Determination of Some Parameters of a Porous Medium–Liquid System by the Pulsed Field Gradient NMR

A possibility was considered to estimate the parameter of a porous medium S/V _p, whereSand V _p are the surface area and the volume of pores, respectively, as well as the power of nuclear magnetic energy sinks of a porous medium–liquid system by the example of randomly packed glass spheres 53–63 m in diameter and acetone, water, or decane as a liquid medium. Estimates were made by analyzing the time dependences of the effective self-diffusion coefficient D(t) and P(t), the probability of return of a molecule to its initial position by time t. It was shown that the short-time parts of D(t) dependence allow us to obtain parameters S/V _p and , whereas those of P(t), only the S/V _p parameter. The values of , obtained from D(t), and from the time of relaxation of longitudinal nuclear magnetization, differ from each other by an order of magnitude. As expected, the value of S/V _p, obtained for a given porous medium, is independent of the nature of introduced liquid.     

First and second thermodynamic mixing properties of ethylbenzene +n-alkanes: Experimental and theory

Isobaric expansibilities _P and isothermal compressibilities _T have been determined at 25 and 45°C for binary mixtures of ethylbenzene + n-tetradecane and + n-hexadecane and the corresponding excess functions (V ^E /T)_P and (V ^E /P)_T have also been obtained. With these data and supplementary literature values, the following second order mixing properties are also reported at 25°C: _S ^E , (V ^E /P)_T, C_V and (VT). All mixing quantities have been compared with the results obtained at 25°C by using the Prigogine-Flory-Patterson theory of liquid mixtures. The predicted values suggest that the ability of ethylbenzene as a breaker of the pure n-C_n orientations is similar to what we found for toluene and higher than for p-xylene.     

Synthesis,Structure, and Magnetic Properties of the Silicides <Emphasis Type="BoldItalic">RE</Emphasis>IrSi (<Emphasis Type="Italic">RE</Emphasis> = Ce,Pr, Er,Tm, Lu) and SmIr<Subscript>0.266(8)</Subscript>Si<Subscript>1.734(8)</Subscript>

Summary. The equiatomic rare earth metal–iridium–silicides REIrSi (RE=Ce, Pr, Er, Tm, Lu) were prepared by arc-melting of the elements and subsequent annealing. All silicides were characterized through their X-ray powder patterns. The structures of CeIrSi, ErIrSi, and LuIrSi were refined from X-ray single crystal diffractometer data: LaIrSi type, P2₁3, a=629.15(2)pm, wR2=0.1232, 280F² values, and 11 variable parameters for CeIrSi; TiNiSi type, Pnma, a=673.4(1), b=416.07(5), c=744.88(9)pm, wR2=0.0705, 339F² values, and 20 variable parameters for ErIrSi, and a=664.0(3), b=412.9(1), c=742.6(1)pm, wR2=0.0398, 496F² values, and 20 variable parameters for LuIrSi. The iridium and silicon atoms in CeIrSi, ErIrSi, and LuIrSi build three-dimensional [IrSi] networks where the iridium atoms have three (CeIrSi, Ir–Si 229pm) and four (ErIrSi, Ir–Si 247–258pm; LuIrSi, Ir–Si 245–256pm) silicon neighbors. The [IrSi] networks leave larger channels in which the cerium, erbium, and lutetium atoms are located. Temperature dependent susceptibility data for LuIrSi indicate Pauli paramagnetism. CeIrSi shows Curie-Weiss paramagnetism above 100K with an experimental magnetic moment of 2.56(2)_B/Ce atom. With samarium as rare earth metal component the silicide SmIr_0.266(8)Si_1.734(8) with -ThSi₂ type structure was obtained: I4₁/amd, a=409.3(1), c=1397.2(5)pm, wR2=0.0575, 161F² values, and 9 variable parameters. Within the three-dimensional [Ir_0.266Si_1.734] network the Ir/Si–Ir/Si distances range from 230 to 237pm.     

Zr<Subscript>5</Subscript>Ir<Subscript>2</Subscript>In<Subscript>4</Subscript> – A Superstructure of the Lu<Subscript>5</Subscript>Ni<Subscript>2</Subscript>In<Subscript>4</Subscript> Type

Summary. Zr₅Ir₂In₄ was synthesized by reaction of the elements in a glassy carbon crucible in a water-cooled sample chamber of an induction furnace. The sample was characterized by X-ray diffraction on both powder and single crystals. Zr₅Ir₂In₄ crystallizes with a pronounced Lu₅Ni₂In₄ type subcell, space group Pbam, a=1739.5(6), b=766.3(2), c=338.9(2) pm. Weak additional reflections force a doubling of the subcell c axis. The superstructure of Zr₅Ir₂In₄ is of a new type: Pnma, a=1739.5(6), b=677.8(2), c=766.3(2) pm, wR2=0.0529, 1592 F² values, and 60 variable parameters. The group-subgroup scheme for the klassengleiche symmetry reduction is presented. The formation of the superstructure is most likely due to a puckering effect (size of the iridium atoms). The crystal chemistry of Zr₅Ir₂In₄ is briefly discussed.     

A kinetic study of the oxidation of 2-(2-hydroxyethyl)pyridine by chromium(VI) in strongly acidic aqueous solutions of HClO4

Oxidation of 2-(2-hydroxyethyl)pyridine (pyeol) to 2-pyridylacetaldehyde (pyeal) by Cr^VI has been studied in the 0.5–2.0M HClO₄ range at I=2.2M and in super acidic media within the 3–7M HClO₄ range. In all cases the reaction has been examined under pseudo-first order conditions keeping the alcohol and H⁺ _aq in excess. Cr^III-complexes formed during reduction of Cr^VI by pyeol at different molar ratios of the reactants, were isolated chromatographically and identified as [Cr(H₂O)₆]³⁺ and [Cr(pyeac)(H₂O)₄]²⁺ ions (pyeac=2-pyridylacetic acid). Free 2-pyridylacetaldehyde (pyeal) was separated and determined as its 2,4-dinitro-phenylhydrazone derivative. A dependence of the rate constants on [pyeol] and [H⁺] has been established at I=1.2M and I=2.2M. The apparent activation parameters at [H⁺]=1 and 2M have been determined. A rate law of the form d[Cr^VI]/dt= (k ₁[H ⁺]+k ₂[H ⁺]²)[pyeol][Cr^VI] is proposed. A linear dependence of log k _obs on H₀ in the super acidic media is obeyed. A rate decrease is observed if oxygen instead of argon is in the reaction cell. The reaction mechanism has been discussed.     

Crystal Structure of Curcumenol: Evidence of Asymmetric O–H...O (bridged) Hydrogen-Bonded Closed Dimer

Curcumenol, C₁₅H₂₂O₂, was isolated from Globba malaccensis Ridl. The compound was crystallized from ethylacetate/hexane solution in the monoclinic system, space group C2, with cell dimensions a = 16.8467(4) , b = 7.6799(2) , c = 11.8613(10) , = 115.9970(10)°. The molecules form a distorted centrosymmetric dimer linked by hydrogen bonds between the hydroxyl O2 atom and the bridged O1 ether atom (O2...O1(–x+2, y, –z+1), 2.8297(15) ; (O2–H2O–O1), 169(2)°). This is an interesting example of an O–H...O (bridged ether) asymmetric hydrogen-bonded dimer.     

Tishchenko Reaction Over Solid Base Catalysts

Catalytic behavior of solid bases for mixed Tishchenko reaction in which an equimolar mixture of two different aldehydes is allowed to react was investigated employing the combinations of benzaldehyde and pivalaldehyde, pivalaldehyde and cyclopropanecarbaldehyde, and cyclopropanecarbaldehyde and benzaldehyde. The reactions were performed at 353K for 4h in vacuo without solvent using 5mmol of each aldehyde and 100mg of solid base catalyst. For all the combinations, the catalytic activity of alkaline earth oxides increased in the order of BaOMgO2O₃, ZrO₂, ZnO, -alumina, hydrotalcite, KF/alumina, and KOH/alumina produced either no amount or very small amounts of cross-esterification and self-esterification products. Quantum chemical calculations carried out at the PM3-MO level for the positive charges on the carbonyl carbon atoms of aldehydes and the structure parameters of the active species for the ester formations indicated that the selectivities to four Tishchenko dimers over MgO and CaO are determined primarily in the step of the nucleophilic addition of the active species (PhCH₂O^-, ^tBuCH₂O^-, and C₃H₅CH₂O^-) to the carbonyl carbon atoms of aldehydes. The reaction of the aldehyde having more positively charged and sterically less hindered carbonyl carbon atom with the active species having less hindered oxygen atom proceeds faster.We also attempted the application of solid base catalysts to the challenging Tishchenko reaction of furfural, and excellent results were obtained with CaO and SrO. For instance, when furfural (10mmol) was treated with SrO (100mg) without solvent at 353K for 6h in vacuo, almost quantitative conversion to the corresponding ester was accomplished. Furthermore, application of SrO to the Tishchenko reaction of 3-furaldehyde was carried out successfully. The catalytic systems were also successfully applicable to the intramolecular Tishchenko reaction (lactonization) of o-phthalaldehyde to phthalide. For example, treatment of o-phthalaldehyde (1mmol) with CaO (50mg) in benzene (1mL) solvent at 313K under N₂ produced phthalide quantitatively in a short time of 15min. We finally refer to the perspective of application of solid base catalysts to Tishchenko reaction.     

Another Example of Eight-Coordinated Molybdenum(IV): Molecular and Crystal Structure of Tetrakis(methyl-2-mercaptonicotinato-N,S,N′,S′,N′′,S′′,N′′′,S′′′)molybdenum(IV), [Mo(C5H3NSCOOCH3)4]

Tetrakis(methyl-2-mercaptonicotinato-N,S,N,S,N,S,N,S)molybdenum(IV), has been obtained by the reaction of [MoCl₂(acac)₂] (or MoCl₄·2CH₃CN) and 2-mercaptonicotinic acid in methanol. Esterification of 2-mercaptonicotinic acid resulted from the catalytic action of molybdenum. The complex molecule contains molybdenum dodecahedraly coordinated by four sulfur and four nitrogen atoms.     

Orbital interactions in anti- and syn- tricyclooctadienes and their homoderivatives

Photoelectron spectroscopy and molecular orbital calculations of the Extended Hückel, MINDO/3 and STO-3G Hartree-Fock type have been applied to anti- and syn-tricyclo[4.2.0.0^2,5]octadiene (1 and 2) and their homo and bishomo derivatives. The resulting ordering of the one-electron levels for 1 and 2 are 7a _g ( ₊), [6b _u (), 5b _u (_–)], 4a _u (), 3a _u () and 7a ₁(₊), 5b ₂(), 6b ₂(_–), 3a ₂(), 4b ₁(), respectively. The present results differ substantially from those previously published.     

Protolytic, Redox, and Polar Properties of Diphenylamine and Related Reagents: Quantum-Chemical Evaluation

Based on the results of quantum-chemical PM3 calculations, correlations were found between the redox potentials (E) and the first ionization potentials of diaryamines; between the pK _a values of diarylamines, which characterize the protonation of the nitrogen atom and the dissociation of carboxy-substituted reagents at the COOH group, and the proton affinity of diphenylamines and carboxy-substituted anions; and between the experimental and calculated dipole moments () of molecules. It was shown that E, pK _a, and can easily be estimated by quantum-chemical calculations. A method for the prediction of the selectivity of analytical reagents was developed.     

The Electrochemical Behavior of p-Aminophenol at a ω-Mercaptopropionic Acid Self-Assembled Gold Electrode

A -mercaptopropionic acid (MPA) self-assembled monolayer modified electrode (MPA/SAM/Au) on a gold electrode has been fabricated. The characterization of the MPA/SAM/Au was investigated using attenuated total reflection-fourier transform infrared (ATR-FTIR) and A.C. impedance. The electrochemical behaviors of p-aminophenol (p-AP) were studied at the MPA/SAM/Au by cyclic voltammetry and semi-derivative voltammetry (SDV) in BR buffer solution. The modified electrode shows excellent electrocatalytic activity for the redox of p-AP and accelerates the electron transfer rate. The diffusion coefficient (D) is 4.55×10^–6cm²s^–1. The oxidative peak current increases linearly with the concentration of p-AP in the range of 4.0×10^–88×10^–6molL^–1 and 1.0×10^–52×10^–4molL^–1 by square wave voltammetry response, respectively. The detection limit (three times the signal blank/slope) is up to 1.2×10^–8molL^–1. The modified electrode is able to eliminate the interference of p-benzenediol, o-benzenediol and o-AP at a 40-, 90- or 70-fold concentration of p-AP, and it has been satisfactorily used for the determination of the real sample.     

In vitro and in vivo antitumour studies of a new thiosemicarbazide derivative and its complexes with 3d-metal ions

A new ligand, 1-(2-furanthiocarbo)-3-thiosemicarbazide (H₂ftsc), prepared from thiosemicarbazide and carboxymethyl-2-furandithioate, forms complexes [Mn(ftsc)(H₂O)₂], [Pd(ftsc)] · 2H₂O, [M(Hftsc)(acac)₂] (M=Co^III or Cr^III), [M(Hftsc)₂(acac)] (M=Mn^III or Fe^III) and [Zn(Hftsc)₂] · 2H₂O, which were characterized by elemental analyses, magnetic susceptibility, i.r., electronic and n.m.r. spectral data. The Mössbauer spectra of [Fe(Hftsc)₂(acac)] at 298K and 80K suggest the presence of high-spin iron(III) with an S=5/2 state. In vivo and in vitro antitumour activity of the ligand and the complexes have been screened towards several tumour cell-lines.     

Synthesis and X‐Ray Study of Single Crystals of K5(Cd0.5Zr1.5)(MoO4)6 Triple Molybdate

Single crystals of K₅(Cd_0.5Zr_1.5)₂(MoO₄)₆ molybdate have been grown. Its composition and crystal structure have been established from Xray diffraction data CAD4 automatic diffractometer, MoK radiation, 940 F(hkl), R = 0.0234. The crystals have a trigonal unit cell a = b = 10.624(1), c = 37.694(6), V = 3684.5(8)³, and space group R3c. The 3D mixed framework of the molybdate structure is formed by two kinds of Mo tetrahedra and (Cd, Zr) octahedra joined by shared O vertices. The large cavities in the framework are occupied by K atoms of three kinds. The distribution of Cd²⁺ and Zr⁴⁺ cations over two crystallographic positions has been refined.     

Interaction of a Single State with a Known Infinite System Containing One-Parameter Eigenvalue Band

Interaction of a quantum system S ₁ ^a containing a single state |> with a known infinite-dimensional quantum system S ^b containing an eigenvalue band [ _a , _b ] is considered. A new approach for the treatment of the combined system S =S ₁ ^a S ^b is developed. This system contains embedded eigenstates |()> with continuous eigenvalues [ _a , _b ], and, in addition, it may contain isolated eigenstates | _I > with discrete eigenvalues _I [ _a , _b ]. Exact expressions for the solution of the combined system are derived. In particular, due to the interaction with the system S ^b , eigenvalue E of the state |> shifts and, in addition, if E[ _a , _b ] this shifted eigenvalue broadens. Exact expressions for the eigenvalue shift and for the eigenvalue distribution of the state |> are derived. In the case of the weak coupling this eigenvalue distribution reduces to the standard resonance curve. Also, exact expressions for the time evolution of the state |(t)> that is initially prepared in the state |(0)>|> are obtained. Here again in the case of the weak coupling this time evolution reduces to the familiar exponential decay. The suggested method is exact and it applies to each coupling of the system S ₁ ^a with the system S ^b , however strong. It also presents a relatively good approximation for the interaction of a nondegenerate eigenstate | _s > of an arbitrary system S ^a with an infinite system S ^b containing a single eigenvalue band, provided this eigenstate is relatively well separated from other eigenstates of S ^a and provided the interaction between the systems S ^a and S ^b is not excessively strong.     

Preparation and x-ray structure determination of penta-and tetracyano-oxomolybdenum(IV) anions. The influence of water on their reactivity

Summary Several penta-and tetracyanooxomolybdenum(IV) anions have been synthesized containing different numbers of H₂O molecules, either coordinated or present as crystallisation molecules. The influence of these molecules on the reactivity of the complex, especially towards O₂, is discussed. Three compounds were characterized by x-ray structure determination. [Mo(O)(CN)₅(H₂O)₂(MeCN)₂][PPh₄]₄Cl belongs to triclinic space group P-1 witha=13.146(3) Å,b=16.944(5) Å,c=21.761(6) Å, =84.72(2)°, =87.15(2)° and =85.25(2)°. The volume of the unit cell is 4678(6)ų withz=2. The structure was refined to R=6.5%. [Mo(O)(CN)₄(H₂O)·6H₂O][PPh₄]₂ belongs to monoclinic space group P2₁/n witha=15.313(2)Å,b=19.983(3)Å,c=17.006(2)Å, =100.51(2)°. The volume of the unit cell is 5117(3)ų withz=4. The structure was refined to R=8.7%. [Mo(O)(CN)₄(MeCN)](PH₃)₂N]₂ belongs to triclinic space group P-1 witha=13.770(4)Å,b=16.292(5)Å,c=16.889(5)Å, =73.23(2)°, =72.02(2)° and =71.57(2)°. The volume of the unit cell is 3342(3)ų withz=2. The structure was refined to R=7.2%.     

Solution properties of celluloses from different biological origins in LiCl · DMAc

Differences in the solution properties of cellulose in 8%LiCl·DMAc (dimethyl acetamide) were investigated usingcelluloses from different origins. The latter included plants (dissolving pulp(DP), cotton linters (CC), and kraft pulp), bacteria (Acetobacterxylinum, BC), and marine animals (tunicin fromHalocynthia). The celluloses from plants and bacteriaformed LiCl·DMAc solutions that were isotropic andanisotropic, respectively; and the animal cellulose was insoluble. The weightaverage molecular weights, M_w, of DP, CC and BC were found to be98.2×10⁴,170×10⁴ and192×10⁴, respectively. The solutionviscositieswere proportional to c (c; polymer concentration) in thedilute and semi-dilute regions, where the exponent was 1 for allsamplesin the dilute region; in the semi-dilute region, it was 4 for the DP and CCsolutions and 3 for the BC solution. Molecular weight differences werecompensated by plotting the viscosity against cM_w orc[] (where [] is the limiting viscosity number).The difference in viscosity behavior at elevated solutionconcentration indicates that the cellulose molecules from DP and CC behave asflexible polymer chains and those of BC as rod-like ones.These results suggest that differences in molecular structure andproperties exist between celluloses from different sources, and that thesedifferences relate to the mechanism or the type of the intermolecularinteraction between the celluloses of plants (DP and CC) and those of bacteria(BC).     

Strukturelle Abwandlungen an partiell silylierten Kohlenhydraten mittels Triphenylphosphan/Azodicarbonsäurediethylester, 4. Mitt.: Transformationen an Mannose und Galaktose

Reaction of methyl -D-galactopyranoside (1) with two equivalents oft-butyldimethylchlorosilane yields methyl 2,6-bis-O-(tBDMSi)--D-galactopyranoside (1 b), methyl 3,6-bis-O-(tBDMSi)--D-galactopyranoside (1 c) and methyl 4,6-bis-O-(tBDMSi)--D-galactopyranoside (1 d). Likewise methyl -D-mannopyranoside (6) affords methyl 2,6-bis-O-(tBDMSi)--D-mannopyranoside (6 d) and methyl 3,6-bis-O-(tBDMSi)--D-mannopyranoside (6 b), which can be isomerised withTPP/DEAD to methyl 4,6-bis-O-(tBDMSi)--D-mannopyranoside (6 f). Methyl 6-O-(tBDMSi)--D-galactopyranoside (1 a) and methyl 6-O-(tBDMSi)--D-mannopyranoside (6 a) can be prepared from1 or6 with one equivalent oft-butyldimethylchlorosilane.Without an external nucleophile the sugar derivatives1 a and1 b react withTPP/DEAD to form the 3,4-carbonato--D-galactopyranosides1 h and1 i and the 3,4-carbonato-2-O-ethoxycarbonyl--D-galactoside (1 j). In contrast to the formation of the compound1 i by means ofTPP/DEAD the reaction of1 a withTPP and Di-t-butyl-azodicarboxylate (DTBAD) yields the 2,3-anhydro--D-taloside (4 b) and only a small amount of1 i. The epoxide4 b can be cleaved withp-nitrobenzoylchloride/pyridine to the 3-chloro-3-deoxy-2,6-di-O-p-nitrobenzoyl--D-idoside (5). Reaction of1 c and1 d withTPP/DEAD yields the 2,3-anhydro--D-gulopyranoside (2), which can be transformed with NaN₃/NH₄Cl to the 2-azido-2-deoxy--D-idopyranoside (3).Likewise6 a and6 d can be converted to the 3,4-anhydro--D-talosides (7 a and7 b). Reaction of7 b or6 d withTPP/DEAD/NH₃ leads to 3,4-anhydro-2-azido-2-deoxy--D-galactopyranoside (8) and 3-azido-3-deoxy--D-altropyranoside (10), resp.The epoxide7 b is opened with NaN₃/NH₄Cl to the 4-azido-4-deoxymannosides (11 a and11 c) and the 3-azido-3-deoxy--D-idopyranoside (12), while the epoxide8 affords the 2,4-di-azido-2,4-dideoxy--D-glucopyranoside (9).Structures were elucidated by¹H-NMR-analysis of the corresponding acetates.

H. H. Brandstetter undE. Zbiral, Helv., im Druck.     

Prins-Reaktionen mit Arylaldehyden, 5. Mitt.: Zur Umsetzung mit 2-Buten und mit Cyclohexen

By reaction of 2-[(1RS, 2RS)-2-hydroxy-1-methyl-propyl]-2-phenyl-1,3-dithiane (1 a) withcis-2-butene oxide, subsequent reduction and acetalizationc-4,t-5-dimethyl-r-2,c-6-diphenyl-1,3-dioxane (3 a) andt-4,c-5-dimethyl-r-2,c-6-diphenyl-1,3-dioxane (3 b) were synthesized as model compounds. For the same purpose by aldol reaction of cyclohexanone and reduction (1RS, 2SR)-2[(RS)-hydroxy-(4-methoxyphenyl)methyl]cyclohexanol (7 a), (1RS, 2RS)-2[(SR)-hydroxy-(4-methoxyphenyl)methyl]cyclohexanol (8 a), and (1RS, 2RS)-2[(RS)-hydroxy-(4-nitrophenyl)methyl]cyclohexanol (8 b) and by acetalization (2 , 4 , 4 a, 8 a)-2,4-bis(4-methoxyphenyl)hexahydro-4H-1,3-benzodioxin (9 a) and (2 , 4 , 4 a, 8 a)-2,4-bis(4-nitrophenyl)hexahydro-4H-1,3-benzodioxin (10 b) were obtained. FromPrins reactions, starting with 2-butene3 a,c-4,c-5-dimethyl-r-2,c-6-diphenyl-1,3-dioxane (3 c),r-4,t-5-dimethyl-c-6-phenyl-1,3,2-dioxathiane-2,2-dioxide (4), and (2Z, 4E)-1,5-diphenyl-4-methyl-2,4-pentadien-1-on (5), and starting with cyclohexene (E)-3-(4-methoxybenzylidene)cyclohexenyl-4-methoxyphenyl ketone (11) have been isolated in low yields.

4. Mitt.:Griengl, H., Nowak, P., Mh. Chem.109, 11 (1978).     

The Dissociation Constants of 1,1′-Bis (pyridinium-4-aldoxime)trimethylene dibromide

Summary. The dissociation constants of the two oxime groups of 1,1-bis(pyridinium-4-aldoxime)trimethylene dibromide (TMB-4) were determined using spectrophotometric data. Two numerical methods were applied to treat the overlapping equilibria. The results obtained by both agreed with each other and their mean values at 25°C corrected for the ionic strength of 0.05moldm^–3 are pK_a1=7.49±0.11 and pK_a2=8.96±0.09. These values were discussed in terms of the pK_as of 1,1-bis(pyridinium-4-aldoxime)oxydimethylene dichloride (Toxogonin), a similar dioxime, which were derived by extrapolation of literature data.     

Synthesis and structure of [(OC)4Os(PbMe2)]2 and some derivatives of the type Os2(CO)7(SnMe2)2(L)

The complexes [(OC)₄Os(PbMe₂)]₂ (3) and [(OC)₄OsSnBu ₂ ]₂ (4) have been prepared from be reaction of Na₂[Os(CO)₄] with Me₂PbCl₂ and Bu ₂ SnCl₂, respectively, in THF and their X-ray crystal structures determined. The red derivative,3, was light-sensitive in solution. The reactions or [(OC)₄ Os(SnMe₂)]₂ (2), or its decarbonylated derivative [Os₃(CO)₇(SnMe₂)₂]₂ (7), with olefins or phosphorus donor ligands have also been investigated, and the structures of two derivatives, viz. [Os₂(CO)₇(SnMe₂)₂(C₂H₄)] (5a) and [Os₂(CO)₇(SnMe₂)₂(PMe₃)] (6a), have been determined; the noncarbonyl ligand occupies an equatorial site in each case. The X-ray crystal structures of all these compounds, like those of [(OC)₄Os(EMe₂)]₂ (E=Ge (1), Sn (2)) which have been reported previously, show leaning of the axial carbonyl ligands toward the metal tetracycle, i.e., an umbrella effect. Crystallographic data for compound3: space group, P2₁/a;a=13.4404(13) Å,b=10.7494(14) A,c=148967(18) A,=98.204(9)°,R=0.035, 1983 observed reflections. For compound4: space group,P1;a=9.016(1) Å,b=9.370(1),c=11.334(1) A, =103.67(1)°,=100.30(1)°, =115.03(1)°, R=0.046, 2026 observed reflections. For compound5a: space group,P1;a=9.2933(11)Å,b=9.7181(3),c=12.2508(15) A, =89.21(1)°,=87.61(1)°, =86.13(1)°,R=0.038, 2770 observed reflections. For compound6a space groupP1:a=8.7244(9)Å,b=10.9318(6),c=13.2560(13) A, =87.815(6)°,=83.655(8)°, =82.343(6)°, R=0.030, 3497 observed reflections.