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Two cis-dioxomolybdenum(VI) complexes [MoO2L] (L: L 1, 2 and L: L 2, 3) in a phenol-based sterically encumbered N2O2 ligand environment have been synthesized, and their crystallographic characterizations are reported. The orange crystals of 2 are monoclinic, space group P21/a with unit cell dimensions as a=16.2407(17) A, b=7.2857(8) A, c=18.400(2) A, β=98.002(9)°, Z=4, and d cal=1.486 g cm−3. The light orange crystals of 3, however, are orthorhombic, space group, Pbcn, with unit cell dimensions a=8.3110(12) A, b=12.637(3) A, c=34.673(5) A, Z=4, and d cal=1.187 g cm−3. The structures were refined by a full-matrix least-squares procedure on F 2 to a final R=0.046 (0.055 for 3) using 4944 (3677) all independent data. In both the cases, the Mo atom exists in a distorted octahedral geometry defined by a N2O4 donor set, which features a cis-Mo(–O)2 and a trans-Mo(OPh)2 arrangement. Compound 2 undergoes a quasireversible one-electron reduction at −1.3 V vs Ag/AgCl reference due to MoVIO2/MoVO2 electron transfer and thus providing a rare example of steric solution to the comproportionation–dimerization problem encountered frequently in the development of valid biomimetic models for the active sites of oxomolybdenum enzymes.

Methods for the synthesis of cyclic monomers that have both metal–metal bonds and carbon–carbon double bonds are reported. Ring opening metathesis polymerization (ROMP) of these monomers would yield polymers that are photochemically degradable. The first method investigated involved substitution of Cp2Fe2(CO)4 by the bidentate phosphine ligand DPPEN (Ph2P $${-}$$ CH=CH–PPh2). Cp2Fe2(CO)2( $$\upmu$$ -DPPEN) was synthesized and the X-ray crystal structure is reported but the molecule could not be polymerized by a ROMP method using Grubbs’s catalyst. The inability of this monomer to polymerize (or copolymerize with cyclooctatetraene) was attributed to the bulky phenyl rings being in close proximity to the C=C in the DPPEN ligand, which prevents coordination of the monomer to the catalyst. To decrease the steric interactions, the DPPBN ligand was synthesized (DPPBN=Ph $$_{2}{-}$$ CH $$_{2}{-}$$ CH=CH $${-}$$ CH $$_{2}{-}$$ PPh2). However, the reaction of DPPBN with Cp2Fe2(CO)4 yielded the product Cp2Fe2(CO)2( $$\upmu$$ -1,2,4-triphos), where the 1,2,4-triphos ligand is a tridentate ligand formed by the formal additional of Ph2PH to DPPBN (1,2,4-triphos=Ph $$_{2}{-}$$ CH $$_{2}{-}$$ CH(PPh2) $${-}$$ CH $$_{2}{-}$$ CH $$_{2}{-}$$ PPh2). An X-ray structure of the Cp2Fe2(CO)2( $$\upmu$$ -1,2,4-triphos) complex revealed that the 1,2,4-triphos ligand chelates exclusively through the two phosphorus atoms that are bridged by two carbon atoms. It is suggested that this structural feature may simply reflect the increased stability of the 6-membered ring over the 7- and 8-membered rings. The reactions of the Cp2Mo2(CO)6 and Cp2Mo2(CO)4 dimers with DPPBN were investigated next. Reactions of Cp2Mo2(CO)6 and Cp2Mo2(CO)4 with the DPPEN and DPPBN ligands resulted in the disproportionation of the dimers. The X-ray crystal structure of [CpMo(CO)2(DPPEN)][CpMo(CO)3] was determined and is reported. The CpMo(CO)(DPPEN)Cl complex was formed when these same reactions were carried out in the presence of CH2Cl2. The X-ray crystal structure of this molecule is also reported.

Novel liquid crystals based on fluorinated carbon chains and terminated with SF5 groups are presented for the first time. Attachment of an SF5 group separated from a benzylidine group by a fluorinated spacer leads to monotropic nematic and smectic phases, while an enantiotropic nematic phase is observed in mixtures. The phase sequence of these new compounds is comparable to hydrocarbon analogues of nO.m (n-alkoxy-m-alkylbenzylidine) series. Despite a long alkoxy chain, the nematic → smectic A transition is closer to second order, with ≈ 0.995 values that are even higher than for the nCB (n-alkylcyanobiphenyls) series. Single crystal and quantum computational studies suggest that electrostatic interactions play a major role in governing the value of MTCP. Molecular packing in the crystal structure exhibits monoclinic P21/a symmetry. A flexible synthetic strategy that allows the synthesis of another homologous series with a bend in the molecular structure is also presented. The bent core structure of 10O.2 ...

Our prediction that phase II of dipotassium hydrogen chromatoarsenate, K(2)[HCr(2)AsO(10)], is ferroelectric, based on the analysis of the atomic coordinates by Averbuch-Pouchot, DurifGuitel [Acta Cryst. (1978), B34, 3725-3727], led to an independent redetermination of the structure using two separate crystals. The resulting improved accuracy allows the inference that the H atom is located in the hydrogen bonds of length 2.555 (5) angstroms which form between the terminal O atoms of shared AsO(3)OH tetrahedra in adjacent HCr(2)AsO(10)(2-) ions. The largest atomic displacement of 0.586 angstroms between phase II and the predicted paraelectric phase I is by these two O atoms. The H atoms form helices of radius approximately 0.60 A about the 3(1) or 3(2) axes. Normal probability analysis reveals systematic error in seven or more of the earlier atomic coordinates.

The trans-palladium bis(σ-acetylide) complex (Et3P)2Pd(C30H12) (2) was synthesized from hexane 4 in 77% yield via a simple three-step process. The X-ray crystal structure of 2 shows a strained and warped annulenic core upon insertion of the organometallic fragment. UV–vis data of the molecule suggest limited electronic delocalization throughout the metallacycle.

The reaction of [Bi2W22O74(OH)2]12− with Cu2+ in hot aqueous solution in the presence of Na+ affords the polyoxometalate salt Na12[Cu3Bi2W18O66]⋅32H2O. Single-crystal X-ray analysis [monoclinic, space-group C2/m, a = 33.082(6) A, b = 19.615(5) A, c = 14.885(2) A, β = 90.632(12)°, Z = 4; R(F) = 0.065 for 6029 data with I>σ (I), wR(F2) = 0.135 for all 8793 independent reflections] shows that the anion [{Cu(H2O)}3{BiW9O33}2]12−, on a crystal mirror-plane, has noncrystallographic symmetry close to D3h. Two B-α-[BiIIIW9O33]9− units are linked by an equatorial belt of three Cu(H2O)2+ units. Three Na(H2O)2+ units are also attached in the equatorial plane. The bond geometry is square-pyramidal about each Cu atom and trigonal–prismatic about each Na.

Pyridinium gambogate, (C5H6N)+(C38H43O8)−, crystallizes in space group P2 12121 with cell parameters a = 9.536(3) A, b = 18.502(4) A, c = 22.223(4) A, Z = 4. The X-ray structural analysis [R(F) = 0.098 for 1714 data with I ≥ σ(I); wR(F 2) = 0.157 for all 3874 independent data] confirms the structure assigned to gambogic acid on the basis of NMR analysis and of the X-ray structure of isomorellin p-bromobenzenesulfonate. A hydrogen bond links the pyridinium nitrogen atom to a carboxylate oxygen atom. The gambogate ion has two distinct faces that differ in polarity. The hydrophobic face is dominated by the alkenyl chains attached to C(2) and C(17) and a segment of the polycyclic ring system. The hydrophilic face includes the carboxylate ion and several oxygen atoms.

Three tin compounds, Cs8Sn44, Cs8Ga8Sn38, and Cs8Zn4Sn42, representative of the type-I clathrate hydrate crystal structure are structurally characterized by temperature-dependent neutron powder diffraction, 87 K Sn-119 Mossbauer spectroscopy, and room-temperature single-crystal X-ray diffraction. These compounds form in cubic space group Pm (3) over bar n with alkalimetal atoms residing in the polyhedral cavities formed by the tetrahedrally bonded network of Sn atoms. Of particular interest are the atomic displacement parameters (ADPs) exhibited by the alkali-metal atom inside the polyhedral "cages" formed by the framework Sn atoms. The "guest" Cs atoms inside the larger tetrakaidecahedra show a relatively large room-temperature ADP for Cs8Ga8Sn38 and Cs8Zn4Sn42; however, in the defect Cs8Sn44 compound this is not the case. This is due to two Sn vacancies in Cs8Sn44 which affect the local symmetry and Sn-Sn bonding. Temperature-dependent ADPs for the defect Cs8Sn44 compound are compared to those for Cs8Zn8Sn42. These data help elucidate the cause of the different lattice thermal conductivities of these two compounds.

Single crystal X-ray structures of two polymorphs of 1-(1,6-dithiahexyl)anthracene-9,10-dione are reported. These structures reveal a conformational difference in the orientation of the hydrocarbon chain between the two polymorphs. This small change in the molecular conformation dramatically influences the packing of the anthraquinone ring systems; in one case the anthraquinone rings exist as discrete pairs, and in the other they exist in infinite lamellar stacks. Differences in the packing results in different thermal behavior and spectroscopic properties of the two polymorphs. The yellow, triclinic structure is lower melting, whereas the orange, monoclinic structure is higher melting. Uses of this compound as a model for de novo computation of crystal structures and tuning of crystal packing through side chain variation are discussed.

Site specifically functionalized dehydrobenzo[18]annulenes (DBAs) with previously inaccessible topologies (C2v and Cs symmetry) were prepared by utilizing an in situ protiodesilylation/alkynylation reaction. By application of a stepwise synthetic route, donor and/or acceptor functional groups were introduced to the annulenic core in a designed manner. The electronic absorption spectra of the DBAs revealed moderate to dramatic changes in the electronic structure of the [18]annulene core when subtle changes were made in substitution patterns and/or functional groups. Macrocycles containing C2v symmetry exhibited progressive and predictable bathochromic shifts ranging from 20 to 80 nm along with increasing intramolecular excited state change transfer (CT) behavior. Asymmetric (Cs) molecules presented more interesting absorption behavior, such as accentuation of bands in the visible region. X-ray crystal structures of [18]DBAs 20, 22, 23, and 25 showed normal bond lengths and bond angles within the planar ann...

A new crystalline strontium-copper ethylene glycol complex has been isolated and structurally characterized by single-crystal X-ray diffraction. The solution-phase complex has also been investigated as a possible molecular precursor for use in sol-gel synthesis of SrCuO2. [Sr(C2H6O2)5][Cu(C2H4O2)2]·C2H6O2 has been isolated by crystallization from an ethylene glycol/methylethylketone solution of the strontium-copper salt. Crystallographic data are as follows: orthorhombic, space group Pna21, a = 18.494(3), b = 9.3076(8), c = 16.615(3)A, V = 2860(2) A 3 , Z = 4, R = 0.044 . In this molecule, copper is coordinated by two bidentate ethylene glycolate ligands in roughly a square planar geometry. Strontium is coordinated by three bidentate ethylene glycol molecules and two monodentate ethylene glycol molecules; the eight-fold coordination resembles a highly-distorted square antiprism. An additional ethylene glycol of crystallization is present which does not directly coordinate the strontium ion. Copper and strontium ion complexes are held together by hydrogen bonding. The solution-phase bimetallic complex is hydrolytically unstable, giving rise to a ‘muddy’ brown precipitate upon exposure to water. The apparent decomposition is in direct contrast with hydrolysis of similar barium-copper complexes which gives rise to stable blue gels. This decomposition made the strontium-copper diol complex unsuitable for use in alkoxide sol-gel synthesis of strontium-copper oxides.

The orthorhombic crystal structures of [NEt3H]5[XCoIIW11O39]·3H2O for X = P and As have been determined with data collected at room temperature, and for X = P at –100 °C, using Mo-Kα radiation. For the latter the space group is Pna21, a= 21.670(11), b= 14.805(4), c= 20.393(5)A and Z= 4. The structure consists of chains of α-Keggin-type molecules joined by W–O–links aligned in the a-axis direction. The Co/W occupancy at the link is disordered, with 61% Co on one side and 39% on the other. Further probable disorder, by lamellar merohedral twinning on (001) and by misorientation of the triethylammonium ions, has obscured the ethyl groups and the water molecules. In polarized light the crystals are deep wine-red normal to the chains (in the b direction), but nearly colourless in the a and c directions. The structure of the arsenate is similar to that of the phosphate.

Titanacyclobutenes react with 2-methyl-2-nitrosopropane and nitrosoarenes to afford products of insertion into the TiCH 2 bond of the metallacycle. Structural confirmation was obtained through single crystal X-ray diffraction analysis of the insertion product of the diphenyltitanacyclobutene and 2-methyl-2-nitrosopropane: C 29 H 31 NOTi, monoclinic, P 2 1 / n , a =7.984(2), b =20.383(8), c =15.005(4) A, β=100.55(2)°, V =2400(2) A 3 , Z =4. The insertion products display dynamic NMR behavior consistent with pyramidal inversion at nitrogen, with activation barriers of c . 14 kcal mol −1 . Hydrolysis of the insertion products affords the corresponding hydroxylamines, while treatment of them or of the titanacyclobutenes with excess nitrosoarene results in metallacycle degradation and formation of azoxyarene.

Interdiffusion of solutions of zinc chloride in diethyl ether and 18-crown-6 in 1,2-dichloroethane affords a crystalline complex, [18-crown-6-ZnCl-H 2 O] + 2 °Zn 2 Cl 6 ] 2- . Single-crystal X-ray diffraction analysis (C 24 H 52 Cl 8 O 14 Zn 4 ; triclinic; P1; a=7.659(3) A, b=11.696(6) A, c=13.190(4) A, α=105.23(3) o , β=106.52(3) o , γ=91.07(3) o ; Z=1) reveals the ZnCl(H 2 O) + cation to be coordinated to three crown ether oxygens, providing a five-coordinate distorted trigonal bipyramidal zinc

Crystals of Na16[Zn4(H2O)2(α-P2W15O56)2]·∼50H2O are triclinic, $$P\bar 1$$ , witha+14.670(5),b+14.661(5),c+19.817(3)A, α=84.95(3), β=81.51(3), γ=65.73(3)o. Least-squares refinement converged atR+0.053 for 5906 independent data withl>3σ(I). The centrosymmetric anion consists of two α-P2W15O 56 12− ligands attached to a planar group of four Zn2+, two of which also carry water molecules. The distortions in the ZnO6 octahedra and in the W15 framework of the ligands are smaller than the corresponding distortions in the otherwise similar [Cu4(H2O)2(P2W15O56)2]16− anion.

The compound bis(η5-methylcyclopentadienyl)-bis(4-methylbenzenesulfonato-O)-molybdenum (IV) crystallizes in space-group P21/c, a = 8.2956(5), b = 26.896(3), c = 11.4196(11) A, β = 96.101(7)°, Z = 4. The sulfonate ligands are monodentate and the molybdenum atom has pseudotetrahedral coordination geometry, with angles O–Mo–O 72.0(1)° and Cp–Mo–Cp 134.9(1)° (Cp = ring centroid).

Single crystals of Cd(H 2 O) 2 Ni(CN) 4 · 4H 2 O have been synthesized and characterized by single-crystal X-ray diffraction. The crystallographic data are as follows: orthorhombic space group Pnma , a = 12.393(2) A, b = 14.278(5) A, c = 7.427(1) A, Z = 4; R = 0.033, wR = 0.042 for 949 reflections. This material is similar to the Hofmann-type clathrates; it is structurally composed of two-dimensional sheets of alternating square planar and octahedrally coordinated metal atoms bridged by cyanide ligands. However, unlike Hofmann-type clathrates for which structures have been reported, this material does not contain ammonia, amines, or a clathrated aromatic molecule between the metal tetracyanonickelate sheets. Instead, the interlayer regions are filled by a distorted hexagonal hydrogen-bonded net of water molecules.

The previously unknown polyoxometalate A-[beta]-Si[sub 2]W[sub 18]Ti[sub 6]O[sub 77][sup 14[minus]] has been prepared by the reaction of A-[beta]-HSiW[sub 9]O[sub 34][sup 9[minus]] with Ti(O)(C[sub 2]O[sub 4])[sub 2][sup 2[minus]] or Ti(O)SO[sub 4] under controlled pH conditions; yield optimization experiments are also reported. Isolation of this new Ti[sup IV]-substituted polyoxometalate was accomplished both as its water-soluble K[sup +] salt and as its organic-solvent-soluble Bu[sub 4]N[sup +] salt. The unambiguous characterization of A-[beta]-Si[sub 2]W[sub 18]Ti[sub 6]O[sub 77][sup 14[minus]] was accomplished by means of elemental analysis, IR and [sup 183]W NMR spectroscopy, and a single-crystal X-ray structural analysis of the Bu[sub 4]N[sup +]/H[sup +] salt, (Bu[sub 4]N)[sub 7]H[sub 7]Si[sub 2]W[sub 18]Ti[sub 6]O[sub 77] (Pbcm; a = 19.958(11), b = 36.880(8), c = 28.936(5) [angstrom]; Z = 4; R = 0.072 for 4614 observed independent reflections). The X-ray diffraction structural analysis reveals that the correct structural formulation is A-[beta]-(SiW[sub 9]O[sub 37])[sub 2](Ti-O-Ti)[sub 3][sup 14[minus]], a condensed aggregate of two hypothetical [open quotes]A-[beta]-SiW[sub 9](TiOH)[sub 3]O[sub 37][sup 7[minus]][close quotes] Keggin units that have lost three H[sub 2]O by forming three Ti-O-Ti bridges. The present synthesis and characterization, plus recent results from the literature, reveal that a new subclass of polyoxoanions of general formula X[sub 2]M[sub 18]M[prime][sub 6]O[sub 77][supmore » n[minus]] can be prepared for M[prime] in at least three different oxidation states, M[prime](III), M[prime](IV), and M[prime](V).« less

The synthesis and unequivocal characterization by X-ray crystallography of a Ru-containing polyoxoanion bimetallic inorganic-porphyrin analog is reported, [O[l brace]Ru[sup IV]Cl([alpha][sub 2]-P[sub 2]W[sub 17]O[sub 61])[r brace][sub 2]][sup 16[minus]]. The structural results reveal a new polyoxoanion structural type, a Ru-O-Ru oxo-bridged-dimer anion that is structurally analogous to bimetallic metalloporphyrins containing a [mu]-oxo M-O-M bridge. Such new types of polyanions are of current interest as oxidation-resistant oxidation catalysts and for their possible multielectron redox reactivity. 28 refs., 2 figs., 2 tabs.

The Mn-Mn bonds in the two independent molecules of the unsolvated title compound, [Mn(2)(C(25)H(22)P(2))(CO)(8)], (I), are 2.9714 (7) and 2.9746 (7) A. This bond is distinctly shortened in the toluene hemisolvate, [Mn(2)(C(25)H(22)P(2))(CO)(8)] x 0.5C(7)H(8), (II), to 2.9338 (14) A and this shortening is accompanied by an increase in magnitude of the P-Mn-Mn-P torsion angle [26.93 (3) and 28.44 (3) degrees in (I), and 33.25 (7) degrees in (II)], while the P...P 'bite' is much less affected [3.092 (2) and 3.099 (2) A in (I), and 3.091 (3) A in (II)]. The toluene solvate molecule in (II) lies on a twofold axis.

Crystallization of 1,4,7,10,13,16-hexaoxacyclooctadecane (18-crown-6) from CHCl 3 /CH 2 Cl 2 solution in the presence of dipotassium tartrate affords a nine-coordinate potassium complex incorporating chloride rather than tartrate as the counteranion. This complex, [(18-crown-6)K(H 2 O) 3 ](H 3 O)(H 2 O)Cl 2 , displays an unusual asymmetrical conformation of the crown ether ring. The structure of the complex is discussed and compared with other reported 18-crown-6 complexes of potassium, in which the 18-crown-6 moiety always adopts a much more symmetrical conformation

The synthesis and structural characterization of 1,3,4-triphenyl-1,2-dihydrophosphete and its complexes with mercuric chloride and tungsten pentacarbonyl are reported. Changes in bond lengths and angles upon metal coordination are consistent with an increased bonding contribution from the phosphorus s orbital. This rehybridization is supported by {sup 1}H, {sup 13}C, and {sup 31}P NMR spectral studies. Metal coordination does not lead to any significant skewing of the geometry of the phosphacyclobutene ring toward the corresponding ring-opened 1-phosphabutadiene form, and in fact may have the reverse effect.

Cristallisation dans P1 avec a=13,341, b=15,890, c=21,395 A, α=87,85, β=77,18, γ=71,87 o , Z=2; affinement jusqu'a R=0,062. L'anion a la structure bien connue de α-(P 2 W 18 O 62 ) 6− avec trois atomes Nb a la place des atomes W dans une des deux capsules W 3 O 13 , comprenant trois octaedres contigus WO 6

The title complex molecule, [Mo2(C 10 H 17 OSi) 2 (CO) 6 ], lies on a crystallographic inversion center. Each Mo atom exhibits 'four-legged piano-stool' bond geometry, with the other Mo atom at a basal position [Mo-Mo 3.219(1) A].

The title compound, [Co(C9H12N)(C4H7N2O2)2(C5H5N)], has the expected structure with the C-bonded heterocyclic ligand trans to pyridine. The Co—C bond lengths in the two independent molecules [2.032 (5) and 2.009 (6) A] are near the lower end of the range found for related compounds and do not account for the observed thermal instability.

Dimerization of the molecule of the title compound, [Co(C 36 H 54 N 2 O 2 )], an efficient dioxygen carrier, is prevented by the methyl and tert-butyl substituents. The square-planar complex is bisected by a crystallographic mirror plane, with disorder of the -CMe 2 -CMe 2 -region. Molecular dimensions [Co-O 1.846(2) and Co-N 1.850(2)A] are very similar to those of the related 3-tert-butylsalicylidenato complex.

Crystals of (C5H4COOMe)Mo(CO)2I3 are monoclinic, space-group P21/c, with a = 9.402(2), b = 10.675(3), c = 15.314(2) A, β = 106.79(1)°, and Z = 4. The coordination geometry is distorted octahedral with the ring centroid at one vertex and the iodide ligands defining a face.

This report describes an investigation into the coordination chemistry of trivalent lanthanides in solution and the solid state with acyclic and preorganized bicyclic malonamide ligands. Two experimental investigations were performed: solution binding affinities were determined through single-phase spectrophotometric titrations and the extent of conformational change upon binding was investigated with single-crystal X-ray crystallography. Both experimental methods compare the bicyclic malonamide (BMA), which is designed to be preorganized for binding trivalent lanthanides, to an analogous acyclic malonamide. Results from the spectrophotometric titrations indicate that BMA exhibits a 10-100x increase in binding affinity to Ln(III) over acyclic malonamide. In addition, BMA forms compounds with high ligand-metal ratios, even when competing with water and nitrate ligands for binding sites. The crystal structures exhibit no significant differences in the nature of the binding between Ln(III) and the BMA or acyclic malonamide. These results support the conclusion that rational ligand design can lead to compounds that enhance the binding affinities within a ligand class.

The title compound, Mo(4-CH3C5H4N)3(CO)3, is monoclinic, P21/c, with cell dimensionsa=10.385(1),b=13.572(2),c=15.522(2) A, β=105.08(1)°,Z=4. The complex isfac-octahedral with approximate three-fold symmetry. The Mo−C bond lengths are 1.901–1.904(7) A, distinctly shorter than in the parent Mo(CO)6, and the Mo−N bond lengths are 2.297–2.331(5) A.

The crystal structure of FSO2CFHCOOH has been determined by a single-crystal X-ray study. The crystals are monoclinic, of space group P21/c, and have the following cell parameters: a = 5.0164(6) A, b = 9.658(2) A, c = 11.061(2) A, β = 90.54(1)°, Z = 4. The carboxyl groups of the molecules form the usual hydrogen-bonded, centrosymmetric dimers, but each molecule also interacts with three other neighboring molecules by hydrogen bonds from the methine hydrogen to two sulfonyl oxygens and to a carbonyl oxygen, making a four-center system. The extensive network of hydrogen bonding in this material appears to be responsible for its existence as a solid. This material has also been characterized by 1H, 13C, and 19F NMR, IR, and mass spectroscopy.

Crystals of phase II K2Cr2O7, potassium dichromate, space group P\overline 1, grown from aqueous solution undergo a first-order transition to phase I, space group reportedly P21/n, at a phase-transition temperature, T PT, of 544 (2) K on first heating; the corresponding transition on cooling is at 502 (2) K. The endotherm on subsequent heatings occurs reproducibly at T PT = 531 (2) K. Mass loss between ca 531 and 544 K, identified as included water, is rapid and continues more slowly to higher temperatures for a total loss of ca 0.20%. The higher T PT on first heating is associated with the increasing pressure of superheated water occupying inclusion defects. The latent diagonal glide plane in phase II allows the structure of phase I to be inferred. The triclinic structure at 296 K has been independently redetermined. Normal probability analysis shows high consistency between the resulting and previous atomic coordinates, but with uncertainties reduced by a factor of ca 2. The earlier uncertainties are systematically underestimated by a comparable factor. The structure of phase IIb, space group A2/a on transposing axes, was determined at ca 300 K by Krivovichev et al. [Acta Cryst. (2000), C56, 629–630]. The first-order transition between phases I and II arises from the ca 60° relative rotation of terminal O atoms in each tetrahedron as the n glide plane is gained or lost. A transition between phases IIb and I, also of first order, is likely but not between phases II and IIb. An intermediate phase may exist between phases IIb and I.

Crystals of [Co(C5H4COOMe)2](PF6) are triclinic, spacegroup $$P\bar 1$$ witha=6.854(3),b=7.367(4),c=9.430(4) A, α=69.12(3), β=86.56(4), γ=67.20(4)°,Z=1. The cation and anion both lie on crystal inversion centers. The Co−C bond lengths are in the range 2.030–2.041(3) A. The COOMe groups are twisted 5.4° from the cyclopentadienyl ring planes. Refinement with 1574 data [I>3σ(I)] converged atR 0.041.

Treatment of nitrile 1 with an equimolar amount of DIBAL produces the alane complex [(1,2,3-(t-Bu)3-cyclo-C3)CHNAl(i-Bu)2]2 (3), which reacts sluggishly with protic nucleophiles. The X-ray crystal structure of 3 shows unusual geometric distortions in the Al2N2 core and about the imine carbon, as well as in the cyclopropene ring, all of which are attributed to the extreme steric bulk of the hydrocarbon ligands.

C18H15F2P, M(r) = 300.29, orthorhombic, Pbcn, a = 6.105 (2), b = 16.634 (3), c = 14.356 (3) A, V = 1458 (1) A3, Z = 4, Dx = 1.368 Mg m-3, lambda(Mo K alpha) = 0.71069 A, mu = 0.194 mm-1, F(000) = 624, T = 294 K, R = 0.045 for 729 observed independent reflections. Difluorotriphenylphosphorane [(C6H5)3PF2] displays a trigonal bipyramidal geometry about the P atom, with the two F atoms occupying axial positions. The three phenyl groups in the equatorial positions are not 'geared' in a regular propeller arrangement; one of the three rings is twisted in the opposite direction to that of the other two.

In the title compound, C2H10N22+·2C3H3O4−·H2O, the hydrogen malonate anion has an intramolecular O—H⋯O hydrogen bond of 2.430 (2) A. The water mol­ecule lies on a twofold axis and connects the anions into pairs through hydrogen bonds of 2.734 (1) A. The ethyl­enedi­ammonium cation lies across an inversion centre. Each of the ammonium protons is involved in hydrogen bonding to an anion or a water mol­ecule [N⋯O 2.815 (2)–2.875 (2) A].

The title compound can be formulated as [Cr(H(2)O)(6)][Na(2)(H(2)O)(10)][IMo(6)O(24)].8H(2)O. The anion has the I atom on an inversion centre and has close to $\overline 3$m symmetry, with I-O bond lengths in the range 1.881-1.890 (2) A and Mo-O bond lengths in the ranges 1.697 (3)-1.714 (3), 1.915 (2)-1.948 (2) and 2.317 (2)-2.357 (2) A.

N-(2-Iodophenyl)-N'-(tricyclo[3.3.1.1(3,7)]-decan-1-yl) guanid inium chloride, C17H23ClIN3, Mr = 431.75, monoclinic, P2(1)/c, a = 11.696 (5), b = 20.120 (4), c = 7.754 (2) A, beta = 95.26 (3) degrees, V = 1817 (1) A3, Z = 4, Dx = 1.578 Mg m-3, lambda (Mo K alpha) = 0.71069 A, mu = 1.89 mm-1, F(000) = 864, T = 295 K, R = 0.071 for 1169 observed [I greater than or equal to 3 sigma(I)] reflections. Both the phenyl and the adamantyl groups lie syn to the unsubstituted nitrogen of the guanidinium ion. The plane of the phenyl ring is nearly perpendicular to that of the guanidinium group.

C 20 H 14 O 10 W 2 cristallise dans P2 1 /n avec a=9.825, b=12.101, c=9.980A, β=110.14°, Z=2; affinement jusqu'a R=0.034. La molecule est situee sur un centre d'inversion cristallographique, avec un arrangement anti des cyclopentadienyl. La longueur de la liaison W-W est de 3.216A. L'angle diedre entre les plans moyens du cyclopentadienyl et du groupement C-C(O)-O-C est de 7.1°.

Better data have enabled eight Na+ cations per [Ce(W5O18)2]8− anion to be identified, in contrast to the six found earlier [Iball et al. (1974). J. Chem. Soc. Dalton Trans. pp. 2021–2024]. The two W5O186− ligands, related by a crystallographic twofold axis through Ce, are therefore unprotonated.

In the title compound, C2H10N22+.2C4H3O4−, ethylene diammonium cations are centred on inversion centres and the monhydrogenmaleate anions are in general positions. The components are assembled into double layers by hydrogen bonding. The unique NH3+ group connects the planar rings of the intramolecularly hydrogen-bonded anions into chains and cross-links the chains into centrosymmetric 18-membered rings, with intra­molecular O⋯O 2.452 (2) A and O⋯N in the range 2.816 (2)–2.852 (2) A.