Structure Co2-1T can be constructed from the stable known species Cp2Co2(μ-CO)2 with a formal Co=Co double bond and 18-electron cobalt configurations by adding a CpCo moiety across the Co=Co double bond. This reduces the original Co=Co double bond order in the Cp2Co2(μ-CO)2 moiety to a single Co–Co bond. However, the new Co–Co linkages from the CpCo moiety give that moiety a 16-electron configuration. In a high-spin system, this can account for the two unpaired electrons of the triplet spin state of Co2-1T. During this process, the two edge-bridging μ-CO groups in the binuclear Cp2Co2(μ-CO)2 moiety become face-bridging μ3-CO groups in the trinuclear structure.

3.1.3. Cp3Co3(CO) and Cp3Ni3(CO)

All of the low-energy Cp3M3(CO) (M = Co, Ni) structures have a μ3-CO group bridging a central M3 triangle (Figure 5 and Table 4). For both cobalt and nickel, the same type of structure with different spin states is closely spaced in energy. Thus, the singlet Cp3Co3(μ3-CO) structure Co1-2S lies only 4.0 kcal/mol in energy above its triplet isomer Co1-1T. Similarly, the quartet Cp3Ni3(μ3-CO) structure Ni1-2Q lies only 1.9 kcal/mol in energy above its doublet isomer Ni1-1D. The singlet Cp3Co3(μ3-CO) structure Co1-2S has ideal C3v symmetry with a central equilateral Co3 triangle with 2.248 Å edges short enough to suggest multiple bonding. A delocalized resonance hybrid having three equivalent canonical structures with two Co=Co double bonds and one Co–Co single bond for Co1-2S gives each cobalt atom the favored 18-electron configuration. The triplet Cp3Co3(μ3-CO) structure Co1-1T, however, appears to be distorted from ideal C3v symmetry with Co=Co distances of 2.264 and 2.314 Å suggesting Co=Co double bonds and a longer Co–Co distance of 2.389 Å suggesting a Co–Co single bond. For the nickel systems, the quartet Cp3Ni3(μ3-CO) structure Ni1-2Q has ideal C3v symmetry with equivalent Ni–Ni distances of 2.327 Å with WBIs of 0.32 in the central Ni3 triangle and equivalent spin densities of 0.75 on each nickel atom. The doublet Cp3Ni3(μ3-CO) structure Ni1-1D is only slightly distorted from C3v symmetry with Ni–Ni distances of 2.29, 2.29, and 2.33 Å with WBIs of 0.38 falling within a fairly narrow 0.04 Å range. However, in Ni1-1D, the spin density is concentrated mainly on one of the three nickel atoms, which bears a spin density of 0.72 as compared with spin densities of only 0.02 on each of the other two nickel atoms.

Figure 5.

Figure 5

Open in a new tab

Two lowest-energy Cp3Co3(CO) structures and the two lowest energy Cp3Ni3(CO)2 structures.

Table 4. Lowest-Energy Cp3M3(CO) (M = Co, Ni) Structures.
structure ΔE, kcal/mol ⟨S2⟩ M–M distances, Å carbonyl configuration ν(CO), cm–1
          BP86
Co1-1T 0.0 2.97 2.264, 2.314, 2.389 μ3-CO 1738
Co1-2S 4.0   2.247, 2 × 2.248 μ3-CO 1739
Ni1-1D 0.0 0.87 2 × 2.292, 2.331 μ3-CO 1761
Ni1-2Q 1.9 3.85 3 × 2.327 μ3-CO 1748
Open in a new tab

3.1.4. Cp3Co3 and Cp3Ni3

The lowest-energy structure for the carbonyl-free Cp3Co3, namely, Co-1T, has ideal C3v symmetry with three equivalent Co–Co distances of 2.305 Å (Figure 6 and Table 5). The triplet spin density is also distributed evenly among the equivalent cobalt atoms with 0.70 on each atom. The locations of the Cp rings relative to the central Co3 triangle in Co-1T are distorted enough to bring one of the hydrogen atoms within 2.47 Å of a cobalt atom suggesting agostic C–H–Co bonding. The triplet spin state is greatly favored for Cp3Co3 since the singlet isomer Co-2S lies 16.7 kcal/mol in energy above the triplet isomer Co-1T. The central Co3 triangle in Co-2S has two short Co=Co distances of 2.139 and 2.151 Å with WBIs of 1.05 and 0.97 suggesting formal double bonds and one longer Co–Co distance of 2.478 Å with a WBI of 0.59 suggesting a formal single bond.

Table 5. Lowest-Energy Cp3M3 (M = Co, Ni) Structures.
structure ΔE, kcal/mol ⟨S2⟩ M–M distances, Å structural features
Co-1T 0.0 2.23 3 × 2.305 Co–H(Cp): 3 × 2.47 Å
Co-2S 16.9   2.139, 2.151, 2.478 Co–H(Cp): 2 × 2.79 Å
Ni-1Q 0.0 3.80 2.336, 2.374, 2.406 bridging μ-η3,η2-Cp
Ni-2D 14.4 1.99 2.317, 2.355, 2.356 no short Ni–H(Cp)
Open in a new tab

The lowest-energy Cp3Ni3 structure is a rather unusual quartet structure Ni-1Q in which each Cp ring is a η3,η2 ligand bridging a Ni–Ni edge of the Ni3 triangle by forming a trihapto ligand to one nickel atom and a dihapto ligand to the other nickel atom (Figure 6 and Table 5). This is the only Cp3M3(CO)n structure found in this work with bridging Cp ligands rather than terminal Cp ligands. Furthermore, one hydrogen atom in each of the bridging Cp ligands of Ni-1Q lies within 2.127 Å, indicating a C–H–Ni agostic interaction. The Ni–Ni distances of 2.336, 2.374, and 2.406 Å with WBIs of 0.32 are in a reasonable range for formal single bonds. Each nickel atom in Ni-1Q has a 19-electron configuration by receiving five electrons from portions of two bridging η3,η2-Cp ligands, two electrons from an agostic C–H–Ni interaction, and two electrons from Ni–Ni single bonds to adjacent nickel atoms. The quartet Cp3Ni3 structure Ni-1Q is favored significantly over its doublet isomer Ni-2D lying 14.4 kcal/mol in energy above Ni-2D. Structure Ni-2D has the usual terminal pentahapto Cp rings, no Ni–H distances short enough to indicate C–H–Ni agostic interactions, and fairly similar Ni–Ni distances of 2.317, 2.355, and 2.356 Å with WBIs of 0.57, 0.51, and 0.51 and in its central Ni3 triangle. One of the nickel atoms in Ni-2D has a spin density of 0.89 corresponding to the unpaired electron of its doublet spin state. The other two nickel atoms in Ni-2D have negligible spin densities with absolute values less than 0.07.

3.2. Thermochemistry

In order to check the viability of the Cp3M3(CO)n (M = Co, Ni; n = 3, 2, 1) derivatives, the CO dissociation energies (ΔEdiss) based on the lowest-energy structures were determined for the following processes:

3.2.

In addition, the following formulas were used to calculate the energies of formation (ΔH) and the Gibbs free energy (ΔG), where Eelec, Evib, Erot, and Etranst correspond to the electronic energy, vibrational energy, rotational energy, and transition energy, respectively:

3.2.

For all of these systems, the CO dissociation process is endothermic except for the trinickel tricarbonyl derivative Cp3Ni3(CO)3 for which CO dissociation to give the very stable dicarbonyl Cp3Ni3(μ3-CO)2 is clearly exothermic (see the red line in Table 6). The instability of Cp3Ni3(CO)3 toward CO loss clearly relates to the 19-electron configurations of its nickel atoms and the resulting need to shed one of its CO groups to bring the electron configurations of the nickel atoms down to 18 electrons or less.

Table 6. Energies (kcal/mol) for Carbonyl Dissociation of Cp3M3(CO)n (M = Co, Ni; n = 3, 2, 1) Derivatives Based on the Global Minima for Each Structure by the M06L Methoda.

  ΔE, kcal/mol ΔH298, kcal ΔG298, kcal
Cp3Co3(CO)3 (Co3-1S) → Cp3Co3(CO)2 (Co2-1T) + CO 23.5 24.1 9.0
Cp3Co3(CO)2(Co2-1T) → Cp3Co3(CO) (Co1-1T) + CO 55.6 56.2 43.8
Cp3Co3(CO) (Co1-1T) → Cp3Co3 (Co-1T) + CO 62.7 63.3 54.1
Cp3Ni3(CO)3 (Ni3-1D) → Cp3Ni3(CO)2 (Ni2-1D) + CO –7.4 –6.8 –14.3
Cp3Ni3(CO)2(Ni2-1D) → Cp3Ni3(CO) (Ni1-1D) + CO 42.7 43.3 27.2
Cp3Ni3(CO) (Ni1-1D) → Cp3Ni3 (Ni-2Q) + CO 47.6 48.2 38.8
Open in a new tab
a

The single exothermic process is indicated in red.

3.3. Electron Paramagnetic Resonance

EPR has been shown to be an efficient and reliable tool to reveal the local structures of transition metals in their paramagnetic compounds. The EPR spectra of triplet Cp3Co3(CO)n (n = 3, 2, 1, 0) and doublet and quartet Cp3Ni3(CO)n (n = 3, 2, 1, 0) have been simulated by ORCA47,48 and EasySpin49 programs based on the optimized structures (Figure 7). The shapes of the simulated EPR spectra and the positions of resonant magnetic fields are quite close to each other except for Ni3-1D. The anisotropy g exhibits slight differences for the different coordination numbers (Table 7). Our calculated values of gx, gy, and gz of 2.02, 2.02, and 2.06, respectively, for the experimentally known and very stable Ni2-1D structure of Cp3Ni3(μ3-CO)2 are close to the corresponding experimental values of 2.02, 2.02, and 2.10 in the most recent reported EPR study.50

Figure 7.

Figure 7

Open in a new tab

Simulated EPR spectra for triplet Cp3Co3(CO)n (n = 3, 2, 1, 0), doublet, and quartet Cp3Ni3(CO)n (n = 3, 2, 1, 0).

Table 7. Calculated g Factors and Hyperfine Structure Constants (in 10–4 cm–1) for Cp3M3(CO)n (Cp = η5-C5H5); M = Co, Ni; n = 3, 2, 1, 0).

  gx gy gz A1 A2 A3
Co-1T 2.01 2.02 2.11 0.31 0.80 4.35
Co1-1T 2.04 2.06 2.09 –0.32 0.70 1.81
Co2-1T 2.01 2.13 2.18 –0.13 –0.55 –1.81
Co3-4 T 2.02 2.06 2.08 –0.23 –0.45 1.18
Co3-2T 2.02 2.03 2.06 –0.46 –1.87 2.83
Ni-1Q 2.04 2.08 2.10 1.60 –3.18 –3.28
Ni1-2Q 2.08 2.08 2.09 –1.59 –1.71 4.71
Ni2-2Q 2.02 2.05 2.07 –1.70 –1.81 4.23
Ni3-3Q 2.02 2.02 2.04 –0.38 0.73 –4.39
Ni3-4Q 2.01 2.02 2.04 –2.34 –2.55 5.23
Ni-2D 2.03 2.03 2.17 –2.36 –3.08 19.30
Ni1-1D 2.01 2.11 2.14 –0.51 –0.80 1.34
Ni2-1D 2.02 2.02 2.06 1.68 –2.05 –2.54
Ni3-1D 1.81 2.01 2.03 0.27 –1.09 2.19
Ni3-2D 1.99 2.02 2.05 –1.94 –2.51 17.32
Open in a new tab

4. Summary

The small calculated energy separation of 5.0 kcal/mol between the two lowest-energy singlet Cp3Co3(μ3-CO)(μ-CO)2 and Cp3Co3(μ-CO)3 isomers accounts for the experimental results, indicating that both isomers are stable species that can be isolated separately and structurally characterized by X-ray crystallography. The corresponding Cp3Ni3(CO)3 species in the nickel system are not viable owing to exothermic CO dissociation to give the experimentally observed very stable Cp3Ni3(μ-CO)2, which is found to be the lowest-energy isomer by a substantial margin of ∼25 kcal/mol. In all of the low-energy Cp3M3(CO)n (n = 2, 1) structures, all of the carbonyl groups are face-bridging or semi-face-bridging μ3-CO groups bonded to all three metal atoms of the M3 triangle. In the lowest-energy carbonyl-free Cp3M3 (M = Co, Ni) structures, the Cp rings are oriented to bring one of their hydrogen atoms into bonding distance to a metal atom leading to agostic C–H–M interactions. In addition, the lowest-energy Cp3Ni3 is the only structure among all of the low-energy Cp3M3(CO)n (M = Co, Ni; n = 3, 2, 1, 0) structures in which each Cp ring bridges an M–M edge of the M3 triangle rather than functioning as a terminal pentahapto ligand to a single metal atom.

Acknowledgments

Hongyan Wang is grateful to the Sichuan Science and Technology program (Grant No. 2021YFG0228) for supporting this work.

Supporting Information Available

The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/acsomega.3c02849.

  • Energies, relative energies, and metal–metal distances for the Cp3M3(CO)n (M = Co, Ni, n = 3, 2, 1, 0) structures by the B3LYP and BP86 methods; complete tables of metal–carbon and carbon–carbon distances (in Å) for the Cp3M3(CO)n (M = Co, Ni, n = 3, 2, 1, 0) structures by the M06L, B3LYP, and BP86 methods; harmonic vibrational frequencies of the Cp3M3(CO)n (M = Co, Ni, n = 3, 2, 1, 0) structures by the BP86 method; Wiberg bond indices for the M–M bonds in Cp3M3(CO)n (M = Co, Ni, n = 3, 2, 1, 0); and spin densities for the M atoms in Cp3M3(CO)n (M = Co, Ni, n = 3, 2, 1, 0) (PDF)

  • Coordinates (XYZ)

The authors declare no competing financial interest.

Supplementary Material

ao3c02849_si_001.pdf (494.2KB, pdf)
ao3c02849_si_002.xyz (49.5KB, xyz)

References

  1. Mond L.; Langer C.; Quinncke F. L.–Action of carbon monoxide on nickel. J. Chem. Soc., Trans. 1890, 57, 749–753. 10.1039/CT8905700749. [DOI] [Google Scholar]; reprinted in J. Organomet. Chem.1990, 383, 1–5
  2. Mond L.; Langer C. XCIII. On iron carbonyls. J. Chem. Soc., Trans. 1891, 59, 1090–1093. 10.1039/CT8915901090. [DOI] [Google Scholar]
  3. Dewar J.; Jones H. O. On a new iron carbonyl, and on the action of light and heat on the iron carbonyls. Proc. R. Soc. A 1907, 79A, 66–80. 10.1098/rspa.1907.0015. [DOI] [Google Scholar]
  4. Hieber W.; Becker E. Iron tetracarbonyl and its chemical behaviour. Chem. Ber. 1930, 63, 1405–1417. [Google Scholar]
  5. Wei C. H.; Dahl L. F. Molecular structures of triiron dodecacarbonyl and tetracobalt dodecacarbonyl. J. Am. Chem. Soc. 1966, 88, 1821–1822. 10.1021/ja00960a046. [DOI] [Google Scholar]
  6. Wei C. H.; Dahl L. F. Dodecacarbonyltriiron: analysis of its stereochemistry. J. Am. Chem. Soc. 1969, 91, 1351–1361. 10.1021/ja01034a016. [DOI] [Google Scholar]
  7. Cotton F. A.; Troup J. M. Further refinement of the molecular structure of triiron dodecacarbonyl. J. Am. Chem. Soc. 1974, 96, 4155–4159. 10.1021/ja00820a016. [DOI] [Google Scholar]
  8. Kealy T. J.; Pauson P. L. A new type of organo-iron compound. Nature 1951, 168, 1039–1040. 10.1038/1681039b0. [DOI] [Google Scholar]
  9. Miller S. A.; Tebboth J. A.; Tremaine J. F. Dicyclopentadienyliron. J. Chem. Soc. 1952, 632–635. 10.1039/JR9520000632. [DOI] [Google Scholar]
  10. Piper T. S.; Wilkinson G. Alkyl and aryl derivatives of pi-cyclopentadienyl compounds of chromium, molybdenum, tungsten, and iron. J. Inorg. Nucl. Chem. 1956, 3, 104–124. 10.1016/0022-1902(56)80073-0. [DOI] [Google Scholar]
  11. Fischer E. O.; Hafner W.; Stahl H. O. On cyclopentadienylmetal-carbonyl hydrogens of chromium, molybdenum, and tungsten. Z. Anorg. Allg. Chem. 1955, 282, 47–62. 10.1002/zaac.19552820109. [DOI] [Google Scholar]
  12. Shore N. E.; Ilenda C. S.; Bergman R. G. Crystal and molecular structure, spectroscopic properties, and redox behavior of [η5-C5H5CoCO]•–, a “mixed-valence” organometallic radical anion having a high degree of intramolecular delocalization and cobalt in formal oxidation state +0.5. J. Am. Chem. Soc. 1976, 98, 256–258. 10.1021/ja00417a053. [DOI] [Google Scholar]
  13. Barnes C. E.; Orvis J. A.; Staley D. E.; Rheingold A. L.; Johnson D. C. Synthesis, structure, and reactivity of Cp3Co3(CO)2. J. Am. Chem. Soc. 1989, 111, 4992–4994. 10.1021/ja00195a070. [DOI] [Google Scholar]
  14. Fedrigo S.; Haslett T. L.; Moskovits M. A new binary carbonyl of iron: the synthesis of Fe4(CO)14 by co-deposition of mass-selected Fe4 with CO. Chem. Phys. Lett. 1999, 307, 333–338. 10.1016/S0009-2614(99)00549-7. [DOI] [Google Scholar]
  15. Piper T. S.; Cotton F. A.; Wilkinson G. Cyclopentadienyl-carbon monoxide and related compounds of some transitional metals. J. Inorg. Nucl. Chem. 1955, 1, 165–174. 10.1016/0022-1902(55)80053-X. [DOI] [Google Scholar]
  16. Fischer E. O.; Jira R. Cyclopentadienylcobalt dicarbonyl. Z. Naturforsch. 1955, 10b, 355. [Google Scholar]
  17. Vollhardt K. P. C.; Bercaw J. E.; Bergman R. G. Photochemistry of η5-cyclopentadienylcobalt dicarbonyl and thermal decomposition of derived cobalt cluster complexes. Isolation of bis(η5-cyclopentadienylcobalt) tricarbonyl, tris(η5-cyclopentadienylcobalt monocarbonyl), and tetra(η5-cyclopentadienylcobalt) dicarbonyl. J. Organomet. Chem. 1975, 97, 283–297. [Google Scholar]
  18. King R. B. Polynuclear cyclopentadienylmetal carbonyls of iron and cobalt. Inorg. Chem. 1966, 5, 2227–2230. 10.1021/ic50046a032. [DOI] [Google Scholar]
  19. Lee W.-S.; Brintzinger H. H. Reactive intermediates in the photolysis of cyclopentadienylcobalt(I) dicarbonyl and in the reduction of cyclopentadienylcobalt(III) diiodide. J. Organomet. Chem. 1977, 127, 87–92. 10.1016/S0022-328X(00)84198-4. [DOI] [Google Scholar]
  20. Robben M. R.; Rieger P. H.; Geiger W. E. Geometric preferences of tricobalt clusters having 47–49 valence electron counts: Deceptively simple cyclic voltammetric responses and EPR evidence for exchange-coupled dimers in frozen solutions. J. Am. Chem. Soc. 1999, 121, 367–375. 10.1021/ja983341+. [DOI] [Google Scholar]
  21. Bailey W. I. Jr.; Cotton F. A.; Jamerson J. D.; Kolthammer B. W. S. Structure and infrared spectra of tricyclopentadienyltricobalt tricarbonyl and its methylcyclopentadienyl analogue. Inorg. Chem. 1982, 21, 3131–3135. 10.1021/ic00138a042. [DOI] [Google Scholar]
  22. Robben M. P.; Geiger W. E.; Rheingold A. L. Isolation of the all-bridging CO isomer of Cp3Co3(CO)3 and observations concerning a highly deformable small metal cluster. Inorg. Chem. 1994, 33, 5615–5616. 10.1021/ic00103a003. [DOI] [Google Scholar]
  23. Shapley J. R.; Adair P. C.; Lawson R. J.; Pierpont C. G. Thermal elimination of dihydrogen from (η5-C5H5)Ir(CO)H2. Formation, structure, and reactivity of Cs-(η5-C5H5)3Ir3(CO)3. Inorg. Chem. 1982, 21, 1701–1702. 10.1021/ic00134a096. [DOI] [Google Scholar]
  24. Fischer E. O.; Palm C. Cyclopentadienyl-metal carbonyls of nickel. Chem. Ber. 1958, 91, 1725–1731. 10.1002/cber.19580910823. [DOI] [Google Scholar]
  25. Byers L. R.; Uchtman V. A.; Dahl L. F. Synthesis and stereochemical analysis of the triangular cobalt-dinickel clusters (η5-C5H5–nMen)CoNi2(μ3-CO)2 (where n = 0, 1, 5): Direct evidence for the antibonding trimetal character of the unpaired electron in the Fischer-Palm Ni(η5-C5H5)3(μ3-CO)2 and resulting geometrical effects upon formal oxidation by replacement of a nickel with a cobalt atom. J. Am. Chem. Soc. 1981, 103, 1942–1951. [Google Scholar]
  26. Maj J. J.; Rae A. D.; Dahl L. F. Experimental analysis of the antibonding trimetal character of the HOMO in the paramagnetic Fischer-Palm Ni(η5-C5H5)(μ3-CO)2 cluster: synthesis and stereochemical characterization of the electronically equivalent [(η5-C5Me5)CoNi2(η5-C5H5)2(μ3-CO)2]− monoanion and neutral Ni3(η5-C5Me5)3(μ3-CO)2 analogue and of the [Ni3(η5-C5H5)3(μ3-CO)2]− monoanion. J. Am. Chem. Soc. 1982, 104, 3054–3063. [Google Scholar]
  27. Fachinetti G. Effect of the countercation and solvent on the formation of anionic tricobalt carbonyl clusters. J. Chem. Soc., Chem. Commun. 1979, 396. 10.1039/c39790000396. [DOI] [Google Scholar]
  28. Ziegler T.; Autschbach J. Theoretical methods of potential use for studies of inorganic reaction mechanisms. Chem. Rev. 2005, 105, 2695–2722. 10.1021/cr0307188. [DOI] [PubMed] [Google Scholar]
  29. Bühl M.; Kabrede H. Geometries of transition-metal complexes from density-functional theory. J. Chem. Theory Comput. 2006, 2, 1282–1290. 10.1021/ct6001187. [DOI] [PubMed] [Google Scholar]
  30. Brynda M.; Gagliardi L.; Widmark P. O.; Power P. P.; Roos B. O. A quantum chemical study of the quintuple bond between two chromium centers in [PhCrCrPh]: trans-bent versus linear geometry. Angew. Chem., Int. Ed. 2006, 45, 3804–3807. 10.1002/anie.200600110. [DOI] [PubMed] [Google Scholar]
  31. Sieffert N.; Bühl M. Hydrogen generation from alcohols catalyzed by ruthenium triphenylphosphine complexes: multiple reaction pathways. J. Am. Chem. Soc. 2010, 132, 8056–8070. 10.1021/ja101044c. [DOI] [PubMed] [Google Scholar]
  32. Schyman P.; Lai W.; Chen H.; Wang Y.; Shaik S. The directive of the protein: how does cytochrome P450 select the mechanism of dopamine formation?. J. Am. Chem. Soc. 2011, 133, 7977–7984. 10.1021/ja201665x. [DOI] [PubMed] [Google Scholar]
  33. Adams R. D.; Pearl W. C.; Wong Y. O.; Zhang Q.; Hall M. B.; Walensky J. R. Tetrarhena-heterocycle from the palladium-catalyzed dimerization of Re2(CO)8(μ-SbPh2)(μ-H) exhibits an unusual host-guest behavior. J. Am. Chem. Soc. 2011, 133, 12994–12997. 10.1021/ja205515u. [DOI] [PubMed] [Google Scholar]
  34. Lonsdale R.; Olah J.; Mulholland A. J.; Harvey J. N. Does compound I vary significantly between isoforms of cytochrome P450?. J. Am. Chem. Soc. 2011, 133, 15464–15474. 10.1021/ja203157u. [DOI] [PMC free article] [PubMed] [Google Scholar]
  35. Gusev D. G. Assessing the accuracy of M06-L organometallic thermochemistry. Organometallics 2013, 32, 4239–4243. 10.1021/om400412p. [DOI] [Google Scholar]
  36. Zhao Y.; Truhlar D. G. A new local density functional for main-group thermochemistry transition metal bonding, thermochemical kinetics, and nocovalent interactions. J. Chem. Phys. 2006, 125, 194101. 10.1063/1.2370993. [DOI] [PubMed] [Google Scholar]
  37. Becke A. D. Density functional thermochemistry. III. The role of exact exchange. J. Chem. Phys. 1993, 98, 5648–5652. 10.1063/1.464913. [DOI] [Google Scholar]
  38. Lee C.; Yang W.; Parr R. G. Development of the Colle-Salvetti correlation-energy formula into a functional of the electron density. Phys. Rev. B 1988, 37, 785–789. 10.1103/PhysRevB.37.785. [DOI] [PubMed] [Google Scholar]
  39. Becke A. D. Density functional exchange-energy approximation with correct asymptotic behavior. Phys. Rev. A 1988, 38, 3098–3100. 10.1103/PhysRevA.38.3098. [DOI] [PubMed] [Google Scholar]
  40. Perdew J. P. Density-functional approximation for the correlation energy of the inhomogeneous electron gas. Phys. Rev. B 1986, 33, 8822–8824. 10.1103/PhysRevB.33.8822. [DOI] [PubMed] [Google Scholar]
  41. Wachters A. J. H. Gaussian basis set for molecular wavefunctions containing third-row atoms. J. Chem. Phys. 1970, 52, 1033–1036. 10.1063/1.1673095. [DOI] [Google Scholar]
  42. Hood D. M.; Pitzer R. M.; Schaefer H. F. Electronic structure of homoleptic transition metal hydrides: TiH4, VH4, CrH4, MnH4, FeH4, CoH4, and NiH4. J. Chem. Phys. 1979, 71, 705–712. 10.1063/1.438357. [DOI] [Google Scholar]
  43. Papas B. N.; Schaefer H. F. Concerning the precision of standard density functional programs: GAUSSIAN, MOLPRO, NWCHEM, Q-VCHEM and GAMESS. J. Mol. Struct.: THEOCHEM 2006, 768, 175–181. 10.1016/j.theochem.2006.05.010. [DOI] [Google Scholar]
  44. Jacobsen H.; Ziegler T. Octacarbonyl diiron. A density functional study. J. Am. Chem. Soc. 1996, 118, 4631–4635. 10.1021/ja953509g. [DOI] [Google Scholar]
  45. Martin J. M. L.; Bauschlicher C. W.; Ricca A. On the integration accuracy in molecular density functional theory calculations using Gaussian basis sets. Comput. Phys. Commun. 2001, 133, 189–201. 10.1016/S0010-4655(00)00174-0. [DOI] [Google Scholar]
  46. Frisch M. J.; et al. Gaussian 09, Revision B.01; Gaussian, Inc.: Wallingford CT, 2010. [Google Scholar]
  47. Neese F.ORCA – An ab Initio, DFT and semiempirical program package, version 3.0; Max-Planck-Institute for Chemical Energy Conversion: Mülheim a. d. Ruhr, 2013. [Google Scholar]
  48. Ding C. C.; Wu S. Y.; Xu Y. Q.; Wu L. N.; Zhang L. DFT studies for three Cu(II) coordination polymers: Geometrical and electronic structures, g factors and UV-visible spectra. J. Chem. Phys. 2018, 508, 20–25. 10.1016/j.chemphys.2018.04.016. [DOI] [Google Scholar]
  49. Stoll S.; Schweiger A. EasySpin, a comprehensive software package for spectral simulation and analysis in EPR. J. Magn. Reson. 2006, 178, 42–55. 10.1016/j.jmr.2005.08.013. [DOI] [PubMed] [Google Scholar]
  50. North T. E.; Thoden J. B.; Spencer B.; Bjarnason A.; Dahl L. F. Synthesis and stereophysical characterization of the Fischer-Palm-related 49-electron thiocarbonyl-capped triangular nickel clusters Ni3(η5-C5H5–xMex)3(μ3-X)(μ3-Y) (x = 0, 1), containing π-acceptor X and Y capping ligands (X = Y = CS; X = CS, Y = CO): Comparative experimental/theoretical analysis of the triply bridging carbonyl and thiocarbonyl ligands in analogous molecular environments. Organometallics 1992, 11, 4326–4337. [Google Scholar]

Associated Data

This section collects any data citations, data availability statements, or supplementary materials included in this article.

Supplementary Materials

ao3c02849_si_001.pdf (494.2KB, pdf)
ao3c02849_si_002.xyz (49.5KB, xyz)

Articles from ACS Omega are provided here courtesy of American Chemical Society

RESOURCES