Helical Bilayer Nanographenes: Impact of the Helicene Length on the Structural, Electrochemical, Photophysical, and Chiroptical Properties.

Helical bilayer nanographenes (HBNGs) are chiral π-extended aromatic compounds consisting of two π-π stacked hexabenzocoronenes (HBCs) joined by a helicene, thus resembling van der Waals layered 2D materials. Herein, we compare [9]HBNG, [10]HBNG, and [11]HBNG helical bilayers endowed with [9], [10], and [11]helicenes embedded in their structure, respectively. Interestingly, the helicene length defines the overlapping degree between the two HBCs (number of benzene rings involved in π-π interactions between the two layers), being 26, 14, and 10 benzene rings, respectively, according to the X-ray analysis. Unexpectedly, the electrochemical study shows that the lesser π-extended system [9]HBNG shows the strongest electron donor character, in part by interlayer exchange resonance, and more red-shifted values of emission. Furthermore, [9]HBNG also shows exceptional chiroptical properties with the biggest values of gabs and glum (3.6 × 10-2) when compared to [10]HBNG and [11]HBNG owing to the fine alignment in the configuration of [9]HBNG between its electric and magnetic dipole transition moments. Furthermore, spectroelectrochemical studies as well as the fluorescence spectroscopy support the aforementioned experimental findings, thus confirming the strong impact of the helicene length on the properties of this new family of bilayer nanographenes.

Electronic Control of the Scholl Reaction: Selective Synthesis of Spiro vs Helical Nanographenes.

Scholl oxidation has become an essential reaction in the bottom-up synthesis of molecular nanographenes. Herein, we describe a Scholl reaction controlled by the electronic effects on the starting substrate (1 a, b). Anthracene-based polyphenylenes lead to spironanographenes under Scholl conditions. In contrast, an electron-deficient anthracene substrate affords a helically arranged molecular nanographene formed by two orthogonal dibenzo[fg,ij]phenanthro-[9,10,1,2,3-pqrst]pentaphene (DBPP) moieties linked through an octafluoroanthracene core. Density Functional Theory (DFT) calculations predict that electronic effects control either the first formation of spirocycles and subsequent Scholl reaction to form spironanographene 2, or the expected dehydrogenation reaction leading solely to the helical nanographene 3. The crystal structures of four of the new spiro compounds (syn 2, syn 9, anti 9 and syn 10) were solved by single crystal X-ray diffraction. The photophysical properties of the new molecular nanographene 3 reveal a remarkable dual fluorescent emission.

Tetrahedraphene: A Csp3 -centered 3D Molecular Nanographene Showing Aggregation-Induced Emission.

The bottom-up synthesis of 3D tetrakis(hexa-peri-hexabenzocoronenyl)methane, "tetrahedraphene", is reported. This molecular nanographene constituted by four hexa-peri-hexabenzocoronene (HBC) units attached to a central sp3 carbon atom, shows a highly symmetric arrangement of the HBC units disposed in the apex of a tetrahedron. The X-ray crystal structure reveals a tetrahedral symmetry of the molecule and the packing in the crystal is achieved mostly by CH⋅⋅⋅π interactions since the interstitial solvent molecules prevent the π⋅⋅⋅π interactions. In solution, tetrahedraphene shows the same electrochemical and photophysical properties as the hexa-t Bu-substituted HBC (t Bu-HBC) molecule. However, upon water addition, it undergoes a fluorescence change in solution and in the precipitated solid, showing an aggregation induced emission (AIE) process, probably derived from the restriction in the rotation and/or vibration of the HBCs. Time-Dependent Density Functional Theory (TDDFT) calculations reveal that upon aggregation, the high energy region of the emission band decreases in intensity, whereas the intensity of the red edge emission signal increases and presents a smoother decay, compared to the non-aggregated molecule. All in all, the excellent correlation between our simulations and the experimental findings allows explaining the colour change observed in the different solutions upon increasing the water fraction.

Helically Arranged Chiral Molecular Nanographenes.

A benchtop solution-phase synthesis of molecular nanographenes composed of two orthogonal dibenzo[fg,ij]phenanthro[9,10,1,2,3-pqrst]pentaphene (DBPP) moieties covalently connected through a tetrafluorobenzene ring is described. The helical arrangement of these three covalently linked molecular fragments leads to the existence of a chiral axis which gives rise to a racemic mixture, even with the molecular moieties being symmetrically substituted. X-ray diffraction studies show that both enantiomers cocrystallize in a single crystal, and the racemic mixture can be resolved by chiral HPLC. Asymmetric substitution in DBPP moieties affords a pair of diastereoisomers whose rotational isomerization has been studied by 1H NMR. Additionally, the electrochemical and photophysical properties derived from these new molecular nanographenes reveal an electroactive character and a significant fluorescent behavior.

Homo and Hetero Molecular 3D Nanographenes Employing a Cyclooctatetraene Scaffold.

Two novel homo and hetero three-dimensional nanographenes, NG1 and NG2, featuring a cyclooctatetraene core are designed, synthesized, and characterized. A concise and efficient bottom-up methodology was employed during which 24 new carbon-carbon bonds were formed. By means of a Scholl reaction nanographenes with 53 fused rings are realized, which exhibited good solubility in common organic solvents. The resulting saddle-like structures of NG1 and NG2 are electron-rich and show good chemical and electrochemical stability. Their molecular structures are fully elucidated by single-crystal X-ray crystallography. From their crystal structure analysis is concluded that both nanographenes are chiral and crystallize as a racemic mixture. Our work was rounded-off by excited state investigations such as electron and energy transfer with electron-acceptors and -donors.

pH- and Time-Dependent Release of Phytohormones from Diruthenium Complexes.

The controlled release of functionally active compounds is important in a variety of applications. Here, we have synthesized, characterized, and studied the magnetic properties of three novel metal-metal-bonded tris(formamidinato) Ru25+ complexes. We have used different auxin-related hormones, indole-3-acetate (IAA), 2,4-dichlorophenoxyacetate (2,4-D), and 1-naphthaleneacetate (NAA), to generate [Ru2Cl(µ-DPhF)3(µ-IAA)] (RuIAA), [Ru2Cl(µ-DPhF)3(µ-2,4-D)] (Ru2,4-D), and [Ru2Cl(µ-DPhF)3(µ-NAA)] (RuNAA) (DPhF = N,N'-diphenylformamidinate). The crystal structures of RuIAA, RuIAA·THF, Ru2,4-D·CH2Cl2, and RuNAA·0.5THF have been determined by single-crystal X-ray diffraction. To assess the releasing capacity of the bound hormone, we have employed a biological assay that relied on Arabidopsis thaliana plants expressing an auxin reporter gene and we demonstrate that the release of the phytohormones from RuIAA, Ru2,4-D, and RuNAA is pH- and time-dependent. These studies serve as a proof of concept showing the potential of these types of compounds as biological molecule carriers.

Structural Study of the Compounds Formed in the Reactions of FeCl3·6H2O with Ni(OH)2 in the Presence of Dithiolenes HSRSH (R = C6H2Cl2 or C6H4).

In our attempts to prepare coordination polymers by reaction of FeCl3·6H2O and Ni(OH)2 in the presence of dithiolenes HSC6H2X2SH (X = Cl or H), several ion pairs of compounds containing the anionic entity [Ni(SC6H2X2S)2]- were obtained instead. It was also found that other species without dithiolene ligands were formed in these reactions, giving rise to different ion pairs and a tetrametallic cluster. The careful isolation of the different types of crystalline solids allowed the characterization of all of the resulting compounds by single crystal X-ray diffraction (SCXRD). In order to establish the amount of nickel and iron present in the crystals, complementary total reflection X-ray fluorescence (TXRF) analyses were performed. The eight different structural types that were obtained are described and compared with related ones found in the literature.

Multifunctional Copper(I) Coordination Polymers with Aromatic Mono- and Ditopic Thioamides.

Direct reactions under ambient conditions between CuX (X = Br, I) and thiobenzamide (TBA) were carried out at different ratios, giving rise to the formation of a series of one-dimensional (1D) coordination polymers, (CPs) [CuI(TBA)] n (1), [Cu3I3(TBA)2] n (4), and [CuBr(TBA)] n (5), as well as two molecular complexes, [CuI(TBA)3] (2) and [Cu2I2(TBA)4]·2MeCN (3). Recrystallization of 1 and 5 yielded a series of isostructural 1D CP solvated species, [CuI(TBA)·S] n] n (1·S; S = tetrahydrofuran, acetone, methanol) and [CuBr(TBA)·S] n (5·S; S = tetrahydrofuran, acetone), respectively. Similar reactions between CuI and 1,4-dithiobenzamide (DTBA) allowed the isolation of a series of two-dimensional (2D) CPs [CuI(DTBA)·S] n (6·S; S = N, N-dimethylformamide, acetonitrile, methanol). Interestingly, 1·S and 5·S showed variable luminescence and electrical semiconductivity depending on the different solvents located in their structures. Thus, 1 and 5 could display potential application for sensing volatile organic vapors by virtue of the significant changes in their emission upon solvent exposure, even by the naked eye. Theoretical calculations have been used to rationalize these electronic properties.

π-Extended Corannulene-Based Nanographenes: Selective Formation of Negative Curvature.

A geometrically selective bottom-up synthesis of curved nanographenes is described. The synthetic methodology used involves the extension of the π-system of positively curved corannulene by a [4+2] cycloaddition reaction followed by cyclodehydrogenation (Scholl oxidation). By selecting the conditions for the Scholl oxidation, the formation of a seven-membered ring that also confers negative curvature to the resulting nanographene can be activated, offering two topologically distinct, curved nanographenes from a common precursor. Additionally, the structure-property relationship in these new nanographenes is explored via theoretical, electrochemical, photophysical, Raman, and X-ray crystallographic studies.

Synthesis of a Helical Bilayer Nanographene.

A rigid, inherently chiral bilayer nanographene has been synthesized as both the racemate and enantioenriched M isomer (with 93 % ee) in three steps from established helicenes. This folded nanographene is composed of two hexa-peri-hexabenzocoronene layers fused to a [10]helicene, with an interlayer distance of 3.6 Šas determined by X-ray crystallography. The rigidity of the helicene linker forces the layers to adopt a nearly aligned AA-stacked conformation, rarely observed in few-layer graphene. By combining the advantages of nanographenes and helicenes, we have constructed a bilayer system of 30 fused benzene rings that is also chiral, rigid, and remains soluble in common organic solvents. We present this as a molecular model system of bilayer graphene, with properties of interest in a variety of potential applications.

Luminescent Thermochromism of 2D Coordination Polymers Based on Copper(I) Halides with 4-Hydroxythiophenol.

Solvothermal reactions between copper(I) halides and 4-mercaptophenol give rise to the formation of three coordination polymers with general formula [Cu3 X(HT)2 ]n (X=Cl, 1; Br, 2; and I, 3). The structures of these coordination polymers have been determined by X-ray diffraction at both room- and low temperature (110 K), showing a general shortening in Cu-S, Cu-X and Cu-Cu bond lengths at low temperatures. 1 and 2 are isostructural, consisting of layers in which the halogen ligands act as µ3 -bridges joining two Cu1 and one Cu2 atoms whereas in 3 the iodine ligands is as µ4 -mode but the layers are quasi-isostructural with 1 or 2. These compounds show a reversible thermochromic luminescence, with strong orange emission for 1 and 2, but weaker for 3 at room temperature, whereas upon cooling at 77 K 1 and 2 show stronger yellow emission, and 3 displays stronger green emission. DFT calculations have been used to rationalize these observations. These results suggest a high potential for this novel and promising stimuli-responsive materials.

Coordination polymers based on diiron tetrakis(dithiolato) bridged by alkali metals, electrical bistability around room temperature, and strong antiferromagnetic coupling.

Coordination polymer chains have been formed by the direct reaction between HSC6H2Cl2SH and FeCl3·6H2O in the presence of an aqueous solution of the corresponding alkali-metal hydroxide (M = Li, Na, and K) or carbonate (M = Rb and Cs). The structures consist of dimeric [Fe2(SC6H2Cl2S)4](2-) entities bridged by [M2(THF)4] [M = K (1), Rb (2), and Cs (3); THF = tetrahydrofuran] or {[Na2(µ-H2O)2(THF)2] (5 and 5') units. The smaller size of the lithium atom yields an anion/cation ion-pair molecule, [Li(THF)4]2[Fe2(SC6H2Cl2S)4] (4), in which the dianionic moieties are held together by Cl···Cl interactions. Electrical characterization of these compounds shows a general semiconductor behavior in which the conductivity and activation energies are mainly determined by the M-Cl and M-S bond distances. Compounds 1 and 5' are interesting examples of bistability showing reversible transitions centered at ca. 350 and 290 K with very large hysteresis of ca. 60 and 35 K, respectively. All of these compounds exhibit intradimer strong antiferromagnetic Fe···Fe interactions.

Crystal structure of poly[[trans-di-aqua-bis-[µ2-trans-4,4'-(diazenedi-yl)dipyridine]-nickel(II)] diiodide ethanol disolvate].

In the title compound, {[Ni(C10H8N4)2(H2O)2]I2·2C2H5OH} n , the complex shows an octa-hedral environment of the Ni(2+) cation in which it is located on a centre of symmetry, linked to two water mol-ecules and the pyridine-N atoms of four 4,4'-(diazenediyl)dipyridine ligands bridging Ni(2+) cations along the b- and c-axis directions, giving rise to a two-dimensional arrangement. The Ni-N bond lengths are in the range 2.109 (4)-2.186 (3) Šand the Ni-O bond length is 2.080 (3) Å. The 4,4'-(diazenedi-yl)dipyridine ligand lies on an inversion centre. An O-H⋯O hydrogen-bond inter-action is observed between water and ethanol mol-ecules. The I(-) ions can be regarded as free anions in the crystal lattice.

Torsion Effects Beyond the δ Bond and the Role of π Metal-Ligand Interactions.

Previous studies on bimetallic paddlewheel compounds have established a direct correlation between metal-metal distance and ligand torsion angles, leading to the rule that higher torsion results in longer metal-metal bond distances. Here, the new discovery based on diarylformamidinate Ru25⁺ paddlewheel compounds [Ru2Cl(DArF)4] that show an opposite behavior is reported: higher torsions lead to shorter metal-metal distances. This discovery challenges the assumption that internal rotation solely impacts the δ bond. By combining experimental and theoretical techniques, it is demostrated that this trend is associated with previously overlooked π metal-ligand interactions. These π metal-ligand interactions are a direct consequence of the paddlewheel structure and the conjugated nature of the bidentate ligands. This findings offer far-reaching insights into the influence of equatorial ligands and their π-conjugation characteristics on the electronic properties of paddlewheel complexes. That this effect is not exclusive of diruthenium compounds but also occurs in other bimetallic cores such as ditungsten or dirhodium is demonstrated, and with other ligands showing allyl type conjugation. These results provide a novel approach for fine-tuning the properties of these compounds with significant implications for materials design.

Di-hydro-cyclam dimaleate [H2(cyclam)(maleate)2].

The asymmetric unit of the title mol-ecular salt [systematic name: 1,4,8,11-tetraazacyclotetradecane-1,8-diium bis(3-carboxy-prop-2-enoate)], C10H26N4 (2+)·2C4H3O4 (-), contains two half-cations (both completed by crystallographic inversion symmetry) and two maleate anions. The cyclam macrocycles adopt trans-III conformations, supported by two intra-molecular N-H⋯O hydrogen bonds. The O-bonded H atom of each maleate ion is disordered over two positions with an occupancy ratio of 0.61 (5):0.39 (5): each one generates an intra-molecular O-H⋯O hydrogen bond. In the crystal, the cations are linked to the anions by N-H⋯O hydrogen bonds, generating [001] chains.

A convergent growth approach to electroactive ferrocene rich carbosilane- and siloxane-based dendrons, dendrimers, and dendronized polymers.

The construction of the first members of a novel family of structurally well-defined, ferrocenyl rich, dendritic macromolecules based on carbosilane skeletons and siloxane linkages has been achieved via a convergent growth approach. Starting from triferrocenylvinylsilane Fc3SiCHCH2 (1) (Fc = Fe(η5-C5H4)(η5-C5H5) as the key monomer, the sequential utilization of platinum-catalyzed hydrosilylation and alkenylation steps with Grignard reagents (allylmagnesium bromide) can be applied to prepare three different branched structures: multiferrocenyl-terminated dendrons 2 and 3, dendrimers 4 and 5, and dendronized polymers 7n-9n. All of the dendritic metallomacromolecules have been thoroughly characterized using a combination of elemental analysis, multinuclear (1H, 13C, 29Si) NMR spectroscopy, FT-IR and MALDI-TOF mass spectrometry, to establish their chemical structures and properties. The molecular structures of G1-dendron 3 and dendrimer 4, containing six and nine ferrocenyl units, respectively, have been successfully determined by single-crystal X-ray analysis, compound 4 being the branched multiferrocenyl-containing siloxane with the highest number of Fc substituents whose structure has been reported so far. Electrochemical studies (using cyclic voltammetry (CV) and square wave voltammetry (SWV) performed in dichloromethane solution with [PF6]- and [B(C6F5)]4- as supporting electrolyte anions of different coordinating abilities) reveal that all the macromolecular compounds obtained exhibit a three-wave redox pattern, suggesting appreciable electronic interactions between the silicon-bridged triferrocenyl moieties as they are successively oxidized. In addition, dendrimer 5 and dendronized polymers 7n-9n, with 12 and 4 < n < 14 ferrocenyl units, respectively, linked in threes around the periphery, undergo remarkable oxidative precipitation in CH2Cl2/[n-Bu4N][PF6] and are able to form chemically modified electrodes with stable electroactive films.

Structural and Theoretical Study of Copper(II)-5-fluoro Uracil Acetate Coordination Compounds: Single-Crystal to Single-Crystal Transformation as Possible Humidity Sensor.

This paper describes the synthesis and characterization of seven different copper(II) coordination compounds, as well as the formation of a protonated ligand involving all compounds from the same reaction. Their synthesis required hydrothermal conditions, causing the partial in situ transformation of 5-fluoro uracil-1-acetic acid (5-FUA) into an oxalate ion (ox), as well as the protonation of the 4,4'-bipyridine (bipy) ligand through a catalytic process resulting from the presence of Cu(II) within the reaction. These initial conditions allowed obtaining the new coordination compounds [Cu2(5-FUA)2(ox)(bipy)]n·2n H2O (CP2), [Cu(5-FUA)2(H2O)(bipy)]n·2n H2O (CP3), as well as the ionic pair [(H2bipy)+2 2NO3-] (1). The mother liquor evolved rapidly at room temperature and atmospheric pressure, due to the change in concentration of the initial reagents and the presence of the new chemical species generated in the reaction process, yielding CPs [Cu(5-FUA)2(bipy)]n·3.5n H2O, [Cu3(ox)3(bipy)4]n and [Cu(ox)(bipy)]n. The molecular compound [Cu(5-FUA)2(H2O)4]·4H2O (more thermodynamically stable) ended up in the mother liquor after filtration at longer reaction times at 25 °C and 1 atm., cohabiting in the medium with the other crystalline solids in different proportions. In addition, the evaporation of H2O caused the single-crystal to single-crystal transformation (SCSC) of [Cu(5-FUA)2(H2O)(bipy)]n·2n H2O (CP3) into [Cu(5-FUA)2(bipy)]n·2n H2O (CP4). A theoretical study was performed to analyze the thermodynamic stability of the phases. The observed SCSC transformation also involved a perceptible color change, highlighting this compound as a possible water sensor.

Structure and properties of one-dimensional heterobimetallic polymers containing dicyanoaurate and dirhodium(II) fragments.

The synthesis and characterization of compound [Rh(2)(O(2)CEt)(4)(H(2)O)(2)] (1) and one-dimensional heterobimetallic polymers K(n){Rh(2)(O(2)CEt)(4)[Au(CN)(2)]}(n) (2) and K(n){Rh(2)(O(2)CMe)(4)[Au(CN)(2)]}(n)·4nH(2)O (3), constructed from dirhodiumtetracarboxylato units, [Rh(2)(O(2)CR)(4)](+), and dicyanoaurate, [Au(CN)(2)](-), fragments are described. In both compounds 2 and 3 the resulting polymeric chains are nonlinear and have in common similar structural parameters, although the solid state supramolecular arrangement is very different. These structural differences explain the fact that complex 2 displays aurophilic interactions while this type of interactions are absent in complex 3. As a result, compound 2 shows rich blue luminescent properties whereas compound 3 is not luminescent. The electrical conductivity in solid state of compounds 2 and 3 is also studied.

New insights into progressive ligand replacement from [Ru2Cl(O2CCH3)4]: synthetic strategies and variation in redox potentials and paramagnetic shifts.

The complete series of [Ru2Cl(Dp-FPhF)x(O2CCH3)4-x] (x = 1-4; Dp-FPhF- = N,N'-bis(4-fluorophenyl)formamidinate) compounds, has been prepared and characterized by a multi-technique approach, including single crystal X-ray diffraction. A careful study of the different methodologies has allowed us to prepare four compounds with good yields and without an inert atmosphere or further purification. Specifically, [Ru2Cl(Dp-FPhF)(O2CCH3)3] (1) was obtained using an ultrasound-assisted (USS) method, while [Ru2Cl(Dp-FPhF)4] (4) was prepared by microwave assisted solvothermal synthesis (MWS). The intermediate substitution products cis-[Ru2Cl(Dp-FPhF)2(O2CCH3)2] (2) and [Ru2Cl(Dp-FPhF)3(O2CCH3)] (3) have been prepared by conventional heating, controlling the molar ratio of the starting materials. ESI-MS and infrared spectroscopy were used to follow all the reactions and permitted a qualitative evaluation of the axial reactivity in this series. Magnetic and absorption measurements confirmed a high spin σ2π4δ2(π*δ*)3 electronic configuration in all cases. However, the effect of the gradual modification of the electronic density in the diruthenium core markedly affects other properties. The cyclic voltammograms of the compounds show a strong decrease in the one electron oxidation potential and an increase in the reduction potential in the series from 1 to 4. Furthermore, despite their paramagnetic nature, 1H- and 19F-NMR spectra were recorded, and a correlation between the paramagnetic shift of the signals and the substitution degree of the diruthenium species was observed. These results provide a comprehensive guide to synthesise and understand the effects of equatorial ligand substitution on the properties of Ru25+ compounds.

Antitumoral potential of carbamidocyclophanes and carbamidocylindrofridin A isolated from the cyanobacterium Cylindrospermum stagnale BEA 0605B.

Three carbamidocyclophanes, A, F and V, and carbamidocylindrofridin A were isolated from the cultured freshwater cyanobacterium Cylindrospermum stagnale, collected in the Canary Islands. The chemical structures of these compounds were elucidated through NMR, HRMS and ECD spectroscopy. The absolute configuration of carbamidocyclophane A was confirmed using X-ray-diffraction. All compounds showed apoptotic capacity against the SK-MEL-1, SK-MEL-28 and SK-MEL-31 tumour cells. Carbamidocylindrofridin A had the highest anti-tumour potential, with an IC50 of 1 ± 0.3 µM in the SK-MEL-1 cell line.