Coverage‐Controlled Superstructures of C3‐Symmetric Molecules: Honeycomb versus Hexagonal Tiling

The competition between honeycomb and hexagonal tiling of molecular units can lead to large honeycomb superstructures on surfaces. Such superstructures exhibit pores that may be used as 2D templates for functional guest molecules. Honeycomb superstructures of molecules that comprise a C₃ symmetric platform on Au(111) and Ag(111) surfaces are presented. The superstructures cover nearly mesoscopic areas with unit cells containing up to 3000 molecules, more than an order of magnitude larger than previously reported. The unit cell size may be controlled by the coverage. A fairly general model was developed to describe the energetics of honeycomb superstructures built from C₃ symmetric units. Based on three parameters that characterize two competing bonding arrangements, the model is consistent with the present experimental data and also reproduces various published results. The model identifies the relevant driving force, mostly related to geometric aspects, of the pattern formation.     

Poly[[diaqua(μ3‐2,2‐dimethylmalonato)cadmium(II)] tetrahydrate]

In the title complex, {[Cd(C₅H₆O₄)(H₂O)₂]·4H₂O}_n, the dimethylmalonate–cadmium metal–organic framework co‐exists with an extended structure of water molecules, which resembles a sodalite‐type framework. In the asymmetric unit, there are five independent solvent water molecules, two of which are in special positions. The Cd atoms are eight‐coordinated in a distorted square‐antiprismatic geometry by six O atoms of three different dimethylmalonate groups and by two water molecules, and form a two‐dimensional honeycomb layer parallel to the bc plane. Two such layers sandwich the hydrogen‐bonded water layer, which has a sodalite‐type structure with truncated sodalite units composed of coordinated and solvent water molecules. This work is the first example of a dimethylmalonate cadmium complex containing truncated sodalite‐type water clusters.     

Peptide Conjugates for Directing the Morphology and Assembly of 1D Nanoparticle Superstructures

Designed peptide conjugates molecules are used to direct the synthesis and assembly of gold nanoparticles into complex 1D nanoparticle superstructures with various morphologies. Four peptide conjugates, each based on the gold‐binding peptide (AYSSGAPPMPPF; PEP_Au), are prepared: C₁₂H₂₃O‐AYSSGAPPMPP ( 1 ), C₁₂H₂₃O‐AYSSGAPPMPPF ( 2 ), C₁₂H₂₃O‐AYSSGAPPMPPFF ( 3 ), and C₁₂H₂₃O‐AYSSGAPPMPPFFF ( 4 ). The affect that C‐terminal hydrophobic F residues have on both the soft‐assembly of the peptide conjugates and the resulting assembly of gold nanoparticle superstructures is examined. It is shown that the addition of two C‐terminal F residues ( 3 ) leads to thick, branched 1D gold nanoparticle superstructures, whereas the addition of three C‐terminal F residues ( 4 ) leads to bundling of thin 1D nanoparticle superstructures.     

A New Approach to Enantiopure C3‐Symmetric Molecules

Chiral base chemistry has been used to create three chiral centres in one pot on a C₃‐symmetric substrate. The potential of this new approach to C₃‐symmetric molecules is exemplified by the creation of an enantiopure C_3v‐symmetric triol, triphosphane and tripyridine. A ruthenium complex of the last compound has been studied by X‐ray crystallography.     

ECSTM study of adsorption of C60, C70, C86 and Y@C82 on Au(111)

The adsorption of a variety of fullerenes (C₆₀, C₇₀, C₈₆, Y@C₈₂) on Au(111) electrode surfaces was comprehensively investigated in 0.1 M HClO₄ by electrochemical scanning tunneling microscopy (ECSTM). In the ordered C₆₀’s adlayer, C₆₀ molecules formed either (2 $ \sqrt 3 $ ×2 $ \sqrt 3 $ ) or “in-phase” structure. The high resolution STM image shows that the C₆₀ cage is not simply round but shows a bifurcated feature. The adsorption orientation of C₆₀ on Au(111) is tentatively suggested. In the ordered C₇₀’s adlayer, the perpendicular fullerene molecules are the main adsorption mode and form (2 $ \sqrt 3 $ ×2 $ \sqrt 3 $ ) structure. However, for C₈₆ and Y@C₈₂, the ordered adlayer could not be obtained on Au(111) under the present condition. These differences may be due to the different molecular shapes and sizes, and the encapsulated metal atom which affects the lattice matches with the substrate. The adsorption of fullerene molecules on Au(111) from disorder to order could be tuned simply by steering the dimensional sizes or shapes of the fullerenes used.     

Impact of Molecular Size and Shape on the Supramolecular Co-Assembly of Chiral Tricarboxamides: A Comparative Study

A comparative investigation of the chiral amplification features of a series of three families of C₃-symmetric tricarboxamides, 1,3,5-triphenylbenzenetricarboxamides (TPBAs), benzenetricarboxamides (BTAs) and oligo(phenylene ethynylene) tricarboxamides (OPE-TAs), is here reported. As previously observed for BTAs and OPE-TAs, a similar dichroic response is obtained for TPBAs decorated with one, two or three chiral side chains bearing stereogenic centers, thus confirming the efficient transfer of point chirality to the supramolecular helical aggregates. Unlike BTAs and OPE-TAs, the chiral amplification ability of TPBAs in majority rules experiments shows a negligible dependence on the number of chiral centers per monomeric unit, and stands the largest among the series of tricarboxamides. Detailed experimental and theoretical studies demonstrate that the rotation angle between the TPBA units in the helical stack is intermediate to that observed for BTAs and OPE-TAs. This feature strongly conditions the steric interactions between vicinal molecules in the stack and the final chiral amplification outcome. Furthermore, theoretical calculations show that achiral side chains favor the interdigitation of the helical aggregates and thereby the formation of bundle superstructures.     

Anisole at 100 K: the first crystal structure determination

The simplest alkyl aryl ether, anisole (methoxybenzene), C₇H₈O, is a feedstock chemical and is widely used in the pharmaceutical industry. The structure of anisole at 100 K, as determined by single‐crystal X‐ray analysis, is reported. A crystal (m.p. 236 K) suitable for X‐ray diffraction was obtained from the melt. The title compound crystallizes in the centrosymmetric space group P2₁/c with two molecules in the asymmetric unit (Z′ = 2). Both crystallographically distinct molecules adopt a virtually flat (C_s‐symmetric) conformation. The arrangement of the molecules in the solid state appears to be governed by close packing. No face‐to‐face π–π stacking of the molecules is observed, but rather edge‐to‐face interactions result in a herringbone packing motif.     

Synthesis and Enhanced Photocatalytic Activity of a Hierarchical Porous Flowerlike p–n Junction NiO/TiO2 Photocatalyst

Hierarchical flowerlike β‐Ni(OH)₂ superstructures composed of intermeshed nanoflakes are synthesized by hydrothermal treatment with a mixed solution of C₂H₄(NH₂)₂, NaOH, and Ni(NO₃)₂. The as‐prepared β‐Ni(OH)₂ superstructures could be easily changed into NiO superstructures without great morphology change by calcination at 400 °C for 5 h. Furthermore, the TiO₂ nanoparticles can be homogeneously deposited on the surface of NiO superstructures by dispersing β‐Ni(OH)₂ powders in Ti(OC₄H₉)₄–C₂H₅OH mixed solution and then vaporizing to remove the ethanol at 100 °C, and finally calcination at 400 °C for 5 h. The prepared NiO/TiO₂ p–n junction superstructures show much higher photocatalytic activity for photocatalytic degradation of p‐chlorophenol aqueous solution than conventional TiO₂ powders and NiO superstructures prepared under the same experimental conditions. An obvious enhancement in the photocatalytic activity can be related to several factors, including formation of hierarchical porous structures, dispersion of TiO₂ particles on the surface of NiO superstructures, and production of a p–n junction. Further results show that NiO/TiO₂ composite superstructures can be more readily separated from the slurry system by filtration or sedimentation after photocatalytic reaction and re‐used, compared with conventional powder photocatalysts. After many recycling experiments for the photodegradation of p‐chlorophenol, the NiO/TiO₂ composite sample does not exhibit any great activity loss, confirming that NiO/TiO₂ sample is stable and not photocorroded.     

On-surface isostructural transformation from a hydrogen-bonded network to a coordination network for tuning the pore size and guest recognition

Rational manipulation of supramolecular structures on surfaces is of great importance and challenging. We show that imidazole-based hydrogen-bonded networks on a metal surface can transform into an isostructural coordination network for facile tuning of the pore size and guest recognition behaviours. Deposition of triangular-shaped benzotrisimidazole (H₃btim) molecules on Au(111)/Ag(111) surfaces gives honeycomb networks linked by double N–H⋯N hydrogen bonds. While the H₃btim hydrogen-bonded networks on Au(111) evaporate above 453 K, those on Ag(111) transform into isostructural [Ag₃(btim)] coordination networks based on double N–Ag–N bonds at 423 K, by virtue of the unconventional metal–acid replacement reaction (Ag reduces H⁺). The transformation expands the pore diameter of the honeycomb networks from 3.8 Å to 6.9 Å, giving remarkably different host–guest recognition behaviours for fullerene and ferrocene molecules based on the size compatibility mechanism.

A hydrogen-bonded network on a Ag(111) surface can transform into an isostructural Ag(i) coordination network, giving drastically different host–guest recognition behaviours.     

Textural transformations of a smectic phase with asymmetric banana-shaped molecules

Materials consisting of asymmetric banana-shaped molecules may form a smectic C_G phase having C₁ symmetry. We have studied textural transformations in a smectic phase of an asymmetric chlorine-substituted banana-shaped material under electric and mechanical fields. We observed two novel features that have not been observed so far on corresponding materials with symmetric banana-shaped molecules. These observations, however, could be explained by the same arguments as were used for the symmetric molecules. Although our studies do not exclude the possibility that the material has C₁ symmetry, we suggest that the chlorine molecules are positioned arbitrarily and the bulk has C₂ symmetry.     

Mono‐ and Bis(pyrrolo)tetrathiafulvalene Derivatives Tethered to C60: Synthesis,Photophysical Studies,and Self‐Assembled Monolayers

A series of mono‐ (MPTTF) and bis(pyrrolo)tetrathiafulvalene (BPTTF) derivatives tethered to one or two C₆₀ moieties was synthesized and characterized. The synthetic strategy for these dumbbell‐shaped compounds was based on a 1,3‐dipolar cycloaddition reaction between aldehyde‐functionalized MPTTF/BPTTF derivatives, two different tailor‐made amino acids, and C₆₀. Electronic communication between the MPTTF/BPTTF units and the C₆₀ moieties was studied by a variety of techniques including cyclic voltammetry and absorption spectroscopy. These solution‐based studies indicated no observable electronic communication between the MPTTF/BPTTF units and the C₆₀ moieties. In addition, femtosecond and nanosecond transient absorption spectroscopy revealed, rather surprisingly, that no charge transfer from the MPTTF/BPTTF units to the C₆₀ moieties takes place on excitation of the fullerene moiety. Finally, it was shown that the MPTTF–C₆₀ and C₆₀–BPTTF‐C₆₀ dyad and triad molecules formed self‐assembled monolayers on a Au(111) surface by anchoring to C₆₀.     

A quantum chemical study of [1.1.1.1]pagodane and its related compounds

The PBE0/6-31G** quantum chemical method is used to determine the symmetry and equilibrium structural parameters of the molecules of [1.1.1.1]pagodane (C₂₀H₂₀, D _2h ), two dienes (C₂₀H₂₀, D _2h ), two diradicals (C₂₀H₂₀, C _2ν ), and two dications (C₂₀H₂₀²⁺, D _2h and C _2ν ). The energy of a highly symmetric dication with a rectangular cycle is lower by 36 kcal/mole than that of a low symmetric dication with a trapezoidal cycle. The polarization interaction with liquid methylene chloride causes its decrease by 147 kcal/mole.     

Chemisorption of thiol‐functionalized metallocene molecules on Si(111)‐ Ag√3×√3 surface: A density functional theory study

Herein, chemical adsorption properties of the thiol‐functionalized metallocene molecules [M(C₅H₄SH)₂] on Si(111)‐Ag√3×√3 surface were investigated using density functional theory calculation. For this purpose, thiol‐modified ferrocene [Fe(C₅H₄SH)₂], osmocene [Os(C₅H₄SH)₂], and ruthenocene [Ru(C₅H₄SH)₂] molecules were attached on the surface via two different binding models. The more favorable chemical binding energies of [Fe(C₅H₄SH)₂], [Os(C₅H₄SH)₂], and [Ru(C₅H₄SH)₂] molecules were calculated as ?3.42, ?2.15, and ?2.00 eV, respectively. The results showed that the adsorption energies of metallocene molecules change independently by increasing the radius of metal ions where on going down the group of the periodic table. The calculated adsorption energies showed that [Fe(C₅H₄SH)₂] molecule was more stable on the Si(111)‐Ag√3×√3 surface. By calculating the electronic band structure for metallocene/Si(111)‐Ag√3×√3 surfaces, we identified a flat dispersion band in a part of the surface Brillouin zone. © 2015 Wiley Periodicals, Inc.     

(Acetato‐κO)aqua(1H‐imidazole‐κN3)(picolinato‐κ2N,O)copper(II) 0.87‐hydrate: a Z′> 1 structure

The crystal structure of the title compound, [Cu(C₆H₄NO₂)(C₂H₃O₂)(C₃H₄N₂)(H₂O)]·0.87H₂O, has a square‐pyramidal‐coordinated Cu^II centre (the imidazole is trans to the picolinate N atom, the acetate is trans to the picolinate –CO₂ group and the aqua ligand is in a Jahn–Teller‐elongated apical position) and has two symmetry‐independent molecules in the unit cell (Z′ = 2), which are connected through complementary imidazole–picolinate N—H...O hydrogen bonding. The two partially occupied solvent water molecules are each disordered over two positions. The disordered solvent water molecules, together with pseudosymmetry elements, support the notion that a crystal structure with multiple identical chemical formula units in the structural asymmetric unit (Z′ > 1) can represent a crystal `on the way', that is, a kinetic intermediate form which has not yet reached its thermodynamic minimum. Neighbouring molecules form π–π stacks between their imidazole and picolinate N‐heterocycles, with centroid–centroid distances in the range 3.582 (2)–3.764 (2) Å.     

2‐Bromo‐1,3‐bis[2‐(2‐naphthyl)vinyl]benzene benzene hemisolvate and 9‐bromodinaphth[1,2‐a:2′,1′‐j]anthracene

2‐Bromo‐1,3‐bis[2‐(2‐naphthyl)vinyl]benzene benzene hemisolvate, C₃₀H₂₁Br·0.5C₆H₆, (I), with two formula units in the asymmetric unit, exists in the crystal structure in a conformation in which the trans (2‐naphthyl)vinyl substituents on the central bromobenzene moiety appear as nearly fully extended `wings', while 9‐bromodinaphth[1,2‐a:2′,1′‐j]anthracene, C<sub>30</sub>H<sub>17</sub>Br, (II), adopts a highly nonplanar `manta‐ray' shape, with the H atoms in the interior of the molecule within van der Waals contact distances. The packing of the significantly twisted molecules of (I) generates large voids which are filled by benzene solvent molecules, while molecules of (II) stack compactly with all C—Br bonds parallel within the stack.     

A new polymorph of 1,4‐bis(imidazol‐1‐ylmethyl)benzene dihydrate and its hydrogen‐bonded fivefold interpenetrated CdSO4 network

Single crystals of a new polymorph of 1,4‐bis(imidazol‐1‐ylmethyl)benzene dihydrate (bix·2H₂O), C₁₄H₁₄N₄·2H₂O, have been obtained by the hydrothermal method. The asymmetric unit is composed of two independent half‐bix molecules, one on an inversion center and one on a twofold axial site, and two water molecules. The disordered water molecules link into discrete tetrameric water units via two O—H...O hydrogen bonds, forming planar R₄⁴(8) rings. These tetrameric water units and bix molecules are further linked by two O—H...N hydrogen bonds into a three‐dimensional network in which an (106) hydrogen‐bonded ring is observed. These large rings lead to the formation of a fivefold interpenetrated network. If both the tetrameric water units and the bix molecules can be regarded as connected nodes, one single three‐dimensional net can then be rationalized as a CdSO₄ network. This study indicates that topological methodology can be applied in some cases in order to understand the inherent characteristics of some hydrogen‐bonded supramolecular assemblies.     

1,4‐Phenylenebis(methylene) bis(9H‐carbazole‐9‐carbodithioate)

The molecules of the title compound, C₃₄H₂₄N₂S₄, lie across centres of inversion in the space group P2₁/n. The spacer unit linking the benzene rings and carbazole units is effectively planar, while the carbazole unit itself is slightly folded. Molecules are linked into sheets by a single C—H...π(arene) hydrogen bond and the hydrogen‐bonded sheets are themselves linked into a three‐dimensional framework structure by a single π–π stacking interaction.     

Polymeric dihydroxydiphthalatotricobalt(II)

In the crystal structure of di­hydroxy­diphthalatotricobalt(II), [Co₃(C₈H₄O₄)₂(OH)₂]_n, two of the four independent Co atoms lie at special positions of site symmetry 2. The hydroxy groups link three Co atoms to form a pyramidal Co₃O unit, and adjacent Co₃O units are linked through the Co base atoms into a honeycomb layer motif. Each of the phthalate dianions uses the O atoms of one carboxyl group to bind to three Co atoms, the bonding mode giving rise to six‐coordinate Co atoms.     

Shape‐Induced,Hexagonal, Open Frameworks: Rubidium Ion Complexed Cucurbituril

A honeycomb structure is shown by the one‐dimensional coordination polymer comprising D_6h‐symmetric cucurbituril molecules and rubidium ions (see picture). The cucurbituril molecules stack atop one another and show coordination of their carbonyl groups to the rubidium ions in between. The shape and symmetry of the building blocks encourage the coordination polymer chains to be arranged in such a way as to produce an open‐framework structure with large, linear, hexagonal channels.     

Bis[(dihydrogen pyrophosphato‐κ2O,O′)(2,2′:6′,2′′‐terpyridine‐κ3N,N′,N′′)copper(II)] 4.5‐hydrate

The title copper complex, [Cu(H₂P₂O₇)(C₁₅H₁₁N₃)]₂·4.5H₂O, consists of two very similar independent Cu(Tpy)H₂P₂O₇ monomeric units (Tpy is 2,2′:6′,2′′‐terpyridine) plus four and a half water molecules of hydration, some of which are disordered. Tpy units bind through the usual triple bite via their N atoms, and the H₂P₂O₇²⁻ anions coordinate through two O atoms from two different phosphate units. Each independent CuN₃O₂ chromophore can be described as a slightly deformed square pyramid, with one of them having a sixth, semicoordinated, O atom from a centrosymmetrically related CuN₃O₂ unit in a weakly bound second apical position suggesting an octahedral environment for the cation and weak dimerization of the molecule. The two independent complex molecules are connected via two strong O—H...O interactions between the phosphate groups to form hydrogen‐bonded dinuclear units, further linked into [111] columns, resulting in a very complex three‐dimensional supramolecular structure through a variety of classical and nonclassical hydrogen bonds, as well as π–π interactions.