A novel hydrogen-bonded cyclic dibromide in an organic diammonium salt

The organic diammonium salt N,N′-dibenzyl-N,N,N′,N′-tetramethylethylenediammonium dibromide dihydrate, (dbtmen)Br₂.2H₂O (1), was prepared by the reaction of N,N,N′,N′-tetramethyl-ethylenediamine (tmen) with benzyl bromide.1 crystallizes in the triclinic space group with the following unit cell dimensions for C₂₀H₃₄Br₂N₂O₂ (M = 494.31):a = 8.6672(6) ?,b = 11.7046(8) ?,c = 11.7731(8) ?, α = 76.988(8)°, β = 88.978(8)°, γ= 76.198(8)γ,V= 1129.26(13) ?³, Z=2. Three components, namely the (dbtmen)²⁺ dication, two bromide anions and two crystal water molecules constitute the structural arrangement of1. H₂O molecules are linked to bromide anions via O-H...Br hydrogen bonding interactions resulting in the formation of a four-membered O₂Br₂ cyclic dibromide. The O₂Br₂ units and the dications are arranged as alternating layers extending in the crystallographicbc plane. The arrangement of anions and cations may be viewed as a typical lamellar structure. The crystal water molecules can be removed by heating 1 at 140°C and the anhydrous dibromide thus formed can be fully rehydrated as evidenced by IR spectra and X-ray powder patterns. Dedicated to Prof S Chandrasekaran on the occasion of his 60th birthday     

Supramolecular architectures with ladder and lamellar topologies using metal-ligand coordination units via C–H···Cl and O–H···Cl hydrogen bonding

New Mn^II/Cu^II/Zn^II complexes [(L¹)MnCl₂] (1), [(L²)CuCl₂]·0.5H₂O (2) and [(L²)ZnCl(H₂O)][ClO₄] (3), containing (2-pyridyl)alkylamine ligands, N-methyl-N,N-bis(2-pyridylmethyl)amine (L¹) and methyl[2-(2-pyridyl)ethyl](2-pyridylmethyl)amine (L²), have been prepared and characterized, including X-ray crystallography. The most striking feature of the structures of these complexes is the formation of molecular ladder and lamellar topology through the crystal packing arrangement, determined by both strong O–H···Cl and weak (however, multiple) C–H···Cl hydrogen-bonding interactions, to maintain the neutral/cationic metal-ligand coordination units linked to each other. In 3, additional secondary interactions are observed involving coordinated solvent and the counter-ion. The results presented here demonstrate that (i) the choice of organic ligands to provide flexibility and inherent potential to participate in hydrogen-bonding interactions, (ii) the coordination geometry preferences of metal ions, (iii) the number of metal-bound chloride ion and (iv) the presence of solvent/counter-anion have a great influence on supramolecular network topology.     

Crystallographic and theoretical studies of 4,4′-dimethyl-7,7′-bi([1,2,5]thiadiazolo[3,4-b]pyridylidene)–chloranilic acid (1/1) with intermolecular O–H···N hydrogen bonds and S···O heteroatom interactions

Abstract  The molecular and crystal structure of a 1:1 co-crystal of 4,4′-dimethyl-7,7′-bi([1,2,5]thiadiazolo[3,4-b]pyridylidene)–chloranilic acid, (1), has been determined by X-ray diffraction at the monoclinic space group P2₁/c with cell parameters of a = 8.422(6), b = 7.343(4), c = 16.112(7) ?, β = 104.988(8)°, V = 962.5(10) ?³ and Z = 2. In the crystal structure, two components connect via the intermolecular O–H···N hydrogen bonds [2.804(4) ?] and S···O heteroatom interaction [2.945(3) ?] with R ₂ ²(7) couplings to form a unique and infinite one-dimensional supramolecular tape structure. The calculations of (1) at the HF/6-31G(d), MP2/6-31G(d), and B3LYP/6-31G(d) levels can almost reproduce X-ray geometry. In addition, the distances of the intermolecular O–H···N and S···O interactions by MP2/6-31G(d) and B3LYP/6-31G(d) levels agree well with those in the crystal. The calculated binding energies corrected BSSE and ZPE are −4.487 (HF), −7.473 (MP2), and −5.640 (B3LYP) kcal/mol. The results suggest that the complex (1) is very stable and the dispersion interaction is significantly important for the attractive intermolecular interaction in (1). The NBO analysis has revealed that the n(N) → σ*(O–H) interaction gives the strongest stabilization to the system and the major interaction for the intermolecular S···O contact is n(O) → σ*(S–N). Index Abstract  In the crystal structure of the title compound, the molecules are linked by intermolecular O–H···N hydrogen bonds and short S···O heteroatom interactions with R ₂ ²(7) couplings to construct a unique and infinite one-dimensional supramolecular tape structure.      

Crystal structures of seven-coordinate (NH4)2[MnII(edta)(H2O)]·3H2O, (NH4)2[MnII(cydta)(H2O)]·4H2O and K2[MNII(hdtpa)]·3.5H2O complexes

The title compounds, (NH₄)₂[Mn^II(edta)(H₂O)]·3H₂O (H₄edta = ethylenediamine-N,N,N′,N′-tetraacetic acid), (NH₄)₂[Mn^II(cydta)(H₂O)]·4H₂O (H₄cydta = trans-1,2-cyclohexanediamine-N,N,N′,N′-tetraacetic acid) and K₂[Mn^II(Hdtpa)]·3.5H₂O (H₅dtpa = diethylenetriamine-N,N,N′,N″,N″-pentaacetic acid), were prepared; their compositions and structures were determined by elemental analysis and single-crystal X-ray diffraction technique. In these three complexes, the Mn²⁺ ions are all seven-coordinated and have a pseudomonocapped trigonal prismatic configuration. All the three complexes crystallize in triclinic system in P-1 space group. Crystal data: (NH₄)₂[Mn^II(edta)(H₂O)]·3H₂O complex, a = 8.774(3) ?, b = 9.007(3) ?, c = 13.483(4) ?, α = 80.095(4)°, β = 80.708(4)°, γ = 68.770(4)°, V = 972.6(5) ?³, Z = 2, D _c = 1.541 g/cm³, μ = 0.745 mm⁻¹, R = 0.033 and wR = 0.099 for 3406 observed reflections with I ≥ 2σ(I); (NH₄)₂[Mn^II(cydta)(H₂O)]·4H₂O complex, a = 8.9720(18) ?, b = 9.4380(19) ?, c = 14.931(3) ?, α = 76.99(3)°, β = 83.27(3)°, γ = 75.62(3)°, V = 1190.8(4)?³, Z = 2, D _c = 1.426 g/cm³, μ = 0.625 mm⁻¹, R = 0.061 and wR = 0.197 for 3240 observed reflections with I ≥ 2σ(I); K₂[Mn^II(Hdtpa)]·3.5H₂O complex, a = 8.672(3) ?, b = 9.059(3) ?, c = 15.074(6) ?, α = 95.813(6)°, β = 96.665(6)°, γ = 99.212(6)°, V = 1152.4(7) ?³, Z = 2, D _c = 1.687 g/cm³, μ = 1.006 mm⁻¹, R = 0.037 and wR = 0.090 for 4654 observed reflections with I ≥ 2σ(I). Original Russian Text Copyright ? 2008 by X. F. Wang, J. Gao, J. Wang, Zh. H. Zhang, Y. F. Wang, L. J. Chen, W. Sun, and X. D. Zhang The text was submitted by the authors in English. Zhurnal Strukturnoi Khimii, Vol. 49, No. 4, pp. 753–759, July–August, 2008.     

Hydrogen-bonded supramolecular motifs in crystal structures of trimethoprim barbiturate monohydrate (I) and 2-amino-4,6-dimethylpyrimidinium barbiturate trihydrate (II)

In the present study, we report the crystal structures of two organic salts, namely 2,4-diamino-5-(3′,4′,5′-trimethoxybenzyl)pyrimidinium (TMP) barbiturate monohydrate (TMPBAR) (I), 2-amino-4,6-dimethylpyrimidinium (AMPY) barbiturate trihydrate (AMPYBAR) (II). In both complexes, one ring nitrogen of TMP and AMPY are protonated as a result of proton transfer from the−CH₂ group of barbituric acid. In compound (I), the TMP cation and barbiturate anion are paired through twoN−H···O and one N−H···N hydrogen bonds. This pair further self-organizes through N−H···O hydrogen bonds to generate an array of six hydrogen bonds. These arrays are further cross-linked by N−H···O hydrogen bonds forming a sheet-like structure. The water molecule is also embedded in the sheet via O−H···O and C−H···O hydrogen bonds, forming a rosette-like supramolecular motif. TMP cations are also bridged by alternating water molecules via C−H···O and O−H···N hydrogen bonds. In compound (II), the symmetrical barbiturate anions self-organize on both sides through N−H···O hydrogen bonds generating a supramolecular chain. These chains are cross-linked by the three water molecules. A pair of barbiturate anions and two water molecules constitute an array of four hydrogen bonds (DADA quadruple array). These arrays are cross-linked by another water molecule. 2-Amino-4,6-dimethylpyrimidine cations are paired through N−H···N hydrogen bonds. These pairs are bridged by three water molecules generating a supramolecular ribbon. The barbiturate chains and base pairs are arranged in an alternate manner via N−H···O and O−H···O hydrogen bonds to generate a 3-D network.     

The directional polymeric chain of [(BiCl<Subscript>5</Subscript>)<Superscript>2−</Superscript>]<Subscript><Emphasis Type="Italic">n</Emphasis></Subscript> in 2,2′-Bi(2-1H-imidazolium) pentachlorobismuthate dihydrate

The title compound, (C₆H₆N₄)(BiCl₅) · 2H₂O, is built up by 2,2′-bi(2-1H-imidazolium) dications and (BiCl₅)²⁻ anions. Distorted BiCl₆ octahedra are joined with each other alternatively to form [(BiCl₅)²⁻] _n polymeric chains, where the bridging chlorine atoms are shared by two octahedra. The lone pair at the Bi atom shows obviously stereochemical activity, leading to distortion of the BiCl₆ octahedra and formation of the chain directionality. In solid state, the chains are stabilized by O-H···Cl and C-H···Cl hydrogen bonds. The article was submitted by the authors in English.     

Crystal Structure of a Supramolecular Complex Formed between 1-bromo-2-iodo-tetrafluoroethane and N,N,N′,N′-tetramethyl-ethylenediamine

X-ray analysis has revealed that N,N,N′,N′-tetramethyl-ethylenediamine 1 form donor–acceptor complex 3 with 1-bromo-2-iodo-tetrafluoroethane 2, in which the N X (X = Br, I) distances are longer than the average covalent bond length between X and N, but are also definitively shorter than the sum of the corresponding van der Waals radii of X and N, thus that indicating weak interactions between the nitrogen and bromine or iodine atoms. In our experimental section, a valuable method for recrystallization and collect X-ray data from crystals that easily exhibit decay and can be cracked is reported.     

Synthesis and crystal structure of 2-{5-[2-(2,6-dichlorophenylamino)benzyl]-4-p-tolyl-4H-1,2,4-triazol-3-ylthio}acetate

The compound 2-{5-[2-(2,6-dichlorophenylamino)benzyl]-4-p-tolyl-4H-1,2,4-triazol-3-ylthio}acetate has been prepared and characterized by IR, ¹H NMR, ¹³C NMR and mass spectra. The crystal and molecular structure were further confirmed using single crystal X-ray diffraction. The crystal structure has been found to be stabilized by intermolecular C–H···O interaction generating bifurcated hydrogen bonds whereas the C–H···N interactions generate chain of molecules. The intramolecular N–H···N hydrogen bond forms a ring with S(7) graph-set motif.     

A one-dimensional barium(II) coordination polymer with a coordinated nitro group of 2-nitrobenzoate

The aqueous reaction of barium carbonate with 2-nitrobenzoic acid (2-nbaH) results in the formation of a one-dimensional coordination polymer, catena-poly[[hexa(aqua)dibarium(II)]bis[(μ ₂-2-nitrobenzoate-O,O,O-NO₂)(μ ₂-2-nitrobenzoate-O,O,O′)]] 1. On heating at 100°C compound 1 is dehydrated to anhydrous barium bis(2-nitrobenzoate) 2. The anhydrous compound can be re-hydrated to 1 on exposure to water vapour. Compounds 1 and 2 were characterized by elemental analysis, IR and UV-Vis spectra, DSC thermograms, weight loss studies and the structure of 1 was determined. 1 and 2 can be thermally decomposed to BaCO₃ by heating at 800°C. The polymer [[Ba(H₂O)₃]₂(μ ₂-2-nba-O,O,O-NO₂)₂ (μ ₂-2-nba-O,O,O′)₂] _n 1 crystallizes in the centrosymmetric triclinic space group Pī and all atoms are located in general positions. The polymeric structure is based on a dimeric unit and consists of three water molecules coordinated to a central Ba(II) and two unique 2-nitrobenzoate (2-nba) anions, one of which (μ ₂-2-nba-O,O,O-NO₂) functions as a tridentate ligand and is linked to a Ba(II) through the oxygen atom of the-NO₂ group and forms a monoatomic μ ₂-carboxylate bridge between two symmetry related Ba(II) ions with a Ba···Ba distance of 4·5726(14) ?. The second unique 2-nba anion (μ ₂-2-nba-O,O,O′) also functions as a tridentate ligand with the carboxylate oxygen atoms linked to a Ba(II) ion in a bidentate fashion and one of the carboxylate oxygen atoms forming a monoatomic bridge between two symmetry related Ba(II) ions resulting in a Ba···Ba separation of 4·5406(15) ?. These differing tridentate 2-nba ligands link {Ba(H₂O)₃} units into a one-dimensional polymeric chain extending along b axis. In the infinite chain each nine coordinated Ba(II) is bonded to three water molecules and further linked to six oxygen atoms of four different 2-nitrobenzoate anions with alternating pairs of Ba(II) ions in the chain bridged by a pair of (μ ₂-2-nba-O,O,O-NO₂) and (μ ₂-2-nba-O,O,O′) ligands resulting in alternating Ba···Ba distances of 4·5406(15) and 4·5726(14) ? across the chain. Dedicated to Prof. S. K. Paknikar on the occasion of his 73rd birthday.     

A novel porous supramolecular complex constructed by the co-crystallization of melamine and sulfate via hydrogen bonds and aromatic π-π interaction

Co-crystallization of melamine(MA) and sulfate results in crystalline product [(C₃H₇N₆⁺)₂(SO₄²⁻)] · 2H₂O. The novel supramolecular complex has been characterized by elemental analysis, thermal analysis (TGA and DSC), nuclear magnetic resonance (NMR), and single crystal X-ray diffraction. X-ray crystallographic studies of the complex reveal that the title complex has a 3-D microporous structure which is linked by intense intermolecular hydrogen-bonding interactions (N–H······O, N–H······N, O–H······O) and aromatic π-π interaction, which stabilize the whole crystal framework. The TGA curve shows that the complex is stable up to 500 °C, above which its structure begins to collapse.     

Binary and Ternary Complexes of Copper(II) Involving N,N,N′,N′-Tetramethylethylenediamine (Me4en) and Various Biologically Relevant Ligands

Binary and ternary complexes of copper(II) involving N,N,N′,N′-tetramethylethylene-diamine (Me₄en) and various biologically relevant ligands containing different functional groups are investigated. The ligands (L) used are dicarboxylic acids, amino acids, peptides and DNA unit constituents. The ternary complexes of amino acids, dicarboxylic acids or peptides are formed by simultaneous reactions. The results showed the formation of Cu(Me₄en)(L) complexes with amino acids and dicarboxylic acids. The effect of chelate ring size of the dicarboxylic acid complexes on their stability constants was examined. Peptides form both Cu(Me₄en)(L) complexes and the corresponding deprotonated amide species Cu(Me₄en)(LH₋₁). The ternary complexes of copper(II) with (Me₄en) and DNA are formed in a stepwise process, whereby binding of copper(II) to (Me₄en) is followed by ligation of the DNA components. DNA constituents form both 1:1 and 1:2 complexes with Cu(Me₄en)²⁺. The concentration distribution of the complexes in solution was evaluated. [Cu(Me₄en)(CBDCA)] and [Cu(Me₄en)(malonate)] are isolated and characterized by elemental analysis and infrared measurements.     

2,8‐Di­hydroxy‐1,3,7,9‐tetra­methyl‐6,12‐di­hydro­dipyrido­[1,2‐a:1′,2′‐d]pyrazine­diyl­ium dichloride dihydrate

The 2,8‐di­hydroxy‐1,3,7,9‐tetra­methyl‐6,12‐di­hydro­di­pyrido[1,2‐a:1′,2′‐d]pyrazine­diyl­ium dication possesses 2/m symmetry and lies in the mirror plane together with a chloride anion and the water O atom. The dication also lies on an inversion centre, i.e. C₁₆H₂₀N₂O₂²⁺·2Cl^?·2H₂O. Due to these symmetry constrictions the dication adopts an unexpected planar conformation. Molecules are linked by O—H?O and O—H?Cl hydrogen bonds to form chains, which are cross‐connected by C—H?Cl attractive interactions forming a complex three‐dimensional hydrogen‐bond network.     

Synthesis and Characterization of Some Ru(tmeda) Complexes Containing Chloride, Hydride, and Vinylidene Ligands

Summary.  The polymeric compound [Ru(cod)Cl₂] _x (cod = cyclooctadiene) reacts with 2 equivalents of tmeda (N,N,N′,N′-tetramethylethylenediamine) in refluxing MeOH to afford trans-[Ru(cod)(tmeda)(Cl)(H)] (1), which upon treatment with CHCl₃ is readily converted to the dichloro complex trans-[Ru(cod)(tmeda)Cl₂] (2). When [Ru(cod)Cl₂] _x is reacted with tmeda under an atmosphere of H₂ (3 bar), the bis-tmeda complex trans-[Ru(tmeda)₂Cl₂] (3) is obtained in 80% yield. DFT calculations revealed that 3 is by 52 kJ/mol more stable than the corresponding cis isomer. Attempts to prepare the coordinatively unsaturated complex [Ru(tmeda)₂Cl]⁺ by reacting 1 with TICF₃SO₃ were unsuccessful. According to DFT calculations, however, such a complex should be stable and, interestingly, should adopt a square pyramidal rather than a trigonal bipyramidal structure. If halide abstraction of 3 is performed in the presence of terminal alkynes HC*CR (R*t-Bu, n-Bu), the cationic vinylidene complexes [Ru(tmeda)₂(Cl)(*C*CHR)]⁺ (4a,b) are obtained. Received March 26, 2001. Accepted April 26, 2001     

Lone pair···π interactions on the stabilization of intra and intermolecular arrangements of coordination compounds with 2-methyl imidazole and benzimidazole derivatives

Abstract

Spectroscopic and single crystal X-ray diffraction studies of coordination compounds of Co^II, Ni^II, Zn^II, and Pd^II with phenylsulfonyl imidazole and benzimidazole derivatives (2-mfsiz, 2-mfsbz) were performed. The relevance of non-covalent interactions on the stabilization of intra and intermolecular arrangements in the ligands and their coordination compounds was investigated. The imidazole 2-mfsiz ligand presents two enantiomeric conformers, where the ethylphenylsulfone moiety stabilizes intermolecular lone pair···π (S–O···π_(phe)) and H···π contacts, while its tetrahedral coordination compounds, [M(2-mfsiz)₂X₂] (M²⁺?=?Co, Ni, Zn; X?=?Cl, Br) showed intramolecular lone pair···π interactions (S–O···π_(iz)). On the other hand, compounds [Cu₂(2-mfsiz)₂(µ₂-AcO)₄] and trans-[Pd(2-mfsiz)₂Cl₂] do not present lone pair···π interactions due to the metal ion geometry (square base pyramidal or square planar), which leads to formation of π_(iz)···π_(phe) interactions. For the benzimidazole ligand 2-mfsbz, an intramolecular, H_(phe)···π_(bz) contact was observed, remaining in its tetrahedral and octahedral coordination compounds, [M(2-mfsbz)₂X₂] (M²⁺?=?Co, Zn; X?=?Cl, Br, NO₃). This interaction limits the free rotation of the ethylphenylsulfone moiety for stabilization of an intermolecular lone pair···π interaction (S–O···π_(iz)). The dimeric [Zn₂(2-mfsiz)₂(µ²-AcO)₄] compound has a π_(bz)···π_(phe) contact. Theoretical calculations confirmed the non-covalent interactions in the ligands and their coordination compounds.     

Fluorimetric determination of traces of europium(III) using a new chelator and acetate or phosphate in dimethylsulfoxide as enhancers

A new Schiff-base ligand [N, N′, N″-Tri- (2,4-dihydroxyacetophenone) – triaminotriethylamine (TDATA)] with a tripodal structure was synthesized. Its fluorescence intensity with the europium(III) complex was increased about 178-fold in the presence of sodium acetate (NaAc) and about 126-fold in the presence of sodium phosphate (Na₃PO₄) solution. After adding the organic solvent dimethylsulfoxide (DMSO) to the above system, which leads to Eu³⁺ the fluorescence was further enhanced about 12-fold. Spectrofluorimetric determination of trace amounts of Eu³⁺ based on the phenomenon was performed. The excitation and emission wavelength is 365 nm and 615 nm, respectively. Under optimum conditions, the fluorescence intensities vary linearly with the concentration of Eu³⁺ in the range of 4.9 × 10⁻¹²–3.2 × 10⁻⁶ mol · L⁻¹ with a detection limit of 4.5 × 10⁻¹² mol · L⁻¹ (for the TDATA-NaAc-DMSO system) or 6.2 × 10⁻¹¹–8.6 × 10⁻⁶ mol · L⁻¹ with a detection limit of 6.0 × 10⁻¹¹ mol · L⁻¹ (for the TDATA-Na₃PO₄-DMSO system). Interferences of some rare earth metals and other inorganic ions are described. The method is a selective, sensitive, rapid and simple analytical procedure for the determination of europium(III) in a high purity yttrium oxide and synthetic sample. The mechanism for the fluorescence enhancement is also discussed.     

Use of 13C NMR Spectroscopy to Establish the Structure of 6(7)-R-Quinoxaline N,N′-Dioxides

The effect of substituents in position 6 on the positions of the signals of the carbon atoms in the ¹³C NMR spectra of substituted 1,2,3,4-tetrahydro-5,10-phenazine N,N′-dioxides has been analyzed, increments of substituents have been found, and a scheme has been proposed for the calculation of the chemical shifts of carbon atoms in the ¹³C NMR spectra of 6(7)-R-quinoxaline N,N′-dioxides. __________ Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 7, 1076–1080, July, 2005.     

The first C(O)NHP(O)-based phosphoric triamide structure with an N‒H···π hydrogen bonding: A combination of X-ray crystallography and theoretical study to evaluate the strength of hydrogen bonds

The hydrogen bond pattern of N-(4-methoxybenzoyl)-N′,N″-bis(4-methylbenzyl)-phosphoric triamide, C₂₄H₂₈N₃O₃P, (I), was investigated. In the crystal structure, the molecules are aggregated through N_CP―H···O═P and N_P―H···O═C hydrogen bonds in a one-dimensional arrangement parallel to the c axis (N_CP is the nitrogen atom in the C(O)NHP(O) segment and N_P stands for the two other nitrogen atoms bonded to the P atom). There is also a novel N_P?H···π hydrogen bond in the crystal which extends the aggregation of the molecules to a two-dimensional array parallel to the bc plane. A Cambridge Structural Database (CSD, version 5.37, Feb 2016) analysis shows that the N―H···π hydrogen bond was not observed in any of 156 [RC(O)NH]P(O)[NR¹R² Allen, F. H.; Taylor, R. Chem. Soc. Rev. 2004, 33, 463-475.[Crossref], [PubMed], [Web of Science ®] , [Google Scholar]]₂ (R¹ ≠ H, R² = H or ≠ H) phosphoric triamide structures reported so far. The theoretical calculations at the B3LYP/6-311G^** level of theory (DFT, AIM, and NBO) were performed to evaluate the strengths of N_CP―H···O═P, N_P―H···O═C and N_P―H···π hydrogen bonds, considering two-aggregate molecular assemblies containing these hydrogen bonds. The calculations on the title compound suggest that the intermolecular N_CP―H···O═P hydrogen bond is stronger than N_P―H···O═C and N_P―H···π interactions. The hydrogen bond strength was investigated by NBO, topological analysis, geometry calculation, Hirshfeld surface analysis and experimental spectroscopic results, which are in agreement with each other.     

1‐Carboxymethyl‐3‐methyl‐1H‐imidazol‐3‐ium chloride 2‐(3‐methyl‐1H‐imidazol‐3‐ium‐1‐yl)acetate monohydrate: a crystal stabilized by imidazolium zwitterions

The title compound, C₆H₉N₂O₂⁺·Cl⁻·C₆H₈N₂O₂·H₂O, contains one 2‐(3‐methyl‐1H‐imidazol‐3‐ium‐1‐yl)acetate inner salt molecule, one 1‐carboxymethyl‐3‐methyl‐1H‐imidazol‐3‐ium cation, one chloride ion and one water molecule. In the extended structure, chloride anions and water molecules are linked via O—H...Cl hydrogen bonds, forming an infinite one‐dimensional chain. The chloride anions are also linked by two weak C—H...Cl interactions to neighbouring methylene groups and imidazole rings. Two imidazolium moieties form a homoconjugated cation through a strong and asymmetric O—H...O hydrogen bond of 2.472 (2) Å. The IR spectrum shows a continuous D‐type absorption in the region below 1300 cm⁻¹ and is different to that of 1‐carboxymethyl‐3‐methylimidazolium chloride [Xuan, Wang & Xue (2012). Spectrochim. Acta Part A, 96 , 436–443].     

Remarkable shifts of Csp2-H and O-H stretching frequencies and stability of complexes of formic acid with formaldehydes and thioformaldehydes

Thirty-six stable complexes of formic acid with formaldehydes and thioformaldehydes were determined on the potential energy surface, in which the XCHO···HCOOH complexes are found to be more stable than the XCHS···HCOOH counterparts, with X = H, F, Cl, Br, CH₃, NH₂. All complexes are stabilized by hydrogen bonds, and their contribution to the total stabilization energy of the complexes increases in going from C-H···S to C-H···O to O-H···S and finally to O-H···O. Remarkably, a significant blueshift of C_sp2-H bond by 81–96 cm⁻¹ in the C_sp2-H···O hydrogen bond has hardly ever been reported, and a considerable redshift of O-H stretching frequency by 206–544 cm⁻¹ in the O-H···O/S hydrogen bonds is also predicted. The obtained results in our present work and previous literatures support that a distance contraction and a stretching frequency blueshift of C-H bond involving hydrogen bond depend mainly on its polarity and gas phase basicity of proton acceptor, besides the rearrangement of electron density due to complex formation. Markedly, we suggest the ratio of deprotonation enthalpy to proton affinity (R _c) as an indicator to prospect for classification of hydrogen bonds. The symmetry adapted perturbation theory results show a larger role of attractive electrostatic term in XO-n as compared to that in XS-n and the electrostatic interaction is overwhelming dispersion or induction counterparts in stabilizing XO-n and XS-n , with n = 1, 2, 3. © 2019 Wiley Periodicals, Inc.     

Tricarbonylrhenium(I) complexes with <Emphasis Type="Italic">N,N′</Emphasis>-bis(2- and 4-nitrobenzaldehyde)-1,2-diiminoethane Schiff base ligands: synthesis,spectroscopic and crystal structure studies

fac-[Re(CO)₃(2-nben)Cl] and fac-[Re(CO)₃(4-nbzen)Cl] complexes consisting of 2-nbzen = N,N′-bis(2-nitrobenzaldehyde)-1,2-diiminoethane and 4-nbzen = N,N′-bis(4-nitrobenzaldehyde)-1,2-diiminoethane were synthesized by the reaction of Re(CO)₅Cl with nbzen ligands. These complexes were characterized by physico-chemical, spectroscopic methods and X-ray crystallography. The electrochemical behavior of the two complexes was investigated by cyclic voltammetry. In the crystal structure of [Re(CO)₃(4-nbzen)Cl], the neighbouring molecules are linked together by intermolecular C–H···Cl interactions to form 1D extended chains along the b-axis. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.