4-{3-[(Pyridin-4-ylmethyl)amino]-[1,2,4]triazolo[4,3-b][1,2,4]triazin-6-yl}phenol: An improved anticancer agent in hepatocellular carcinoma and a selective MDR1/MRP modulator.

Hepatocellular carcinoma is the most common type of primary liver cancer. However, multidrug resistance (MDR) is a major obstacle to the effective chemotherapy of cancer cells. This report documents the rational design, synthesis, and biological evaluation of a novel series of triazolotriazines substituted with CH2NH-linked pyridine for use as dual c-Met/MDR inhibitors. Compound 12g with IC50 of 3.06 µM on HepG2 cells showed more potency than crizotinib (IC50 = 5.15 µM) in the MTT assay. In addition, 12g inhibited c-Met kinase at a low micromolar level (IC50 = 0.052 µM). 12g significantly inhibited P-gp and MRP1/2 efflux pumps in both cancerous HepG2 and BxPC3 cells starting from the lower concentrations of 3 and 0.3 µM, respectively. 12g did not inhibit MDR1 and MRP1/2 in noncancerous H69 cholangiocytes up to the concentration of 30 and 60 µM, respectively. Current results highlighted that cancerous cells were more susceptible to the effect of 12g than normal cells, in which the inhibition occurred only at the highest concentrations, suggesting a further interest in 12g as a selective anticancer agent. Overall, 12g, as a dual c-Met and P-gp/MRP inhibitor, is a promising lead compound for developing a new generation of anticancer agents.

Ligand-Structure Effects on N-Heterocyclic Carbene Rhenium Photo- and Electrocatalysts of CO2 Reduction.

Three novel rhenium N-heterocyclic carbene complexes, [Re]-NHC-1-3 ([Re] = fac-Re(CO)3Br), were synthesized and characterized using a range of spectroscopic techniques. Photophysical, electrochemical and spectroelectrochemical studies were carried out to probe the properties of these organometallic compounds. Re-NHC-1 and Re-NHC-2 bear a phenanthrene backbone on an imidazole (NHC) ring, coordinating to Re by both the carbene C and a pyridyl group attached to one of the imidazole nitrogen atoms. Re-NHC-2 differs from Re-NHC-1 by replacing N-H with an N-benzyl group as the second substituent on imidazole. The replacement of the phenanthrene backbone in Re-NHC-2 with the larger pyrene gives Re-NHC-3. The two-electron electrochemical reductions of Re-NHC-2 and Re-NHC-3 result in the formation of the five-coordinate anions that are capable of electrocatalytic CO2 reduction. These catalysts are formed first at the initial cathodic wave R1, and then, ultimately, via the reduction of Re-Re bound dimer intermediates at the second cathodic wave R2. All three Re-NHC-1-3 complexes are active photocatalysts for the transformation of CO2 to CO, with the most photostable complex, Re-NHC-3, being the most effective for this conversion. Re-NHC-1 and Re-NHC-2 afforded modest CO turnover numbers (TONs), following irradiation at 355 nm, but were inactive at the longer irradiation wavelength of 470 nm. In contrast, Re-NHC-3, when photoexcited at 470 nm, yielded the highest TON in this study, but remained inactive at 355 nm. The luminescence spectrum of Re-NHC-3 is red-shifted compared to those of Re-NHC-1 and Re-NHC-2, and previously reported similar [Re]-NHC complexes. This observation, together with TD-DFT calculations, suggests that the nature of the lowest-energy optical excitation for Re-NHC-3 has π→π*(NHC-pyrene) and dπ(Re)→π*(pyridine) (IL/MLCT) character. The stability and superior photocatalytic performance of Re-NHC-3 are attributed to the extended conjugation of the π-electron system, leading to the beneficial modulation of the strongly electron-donating tendency of the NHC group.

Self-Immolative System for Disclosure of Reactive Electrophilic Alkylating Agents: Understanding the Role of the Reporter Group.

The development of stable, efficient chemoselective self-immolative systems, for use in applications such as sensors, requires the optimization of the reactivity and degradation characteristics of the self-immolative unit. In this paper, we describe the effect that the structure of the reporter group has upon the self-immolative efficacy of a prototype system designed for the disclosure of electrophilic alkylating agents. The amine of the reporter group (a nitroaniline unit) was a constituent part of a carbamate that functioned as the self-immolative unit. The number and position of substituents on the nitroaniline unit were found to play a key role in the rate of self-immolative degradation and release of the reporter group. The position of the nitro substituent (meta- vs para-) and the methyl groups in the ortho-position relative to the carbamate exhibited an influence on the rate of elimination and stability of the self-immolative system. The ortho-methyl substituents imparted a twist on the N-C (aromatic) bond leading to increased resonance of the amine nitrogen's lone pair into the carbonyl moiety and a decrease of the leaving character of the carbamate group; concomitantly, this may also make it a less electron-withdrawing group and lead to less acidification of the eliminated ß-hydrogen.

Multiple Roles of 1,4-Diazabicyclo[2.2.2]octane in the Solvothermal Synthesis of Iodobismuthates.

Hybrid bismuth-containing halides are emerging as alternative candidates to lead-containing perovskites for light-harvesting applications, as Bi3+ is isoelectronic with Pb2+ and the presence of an active lone pair of electrons is expected to result in outstanding charge-carrier transport properties. Here, we report a family of one binary and three ternary iodobismuthates containing 1,4-diazabicyclo[2.2.2]octane (DABCO). These materials have been prepared solvothermally and their crystal structures, thermal stability, and optical properties determined. Reactions carried out in the presence of bismuth iodide and DABCO produced (C6H12N2)BiI3 (1), which consists of hybrid ribbons in which pairs of edge-sharing bismuth octahedra are linked by DABCO ligands. Short I···I contacts give rise to a three-dimensional network. Similar reactions in the presence of copper iodide produced (C8H17N2)2Bi2Cu2I10 (2) and [(C6H13N2)2BiCu2I7](C2H5OH) (3) in which either ethylated DABCO cations (EtDABCO)+ or monoprotonated DABCO cations (DABCOH)+ are coordinated to copper in discrete tetranuclear and trinuclear clusters, respectively. In the presence of potassium iodide, a unique three-dimensional framework, (C6H14N2)[(C6H12N2)KBiI6] (4), was formed, which contains one-dimensional hexagonal channels approximately 6 Å in diameter. The optical band gaps of these materials, which are semiconductors, range between 1.82 and 2.27 eV, with the lowest values found for the copper-containing discrete clusters. Preliminary results on the preparation of thin films are presented.

Intra- and Interchain Interactions in (Cu1/2Au1/2)CN, (Ag1/2Au1/2)CN, and (Cu1/3Ag1/3Au1/3)CN and Their Effect on One-, Two-, and Three-Dimensional Order.

Mixed-metal cyanides (Cu1/2Au1/2)CN, (Ag1/2Au1/2)CN, and (Cu1/3Ag1/3Au1/3)CN adopt an AuCN-type structure in which metal-cyanide chains pack on a hexagonal lattice with metal atoms arranged in sheets. The interactions between and within the metal-cyanide chains are investigated using density functional theory (DFT) calculations, 13C solid-state NMR (SSNMR), and X-ray pair distribution function (PDF) measurements. Long-range metal and cyanide order is found within the chains: (-Cu-NC-Au-CN-)∞, (-Ag-NC-Au-CN-)∞, and (-Cu-NC-Ag-NC-Au-CN-)∞. Although Bragg diffraction studies establish that there is no long-range order between chains, X-ray PDF results show that there is local order between chains. In (Cu1/2Au1/2)CN and (Ag1/2Au1/2)CN, there is a preference for unlike metal atoms occurring as nearest neighbors within the metal sheets. A general mathematical proof shows that the maximum average number of heterometallic nearest-neighbor interactions on a hexagonal lattice with two types of metal atoms is four. Calculated energies of periodic structural models show that those with four unlike nearest neighbors are most favorable. Of these, models in space group Immm give the best fits to the X-ray PDF data out to 8 Å, providing good descriptions of the short- and medium-range structures. This result shows that interactions beyond those of nearest neighbors must be considered when determining the structures of these materials. Such interactions are also important in (Cu1/3Ag1/3Au1/3)CN, leading to the adoption of a structure in Pmm2 containing mixed Cu-Au and Ag-only sheets arranged to maximize the numbers of Cu···Au nearest- and next-nearest-neighbor interactions.

A macrocyclic receptor containing two viologen species connected by conjugated terphenyl groups.

A macrocyclic receptor molecule containing two viologen species connected by conjugated terphenyl groups has been designed and synthesised. The single-crystal X-ray structure shows that the two viologen residues have a transannular NN separation of ca. 7.4 Å. Thus, the internal cavity dimensions are suitable for the inclusion of π-electron-rich species. The macrocycle is redox active, and can accept electrons from suitable donor species including triethylamine, resulting in a dramatic colour change from pale yellow to dark green as a consequence of the formation of a paramagnetic bis(radical cationic) species. Cyclic voltammetry shows that the macrocycle can undergo two sequential and reversible reduction processes (E1/2 = -0.65 and -0.97 V vs. Fc/Fc+). DFT and TD-DFT studies accurately replicate the structure of the tetracationic macrocycle and the electronic absorption spectra of the three major redox states of the system. These calculations also showed that during electrochemical reduction, the unpaired electron density of the radical cations remained relatively localised within the heterocyclic rings. The ability of the macrocycle to form supramolecular complexes was confirmed by the formation of a pseudorotaxane with a guest molecule containing a π-electron-rich 1,5-dihydroxynaphthalene derivative. Threading and dethreading of the pseudorotaxane was fast on the NMR timescale, and the complex exhibited an association constant of 150 M-1 (±30 M-1) as calculated from 1H NMR titration studies.

Local and average structure in zinc cyanide: toward an understanding of the atomistic origin of negative thermal expansion.

Neutron diffraction at 11.4 and 295 K and solid-state (67)Zn NMR are used to determine both the local and the average structures in the disordered, negative thermal expansion (NTE) material, Zn(CN)2. Solid-state NMR not only confirms that there is head-to-tail disorder of the C≡N groups present in the solid, but yields information about the relative abundances of the different Zn(CN)4­n(NC)n tetrahedral species, which do not follow a simple binomial distribution. The Zn(CN)4 and Zn(NC)4 species occur with much lower probabilities than are predicted by binomial theory, supporting the conclusion that they are of higher energy than the other local arrangements. The lowest energy arrangement is Zn(CN)2(NC)2. The use of total neutron diffraction at 11.4 K, with analysis of both the Bragg diffraction and the derived total correlation function, yields the first experimental determination of the individual Zn­N and Zn­C bond lengths as 1.969(2) and 2.030(2) Å, respectively. The very small difference in bond lengths, of ~0.06 Å, means that it is impossible to obtain these bond lengths using Bragg diffraction in isolation. Total neutron diffraction also provides information on both the average and the local atomic displacements responsible for NTE in Zn(CN)2. The principal motions giving rise to NTE are shown to be those in which the carbon and nitrogen atoms within individual Zn­C≡N­Zn linkages are displaced to the same side of the Zn···Zn axis. Displacements of the carbon and nitrogen atoms to opposite sides of the Zn···Zn axis, suggested previously in X-ray studies as being responsible for NTE behavior, in fact make negligible contributions at temperatures up to 295 K.

Mixed copper, silver, and gold cyanides, (M(x)M'(1-x))CN: tailoring chain structures to influence physical properties.

Binary mixed-metal variants of the one-dimensional MCN compounds (M = Cu, Ag, and Au) have been prepared and characterized using powder X-ray diffraction, vibrational spectroscopy, and total neutron diffraction. A solid solution with the AgCN structure exists in the (Cu(x)Ag(1-x))CN system over the range (0 ≤ x ≤ 1). Line phases with compositions (Cu(1/2)Au(1/2))CN, (Cu(7/12)Au(5/12))CN, (Cu(2/3)Au(1/3))CN, and (Ag(1/2)Au(1/2))CN, all of which have the AuCN structure, are found in the gold-containing systems. Infrared and Raman spectroscopies show that complete ordering of the type [M-C≡N-M'-N≡C-](n) occurs only in (Cu(1/2)Au(1/2))CN and (Ag(1/2)Au(1/2))CN. The sense of the cyanide bonding was determined by total neutron diffraction to be [Ag-NC-Au-CN-](n) in (Ag(1/2)Au(1/2))CN and [Cu-NC-Au-CN-](n) in (Cu(1/2)Au(1/2))CN. In contrast, in (Cu(0.50)Ag(0.50))CN, metal ordering is incomplete, and strict alternation of metals does not occur. However, there is a distinct preference (85%) for the N end of the cyanide ligand to be bonded to copper and for Ag-CN-Cu links to predominate. Contrary to expectation, aurophilic bonding does not appear to be the controlling factor which leads to (Cu(1/2)Au(1/2))CN and (Ag(1/2)Au(1/2))CN adopting the AuCN structure. The diffuse reflectance, photoluminescence, and 1-D negative thermal expansion (NTE) behaviors of all three systems are reported and compared with those of the parent cyanide compounds. The photophysical properties are strongly influenced both by the composition of the individual chains and by how such chains pack together. The NTE behavior is also controlled by structure type: the gold-containing mixed-metal cyanides with the AuCN structure show the smallest contraction along the chain length on heating.

Structures of Pd(CN)2 and Pt(CN)2: intrinsically nanocrystalline materials?

Analysis and modeling of X-ray and neutron Bragg and total diffraction data show that the compounds referred to in the literature as "Pd(CN)(2)" and "Pt(CN)(2)" are nanocrystalline materials containing small sheets of vertex-sharing square-planar M(CN)(4) units, layered in a disordered manner with an intersheet separation of ~3.44 Å at 300 K. The small size of the crystallites means that the sheets' edges form a significant fraction of each material. The Pd(CN)(2) nanocrystallites studied using total neutron diffraction are terminated by water and the Pt(CN)(2) nanocrystallites by ammonia, in place of half of the terminal cyanide groups, thus maintaining charge neutrality. The neutron samples contain sheets of approximate dimensions 30 Å × 30 Å. For sheets of the size we describe, our structural models predict compositions of Pd(CN)(2)·xH(2)O and Pt(CN)(2)·yNH(3) (x ≈ y ≈ 0.29). These values are in good agreement with those obtained from total neutron diffraction and thermal analysis, and are also supported by infrared and Raman spectroscopy measurements. It is also possible to prepare related compounds Pd(CN)(2)·pNH(3) and Pt(CN)(2)·qH(2)O, in which the terminating groups are exchanged. Additional samples showing sheet sizes in the range ~10 Å × 10 Å (y ~ 0.67) to ~80 Å × 80 Å (p = q ~ 0.12), as determined by X-ray diffraction, have been prepared. The related mixed-metal phase, Pd(1/2)Pt(1/2)(CN)(2)·qH(2)O (q ~ 0.50), is also nanocrystalline (sheet size ~15 Å × 15 Å). In all cases, the interiors of the sheets are isostructural with those found in Ni(CN)(2). Removal of the final traces of water or ammonia by heating results in decomposition of the compounds to Pd and Pt metal, or in the case of the mixed-metal cyanide, the alloy, Pd(1/2)Pt(1/2), making it impossible to prepare the simple cyanides, Pd(CN)(2), Pt(CN)(2), or Pd(1/2)Pt(1/2)(CN)(2), by this method.

Effect of the 2-R-Allyl and Chloride Ligands on the Cathodic Paths of [Mo(η3-2-R-allyl)(α-diimine)(CO)2Cl] (R = H, CH3; α-diimine = 6,6'-Dimethyl-2,2'-bipyridine, Bis(p-tolylimino)acenaphthene).

The new, formally Mo(II) complexes [Mo(η3-2-R-allyl)(6,6'-dmbipy)(CO)2Cl] (6,6'-dmbipy = 6,6'-dimethyl-2,2'-bipyridine; 2-R-allyl = allyl for R = H, 2-methallyl for R = CH3) and [Mo(η3-2-methallyl)(pTol-bian)(CO)2Cl] (pTol-bian = bis(p-tolylimino)acenaphthene) share, in this rare case, the same structural type. The effect of the anionic π-donor ligand X (Cl- vs NCS-) and the 2-R-allyl substituents on the cathodic behavior was explored. Both ligands play a significant role at all stages of the reduction path. While 2e--reduced [Mo(η3-allyl)(6,6'-dmbipy)(CO)2]- is inert when it is ECE-generated from [Mo(η3-allyl)(6,6'-dmbipy)(CO)2(NCS)], the Cl- ligand promotes Mo-Mo dimerization by facilitating the nucleophilic attack of [Mo(η3-allyl)(6,6'-dmbipy)(CO)2]- at the parent complex at ambient temperature. The replacement of the allyl ligand by 2-methallyl has a similar effect. The Cl-/2-methallyl ligand assembly destabilizes even primary radical anions of the complex containing the strongly π-accepting pTol-Bian ligand. Under argon, the cathodic paths of [Mo(η3-2-R-allyl)(6,6'-dmbipy)(CO)2Cl] terminate at ambient temperature with 5-coordinate [Mo(6,6'-dmbipy)(CO)3]2- instead of [Mo(η3-2-R-allyl)(6,6'-dmbipy)(CO)2]-, which is stabilized in chilled electrolyte. [Mo(η3-allyl)(6,6'-dmbipy)(CO)2]- catalyzes CO2 reduction only when it is generated at the second cathodic wave of the parent complex, while [Mo(η3-2-methallyl)(6,6'-dmbipy)(CO)2]- is already moderately active at the first cathodic wave. This behavior is fully consistent with absent dimerization under argon on the cyclic voltammetric time scale. The electrocatalytic generation of CO and formate is hampered by the irreversible formation of anionic tricarbonyl complexes replacing reactive [Mo(η3-2-methallyl)(6,6'-dmbipy)(CO)2]2 along the cathodic route.

Helices, chirality and interpenetration: the versatility and remarkable interconversion of silver-copper cyanide frameworks.

The structural transformations between cesium silver-copper cyanides under modest conditions, both in solution and in the solid state, are described. Three new cesium silver(I) copper(I) cyanides with three-dimensional (3-D) framework structures were prepared as single crystals from a one-pot reaction initially heated under hydrothermal conditions. The first product to appear, Cs(3)Ag(2)Cu(3)(CN)(8) (I), when left in contact with the supernatant produced CsAgCu(CN)(3) (II) and CsAgCu(CN)(3).1/3H(2)O (III) over a few months via a series of thermodynamically controlled cascade reactions. Crystals of the hydrate (III) can be dehydrated to polycrystalline CsAgCu(CN)(3) (II) on heating at 100 degrees C in a remarkable solid-state transformation involving substantial breaking and reconnection of metal-cyanide linkages. Astonishingly, the conversion between the two known polymorphs of CsAg(2)Cu(CN)(4), which also involves a major change in connectivity and topology, occurs at 180 degrees C as a single-crystal to single-crystal transformation. Structural features of note in these materials include the presence of helical copper-cyanide chains in (I) and (II), which in the latter compound produce a chiral material. In (II) and (III), the silver-copper cyanide networks are both self- and interpenetrating, features also seen in the known polymorphs of CsAg(2)Cu(CN)(4).

Enantioselective intramolecular michael addition of nitronates onto conjugated esters: access to cyclic gamma-amino acids with up to three stereocenters.

A highly stereoselective synthesis of conformationally constrained cyclic gamma-amino acids has been devised. The key step involves an intramolecular cyclization of a nitronate onto a conjugated ester, promoted by a bifunctional thiourea catalyst. This methodology has been successfully applied to generate a variety of gamma-amino acids, including some containing three contiguous stereocenters, with very high diastereoselectivity and excellent enantioselectivity. It is postulated that an interaction that is key to the success of the process is the simultaneous coordination of the thiourea functionality to both the conjugated ester and the nitronate. Finally, the synthetic utility of these compounds is demonstrated in the synthesis of two dipeptides derived from the C- and N-termini.

Bis[bis(methoxycarbimido)aminato]copper(II) 1-methylpyrrolidin-2-one disolvate.

The title compound, [Cu(C(4)H(8)N(3)O(2))(2)].2C(5)H(9)NO, consists of a neutral copper complex, in which the Cu(II) centre coordinates to two bis(methoxycarbimido)aminate ligands, solvated by two molecules of 1-methylpyrrolidin-2-one. The complex is planar and centrosymmetric, with the Cu(II) centre occupying a crystallographic inversion centre and adopting approximately square-planar geometry. N-H...O hydrogen-bonding interactions exist between the amine NH groups of the ligands and the O atoms of the 1-methylpyrrolidin-2-one molecules. The associated units pack to form sheets.

Dicopper(II) trihydroxide cyanoureate dihydrate.

The title compound, poly[[mu-cyanoureato-tri-mu-hydroxido-dicopper(II)] dihydrate], {[Cu(2)(C(2)H(2)N(3)O)(OH)(3)].2H(2)O}(n), is a new layered copper(II) hydroxide salt (LHS) with cyanoureate ions and water molecules in the interlayer space. The three distinct copper(II) ions have distorted octahedral geometry: one Cu (symmetry 1) is coordinated to six hydroxide groups (4OH + 2OH), whilst the other two Cu atoms (symmetries 1 and 1) are coordinated to four hydroxides and two N atoms from nitrile groups of the cyanoureate ions (4OH + 2N). The structure is held together by hydrogen-bonding interactions between the terminal -NH(2) groups and the central cyanamide N atoms of organic anions associated with neighbouring layers.

Potassium nickel(II) gallium phosphate hydrate, K[NiGa(2)(PO(4))(3)(H(2)O)(2)].

The title compound, potassium nickel(II) digallium tris-(phosphate) dihydrate, K[NiGa(2)(PO(4))(3)(H(2)O)(2)], was synthesized hydro-thermally. The structure is constructed from distorted trans-NiO(4)(H(2)O)(2) octa-hedra linked through vertices and edges to GaO(5) trigonal bipyramids and PO(4) tetra-hedra, forming a three-dimensional framework of formula [NiGa(2)(PO(4))(3)(H(2)O)(2)](-). The K, Ni and one P atom lie on special positions (Wyckoff position 4e, site symmetry 2). There are two sets of channels within the framework, one running parallel to the [10] direction and the other parallel to [001]. These inter-sect, forming a three-dimensional pore network in which the water mol-ecules coordinated to the Ni atoms and the K(+) ions required to charge balance the framework reside. The K(+) ions lie in a highly distorted environment surrounded by ten O atoms, six of which are closer than 3.1Å. The coordinated water mol-ecules are within hydrogen-bonding distance to O atoms of bridging Ga-O-P groups.

A crystallographic and theoretical study of an (E)-2-Hydroxyiminoethanone derivative: prediction of cyclooxygenase inhibition selectivity of stilbenoids by MM-PBSA and the role of atomic charge.

We recently reported that the hydroxyiminoethanone derivative, (E)-OXM, behaves as a highly selective COX-1 inhibitor (COX-1 SI = 833), and also an interesting scaffold with unique characteristics. In the current study, a comprehensive crystallographic and computational study was performed to elucidate its conformational stability and pharmacological activity. Its conformational energy was studied at the B3LYP/6-311G** level of theory and compared to the single-crystal X-ray diffraction data. In addition, computational studies of three structurally different stilbenoid derivatives used as selective COX-1 or COX-2 inhibitors were undertaken to predict their COX selectivity potentials. Flexible docking was performed for all compounds at the active site of both COX-1 and COX-2 enzymes by considering some of the key residues as flexible during the docking operation. In the next step, molecular dynamic simulation and binding free energy calculations were performed by MM-PBSA. Final results were found to be highly dependent on the atomic charges of the inhibitors and the choice of force field used to calculate the atomic charges. The binding conformation of the hydroxyiminoethanone derivative is highly correlated with the type of COX isoform inhibited. Our predictive approach can truly predict the cyclooxygenase inhibition selectivity of stilbenoid inhibitors.

Discovery of novel 1,2,4-triazolo-1,2,4-triazines with thiomethylpyridine hinge binders as potent c-Met kinase inhibitors.

Aim: Mesenchymal-epithelial transition factor (c-Met)/HGF overactivation is involved in diverse human cancers. Materials & methods: Herein, we report the synthesis and biological evaluation of thiomethylpyridine-linked triazolotriazines as c-Met kinase inhibitors. Results: Compounds 10b and 11e were more potent than crizotinib on HepG2 cells with IC50 values of 0.74 and 0.71 µM in the MTT assay, respectively. Interestingly, all of the target compounds displayed IC50 values in the range of 3.9-11.1 nM in the c-Met kinase inhibition assay which were lower than the value for crizotinib (11.1 nM). Conclusion: Target compound 10b can be considered as a leading drug candidate due to its lower IC50 values than crizotinib in both HGF-induced proliferation and c-Met kinase inhibition assays.

Crystallization and lamellar nanosheet formation of an aromatic dipeptoid.

An aromatic peptoid analogue of the diphenylalanine dipeptide self-assembles in aqueous solution and the first crystal structure was obtained for this class of compound. This reveals molecular packing stabilized by networks of hydrogen bonds. Free-floating nanosheet lamellar structures are observed in solution, which form via cooperative intermolecular interactions driven by π stacking.

Simple linear asymmetrical complexes of silver(I): NC-Ag-NH3 and Br-Ag-NH3.

The compounds Ag(CN)(NH(3)) and Ag(Br)(NH(3)) are remarkable in that they form solids containing the simple molecular units NC-Ag-NH(3) and Br-Ag-NH(3), rather than extended solids, and are the first examples of simple linear asymmetric complexes of silver(I).

A tungsten complex containing a highly delocalized metal-ligand system.

Nucleophilic attack of (triphenylphosphonio)cyclopentadienide on the dichlorodiazomethane-tungsten complex trans-[BrW(dppe)(2)(N(2)CCl(2))]PF(6) [dppe is 1,2-bis(diphenylphosphino)ethane] results in C-C bond formation and affords the title compound, trans-[W(C(24)H(18)ClN(2)P)Br(C(26)H(24)P(2))(2)]PF(6) x 0.6CH(2)Cl(2). This complex, bis[1,2-bis(diphenylphosphino)ethane]bromido{chloro[3-(triphenylphosphonio)cyclopentadienylidene]diazomethanediido}tungsten hexafluorophosphate dichloromethane 0.6-solvate, contains the previously unknown ligand chloro[3-(triphenylphosphonio)cyclopentadienylidene]diazomethane. Evidence from bond lengths and torsion angles indicates significant through-ligand delocalization of electron density from tungsten to the nominally cationic phosphorus(V) centre. This structural analysis clearly demonstrates that the tungsten-dinitrogen unit is a powerful pi-electron donor with the ability to transfer electron density from the metal to a distant acceptor centre through an extended conjugated ligand system. As a consequence, complexes of this type could have potential applications as nonlinear optical materials and molecular semiconductors.