Binuclear Nickel Carbonyl Thiocarbonyls: MetalâMetal Multiple Bonds

J. Phys. Chem. A 2010, 114, 2365–2375

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Binuclear Nickel Carbonyl Thiocarbonyls: Metal-Metal Multiple Bonds versus Four-Electron Donor Thiocarbonyl Groups Zhong Zhang,† Qian-shu Li,*,†,‡ Yaoming Xie,§ R. Bruce King,*,†,§ and Henry F. Schaefer III§ Center for Computational Quantum Chemistry, South China Normal UniVersity, Guangzhou 510631, People’s Republic of China, Institute of Chemical Physics, Beijing Institute of Technology, Beijing 100081, People’s Republic of China, and Department of Chemistry and Center for Computational Chemistry, UniVersity of Georgia, Athens, Georgia 30602 ReceiVed: October 20, 2009; ReVised Manuscript ReceiVed: December 21, 2009

The structures of the mononuclear derivatives Ni(CS)(CO)n (n ) 3, 2, 1, 0) and the binuclear derivatives Ni2(CS)2(CO)n (n ) 5, 4, 3, 2) have been optimized by density functional theory for comparison with the corresponding structures of Ni(CO)n+1 and Ni2(CO)n+2, respectively. In the lowest energy structures for Ni(CS)(CO)n (n ) 3, 2, 1), the nickel atom has approximate tetrahedral (n ) 3), trigonal planar (n ) 2), or bent coordination (n ) 1) corresponding to 18-, 16-, and 14-electron metal configurations, respectively. The six lowest energy Ni2(CS)2(CO)5 structures all have a single CE (E ) S, O) bridge and a formal Ni-Ni single bond of length ∼2.6 to ∼2.7 Å analogous to the lowest energy Ni2(CO)7 structure. The Ni2(CS)2(CO)5 structures with a bridging CS group are of lower energies than similar structures with a bridging CO group. Higher energy Ni2(CS)2(CO)5 structures with a linear bridging CE group (E ) O, S) and no Ni · · · Ni bond are also found with tetrahedral coordination for both nickel atoms. The lowest energy Ni2(CS)2(CO)4 structures are doubly bridged structures with only two-electron donor CO and CS groups and NidNi distances of ∼2.5 Å suggesting the formal double bond needed to give both nickel atoms the favored 18-electron configuration. For Ni2(CS)2(CO)3 the structures with one four-electron donor bridging η2-µ-CS group and a formal NidNi double bond of ∼2.4 to ∼2.5 Å are energetically preferred over triply bridged structures with a shorter NitNi distance of ∼2.2 Å, corresponding to a formal triple bond and similar to the lowest energy Ni2(CO)5 structure. The lowest energy Ni2(CS)2(CO)2 structures are generally derived from Ni2(CS)2(CO)3 structures by removal of a carbonyl group. No formal quadruple bonds are found in any of the Ni2(CS)2(CO)2 structures, as indicated by the absence of ultrashort Ni 4 Ni distances. 1. Introduction Metal carbonyl chemistry dates back to the discovery of [Pt(CO)Cl2]2 in 1868.1 The first binary metal carbonyl was nickel tetracarbonyl, Ni(CO)4, which was originally synthesized by Mond, Langer, and Quincke in 1890.2 A critical factor in the subsequent development of metal carbonyl chemistry as a major area of organometallic and coordination chemistry has been the ready availability of the highly stable carbon monoxide molecule. For this reason carbon monoxide can often be used to introduce carbonyl groups into a variety of transition metal complexes, often by reactions at elevated pressures. The stability and ready availability of carbon monoxide as a reagent for the synthesis of diverse metal carbonyls contrasts with the instability of the analogous carbon monosulfide, CS, at temperatures above -100 °C. Thus indirect methods must be used to introduce thiocarbonyl groups into transition metal complexes, using compounds like carbon disulfide (CS2) or thiophosgene (SdCCl2) as sources of CS groups.3–7 In this connection the metal thiocarbonyls Fe(CO)4(CS)8 and Cr(CO)5(CS),9 analogous to Fe(CO)5 and Cr(CO)6 and with similar physical properties, have been synthesized using SdCCl2 as the source of the thiocarbonyl groups in reactions with the corresponding anions Fe(CO)42- and Cr(CO)52-. However, an * To whom correspondence should be addressed. † South China Normal University. ‡ Beijing Institute of Technology. § University of Georgia.

Figure 1. The progression of structures in the series Ni2(CO)7 f Ni2(CO)6 f Ni2(CO)5 predicted by density functional theory.

analogous synthesis of Ni(CO)3(CS) has not been reported. One difficulty is the unavailability of the dianion Ni(CO)32- as a reagent to react with thiophosgene, since reduction of Ni(CO)4 gives polynuclear nickel carbonyl anions rather than Ni(CO)32-. In addition, Ni(CO)4 is significantly less stable than either Cr(CO)6 or Fe(CO)5, suggesting that Ni(CO)3(CS) is likely to be significantly less stable than Fe(CO)4(CS) or Cr(CO)5(CS). Binuclear homoleptic nickel carbonyls are unknown experimentally. However, they have been studied theoretically using density functional methods.10 These studies predict a systematic progression of structures for the binuclear Ni2(CO)n (n ) 7, 6, 5) derivatives (Figure 1). Thus the lowest energy structure for Ni2(CO)7 has one bridging CO group and a Ni-Ni distance corresponding to a formal single bond, while the lowest energy structure for Ni2(CO)6 has two bridging CO groups and a shorter NidNi distance corresponding to a formal double bond. Furthermore, the next member of this series, namely, Ni2(CO)5,

10.1021/jp910033v  2010 American Chemical Society Published on Web 01/27/2010

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Figure 2. Optimized structures for mononuclear derivatives. In Figures 2-7, the upper distances are obtained by the B3LYP method and the lower distances by the BP86 method.

is predicted to have an interesting structure with three bridging CO groups and a still shorter NitNi distance suggestive of a formal triple bond. All of these structures have the favored 18electron configuration for both nickel atoms. Furthermore, all of the carbonyl groups in these Ni2(CO)n (n ) 7, 6, 5) structures are the usual type of two-electron donor carbonyl groups with nonbonding Ni · · · O distances in all cases. This is not particularly surprising since nickel, as a late transition metal, is not predicted to be particularly oxophilic. Recently we have used similar theoretical methods to study mononuclear and binuclear thiocarbonyl derivatives of the firstrow transition metals. Derivatives with a CS/M ratio of 1 have been chosen for this work since such compounds are more likely to be experimentally accessible, as exemplified by the known Fe(CO)4(CS)8 and Cr(CO)5(CS).9 Our theoretical studies on Fe2(CS)2(CO)n,11 Co2(CS)2(CO)n-1 (n ) 7, 6, 5, 4),12 and Fe3(CS)3(CO)m (m ) 9, 8, 7, 6)13 indicate not only that CS is a preferred bridging ligand to CO but also that four-electron donor CS groups are frequently found in the low-energy structures of binuclear derivatives in preference to higher order metal-metal multiple bonds. This makes of interest whether the lowest energy structures for the unsaturated binuclear nickel carbonyl thiocarbonyls Ni2(CS)2(CO)n (n ) 4, 3, 2) have similar nickel-nickel multiple bonds to the corresponding homoleptic carbonyl derivatives Ni2(CO)n+2 (Figure 1), or whether they have fourelectron donor bridging thiocarbonyl groups. We report now our theoretical studies on both mononuclear Ni(CS)(CO)n (n ) 3, 2, 1, 0) and binuclear Ni2(CS)2(CO)n (n ) 5, 4, 3, 2) structures. 2. Theoretical Methods Electron correlation effects were considered using density functional theory (DFT) methods, which have evolved as a practical and effective computational tool, especially for organometallic compounds.14–28 For the closely related homoleptic binuclear metal carbonyls,10,29,30 the B3LYP method often provides more reliable geometric parameters and energy terms, and the BP86 method usually predicts more reliable vibrational frequencies. Thus, two DFT methods were used in this study. The first functional is the popular B3LYP method, which is the hybrid HF/DFT method using a combination of the threeparameter Becke exchange functional (B3) with the LeeYang-Parr (LYP) generalized gradient correlation functional.31,32 The other DFT method used in the present paper is BP86, which combines Becke’s 1988 exchange functional (B) with Perdew’s 1986 gradient corrected correlation functional method (P86).33,34 Our DZP basis sets used for carbon, oxygen, and sulfur add one set of pure spherical harmonic d functions with orbital

exponents Rd(C) ) 0.75, Rd(O) ) 0.85, and Rd(S) ) 0.70 to the standard Huzinaga-Dunning-Hay contracted DZ sets.35–37 The C and O basis sets are designated as (9s5p1d/4s2p1d) and the S basis set is designated as (12s8p1d/6s4p1d). For Ni, in our loosely contracted DZP basis set, the Wachters primitive set38 is used augmented by two sets of p functions and one set of d functions, contracted following Hood, Pitzer, and Schaefer,39 and designated (14s11p6d/10s8p3d). For Ni2(CS)2(CO)5, Ni2(CS)2(CO)4, Ni2(CS)2(CO)3, and Ni2(CS)2(CO)2, there are 324, 294, 264, and 234 contracted Gaussian functions, respectively, in the present basis sets. The geometries of all structures were fully optimized using the B3LYP/DZP and BP86/DZP methods. Vibrational frequencies were determined by evaluating analytically the second derivatives of the energy with respect to the nuclear coordinates. The corresponding infrared intensities were also evaluated analytically. All of the computations were carried out with the Gaussian 03 program,40 exercising the fine grid option (75 radial shells, 302 angular points) for evaluating integrals numerically,41 while the tight (10-8 hartree) designation is the default for the self-consistent field (SCF) convergence. In the search for minima using currently implemented DFT methods, low magnitude imaginary vibrational frequencies are suspect because of significant limitations in the numerical integration procedures used in the DFT computations. Thus all imaginary vibrational frequencies with magnitude less than 100i cm-1 are considered questionable and are given less weight in the analysis.42,43 Therefore, we do not always follow such low imaginary vibrational frequencies. The optimized structures are reported in Figures 2-7 and Tables 1-5. A given Nia(CS)a(CO)b structure is designated as ab-c where a is the number of nickel atoms (the same as the number of CS groups), b is the number of CO groups, and c orders the structures according to their relative energies. Thus the lowest energy singlet structure of Ni2(CS)2(CO)5 is designated 25-1. 3. Results 3.1. Mononuclear Derivatives. All of the lowest energy mononuclear Ni(CS)(CO)n (n ) 3, 2, 1, 0) structures (Figure 2) (except for 10-2 with a four-electron donor η2-CS group) can be derived from the previously found low energy structures of the corresponding homoleptic derivatives10 by replacement of one CO group by a CS group. Structure 10-2 with a η2-CS ligand is predicted to lie 18.6 kcal/mol (B3LYP) or 20.7 kcal/ mol above 10-1. Structure 10-2 is characterized by a significantly lower ν(CS) frequency of 950 cm-1 (BP86). The Ni-C distances decrease monotonically in these Ni(CS)(CO)n (n ) 3, 2, 1, 0)

Binuclear Nickel Carbonyl Thiocarbonyls

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TABLE 1: The Total Energies (E, in hartree), Relative Energies (∆E, in kcal/mol), and Numbers of Imaginary Vibrational Frequencies (Nimg) for the First Seven Optimized Ni2(CS)2(CO)5 Structures B3LYP BP86

-E ∆E Nimg -E ∆E Nimg

25-1 (Cs)

25-2 (Cs)

25-3 (Cs)

25-4 (C2)

25-5 (Cs)

25-6 (C2)

25-7 (C2V)

4456.13246 0.0 0 4456.71336 0.0 0

4456.13208 0.2 0 4456.71223 0.7 0

4456.13157 0.6 4i 4456.71223 0.8 0

4456.12698 3.4 0 4456.7078 3.5 0

4456.12648 3.8 0 4456.70718 3.9 0

4456.12471 4.9 10i 4456.70523 5.1 9i

4456.12367 5.5 3i 4456.70443 5.6 2i

structures with successive loss of CO groups, consistent with a increase in the negative charge on nickel atom as the number of strong back-bonding carbonyl ligands is decreased. All of these mononuclear Ni(CS)(CO)n (n ) 3, 2, 1, 0) structures are genuine minima without any imaginary vibrational frequencies. 3.2. Binuclear Derivatives. 3.2.1. Ni2(CS)2(CO)5 Structures. Nine structures have been optimized for Ni2(CS)2(CO)5, including seven singly bridged structures with short Ni-Ni distances suggesting a formal single bond (Figure 3 and Table 1), as well as two structures with a linear CE (E ) O, S) bridge between the two nickel atoms and very long nonbonding Ni · · · Ni

distances (Figure 4 and Table 2). In the latter structures the linear bridging CE ligand donates a total of four electrons, namely, two to each nickel atom. The three Ni2(CS)(µ-CS)(CO)5 structures with a single bridging CS group and a Ni-Ni bond, namely, 25-1, 25-2, and 25-3 (Figure 3 and Table 1) are essentially degenerate, lying within ∼1 kcal/mol of each other. These structures can be derived from the previously found10 global minimum structure of Ni2(CO)7 by replacement of the bridging CO group and one terminal CO group by CS groups. These three structures differ only in the location of the terminal CS group relative to the

Figure 3. Seven singly bridged structures for Ni2(CS)2(CO)5 with Ni-Ni bonds.

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Figure 4. The two structures for Ni2(CS)2(CO)5 with linear CE bridges and no Ni-Ni bond.

TABLE 2: The Total Energies (E, in hartree), Relative Energies (∆E, in kcal/mol), and Numbers of Imaginary Frequencies (Nimg) for the Two Optimized Ni2(CS)2(CO)5 Structures with Linear Bridging CE Groups B3LYP BP86


25-8 (C1)

25-9 (C1)

4456.12667 3.6 0 4456.70159 7.4 0

4456.12675 3.6 0 4456.69431 11.9 0

central Ni2(µ-CS) unit. The Ni-Ni distances in these structures fall in the range 2.63 ( 0.03 Å consistent with the formal single bond required to give both nickel atoms the favored 18-electron configuration. Four Ni2(CS)2(CO)4(µ-CO) structures were found with a single bridging CO group, namely, 25-4, 25-5, 25-6, and 25-7 (Figure 3 and Table 1). These structures fall in a relatively narrow energy range of 4.5 ( 1.2 kcal/mol and again differ only in the relative locations of the two terminal CS groups. The Ni2(CS)2(CO)5 structures with bridging CO groups are thus seen to be higher energy structures than those with bridging CS groups in accord with previous observations on binuclear iron11 and cobalt12 carbonyl thiocarbonyl derivatives. The Ni-Ni bond distances of 2.73 ( 0.05 Å in the carbonyl bridged Ni2(CS)2(CO)4(µ-CO) structures (25-4, 25-5, 25-6, and 25-7) are predicted to be significantly longer (by ∼0.1 Å) than those in the thiocarbonyl bridged Ni2(CS)(µ-CS)(CO)5 structures (25-1, 25-2, and 25-3) but can still be interpreted as the formal single bonds required to give both metal atoms the favored 18electron configuration. A similar increase in the Co-Co single bond distance in the predicted saturated Co2(CS)2(CO)6 structures was previously noted,12 as bridging CS groups are replaced by bridging CO groups in doubly bridged structures. The remaining two Ni2(CS)2(CO)5 structures 25-8 and 25-9 have unprecedented linear bridging CE (E ) O, S) groups in which the carbon atom of the bridging CE group is bonded to one nickel atom and the oxygen or sulfur of the bridging CE group is bonded to the other nickel atom (Figure 4 and Table 2). There is clearly no direct Ni-Ni bond in these structures. However, since the linear bridging CE groups are formal fourelectron donors, each nickel atom has the favored 18-electron configuration. The local environment of each nickel atom is approximately tetrahedral like the nickel atom in Ni(CO)4. In fact these derivatives can be considered as substitution products of Ni(CO)4 in which an Ni(CS)(CO)3 molecule is coordinated to a Ni(CS)(CO)2 fragment through either the sulfur (25-8) or the oxygen (25-9) atom. These two structures (25-8 and 25-9)

are essentially degenerate by the B3LYP method (Table 2). However, by the BP86 method structure 25-8 with a Ni-S bond lies at lower relative energy (7.4 kcal/mol relative to 25-1) than structure 25-9 with an Ni-O bond. In 25-9 the relatively long Ni-O distance of 3.090 Å (B3LYP) or 2.798 Å (BP86) suggests facile dissociation into mononuclear fragments, since there is no Ni-Ni bond holding the two halves of the molecule together. 3.2.2. Ni2(CS)2(CO)4. A total of seven structures are found for Ni2(CS)2(CO)4 (Figure 5 and Table 3). The global minimum structure for Ni2(CS)2(CO)4 is 24-1 with two bridging CS groups. This structure is predicted to be a genuine minimum with both methods. The predicted Ni · · · S distances for both bridging CS groups in 24-1 are more than 3.0 Å using either method thereby indicating that each CS group is a donor of only two electrons. The NidNi distance of 2.489 Å (B3LYP) or 2.461 Å (BP86) in 24-1 is ∼0.15 Å shorter than that in the Ni2(CS)2(CO)5 structure 25-1 (Figure 3), consistent with the formal double bond in 24-1 required to give both nickel atoms the favored 18-electron configuration. Furthermore, structure 24-1 for Ni2(CS)2(CO)4 can be derived from the previously found10 global minimum structure of Ni2(CO)6 by replacement of the two bridging CO groups with CS groups, with concurrent slight bending of two S atoms toward the “right” nickel in Figure 4. However, the Ni · · · S distance of ∼3.1 Å in 24-1 is too long to indicate a four-electron donor η2-µ-CS group. Two Ni2(CS)2(CO)4 structures with one bridging CO and one bridging CS group were found (Figure 5 and Table 3). Structure 24-2, at only 2.1 kcal/mol (B3LYP) or 4.2 kcal/mol above 24-1, is reported to be a genuine minimum with both methods. With the BP86 method the short Ni-C(O) distance to the bridging CO group in 24-2 is predicted to be 1.887 Å whereas the long Ni-C(O) distance to the bridging CO group is predicted to be 2.113 Å by BP86 indicating a bridging CO ligand fairly close to symmetrical. The NidNi distance predicted by BP86 for 24-2 is 2.502 Å consistent with the formal double bond required to give both nickel atoms the favored 18-electron configuration. However, using the B3LYP method this long Ni-C(O) distance is predicted to be 2.719 Å suggesting only a rather weakly semibridging CO group. The longer Ni-Ni distance of 2.606 Å in 24-2 by the B3LYP method suggests only a formal single bond thereby giving the “right” nickel atom the favored 18-electron configuration but the “left” nickel atom only a 16-electron configuration. The Ni2(CS)2(CO)4 structure 24-3 with one bridging CS group and one bridging CO group is predicted to lie ∼4.9 kcal/mol above 24-1 by either DFT method and is a genuine minimum with no imaginary vibrational frequencies. The Ni-S distance to the bridging CS group is found to be ∼2.63 Å, suggesting a four-electron donor bridging η2-µ-CS group. The Ni-Ni distance of ∼2.56 Å in 24-3 suggests a formal Ni-Ni single bond thereby leading to the favored 18-electron configuration for each nickel atom. An attempt to optimize a Ni2(η2-µ-CS)(µCS)(CO)4 structure with one two-electron donor bridging CS group and one four-electron donor bridging η2-µ-CS group led instead to the global minimum 24-1 with two two-electron donor bridging CS groups and a formal NidNi double bond. The two doubly carbonyl bridged Ni2(CS)2(CO)4 structures 24-4 and 24-5 lie ∼8.4 kcal/mol above 24-1. Note that structure 24-4 is predicted to have Cs symmetry and a tiny imaginary frequency of 14i cm-1 by B3LYP, but to have C2V symmetry and all real vibrational frequencies by BP86. In both Ni2(CS)2(CO)4 structures 24-4 and 24-5 the CS groups are bonded to different nickel atoms. In structure 24-4 these terminal CS groups are in cisoid relative positions whereas in structure



Figure 5. Seven optimized structures for Ni2(CS)2(CO)4.

TABLE 3: The Total Energies (E, in hartree), Relative Energies (∆E, in kcal/mol), and Numbers of Imaginary Frequencies (Nimg) for the Optimized Ni2(CS)2(CO)4 Structures B3LYP BP86


24-1 (Cs)

24-2 (C1)

24-3 (C1)

4342.78334 0.0 0 4343.36087 0.0 0

4342.77997 2.1 0 4343.35413 4.2 0

4342.77559 4.9 0 4343.35307 4.9 0

24-5 these CS groups are in transoid relative positions. This subtle change in the relative positions of the CS groups is seen to make very little difference in the total energy. The doubly µ-CO bridged NidNi distances in 24-4 and 24-5 are reported to be ∼2.55 Å with both methods, corresponding to the formal double bond needed to give both nickel atoms the favored 18electron configurations. However, these NidNi double bond distances of ∼2.55 Å in the doubly carbonyl bridged 24-4 and 24-5 are significantly longer than the NidNi double bond distance of ∼2.47 Å in the global minimum doubly bridged Ni2(CS)2(CO)4 structure 24-1. Again this lengthening of the metal-metal distance upon replacing bridging CS groups with

24-4 (Cs/ C2V) 4342.76988 8.4 14i 4343.34794 8.1 0

24-5 (C1)

24-6 (C2)

24-7 (C2V)

4342.76986 8.5 0 4343.34774 8.2 0

4342.76417 12.0 0 leads to 24-1

4342.76197 13.4 16i 4343.32232 24.2 34i, 32i, 16i

CO groups in a doubly bridged structure was previously observed12 in Co2(CS)2(CO)6. The two unbridged Ni2(CS)2(CO)4 structures 24-6 and 24-7 lie more than 12.0 kcal/mol above 24-1. Structure 24-6 is found to be a genuine minimum by B3LYP but to have an imaginary vibrational frequency of 91i cm-1 by BP86. Following the corresponding normal mode leads to 24-1. Structure 24-7 is reported to have at least one small imaginary frequency by either method. The Ni · · · Ni distances in 24-6 and 24-7 are predicted to be at least 2.95 Å, suggesting only a weak interaction between the two Ni(CO)3 fragments with trigonal planar nickel coordination.

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Figure 6. Eight optimized structures of Ni2(CS)2(CO)3.

3.2.3. Ni2(CS)2(CO)3. The eight structures found for Ni2(CS)2(CO)3 within 25 kcal/mol of the global minimum (Figure 6 and Table 4) are all predicted to have only real vibrational frequencies except for 23-5 with a very small imaginary frequency of 15i cm-1 (B3LYP) or 38i cm-1(BP86). In the lowest lying Ni2(CS)2(CO)3 structure, namely, 23-1, the four-electron donor η2-µ-CS group is supplemented by a twoelectron donor CS group bridging the Ni-Ni bond. The NidNi distance in 23-1, namely, 2.447 Å (B3LYP) or 2.428 Å (BP86), is ∼0.05 Å shorter than that in 24-1. This can be interpreted as the formal double bond needed to give both nickel atoms the favored 18-electron configuration in an Ni2(CS)2(CO)3 structure in which one of the CS groups is a four-electron donor bridging η2-µ-CS group. This Ni2(CS)2(CO)3 structure may be derived from 24-1 by loss of a terminal CO group. Structure 23-2 at ∼4.2 kcal/mol above the global minimum 23-1 is similar to 23-1 except for substitution of a bridging CS group by a bridging CO group. The predicted NidNi distance in 23-2, namely, 2.494 Å (B3LYP) or 2.469 Å (BP86), is quite close to that in 24-1 and can correspond to the double bond required to give both nickel atoms the favored 18-electron configuration in the presence of a single four-electron donor bridging η2-µ-CS group.

TABLE 4: The Total Energies (E, in hartree), Relative Energies (∆E, in kcal/mol), and Numbers of Imaginary Vibrational Frequencies (Nimg) for the Optimized Ni2(CS)2(CO)3 Structures 23-1 (Cs)

23-2 (Cs)

23-3 (Cs)

23-4 (C1)

B3LYP -E ∆E Nimg BP86 -E ∆E Nimg

4229.43823 0.0 0 4230.00534 0.0 0

4229.43141 4.3 0 4229.99880 4.1 0

4229.42527 8.1 0 4229.98891 10.3 0

4229.42503 8.3 0 4229.98709 11.5 0

23-6 (C2V)

23-7 (Cs)

23-8 (D3h)

B3LYP -E ∆E Nimg BP86 -E ∆E Nimg

4229.41682 13.4 15i 4229.98211 14.6 38i

23-5 (Cs)

leads to 23-1 leads to 23-5 4229.40533 20.6 0 4229.98725 4229.98420 4229.98063 11.4 13.3 15.5 0 0 0

These four-electron donor η2-µ-CS bridges are predicted to exhibit ν(CS) frequencies in the narrow range of 1141 ( 5 cm-1 (Table 7).



Figure 7. Seven optimized structures of Ni2(CS)2(CO)2.

The two Ni2(CS)2(CO)3 structures (23-3 and 23-4) lie ∼8 kcal/ mol (B3LYP) or ∼11 kcal/mol (BP86) above 23-1 (Figure 6 and Table 4). Both structures have a two-electron donor bridging CS group. However, the two methods give different geometries for one of the carbonyl groups in these two structures, as indicated by the long Ni-C(O) distances of 2.816 and 2.892 Å for the B3LYP structures but 2.183 and 2.562 Å for the BP86 structures for in 23-3 and 23-4, respectively. Thus the B3LYP geometries of 23-3 and 23-4 by B3LYP indicate that this unique carbonyl group is weakly semibridging whereas the BP86 geometries indicate more strongly bridging CO groups in both structures. The predicted NidNi distances of ∼2.46 Å (B3LYP) or ∼2.39 Å (BP86) can correspond to a formal double bond, leading to an 18-electron configuration for one nickel atom but only a 16-electron configuration for the other nickel atom. We suspect that the nickel atoms in both 23-3 and 23-4 with the 16-electron configuration are the “right” nickel atoms in Figure 6 where the coordination may be approximated by square planar, with distortion arising from the geometry of the Ni2C ring containing the semibridging carbonyl group. The Ni2(CS)2(CO)3 structure 23-5 with a normal two-electron donor bridging CS group (Figure 6 and Table 4) is found to have a small imaginary frequency of 15i cm-1 (B3LYP) or 38i cm-1 (BP86) and lie ∼14 kcal/mol above 23-1. The short Ni-Ni

distance of ∼2.35 Å in 23-5 may correspond to a singly bridged formal NitNi triple bond, thereby giving both nickel atoms the favored 18-electron configuration. The remaining three Ni2(CS)2(CO)3 structures, namely, 23-6, 23-7, and 23-8, are triply bridged structures that are predicted to be genuine minima with the BP86 method (Figure 6 and Table 4). However, attempts to optimize the structures using B3LYP leads to 23-1 from 23-6 and 23-5 from 23-7. All three of these Ni2(CS)2(CO)3 structures can arise from the previously optimized10 homoleptic nickel carbonyl structure Ni2(µ-CO)3(CO)2 by substituting different pairs of CO groups with CS groups. The Ni2(CS)2(CO)3 structure 23-6 with two bridging CS groups and a bridging CO group lies 11.4 kcal/ mol (BP86) above 23-1, whereas the Ni2(CS)2(CO)3 structure 23-7 with a single bridging CS group and two bridging CO groups lies 13.3 kcal/mol (BP86) above 23-1. The beautifully symmetric Ni2(µ-CO)3(CS)2 structure 23-8 with three bridging CO groups and two terminal CS groups lies at an even higher energy of 20.6 kcal/mol (B3LYP) or 15.5 kcal/mol (BP86) above 23-1. This is another example of the lower energies of structures with bridging CS groups relative to otherwise similar structures with bridging CO groups. The predicted NitNi distances of 2.20 ( 0.03 Å in these triply bridged Ni2(CS)2(CO)3 structures (Figure 6 and Table 4) are comparable to that in the

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TABLE 5: The Total Energies (E, in hartree), Relative Energies (∆E, in kcal/mol), and Numbers of Imaginary Frequencies (Nimg) for the Optimized Ni2(CS)2(CO)2 Structures B3LYP BP86

-E ∆E Nimg E ∆E Nimg

22-1 (Cs)

22-2 (Cs)

22-3 (Cs)

22-4 (C2V)

22-5 (C2h)

22-6 (Cs)

22-7 (Cs)

4116.07604 0.0 0 4116.63214 0.0 0

4116.06684 5.8 0 4116.62378 5.2 0

4116.06555 6.6 0 4116.62244 6.1 0

4116.05532 13.0 48i 4116.61596 10.1 0

4116.05374 14.0 0 4116.60771 15.3 13i

4116.05228 14.9 0 4116.60800 15.1 0

4116.04180 21.5 0 collapses to 22-4

global minimum of Ni2(CO)5 thereby suggesting the (strong) formal triple bond needed to give both nickel atoms the favored 18-electron configuration. 3.2.4. Ni2(CS)2(CO)2. Seven optimized structures for Ni2(CS)2(CO)2 were found within 25 kcal/mol of the global minimum (Figure 7 and Table 5). The lowest energy Ni2(CS)2(CO)2 structure 22-1 has one two-electron donor bridging CS group and one four-electron donor bridging η2-µCS group with a predicted short Ni-S distance of 2.29 Å. Structure 22-1 can be derived from 23-1 by loss of a terminal CO group. The next two Ni2(CS)2(CO)2 structures, namely, 22-2 and 22-3, at ∼5.5 ( 0.8 kcal/mol above 22-1, are similar to 22-1, except that the two-electron donor bridging group is a CO group rather than a CS group. The NidNi distance in 22-1 is predicted to be 2.404 Å (B3LYP) or 2.384 Å (BP86), which is slightly shortened by ∼0.04 Å from that in 23-1. The NidNi distances in 22-2 and 22-3 of ∼2.45 Å (B3LYP) or ∼2.42 Å (BP86) are comparable to that in 23-1. Therefore, each of these three structures can be considered to contain a formal NidNi double bond to give one Ni atom an 18-electron configuration and the other Ni atom only a 16-electron configuration. The elegant structure 22-4 for Ni2(CS)2(CO)2 with two symmetric CS bridges (Figure 7 and Table 5) lies 13.0 kcal/ mol (B3LYP) or 10.1 kcal/mol (BP86) above 22-1 with all real vibrational frequencies by the BP86 method but a small imaginary frequency of 48i cm-1 by B3LYP. The doubly CS bridged Ni-Ni distance is ∼2.285 Å, which could correspond to the formal Ni 4 Ni quadruple bond, thereby allowing each nickel atom to attain the favored 18-electron configuration. Structure 22-5 with two four-electron donor bridging CS groups (Figure 7 and Table 5) is predicted to lie 14.0 kcal/mol (B3LYP) or 15.3 kcal/mol above 22-1. This structure is found to be a local minimum by B3LYP but to have a tiny imaginary vibrational frequency of 13i cm-1 by BP86. The long Ni · · · Ni distance of 2.919 Å (B3LYP) or 2.955 Å (BP86) suggests only a weak interaction so that each nickel atom can be considered to be effectively a tricoordinate NiL3 unit with a 16-electron configuration. The remaining two planar Ni2(CS)2(CO)2 structures 22-6 and 22-7 are found to have a bridging CE (E ) O, S) group and a semibridging CO group (Figure 7 and Table 5). In 22-6 (at 15.0 ( 0.1 kcal/mol above 22-1) the bridging group is a CS group, which is slightly bent toward one of the nickel atoms but with a long nonbonding Ni · · · S distance of ∼3.14 Å. Structures 22-6 and 22-7 differ in the position of CS ligand. In 22-7 at 21.5 kcal/mol (B3LYP) the bridging group as well as the semibridging group are CO groups and there are thus two terminal CS groups. An attempt to optimize 22-7 by the BP86 method led to 22-4 where both bridging groups are CS groups rather than CO groups. 3.3. Vibrational Frequencies. The harmonic vibrational frequencies and infrared intensities for all of the structures have been evaluated by both the B3LYP and BP86 methods. These results were initially used to determine if a structure is a genuine

TABLE 6: The ν(CO) and ν(CS) Vibrational Frequencies and Corresponding Infrared Intensities (in parentheses) Predicted by the BP86 Method for Ni(CS)(CO)n (n ) 3, 2, 1, 0) 13-1(C3V) 12-1(C2V) 11-1(Cs) 10-1(Cν) 10-2(Cs)

ν(CO)

CS

2064 (a1, 346), 2016 (e, 871), 2016 (e, 871) 2046 (a1, 553), 1999 (b2, 1140) 2017 (a′, 952)

1319 (a1, 577) 1316 (a1, 606) 1329 (a′, 596) 1370 (ag, 254) 950 (a′, 59)

minimum. The predicted ν(CO) and ν(CS) harmonic vibrational frequencies and infrared intensities for the most stable structures of Ni2(CS)2(CO)n (n ) 5, 4, 3, 2) are of particular interest. The ν(CO) and ν(CS) stretching frequencies are listed in Tables 6 and 7 for the mononuclear Ni(CS)(CO)n (n ) 3, 2, 1, 0) and binuclear Ni2(CS)2(CO)n (n ) 7, 6, 5, 4) derivatives, respectively. These results were obtained with the BP86 method, which has been shown to be more reliable than the B3LYP method for such infrared frequencies.17,44 The results in Tables 6 and 7 indicate that terminal ν(CS) frequencies fall in the range 1280-1340 cm-1 with the mononuclear Ni(CS)(CO)n derivatives falling at the upper end of this range. The side-on bonded η2-CS group in structure 10-2 is predicted to have a much lower ν(CS) frequency at 950 cm-1. The ν(CS) frequency of 1266 cm-1 for the linear bridging CS group in the structure 25-9 of Ni2(CS)2(CO)5 is slightly lower than the terminal ν(CS) frequencies. The normal bridging ν(CS) frequencies fall in the range 1135-1250 cm-1. The lowest ν(CS) frequencies belong to the four-electron donor η2-µ-CS groups, which fall in the narrow range 1120-1150 cm-1 except for the ν(CS) frequency of 1209 cm-1 for the Ni2(CS)2(CO)4 structure 24-3. 3.4. Dissociation Energies. Table 8 reports the bond dissociation energies (BDEs) in terms of the single carbonyl dissociation steps

Ni(CS)(CO)m f Ni(CS)(CO)m-1 + CO

(m ) 3, 2)

(1) Ni2(CS)2(CO)n f Ni2(CS)2(CO)n-1 + CO

(n ) 5, 4, 3) (2)

The BDE for the loss of CO from the mononuclear Ni(CS)(CO)3 (13-1) is 22.2 kcal/mol (B3LYP), which is somewhat lower than the experimental BDE45 of 27 kcal/mol for Ni(CO)4. As the number of CO groups decrease, the BDEs for the loss of CO from the mononuclear Ni(CS)(CO)m derivatives (m ) 3, 2, 1) gradually increase to 41.9 kcal/mol (B3LYP) or 49.0 kcal/mol (BP86) for Ni(CS)(CO). The BDEs for loss of CO from the binuclear Ni2(CS)2(CO)n derivatives (n ) 4, 3, 2) are somewhat lower than those for the mononuclear Ni(CS)(CO)m derivatives. However, the BDE for



TABLE 7: The ν(CO) and ν(CS) Vibrational Frequencies and Corresponding Infrared Intensities (in parentheses) Predicted by the BP86 Method for Ni2(CS)2(CO)n (n ) 5, 4, 3, 2), Bridging ν(CO) and ν(CS) Frequencies in bold Type ν(CO)

ν(CS)

25-1 25-2 25-3 25-4 25-5 25-6 25-7 25-8 25-9

(Cs) (Cs) (Cs) (C2) (Cs) (C2) (C2V) (C1) (Cs)

2064 2061 2061 2054 2052 2052 2057 2064 2067

Ni2(CS)2(CO)5 (550), 2029 (921), 2018 (1425), 2008 (154), 2006 (235) (106), 2039 (980), 2019 (1594), 2015 (6), 2011 (502) (101), 2038 (1025), 2017 (1524), 2015 (492), 2009 (35) (514), 2024 (1170), 2009 (354), 2006 (454), 1899 (420) (196), 2029 (826), 2016 (1583), 2008 (2), 1898 (391) (30), 2032 (1382), 2017 (1127), 2001 (42), 1898 (391) (457), 2036 (907), 2016 (1643), 2012 (0), 1890 (352) (340), 2041 (563), 2019 (829), 2006 (1276), 1995 (990) (673), 2031 (648), 2021 (945), 2021 (579), 2002 (702)

1326 1301 1300 1326 1326 1315 1322 1321 1314

(596), 1187 (305) (464), 1182 (504) (461), 1185 (500) (268), 1317 (990) (550), 1300 (641) (1), 1306 (1283) (791), 1283 (164) (711), 1313 (418) (612), 1266 (842)

24-1 24-2 24-3 24-4 24-5 24-7

(Cs) (C1) (C1) (Cs/ C2V) (C1) (C2V)

2049 2045 2049 2035 2033 2051

Ni2(CS)2(CO)4 (9), 2023 (1525), 2008 (1406), 2005 (365) (554), 2015 (1382), 2007 (733), 1941 (454) (495), 2023 (1204), 2012 (760), 1920 (340) (1126), 2011 (741), 1939 (84), 1924 (902) (0), 2013 (1762), 1939 (0), 1923 (911) (879), 2021 (275), 2008 (1754), 1983 (0)

1241 1305 1320 1321 1319 1320

(8), 1205 (729) (690), 1216 (393) (634), 1209 (397) (598), 1306 (901) (0), 1302 (1635) (862), 1293 (194)

23-1 23-2 23-3 23-4 23-5 23-6 23-7 23-8

(Cs) (Cs) (Cs) (C1) (Cs) (C2V) (Cs) (D3h)

2051 2050 2047 2039 2053 2033 2030 1980

Ni2(CS)2(CO)3 (83), 2034 (1512), 2015 (856) (888), 2015 (872), 1914 (347) (899), 2011 (969), 1944 (531) (555), 2015 (1459), 1985 (556) (734), 2015 (614), 2003 (861) (75), 2014 (2145), 1951 (624) (1200), 1963 (368), 1943 (895) (0), 1944 (871), 1944 (871)

1222 1344 1333 1312 1335 1259 1339 1348

(274), 1135 (322) (703), 1147 (262) (764), 1230 (416) (653), 1222 (411) (680), 1227 (441) (227), 1230 (800) (761), 1247 (505) (0), 1332 (1713)

22-1 22-2 22-3 22-4 22-5 22-6

(Cs) (Cs) (Cs) (C2V) (C2h) (Cs)

2044 2042 2028 2023 2031 2028

(239), 2020 (1728) (1090), 1893 (351) (1308), 1892 (358) (4), 2001 (2443) (0), 2017 (2162) (1308), 1892 (358)

1213 1330 1341 1235 1158 1341

(249), 1121 (306) (753), 1128 (394) (728), 1135 (243) (48), 1196 (814) (362), 1138 (0) (728), 1135 (243)

Ni2(CS)2(CO)2

TABLE 8: Bond Dissociation Energies (kcal/mol) for Successive Removal of Carbonyl Groups from Ni2(CS)2(CO)n (n ) 5, 4, 3), All Dissociation Energies Refer to Global Minima Ni(CS)(CO)3 f Ni(CS)(CO)2 + CO Ni(CS)(CO)2 f Ni(CS)(CO) + CO Ni(CS)(CO) f Ni(CS) + CO Ni2(CS)2(CO)5 f Ni2(CS)2(CO)4 + CO Ni2(CS)2(CO)4 f Ni2(CS)2(CO)3 + CO Ni2(CS)2(CO)3 f Ni2(CS)2(CO)2 + CO

B3LYP

BP86

22.2 29.7 41.9 12.8 10.3 21.0

30.0 36.0 49.0 15.8 17.8 28.8

loss of CO from Ni2(CS)2(CO)3 suddenly increases to 21.0 kcal/ mol (B3LYP). All of the binuclear derivatives are thermodynamically viable with respect to dissociation into mononuclear fragments (Table 9). The lowest energy dissociation processes of this type are the dissociations of Ni2(CS)2(CO)5 and Ni2(CS)2(CO)4 into Ni(CS)(CO)3 + Ni(CS)(CO)x (x ) 2, 1). This is similar to the previously reported10 dissociations of the homoleptic nickel carbonyl analogues Ni2(CO)n (n ) 7, 6) into Ni(CO)4 + Ni(CO)n-4. This may relate to the favorable 18-electron configuration of the mononuclear Ni(CS)(CO)3 fragment. However, the dissociation energy of Ni2(CS)2(CO)3 into Ni(CS)(CO)2 and Ni(CS)(CO), although highly endothermic at 33.2 kcal/mol (B3LYP) or 45.0 kcal/mol (BP86), is more thermodynamically favorable than that into Ni(CS)(CO)3 + Ni(CS) at 52.9 kcal/ mol (B3LYP) or 64.0 kcal/mol (BP86). The much higher energy for the dissociation of Ni2(CS)2(CO)3 into mononuclear fragments relative to Ni2(CS)2(CO)4 and Ni2(CS)2(CO)5 may relate

TABLE 9: Energies (kcal/mol) for Dissociation of the Binuclear Complexes Ni2(CS)2(CO)n into Two Mononuclear Fragments Ni2(CS)2(CO)5 Ni2(CS)2(CO)4 Ni2(CS)2(CO)4 Ni2(CS)2(CO)4 Ni2(CS)2(CO)4 Ni2(CS)2(CO)3 Ni2(CS)2(CO)3 Ni2(CS)2(CO)2

f f f f f f f f

Ni(CS)(CO)3 + Ni(CS)(CO)2 Ni(CS)(CO)3 + Ni(CS)(CO) Ni(CS)(CO)2 + Ni(CS)(CO)2 Ni(CO)4 + Ni(CS)2 Ni(CS)2(CO)2 + Ni(CO)2 Ni(CS)(CO)3 + Ni(CS) Ni(CS)(CO)2 + Ni(CS)(CO) Ni(CS)(CO) + Ni(CS)(CO)

B3LYP

BP86

4.4 2.3 13.8 18.0 24.4 52.9 33.2 41.9

12.6 3.5 26.7 29.2 36.1 64.0 45.0 52.1

to the η2-µ-CS groups in 23-1 and 23-2 strengthening the interaction between the two nickel atoms. 4. Discussion The structures predicted for the mononuclear Ni(CS)(CO)n (n ) 3, 2, 1, 0) are analogous to those previously predicted10 for the corresponding homoleptic derivatives Ni(CO)n+1 as well as for the isoelectronic cobalt carbonyl nitrosyls46 Co(NO)(CO)n. The coordination of the nickel is tetrahedral in the 18-electron four-coordinate complex Ni(CS)(CO)3 (13-1) and trigonal planar in the 16-electron three-coordinate complex Ni(CS)(CO)2. For the two-coordinate 14-electron complex Ni(CS)(CO) the nickel coordination is predicted not to be linear but bent at an angle of 144 ( 5°. The potential energy surfaces for the heteroleptic binuclear complexes Ni2(CS)2(CO)n (n ) 5, 4, 3, 2) are much more complicated than those of the corresponding homoleptic com-

2374


plexes Ni2(CO)n+2 because of the presence of two different types of ligands. The lowest energy Ni2(CO)7 structure is predicted10 to be a singly bridged structure Ni2(CO)6(µ-CO) with a Ni-Ni distance of ∼2.70 Å suggesting the formal single bond to give both nickel atoms the favored 18-electron configuration. In contrast, seven related Ni2(CS)2(CO)5 structures are found within 6 kcal/mol of the global minimum (Figure 3) with different arrangements of the CO and CS ligands. The three structures with a CS ligand in the bridging position (25-1, 25-2, and 25-3 in Figure 3) are slightly lower in energy (by 3 to 6 kcal/mol) than the four related structures with a CO ligand in the bridging position (25-4, 25-5, 25-6, and 25-7 in Figure 3). This is in accord with previous observations for other metals11–13 that bridging CS groups are more favorable energetically than bridging CO groups. Three Ni2(CS)2(CO)5 structures are also found with linear bridging CE (E ) O, S) groups, no Ni · · · Ni bonding, and approximate tetrahedral coordination for each nickel atom (25-8 and 25-9 in Figure 4). In such structures the linear bridging CE ligand donates an electron pair to one nickel atom through the carbon atom and another electron pair to the second nickel atom through the E atom, leading to tetrahedral coordination and an 18-electron configuration for each nickel atom. However, these structures have relatively long Ni-E distances and thus are prone to dissociation into mononuclear fragments. The lowest energy Ni2(CO)6 structure is a doubly bridged Ni2(CO)4(µ-CO)2 structure with a NidNi distance of 2.54 ( 0.02 Å, interpreted to be the formal double bond needed to give both nickel atoms the favored 18-electron configuration. The two lowest energy Ni2(CS)2(CO)4 structures (24-1 and 24-2 in Figure 5) have related structures with similar NidNi distances of ∼2.5 Å, likewise interpreted as a formal NidNi double bond to give each nickel atom the favored 18-electron configuration. The Ni2(CS)2(CO)4 structure with two bridging CS groups (24-1 in Figure 5) is of slightly lower energy (by 3 ( 1 kcal/mol) than that with one semibridging CS group and one bridging CO group (24-2 in Figure 5). This is in accord with the general observation11–13 that structures with bridging CS groups are of lower energy than similar structures with bridging CO groups. There is some tendency for the sulfur atoms of the bridging CS groups in these Ni2(CS)2(CO)4 structures (24-1 and 24-2) to bend toward one of the nickel atoms. However, the resulting Ni · · · S distances of ∼3.1 Å are too long to interpret as a formal bond. A slightly higher energy Ni2(CS)2(CO)4 structure 24-3 was found with a four-electron donor bridging η2-µ-CS group indicated by a short Ni-S bonding distance of ∼2.6 Å. The lowest energy Ni2(CO)5 structure predicted in the previous work10 is a triply bridged Ni2(CO)2(µ-CO)3 structure with a very short NitNi distance of ∼2.2 Å, interpreted to be the formal triple bond needed to give both nickel atoms the favored 18-electron configuration. Three structures of this type are found for Ni2(CS)2(CO)3 (Figure 6), namely, (a) 23-6 with two bridging CS groups and one bridging CO group, (b) 23-7 with one bridging CS group and two bridging CO groups, and (c) 23-8 with three bridging CO groups. The predicted NitNi distances are ∼2.2 Å and likewise can be interpreted as formal triple bonds to give each nickel atom the favored 18-electron configuration. However, these three Ni2(CS)2(CO)3 structures are not particularly low energy structures, since they lie 11-21 kcal/mol above the global minimum 23-1. The two lowest energy Ni2(CS)2(CO)3 structures (23-1 and 23-2 in Figure 6) have a four-electron donor bridging η2-µ-CS group, as indicated by short Ni-S distances around ∼2.3 Å. There is a second two-electron donor bridging group, which

Zhang et al. may be a CS group (structure 23-1) or a CO group (structure 23-2). The NidNi distances in both 23-1 and 23-2 of ∼2.4 to ∼2.5 Å can be interpreted as the formal double bond needed to give both nickel atoms the favored 18-electron configuration. Thus Ni2(CS)2(CO)3 structures with one four-electron donor bridging η2-µ-CS group and a formal NidNi double bond are more favorable energetically than Ni2(CS)2(CO)3 structures with exclusively two-electron donor CO and CS groups and a formal NitNi triple bond. Generally speaking, a Ni2(CS)2(CO)2 structure with only twoelectron donor CO and CS groups requires a formal Ni 4 Ni quadruple bond to give both nickel atoms the favored 18electron configuration. However, there is no Ni 4 Ni distance in any of the optimized Ni2(CS)2(CO)2 structures (Figure 7) that appears to be short enough for such a formal quadruple bond with the possible exception of the higher energy structure 22-4. In fact most of the Ni2(CS)2(CO)2 structures appear to be derived from Ni2(CS)2(CO)3 structures (Figure 6) by removal of a carbonyl group. The three lowest energy Ni2(CS)2(CO)2 structures (22-1, 22-2, and 22-3 in Figure 7) all have a single fourelectron donor η2-µ-CS group, as indicated by short Ni-S distances of ∼2.3 Å. Such Ni2(CS)2(CO)2 structures still require a formal NitNi triple bond to give both nickel atoms the favored 18-electron configuration. However, the NidNi distances in 22-1, 22-2, and 22-3 are ∼2.4 Å and thus are more consistent with a formal double bond rather than a formal triple bond with an expected NitNi distance of ∼2.2 Å. This means that one of the two nickel atoms in these three Ni2(CS)2(CO)2 structures (22-1, 22-2, and 22-3) can have only a 16-electron configuration. The nickel atoms with 16-electron configurations are most likely the nickel atoms not within bonding distance of the sulfur atom of the η2-µ-CS group (the “right” nickel atoms in Figure 7) since these nickel atoms appear to have a “hole” in their coordination sphere. Acknowledgment. We are indebted to the National Natural Science Foundation (20873045 and 20973066) of China as well as the U.S. National Science Foundation (Grants CHE-0749868 and CHE-0716718) for support of this research. Supporting Information Available: Tables S1-S5, theoretical harmonic vibrational frequencies for Ni(CS)(CO)n (n ) 3, 2, 1, 0) (five structures), Ni2(CS)2(CO)5 (eight structures), Ni2(CS)2(CO)4 (seven structures), Ni2(CS)2(CO)3 (eight structures), Ni2(CS)2(CO)2 (seven structures) using the BP86 method; Tables S6-S38, theoretical Cartesian coordinates for Ni(CS)(CO)n (n ) 3, 2, 1, 0) (five structures), Ni2(CS)2(CO)5 (eight structures), Ni2(CS)2(CO)4 (six structures), Ni2(CS)2(CO)3 (six structures), Ni2(CS)2(CO)2 (seven structures) using the B3LYP method; complete Gaussian 03 reference (ref 41).This material is available free of charge via the Internet at http://pubs.acs.org. References and Notes (1) Schu¨tzenberger, P. Bull Soc. Chim. Fr. 1868, 10, 188. (2) Mond, L.; Langer, C.; Quinncke, F. J. Chem. Soc. 1890, 57, 749. (3) Butler, I. S.; Fenster, A. E. J. Organomet. Chem. 1974, 66, 161. (4) Yaneff, P. V. Coord. Chem. ReV. 1977, 23, 183. (5) Butler, I. S. Acc. Chem. Res. 1977, 10, 359. (6) Broadhurst, P. V. Polyhedron 1985, 4, 1801. (7) Petz, W. Coord. Chem. ReV. 2008, 257, 1689. (8) Petz, W. J. Organomet. Chem. 1978, 146, C23. (9) Dombek, B. D.; Angelici, R. J. J. Am. Chem. Soc. 1973, 95, 7516. (10) Ignatyev, I. S.; Schaefer, H. F.; King, R. B.; Brown, S. T. J. Am. Chem. Soc. 2000, 122, 1989. (11) Zhang, Z.; Li, Q. S.; Xie, Y. M.; King, R. B.; Schaefer, H. F. Inorg. Chem. 2009, 48, 1974.

Binuclear Nickel Carbonyl Thiocarbonyls (12) Zhang, Z.; Li, Q. S.; Xie, Y. M.; King, R. B.; Schaefer, H. F. Inorg. Chem. 2009, 48, 5973. (13) Zhang, Z.; Li, Q. S.; Xie, Y. M.; King, R. B.; Schaefer, H. F. Inorg. Chem. 2009, 48, 6167. (14) Ehlers, A. W.; Frenking, G. J. Am. Chem. Soc. 1994, 116, 1514. (15) Delley, B.; Wrinn, M.; Lu¨thi, H. P. J. Chem. Phys. 1994, 100, 5785. (16) Li, J.; Schreckenbach, G.; Ziegler, T. J. Am. Chem. Soc. 1995, 117, 486. (17) Jonas, V.; Thiel, W. J. Chem. Phys. 1995, 102, 8474. (18) Barckholtz, T. A.; Bursten, B. E. J. Am. Chem. Soc. 1998, 120, 1926. (19) Niu, S.; Hall, M. B. Chem. ReV. 2000, 100, 353. (20) Macchi, P.; Sironi, A. Coord. Chem. ReV. 2003, 238, 383. (21) Carreon, J.-L.; Harvey, J. N. Phys. Chem. Chem. Phys. 2006, 8, 93. (22) Bu¨hl, M.; Kabrede, H. J. Chem. Theory Comput. 2006, 2, 1282. (23) Ziegler, T.; Autschbach, J. Chem. ReV. 2005, 105, 2695. (24) Waller, M. P.; Bu¨hl, M.; Geethanakshmi, K. R.; Wang, D.; Thiel, W. Chem.sEur. J. 2007, 13, 4723. (25) Hayes, P. G.; Beddie, C.; Hall, M. B.; Waterman, R.; Tilley, T. D. J. Am. Chem. Soc. 2006, 128, 428. (26) Bu¨hl, M.; Reimann, C.; Pantazis, D. A.; Bredow, T.; Neese, F. J. Chem. Theory Comput. 2008, 4, 1449. (27) Besora, M.; Carreon-Macedo, J.-L.; Cowan, J.; George, M. W.; Harvey, J. N.; Portius, P.; Ronayne, K. L.; Sun, X.-Z.; Towrie, M. J. Am. Chem. Soc. 2009, 131, 3583. (28) Ye, S.; Tuttle, T.; Bill, E.; Simkhorich, L.; Gross, Z.; Thiel, W.; Neese, F. Chem.sEur. J. 2008, 14, 10839. (29) Xie, Y.; Schaefer, H. F.; King, R. B. J. Am. Chem. Soc. 2000, 122, 8746.

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Binuclear Nickel Carbonyl Thiocarbonyls: MetalâMetal Multiple Bonds

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