Structure determination of three furan‐substituted benzimidazoles and calculation of π–π and C—H...π interaction energies

The synthesis and structural characterization of 2‐(furan‐2‐yl)‐1‐(furan‐2‐ylmethyl)‐1H‐benzimidazole [C₁₆H₁₂N₂O₂, (I)], 2‐(furan‐2‐yl)‐1‐(furan‐2‐ylmethyl)‐1H‐benzimidazol‐3‐ium chloride monohydrate [C₁₆H₁₃N₂O₂⁺·Cl⁻·H₂O, (II)] and the hydrobromide salt 5,6‐dimethyl‐2‐(furan‐2‐yl)‐1‐(furan‐2‐ylmethyl)‐1H‐benzimidazol‐3‐ium bromide [C₁₈H₁₇N₂O₂⁺·Br⁻, (III)] are described. Benzimidazole (I) displays two sets of aromatic interactions, each of which involves pairs of molecules in a head‐to‐tail arrangement. The first, denoted set (Ia), exhibits both intermolecular C—H...π interactions between the 2‐(furan‐2‐yl) (abbreviated as Fn) and 1‐(furan‐2‐ylmethyl) (abbreviated as MeFn) substituents, and π–π interactions involving the Fn substituents between inversion‐center‐related molecules. The second, denoted set (Ib), involves π–π interactions involving both the benzene ring (Bz) and the imidazole ring (Im) of benzimidazole. Hydrated salt (II) exhibits N—H...OH₂...Cl hydrogen bonding that results in chains of molecules parallel to the a axis. There is also a head‐to‐head aromatic stacking of the protonated benzimidazole cations in which the Bz and Im rings of one molecule interact with the Im and Fn rings of adjacent molecules in the chain. Salt (III) displays N—H...Br hydrogen bonding and π–π interactions involving inversion‐center‐related benzimidazole rings in a head‐to‐tail arrangement. In all of the π–π interactions observed, the interacting moieties are shifted with respect to each other along the major molecular axis. Basis set superposition energy‐corrected (counterpoise method) interaction energies were calculated for each interaction [DFT, M06‐2X/6‐31+G(d)] employing atomic coordinates obtained in the crystallographic analyses for heavy atoms and optimized H‐atom coordinates. The calculated interaction energies are −43.0, −39.8, −48.5, and −55.0 kJ mol⁻¹ for (Ia), (Ib), (II), and (III), respectively. For (Ia), the analysis was used to partition the interaction energies into the C—H...π and π–π components, which are 9.4 and 24.1 kJ mol⁻¹, respectively. Energy‐minimized structures were used to determine the optimal interplanar spacing, the slip distance along the major molecular axis, and the slip distance along the minor molecular axis for 2‐(furan‐2‐yl)‐1H‐benzimidazole.     

π–π stacking motifs in dialkylbis{5‐[(E)‐2‐aryldiazen‐1‐yl]‐2‐hydroxybenzoato}tin(IV) complexes

The diorganotin(IV) complexes of 5‐[(E)‐2‐aryldiazen‐1‐yl]‐2‐hydroxybenzoic acid are of interest because of their structural diversity in the crystalline state and their interesting biological activity. The structures of dimethylbis{2‐hydroxy‐5‐[(E)‐2‐(4‐methylphenyl)diazen‐1‐yl]benzoato}tin(IV), [Sn(CH₃)₂(C₁₄H₁₁N₂O₃)₂], and di‐n‐butylbis{2‐hydroxy‐5‐[(E)‐2‐(4‐methylphenyl)diazen‐1‐yl]benzoato}tin(IV) benzene hemisolvate, [Sn(C₄H₉)₂(C₁₄H₁₁N₂O₃)₂]·0.5C₆H₆, exhibit the usual skew‐trapezoidal bipyramidal coordination geometry observed for related complexes of this class. Each structure has two independent molecules of the Sn^IV complex in the asymmetric unit. In the dimethyltin structure, intermolecular O—H…O hydrogen bonds and a very weak Sn…O interaction link the independent molecules into dimers. The planar carboxylate ligands lend themselves to π–π stacking interactions and the diversity of supramolecular structural motifs formed by these interactions has been examined in detail for these two structures and four closely related analogues. While there are some recurring basic motifs amongst the observed stacking arrangements, such as dimers and step‐like chains, variations through longitudinal slipping and inversion of the direction of the overlay add complexity. The π–π stacking motifs in the two title complexes are combinations of some of those observed in the other structures and are the most complex of the structures examined.     

Multiple N—H...NC,C—H...NC and nitrile...π interactions in 4,4′‐bipyridine‐1,1′‐diium bis(1,1,3,3‐tetracyano‐2‐ethoxypropenide): structure determination and DFT calculations of anion...π cation interaction energies

Polynitrile anions are important in both coordination chemistry and molecular materials chemistry, and are interesting for their extensive electronic delocalization. The title compound crystallizes with two symmetry‐independent half 4,4′‐bipyridine‐1,1′‐diium (bpyH₂²⁺) cations and two symmetry‐independent 1,1,3,3‐tetracyano‐2‐ethoxypropenide (tcnoet⁻) anions in the asymmetric unit. One of the bpyH₂²⁺ ions is located on a crystallographic twofold rotation axis (canted pyridine rings) and the other is located on a crystallographic inversion center (coplanar pyridine rings). The ethyl group of one of the tcnoet⁻ anions is disordered over two sites with equal populations. The extended structure exhibits two separate N—H...NC hydrogen‐bonding motifs, which result in a sheet structure parallel to (010), and weak C—H...NC hydrogen bonds form joined rings. Two types of multicenter CN...π interactions are observed between the bpyH₂²⁺ rings and tcnoet⁻ anions. An additonal CN...π interaction between adjacent tcnoet⁻ anions is observed. Using density functional theory, the calculated attractive energy between cation and anion pairs in the tcnoet⁻...π(bipyridinediium) interactions were found to be 557 and 612 kJ mol⁻¹ for coplanar and canted bpyH₂²⁺ cations, respectively.     

Supramolecular hydrogen‐bonding patterns in the organic–inorganic hybrid compound bis(4‐amino‐5‐chloro‐2,6‐dimethylpyrimidinium) tetrathiocyanatozinc(II)–4‐amino‐5‐chloro‐2,6‐dimethylpyrimidine–water (1/2/2)

Zinc thiocyanate complexes have been found to be biologically active compounds. Zinc is also an essential element for the normal function of most organisms and is the main constituent in a number of metalloenzyme proteins. Pyrimidine and aminopyrimidine derivatives are biologically very important as they are components of nucleic acids. Thiocyanate ions can bridge metal ions by employing both their N and S atoms for coordination. They can play an important role in assembling different coordination structures and yield an interesting variety of one‐, two‐ and three‐dimensional polymeric metal–thiocyanate supramolecular frameworks. The structure of a new zinc thiocyanate–aminopyrimidine organic–inorganic compound, (C₆H₉ClN₃)₂[Zn(NCS)₄]·2C₆H₈ClN₃·2H₂O, is reported. The asymmetric unit consist of half a tetrathiocyanatozinc(II) dianion, an uncoordinated 4‐amino‐5‐chloro‐2,6‐dimethylpyrimidinium cation, a 4‐amino‐5‐chloro‐2,6‐dimethylpyrimidine molecule and a water molecule. The Zn^II atom adopts a distorted tetrahedral coordination geometry and is coordinated by four N atoms from the thiocyanate anions. The Zn^II atom is located on a special position (twofold axis of symmetry). The pyrimidinium cation and the pyrimidine molecule are not coordinated to the Zn^II atom, but are hydrogen bonded to the uncoordinated water molecules and the metal‐coordinated thiocyanate ligands. The pyrimidine molecules and pyrimidinium cations also form base‐pair‐like structures with an R₂²(8) ring motif via N—H…N hydrogen bonds. The crystal structure is further stabilized by intermolecular N—H…O, O—H…S, N—H…S and O—H…N hydrogen bonds, by intramolecular N—H…Cl and C—H…Cl hydrogen bonds, and also by π–π stacking interactions.     

Synthesis and Crystal Structure of a [Mo8O26]4– Cluster Derivative with 4‐MePyH+. First β‐Octamolybdate Derivative with π–π Stacking

Dioxobis(pyridine‐2‐thiolate‐N, S)molybdenum(VI) (MoO₂(Py‐S)₂), reacts with of 4‐methylpyridine (4‐MePy) in acetonitrile, by slow diffusion, to afford the title compound. This has been characterized by elemental analysis, IR and ¹H NMR spectroscopy. The X‐ray single crystal structure of the complex is described. Structural studies reveal that the molecular structure consists of a β‐Mo₈O₂₆ polyanion with eight MoO₆ distorted edge‐shared octahedra with short terminal Mo–O bonds (1.692–1.714 Å), bonds of intermediate length (1.887–1.999 Å) and long bonds (2.150–2.473 Å). Two different types of hydrogen bonds have been found: N–H···O (2.800–3.075 Å) and C–H···O (3.095–3.316 Å). The presence of π–π stacking interactions and strong hydrogen bonds are presumably responsible for the special disposition of the pyridinic rings around the polyanion cluster.     

Complexes of nickel(II) and copper(II) with 1,2,4‐triazole‐3‐carboxylic acid and of cobalt(III) with 3‐amino‐1,2,4‐triazole‐5‐carboxylic acid

Because of their versatile coordination modes and strong coordination ability for metals, triazole ligands can provide a wide range of possibilities for the construction of metal–organic frameworks. Three transition‐metal complexes, namely bis(μ‐1,2,4‐triazol‐4‐ide‐3‐carboxylato)‐κ³N ²,O :N ¹;κ³N ¹:N ²,O‐bis[triamminenickel(II)] tetrahydrate, [Ni₂(C₃HN₃O₂)₂(NH₃)₆]·4H₂O, (I), catena‐poly[[[diamminediaquacopper(II)]‐μ‐1,2,4‐triazol‐4‐ide‐3‐carboxylato‐κ³N ¹:N ⁴,O‐[diamminecopper(II)]‐μ‐1,2,4‐triazol‐4‐ide‐3‐carboxylato‐κ³N ⁴,O :N ¹] dihydrate], {[Cu₂(C₃HN₃O₂)₂(NH₃)₄(H₂O)₂]·2H₂O}_n , (II), (μ‐5‐amino‐1,2,4‐triazol‐1‐ide‐3‐carboxylato‐κ²N ¹:N ²)di‐μ‐hydroxido‐κ⁴O :O‐bis[triamminecobalt(III)] nitrate hydroxide trihydrate, [Co₂(C₃H₂N₄O₂)(OH)₂(NH₃)₆](NO₃)(OH)·3H₂O, (III), with different structural forms have been prepared by the reaction of transition metal salts, i.e. NiCl₂, CuCl₂ and Co(NO₃)₂, with 1,2,4‐triazole‐3‐carboxylic acid or 3‐amino‐1,2,4‐triazole‐5‐carboxylic acid hemihydrate in aqueous ammonia at room temperature. Compound (I) is a dinuclear complex. Extensive O—H…O, O—H…N and N—H…O hydrogen bonds and π–π stacking interactions between the centroids of the triazole rings contribute to the formation of the three‐dimensional supramolecular structure. Compound (II) exhibits a one‐dimensional chain structure, with O—H…O hydrogen bonds and weak O—H…N, N—H…O and C—H…O hydrogen bonds linking anions and lattice water molecules into the three‐dimensional supramolecular structure. Compared with compound (I), compound (III) is a structurally different dinuclear complex. Extensive N—H…O, N—H…N, O—H…N and O—H…O hydrogen bonding occurs in the structure, leading to the formation of the three‐dimensional supramolecular structure.     

Hydrogen bonding and π–π interactions in the cocrystal salt [Fe(bpe)2(H2O)4](TCEP)2·2(bpe) [bpe is trans‐1,2‐bis(pyridin‐4‐yl)ethene and TCEP is 1,1,3,3‐tetracyano‐2‐ethoxypropenide]

The cocrystal salt tetraaquabis[trans‐1,2‐bis(pyridin‐4‐yl)ethene‐κN]iron(II) bis(1,1,3,3‐tetracyano‐2‐ethoxypropenide)–trans‐1,2‐bis(pyridin‐4‐yl)ethene (1/2), [Fe(C₁₂H₁₀N₂)₂(H₂O)₄](C₉H₅N₄O)₂·2C₁₂H₁₀N₂, is a rare example of a mononuclear Fe^II compound with trans‐1,2‐bis(pyridin‐4‐yl)ethane (bpe) ligands. The complex cation resides on a crystallographically imposed inversion center and exhibits a tetragonally distorted octahedral coordination geometry. Both the symmetry‐independent bpe ligand and the cocrystallized bpe molecule are essentially planar. The 1,1,3,3‐tetracyano‐2‐ethoxypropenide counter‐ion is nonplanar and the bond lengths are consistant with significant electron delocalization. The extended structure exhibits an extensive O—H…N hydrogen‐bonding network with layers of complex cations joined by the cocrystallized bpe. Both the coordinated and the cocrystallized bpe are involved in π–π interactions. Hirshfeld and fingerprint plots reveal the important intermolecular interactions. Density functional theory was used to estimate the strengths of the hydrogen‐bonding and π–π interactions, and suggest that the O—H…N hydrogen bonds enhance the strength of the π‐interactions by increasing the polarization of the pyridine rings.     

Supramolecular architectures in the salt trimethoprimium ferrocene‐1‐carboxylate and the cocrystal 4‐amino‐5‐chloro‐2,6‐dimethylpyrimidine–ferrocene‐1‐carboxylic acid (1/1)

In the salt trimethoprimium ferrocenecarboxylate [systematic name: 2,4‐diamino‐5‐(3,4,5‐trimethoxybenzyl)pyrimidin‐1‐ium ferrocene‐1‐carboxylate], (C₁₄H₁₉N₄O₃)[Fe(C₅H₅)(C₆H₄O₂)], (I), of the antibacterial compound trimethoprim, the carboxylate group interacts with the protonated aminopyrimidine group of trimethoprim via two N—H…O hydrogen bonds, generating a robust R ₂²(8) ring motif (heterosynthon). However, in the cocrystal 4‐amino‐5‐chloro‐2,6‐dimethylpyrimidine–ferrocene‐1‐carboxylic acid (1/1), [Fe(C₅H₅)(C₆H₅O₂)]·C₆H₈ClN₃, (II), the carboxyl–aminopyrimidine interaction [R ₂²(8) motif] is absent. The carboxyl group interacts with the pyrimidine ring via a single O—H…N hydrogen bond. The pyrimidine rings, however, form base pairs via a pair of N—H…N hydrogen bonds, generating an R ₂²(8) supramolecular homosynthon. In salt (I), the unsubstituted cyclopentadienyl ring is disordered over two positions, with a refined site‐occupation ratio of 0.573 (10):0.427 (10). In this study, the two five‐membered cyclopentadienyl (Cp) rings of ferrocene are in a staggered conformation, as is evident from the C…Cg …Cg …C pseudo‐torsion angles, which are in the range 36.13–37.53° for (I) and 22.58–23.46° for (II). Regarding the Cp ring of the minor component in salt (I), the geometry of the ferrocene ring is in an eclipsed conformation, as is evident from the C…Cg …Cg …C pseudo‐torsion angles, which are in the range 79.26–80.94°. Both crystal structures are further stabilized by weak π–π interactions.     

Copper(II) bis(4,4,4‐trifluoro‐1‐phenylbutane‐1,3‐dionate) complexes with pyridin‐2‐one, 3‐hydroxypyridine and 3‐hydroxypyridin‐2‐one ligands: molecular structures and hydrogen‐bonded networks

Copper(II) bis(4,4,4‐trifluoro‐1‐phenylbutane‐1,3‐dionate) complexes with pyridin‐2‐one (pyon), 3‐hydroxypyridine (hpy) and 3‐hydroxypyridin‐2‐one (hpyon) were prepared and the solid‐state structures of (pyridin‐2‐one‐κO )bis(4,4,4‐trifluoro‐3‐oxo‐1‐phenylbutan‐1‐olato‐κ²O ,O ′)copper(II), [Cu(C₁₀H₆F₃O₂)₂(C₅H₅NO)] or [Cu(tfpb‐κ²O ,O ′)₂(pyon‐κO )], (I), bis(pyridin‐3‐ol‐κO )bis(4,4,4‐trifluoro‐3‐oxo‐1‐phenylbutan‐1‐olato‐κ²O ,O ′)copper(II), [Cu(C₁₀H₆F₃O₂)₂(C₅H₅NO)₂] or [Cu(tfpb‐κ²O ,O ′)₂(hpy‐κO )₂], (II), and bis(3‐hydroxypyridin‐2‐one‐κO )bis(4,4,4‐trifluoro‐3‐oxo‐1‐phenylbutan‐1‐olato‐κ²O ,O ′)copper(II), [Cu(C₁₀H₆F₃O₂)₂(C₅H₅NO₂)₂] or [Cu(tfpb‐κ²O ,O ′)₂(hpyon‐κO )₂], (III), were determined by single‐crystal X‐ray analysis. The coordination of the metal centre is square pyramidal and displays a rare example of a mutual cis arrangement of the β‐diketonate ligands in (I) and a trans‐octahedral arrangement in (II) and (III). Complex (II) presents the first crystallographic evidence of κO‐monodentate hpy ligation to the transition metal enabling the pyridine N atom to participate in a two‐dimensional hydrogen‐bonded network through O—H…N interactions, forming a graph‐set motif R ₂²(7) through a C—H…O interaction. Complex (III) presents the first crystallographic evidence of monodentate coordination of the neutral hpyon ligand to a metal centre and a two‐dimensional hydrogen‐bonded network is formed through N—H…O interactions facilitated by C—H…O interactions, forming the graph‐set motifs R ₂²(8) and R ₂²(7).     

Comparative studies on group III σ‐hole and π‐hole interactions

The σ‐hole of M₂H₆ (M = Al, Ga, In) and π‐hole of MH₃ (M = Al, Ga, In) were discovered and analyzed, the bimolecular complexes M₂H₆···NH₃ and MH₃···N₂P₂F₄ (M = Al, Ga, In) were constructed to carry out comparative studies on the group III σ‐hole interactions and π‐hole interactions. The two types of interactions are all partial‐covalent interactions; the π‐hole interactions are stronger than σ‐hole interactions. The electrostatic energy is the largest contribution for forming the σ‐hole and π‐hole interaction, the polarization energy is also an important factor to form the M···N interaction. The electrostatic energy contributions to the interaction energy of the σ‐hole interactions are somewhat greater than those of the π‐hole interactions. However, the polarization contributions for the π‐hole interactions are somewhat greater than those for the σ‐hole interactions. © 2016 Wiley Periodicals, Inc.     

Three zinc(II) and cadmium(II) complexes containing 4‐amino‐3,5‐bis(pyridin‐2‐yl)‐1,2,4‐triazole and polynitrile ligands: synthesis,molecular and supramolecular structures,and photoluminescence properties

Three photoluminescent complexes containing either Zn^II or Cd^II have been synthesized and their structures determined. Bis[4‐amino‐3,5‐bis(pyridin‐2‐yl)‐1,2,4‐triazole‐κ²N ¹,N ⁵]bis(dicyanamido‐κN ¹)zinc(II), [Zn(C₁₂H₁₀N₆)₂(C₂N₃)₂], (I), bis[4‐amino‐3,5‐bis(pyridin‐2‐yl)‐1,2,4‐triazole‐κ²N ¹,N ⁵]bis(dicyanamido‐κN ¹)cadmium(II), [Cd(C₁₂H₁₀N₆)₂(C₂N₃)₂], (II), and bis[4‐amino‐3,5‐bis(pyridin‐2‐yl)‐1,2,4‐triazole‐κ²N ¹,N ⁵]bis(tricyanomethanido‐κN ¹)cadmium(II), [Cd(C₁₂H₁₀N₆)₂(C₄N₃)₂], (III), all crystallize in the space group P , with the metal centres lying on centres of inversion, but neither analogues (I) and (II) nor Cd^II complexes (II) and (III) are isomorphous. A combination of N—H…N and C—H…N hydrogen bonds and π–π stacking interactions generates three‐dimensional framework structures in (I) and (II), and a sheet structure in (III). The photoluminescence spectra of (I)–(III) indicate that the energies of the π–π* transitions in the coordinated triazole ligand are modified by minor changes of the ligand geometry associated with coordination to the metal centres.     

π–π Stacking‐Interlinked Molecular Squares with Hepta‐Coordinated Cadmium(II) Corners, [Cd(DMAP)3(NO2)2]·0.5H2O

The single crystal X‐ray analysis data of the new hepta‐coordinate cadmium(II) complex of N,N‐dimethyl‐N‐(4‐pyridyl)amine (DMPA), [Cd(DMPA)₃(NO₂)₂]·0.5H₂O, shows that the coordination environment around the Cd^II is pentagonal bipyramidal. Furthermore, self‐assembly of this complex as molecular squares that interlink via π–π stacking interactions is observed. This network contains voids that are filled by water molecules.     

Supramolecular architectures in two 1:1 cocrystals of 5‐fluorouracil with 5‐bromothiophene‐2‐carboxylic acid and thiophene‐2‐carboxylic acid

In solid‐state engineering, cocrystallization is a strategy actively pursued for pharmaceuticals. Two 1:1 cocrystals of 5‐fluorouracil (5FU; systematic name: 5‐fluoro‐1,3‐dihydropyrimidine‐2,4‐dione), namely 5‐fluorouracil–5‐bromothiophene‐2‐carboxylic acid (1/1), C₅H₃BrO₂S·C₄H₃FN₂O₂, (I), and 5‐fluorouracil–thiophene‐2‐carboxylic acid (1/1), C₄H₃FN₂O₂·C₅H₄O₂S, (II), have been synthesized and characterized by single‐crystal X‐ray diffraction studies. In both cocrystals, carboxylic acid molecules are linked through an acid–acid R ₂²(8) homosynthon (O—H…O) to form a carboxylic acid dimer and 5FU molecules are connected through two types of base pairs [homosynthon, R ₂²(8) motif] via a pair of N—H…O hydrogen bonds. The crystal structures are further stabilized by C—H…O interactions in (II) and C—Br…O interactions in (I). In both crystal structures, π–π stacking and C—F…π interactions are also observed.     

Unexpected Formation of a π‐Coordinate Schiff Base Cobalt(0) Complex

Both tetrakis(trimethylphosphine)cobalt(0) and methyltetrakis(trimethylphosphine)cobalt(I) react with 2‐(benzylideneamino)pyridine ( 1 ) exclusively giving a complex of composition (η²(N,C)‐2‐Py‐N=CH‐C₆H₅)Co(PMe₃)₃ ( 2 ), which is shown by single‐crystal X‐ray diffraction to constitute the first π‐coordinate imine cobalt(0) complex. The route of formation is proposed and discussed.     

Synthesis,Crystal Structure and Properties of [Cu(phen)3][Cu(pheida)2]·10H2O and [(phen)2Cu(μ‐BAAP)Cu(μ‐BAAP)Cu(phen)2][Cu(BAAP)2]·8.5H2O (H2pheida = N‐phenetyl‐iminodiacetic acid,H2BAAP = N‐benzylaminoacetic‐2‐propionic acid)

The salts [Cu(phen)₃][Cu(pheida)₂]·10H₂O ( 1 ) and [(phen)₂Cu(μ‐BAAP)Cu(μ‐BAAP)Cu(phen)₂][Cu(BAAP)₂]·8.5H₂O ( 2 ) (H₂pheida = N‐phenetyl‐iminodiacetic acid, H₂BAAP = N‐benzylaminoacetic‐2‐propionic acid, phen = 1, 10‐phenanthroline) have been prepared and studied by thermal, spectroscopic and X‐ray diffraction methods. 1 has the rather unusual [Cu(phen)₃]²⁺ cation and two non‐equivalent [Cu(pheida)₂]^2— anions with a coordination type 4+2 but quite different tetragonality (T = 0.848 and 0.703 for anions 1 and 2, respectively). The crystal consists of multi‐π, π‐stacked chains (…anion 2 — cation — cation — anion 2…) connected by hydrophobic interactions; these chains build channels which are partially filled by anions 1 and water molecules. In contrast, compound 2 has a mixed‐ligand trinuclear cation with a bridging central moiety close similar to the counter anion. The formation of such a trinuclear cation is discussed as a consequence of the most advantageous molecular recognition process between [Cu(phen)₂(H₂O)_{1 or 2}]²⁺ and [Cu(BAAP)₂]^2— in solution. In the crystal of 2, multi‐π, π‐stacked arrays of C₆‐rings from phen and (BAAP)^2— ligands of trinuclear cations generate channels where counter anions and water molecules are located.     

The tropolone–isobutylamine complex: a hydrogen‐bonded troponoid without dominant π–π interactions

Tropolone long has served as a model system for unraveling the ubiquitous phenomena of proton transfer and hydrogen bonding. This molecule, which juxtaposes ketonic, hydroxylic, and aromatic functionalities in a framework of minimal complexity, also has provided a versatile platform for investigating the synergism among competing intermolecular forces, including those generated by hydrogen bonding and aryl coupling. Small members of the troponoid family typically produce crystals that are stabilized strongly by pervasive π–π, C—H…π, or ion–π interactions. The organic salt (TrOH·iBA) formed by a facile proton‐transfer reaction between tropolone (TrOH) and isobutylamine (iBA), namely isobutylammonium 7‐oxocyclohepta‐1,3,5‐trien‐1‐olate, C₄H₁₂N⁺·C₇H₅O₂⁻, has been investigated by X‐ray crystallography, with complementary quantum‐chemical and statistical‐database analyses serving to elucidate the nature of attendant intermolecular interactions and their synergistic effects upon lattice‐packing phenomena. The crystal structure deduced from low‐temperature diffraction measurements displays extensive hydrogen‐bonding networks, yet shows little evidence of the aryl forces (viz. π–π, C—H…π, and ion–π interactions) that typically dominate this class of compounds. Density functional calculations performed with and without the imposition of periodic boundary conditions (the latter entailing isolated subunits) documented the specificity and directionality of noncovalent interactions occurring between the proton‐donating and proton‐accepting sites of TrOH and iBA, as well as the absence of aromatic coupling mediated by the seven‐membered ring of TrOH. A statistical comparison of the structural parameters extracted for key hydrogen‐bond linkages to those reported for 44 previously known crystals that support similar binding motifs revealed TrOH·iBA to possess the shortest donor–acceptor distances of any troponoid‐based complex, combined with unambiguous signatures of enhanced proton‐delocalization processes that putatively stabilize the corresponding crystalline lattice and facilitate its surprisingly rapid formation under ambient conditions.     

Zinc(II) and Cadmium(II) Complexes of the 3‐(2‐Pyridyl)‐5,6‐diphenyl‐1,2,4‐triazine (PDPT) Ligand,Structural Studies of [Zn(PDPT)2Cl(ClO4)] and [Cd(PDPT)2(NO3)(ClO4)]

Two new mixed‐anion zinc(II) and cadmium(II) complexes of 3‐(2‐pyridyl)‐5,6‐diphenyl‐1,2,4‐triazine (PDPT) ligand, [Zn(PDPT)₂Cl(ClO₄)] and [Cd(PDPT)₂(NO₃)(ClO₄)], have been synthesized and characterized by elemental analysis, IR‐ and ¹H NMR spectroscopy. The single crystal X‐ray analyses show that the coordination number in these complexes is six with four N‐donor atoms from two “PDPT” ligand and two of the anionic ligands, ZnN₄ClO_perchlorate, CdN₄O_nitrateO_perchlorate. Self‐assembly of these compounds in the solid state via π–π‐stacking interactions is discussed.     

CH–π and CF–π Interactions Lead to Structural Changes of N‐Heterocyclic Carbene Palladium Complexes

The role of CH–π and CF–π interactions in determining the structure of N‐heterocyclic carbene (NHC) palladium complexes were studied using ¹H NMR spectroscopy, X‐ray crystallography, and DFT calculations. The CH–π interactions led to the formation of the cis‐anti isomers in 1‐aryl‐3‐isopropylimidazol‐2‐ylidene‐based [(NHC)₂PdX₂] complexes, while CF–π interactions led to the exclusive formation of the cis‐syn isomer of diiodobis(3‐isopropyl‐1‐pentafluorophenylimidazol‐2‐ylidene) palladium(II).     

Crystal structure and hydrogen bonding in the hydrated cocrystalline salt tryptaminium–3,5‐dinitrobenzoate–quinoline–water (3/3/2/2)

The study of ternary systems is interesting because it introduces the concept of molecular preference/competition into the system where one molecule may be displaced because the association between the other two is significantly stronger. Current definitions of a tertiary system indicate that solvent molecules are excluded from the molecule count of the system and some of the latest definitions state that any molecule that is not a solid in the parent form at room temperature should also be excluded from the molecule count. In the structure of the quinoline adduct hydrate of tryptaminium 3,5‐dinitrobenzoate, 3C₁₀H₁₃N₂⁺·3C₇H₃N₂O₆⁻·2C₉H₇N·2H₂O, the asymmetric unit comprises multiple cation and anion species which are conformationally similar among each type set. In the crystal, a one‐dimensional hydrogen‐bonded supramolecular structure is generated through extensive intra‐ and inter‐unit aminium N—H…O and N—H…N, and water O—H…O hydrogen bonds. Within the central‐core hydrogen‐bonding associations, conjoined cyclic R₄⁴(10), R₅³(10) and R₄⁴(12) motifs are generated. The unit is expanded into a one‐dimensional column‐like polymer extending along [010]. Present also in the crystal packing of the structure are a total of 19 π–π interactions involving both cation, anion and quinoline species [ring‐centroid separation range = 3.395 (3)–3.797 (3) Å], as well as a number of weak C—H…O hydrogen‐bonding associations. The presence of the two water molecules in the crystal structure is considered to be the principal causative factor in the low symmetry of the asymmetric unit.     

Supramolecular interactions in carboxylate and sulfonate salts of 2,6‐diamino‐4‐chloropyrimidinium

Two new salts, namely 2,6‐diamino‐4‐chloropyrimidinium 2‐carboxy‐3‐nitrobenzoate, C₄H₆ClN₄⁺·C₈H₄NO₆⁻, (I), and 2,6‐diamino‐4‐chloropyrimidinium p‐toluenesulfonate monohydrate, C₄H₆ClN₄⁺·C₇H₇O₃S⁻·H₂O, (II), have been synthesized and characterized by single‐crystal X‐ray diffraction. In both crystal structures, the N atom in the 1‐position of the pyrimidine ring is protonated. In salt (I), the protonated N atom and the amino group of the pyrimidinium cation interact with the carboxylate group of the anion through N—H…O hydrogen bonds to form a heterosynthon with an R ₂²(8) ring motif. In hydrated salt (II), the presence of the water molecule prevents the formation of the familiar R ₂²(8) ring motif. Instead, an expanded ring [i.e. R ₃²(8)] is formed involving the sulfonate group, the pyrimidinium cation and the water molecule. Both salts form a supramolecular homosynthon [R ₂²(8) ring motif] through N—H…N hydrogen bonds. The molecular structures are further stabilized by π–π stacking, and C=O…π, C—H…O and C—H…Cl interactions.