Theoretical study of bifurcated hydrogen bonding effects on the 1J(N,H), 1hJ(N,H), 2hJ(N,N) couplings and 1H, 15N shieldings in model pyrroles

According to the density functional theory calculations, the X···H···N (X?N, O) intramolecular bifurcated (three‐centered) hydrogen bond with one hydrogen donor and two hydrogen acceptors causes a significant decrease of the ^1hJ(N,H) and ^2hJ(N,N) coupling constants across the N? H···N hydrogen bond and an increase of the ¹J(N,H) coupling constant across the N? H covalent bond in the 2,5‐disubsituted pyrroles. This occurs due to a weakening of the N? H···N hydrogen bridge resulting in a lengthening of the N···H distance and a decrease of the hydrogen bond angle at the bifurcated hydrogen bond formation. The gauge‐independent atomic orbital calculations of the shielding constants suggest that a weakening of the N? H···N hydrogen bridge in case of the three‐centered hydrogen bond yields a shielding of the bridge proton and deshielding of the acceptor nitrogen atom. The atoms‐in‐molecules analysis shows that an attenuation of the ^1hJ(N,H) and ^2hJ(N,N) couplings in the compounds with bifurcated hydrogen bond is connected with a decrease of the electron density ρ_H···N at the hydrogen bond critical point and Laplacian of this electron density ?²ρ_H···N. The natural bond orbital analysis suggests that the additional N? H···X interaction partly inhibits the charge transfer from the nitrogen lone pair to the σ*_{N? H} antibonding orbital across hydrogen bond weakening of the ^1hJ(N,H) and ^2hJ(N,N) trans‐hydrogen bond couplings through Fermi‐contact mechanism. An increase of the nitrogen s‐character percentage of the N? H bond in consequence of the bifurcated hydrogen bonding leads to an increase of the ¹J(N,H) coupling constant across the N? H covalent bond and deshielding of the hydrogen donor nitrogen atom. Copyright © 2010 John Wiley & Sons, Ltd.     

Experimental and theoretical study of the intramolecular C–H···N and C–H···S hydrogen bonding effects in the 1H and 13C NMR spectra of the 2‐(alkylsulfanyl)‐5‐amino‐1‐vinylpyrroles: a particular state of amine nitrogen

In the ¹H NMR spectra of the 1‐vinylpyrroles with amino‐ and alkylsulfanyl groups in 5 and 2 positions, an extraordinarily large difference between resonance positions of the H_A and H_B terminal methylene protons of the vinyl group is discovered. Also, the one‐bond ¹J(C_β,H_B) coupling constant is surprisingly greater than the ¹J(C_β,H_A) coupling constant in pyrroles under investigation, while in all known cases, there was a reverse relationship between these coupling constants. These spectral anomalies are substantiated by quantum chemical calculations. The calculations show that the amine nitrogen lone pair is removed from the conjugation with the π‐system of the pyrrole ring so that it is directed toward the H_B hydrogen. These factors are favorable to the emergence of the intramolecular C–H_B???N hydrogen bonding in the s‐cis(N) conformation. On the other hand, the spatial proximity of the sulfur to the H_B hydrogen provides an opportunity of the intramolecular C–H_B???S hydrogen bonding in the s‐cis(S) conformation. Presence of the hydrogen bond critical points as well as ring critical point for corresponding chelate ring revealed by a quantum theory of atoms in molecules (QTAIM) approach confirms the existence of the weak intramolecular C–H???N and C–H???S hydrogen bonding. Therefore, an unusual high‐frequency shift of the H_B signal and the increase in the ¹J(C_β,H_B) coupling constant can be explained by the effects of hydrogen bonding. Copyright © 2013 John Wiley & Sons, Ltd.     

GIAO,DFT, AIM and NBO analysis of the N?H···O intramolecular hydrogen‐bond influence on the 1J(N,H) coupling constant in push–pull diaminoenones

In the series of diaminoenones, large high‐frequency shifts of the ¹H NMR of the N? H group in the cis‐position relative to the carbonyl group suggests strong N? H···O intramolecular hydrogen bonding comprising a six‐membered chelate ring. The N? H···O hydrogen bond causes an increase of the ¹J(N,H) coupling constant by 2–4 Hz and high‐frequency shift of the ¹⁵N signal by 9–10 ppm despite of the lengthening of the relevant N? H bond. These experimental trends are substantiated by gauge‐independent atomic orbital and density functional theory calculations of the shielding and coupling constants in the 3,3‐bis(isopropylamino)‐1‐(aryl)prop‐2‐en‐1‐one (12) for conformations with the Z‐ and E‐orientations of the carbonyl group relative to the N? H group. The effects of the N? H···O hydrogen‐bond on the NMR parameters are analyzed with the atoms‐in‐molecules (AIM) and natural bond orbital (NBO) methods. The AIM method indicates a weakening of the N? H···O hydrogen bond as compared with that of 1,1‐di(pyrrol‐2‐yl)‐2‐formylethene (13) where N? H···O hydrogen bridge establishes a seven‐membered chelate ring, and the corresponding ¹J(N,H) coupling constant decreases. The NBO method reveals that the LP(O) →σ*_{N? H} hyperconjugative interaction is weakened on going from the six‐membered chelate ring to the seven‐membered one due to a more bent hydrogen bond in the former case. A dominating effect of the N? H bond rehybridization, owing to an electrostatic term in the hydrogen bonding, seems to provide an increase of the ¹J(N,H) value as a consequence of the N? H···O hydrogen bonding in the studied diaminoenones. Copyright © 2010 John Wiley & Sons, Ltd.     

Interpreting 2hJ(F,N), 1hJ(H,N) and 1J(F,H) in the hydrogen‐bonded FH–collidine complex

Ab initio EOM‐CCSD calculations were performed to determine ¹⁹F,¹H, ¹⁹F,¹⁵N and ¹H,¹⁵N spin–spin coupling constants in model complexes FH–NH₃ and FH–pyridine as a function of the F—H and F—N distances. The absolute value of ¹J(F,H) decreases and that of ^1hJ(H,N) increases rapidly along the proton‐transfer coordinate, even in the region of the proton‐shared F—H—N hydrogen bond. In contrast, ^2hJ(F,N) remains essentially constant in this region. These results are consistent with the recently reported experimental NMR spectra of FH–collidine which show that ^1hJ(H,N) increases and ¹J(F,H) decreases, while ^2hJ(F,N) remains constant as the temperature of the solution decreases. They suggest that the FH–collidine complex is stabilized by a proton‐shared hydrogen bond over the range of experimental temperatures investigated, being on the traditional side of quasi‐symmetric at high temperatures, and on the ion‐pair side at low temperatures. Copyright © 2002 John Wiley & Sons, Ltd.     

Heterolytic Cleavage of Hydrogen by an Iron Hydrogenase Model: An Fe‐H⋅⋅⋅H‐N Dihydrogen Bond Characterized by Neutron Diffraction

Hydrogenase enzymes in nature use hydrogen as a fuel, but the heterolytic cleavage of H? H bonds cannot be readily observed in enzymes. Here we show that an iron complex with pendant amines in the diphosphine ligand cleaves hydrogen heterolytically. The product has a strong Fe‐H???H‐N dihydrogen bond. The structure was determined by single‐crystal neutron diffraction, and has a remarkably short H???H distance of 1.489(10) Å between the protic N‐H^δ+ and hydridic Fe‐H^δ? part. The structural data for [CpFe H (P^tBu₂N^tBu₂ H )]⁺ provide a glimpse of how the H? H bond is oxidized or generated in hydrogenase enzymes. These results now provide a full picture for the first time, illustrating structures and reactivity of the dihydrogen complex and the product of the heterolytic cleavage of H₂ in a functional model of the active site of the [FeFe] hydrogenase enzyme.     

Stereospecificity of 1H, 13C and 15N shielding constants in the isomers of methylglyoxal bisdimethylhydrazone: problem with configurational assignment based on 1H chemical shifts

In the ¹³C NMR spectra of methylglyoxal bisdimethylhydrazone, the ¹³C‐5 signal is shifted to higher frequencies, while the ¹³C‐6 signal is shifted to lower frequencies on going from the EE to ZE isomer following the trend found previously. Surprisingly, the ¹H‐6 chemical shift and ¹J(C‐6,H‐6) coupling constant are noticeably larger in the ZE isomer than in the EE isomer, although the configuration around the –CH═N– bond does not change. This paradox can be rationalized by the C–H?N intramolecular hydrogen bond in the ZE isomer, which is found from the quantum‐chemical calculations including Bader's quantum theory of atoms in molecules analysis. This hydrogen bond results in the increase of δ(¹H‐6) and ¹J(C‐6,H‐6) parameters. The effect of the C–H?N hydrogen bond on the ¹H shielding and one‐bond ¹³C–¹H coupling complicates the configurational assignment of the considered compound because of these spectral parameters. The ¹H, ¹³C and ¹⁵N chemical shifts of the 2‐ and 8‐(CH₃)₂N groups attached to the –C(CH₃)═N– and –CH═N– moieties, respectively, reveal pronounced difference. The ab initio calculations show that the 8‐(CH₃)₂N group conjugate effectively with the π‐framework, and the 2‐(CH₃)₂N group twisted out from the plane of the backbone and loses conjugation. As a result, the degree of charge transfer from the N‐2– and N‐8– nitrogen lone pairs to the π‐framework varies, which affects the ¹H, ¹³C and ¹⁵N shieldings. Copyright © 2012 John Wiley & Sons, Ltd.     

1H‐NMR Analysis of Intra‐ and Intermolecular H‐Bonds of Alcohols in DMSO: Chemical Shift of Hydroxy Groups and Aspects of Conformational Analysis of Selected Monosaccharides,Inositols, and Ginkgolides

The interpretation of ¹H‐NMR chemical shifts, coupling constants, and coefficients of temperature dependence (δ(OH), J(H,OH), and Δδ(OH)/ΔT values) evidences that, in (D₆)DMSO solution, the signal of an OH group involved as donor in an intramolecular H‐bond to a hydroxy or alkoxy group is shifted upfield, whereas the signal of an OH group acting as acceptor of an intramolecular H‐bond and as donor in an intermolecular H‐bond to (D₆)DMSO is shifted downfield. The relative strength of the intramolecular H‐bond depends on co‐operativity and on the acidity of OH groups. The acidity of OH groups is enhanced when they are in an antiparallel orientation to a C−O bond. A comparison of the ¹H‐NMR spectra of alcohols in CDCl₃ and (D₆)DMSO allows discrimination between weak and strong intramolecular H‐bonds. Consideration of IR spectra (CHCl₃ or CH₂Cl₂) shows that the rule according to which the downfield shift of δ(OH) for H‐bonded alcohols in CDCl₃ parallels the strength of the H‐bond is valid only for alcohols forming strong intramolecular H‐bonds. The combined analysis of J(H,OH) and δ(OH) values is illustrated by the interpretation of the spectra of the epoxyalcohols 14 and 15 (Fig. 3). H‐Bonding of hexopyranoses, hexulopyranoses, alkyl hexopyranosides, alkyl 4,6‐O‐benzylidenehexopyranosides, levoglucosans, and inositols in (D₆)DMSO was investigated. Fully solvated non‐anomeric equatorial OH groups lacking a vicinal axial OR group (R=H or alkyl, or (alkoxy)alkyl) show characteristic J(H,OH) values of 4.5 – 5.5 Hz and fully solvated non‐anomeric axial OH groups lacking an axial OR group in β‐position are characterized by J(H,OH) values of 4.2 – 4.4 Hz (Figs. 4 – 6). Non‐anomeric equatorial OH groups vicinal to an axial OR group are involved in a partial intramolecular H‐bond (J(H,OH)=5.4 – 7.4 Hz), whereas non‐anomeric equatorial OH groups vicinal to two axial OR form partial bifurcated H‐bonds (J(H,OH)=5.8 – 9.5 Hz). Non‐anomeric axial OH groups form partial intramolecular H‐bonds to a cis‐1.3‐diaxial alkoxy group (as in 29 and 41 : J(H,OH)=4.8 – 5.0 Hz). The persistence of such a H‐bond is enhanced when there is an additional H‐bond acceptor, such as the ring O‐atom ( 43 – 47 : J(H,OH)=5.6 – 7.6 Hz; 32 and 33 : 10.5 – 11.3 Hz). The (partial) intramolecular H‐bonds lead to an upfield shift (relative to the signal of a fully solvated OH in a similar surrounding) for the signal of the H‐donor. The shift may also be related to the signal of the fully solvated, equatorial HO−C(2), HO−C(3), and HO−C(4) of β‐D ‐glucopyranose ( 16 : 4.81 ppm) by using the following increments: −0.3 ppm for an axial OH group, 0.2 – 0.25 ppm for replacing a vicinal OH by an OR group, ca. 0.1 ppm for replacing another OH by an OR group, 0.2 ppm for an antiperiplanar C−O bond, −0.3 ppm if a vicinal OH group is (partially) H‐bonded to another OR group, and −0.4 to −0.6 for both OH groups of a vicinal diol moiety involved in (partial) divergent H‐bonds. Flip‐flop H‐bonds are observed between the diaxial HO−C(2) and HO−C(4) of the inositol 40 (J(H,OH)=6.4 Hz, δ(OH)=5.45 ppm) and levoglucosan ( 42 ; J(H,OH)=6.7 – 7.1 Hz, δ(OH)=4.76 – 4.83 ppm; bifurcated H‐bond); the former is completely persistent and the latter to ca. 40%. A persistent, unidirectional H‐bond C(1)−OH⋅⋅⋅O−C(10) is present in ginkgolide B and C, as evidenced by strongly different δ(OH) and Δδ(OH)/ΔT values for HO−C(1) and HO−C(10) (Fig. 9). In the absence of this H‐bond, HO−C(1) of 52 resonates 1.1 – 1.2 ppm downfield, while HO−C(10) of ginkgolide A and of 48 – 50 resonates 0.5 – 0.9 ppm upfield.     

Fast Proton Exchange in Histidine: Measurement of Rate Constants through Indirect Detection by NMR Spectroscopy

Owing to its imidazole side chain, histidine participates in various processes such as enzyme catalysis, pH regulation, metal binding, and phosphorylation. The determination of exchange rates of labile protons for such a system is important for understanding its functions. However, these rates are too fast to be measured directly in an aqueous solution by using NMR spectroscopy. We have obtained the exchange rates of the NH₃⁺ amino protons and the labile NH^ε2 and NH^δ1 protons of the imidazole ring by indirect detection through nitrogen‐15 as a function of temperature (272 K<T<293 K) and pH (1.3<pH<4.9) of uniformly nitrogen‐15‐ and carbon‐13‐labeled L ‐histidine ? HCl ? H₂O. Exchange rates up to 8.5×10⁴ s^?1 could be determined (i.e., lifetimes as short as 12 μs). The three chemical shifts δ_Hi of the invisible exchanging protons H_i and the three one‐bond scalar coupling constants ¹J(N,H_i) could also be determined accurately.     

4‐Iodo­anilinium 3‐nitro­phthalate(1–): tripartite sheets built from O—H...O and N—H...O hydrogen bonds

In the title compound, 4‐iodoanilinium 2‐carboxy‐6‐nitrobenzoate, C₆H₇IN⁺·C₈H₄NO₆⁻, the anions are linked by an O—H...O hydrogen bond [H...O = 1.78 Å, O...O = 2.614 (3) Å and O—H...O = 171°] into C(7) chains, and these chains are linked by two two‐centre N—H...O hydrogen bonds [H...O = 1.86 and 1.92 Å, N...O = 2.700 (3) and 2.786 (3) Å, and N—H...O = 153 and 158°] and one three‐centre N—H...(O)₂ hydrogen bond [H...O = 2.02 and 2.41 Å, N...O = 2.896 (3) and 2.789 (3) Å, N—H...O = 162 and 105°, and O...H...O = 92°], thus forming sheets con­taining R(6), R(8), R(13) and R(18) rings.     

[Pd(Fmes)2(tmeda)]: A Case of Intermittent C?H⋅⋅⋅F?C Hydrogen‐Bond Interaction in Solution

The X‐ray structure of the title compound [Pd(Fmes)₂(tmeda)] (Fmes=2,4,6‐tris(trifluoromethyl)phenyl; tmeda=N,N,N′,N′‐tetramethylethylenediamine) shows the existence of uncommon C? H???F? C hydrogen‐bond interactions between methyl groups of the TMEDA ligand and ortho‐CF₃ groups of the Fmes ligand. The ¹⁹F NMR spectra in CD₂Cl₂ at very low temperature (157 K) detect restricted rotation for the two ortho‐CF₃ groups involved in hydrogen bonding, which might suggest that the hydrogen bond is responsible for this hindrance to rotation. However, a theoretical study of the hydrogen‐bond energy shows that it is too weak (about 7 kJ mol^?1) to account for the rotational barrier observed (ΔH^≠=26.8 kJ mol^?1), and it is the steric hindrance associated with the puckering of the TMEDA ligand that should be held responsible for most of the rotational barrier. At higher temperatures the rotation becomes fast, which requires that the hydrogen bond is continuously being split up and restored and exists only intermittently, following the pulse of the conformational changes of TMEDA.     

2‐Ethyl‐1‐[5‐(4‐methylphenyl)pyrazol‐3‐yl]‐3‐(thiophene‐2‐carbonyl)isothiourea: molecular ribbons containing three types of hydrogen‐bonded ring

The title compound, C₁₈H₁₈N₄OS₂, was prepared by reaction of S,S‐diethyl 2‐thenoylimidodithiocarbonate with 5‐amino‐3‐(4‐methylphenyl)‐1H‐pyrazole using microwave irradiation under solvent‐free conditions. In the molecule, the thiophene unit is disordered over two sets of atomic sites, with occupancies of 0.814 (4) and 0.186 (4), and the bonded distances provide evidence for polarization in the acylthiourea fragment and for aromatic type delocalization in the pyrazole ring. An intramolecular N—H...O hydrogen bond is present, forming an S(6) motif, and molecules are linked by N—H...O and N—H...N hydrogen bonds to form a ribbon in which centrosymmetric R₂²(4) rings, built from N—H...O hydrogen bonds and flanked by inversion‐related pairs of S(6) rings, alternate with centrosymmetric R₂²(6) rings built from N—H...N hydrogen bonds.     

Constructor graph description of the hydrogen‐bonding supramolecular assembly in two ionic compounds: 2‐(pyrazol‐1‐yl)ethylammonium chloride and diaquadichloridobis(2‐hydroxyethylammonium)cobalt(II) dichloride

Covalent bond tables are used to generate hydrogen‐bond pattern designator symbols for the crystallographically characterized title compounds. 2‐(Pyrazol‐1‐yl)ethylammonium chloride, C₅H₁₀N₃⁺·Cl⁻, (I), has three unique, strong, charge‐assisted hydrogen bonds of the types N—H...Cl and N—H...N that form unary through ternary levels of graph‐set interactions. Diaquadichloridobis(2‐hydroxyethylammonium)cobalt(II) dichloride, [CoCl₂(C₂H₈NO)₂(H₂O)₂]Cl₂, (II), forms five unique charge‐assisted hydrogen bonds of the types O—H...Cl and N—H...Cl. These form graph‐set patterns up to the quinary level. The Co complex in (II) resides at a crystallographic inversion center; thus the number of hydrogen bonds to consider doubles due to their G‐equivalence, and the handling of such a case is demonstrated.     

15N chemical shifts and one bond 15N?1H coupling constants in simple amides

An indirect method is employed for determining the ¹⁵N parameters at the natural abundance level in a series of simple acyclic and cyclic amides. The one bond coupling constant, ¹J(¹⁵N¹H), and the ¹⁵N chemical shift are measured as a function of the carbonyl substituent group or the ring size and the nature of the solvent (CCl₄ or H₂O). These ¹⁵N parameters are related to the amide bond structure, the nitrogen configuration and possible intermolecular hydrogen bonding (amide-amide or amide-water).     

Charge‐assisted hydrogen‐bonded supramolecular networks in acetoguanaminium hydrogen phthalate,acetoguanaminium hydrogen maleate and acetoguanaminium 3‐hydroxypicolinate monohydrate

In 2,4‐diamino‐6‐methyl‐1,3,5‐triazin‐1‐ium (acetoguanaminium) hydrogen phthalate, C₄H₈N₅⁺·C₈H₅O₄⁻, (I), acetoguanaminium hydrogen maleate, C₄H₈N₅⁺·C₄H₃O₄⁻, (II), and acetoguanaminium 3‐hydroxypicolinate monohydrate, C₄H₈N₅⁺·C₆H₄NO₃⁻·H₂O, (III), the acetoguanaminium cations interact with the carboxylate groups of the corresponding anions via a pair of nearly parallel N—H...O hydrogen bonds, forming R₂²(8) ring motifs. In (II) and (III), N—H...N base‐pairing is observed, while there is none in (I). In (II), a series of fused R₃²(8), R₂²(8) and R₃²(8) hydrogen‐bonded rings plus fused R₂²(8), R₆²(12) and R₂²(8) ring motifs occur alternately, aggregating into a supramolecular ladder‐like arrangement. In (III), R₂²(8) motifs occur on either side of a further ring formed by pairs of N—H...O hydrogen bonds, forming an array of three fused hydrogen‐bonded rings. In (I) and (II), the anions form a typical intramolecular O—H...O hydrogen bond with graph set S(7), whereas in (III) an intramolecular hydrogen bond with graph set S(6) is formed.     

Three‐dimensional hydrogen‐bonded structures in the hydrated proton‐transfer salts of isonipecotamide with the dicarboxylic oxalic and adipic acid homologues

The structures of the 1:1 hydrated proton‐transfer compounds of isonipecotamide (piperidine‐4‐carboxamide) with oxalic acid, 4‐carbamoylpiperidinium hydrogen oxalate dihydrate, C₆H₁₃N₂O⁺·C₂HO₄⁻·2H₂O, (I), and with adipic acid, bis(4‐carbamoylpiperidinium) adipate dihydrate, 2C₆H₁₃N₂O⁺·C₆H₈O₄²⁻·2H₂O, (II), are three‐dimensional hydrogen‐bonded constructs involving several different types of enlarged water‐bridged cyclic associations. In the structure of (I), the oxalate monoanions give head‐to‐tail carboxylic acid O—H...O_carboxyl hydrogen‐bonding interactions, forming C(5) chain substructures which extend along a. The isonipecotamide cations also give parallel chain substructures through amide N—H...O hydrogen bonds, the chains being linked across b and down c by alternating water bridges involving both carboxyl and amide O‐atom acceptors and amide and piperidinium N—H...O_carboxyl hydrogen bonds, generating cyclic R₄³(10) and R₃²(11) motifs. In the structure of (II), the asymmetric unit comprises a piperidinium cation, half an adipate dianion, which lies across a crystallographic inversion centre, and a solvent water molecule. In the crystal structure, the two inversion‐related cations are interlinked through the two water molecules, which act as acceptors in dual amide N—H...O_water hydrogen bonds, to give a cyclic R₄²(8) association which is conjoined with an R₄⁴(12) motif. Further N—H...O_water, water O—H...O_amide and piperidinium N—H...O_carboxyl hydrogen bonds give the overall three‐dimensional structure. The structures reported here further demonstrate the utility of the isonipecotamide cation as a synthon for the generation of stable hydrogen‐bonded structures. The presence of solvent water molecules in these structures is largely responsible for the non‐occurrence of the common hydrogen‐bonded amide–amide dimer, promoting instead various expanded cyclic hydrogen‐bonding motifs.     

Three‐centre Rh?H?Sn bonds: an NMR study of the effects of varying the electron density on rhodium

The complexes [Rh(X)(H)(SnPh₃)(PPh₃)(L)] (X = NCBPh₃ (a), N(CN)₂ (b), NCS (c), NCO (d), N₃ (e); L = 1‐methylimidazole) ( 1 ) show systematic changes in δ(¹¹⁹Sn), δ(¹⁰³Rh), J(¹¹⁹Sn–¹H) and J(¹¹⁹Sn–¹⁰³Rh) that are related to the electron‐donating properties of X. As X becomes more electron‐rich, δ(¹⁰³Rh), J(¹¹⁹Sn–¹H) and J(¹¹⁹Sn–¹⁰³Rh) increase and δ¹¹⁹Sn) decreases. The related complexes trans‐[Rh(X)(H)(SnPh₃)(PPh₃)₂(L)] (X = N(CN)₂, NCO; L = 4‐carboxymethylpyridine (x), pyridine (y) and 4‐dimethylaminopyridine (z)) ( 2 ), show a continuation of the trends in δ(¹¹⁹Sn) and J(¹¹⁹Sn–¹H), but not δ(¹⁰³Rh) or J(¹¹⁹Sn–¹⁰³Rh). Data for 1 and 2 show that within certain limits of type of ligand varied (X = N‐donor, L = a pyridine) and coordination geometry, the response of δ(¹¹⁹Sn) and J(¹¹⁹Sn–¹H) to changes in electron density on rhodium is largely independent of the means by which the change is effected.Copyright © 2001 John Wiley & Sons, Ltd.     

(S)‐5‐Benzylimidazolidine‐2,4‐dione monohydrate

The crystal structure of the title compound, C₁₀H₁₀N₂O₂·H₂O, also known as l ‐5‐benzylhydantoin monohydrate, is described in terms of two‐dimensional supramolecular arrays built up from infinite chains assembled via N—H...O and O—H...O hydrogen bonds among the organic molecules and solvent water molecules, with graph‐set R³₃(10)C(5)C²₂(6). The hydrogen‐bond network is reinforced by stacking of the layers through C—H...π interactions.     

2,5‐Dicarboxy­anilinium chloride monohydrate

The title compound, C₈H₈NO₄⁺·Cl⁻·H₂O, is the chloro­hydrated form of 2‐amino­benzene‐1,4‐dicarboxylic acid, the basic crystal structure of which is still not known. Mol­ecules are linked by classical N—H⋯O, O—H⋯O, N—H⋯Cl and O—H⋯Cl hydrogen bonds, mainly along the mol­ecular plane, into sheets built by unusual R₆⁴(26), R₆⁴(22) and R₄³(22) rings. The stacking between layers is stabilized by another N—H⋯Cl hydrogen bond and by π–π inter­actions between aromatic rings facing each other.     

Two phosphate–imidazole complexes with and without a hydrogen‐bonded guest mol­ecule

The mol­ecular structures of the complexes imidazolium 6,6′‐di‐tert‐butyl‐4,4′‐dimethyl‐2,2′‐thio­diphenyl phosphate, C₃H₅N₂⁺·C₂₂H₂₈O₄PS⁻, (I), and imidazolium 6,6′‐di‐tert‐butyl‐4,4′‐dimethyl‐2,2′‐thio­diphenyl phosphate diisopropyl hydrazo­dicarboxyl­ate hemisolvate, C₃H₅N₂⁺·C₂₂H₂₈O₄PS⁻·0.5C₈H₁₆N₂O₄, (II), have been determined. While (I) forms the expected hydrogen‐bonded chain utilizing the two imidazole N‐bound H atoms, in (II), the substituted hydrazine solvent mol­ecule inserts itself between the chains. Compound (I) exhibits a strong N—H⋯O hydrogen bond, with an N⋯O distance of 2.603 (2) Å. The hydrazine solvent molecule in (II) lies about a twofold axis and the N‐bound H atoms are involved in bifurcated hydrogen bonds with phosphate O atoms. A C‐bound H atom of the imidazolium cation is involved in a C—H⋯O inter­action with a carbonyl O atom of the hydrazine solvent mol­ecule.     

Hirshfeld surface analysis of two new phosphorothioic triamide structures

Hirshfeld surfaces and two‐dimensional fingerprint plots are used to analyse the intermolecular interactions in two new phosphorothioic triamide structures, namely N,N′,N′′‐tris(3,4‐dimethylphenyl)phosphorothioic triamide acetonitrile hemisolvate, P(S)[NHC₆H₃‐3,4‐(CH₃)₂]₃·0.5CH₃CN or C₂₄H₃₀N₃PS·0.5CH₃CN, (I), and N,N′,N′′‐tris(4‐methylphenyl)phosphorothioic triamide–3‐methylpiperidinium chloride (1/1), P(S)[NHC₆H₄(4‐CH₃)]₃·[3‐CH₃‐C₅H₉NH₂]⁺·Cl⁻ or C₂₁H₂₄N₃PS·C₆H₁₄N⁺·Cl⁻, (II). The asymmetric unit of (I) consists of two independent phosphorothioic triamide molecules and one acetonitrile solvent molecule, whereas for (II), the asymmetric unit is composed of three components (molecule, cation and anion). In the structure of (I), the different components are organized into a six‐molecule aggregate through N—H...S and N—H...N hydrogen bonds. The components of (II) are aggregated into a two‐dimensional array through N—H...S and N—H...Cl hydrogen bonds. Moreover, interesting features of packing arise in this structure due to the presence of a double hydrogen‐bond acceptor (the S atom of the phosphorothioic triamide molecule) and of a double hydrogen‐bond donor (the N—H unit of the cation). For both (I) and (II), the full fingerprint plot of each component is asymmetric as a consequence of the presence of three fragments. These analyses reveal that H...H interactions [67.7 and 64.3% for the two symmetry‐independent phosphorothioic triamide molecules of (I), 30.7% for the acetonitrile solvent of (I), 63.8% in the phosphorothioic triamide molecule of (II) and 62.9% in the 3‐methylpiperidinium cation of (II)] outnumber the other contacts for all the components in both structures, except for the chloride anion of (II), which only receives the Cl...H contact. The phosphorothioic triamide molecules of both structures include unsaturated C atoms, thus presenting C...H/H...C interactions: 17.6 and 21% for the two symmetry‐independent phosphorothioic triamide molecules in (I), and 22.7% for the phosphorothioic triamide molecule of (II). Furthermore, the N—H...S hydrogen bonds in both (I) and (II), and the N—H...Cl hydrogen bonds in (II), are the most prominent interactions, appearing as large red spots on the Hirshfeld surface maps. The N...H/H...N contacts in structure (I) are considerable, whereas for (II), they give a negligible contribution to the total interactions in the system.