Axial Carbonyl Research Articles

Telluride-substituted mixed metal clusters. Crystal structures of [HRuCo3(CO)11(TeMe2)], [HRuCo3(CO)10(TeMe2)2], and [HRuCo3(CO)11(TePh2)

Abstract The synthesis, structures and characterization of dimethyltelluride and diphenyltelluride derivatives of mixed metal clusters [HRuCo 3 (CO) 12 ] and [HRuRh 3 (CO) 12 ] are described. Telluride ligands displace carbonyl ligands in neutral parent clusters to give [HRuCo 3 (CO) 11 (TeMe 2 )] ( 1 ), [HRuCo 3 (CO) 10 (TeMe 2 ) 2 ] ( 2 ), [HRuCo 3 (CO) 11 (TePh 2 )] ( 3 ) and [HRuRh 3 (CO) 9 ] 2 [TeMe 2 ] 3 ( 4 ). The crystal structures of 1 , 2 and 3 have been determined. The ligand substitutions are metalloselective. Dimethyltelluride displaces an apical carbonyl ligand at ruthenium in 1 ; in 2 an additional axial ligand at cobalt is replaced by telluride. Diphenyltelluride coordinates axially at cobalt in 3 . Compound 4 has a dimeric structure in which the axial carbonyls at rhodium centers have been replaced by TeMe 2 ligands. In all four compounds the basic cluster arrangement is retained and the cluster hydride caps the basal metal face.

Exchange of axial and equatorial carbonyl groups in pentacoordinate metal carbonyls in the solid state. The variable temperature magic angle spinning carbon-13 NMR spectroscopy of iron pentacarbonyl, [Ph3PNPPh3][HFe(CO)4], and [NEt4][HFe(CO)4

Exchange of axial and equatorial carbonyl groups in pentacoordinate metal carbonyls in the solid state. The variable temperature magic angle spinning carbon-13 NMR spectroscopy of iron pentacarbonyl, [Ph3PNPPh3][HFe(CO)4], and [NEt4][HFe(CO)4

Substitutions sélectives de carbonyles dans des complexes polynucléaires: IX. Etudes structurales des composés de mono- et disubstitution de CO par le t-butylisonitrile dans un complexe binucléaire non symétrique

The structures of the complexes [(μ-η 2-ROC(1)SFe 2L 1L 2(CO) 4(μ-SMe)] (R = 2,4,6-trimethylphenyl) ( 3b: L 1 = t-BuNC,L 2 = CO and 4b: L 1 = L 2 = t-BuNC), obtained by carbonyl substitution in the hexacarbonyl precursor 1b (L 1 = L 2 = CO), have been determined by single-crystal X-ray diffraction. In 3b, the t-BuNC ligand has replaced the axial carbonyl of Fe(1) of 1b, trans to the carbene C(1). In 4b the second t-BuNC ligand has replaced an equatorial carbonyl of Fe(2), trans to the SMe. The structural modifications that arise from carbonyl replacement are analyzed and the 13C NMR data are discussed.

Crystal and Molecular Structures of (η4-Cyclohexa-1,3-Diene) (2-Tert-Butyl-1,1,4,4-Tetrafluoro-1,4-Disilabutene) Metal Carbonyls. MFe, W

Molecular structures of the two title compounds were investigated to reveal the relationship between the structure of the reaction intermediates and the reaction pathways in the transition metal-mediated cycloaddition reaction between tetrafluorodisilacyclobutene and conjugated dienes. The structures were determined by X-ray diffraction. Both cyrstals are orthorhombic. Compound I. C14H18O2Si2F4Fe. is of space group P212121 with Z=4; a=6.862(7) A. b=10.9560(10) A. c=23.597(25) A. and Dc=1.562 gcm−1. Compound II, C15H18O3Si2F4W, is of space group Pbca with Z=8; a=16.999(8) A, b=15.948(6), c=14.045(7) A, and Dc=1.962 gcm−1. Both structures were solved by heavy-atom methods and refined by full-matrix least-squares using anisotropic temperature factors for all non-hydrogen atoms to R values of 0.092 for 1544 observed reflections and 0.078 for 2751 observed reflections, respectively, for compound I and compound II. The butadiene segment of the cyclohexadiene ligand is essentially planar in compound I while it is twisted with a torsional angle of 22° (2) in compound II. The five-membered disilametallacycle ring is planar in compound II while ii is in an envelope comformation in compound I. The coordination geometry of the iron atom may be considered as a distorted tetragonal-pyramidal with the diene unit occupying the apical site, That of tungsten is a distorted seven-coordinated pentagonal-bipyramidal with the two axial carbonyl groups displaced toward the disilabutene ligand. The disilabutene of compound I lies almost parallel and cis to the plane of the butadiene segment while that of compound II orients almost perpendicular to the diene group. The differences in the structural features of the two complexes explain clearly their product patterns and the reactions are apparently stereo-controlled.

Synthesis, structure, and solution behavior of [Na · 15-crown-5][Mn(CO) 5

The complex [Na · 15-crown05][Mn(CO) 5] was synthesized by the reaction of freshly prepared Na[Mn(CO) 5] with 15-crown-5 in toluene. The formation of two liquid layers indicative of a liquid clathrate was noted immediately. The pale green air-sensitive crystals of the complex belong to the monoclinic space group P2 1/c with a 7.880(2), b 19.157(8), c 13.549(4) Å, β 101.78(2)°, and D c 1.45 g cm −3 for Z = 4 formula units. The structure in the solid state is that of a dimer which resides on a crystallographic center of inversion. The [Mn(CO) 5] − units are bridged together by sodium cations. The latter are coordinated to one equatorial carbonyl oxygen atom, one axial carbonyl oxygen atom, and the five oxygen atoms of the crown ether. The two Na…O(carbonyl) contacts are 2.409 and 2.555 Å, and the sodium ion lies 0.88 Å out of the plane of the crown ether oxygen atoms.

Molecular structure and dynamical behavior of seven-coordinate Mo(CO)3X2(Ar2POPAr2) complexes

Direct reaction of elemental halogens with Mo(CO)4(R2POPR2) yielded seven-coordinate Mo(II) complexes of type Mo(CO)3X2(R2POPR2) (R = phenyl or p-tolyl, X = I or Br). The structures of Mo(CO)3I2(Ph2POPPh2) (I) and Mo(CO)3Br2(tolyl2POPtolyl2) (II) have been determined by X-ray diffraction methods. Crystal data: MoI2P2O4 C27H2O·C2H2Cl4, complexI, triclinic space group P1-; a = 10.019(1), b = 11.876(1), c = 15.342(2)Å; α = 73.96(1)°, β = 79.12(1)°, γ = 78.19(1)°, Zcalc. = 1.88 Mg m−3· The structure was solved by MULTAN on the basis of 5169 reflections to a final R value of 0.035. Crystal data: MoBr2P2O4C31H28, complexII, monoclinic space group P21/c, a = 15.932(2), b = 9.847(1), c = 21.360(2)Å, β = 106.58(1)°, Z = 4, Dcalc. = 1.62 Mg m−3· The structure was solved using MULTAN on the basis of 1588 reflections to a final R value of 0.097. Both structures approximate a pentagonal bipyramidal coordination geometry around the metal center. This stereochemistry is in accord with Kepert's prediction for chelate normalized bites of less than 1.1 (1.03 and 1.05, respectively, for the POP ligands). The equatorial plane contains both halides, the two phosphorus donors, and a carbonyl. The axial carbonyls are distorted from linearity by 8.5(2) and 13(2)°, respectively. Variable-temperature31P NMR studies of these and the related MO(CO)3I2(Ph2PCH2PPh2) Complex confirmed fluxional behavior. Furthermore, for each of the iodo complexes, equilibration with a second solution isomer was observed.

The reactions of (η 5-C 5H 5)NiO(s) 3(μ-H) 3(CO) 9 with group V donor ligands. Spectroscopic characterization of the disubstituted derivatives, and crystal structure of (η 5-C 5H 5)NiO(s) 3(μ-H) 3(CO) 7(PMe 2Ph) 2

The complex (η 5-C 5H 5NiO(s) 3(μ-H) 3(CO) 9 ( 1 reacts with phosphines in the presence of Me 3NO to give monosubsituted derivatives, the main products, along with smaller amounts of disubstituted derivatives. The IR and NMR spectroscopic characterizations of two representative disubstituted derivatives are described. The crystal structure of (η 5-C 5H 5)NiO(s)(μ-H) 3(CO) 7(PMe 2Ph) 2 has been determined by X-ray diffraction. The crystals are monoclinic, space group P2 1/ a with Z = 4 in a unit cell of dimensions a 18.198(8), b 20.865(8), c 8.656(5) Å, β 99.67(2)°. The structure was solved by direct and Fourier methods and refined by full-matrix least-squares to R = 0.061 for 3139 observed reflections. The structure can be regarded as derived from that of 1 (which has a tetrahedral NiO(s) core with three hydride hydrogen atoms bridging the OsOs edges, a cyclopentadienyl group coordinated to the Ni atom,and nine terminal carbonyls bound to the Os atoms, three for each Os atom) by replacing two axial carbonyls by two PMe 2Ph ligands.

Crystal and molecular structure of a highly hindered iron(II) porphyrin complex

The crystal structure of a carbonyl–1-methylimidazole–iron(II) porphyrin complex with one highly hindered face has been determined; the structural parameters indicate that the twelve membered polymethylene bridging chain does not induce steric deformation of the axial carbonyl ligand.

The crystal structure and reactivity of [(η-C5H5)NiOs3(µ-H)3(CO)8(PPh2H)];1H and31P nuclear magnetic resonance spectroscopic characterization of [(η-C5H5)NiOs3(µ-H)2(µ-HgBr)(CO)8(PPh2H)] and related complexes

By reacting [(η-C5H5)NiOs3(µ-H)3(CO)9](1a) with PPh2H in the presence of Me3NO, [(η-C5H5)NiOs3(µ-H)3(CO)8(PPh2H)](3a) has been obtained. The crystal structure of (3a) has been determined by X-ray methods. Crystals are monoclinic, space group P21/n with Z= 4 in a unit cell of dimensions a= 14.110(6), b= 23.962(9), c= 8.479(6)A, and β= 95.73(2)°. The structure has been solved from diffractometer data by direct and Fourier methods and refined by full-matrix least squares to R= 0.033 for 3187 observed reflections. The structure consists of a tetrahedral arrangement of metal atoms with the three hydrides bridging the Os–Os edges; the phosphine ligand replaces an axial carbonyl of the starting complex. Both complexes (1a) and (3a) react with NaH in tetrahydrofuran to give the corresponding monoanions; these react with HgBr2 affording µ-HgBr derivatives which have been characterized by i.r. and n.m.r. spectroscopy. Deuteriation experiments have shown that the faster rate of formation of the anion derived from (3a), with respect to that from (1a), is due to the presence of the P–H group, which is probably the site of attack by NaH.

Synthesis and characterization of a new family of unsaturated triangular rhenium cluster anions of formula [Re3(µ-H)4(CO)9L]–(L = neutral two-electron donor ligand). X-Ray crystal and molecular structures of the tetraethylammonium salts of the anions with L = triphenylphosphine and pyridine

The unsaturated triangular cluster anion [Re3(µ-H)4(CO)10]– can undergo selective substitution of one of the axial carbonyl ligands of the Re(CO)4 vertex by neutral two-electron donor ligands L, giving unsaturated [Re3(µ-H)4(CO)9L]– derivatives. The anions with L = NCMe, PPh3, and pyridine (py) have been synthesized either by thermal activation or, more effectively, by carbonyl elimination using Me3NO·2H2O. X-Ray single-crystal analyses of the PPh3 and py derivatives, as [NEt4]+ salts, have been performed. Both species crystallize in the monoclinic system, space group P21/n, with a= 11.448(2), b= 25.311(6), c= 13.596(3)A, β= 94.00(2)°, and Z= 4 for the PPh3 derivative, and a= 11.087(1), b= 15.951(2), c= 17.598(4)A, β= 104.84(2)°, and Z= 4 for the py derivative. The geometries of the two anions are similar to that of the parent anion, with the PPh3 or the py ligand co-ordinated in an axial position with respect to the Re3 triangle, which presents a short Re–Re bond (close to 2.80 A) doubly bridged by hydrides. The McCN derivative is the most reactive member of this new family, containing two active centres: the labile nitrile and the unsaturated moiety. Its reaction with methanol, leading to the anion [Re3(µ-H)3(CO)9(µ3-OMe)]–, exemplifies the possibility of new reaction paths involving both the active sites of this molecule.

The synthesis and crystal structure of (η 5-C 5H 5)NiOs 3(μ-H) 3(CO) 8(Ph 2PCCPr i) and of (η 5-C 5H 5)NiOs 3(μ-H) 3(CO) 8{(Ph 2PCCPr i)Co 2(CO) 6}(σ-P,η 2-C 2). The reaction of unsaturated “linear” ligands on clusters with metal carbonyl species

The complex (η 5-C 5H 5)NiOs 3(μ-H) 3(CO) 8(Ph 2PCCPr i ( 2a) has been obtained by treating (η 5-C 5H 5)NiOs 3(μ-H) 3(CO) 9 ( 1) with PPh 2C 2Pr i in the presence of Me 3NO. Treatment of 2a with Co 2(CO) 8 in hexane at room temperature gives high yields of (η 5-C 5H 5)NiOs 3(μ-H) 3(CO) 8{(Ph 2PCCPr i)Co 2(CO) 6} ( 3). The complexes 2a and 3 have been characterized by means of elemental analyses and IR, 1H and 13C NMR spectroscopies. Their structures have been determined by X-ray methods. Crystals of 2a are triclinic, space group P 1 with Z = 4 in a unit cell of dimensions a 16.543(7), b 16.578(7), c 16.461(6) Å, α 116.6(3), β 94.1(2), γ 118.8(3)°. Crystals of 3 are monoclinic, space group P2 1/ n with Z = 4 in a unit cell of dimensions a 18.275(9), b 17.804(7), c 13.343(4) Å, β 106.46(3)°. Both structures were solved by direct and Fourier methods and refined by full-matrix least-squares to R = 0.055 for 5882 observed reflections for 2a and to R = 0.046 for 1848 observed reflections for 3. Both structures can be derived from that of 1 (having a tetrahedral NiOs 3 core with three hydridic hydrogen atoms bridging the OsOs edges, a cyclopentadienyl group coordinated to the Ni atom, and nine terminal carbonyls bound to the Os atoms, three for each Os atom) by replacing one of the axial carbonyls by the Ph 2PCCPr i ligand. In 3 a Co 2(CO) 6 unit interacts, through two π bonds, with the acetylenic CC bond of the phosphino-alkyne ligand.

Five-coordinate dicarbonyl complexes of rhodium(I): [RhX(CO)2(PPh3)2] (X = Cl, Br, I)

The complexes trans-[RhX(CO)PPh3)2] (1, X = Cl, Br, I) react with CO to form [RhX(CO)2(PPh3)2] (2), and not to form cis-[RhX(CO)(PPh3)2]. Complexes 2 contain equivalent axial carbonyl ligands. It is proposed that a series of dicarbonyl complexes, including 2, is formed during decarbonylation reactions catalyzed by 1.

Carbon-13 NMR studies of some iron carbonyls: An unexpected trend in the chemical shifts of disubstituted complexes

The Carbon-13 NMR spectra of a series of Fe(CO) 4L and Fe(CO) 3L 2 complexes (L = P(cyclohexyl) 3, PMe 3, PPh 3, P(OMe) 3 or P(OPh) 3) have been measured. A good correlation is observed between 13C chemical shift of the carbonyls and the donor-acceptor properties of the phosphorus ligand. However, an unexpected trend is observed for Fe(CO) 5 → Fe(CO) 4L → Fe(CO) 3L 2 showing high field shifts of δ( 13C) upon successive substitution for some complexes. A variable temperature study was conducted on H 2Fe(CO) 4 and the axial and equatorial carbonyls have been resolved. The energy of interconversion is estimated at ca. 8.1 kcal. In addition the 13C spectrum of [HFe(CO) 4] − is reported for the first time.

A five-coordinate dicarbonyl rhodium(I) complex containing monohapto-2-diphenylphosphinothiophene: [RhCl(CO)2(DPT)2

Facile reversible addition of CO to trans-[RhCl(CO)(Ph2PC4H3S)2] gives the five-coordinate complex [RhCl(CO)2(Ph2PC4H3S)2], which represents the first complex of the type [RhCl(CO)2(PR3)2] to be identified, and which is trigonal bipyramidal with axial carbonyls and equatorial phosphine ligands.

Metal complexes of polycyclic tertiary amines. V. Structure of 1,3,5,7,-tetraazaadamantanepentacarbonylmolybdenum(0), (CH 2) 6N 4·Mo(CO) 5

X-ray analysis of the octahedral coordination compound (CH 2) 6N 4·Mo(CO) 5 has established that that axial and equatorial carbonyl groups have distinctly different dimensions, and the overall molecular geometry indicates significant steric repulsion between the organic ligand and the equatorial carbonyl groups. Moving away from the quaternary nitrogen atom, the three non-equivalent sets of CN bonds vary in the order long, short and normal, relative to the standard bond length in the unsubstituted (CH 2) 6N 4 cage system. A survey of the crystallograpic data for representative (CH 2) 6N 4 adducts utilizing only one nitrogen lone pair leads to the conclusion that cage distortion decreases in the order methylation > borine adduct formation ≅ N-oxide formation ≅ protonation > metal coordination. The crystals are orthorhombic, space group Pbca, with a = 12.800(2), b =13.377(2), c = 17.524(3) Å and Z = 8. The structure has been refined to R = 0.039 for 2491 observed MoKα data.

Hydrido-bridged bimetallic complexes involving gold or silver and chromium, molybdenum, or tungsten: X-ray crystal structure of [AuCr(µ-H)(CO)5(PPh3)

Treatment of tetrahydrofuran solutions of the salts [N(PPh3)2][MH(CO)4L][M = Cr or W, L = CO; M = W, L = P(OMe)3] with [AuCl(PPh3)] in the presence of TIPF6 afforded the compounds [AuM(µ-H)(CO)4L(PPh3)]. The gold–molybdenum compound [AuMo(µ-H)(CO)5(PPh3)] was similarly prepared from a dichloromethane solution of [N(PPh3)2][Mo2(µ-H)(CO)10]. Reactions between [N(PPh3)2][MH(CO)4L][M = Cr or W, L = CO; M = W, L = P(OMe)3], [Agl(PMe3)], and TIPF6 yielded the hydrido-bridged bimetal compounds [AgM(µ-H)(CO)4L(PMe3)]. A single-crystal X-ray diffraction study has been carried out on the complex [AuCr(µ-H)(CO)5(PPh3)]. The molecule has a bent Au(µ-H) Cr geometry [Au–Cr 2.770(2), Au–H 1.72(11), and Cr–H 1.64(12)A; Au–H–Cr 111 (5)°] in accord with the presence of a three-centre two-electron bond. The orientation of the Cr(CO)5 group is staggered relative to the Au(µ-H)Cr bridge, with the hydrido-ligand lying transoid to the axial carbonyl ligand and the phosphine group. Crystals are triclinic, space group P(no. 2), and the structure has been refined to R 0.047 for 3 401 intensities measured at 210 K in the range 4 ⩽ 2θ⩽ 50°. Proton, 31P-{1H}, and 13C-{H} n.m.r. spectroscopic data for the various compounds are reported and show that these species undergo dynamic behaviour in solution involving dissociation of the PPh3 or PMe3 groups, site exchange of CO ligands, and, for the silver-containing complexes, dissociation of the MH(CO)4L fragments.

Nicht‐Berry Pseudorotation beim Carbonylgruppenaustausch von Tetracarbonyl(η‐(Z)‐cycloalken)eisen‐Komplexen

Exchange of Carbonyl Group Sites in Tetracarbonyl(η‐(Z)‐cycloalkene)iron Complexes via Non‐Berry PseudorotationThe tetracarbonyliron complexes of cyclobutene, cyclopentene, 4,4‐dimethyl‐cyclopentene, 2,5‐dihydrofurane, cyclohexen, (Z)‐cyclohepten, ‐octene, ‐nonene, and ‐decene were prepared by thermal or photochemical reaction of the corresponding olefins with nonacarbonyldiiron and pentacarbonyliron, respectively. The low‐temperature behaviour of the mostly new complexes which can be stored over a longer period only below 250 K and which exhibit four C,O‐stretching frequencies in the IR. spectra (cf. Table 2), indicative for a trigonal bipyramidal structure with the olefin ligand in an equatorial position, was studied in CCl2F2 by 13C‐NMR. spectroscopy between 200 and 115 K. In this temperature range all complexed olefin ligands with the exception of (Z)‐cyclooctene (cf. [11]) show an averaged Cs‐symmetry on the NMR. time scale. About 115 K the tetracarbonyliron group gives rise to three 13C‐signals in a ratio of 1:1:2 for the complexes of (Z)‐cycloheptene, (Z)‐cyclodecene and 2,5‐dihydrofurane (Cf. Table 3). This is an agreement with the fixed equatorial position of the non‐rotating olefin ligands. The complexes of cyclooctene and cyclononene give only two 13C‐signals in a ratio of 1:1 for the carbonyl groups. The temperature dependence of the signals indicates that in these cases the two axial carbonyl groups exhibit accidentally the same chemical shift. In all cases a complete line shape analysis of the 13C‐signals of the carbonyl groups could only be accomplished by using two exchange constants (cf. Tables 4 and 5 as well as Fig. 2–5 and Fig. 8). The same is true for the cyclobutene complex, but only one exchange constant could be determined (at 120 K: two 13C‐signals in a ratio of 1:3 with the beginning of a further coalescence). The cyclopentene and cyclohexene complexes showed only one 13C‐signal even at 115 K. The observed temperature‐dependent line shapes of the 13C‐signals can be interpreted in terms of a Non‐Berry pseudorotation mechanism involving a three site exchange with each of the two diastereotopic axial carbonyl groups and the two equatorial carbonyl groups (for activation parameters see Table 4). The differences in the activation parameters can be explained on steric grounds by assuming a transition state (cf. Fig. 8) similar to the C3b‐structure of tetracarbonyliron which lies about 27 kJmol−1 above its C2v‐structure (cf. [30]) comparable with the ground state of our complexes with weak dπ(Fe),pπ(Olefin) back bonding. The transition state model implies that the reorganization process involving the axial carbonyl group in exo‐position possesses the higher exchange barrier (cf. Fig. 8).

Joint x-ray and neutron diffraction structure analysis of [(μ-H) 3Re 3(CO) 8{(EtO) 2POP(OEt) 2} 2

The compound [(μ-H) 3Re 3(CO) 8{(EtO) 2POP(OEt) 2} 2] crystallises in the monoclinic space group P2 1/ c with a 18.053(6), b 16.211(5), c 14.800(3) Å, β = 102.41(2)°, and Z = 4. Simultaneous refinement of a single parameter set to fit 3212 X-Ray (sin θ/λ) > 0.352 Å −1 and 1480 neutron data has led to final weighted residuals R w ( F) of 0.096 (X-Ray) and 0.095 (neutron). The molecule exhibits noncrystallographic C 2 symmetry, with two edges of the Re 3 triangle bridged by (OEt) 2POP(OEt) 2 ligands. The hydride ligands lie close to the trimetal plane with each hydride bridging an ReRe vector. Average molecular parameters involving the hydride ligands are ReH 1.812(17), ReRe 3.282(17) Å, ReHRe 130(3) and HReH 107.6(27)/dg. All eight carbonyl ligands are terminal, the ligand polyhedron being derived from that in H 3Re 3(CO) 12 by substitution of four axial carbonyls by two bidentate phosphite ligands.

Bonding in a binuclear metal carbonyl: experimental charge density in Mn2(CO)10

X-ray diffraction data (Ag Ka and Mo Net radiation) have been collected at 74 K on dimanganese decacarbonyl Mn2(CO)I 0, and the crystal structure was refined. The atomic positional and thermal parameters were determined from high-angle AgKa data to avoid systematic errors due to bonding effects. The molecular geometry is discussed. The distortions are larger than at room temperature: for example, the torsion angle of the two Mn(CO) 5 fragments is 50.2 °, compared to 47.4 ° at room temperature, and 45 ° for an ideal D4a symmetry. 'X-X' deformation-density maps were computed and averaged over chemically equivalent sites. No significant charge-density accumulation is observed on the Mn-Mn bond. The configuration around the Mn atoms is essentially octahedral, with about 75% of the 3d electrons in the diagonal orbitals (dxy,d~z,dy ~) and the remaining 25% in d: and dx2_/. Atomic charges were determined both by direct integration and by least-squares refinement. Directly integrated charges are very small. Mn seems slightly negative. Both methods of charge integration show a clear difference between axial and equatorial carbonyls, which is confirmed by comparing their electron density with that of free carbon monoxide: the differences are characteristic of a a-bonding n-backbonding mechanism, and are larger for the axial carbonyls than for the equatorial carbonyls. This confirms the stronger bonding of the axial carbonyls, also responsible for the longer C-O bond and the shorter Mn-C bond.

Crystal and molecular structures of [Os3(CO)11(NCMe)] and [Os3(CO)10(NCMe)2

Both the complexes [Os3(CO)11(NCMe)](1) and [Os3(CO)10(NCMe)2](2) crystallise in the monoclinic space group P21/n with Z= 4. The cell parameters for (1) are a= 8.284(3), b= 14.787(5), c= 15.944(6)A, and β= 102.50(2)°, and those for (2) are a= 8.520(3), b= 20.096(6), c= 12.747(4)A, and β= 108.77(2)°. The structures have been solved by a combination of direct methods and Fourier-difference techniques, and refined by blocked-cascade least squares to R values of 0.039 for 1 459 diffractomer data, for (1), and 0.046 for 2 397 diffractometer data, for (2). The three Os atoms in (1) define an isosceles triangle. Two of the metal atoms are co-ordinated to two axial and two equatorial terminal carbonyl groups. The third Os atom is co-ordinated to one axial and two equatorial carbonyls and the second axial site is occupied by a linear nitrile ligand. The structure of (2) resembles that of (1) except that an axial carbonyl on an adjacent Os atom to and on the opposite side of the Os3 plane from the co-ordinated nitrile has been replaced by the second NCMe ligand.