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The ethylene dimerization performance of a range of bis(imido)tungsten pre-catalysts, after activation with aluminum co-catalysts, has been assessed. The best performing system achieved an activity of 409,410 (mol C2H4)(mol W)–1h–1 [79.6 wt% 1-butene] with a 1-butene selectivity of 82.4 wt% [290,770 (mol C2H4)(mol W)–1h–1 activity]. In addition to selected previously reported variants, the symmetrical bis(imido)tungsten(VI) complexes [WCl2(NPh)2(tmeda)] (3) and [WCl2(NR)2(dme)] [R = 2,4,6-trifluorophenyl, 7; 2,4,6-triphenylphenyl, 8; 2,4,6-tris(trifluoromethyl)phenyl, 9], were prepared. A series of unsymmetrical bis(imido)tungsten(VI) complexes [WCl2(NDipp)(NR)(dme)] (R = iPr, 11; tBu, 12; 2,4,6-trimethylphenyl, 13; 2,4,6-trichlorophenyl, 14; 2,4,6-trifluorophenyl, 15; 2,6-dinitrophenyl, 16; 2,4,6-triphenylphenyl, 17) were also synthesized using an improved version of a previous preparative route that eases purification. The molecular structures of complexes 5-13 and 15-17 were determined by X-ray crystallographic analysis. Catalysis employing complexes 1-17 unveils a complicated relationship between steric and electronic factors that affects activity and catalyst lifetime, however selectivity is dominated by electronic considerations. Higher reaction temperatures were shown to favor 1-butene selectivity and higher activity, whilst replacement of EtAlCl2 with MeAlCl2 as co-initiator was found to be detrimental. Tungsten(IV) species were demonstrated to be unlikely as the active species during catalysis. Studies of catalysis runs undertaken to varying productivities found that during the nascent phase of reaction a notably lower activity is observed, whilst the selectivity favors C8+ formation during this period, most likely due to activation processes still occurring. The rate of formation of 1-butene was shown to increase with productivity, as a result of the greater solubility of ethylene in the 1-butene generated compared to the chlorobenzene solvent. The formation of C6 by-products was shown to be independent of 1-butene concentrations, consistent with a mechanism whereby 1-butene is only incorporated into secondary products when it reacts prior to dissociation from the tungsten center.

Polymorphism in racemic pharmaceutical compounds is relatively unexplored. However, this phenomenon may provide an additional tool to crystal engineering, opening the doors to rational design of chiral resolution, chiral enrichment, and chiral purification of pharmaceutical compounds. In this work we report two racemic polymorphs occurring for the nitrate salt of the antidepressant drug fluoxetine (FLX): a racemate (P21/n, Z = 4, Z′ = 1) and a kryptoracemate (Pca21, Z = 4, Z′ = 2). The relative stability of these polymorphs was established through a combination of techniques, namely, differential scanning calorimetric (DSC), thermogravimetric analysis (TGA), hot stage microscopy (HSM), and solubility measurements. Though the two polymorphs share some structural features, the N+–H···O– hydrogen bonds have created dissimilar racemic motifs in their packing, resulting in different enantiomer orientations. The racemate is more stable over the temperature ranges we studied and is monotropically related to kryp...

A series of cross-conjugated compounds based on an (E)-4,4′-(hexa-3-en-1,5-diyne-3,4-diyl)bis(N,N-bis(4-methoxyphenyl)aniline) skeleton (1–6) have been synthesized. The linear optical absorption properties can be tuned by modification of the substituents at the 1 and 5 positions of the hexa-3-en-1,5-diynyl backbone (1: Si(CH(CH3)2)3, 2: C6H4C≡CSi(CH3)3, 3: C6H4COOCH3, 4: C6H4CF3, 5: C6H4C≡N, 6: C6H4C≡CC5H4N), although attempts to introduce electron-donating (C6H4CH3, C6H4OCH3, C6H4Si(CH3)3) substituents at these positions were hampered by the ensuing decreased stability of the compounds. Spectroelectrochemical investigations of selected examples, supported by DFT-based computational studies, have shown that one- and two-electron oxidation of the 1,2-bis(triarylamine)ethene fragment also results in electronic changes to the perpendicular π-system in the hexa-3-en-1,5-diynyl branch of the molecule. These properties suggest that (E)-hexa-3-en-1,5-diynyl-based compounds could have applications in molecular sensing and molecular electronics.

The synthesis of new styryl dyes derived from 4-pyridine and 4-quinoline and having an ammonioalkyl N-substituent and benzocrown ether moieties of different sizes and with different sets of heteroatoms was developed. Spontaneous "head-to-tail" dimerization of these dyes via the formation of numerous hydrogen bonds between the terminal NH3(+) groups and crown ether moieties was detected in MeCN solutions. The stability constants of the dimeric complexes having pseudocyclic structure were studied by (1)H NMR titration. The most stable complexes (log Kd up to 8.2) were found in the case of dyes with the 18-crown-6 ether moiety, which is most complementary for binding a primary ammonium group. Stacking interaction of the conjugated systems in the dimeric complexes contributes to their stability to a much lesser extent. In dimeric complexes, the ethylene bonds of the dyes are preorganized for stereospecific [2 + 2] photocycloaddition (PCA) induced by visible light. PCA yields only rctt isomers of bis-crown-containing cyclobutane derivatives. The dyes were studied by X-ray diffraction; it was found that the dimeric arrangement is also retained in the crystalline state. The possibility of topochemical PCA of the dyes in single crystals without their destruction was demonstrated. The possibility of retro-PCA of the obtained cyclobutane derivatives to give the starting dyes was shown. The elucidated regularities of PCA can be used to fabricate optical data recording systems based on ammonioalkyl derivatives of crown ether styryl dyes.

Crystals of molecular complexes of trimethyltrioxane (TMT) with chloroform (CF), bromoform (BF), dichloromethane (DCM), and dibromomethane (DBM) as well as those of pure TMT were grown in situ and characterized by single crystal X-ray crystallography. The CF and BF complexes, as well as those of DCM and DBM, are isostructural. The packing motifs were examined using the vector analysis of pairwise energies of intermolecular interactions. The method shows some deficiencies of the traditional approach based on the analysis of geometrical parameters of short intermolecular contacts.

The reaction of trans-RuCl(C≡CC6H4R1-4)(dppe)2 (2: R1 = Me (a), C5H11 (b), OMe (c), CO2Me (d), NO2 (e), C≡CSiMe3 (f), C≡CBut (g), NH2 (h)), prepared in situ from reactions of [RuCl(dppe)2]OTf ([1]OTf) with terminal alkynes in CH2Cl2 solutions containing 1,8-diazabicycloundec-7-ene (DBU) and TlBF4, provides a convenient and rapid route to bis(acetylide) complexes trans-Ru(C≡CC6H4R1-4)2(dppe)2 (3a–h) and trans-Ru(C≡CC6H4R1-4)(C≡CC6H4R2-4)(dppe)2 (4, R1 = C≡CSiMe3, R2 = NH2; 5, R1 = CO2Me, R2 = NH2; 6, R1 = CO2Me, R2 = OMe). However, even in the absence of the chloride abstracting reagent, more strongly electron donating substituents (e.g., R1 = OMe (2c), NH2 (2h)) promote sufficient ionization of the Ru–Cl bond in trans-RuCl(C≡CC6H4R1-4)(dppe)2 to lead to slow conversion to bis(alkynyl) complexes 3c,h in the presence of excess alkyne and DBU. Desilylation of 2f and 3f affords 2i and 3i (R1 = C≡CH), respectively. The molecular structures of 3a–d,f–i have been determined and are reported together with the str...

Crystallization of 2-fluorophenylacetylene at room temperature using high pressure yields three different polymorphs. These have distinct supramolecular assemblies despite the only variation in the crystallization protocol employed being the rate of compression.

The character of the electronic transitions in the ultraviolet-visible-near infrared (UV-vis-NIR) spectra of platinum-bis(alkynyl) bridged, bis-triarylamine mixed-valence systems trans-[Pt(C≡CC6H4NAr2)2 (PR3)2](n+) (R = ethyl, Ar = C6H4CH3-4 (1) or C6H4OCH3-4 (2); R = Ph, Ar = C6H4CH3-4 (3) or C6H4OCH3-4 (4), n = 0, 1, 2) has been determined from a combination of spectroscopic measurement and density functional theory calculations. The hybrid functional BLYP35 in combination with a suitable solvent model (i.e., conductor-like screening model (COSMO)) has been used to model the UV-vis-NIR and IR spectroscopic properties of [1-4](+), to confirm the description of [1-4](+) as examples of metal-bridged organic mixed-valence compounds, and to assign the principal features of the electronic spectra, including the triarylamine-based intervalence charge transfer transition located in the NIR region. The successful modeling of the charge distribution within the system demonstrates the utility of the BLYP35-COSMO protocol as a tool for use in the study of intramolecular charge transfer properties in mixed-valence complexes.

The delicate balance between solid-state intermolecular interactions and electron-donating methyl-group influences in N-methylurea (NMU) is shown to distinguish its nonlinear optical properties, relative to those of urea, a standard reference material for second harmonic generation (SHG). The solid-state intermolecular interactions in NMU are identified using neutron diffraction data, showing that hydrogen bonding generates an extensive 3D supramolecular network of NMU molecules with secondary and tertiary nonbonded contacts helping to hold this network in a closely packed form. The undulating “urea tape” motif within this network renders an overall packing arrangement that is less SHG-favorable than that of urea, which exhibits a more head-to-tail molecular alignment. The primary, secondary, and tertiary nonbonded contacts are classified using graph-sets, Hirshfeld surfaces, and fingerprint plots. H···H contacts in NMU contribute to the overall Hirshfeld surface area much more than in urea, forming at th...

Novel 2-benzothiazole-, 4-pyridine-, and 2- and 4-quinoline-based styryl dyes containing an N-methylbenzoaza-15(18)-crown-5(6)-ether moiety were synthesized. A detailed electronic spectroscopy study revealed high performance of these compounds as optical molecular sensors for alkali and alkaline-earth metal cations. They were shown to considerably surpass analogous chromoionophores based on N-phenylaza-crown ethers regarding both the ionochromism and the cation-binding ability. In addition, they act as fluorescent sensors for the metal cations by demonstrating cation-triggered emission. Upon complexation with Ba(2+), the fluorescence enhancement factor reaches 61. The structural features of dyes and their metal complexes were studied by NMR spectroscopy and X-ray diffraction. The high degree of macrocycle preorganization was found to be one of the factors determining the high cation-binding ability of the sensor molecules based on N-methylbenzoaza-crown ethers.

The readily available complex 1,1-dibromo-2-ferrocenylethylene provides a convenient entry point for the preparation of a wide range of cross-conjugated 1,1-bis(alkynyl)-2-ferrocenylethenes through simple Pd(0)/Cu(I)-mediated cross-coupling reactions with 1-alkynes. The ferrocene moiety in compounds of the general form FcCH═C(C≡CR)2 is essentially electronically isolated from the cross-conjugated π system, as evidenced by IR and UV–vis spectroelectrochemical experiments and quantum chemical calculations. In contrast to the other examples which give stable ferrocenium derivatives upon electrochemical oxidation, the aniline derivatives [FcCH═C(C≡CC6H4NH2-4)2]+ and [FcCH═C(C≡CC6H4NMe2-4)2]+ proved to be unstable on the time scale of the spectroelectrochemical experiments, leading to passivation of the electrode surface over time. There is no significant thermodynamic stabilization of the radical anion [FcCH═C(C≡CC6H4NO2-4)2]− relative to the neutral and dianionic analogues, although the dianion [FcCH═C(C≡CC6...

A 3D hybrid zinc formate framework, [NH(4)][Zn(HCOO)(3)], possessing an acs topology, shows a high degree of mechanical anisotropy and negative linear compressibility (NLC) along its c axis. High-pressure single-crystal X-ray diffraction studies and density functional theory calculations indicate that contraction of the Zn-O bonds and tilting of the formate ligands with increasing pressure induce changes in structure that result in shrinkage of the a and b axes and the NLC effect along c.

Three polymorphs of pyrene-2,7-bis(Bpin)2 (1) and two of pyrene-2-(Bpin) (2), where Bpin = 4,4,5,5-tetramethyl-[1,3,2]dioxaborolane, two different 1:1 co-crystals of 1 with toluene, and co-crystals of hexafluorobenzene (HFB) with 1 (of highly unusual 2:1 composition) and 2 (of usual 1:1 composition) were isolated, studied by X-ray diffraction and differential scanning calorimetry, and described using Hirshfeld surfaces and two-dimensional fingerprint plots. Centrosymmetric phases β- and γ-1 have densities respectively lower and higher than the chiral α-1; α- and β-2 have different packing modes, both with Z′ = 3. Compound 1 is prone to form channel host–guest structures, for example, α- and β-1·PhMe and 1·2HFB. The drastically different stabilities of α- and β-1·PhMe are discussed. The complex 2·HFB has a mixed-stack packing motif. The structural versatility of 1 and 2 is explained by synthon frustration between structurally incongruent pyrene and Bpin moieties.

A family of complexes (1a-3a and 1b-3b) was prepared, having the structure Ir(N^C^N)(N^C)Cl. Here, N^C(∧)N represents a terdentate, cyclometallating ligand derived from 1,3-di(2-pyridyl)benzene incorporating CH(3) (1a,b), F (2a,b), or CF(3) (3a,b) substituents at the 4 and 6 positions of the benzene ring, and N^C is 2-phenylpyridine (series a) or 2-(2,4-difluorophenyl)pyridine (series b). The complexes are formed using a stepwise procedure that relies on the initial introduction of the terdentate ligand to form a dichloro-bridged iridium dimer, followed by cleavage with the N^C ligand. (1)H NMR spectroscopy reveals that the isomer that is exclusively formed in each case is that in which the pyridyl ring of the N^C ligand is trans to the cyclometallating aryl ring of the N^C^N ligand. This conclusion is unequivocally confirmed by X-ray diffraction analysis for two of the complexes (1b and 3a). All of the complexes are highly luminescent in degassed solution at room temperature, emitting in the green (1a,b), blue-green (2a,b), and orange-red (3a,b) regions. The bidentate ligand offers independent fine-tuning of the emission energy: for each pair, the "b" complex is blue-shifted relative to the analogous "a" complex. These trends in the excited-state energies are rationalized in terms of the relative magnitudes of the effects of the substituents on the highest occupied and lowest unoccupied orbitals, convincingly supported by time-dependent density functional theory (TD-DFT) calculations. Luminescence quantum yields are high, up to 0.7 in solution and close to unity in a PMMA matrix for the green-emitting complexes. Organic light emitting devices (OLEDs) employing this family of complexes as phosphorescent emitters have been prepared. They display high efficiencies, at least comparable, and in some cases superior, to similar devices using the well-known tris-bidentate complexes such as fac-Ir(ppy)(3). The combination of terdentate and bidentate ligands is seen to offer a versatile approach to tuning of the photophysical properties of iridium-based emitters for such applications.

Semiquinone-bridged bisdithiazolyls 3 represent a new class of resonance-stabilized neutral radical for use in the design of single-component conductive materials. As such, they display electrochemical cell potentials lower than those of related pyridine-bridged bisdithiazolyls, a finding which heralds a reduced on-site Coulomb repulsion U. Crystallographic characterization of the chloro-substituted derivative 3a and its acetonitrile solvate 3a·MeCN, both of which crystallize in the polar orthorhombic space group Pna2(1), revealed the importance of intermolecular oxygen-to-sulfur (CO···SN) interactions in generating rigid, tightly packed radical π-stacks, including the structural motif found for 3a·MeCN in which radicals in neighboring π-stacks are locked into slipped-ribbon-like arrays. This architecture gives rise to strong intra- and interstack overlap and hence a large electronic bandwidth W. Variable-temperature conductivity measurements on 3a and 3a·MeCN indicated high values of σ(300 K) (10(-3) S cm(-1)) with correspondingly low thermal activation energies E(act), reaching 0.11 eV in the case of 3a·MeCN. Overall, the strong performance of these materials as f = ½ conductors is attributed to a combination of low U and large W. Variable-temperature magnetic susceptibility measurements were performed on both 3a and 3a·MeCN. The unsolvated material 3a orders as a spin-canted antiferromagnet at 8 K, with a canting angle φ = 0.14° and a coercive field H(c) = 80 Oe at 2 K.

4,4'-Bipyridine and 2,7-diazapyrene derivatives (A) having two ammonioalkyl N-substituents were synthesized. The complex formation of these compounds with bis(18-crown-6)stilbene (D) was studied by spectrophotometry, cyclic voltammetry, (1)H NMR spectroscopy, and X-ray diffraction analysis. In MeCN, π-donor D and π-acceptors A form supramolecular 1:1 (D·A) and 2:1 (D·A·D) charge-transfer complexes. The D·A complexes have a pseudocyclic structure as a result of ditopic binding of the ammonium groups to the crown-ether fragments. The better the geometric matching between the components, the higher the stability of the D·A complexes (log K up to 9.39). A key driving force of the D·A·D complex formation is the excessive steric strain in the precursor D·A complexes. The pseudocyclic D·A complexes involving the ammoniopropyl derivative of 4,4'-bipyridine were obtained as single crystals. Crystallization of the related ammonioethyl derivative was accompanied by transition of the D·A complexes to a structure of the (D·A)(m) coordination polymer type.

A combination of IR spectroelectrochemistry and DFT calculations has been used to demonstrate that the vinyl ligands in the complexes [Ru(CH═CHC6H4Me-4)Cl(CO)(PMe3)3] and [{RuCl(CO)(PMe3)3}2(μ-CH═CHC6H4CH═CH)] are redox noninnocent, and one-electron oxidation results in radical cations that are best described in terms of metal-stabilized organic radicals.

The design and study of organometallic mixed-valence complexes is complicated by the mixing of metal d and bridging ligand π orbitals, which often makes the assignment of metal oxidation states amb...

Highly fluorinated nitrobenzene derivatives are suitable substrates for palladium-catalyzed C-F bond arylation using readily available palladium catalysts under both conventional heating and microwave conditions. Arylation occurs ortho to the nitro group offering a synthetic route to polyfluorinated 2-arylnitrobenzene systems. The regiochemistry of the arylation reactions suggests that there is a significant directing interaction between the nitro group and the incoming nucleophilic palladium catalyst which is facilitated by the presence of several fluorine atoms attached the ring. Investigations into the regioselectivity and reactivity of several tetrafluoro- and trifluoronitrobenzene derivatives provides further evidence for the highly nucleophilic character of the oxidative addition step in contrast to the concerted mechanism of more conventional Suzuki-Miyaura coupling reactions involving aryl iodides and bromides.

A series of molybdenum alkynyl complexes [Mo(C≡CR)(dppe)(η-C7H7)] featuring a range of alkynyl substituents R with varying electron-donating and -withdrawing properties have been prepared. Oxidatio...

A simple N,N′-diaryl urea derivative was found to form four different anhydrous crystal forms (I−IV°), which can be crystallized in pure form by several techniques from solution as well as from the melt. These polymorphs were characterized by thermomicroscopy, differential scanning calorimetry, Fourier-transform infrared spectroscopy and single crystal and powder X-ray diffraction. The polymorphs were found to be purely monotropically related with large differences in their heats of fusion (11.1 kJ mol−1 for the least stable form I, 34.5 kJ mol−1 for the most stable form IV°). The crystal structures of all forms show the same conformer for forms I−III and a second conformer in form IV°. However, the hydrogen bonding motifs in all of the polymorphs are the same and thus the compound can be seen as a model for the importance of the entire crystal packing arrangement to the overall energy and stability of the crystal form, as opposed to just a few dominant interactions.

Reactions of a new imido phosphido complex, Cp2Nb(═NBut)(PPh2) (1), with olefin complexes of rhodium afford two types of compounds. With [(μ-Cl)Rh(C2H4)2]2, an imido/phosphido-bridged complex, Cp(Cl)Nb(μ-NBut)(μ-PPh2)RhCp (2), characterized by NMR and X-ray diffraction, was prepared. Formation of 2 represents a rare example of a Cp/Cl exchange reaction in organometallic chemistry. When 1 reacts with [(μ-Cl)Rh(COD)]2, the target phosphido-bridged bimetallic complex Cp2Nb(═NBut)(μ-PPh2)Rh(Cl)(COD) (4) is formed. The structure of this product was established by NMR and an X-ray diffraction study. Both 2 and 4 are catalyst precursors for hydrosilylation of benzaldehyde and acetophenone. The activity of the neutral complex 4 exceeds that of the cation [Cp2Nb(NBut)(PPh2)Rh(COD)]+ derived from 4 by chloride anion abstraction.

The syntheses and structures of a [2×1+1×2] cocrystal [{CuIIL1NaI(H2O)2}{CuIIL1}2](NO3) (1) and [3×1+5×1] cocrystal [{(CuIIL1)2KI}(NO3)]·[{(CuIIL1)3KI2(μ-NO3)}(NO3)]·0.2H2O (2) derived from the hexadentate Schiff base compartmental ligand N,N′-ethylenebis(3-ethoxysalicylaldimine) (H2L1) are described. Compounds 1 and 2 crystallize in triclinic P1 and monoclinic P21/c systems, respectively. The structure of 1 consists of the [CuIIL1ΝaI(H2O)3]+ cation and two mononuclear [CuIIL1] moieties. In the dinuclear [CuIIL1ΝaI(H2O)3]+ cation, the metal centers are doubly bridged by the two phenolate oxygen atoms. Each of the two coordinated water molecules of the dinuclear unit is encapsulated in the O4 cavities of the two mononuclear [CuIIL1] moieties resulting in the formation of a [2×1+1×2] cocrystal. In compound 2, one trinuclear double-decker system [{(CuIIL1)2KI}(NO3)] and one pentanuclear triple-decker system [{(CuIIL1)3KI2(μ-NO3)}(NO3)] are cocrystallized. Evidently, compound 2 is a [3×1+5×1] cocrystal. Stru...

The reactions of [Ir(PMe3)4]Cl (1) with a variety of substrates (acetonitrile, p-aminobenzonitrile, p-cyanophenol) containing a nitrile group were examined. Cleavage of the X−H bonds occurred selectively over the coordination of the CN moiety in those substrates, and compounds derived from the corresponding X−H (X = C, N, O) oxidative addition reaction, namely, cis-[IrH(CH2CN)(PMe3)4]Cl (2), cis-[IrD(CD2CN)(PMe3)4]Cl (3), cis-[IrH(p-NHC6H4CN)(PMe3)4]Cl (4), and cis-[IrH(p-OC6H4CN)(PMe3)4]Cl (6), were obtained. X-ray diffraction studies have confirmed the structures of 3 and 4. In the case of 6, the compound trans-[IrClH(PMe3)4][p-OC6H4CN] (5b), resulting from exchange of Cl and p-OC6H4CN anions between inner and outer sphere, was also formed, and the solid-state structure (5b·HOC6H4CN), obtained by X-ray diffraction, contained the hydrogen-bonded NCC6H4O···H···OC6H4CN anion. The salt [Ir(PMe3)4][BPh4] (7) was also prepared, characterized by X-ray diffraction and reacted with p-HOC6H4CN. Reaction of 1 with...

The pressure-dependent structural evolution of a neutral zinc-imidazolate framework [Zn(2)(C(3)H(3)N(2))(4)](n) (ZnIm) has been investigated. The as-synthesized three-dimensional ZnIm network (alpha-phase) crystallizes in the tetragonal space group I4(1)cd (a = 23.5028(4) A, c = 12.4607(3) A). The ZnIm crystal undergoes a phase transition to a previously unknown beta-phase within the 0.543(5)-0.847(5) GPa pressure range. The tetragonal crystal system is conserved during this transformation, and the beta-phase space group is I4(1) (a = 22.7482(3) A, c = 13.0168(3) A). The physical mechanism by which the transition occurs involves a complex cooperative bond rearrangement process. The room-temperature bulk modulus for ZnIm is estimated to be approximately 14 GPa. This study represents the first example of a high-pressure single-crystal X-ray diffraction analysis of a metal-organic framework.

The six different solvate structures of trans-1,4-bis(phenylethynyl)-cyclohexane-1,4-diol reported herein show the importance of weak C−H···O bonds and C−H···π interactions in directing crystal packing. The host molecule consists of a unique combination of strong hydrogen bonding (hydroxyl) and weak interactions (phenylethynyl). While strong hydrogen bonds play a central role, the combined influence of the weak interactions is also evident in the structures. It is apparent that the orientation of the phenylethynyl moieties influences the formation of C−H···O and C−H···π interactions. The interesting occurrence of a structure with two different conformers of the host molecule within the same crystal coexisting with ethanol and stabilized by several weak C−H···π interactions is also reported.

The structural ferroelectric phase transition in 2-aminopyridine dihydrogen phosphate (2APP) has been studied by single crystal and powder X-ray diffraction between room temperature and 16 K. It has been shown that α-aminopyridine dihydrogen phosphate (α-2APP) undergoes a transition from the centrosymmetric space group C2/c in the paraelectric phase to the polar space group Cc in the ferroelectric phase. This is a second-order phase transition associated with ordering of protons in short O-H···O hydrogen bonds. This system is found to exhibit rich polymorphism: depending on crystallization conditions, three anhydrate forms and one monohydrate can be isolated. 2APP hydrate and γ-2APP have been identified for the first time, and their structures have been solved from single crystal diffraction data.

"Tritopic" picolinic dihydrazone ligands with tridentate coordination pockets are designed to produce homoleptic [3 x 3] nonanuclear square grid complexes on reaction with transition-metal salts, and many structurally documented examples have been obtained with Mn(II), Cu(II), and Zn(II) ions. However, other oligomeric complexes with smaller nuclearities have also been discovered and identified structurally in some reactions involving Fe(II), Co(II), Ni(II), and Cu(II), with certain tritopic ligands. This illustrates the dynamic nature of the metal-ligand interaction and the conformationally flexible nature of the ligands and points to the possible involvement of some of these species as intermediates in the [3 x 3] grid formation process. Examples of mononuclear, dinuclear, hexanuclear, heptanuclear, and nonanuclear species involving Fe(II), Co(II), Ni(II), and Cu(II) salts with a series of potentially heptadentate picolinic dihydrazone ligands with pyrazine, pyrimidine, and pyridine end groups are described in the present study. Iron and cobalt complexation reactions are complicated by redox processes, which lead to mixed-oxidation-state Co(II)/Co(III) systems when starting with Co(II) salts, and reduction of Fe(III) to Fe(II) when starting with Fe(III). Magnetic exchange within the polynuclear structural frameworks is discussed and related to the structural features.

N,N‘-Diisopropylferrocenecarboxamide is utilized for an asymmetric, directed metalation approach to several planar chiral bifunctional ferrocene derivatives. Directed metalation using n-butyllithium-(−)-sparteine on N,N‘-diisopropylferrocenecarboxamide can be achieved to give high yields of the corresponding boronic acid; however, it was found that a sequence involving asymmetric directed metalation−bromination, followed by lithium−halogen exchange, was more convenient to access the same derivatives since this allowed straightforward determination of the enantiomeric excess. (pR)-2-[(N,N-Diisopropylamino)methyl]ferrocenylboronic acid and derivatives thereof could be readily accessed with high enantiomeric excess, followed by amide reduction.

The structure of the first tetrameric α-lithiated N-phenylphosphazene has been determined in the solid state and shown to persist in toluene solution, an observation that gives insight into the variation in stereoselectivity found for reactions of α-lithiated phosphazenes with aldehydes.

Solvent inclusion in organic crystals is quite uncommon, as it is observed in only 15% of cases. Solvation could be imagined to result from the interruption of the “normal” crystallization process because of the preferential formation of directional hydrogen bonds between the included solvent and the organic component. However, it is surprising to note that only a limited number of studies have been performed using amine based solvents, yet amines, next to hydroxyl groups, are the most extensively studied functional group in the field of crystal engineering. In this work, we attempt to determine a correlation between molecular functionality and crystal structures among the 15 different pseudopolymorphs of 1,5-dichloro-trans-9,10-diethynyl-9,10-dihydroanthracene-9,10-diol (DDDA). This work aims to gain an insight into the interaction hierarchy between four molecular functionalities of a solvent molecule, namely, a hydroxy group (benzylic), an ethynyl group, an aromatic chlorine atom, and an amino group and...

A family of bis-terdentate iridium(III) complexes is reported which contain a cyclometalated, N/\C[wedge]N-coordinating 1,3-di(2-pyridyl)benzene derivative. This coordination mode is favored by blocking competitive cyclometalation at the C4 and C6 positions of the ligand. Thus, 1,3-di(2-pyridyl)-4,6-dimethylbenzene (dpyxH) reacts with IrCl3 x 3H2O to generate a dichlorobridged dimer [Ir(dpyx-N,C,N)Cl(mu-Cl)]2, 1. This dimer is cleaved by DMSO to give [Ir(dpyx)(DMSO)Cl2], the X-ray crystal structure of which is reported here, confirming the N/\C/\N coordination mode of dpyx. The dimer 1 can also be cleaved by a variety of other ligands to generate novel classes of mononuclear complexes. These include charge-neutral bis-terdentate complexes of the form [Ir(N/\C/\N)(C/\N/\C)] and [Ir(N/\C/\N)(C/\N/\O)], by reaction of 1 with C/\N/\C-coordinating ligands (e.g., 2,6-diphenylpyridine and derivatives) and C/\N/\O-coordinating ligands (based on 6-phenylpicolinate), respectively. Treatment of 1 with terpyridines leads to dicationic complexes of the type [Ir(N/\C/\N)(N/\N/\N)]2+, while 2-phenylpyridine gives [Ir(dpyx-N/\C/\N)(ppy-C,N)Cl]. All of the charge-neutral complexes are luminescent in fluid solution at room temperature. Assignment of the emission to charge-transfer excited states with significant MLCT character is supported by DFT calculations. In the [Ir(N/\C/\N)(C/\N/\C)] class, fluorination of the C/\N/\C ligand at the phenyl 2' and 4' positions leads to a blue-shift in the emission and to an increase in the quantum yield (lambda(max) = 547 nm, phi = 0.41 in degassed CH(3)CN at 295 K) compared to the nonfluorinated parent complex (lambda(max) = 585 nm, phi = 0.21), as well as to a stabilization of the compound with respect to photodissociation through cleavage of mutually trans Ir-C bonds. [Ir(dpyx-N/\C/\N)(ppy-C,N)Cl] is an exceptionally bright emitter: phi = 0.76, lambda(max) = 508 nm, in CH(3)CN at 295 K. In contrast, the [Ir(N/\C/\N)(C/\N/\O)] complexes are much less emissive, shown to be due to fast nonradiative decay of the excited state, probably involving reversible Ir-O bond cleavage. The [Ir(N/\C/\N)(N/\N/\N)]2+ complexes are very feeble emitters even at 77 K, probably due to the almost exclusively interligand charge-transfer nature of the lowest-energy excited state in these complexes.

Analysis of crystal packing of related compounds is a necessary ingredient of crystal engineering. We report here the crystal structures of 14 cyclic and fused ring gem-alkynols, compounds that are known for their supramolecular inconsistency because of the juxtaposition of two hydrogen-bond donors (O−H, C⋮C−H) and two hydrogen-bond acceptors (O−H, C⋮C−H) in the molecules. Because of the competition between these hydrogen-bond donors, or hydrogen-bond acceptors, the packing pattern in any particular crystal structure is highly sensitive to substitution by functional groups. The compounds studied here are methyl and chloro derivatives of the parent compounds 1a (benzo series, 1b−1f), 2a (naphtha series, 2b−2f), 3a and 4a (anthra series, 3b, 4b−4d). Structures 2a and 4a are prototypes because the O−H···O, C−H···O, O−H···π, and C−H···π hydrogen bonds form sheets in these cases with the interdigitating hydrocarbon residues perpendicular to the sheets. The hydrogen bonds are arranged to give centrosymmetric sy...

A series of cyclometalated platinum(II) complexes have been prepared, [PtL(n)Cl], containing N--C--N-coordinating, terdentate ligands based on 1,3-dipyridylbenzene (HL(1)), incorporating aryl substituents at the central 5 position of the ligand. All of the new complexes are intensely luminescent in a degassed solution at 298 K (phi = 0.46-0.65 in CH(2)Cl(2)) with lifetimes in the microsecond range (7.9-20.5 micros). The introduction of the aryl substituents leads to a red shift in the lowest-energy, intense charge-transfer absorption band compared to [PtL(1)Cl] (401 nm in CH(2)Cl(2)), in the order H < mesityl < 2-pyridyl < 4-tolyl < 4-biphenylyl < 2-thienyl < 4-(dimethylamino)phenyl (431 nm in CH(2)Cl(2)), which correlates with the decreasing order of oxidation potentials. A similar order is also observed in the emission maxima, ranging from 491 nm for [PtL(1)Cl] to 588 nm for the 4-(dimethylamino)phenyl-substituted complex. The emission spectra of all of the complexes, except for the amino-substituted compound, are highly structured in a dilute solution in CH(2)Cl(2), and the emission is assigned to excited states of primarily (3)LC (ligand-centered) character. At higher concentrations, self-quenching accompanied by structureless excimer emission centered at 700 nm is observed, but the aryl groups attenuate the self-quenching compared to the parent compound [PtL(1)Cl], particularly for the most sterically hindered mesityl complex. The introduction of the strongly electron-donating 4-dimethylamino substituent leads to a switch in the nature of the lowest-energy excited state from (3)LC to one of primarily intraligand charge-transfer (ILCT) character in CH(2)Cl(2): this complex displays a structureless and much broader emission band than the other compounds and a high degree of positive solvatochromism. No excimer emission is observed in CH(2)Cl(2), and self-quenching is an order of magnitude lower than that for the other complexes. However, in nonpolar solvents such as CCl(4), the ILCT state is destabilized, such that the (3)LC remains the lowest-energy excited state. Reversible switching between the ILCT and (3)LC states can also be achieved in a CH(2)Cl(2) solution by protonation of the amine, with an accompanying large change in the emission maxima of >100 nm. The X-ray structures of the biphenylyl- and methyl-substituted complexes are reported, together with those of the 2-pyridyl- and mesityl-substituted ligands and the key synthetic intermediate 1-bromo-3,5-di(2-pyridyl)benzene.

We describe for the first time the full 3D atomic structure of room-temperature α-La2Mo2O9. The material, despite its simple chemical formula, has a remarkable 312 crystallographically unique atoms and is thus one of the most complex oxide structures reported to date. Despite this complexity, the structural results offer significant insight into the O2- migration pathway in the anion conducting high-temperature form, β-La2Mo2O9. The material contains a mixture of 4, 5, and 6 coordinated Mo sites, suggesting that variable Mo coordination number is a key factor in providing a low-energy O2- conduction pathway. We provide quantitative analysis showing that the positions in the ordered array of 216 oxygen sites of α-La2Mo2O9 are directly related to the average sites occupied in β-La2Mo2O9, providing compelling evidence that the high-temperature conducting form of the material has a time-averaged version of the low-temperature structure.

Synthesis of the title compounds, viz. [RN(CH2CHR'O)2]2Ge (1, R = Me, R' = H; 2, R = Me, R' = Ph; 3, R = Ph, R' = H), by the reaction of 2 equiv of corresponding dialkanolamines RN(CH2CHR'OH)2 (4, R = Me, R' = H; 5, R = Me, R' = Ph; 6, R = Ph, R' = H) with (AlkO)4Ge is reported. Composition and structures of all novel compounds were established by 1H and 13C NMR spectroscopy and mass spectrometry as well as elemental analysis data. The single-crystal X-ray diffraction of 2 has clearly indicated the presence of two transannular interactions Ge--N in the compound. N atoms are cis-orientated. The compound 3 possesses long Ge...N distances. The structural data obtained from geometry optimizations by DFT calculations on 1-3 reproduces experimental results. Both cis- and trans-isomers were studied, and cis-configuration was found to be more thermodynamically stable for all three compounds. The transition states for possible cis--trans rearrangement processes in 1-3 were calculated. The properties of the Ge-O and Ge--N bonds in 1-3 were analyzed by the AIM approach. The interactions between the Ge atom and N atoms as well as O atoms possess predominantly ionic character.

The 62-CVE clusters Ru4(μ-RC2R)2(CO)11, which feature a dodecahedral cluster core, are readily reduced to a 64-CVE dianion in a process that is essentially chemically reversible. A combination of e...

The reactions of a series of half-sandwich trihydrides of ruthenium, Cp*(R3P)Ru(H)3 (R3P = Pri3P, Pri2MeP, PriMe2P, PhMe2P), with a family of chlorosilanes (ClSiHMe2, Cl2SiHMe, Cl3SiH) have been st...

Palladium-catalyzed terminal alkyne dimerization, through oxidative homocoupling, is a useful approach to the synthesis of symmetrical 1,4-diynes. Recent investigations have suggested that this reaction might be accomplished in the absence of intentionally added stoichiometric oxidants (to reoxidize Pd(0) to Pd(II)). In this paper, we have fully addressed the question of whether oxygen (or added oxidant) is required to facilitate this process. The presence of a stoichiometric quantity of air (or added oxidant such as I2) is essential for alkyne dimerization. Excess PPh3 inhibits alkyne dimerization to enyne, which only occurs to a significant extent when the reaction is starved of oxidant. Theoretical studies shed more light on the requirement for an oxidant in the homocoupling reaction in order for the process to be theromodynamically favorable. The employment of I2 as the stoichiometric oxidant appears to be the method of choice. The dual role of Cu both in transmetalation of alkynyl units to Pd(II) and in assisting reoxidation of Pd(0) to Pd(II) is suggested.

The crystal and toluene solution structure (X-ray, 1H, 7Li, 13C,31P NMR) of a mixed-anion lithium phosphazene-phenolate, 10, is a six-rung ladder consisting of two LiPCN units fused to a central Li2O2 core, which provides insight into the function of phosphazenyl-stabilized carbanions as reagents. The mixed aggregate showed decreased reactivity toward benzaldehyde with respect to the uncomplexed anion.

Mn(II)9 grid complexes with a [Mn9(mu-O)12] core, obtained by self-assembly of a series of tritopic picolinic dihydrazone ligands with Mn(II) salts, have been oxidized by both chemical and electrochemical methods to produce mixed oxidation state systems. Examples involving [Mn(III)3Mn(II)6] and [Mn(III)4Mn(II)5] combinations have been produced. Structures are reported for [Mn9(2poap-2H)6](NO3)6.14H2O (1), [Mn9(2poap-2H)6](ClO4)10.10H2O (3), and [Mn9(Cl2poap-2H)6](ClO4)9.14H2O.3CH3CN (10). Structural studies show distinct contraction of the corner grid sites on oxidation, with overall magnetic properties consistent with the resulting changes in electron distribution. Antiferromagnetic exchange in the outer ring of eight metal centers creates a ferrimagnetic subunit, which undergoes antiferromagnetic coupling to the central metal, leading to S=1/2 (3) and S2/2 (10) ground states. Two moderately intense absorptions are observed on oxidation of the Mn(II) grids in the visible and near-infrared (1000 nm, 700 nm), associated with charge transfer transitions (LMCT, IVCT respectively). Compound 1 crystallized in the monoclinic system, space group P2 1/n, with a=21.308(2) A, b=23.611(2) A, c=32.178(3) A, beta=93.820(2) degrees . Compound 3 crystallized in the tetragonal system, space group I, with a=b=18.44410(10) A, c = 24.9935(3) A. Compound 10 crystallized in the triclinic system, space group P, with a=19.1150(10) A, b=19.7221(10) A, c=26.8334(14) A, alpha=74.7190(10) degrees, beta=77.6970(10) degrees, gamma=64.7770(10) degrees. The facile oxidation of the Mn(II)9 grids is highlighted in terms of their potential use as molecular based platforms for switching and data storage.

Very short OH···O hydrogen bonds (O···O = 2.2−2.5 A) usually occur when the H-bond is stabilized by a negative or positive charge (OH···O-, O+H···O) or by resonance assistance (···OCCCOH···). We have characterized a very short intermolecular OacidH···Owater hydrogen bond in the title crystal structure, 1, by variable temperature neutron diffraction (O···O = 2.4751(11), 2.4765(10), 2.4807(12), and 2.4906(16) A at 20, 100, 200, and 293 K). The COOH donor is activated by π-cooperative hydrogen bonding (OacidH···OCacid), and the water-acceptor ability is enhanced by polarization assistance (σ-cooperative, OwH···Oacid, OwH···Npyrazine). The absence of proton migration in the temperature range 20−293 K to give ionic or tautomer forms rules out contribution from the charge- or resonance-assisted H-bonds in 1. The shortening of the OacidH···Ow hydrogen bond through synergistic π- and σ-cooperativity in the finite, neutral array I, named as a synthon-assisted hydrogen bond (SAHB), adds a new category to the curren...

Dianilines and diphenols form well-defined crystalline molecular complexes that arise from complementary O−H···N and N−H···O recognition. The crystal structures of four such 1:1 complexes 1, 2, 3 and 4 based on diphenylmethane frameworks are reported and discussed. Three supramolecular synthons are found, the N(H)O based square motif and infinite chain, already reported, and a new cyclohexane chair consisting of N(H)O, O−H···O and N−H···N hydrogen bridges. The replacement of a −CH2− group by an S-atom leads in two cases to little change in the crystal structure and in another to a complete change. It is possible that the dianiline component plays a more important role in molecular recognition in these complexes than does the diphenol component.

A new supramolecular complex of fullerene C60, {(ZnTPP)4·(4-TPyP)}·(C60)2·(C6H5CN)3.5 (ZnTPP: zinc(II) tetraphenylporphyrin; 4-TPyP: tetra(4-pyridyl)porphyrin) involving unusual pentamers containing five porphyrin fragments, was obtained. The crystal structure, IR and UV−vis−NIR spectra of the complex, and the molecular structure of the pentamer are presented.

A novel bismuth calcium vanadate, Bi 4.6 Ca 1.1 VO 10.5 , has been synthesized. Its crystal structure has been determined by synchrotron X-ray diffraction. The compound crystallizes in orthorhombic space group Pnnm, with cell parameters a = 11.930(2) A, b = 16.030(3) A, and c = 11.500(2) A. The crystal structure can be viewed as consisting of fluorite-like slabs of edge-sharing OA4 (A = Bi, Ca) tetrahedra that extend along the c axis of the crystal and interspersed disordered VO 4 groups. Bi and Ca atoms undergo site disorder, with Bi preferentially occupying locations with low site symmetry and irregular coordination environments. Variable temperature powder diffraction measurements reveal a change in the thermal expansion coefficient of Bi 4.6 Ca 1.1 VO 10.5 above 600 °C and this coincides with the change in conductivity as revealed by a.c. impedance measurements.

We report the effects of protonation on the structural and spectroscopic properties of 1,4-dimethoxy-2,5-bis(2-pyridyl)benzene (9) and the related AB coploymer poly{2,5-pyridylene-co-1,4-[2,5-bis(2-ethylhexyloxy)]phenylene} (7). X-ray crystallographic analysis of 9, 1,4-dimethoxy-2,5-bis(2-pyridyl)benzene bis(formic acid) complex 10, and 1,4-dimethoxy-2,5-bis(2-pyridinium)benzene bis(tetrafluoroborate salt) (11) establishes that reaction of formic acid with 9 does not form an ionic pyridinium salt in the solid state, rather, the product 10 is a molecular complex with strong hydrogen bonds between each nitrogen atom and the hydroxyl hydrogen in formic acid. In contrast, reaction of 9 with tetrafluoroboric acid leads to the dication salt 11 with significant intramolecular hydrogen bonding (N−H···O−Me) causing planarization of the molecule. The pyridinium and benzene rings in 11 form a dihedral angle of only 3.9° (cf. pyridine−benzene dihedral angles of 35.4° and 31.4° in 9, and 43.8° in 10). Accordingly, th...

Two related phosphonium aryloxides, [Ph3PCH3]+2[CH2(C6H2-3,5-tert-butyl-4-O)2]2-, 1a, and [Ph3PC2H5]+2[CH2(C6H2-3,5-tert-butyl-4-O)2]2-, 1b have been synthesized by protonation of nonstabilized phosphorus ylides with 4,4‘-methylenebis(2,6-di-tert-butylphenol) LH2. The crystal structures of 1a and 1b have been determined by single-crystal X-ray diffraction, and that of 1b has also been determined by low-temperature (20 K) neutron diffraction. Both crystallize as CH3CN solvates, and both exhibit polymeric supramolecular structures via extensive C−H···O hydrogen bonding. The predominant structural motif is chelation of the aryloxide oxygen atom of the anion by phosphonium alkyl and aryl C−H groups, such as has been previously observed for phosphonium monoaryloxide salts. The use of this motif as a supramolecular synthon in crystal engineering is explored. In the case of 1a, in addition to the expected intermolecular C−H···O hydrogen bonding pattern, C−H···π interactions between the anion and this solvent are...

Carbonyl hydrosilylation catalyzed by (ArN)Mo(H)(SiH(2)Ph)(PMe(3))(3) (3) is unusual in that it does not involve the expected Si-O elimination from intermediate (ArN)Mo(SiH(2)Ph)(O(i)Pr)(PMe(3))(2) (7). Instead, 7 reversibly transfers β-CH hydrogen from the alkoxide ligand to metal.

The mechanism of formation of mer,trans-[(PMe3)3Rh(−C⋮C−R)2H] from [(PMe3)4Rh(Me)] and terminal alkyne has been studied. The initial step of the reaction is the elimination of methane and the formation of the trigonal bipyramidal complex [(PMe3)4Rh(−C⋮C−R)], a reaction that is complete in time of mixing at −78 °C. This intermediate undergoes an oxidative addition reaction with a second equivalent of alkyne to give fac-[(PMe3)3Rh(−C⋮C−R)2H] as the kinetic product. This fac isomer is not stable above −20 °C and isomerizes to the thermodynamic product mer,trans-[(PMe3)3Rh(−C⋮C−R)2H]. fac-[(PMe3)3Rh(−C⋮C−R)2H] will exchange alkynyl groups with free alkyne, a reaction that has a lower energetic barrier than the isomerization to mer,trans-[(PMe3)3Rh(−C⋮C−R)2H]. Density functional theory studies on all stages of the formation of mer,trans-[(PMe3)3Rh(−C⋮C−R)2H] have been carried out and give ground state energies in line with those experimentally observed. Once formed, mer,trans-[(PMe3)3Rh(−C⋮C−R)2H] is configura...