2,2',5,5'-Tetra-chloro-benzidine.

In the crystal structure of the title compound, C(12)H(8)Cl(4)N(2), mol-ecules lie on crystallographic twofold axes at the centre of the C-C bonds linking the benzene rings, such that the asymmetric unit consists of a half-mol-ecule. The individual mol-ecules participate in inter-molecular N-H⋯N, N-H⋯Cl, C-H⋯Cl and Cl⋯Cl [3.4503 (3) Å] inter-actions.

2,4,6-Triphenyl-aniline.

Individual mol-ecules of the title compound, C(24)H(19)N, do not participate in hydrogen-bonding inter-actions due to the steric bulk of the phenyl rings ortho to the amine. The dihedral angles between the central ring and the pendant rings are 68.26 (10), 55.

Guest inclusion and structural dynamics in 2-D hydrogen-bonded metal-organic frameworks.

The structures and dynamic solid-state behavior of four hydrogen-bonded layered metal-organic frameworks are discussed. Three of the complexes incorporate acetone guest molecules between layers; this is attributed to added flexibility in a framework ammonium component. One complex incorporates water guests, in this case an additional -CH(2)OH arm present on the ammonium component accounting for the difference in guest and dynamic behavior.

From crystal engineering to cluster engineering: How to transform cadmium chloride from 2-D to 0-D.

The transformation of a 2-D perovskite structure to "expanded" 2-D and finally to a 0-D hexanuclear cadmium chloride cluster by varying the size of substituents on the associated counterions (H vs. methyl vs. ethyl) is described.

Properties of a mixed-valence (Fe(II))2(Fe(III))2 square cell for utilization in the quantum cellular automata paradigm for molecular electronics.

The di-mixed-valence complex [{(eta(5)-C5H5)Fe(eta(5)-C5H4)}4(eta(4)-C4)Co(eta(5)-C5H5)]2+, 1(2+), has been evaluated as a molecular four-dot cell for the quantum cellular automata paradigm for electronic devices. The cations 1(1+) and 1(2+) are prepared in good yield by selective chemical oxidation of 1(0) and are isolated as pure crystalline materials. The solid-state structures of 1(0) and 1(1+) and the midrange- and near-IR spectra of 1(0), 1(1+), 1(2+), and 1(3+) have been determined.

Molecular recognition of trigonal oxyanions using a ditopic salt receptor: evidence for anisotropic shielding surface around nitrate anion.

A ditopic, macrobicyclic receptor with adjacent anion and cation binding sites is able to extract a range of monovalent salts into chloroform solution. The structures of the receptor complexed with KAcO, LiNO(3), NaNO(3), KNO(3), and NaNO(2) are characterized in solution by NMR spectroscopy and in the solid state by X-ray crystallography. The sodium and potassium salts are bound to the receptor as contact ion-pairs, with the metal cation located in the receptor's crown ether ring and the trigonal oxyanion hydrogen bonded to the receptor NH residues.

Selective solid-liquid extraction of lithium halide salts using a ditopic macrobicyclic receptor.

A ditopic salt receptor that is known to bind and extract solid NaCl, KCl, NaBr, and KBr into organic solution as their contact ion pairs is now shown by NMR and X-ray crystallography to bind and extract solid LiCl and LiBr as water-separated ion pairs. The receptor can transport these salts from an aqueous phase through a liquid organic membrane with a cation selectivity of K+ > Na+ > Li+. However, the selectivity order is strongly reversed when the receptor extracts solid alkali metal chlorides and bromides into organic solution.

Transport of alkali halides through a liquid organic membrane containing a ditopic salt-binding receptor.

A ditopic receptor is shown to have an impressive ability to recognize and extract the ion pairs of various alkali halides into organic solution. X-ray diffraction analysis indicates that the salts are bound in the solid state as contact ion pairs. Transport experiments, using a supported liquid membrane and high salt concentration in the source phase, show that the ditopic receptor can transport alkali halide salts up to 10-fold faster than a monotopic cation or anion receptor and 2-fold faster than a binary mixture of cation and anion receptors.

Proton control of oxidation and spin state in a series of iron tripodal imidazole complexes.

Reaction of iron salts with three tripodal imidazole ligands, H(3)(1), H(3)(2), H(3)(3), formed from the condensation of tris(2-aminoethyl)amine (tren) with 3 equiv of an imidazole carboxaldehyde yielded eight new cationic iron(III) and iron(II), [FeH(3)L](3+or2+), and neutral iron(III), FeL, complexes. All complexes were characterized by EA(CHN), IR, UV, Mössbauer, mass spectral techniques and cyclic voltammetry. Structures of three of the complexes, Fe(2).

Synthesis and characterization of hypoelectronic rhenaboranes. Analysis of the geometric and electronic structures of species following neither borane nor metal cluster electron-counting paradigms.

The reaction of (CpReH(2))(2)B(4)H(4) with monoborane leads to the sequential formation of (CpRe)(2)B(n)()H(n)() (n = 7-10, 1-4). These species adopt closed deltahedra with the same total connectivities as the closo-borane anions [B(n)()H(n)()](2)(-), n = 9-12, but with flattened geometries rather than spherical shapes. These rhenaborane clusters are characterized by high metal coordination numbers, Re-Re cross-cluster distances within the Re-Re single bond range, and formal cluster electron counts three skeletal electron pairs short of that required for a canonical closo-structure of the same nuclearity.

Ruthenacarboranes from the reaction of nido-1,2-(Cp*RuH)2B3H7 with HC [triple bond] CCO2Me, Cp* = eta5-C5Me5. Hydrometalation, alkyne incorporation, and functional group modification via cooperative metal-boron interactions within a metallaborane cluster framework.

Reaction of nido-1,2-(Cp*RuH)2B3H7, 1, and methyl acetylene monocarboxylate under kinetic control generates nido-1,2-(Cp*Ru)2(mu-C[[CO2Me]Me])B3H7 (a pair of geometric isomers, 3 and 5) and nido-1,2-(Cp*Ru)2(1,3-mu-C[[CH2CO2Me]H])B3H7, 4, which display the first examples of exo-cluster mu-alkylidene Ru-B bridges generated by hydrometalation of an alkyne on the cluster framework. Both 3 and 5, but not 4, rearrange into arachno-2,8-mu(C)-5-eta1(O)-Me[CO2Me]C-1,2-(Cp*Ru)2B3H7, 2, in which an unprecedented intramolecular coordination of the carbonyl oxygen atom of the alkyne substituent to a boron framework site opens the ruthenaborane skeleton. Compound 2, in turn, is an intermediate in the formation of the ruthenacarborane nido-1,2-(Cp*Ru)2-3-OH-4-OMe-5-Me-4,5-C2B2H5, 12, in which the carbonyl-oxygen double bond has been cleaved as its oxygen atom inserts into a B-H bond and the carbonyl carbon inserts into the metallaborane framework.

Molecular recognition of alkylammonium contact ion-pairs using a ditopic receptor.

A ditopic, macrobicyclic receptor with adjacent anion and cation binding sites is able to distinguish between various monoalkylammonium salts by binding them as contact ion-pairs. The affinity for linear n-propylammonium chloride is at least 2 orders of magnitude greater than that for n-propylammonium acetate, n-propylammonium p-toluenesulfonate, and branched isopropylammonium chloride. An X-ray structure of the receptor complexed with methylammonium chloride illuminates the basis of the molecular recognition.

Molecular QCA cells. 1. Structure and functionalization of an unsymmetrical dinuclear mixed-valence complex for surface binding.

Utilization of binary information encoded in the charge configuration of quantum-dot cells (the quantum-dot cellular automata, QCA, paradigm) requires molecule-sized dots for room temperature operation. Molecular QCA cells are mixed-valence complexes, and the evaluation and functionalization of an unsymmetrical heterobinuclear, two-dot, Fe-Ru molecular QCA cell is described. The solid state structures of trans-RuCl(dppm)(2)(C[triple bond]CFc) (1) (dppm = methylbis(diphenylphosphane), Fc = (eta(5)-C(5)H(5))Fe(eta(5)-C(5)H(4))) and mixed-valence [trans-RuCl(dppm)(2)(C[triple bond]CFc)][BF(4)] (1a) as well as XPS and spectroscopic data suggest class II behavior suitable for the intended application.

Effect of the sixth axial ligand in CS-ligated iron(II)octaethylporphyrinates: structural and Mössbauer studies.

The effect of a sixth ligand in a series of low-spin thiocarbonyl-ligated iron(II)octaethylporphyrinates has been investigated. Six-coordinate complexes have been synthesized and characterized by Mössbauer and infrared spectroscopy and single-crystal X-ray structure determinations. The results are compared with the five-coordinate parent complex.

Building blocks for the molecular expression of quantum cellular automata. Isolation and characterization of a covalently bonded square array of two ferrocenium and two ferrocene complexes.

The suitability of [{(eta5-C5H5)Fe(eta5-C5H4)}4(eta4-C4)Co(eta5-C5H5)][PF6]2, [1][PF6]2, for use as a molecular quantum cellular automata (QCA) cell is demonstrated. To this end the structure of 1 in the solid state and the conversion of 1 to mono- and dicationic mixed-valence complexes have been accomplished. The latter compounds have been isolated as pure materials and characterized by IR, EPR, and Mössbauer spectroscopies and single-crystal XRD (monocation only) and magnetic susceptibility measurements.

A high-yielding supramolecular reaction.

The X-ray crystal structure determinations of twelve cocrystals involving iso-nicotinamide and a variety of carboxylic acids have revealed a very consistent pattern of hydrogen-bond preferences. The combination of a monocarboxylic acid, an amide, and a pyridine moiety leads, in every case, to discrete "supermolecules" (consisting of two molecules of iso-nicotinamide and two molecules of the relevant carboxylic acid) with well-defined and robust connectivity. The two dominant (regularly occurring) supramolecular synthons in these crystal structures are (1) the heteromeric carboxylic acid.

Solution and solid-state models of peptide CH...O hydrogen bonds.

Fumaramide derivatives were analyzed in solution by (1)H NMR spectroscopy and in the solid state by X-ray crystallography in order to characterize the formation of CH...

Crystal engineering of organic clay mimics from 3,5-pyrazoledicarboxylic acid and amines.

The syntheses and crystal structures of sixteen compounds containing the monoanion of 3,5-pyrazoledicarboxylic acid (H(2)PzDCA) and ammonium-based counterions are reported. The cations contain short-chain alkyl, long-chain alkyl, phenyl, and chloro-, methoxy-, and amine-substituted aryl groups. Self-complementary HPzDCA intermolecular hydrogen bonds create nearly planar sheets, to which the cations connect through hydrogen bonds.

Facile hydrometalation of alkynes by nido-1,2-(CpRuH)(2)B(3)H(7) yielding novel Ru-B edge-bridging alkylidenes. Stepwise conversion of HCtbd1;CC(O)OMe into nido-1,2-(CpRuH)(2)-3-HOB-4-MeC-5-MeOC-BH(3), Cp = eta(5)-C(5)Me(5).

The reaction of the alkyne HCCC(O)OMe with 7 sep 1,2-(Cp*RuH)2B3H7 leads to hydroboration plus hydroruthenation to produce nido-1,3-mu-Me{C(O)OMe}C-1,2-(Cp*Ru)2B3H7, a compound with an exocluster ruthenium-boron mu-alkylidene that exists in two isomeric forms. Both isomers undergo rearrangement with intramolecular chelation of the carbonyl oxygen at a boron site, thereby opening the cluster and generating arachno-2,3,-mu(C)-5-eta1(O)-Me{C(O)OMe}C-1,2-(Cp*Ru)2B3H7. Further heating leads to deoxygenation of the carbonyl fragment by a boron center concurrent with insertion of the carbon atom into the metallaborane cage to give nido-1,2-(Cp*RuH)2-3-HOB-4-MeC-5-MeOC-BH3.

Structure/activity study of tris(2-aminoethyl)amine-derived translocases for phosphatidylcholine.

Sulfonamide and amide derivatives of tris(aminoethyl)amine (TREN) are known to facilitate phospholipid translocation across vesicle and erythrocyte membranes; that is, they act as synthetic translocases. In this report, a number of new TREN-based translocases are evaluated for their abilities to bind phosphatidylcholine and translocate a fluorescent phosphatidylcholine probe. Association constants were determined from (1)H NMR titration experiments, and translocation half-lives were determined via 7-nitrobenz-2-oxa-1,3-diazol-4-yl (NBD)/dithionite quenching assays.

Templated conversion of a crown ether-containing macrobicycle into [2]rotaxanes.

A crown ether-containing macrobicycle was used as the wheel component in a templated synthesis of a [2]rotaxane with an acetal-containing axle. The molecular structures of the macrobicycle and the [2]rotaxane were characterized by NMR spectroscopy and X-ray crystallography. The chloride-binding ability of the macrobicycle, either free in solution or when it is part of a [2]rotaxane, is quite weak as determined by NMR titration experiments.