Crystal structures of 1,1′-di(2-propanone)-2,2′-biimidazole dihydrazone and 2,6-diacetylpyridine dihydrazone

The nucleophilic addition reactions between 1,1′-di(2-propanone)-2,2′-biimidazole or 2,6-diacetylpyridine and hydrazine hydrate afford 1,1′-di(2-propanone)-2,2′-biimidazole dihydrazone (1) and 2,6-diacetylpyridine dihydrazone (2), respectively. Compound1 crystallizes in the orthorhombic space groupP2₁2₁2₁, witha=9.042(2),b=9.731(3),c=15.683(4)Å, V = 1379.9(6)Å^? andZ=4. Compound2 crystallizes in the orthorhombic space groupPnma, witha=10.948(2),b=19.742(6),c=4.566(1)Å, V=986.9(4)Å^? andZ=8. A pseudo center of inversion is present at the midpoint of the C?C bond joining the imidazole rings of1, whose substituents crystallize in atrans configuration. The imidazole rings are rotated 2.5(3)° about the C?C bond. In contrast to the essentially planar structure of2, the hydrazone substituent groups of1 are at angles of 89.9(1)° and 88.4(1)° with respect to the plane of the adjacent imidazole moiety.     

Aryl acetylene inhibitors for cytochrome P450-based monooxygenase isozymes

The structures of 1-propynylpyrene (1), 4-ethynylbiphenyl (2), 3-ethynylphenanthrene (3), 9-propynylphenanthrene (4) and 9-ethynylphenenthrene (5) have been determined using MoKα radiation.1 crystallizes in the monoclinic space groupP2₁/n witha=8.972(2)b=10.136(2),c=14.060(2)Å, β=99.77(1)°,V=1260.0(7) ų,Z=4. Refinement of 1261 reflections gaveR=0.042 andR _w =0.054.2 crystallizes in the orthorhombic space groupPbcn witha=17.7159(9),b=6.250(2),c=18.544(2) Å,V=2053(1) ų,Z=8. Refinement of 1710 observed reflections gaveR=0.046 andR _w =0.053.3 crystallizes in the orthorhombic space group Pbca witha=7.891(1),b=16.459(1),c=16.879(2) Å,V=2192.2(7) ų,Z=8. Refinement of 1520 observed reflections gaveR=0.032 andR _w =0.047.4 crystallizes in the orthorhombic space groupP2₁2₁2₁ witha=5.8867(6),b=13.476(1).c=14.838(2) Å,V=1177.1(4) ų,Z=4. Refinement of 1217 observed reflections gaveR=0.041 andR _w =0.055.5 crystallizes in the monoclinic space groupP2₁/c witha=27.755(7),b=5.1447(9),c=15.500(2) Å, β-105.53(2)°,Z=2133(2) ų,Z=8. There are two independent molecules in the unit cell. Refinement of 1276 observed reflections gaveR=0.061 andR _w =0.065. In2–5 there are no significant intermolecular interactions while in1 the molecules are associated in pairs via π-π stacking intarctions. Bond distances within the pyrene and phenanthrene portions of the molecules compare favorably with those found in other derivatives.     

Intra- vs intermolecular hydrogen bonding. The crystal structure of 5-methyl-2-hydroxyacetophenone thiosemicarbazone monohydrate and salicylaldehyde-2-methylthiosemicarbazone monohydrate

The crystal structure of 5-methyl-acetophenonethiosemicarbazone monohydrate,A, and salicylaldehyde-2-methylthiosemicarbazone monohydrate,B, were determined using single crystal X-ray diffraction.A crystallizes in the monoclinic space groupC2/c, with lattice parametersa=14.161(2),b=15.753(1) Å,c=11.084(1) Å, β=112.59(1)° andZ=4, yielding a calculated density ofD _calc=1.352 mg/m³.B crystallizes in the triclinic space groupP1, witha=7.233(2) Å,b=7.371(2) Å,c=11.841(2) Å, α=82.77(2)°, β=78.33(2)°, γ=63.06(2)° andD _calc=1.371 mg/m³ forZ=2,. In bothA andB the immine nitrogen and the sulfur atom areanti with respect to N2-C8. WhileA presents the usual intramolecular six membered hydrogen bond ring,B has instead an intermolecular hydrogen bond between the hydroxy moiety of the salicyladehyde and a water molecule. AM1 calculations agree with the experimental conformations observed in both compounds.     

Structural investigation of 1-amino-2,4,6-trinitrobenzenes in the solid state and in solution

The crystal structure of 1-pyrrolidino-2,4,6-trinitrobenzene3, 1-morpholino-2,4,6-trinitrobenzene4 and 1-piperidino-2,4,6-trinitrobenzene5 have been determined by single-crystal X-ray diffraction data and the structure in solution was investigated by UV-visible spectrophotometry and¹³C nmr. The three compounds are monoclinic, space groupP2_i/n. Unit cell dimensions area=6.6660(1),b=8.612(1),c=20.696(3) Å, β=90.73(1)^o, andD _c =1.58 g cm^?3 for compound3;a=7.090(2),b=21.493(9),c=8.298(3) Å, β=101.27(1)^o, andD _c 1.60 g cm^?3 for compound4 anda=10.426(1),b=10.038(1),c=12.291(1) Å, β=90.04(1)^o withD _c =1.53 g cm^?3 for compound5 forZ=4. In the solid state, differences regarding the planarity of the aromatic ring in the three substrates were found. Rotation of theortho-nitro groups and of the amino group out of the aromatic plane was observed both in the solid state and in the solution. Greater coplanarity of the two rings was found in3 than in4 and5.     

The molecular structures of three germacrolides related to parthenolide

The germacrolide-class sesquiterpene lactone, 1,10-epoxyparthenolide, C₁₅H₂₀O₄,1, crystallizes with two independent molecules in monoclinic space groupP2₁ witha=10.6845(5),b=9.0763(4),c=15.4326(7) Å, β=105.887(4)°,V=1439.4(3) ų,Z=4.R=0.037 for 2425 observed data. Its 11βH, 13-dihydro-derivative 1,10-epoxydihydroparthenolide, C₁₅H₂₂O₄,2, crystallizes in orthorhombic space groupP2₁2₁2₁ witha=7.6414(10),b=12.559(2),c=14.6821(14) Å,V=1409.0(3) ų Z=4.R=0.031 for 1555 observed data. The corresponding unexposidized compound, 11βH,13-dihydrocostunolide, C₁₅H₂₂O₂,3, crystallizes with three independent molecules in orthorhombic space groupP2₁2₁2₁ witha=7.3576(5),b=23.505(3),c=24.185(2) Å,V=4182(1) ų,Z=12.R=0.070 for 2767 observed data. In all, the 10-membered rings adopt approximate chair-chair conformations. In all, the double bonds or epoxidized double bonds are E, both methyl groups on the 10-ring are β, and the α-methylene-γ-lactone (or α-methyl-γ-lactone) istrans-fused at C6 and C7 with H6 β and H7 α. In the dihydro compounds, the H at C11 is β.     

The molecular structures of two furanoheliangolides

The heliangolide-class sesquiterpene lactone 8β-angeloyloxy-9α-acetoxycalyculatolide, C₂₂H₂₆O₈,1, crystallizes in orthorhombic space groupP2₁2₁2₁ witha=12.455(3),b=12.601(3),c=14.023(5) Å,V=2200(1)Å,³ Z=4.R=0.059 for 1735 observed data. The 11,13-dihydro-11α, 13-epoxyatripliciolide-8β-angelate, C₂₀H₂₂O₇. 1/2 H₂O,2, crystallizes as the hemihydrate with two molecules in the asymmetric unit in triclinic space groupP1 witha=9.422(1),b=9.559(1),c=12.358(3) Å, α=101.62(2)°, β=91.30(2)°, γ=117.80(1)°,V=955.6(7)ų,Z=2.R=0.046 for 3607 observed data. In both, the 10-membered rings adopt approximate chair-boat conformations. Their conformations are typical for heliangolides. The methyl group C14 is α, while the C-15 has a β-orientation. The α-methylene-γ-lactone istrans-fused at C6 and C7 with H6 β and H7 α. In compound2, the epoxide at C11–C13 has an α orientation.     

Tetrahydrophthalic esters of prednisolone

The two biologically active isomers of prednisolone tetrahydrophthalate have been studied by X-ray diffraction methods. The compounds crystallize in the orthorhombic system in the space groupP2₁2₁2₁, with similar lattice parameters. The isomers differ both in configuration [(1′S),(6′R) isomerA and (1′R),(6′S) isomerB] and conformation of the thetetrahydrophthalic part of the molecules. Cell parameters of isomerA:a=9.595(2),b=14.465(2),c=18.988(3) Å andB:a=9.114(2),b=14.283(6),c=20.398(5) Å. The O(3) carbonyl oxygen atom interactsvia hydrogen bonds with three neighboring molecules accepting hydrogen bonds from two hydroxyl groups and one carboxylic group. Additional short intermolecular C?H…O type contacts occur in the structure of theB isomer, which has a somewhat larger unit cell and significantly higher melting point.     

Tirucallane-type triterpenoids: nmr and X-ray diffraction analyses of 24-epi-piscidinol A and piscidinol A

A new tirucallane-type triterpenoid named 24-epi-piscidinol A (1) has been isolated fromCastela texana (T. &; G.) Rose (Simaroubaceae) and determined to have the structure 23R,24R,25-trihydroxytirucall-7-en-3-one by X-ray crystallographic analysis. Crystals of 24-epi-piscidinol A are monoclinic, space groupC2,a=23.84 (3),b=7.012 (7),c=17.35 (2) Å, β=103.46 (2)^o. Another triterpenoid piscidinol A (2), crystallizes in the orthorhombic space groupP2₁2₁2₁ witha=10.659 (2),b=14.499 (3),c=17.922 (4) Å, β=90°. Two coumarino-lignans, cleomiscosin A and C, were also obtained in the course of this work. This is the first time of isolation of tirucallane-type triterpenoids and coumarino-lignans from the genusCastela.     

Crystal structure of nimbin

The crystal structure of nimbin has been determined. The crystals are orthorhombic, space groupP2₁2₁2₁ witha=6.790(2),b=14.875(4),c=27.160(8) Å andZ=4. The packing of the molecules in the lattice is due to C?H…O type of hydrogen bonds.     

The crystal and molecule structure of three 2,4,6-trinitrobenzene derivatives:α,α,α-trifluoro-2,4,6-trinitrotoluene (C7H2F3N3O6), 2,4,6-trinitrobenzamide (C7H4N4O7), 2,4,6-trinitrobenzoic acid (C7H3N3O8)

The crystal and molecular structures of three 2,4,6-trinitrobenzene derivatives have been determined. Forα,α,α-trifluoro-2,4,6-trinitrotoluene (1): monoclinic,P2₁/n,a=7.510(2),b=9.273(2),c=14.984(0) Å,β=99.02(2)°,V=1028.1(4)° ų,Z=4,D=1.816 g cm^?3,R(F)=0.051, andR(wF)=0.055. For 2,4,6-trinitrobenzamide (2): orthorhombic,Pbca,a=9.248(3),b=14.377(6),c=17.729(4) Å,V=1958(1) ų,Z=8,D=1.737 g cm^?3,R(F)=0.073, andR(wF)=0.077. For 2,4,6-trinitrobenzoic acid (3): orthorhombic,P2₁2₁2₁,a=6.553(1),b=11.405(2),c=12.796(2) Å,V=956.3(3) ų,Z=4,D=1.785 g cm^?3,R(F)=0.045, andR(wF)=0.046.1 crystallizes as discrete molecules,2 as weakly hydrogen-bonded dimers and3 as a chiral polymer of hydrogen-bonded helices. In1, the presence of the nonplanar CF₃ substituent causes a large twisting of theα-nitro groups out of the plane of the benzene ring, whereas the nearly planar C(O)NH₂ and C(O)OH substituents in2 and3 are perpendicular to the benzene plane and do not cause a significant rotation of theα-nitro groups.     

The structures of N-(t-butoxycarbonyl)-3-methylbenz[f]indole and N-benzenesulfonyl-4-bromo-3-methylbenz[f]indole

N-(t-butoxycarbonyl)-3-methylbenz[f]indole,1, C₁₈H₁₉NO₂, crystallizes in orthorhombic space groupPna2₁ witha=6.0338(2),b=24.839(4),c=10.2481(7) Å,V=1535.9(3) ų,Z=4. The structure was refined toR=0.051 for 2007 observed reflections. The benz[f]indole ring system is nearly planar, exhibiting mean deviation of 0.048 Å. The ester plane of thet-butoxycarbonyl substituent is nearly coplanar with the benz[f]indole ring system, forming a C?N?C=O torsion angle with magnitude 10.6(5)⁰.N-benzenesulfonyl-4-bromo-3-methyl-benz[f]indole,2, C₁₉H₁₄BrNO₂S crystallizes in triclinic space groupP?1 witha=8.1400(5),b=10.0587(8),c=10.8863(7) Å, α=89.927(7), β=110.495(5), γ=96.846(6)⁰,V=828.2(3) ų,Z=2. The structure was refined toR=0.050 for 2653 observed reflections. The benz[f]indole ring system is nearly planar, with mean deviation 0.016 Å, and forms a dihedral angle of 80.93(9)⁰ with the phenyl plane.     

Formation of copper(II) coordination polymers by a flexible double betaine: [{Cu(L)X2(H2O)} n ]·2nH2O [X=Cl,Br] and [{Cu(L)(H2O)4} n ](ClO4)2n ·2nH2O [L=−O2CCH (Me3N+)CH2CH2CH(Me3N+)CO 2 − ]

Three polymeric copper(II) complexes of a flexible double betaine, namely, [{Cu(L)Cl₂(H₂O)} _n ]·2 _n H₂O (1), [{Cu(L)Br₂(H₂O)} _n ]·2nH₂O (2), and [{Cu(L)(H₂O)₄} _n ](ClO₄)_2n ·2nH₂O (3) [L=?O₂CCH(Me₃N⁺)CH₂CH₂CH(Me₃N⁺CO₂], have been prepared and characterized by singlecrystal X-ray analysis. Isomorphous complexes (1) and (2) crystallize in space groupC2/c (No. 15) witha=17.725(3),b=5.958(2),c=19.077(3) Å, β=110.70(1)^o,V=1881.4(4) ų, Z=4 anda=18.268(4),b=5.948(3),c=19.166(5) Å, β=109.08(2)^o,V=1964.7(9) ų, Z=4, respectively. Complex (3) belongs to space groupPī (No. 2) witha=6.203(1),b=9.293(2),c=12.035(2) Å, α=86.56(2), β=87.33(3), γ=71.23(2)^o,V=655.4(2) ų and Z=1. The crystal structure of (1) and (2) features an infinite zigzag chain composed of an alternate arrangement of metal atoms and double betaines ligands, with each Cu(II) atom in a distorted CuX₂O₃ [X-Cl, Br] square-pyramidal geometry, and hydrogen bonding between adjacent chains leads to a layer structure concentrated the (200) family of planes. Complex (3) exhibits a layer structure corresponding to the (001) family of planes, in which neighboring chains constructed from the metal atoms and the double betaine ligands are cross-linked by hydrogen bonding between the aqua ligands. The Cu(II) atom is coordinated in a CuO₆ octahedral geometry with Jahn-Teller distortion.     

Crystal structures of thecis andtrans isomers of dithiahexahydro[3.3]metacyclophane

Structures of both thecis andtrans isomers of dithiahexahydro[3.3]metacyclophane, ?C₆H₄?CH₂SCH₂?C₆H₁₀?CH₂SCH₂?, have been determined, wherecis andtrans refer to the attachments to the cyclohexane ring. Thecis form crystallizes in the monoclinic space groupP2₁/c witha=8.4299(11)Å,b=21.772(2)Å,c=8.9724(13)Å, β=116.574(11)^o, andZ=4. Thetrans isomer packs into the monoclinic space groupP2₁ witha=8.159(16)Å,b=10.185(5)Å,c=9.558(2)Å, β=112.435(18)^o, andZ=2. The cyclohexane ring of thecis isomer is in the chair conformation, while the cyclohexane of thetrans isomer is found in a twisted boat conformation.     

Crystal structures of 1,1′-di(methylacetato)- and 1,1′-di(chloroethoxyethyl)-2,2′-biimidazole

1,1′-Di(methylacetato)-2,2′-biimidazole, C₁₂H₁₄N₄O₄, crystallizes from methanol in the space groupP2 ₁/c, wherea=9.535(2),b=13.385(2),c=5.1208(8) Å,V=652.2(2) ų, andZ=4.1,1′-Di(chloroethoxyethyl)-2,2′-biimidazole, C₁₄H₂₀Cl₂N₄O₂, crystallizes from cyclohexane in the space groupPbca, wherea=12.372(2),b=8.959(2),c=14.840(2) Å,V=1644.9(5) ų, andZ=8. The structures were refined toR=0.041 (1380 observed reflections) andR=0.043 (3243 observed reflections), respectively. Both molecules crystallize with coplanar rings and the substituents assume atrans configuration with a center of inversion between the bridging carbon atoms.     

Assignment of relative configurations and conformational analysis of α-phenylacyliron complexes (η5-C5H5)Fe(CO)(PPh3)(COCHRPh). X-ray structural determinations of two complexes (η5-C5H5)Fe(CO) (PPh3)(COCHPhR), R=CHOHCH3 and R=COH(CH3)2

Conformational analysis of the alkylation and aldol condensation products of phenylacetyliron complex (4), based on¹H-NMR chemical shifts and¹H-¹H vicinal coupling constants, permitted the assignment of relative configurations to all products obtained. Configurations and conformations of two aldol condensation products,12A and13F, were determined by X-ray structural analysis and were compared with the structures deduced from¹H-NMR data. The crystals of12A and13F are monoclinic, space group of12A isP2₁/_n with cell dimensions:a=10.937(2),b=17.278(5),c=16.412(3)Å, andβ=107.52(2)°; space group of13F isP2₁/c, with cell dimensions:a=11.576(4),b=21.180(2),c=11.854(4)Å, andβ=99.80(3)°. Both structures were solved by direct methods, and refined by a full-matrix, least-squares procedure giving for12A R=0.0599 and for13F R=0.0459.     

X-ray structural investigation of paramagnetic molecular compound of 2,5,9,12-tetramethyl-1,8-cis-1,4,8,11-tetraazacyclotetradeca-4,11-dienenickel(II) diperchlorate,trans-diaquo-2,5,9,12-eramehyl-1,8-trans-1,4,8,11-tetraazacyclotetradeca-4,11-dienenickel(II) diperchlorate,and water 2[cis-C14H28N4Ni](ClO4)2·[trans-C14H28N4Ni· 2H2O](ClO4)2·2H2O

The structure of molecular compoundI (2IA·IB·2H₂O), whereIA is a square-planar 2(e),5,9(a),12-tetramethyl-1,8-cis-1,4,8,11-tetraazacyclotetradeca-4,11-dienenickel(II) diperchlorate andIB is an octahedraltrans-diaquo-2(e),5,9(e),12-tetramethyl-1,8-trans-1,4,8,11-tetraazacyclotetradeca-4,11-dienenickel(II) diperchlorate has been investigated by X-ray diffractometric methods. Compound I crystallizes in an orthorhombic system, space groupPbca, Z=12,a=26.321(3),b=19.919(2),c=13.306(1) Å. The structure was solved by the heavy-atom method followed by a series of Fourier syntheses and refined by full-matrix least-squares to giveR=0.060 (for 3757 independent reflections). Conformations were ascribed to chelate rings and to the macrocyclic rings ofIA andIB, and the results were compared with those of some known 1,4,8,11-tetraazacyclotetradeca-4,11-dienenickel(II) complexes. The relative configurations were found 1RS,2SR,8RS,9RS (a racemate) forIA and 1R,2S,8S,9R (ameso-form) forIB. They differ each from the other by configuration on one nitrogen centre (N-epimeric compounds).     

The structure of the π-molecular complex between 1,4-dihydro-9,10-anthrahydroquinone and 1,4-dihydro-9,10-anthraquinone

The structure of the π-molecular complex (10) was assigned on the basis of the solid state¹³C-nmr spectrum. The solid state¹³C-nmr spectrum of quinhydrone (12) has also been determined. Accurate¹H and¹³C chemical shift assignments have been made for the compounds3,5,6,7,8, and10 on the basis of HMQC and HMBC spectral data. The π-molecular complex10 crystallizes in the space groupP2₁ In with cell parameters:a=4.052 (1) Å,b=6.477 (1) Å,c=19.093 (2) Å, β=90.17 (1)^o,z=1,D _c =1.400 g mc^?32. Crystal and molecular structure of the title compound, C₂₈H₂₂O₄, has been determined by an X-ray analysis of10 by direct methods from diffractometer data and refined by full-matrix least-squares     

Conformational analysis of 13-hydroxy-α-isolupanine epimers

13α-Hydroxy-α-isolupanine (I) and 13β-hydroxy-α-isolupanine (II) crystallize in the space groupP2₁2₁2₁ witha=13.123(2),b=13.221(3),c=8.224(1) Å,Z=4 anda=9.745(2),b=11.383(1),c=12.710(2) Å,Z=4, respectively. Structural differences between the epimeric molecules are concentrated around ringA. In (I) ringA has a half-chair conformation, and in (II) it is a distorted sofa. TheA/B ring junction configuration isquasi-trans in the case of (I) andquasi-cis in (II). The above differences can be explained by the different intermolecular interactions observed in these two structures.     

Imidazolium chloride organophosphate antidotes

The structures of four imidazolium oxime derivatives were solved by direct methods. These compounds have been shown to be effective in the treatmen of organophosphate poisoning. Despite substantial differences in the nature of the substituent on N1, all four compounds have similar shapes when viewed down the plane of the imidazole ring. The potency of these compounds in the treatment of organophosphate poisoning correlates well with the distance between the imidazole ring and the oxygen moiety on the side chain. 2-(hydroxyimino)methyl-3-methyl-1-[1-(3-methyl-sulfonylpropyloxy) methyl]imidazolium chooride (1) crystallizes in the triclinic space groupPī (Z=2). The unit cell parametersa, b, c (Å) and α, β, and γ (^o) were: 8.506(2), 8.787(4), 10.070(4), 73.68(3), 81.37(3), 85.39(3). 2-(hydroxyimino)-methyl-3-methyl-1-(2′-N-phenylsulfonylamino-1′-ethyl) imidazolium chloride (2) crystallizes in the monoclinic space groupP2 ₁ la(Z=4). The unit cell parametersa, b, c (Å) and β (^o) were: 12.690(2), 6.317(4), 20.193(4), 91.47(2). 1-(2′-ethyl-2′-trifluoromethanesulfonyl-aminoethyl)-2-(hydroxyimino) methyl-3-methylimidazolium chloride (3) crystallizes in the triclinic space groupPī (Z=2). The unit cell parametersa, b, c (Å) and α, β, and γ (^o) were: 6.635(1), 11.333(2), 12.274(3), 115.05(3), 98.46(3), 90.11(3). 2-(hydroxyimino)-methyl-3-methyl-1-[2-(2-methyl-3-nitrobutyloxy) methyl]-imidazolium chloride (4) crystallizes in the orthorhombic space groupP2₁2₁2₁ (Z=4). The unit cell parametersa, b, andc (Å) were: 10.034(1), 11.401(2), 13.352(2).     

CO replacement in Ru3(CO)12 by 2,3-bis(diphenylphosphino)maleic anhydride (bma). X-ray structures of Ru3(CO)10(bma)·H2O and

Thermolysis of Ru₃(CO)₁₂ with 2,3-bis(diphenylphosphino)maleic anhydride (bma) in toluene solution gives the new compounds Ru₃(CO)₁₀(bma) (2), Ru₂(CO)₆(bma) (3), and (4). All compounds have been isolated and characterized in solution by IR and³¹P NMR spectroscopy. The solid-state structures of2, as the monohydrate, and4 were established by X-ray crystallography. Ru₃(CO)₁₀(bma)·H₂O crystallizes in the monoclinic space groupC2/c,a=12.741(2) Å,b=19.548(2) Å,c=32.973(4) Å, β=96.847(9)°,V=8154(2) ų,Z=8,d _calc=1.740 g cm^?3;R=0.046,R _w =0.051 for 2541 observed reflections withl>3σ(l). The bma ligand in2 is bound to the triruthenium frame in a bridging fashion, with equatorially disposed PPh₂ groups. The X-ray structure of2 reveals an extreme twisting of the maleic anhydride ring away from the plane defined by the plane of the three ruthenium atoms, along with a significant lengthening of the maleic anhydride C=C π bond. crystallizes in the monoclinic space groupP2₁/c,a=9.3113(5) Å,b=18.164(1) Å,c=20.097(1) Å, β-102.021(4)°,V=3324.5(3) ų,Z=4,d _calc=1.671 g cm^?3;R=0.024,R _w =0.030 for 3499 observed reflections withl>3σ(l). The presence of the μ₂ moiety and P?C (maleic anhydride) bond cleavage attendant in the formation of4 are confirmed by X-ray analysis. The relationship of the compounds3 and4 to the dimeric compounds Ru₂(CO)₆(bpcd) and [where bpcd=4,5-bis(diphenylphosphino)-4-cyclopenten-1,3-dione] is discussed. Independent studies dealing with Ru₃(CO)₁₀(bma) (bridging isomer) have shown that cluster2 is stable in toluene solution at elevated temperature and does not afford compounds3 and4, suggesting the intermediacy of the putative chelating isomer of Ru₃(CO)₁₀(bma) (1) as the source of3 and4.