Effects of Edge Functionalization of Nanographenes with Small Aromatic Systems

Regulation of the physical properties of nanographenes (NGs) by edge functionalization is an active research area. We conducted a computational study of the effects of edge functionalization on the physical properties of NGs. The computed NGs were models of experimentally obtained NGs and composed of a C₁₇₄ carbon framework with one to four 3,5-dimethylnaphthalene units on the edge. The effects were assessed structurally, magnetically, and electronically by the least square planarity index, harmonic oscillator model of aromaticity, nucleus-independent chemical shift, and HOMO–LUMO (H–L) gaps. Density functional theory calculations indicate that although the structures of the model NGs are not very sensitive to edge functionalization, but the magnetic and electronic properties are. The installed substituents narrowed the H−L gap and induced a redshift of the photoluminescence (PL) band by the π conjugation between NG and the substituent. These results are consistent with the extension of the absorption band and the redshift of the PL bands of the experimentally modified NGs. Furthermore, the calculations confirmed the contribution of the charge transfer character to the absorption spectra.     

Edge-Functionalized Nanographenes

Nanographenes (NGs) have recently emerged as new carbon materials. Their nanoscale size results in a size-dependent quantum confinement effect, opening the band gap by a few eV. This energy gap allows NGs to be applied as optical materials. This property has attracted researchers across multiple scientific fields. The photophysical properties of NGs can be manipulated by introducing organic groups onto their basal planes and/or into their edges. In addition, the integration of organic functional groups into NGs results in NG-based hybrid materials. These features make the post-synthetic modification of NGs an active research area. As obtainable information on chemically functionalized NGs is limited owing to their nonstoichiometry and structural uncertainty, their structural characterization requires a combination of multiple spectroscopic methods. Therefore, information on the characterization procedures of recently published chemically functionalized NGs is of value for advancing the field of NG-based hybrid materials. The present review focuses on the structural characterization of chemically functionalized NGs. It is hoped that this review will help to advance this field.     

Eight new crystal structures of 5‐(hydroxymethyl)uracil, 5‐carboxyuracil and 5‐carboxy‐2‐thiouracil: insights into the hydrogen‐bonded networks and the predominant conformations of the C5‐bound residues

In order to examine the preferred hydrogen‐bonding pattern of various uracil derivatives, namely 5‐(hydroxymethyl)uracil, 5‐carboxyuracil and 5‐carboxy‐2‐thiouracil, and for a conformational study, crystallization experiments yielded eight different structures: 5‐(hydroxymethyl)uracil, C₅H₆N₂O₃, (I), 5‐carboxyuracil–N,N‐dimethylformamide (1/1), C₅H₄N₂O₄·C₃H₇NO, (II), 5‐carboxyuracil–dimethyl sulfoxide (1/1), C₅H₄N₂O₄·C₂H₆OS, (III), 5‐carboxyuracil–N,N‐dimethylacetamide (1/1), C₅H₄N₂O₄·C₄H₉NO, (IV), 5‐carboxy‐2‐thiouracil–N,N‐dimethylformamide (1/1), C₅H₄N₂O₃S·C₃H₇NO, (V), 5‐carboxy‐2‐thiouracil–dimethyl sulfoxide (1/1), C₅H₄N₂O₃S·C₂H₆OS, (VI), 5‐carboxy‐2‐thiouracil–1,4‐dioxane (2/3), 2C₅H₄N₂O₃S·3C₆H₁₂O₃, (VII), and 5‐carboxy‐2‐thiouracil, C₁₀H₈N₄O₆S₂, (VIII). While the six solvated structures, i.e. (II)–(VII), contain intramolecular S(6) O—H…O hydrogen‐bond motifs between the carboxy and carbonyl groups, the usually favoured R₂²(8) pattern between two carboxy groups is formed in the solvent‐free structure, i.e. (VIII). Further R₂²(8) hydrogen‐bond motifs involving either two N—H…O or two N—H…S hydrogen bonds were observed in three crystal structures, namely (I), (IV) and (VIII). In all eight structures, the residue at the ring 5‐position shows a coplanar arrangement with respect to the pyrimidine ring which is in agreement with a search of the Cambridge Structural Database for six‐membered cyclic compounds containing a carboxy group. The search confirmed that coplanarity between the carboxy group and the cyclic residue is strongly favoured.     

Bis­[N,N′‐bis(2,4,6‐tri­methyl­phenyl)‐1,2‐ethanediyl­idenedi­amine]copper(I) tetra­fluoro­borate

In the title compound, [Cu(C₂₀H₂₄N₂)₂]BF₄, the complex cation adopts a distorted tetrahedral structure, the dihedral angle between the least‐squares planes of the chelating ligand backbones being 51.1 (2)°. This flattening of the tetrahedral coordination sphere may be driven by the presence of intramolecular π–π stacking interactions between mesityl groups on adjacent ligands.     

Betainium tri­fluoro­acetate

The title compound, C₅H₁₂NO₂⁺·C₂F₃O₂^? or BET⁺·CF₃COO^? [BET is tri­methyl­glycine (betaine); IUPAC: 1‐carboxy‐N,N,N‐tri­methyl­methanaminium inner salt], contains pairs of bet­ainium and tri­fluoro­acetate ions forming a dimer bridged by a strong hydrogen bond between the carboxyl and carboxyl­ate groups of the two ions. The molecular symmetry of the cation is close to C_s, with protonation occurring at the carboxy O atom positioned anti to the N atom. The tri­fluoro­acetate anions are disordered over two positions. In one, the conformation of the CF₃ group is staggered with respect to the carboxyl­ate group, in the other, it is close to an eclipsed conformation. The sole hydrogen bond present in the structure is the strong O—H?O bond between the anion and the cation.     

[N,N′‐Bis­(salicyl­idene)‐1,2‐di­phenyl‐(RS,SR)‐1,2‐ethane­di­amin­ato]­nickel(II)

In crystals of the title compound, [Ni(C₂₈H₂₂N₂O₂)], the coordination geometry around the Ni atom is square planar with a slight tetrahedral distortion. The five‐membered N,N′‐chelate ring adopts a distorted gauche conformation with the two phenyl groups in axial and equatorial orientations.     

[N‐(2‐Hydroxy­ethyl)ethyl­enediamine‐κ3N,N′,O]‐cis‐bis(isothio­cyanato‐κN)copper(II)

In the novel transition metal isothio­cyanate complex of N‐(2‐hydroxy­ethyl)ethyl­enediamine (hydet‐en) with copper, [Cu(NCS)₂(C₄H₁₂N₂O)], the Cu atom lies in a distorted square‐pyramidal environment, coordinated by four N atoms in the basal plane and an apical O atom. The hydet‐en ligand is N,N,O‐tridentate, in contrast to the disposition in previously studied complexes, while the isothio­cyanate ions act as N‐atom donor ligands. The monomeric units are linked to one another by hydrogen bonds.     

(2,2′‐Biquinoline‐κ2N,N′)dichloropalladium(II), ‐copper(II) and ‐zinc(II)

In the three title complexes, namely (2,2′‐biquinoline‐κ²N,N′)dichloro­palladium(II), [PdCl₂(C₁₈H₁₂N₂)], (I), and the corresponding copper(II), [CuCl₂(C₁₈H₁₂N₂)], (II), and zinc(II) complexes, [ZnCl₂(C₁₈H₁₂N₂)], (III), each metal atom is four‐coordinate and bonded by two N atoms of a 2,2′‐biquinoline molecule and two Cl atoms. The Pd^II atom has a distorted cis‐square‐planar coordination geometry, whereas the Cu^II and Zn^II atoms both have a distorted tetra­hedral geometry. The dihedral angles between the N—M—N and Cl—M—Cl planes are 14.53 (13), 65.42 (15) and 85.19 (9)° for (I), (II) and (III), respectively. The structure of (II) has twofold imposed symmetry.     

The exo and endo isomers of [N,N′‐bis­(salicyl­idene)‐1,2‐di­phenyl‐(RS,SR)‐1,2‐ethane­diyl­diamin­ato]­oxo­vanadium(IV)

The title complexes, exo‐ and endo‐[VO(C₂₈H₂₂N₂O₂)], show monomeric structures with a distorted square‐pyramidal coordination. The two phenyl groups on the five‐membered N,N′‐chelate ring are both on the same side as the oxo ligand for the exo isomer and on opposite sides for the endo isomer.     

Poly[(μ6‐rac‐cis‐cyclohexane‐1,2‐dicarboxylato)strontium]

In the title layered coordination polymer, [Sr(C₈H₁₀O₄)]_n, the strontium ion adopts a distorted square‐antiprismatic SrO₈ geometry, arising from its coordination by six different cis‐cyclohexane‐1,2‐dicarboxylate dianions (two bidentate and four monodentate). Within the dianion, the cyclohexane ring adopts a chair conformation and the dihedral angle between the planes of the –CO₂⁻ groups is 80.4 (6)°. The polyhedral linkage pattern leads to (100) sheets in the crystal in which the SrO₈ groups share triangular faces and edges in which the Sr...Sr topological connectivity is a 6³ net. The crystal studied was a nonmerohedral twin, with the components related by a 180° rotation about [100].     

Poly­[[[aqua­manganese(II)]‐μ2‐4,4′‐bi­pyridine‐μ3‐succinato] 4,4′‐bi­pyridine hemisolvate]

The polymeric title complex, {[Mn(C₄H₄O₄)(C₁₀H₈N₂)(H₂O)]·0.5C₁₀H₈N₂}_n, possesses a three‐dimensional open‐framework structure, with the solvate 4,4′‐bi­pyridine (bipy) mol­ecules, which lie around centers of inversion, clathrated in the channels of the framework. The Mn^II center is surrounded by three succinate (succ) ligands, one water mol­ecule and two bipy ligands, and displays a slightly distorted octahedral coordination environment, with cis angles ranging from 84.14 (12) to 96.56 (11)°. Each succ dianion coordinates to three Mn^II atoms, thus acting as a bridging tridentate ligand; in turn, the Mn^II atoms are bridged by three succ ligands, thus forming a two‐dimensional Mn–succ sheet pillared by the bridging bipy ligands. Two hydrogen‐bonding interactions, involving the water mol­ecules and the carboxy O atoms of the succ ligands, are present in the crystal structure.     

Phenanthroline complexes of zinc and calcium carbamates

Bis(N,N‐di‐n‐butyl­di­thio­carbamato‐κ²S,S′)(1,10‐phenanthroline‐κ²N,N′)­zinc(II) ethanol hemisolvate, [Zn(C₉H₁₈NS₂)₂(C₁₂H₈N₂)]·0.5C₂H₆O, (I), and bis(N,N‐di‐n‐hexyldithiocarbamato‐κ²S,S′)­bis(1,10‐phenanthroline‐κ²N,N′)calcium(II), [Ca(C₁₃H₂₆NS₂)₂(C₁₂H₈N₂)₂], (II), are mixed‐ligand com­plexes. In the first compound, the Zn atom has a distorted octahedral coordination, while in the second compound, the Ca atom is eight‐coordinate, with four S and four N atoms forming a highly distorted cube.     

2‐(N,N‐Diphenylamino)benzoic acid

Shaped like a distorted propeller, mol­ecules of the title compound, C₁₉H₁₅NO₂, form centrosymmetric dimers in the crystalline phase in which the carboxy groups are linked through two hydrogen bonds. These dimers are arranged in columns held together via dispersive interactions between the phenyl moieties. The N atom and the three surrounding C atoms lie almost in the same plane, which implies that the lone electron pair of the N atom is involved in conjugation with the π systems of the phenyl fragments.     

(Benzoyl­acetonato)­chloro(1,10‐phen­anthroline)copper(II)

The crystal structure of the title compound, chloro(1,10‐phenanthroline‐N,N′)(1‐phenyl‐1,3‐butane­dion­ato‐O,O′)copper(II), [CuCl(C₁₀H₉O₂)(C₁₂H₈N₂)], has been determined. The Cu^II ion displays a distorted square‐pyramidal coordination, being linked to the two O atoms of the benzoyl­acetonate ligand and the two N atoms of the 1,10‐phenanthroline ligand in the basal plane, and the Cl atom in the apical site. TheCu—N, Cu—O and Cu—Cl bond lengths are 2.043 (2)/2.025 (2), 1.914 (2)/1.941 (2) and 2.485 (1) Å, respectively.     

(Acetonitrile){2,6‐bis[1‐(2,4,6‐trimethylphenylimino)ethyl]pyridine}dichloridoruthenium(II) dichloromethane solvate

In the title compound, [RuCl₂(C₂H₃N)(C₂₇H₃₁N₃)]·CH₂Cl₂, the Ru^II ion is six‐coordinated in a distorted octahedral arrangement, with the two Cl atoms located in the apical positions, and the pyridine (py) N atom, the two imino N atoms and the acetonitrile N atom located in the basal plane. The two equatorial Ru—N_imino distances are almost equal (mean 2.087 Å) and are substantially longer than the equatorial Ru—N_py bond [1.921 (4) Å]. It is observed that the N_imino—M—N_py angle for the five‐membered chelate rings of pyridine‐2,6‐diimine complexes is inversely related to the magnitude of the M—N_py bond. The title structure is stabilized by intra‐ and intermolecular C—H...Cl hydrogen bonds, as well as by van der Waals interactions.     

trans‐Diaquabis(1H‐imidazole‐4,5‐di­carboxyl­ate‐κ2N3,O4)­manganese(II)

In the title compound, [Mn(C₅H₃N₂O₄)₂(H₂O)₂], the Mn^II atom lies on an inversion centre, is trans‐coordinated by two N,O‐bidentate 1H‐imidazole‐4,5‐di­carboxyl­ate monoanionic ligands [Mn—O = 2.202 (3) Å and Mn—N = 2.201 (4) Å] and two water mol­ecules [Mn—O = 2.197 (4) Å], and exhibits a distorted octahedral geometry, with adjacent cis angles of 76.45 (13), 86.09 (13) and 89.20 (13)°. The complete solid‐state structure can be described as a three‐dimensional supramol­ecular framework, stabilized by extensive hydrogen‐bonding interactions involving the coordinated water mol­ecules, the carboxy O atoms and the protonated imidazole N atoms of the imidazole‐4,5‐di­carboxyl­ate ligands.     

Synthesis and Structure of N,N-Dimethyldithiocarbamates of Tetraphenylantimony and Tetra-p-tolylantimony

Tetraphenylantimony N,N-dimethyldithiocarbamate (I) and tetra-p-tolylantimony N,N-dimethyldithiocarbamate (II) were synthesized via the reaction of tetraarylantimony chloride Ar₄SbCl (Ar = C₆H₅ or C₆H₄Me-4) with sodium N,N-dimethyldithiocarbamate in water. According to the X-ray diffraction data, the tetraarylantimony N,N-dimethyldithiocarbamate molecules have a distorted octahedral configuration. The Sb–S bond lengths are equal to 2.7158(5) Å, 2.7440(5) Å and 2.761(2) Å, 2.8002(2) Å for I and II, respectively.     

μ‐3,4′‐Bi‐1,2,4‐triazole‐di‐μ‐chloro‐cuivre(II) monohydraté

In the title compound, μ‐3,4′‐bi‐1,2,4‐triazole‐di‐μ‐chloro‐copper(II) monohydrate, {[CuCl₂(C₄H₄N₆)]·H₂O}_n, the Cu atom is located in a distorted octahedron consisting of two N atoms and four Cl atoms. The structural unit is an infinite chain in which octahedral groups, connected by shared edges, are also linked by bitriazole mol­ecules. The bitriazole ligand, the Cu atom and the water O atom all lie on independent twofold axes. The structure is held together by hydrogen bonds between the water mol­ecules and the non‐coordinated N atoms of the ligand, and by van der Waals forces.     

Syntheses and structures of two new uranyl complexes [UO2(DPDPU)2(NO3)2](C6H5CH3) and [UO2(PMBP)2(DPDPU)](CH3C6H4CH3)0.5

Two new uranyl complexes [UO₂(DPDPU)₂(NO₃)₂](C₆H₅CH₃) (1) and [UO₂(PMBP)₂ (DPDPU)](CH₃C₆H₄CH₃)_0.5 (2), (DPDPU?=?N,N′-dipropyl-N,N′-diphenylurea, HPMBP?= 1-phenyl-3-methyl-4-benzoyl-pyrazolone-5) were synthesized and characterized. The coordination geometry of the uranyl atom in 1 is distorted hexagonal bipyramidal, coordinated by two oxygen atoms of two DPDPU molecules and four oxygen atoms of two bidentate nitrate groups. The coordination geometry of the uranyl atom in 2 is distorted pentagonal bipyramidal, coordinated by one oxygen atom of one DPDPU molecule and four oxygen atoms of two chelating PMBP molecules.     

catena‐Poly­[[[aqua­bis(1H‐benz­imidazole‐κN3)­cadmium(II)]‐μ‐phthalato‐κ3O,O′:O′′] hemihydrate]

The title compound is a polymeric complex bridged by a phthalate dianion, {[Cd(C₈H₄O₄)(C₇H₆N₂)₂(H₂O)]·0.5H₂O}_n. The asymmetric unit contains two Cd complex units, and both Cd^II atoms have the same distorted octahedral coordination geometry. Each phthalate dianion bridges two Cd atoms through the two terminal carboxy groups, one in a monodentate fashion and the other in a chelating mode, thus forming zigzag polymeric chains; π–π stacking occurs between neighboring chains. The bond angle involving the chelating carboxy group is large, but the corresponding bond distance is normal. This implies the existence of an electrostatic interaction between the Cd^II atoms and the carboxy groups.