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1.
ACS Appl Mater Interfaces ; 11(40): 36886-36894, 2019 Oct 09.
Artigo em Inglês | MEDLINE | ID: mdl-31522492

RESUMO

Developing molecular circuits that can function as the active components in electrical devices is an ongoing challenge in molecular electronics. It demands mechanical stability of the single-molecule circuit while simultaneously being responsive to external stimuli mimicking the operation of conventional electronic components. Here, we report single-molecule circuits based on spiropyran derivatives that respond electrically to chemical and mechanical stimuli. The merocyanine that results from the protonation/ring-opening of the spiropyran form showed single-molecule diode characteristics, with an average current rectification ratio of 5 at ±1 V, favoring the orientation where the positively charged end of the molecule is attached to the negative terminal of the circuit. Mechanical pulling of a single spiropyran molecule drives a switch to a more conducting merocyanine state. The mechanical switching is enabled by the strong Au-C covalent bonding between the molecule and the electrodes, which allows the tensile force delivered by the STM piezo to break the molecule at its spiropyran C-O bond.

2.
Angew Chem Int Ed Engl ; 58(30): 10255-10259, 2019 07 22.
Artigo em Inglês | MEDLINE | ID: mdl-31136063

RESUMO

The observation of an unusual crystal habit in the common diuretic drug hydrochlorothiazide (HCT), and identification of its subtle conformational chirality, has stimulated a detailed investigation of its crystalline forms. Enantiomeric conformers of HCT resolve into an unusual structure of conjoined enantiomorphic twin crystals comprising enantiopure domains of opposite chirality. The purity of the domains and the chiral molecular conformation are confirmed by spatially revolved synchrotron micro-XRD experiments and neutron diffraction, respectively. Macroscopic inversion twin symmetry observed between the crystal wings suggests a pseudoracemic structure that is not a solid solution or a layered crystal structure, but an unusual structural variant of conglomerates and racemic twins. Computed interaction energies for molecular pairs in the racemic and enantiopure polymorphs of HCT, and the observation of large opposing unit-cell dipole moments for the enantiopure domains in these twin crystals, suggest a plausible crystal nucleation mechanism for this unusual crystal habit.

3.
Inorg Chem ; 58(6): 3789-3799, 2019 Mar 18.
Artigo em Inglês | MEDLINE | ID: mdl-30835116

RESUMO

Several trinuclear ferrocenes are obtained by Friedel-Crafts reaction of octamethylferrocene with ferrocenoyl chloride and subsequent modifications. 1,1'-Diferrocenoyloctamethylferrocene (3) is transformed to the divinyl derivative (4a) by reaction with MeLi and AlCl3. The reactive 4a cyclizes spontaneously to a [4]ferrocenophane with buta-1,3-diene handle (5) or in the presence of AlCl3 to a [3]ferrocenophane with propene handle (6). Structure assignments are supported by X-ray crystallography and NMR spectroscopy, and mechanisms are proposed. Electrochemical behavior of the compounds was investigated with cyclic voltammetry, and assignments of the redox processes were carried out with the aid of density functional theory calculations. The synthesized compounds and demonstrated transformations represent useful tools for preparation of materials for charge-transport studies in metal-molecule-metal junctions.

4.
J Am Chem Soc ; 141(9): 3965-3976, 2019 03 06.
Artigo em Inglês | MEDLINE | ID: mdl-30761898

RESUMO

High-resolution synchrotron and neutron single-crystal diffraction data of 18-crown-6/(pentakis)urea measured at 30 K are combined, with the aim of better appreciating the electrostatics associated with intermolecular interactions in condensed matter. With two 18-crown-6 molecules and five different urea molecules in the crystal, this represents the most ambitious combined X-ray/synchrotron and neutron experimental charge density analysis to date on a cocrystal or host-guest system incorporating such a large number of unique molecules. The dipole moments of the five urea guest molecules in the crystal are enhanced considerably compared to values determined for isolated molecules, and 2D maps of the electrostatic potential and electric field show clearly how the urea molecules are oriented with dipole moments aligned along the electric field exerted by their molecular neighbors. Experimental electric fields in the range of 10-19 GV m-1, obtained for the five different urea environments, corroborate independent measurements of electric fields in the active sites of enzymes and provide an important experimental reference point for recent discussions focused on electric-field-assisted catalysis.

5.
Dalton Trans ; 46(33): 10899-10907, 2017 Aug 22.
Artigo em Inglês | MEDLINE | ID: mdl-28766632

RESUMO

This paper describes the facile synthesis of a number of electron rich octamethyl[1.4]ferrocenophanes with unsaturated handles from 1,1'-bis(1-chlorovinyl)octamethylferrocene. Treatment of this reactive compound with sodium hydroxide in DMF initiates a series of reactions resulting in the formation of four different ferrocenophanes. The most complex of these products arises from a cascade of cyclisations giving an unusual, unsymmetrical bis-ferrocenophane with a central fused cyclobutene. Control over the reaction outcome is achieved by manipulating the concentration of NaOH. Mechanisms are proposed, and supported by DFT calculations.

6.
Angew Chem Int Ed Engl ; 56(29): 8468-8472, 2017 07 10.
Artigo em Inglês | MEDLINE | ID: mdl-28470995

RESUMO

Bending in molecular crystals is typically associated with the anisotropy of intermolecular interactions. The intriguing observation is reported of plastic bending in dimethyl sulfone, which exhibits nearly isotropic crystal packing and interaction topology, defying the known structural models of bending crystals. The origin of the bending phenomenon has been explored in terms of intermolecular interaction energies, experimental X-ray charge density analysis, and variable temperature neutron diffraction studies. H⋅⋅⋅H dihydrogen interactions and differences in electrostatic complementarity between molecular layers are found to facilitate the bending behavior.

7.
Chem Sci ; 8(12): 8435-8442, 2017 Dec 01.
Artigo em Inglês | MEDLINE | ID: mdl-29619191

RESUMO

The Ley-Griffith reaction is utilized extensively in the selective oxidation of alcohols to aldehydes or ketones. The central catalyst is commercially available tetra-n-propylammonium perruthenate (TPAP, n-Pr4N[RuO4]) which is used in combination with the co-oxidant N-methylmorpholine N-oxide (NMO). Although this reaction has been employed for more than 30 years, the mechanism remains unknown. Herein we report a comprehensive study of the oxidation of diphenylmethanol using the Ley-Griffith reagents to show that the rate determining step involves a single alcohol molecule, which is oxidised by a single perruthenate anion; NMO does not appear in rate law. A key finding of this study is that when pure n-Pr4N[RuO4] is employed in anhydrous solvent, alcohol oxidation initially proceeds very slowly. After this induction period, water produced by alcohol oxidation leads to partial formation of insoluble RuO2, which dramatically accelerates catalysis via a heterogeneous process. This is particularly relevant in a synthetic context where catalyst degradation is usually problematic. In this case a small amount of n-Pr4N[RuO4] must decompose to RuO2 to facilitate catalysis.

8.
Dalton Trans ; 45(47): 18817-18821, 2016 Dec 21.
Artigo em Inglês | MEDLINE | ID: mdl-27774559

RESUMO

This paper describes the facile preparation of 1,1'-diacetyloctamethylferrocene (2) by acylation of octamethylferrocene (1) with acetyl chloride. Chloroformylation with POCl3/DMF of 2 affords a variety of products, including 1,1'-bis-(1-chlorovinyl)octamethylferrocene (3b) in high yield. Compound 3b cyclises in aqueous sodium hydroxide/DMF to an octamethyl[1,4]-ferrocenophane bearing a 1-dimethylaminobuta-1,3-diene-handle (4).

9.
Dalton Trans ; 45(30): 11983-9, 2016 Jul 26.
Artigo em Inglês | MEDLINE | ID: mdl-27385657

RESUMO

Epsilon cobalt (ε-Co) nanoparticles in a number of octahedral morphologies have been synthesised. The particles are polycrystalline, with sizes in the order of 30 nm. Magnetic studies reveal the particles are ferromagnetic, with a room temperature saturation magnetisation of 131 emu g(-1). Unlike other large cubic ε-Co syntheses, we have not added an additional co-surfactant. Instead, we have modified the heating regime and reaction agitation. This alternative method highlights the complex chemistry associated with the formation of cobalt nanoparticles by thermal decomposition.

10.
Dalton Trans ; 44(19): 8812-5, 2015 May 21.
Artigo em Inglês | MEDLINE | ID: mdl-25910077

RESUMO

The inclusion of a ligated ruthenium moiety to ethynyl spiropyran, 5'-ethynyl-1',3',3'-trimethyl-6-nitrospiro[chromene-2,2'-indoline], has been shown to increase the lifetime of the ring-opened merocyanine form twentyfold. Calculations suggest that the higher barrier to thermal reversion of the merocyanine form of the metal alkynyl complex arises from the capacity for greater delocalisation of charge consequent of the presence of the ruthenium moiety. The complex may provide a different switching mechanism to the 5,5'-dithienylperfluorocyclopentene electrode decoupling seen previously.

11.
Acta Crystallogr C Struct Chem ; 71(Pt 3): 188-90, 2015 Mar.
Artigo em Inglês | MEDLINE | ID: mdl-25734847

RESUMO

A previously reported complex, [Ni(C(21)H(21)O(3)P)(3)] or Ni[P(O-o-tolyl(3))(3)] [Gosser & Tolman (1970). Inorg. Chem. 9, 2350-2353], crystallized in the monoclinic space group C2/c, and its solid-state structure was determined. The Ni(0) atom adopts an essentially trigonal-planar geometry as a consequence of the steric congestion of the ligands. Three of the phenoxy rings on two phosphite ligands were modelled as being disordered over two sets of sites, and the occupancy factors were set at 0.5 after trial refinement and intramolecular contact considerations. The exact ligand cone angle has been calculated to be 163.6°.

12.
Dalton Trans ; 44(5): 2132-7, 2015 Feb 07.
Artigo em Inglês | MEDLINE | ID: mdl-25500802

RESUMO

The structure of the oxygen-evolving complex of photosystem II, which contains a cubane-like metal-oxo cluster incorporating four manganese(III,IV) cations, along with a calcium cation, has focussed attention on synthetic analogues of this cluster. Despite this activity, there are relatively few structurally characterised coordination clusters with this combination of metal cations. The calixarenes are synthetically versatile and well established cluster-supporting ligands, which to date have not been reported to support a calcium/manganese cluster. Here we report that p-t-butylthiacalix[4]arene supports CaMn2 and Ca2Mn2 clusters, whereas reactions of p-t-butylcalix[4]arene, p-t-butylsulfinylcalix[4]arene, and p-t-butylsulfonylcalix[4]arene, under the same conditions, produced only homometallic manganese complexes.


Assuntos
Cálcio/química , Calixarenos/química , Manganês/química , Ligantes , Modelos Moleculares , Conformação Molecular
13.
Chemistry ; 20(26): 8089-98, 2014 Jun 23.
Artigo em Inglês | MEDLINE | ID: mdl-24828367

RESUMO

X-ray/neutron (X/N) diffraction data measured at very low temperature (15 K) in conjunction with ab initio theoretical calculations were used to model the crystal charge density (CD) of the host-guest complex of hydroquinone (HQ) and acetonitrile. Due to pseudosymmetry, information about the ordering of the acetonitrile molecules within the HQ cavities is present only in almost extinct, very weak diffraction data, which cannot be measured with sufficient accuracy even by using the brightest X-ray and neutron sources available, and the CD model of the guest molecule was ultimately based on theoretical calculations. On the other hand, the CD of the HQ host structure is well determined by the experimental data. The neutron diffraction data provide hydrogen anisotropic thermal parameters and positions, which are important to obtain a reliable CD for this light-atom-only crystal. Atomic displacement parameters obtained independently from the X-ray and neutron diffraction data show excellent agreement with a |ΔU| value of 0.00058 Å(2) indicating outstanding data quality. The CD and especially the derived electrostatic properties clearly reveal increased polarization of the HQ molecules in the host-guest complex compared with the HQ molecules in the empty HQ apohost crystal structure. It was found that the origin of the increased polarization is inclusion of the acetonitrile molecule, whereas the change in geometry of the HQ host structure following inclusion of the guest has very little effect on the electrostatic potential. The fact that guest inclusion has a profound effect on the electrostatic potential suggests that nonpolarizable force fields may be unsuitable for molecular dynamics simulations of host-guest interaction (e.g., in protein-drug complexes), at least for polar molecules.

14.
Org Lett ; 15(18): 4834-7, 2013 Sep 20.
Artigo em Inglês | MEDLINE | ID: mdl-24006880

RESUMO

A domino alkyne addition/CO insertion/Nu acylation reaction to a series of novel anthrapyran-2-ones in good to excellent yields is described. In addition, an efficient synthetic sequence involving carbonylation, formation of a ß-keto-sulfoxide, and cyclization is presented en route to the antibiotic and antitumor compound (±)-BE-26554A.


Assuntos
Alquinos/química , Antraquinonas/síntese química , Antibacterianos/síntese química , Antineoplásicos/síntese química , Produtos Biológicos/síntese química , Acilação , Antraquinonas/química , Antraquinonas/farmacologia , Antibacterianos/química , Antibacterianos/farmacologia , Antineoplásicos/química , Antineoplásicos/farmacologia , Produtos Biológicos/química , Produtos Biológicos/farmacologia , Catálise , Técnicas de Química Combinatória , Ciclização , Estrutura Molecular , Estereoisomerismo
15.
Dalton Trans ; 42(23): 8188-91, 2013 Jun 21.
Artigo em Inglês | MEDLINE | ID: mdl-23661108

RESUMO

The reaction of 2-pyridyltetrazolate with [Re(CO)5X] (X = Cl, Br) yielded the formation of an unexpected cyclic metallacalix[3]arene, as revealed by X-ray structural studies, characterised by aqua emission and reversible three-electron oxidation.

16.
J Phys Chem A ; 115(45): 12962-72, 2011 Nov 17.
Artigo em Inglês | MEDLINE | ID: mdl-21809888

RESUMO

The crystal structure of the ß-polymorph of hydroquinone (ß-HQ), the apohost of a large family of clathrates, is reported with a specific focus on intermolecular interactions and the electrostatic nature of its cavity. Hirshfeld surface analysis reveals subtle close contacts between two interconnecting HQ networks, and the local packing and related close contacts were examined by breakdown of the fingerprint plot. An experimental multipole model containing anisotropic thermal parameters for hydrogen atoms has been successfully refined against 15(2) K single microcrystal synchrotron X-ray diffraction data. The experimental electron density model has been compared with a theoretical electron density calculated with the molecule embedded in its own crystal field. Hirshfeld charges, interaction energies and the electrostatic potential calculated for both models are qualitatively in good agreement, but small differences in the electrostatic potential persist due to charge transfer from all hydrogen atoms to the oxygen atoms in the theoretical model. The electrostatic potential in the center of the cavity is positive, very shallow and highly symmetric, suggesting that the inclusion of polar molecules in the void will involve a balance between opposing effects. The electric field is by symmetry zero in the center of the cavity, increasing to a value of 0.0185 e/Å(2) (0.27 V/Å) 1 Å along the 3-fold axis and 0.0105 e/Å(2) (0.15 V/Å) 1 Å along the perpendicular direction. While these values are substantial in a macroscopic context, they are quite small for a molecular cavity and are not expected to strongly polarize a guest molecule.


Assuntos
Hidroquinonas/química , Hidroquinonas/síntese química , Substâncias Macromoleculares/síntese química , Substâncias Macromoleculares/química , Modelos Moleculares , Difração de Pó , Teoria Quântica , Eletricidade Estática
17.
Dalton Trans ; 40(16): 4167-74, 2011 Apr 28.
Artigo em Inglês | MEDLINE | ID: mdl-21387073

RESUMO

A variety of Group 10 metal complexes [MXY(dfppp)], M = Ni, X, Y = Cl, Br, M = Pd, Pt, X, Y = Cl or CH(3), containing the recently reported highly fluorous diphosphine ligand, dfppp, 1,3-bis[di(fluoroponytail)phosphino]propane, {(p-F(13)C(6)C(6)H(4))(2)P}(2)(CH(2))(3) have been synthesised. They have been characterised by NMR, mass spectrometry and microanalysis, with two platinum complexes, [PtCl(2)(dfppp)] and [PtClMe(dfppp)], structurally characterised by single crystal X-ray diffraction studies. The highly fluorous nature of the ligands affords the complexes good supercritical CO(2) solubility as measured by supercritical fluid extraction (SFE), and has allowed for the copolymerisation of CO and ethylene using [PdClMe(dfppp)] as the catalyst precursor and CO(2) as the solvent. Additionally, PtCl(2) complexes of the new ligands dfppb, {(p-F(13)C(6)C(6)H(4))(2)P}(2)(CH(2))(4), and dfpop, {(p-F(13)C(6)C(6)H(4)O)(2)P}(2)(CH(2))(3), have also been prepared and characterised.


Assuntos
Dióxido de Carbono/química , Metais Pesados/química , Compostos Organometálicos/química , Pressão , Catálise , Modelos Moleculares , Conformação Molecular , Níquel/química , Paládio/química , Fosfinas/química , Platina/química , Polimerização , Solubilidade
18.
Chem Commun (Camb) ; 47(7): 2029-31, 2011 Feb 21.
Artigo em Inglês | MEDLINE | ID: mdl-21212883

RESUMO

The title compound undergoes two order-disorder transitions between 15 and 299 K, dictated by ordering of the guest molecules in the host cages, and resulting in three related crystal structures. We anticipate behaviour of this kind to be widespread, and speculate that the concept of "the crystal structure" for individual Dianin's clathrates may be elusive.

19.
Dalton Trans ; 39(14): 3433-48, 2010 Apr 14.
Artigo em Inglês | MEDLINE | ID: mdl-20379535

RESUMO

The generation of amphiphiles derived from macrobicyclic hexamines of the "sarcophagine" class can be prepared through efficient and selective reactions involving the reductive alkylation, using long-chain aldehydes, of amino-functionalised sarcophagines when bound to Cu(ii) or Mg(ii). The Mg(ii) pathway is particularly convenient for the ultimate isolation of the free ligands, which can then be used to form metalloamphiphiles with a variety of metal ions. Structural studies have been made of one of the free (protonated) ligands and some of their complexes.


Assuntos
Aminas/química , Alquilação , Aminas/síntese química , Compostos Bicíclicos com Pontes/química , Complexos de Coordenação/química , Cobre/química , Cristalografia por Raios X , Magnésio/química , Metais/química , Conformação Molecular
20.
Inorg Chem ; 49(7): 3152-61, 2010 Apr 05.
Artigo em Inglês | MEDLINE | ID: mdl-20199101

RESUMO

Various 2- and 3-thienylmethylamino-substituted cobalt(III) cage amine complexes, prepared with the objective of obtaining cage-functionalized polythienyls, have been found to be resistant to oxidative polymerization by both electrochemical and chemical procedures. X-ray structure determinations indicate that there is negligible perturbation of the physical dimensions of the thiophene moieties by the cage substituents and thus that the resistance to polymerization must be associated with the high positive charge carried by these substituents.

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