Halogen bonding or close packing? Examining the structural landscape in a series of Cu(II)-acac complexes

A series of four bifunctional ligands based on β-diketonate moieties bearing methyl (2), chloro (3), bromo (4) and iodo (5) substituents and their corresponding Cu(II) complexes have been synthesized and crystallographically characterized in order to explore the possibility of using halogen bonds for the directed assembly of predictable architectures in coordination chemistry. The four ligands have characteristic O-H···O intramolecular hydrogen bonds and the structure of ligand 2 is close packed whereas, ligands 3, 4 and 5 contain extended 1-D architectures based on C=O···X halogen bonds. In each case, the halogen-bond donor seeks out the most powerful halogen-bond acceptor (based on electrostatic considerations). In the corresponding Cu(II) complexes the coordination chemistry remains a constant throughout the series, the four-coordinate metal ion sits in a slightly distorted square-planar arrangement, and there are no unexpected appearances of coordinated or non-coordinated solvent molecules. Furthermore, the most powerful halogen-bond acceptors have been almost depleted of charge as a result of metal chelation and none of the potential halogen-bond interactions are capable of competing with the head-to-head close packing that is observed in the methyl, chloro, and bromo, substituted Cu(II) complexes. The enhanced polarizability of the iodine atom, produces a more electropositive surface which means that this structure cannot accommodate a linear head-to-head arrangement due to electrostatic repulsion, and thus [Cu(5)(2)] adopts a unique close-packed structure very different from the other three iso-structural complexes, [Cu(2)(2)]-[Cu(4)(2)].     

S···X halogen bonds and H···X hydrogen bonds in H2CS-XY (XY = FF, ClF, ClCl, BrF, BrCl, and BrBr) complexes: cooperativity and solvent effect

Using ab initio calculations, we have studied the structures, properties, and nature of halogen bonds in H(2)CS-XY (XY = FF, ClF, ClCl, BrF, BrCl, and BrBr) complexes. The results show that the ring-shaped complexes are formed by a halogen bond (S···X) and a secondary hydrogen bond (H···X). We also analyzed the H(2)CS-ClF-ClF and FCl-H(2)CS-ClF complexes to investigate the cooperative and diminutive halogen bonding. The cooperative effect of halogen bonding is found in the former, while the diminutive effect is present in the latter. We finally considered the solvent effect on the halogen bond in H(2)CS-BrCl complex and found that the solvent has a prominent enhancing effect on it. The complexes have also been analyzed with natural bond orbital, atoms in molecules, and symmetry adapted perturbation theory method.     

Computational studies of σ-type weak interactions between NCO/NCS radicals and XY(X = H,Cl;Y = F,Cl,and Br)

The triatomic radicals NCO and NCS are of interest in atmospheric chemistry,and both the ends of these radicals can potentially serve as electron donors during the formation of σ-type hydrogen/halogen bonds with electron acceptors XY(X = H,Cl;Y = F,Cl,and Br).The geometries of the weakly bonded systems NCO/NCS···XY were determined at the MP2/aug-cc-pVDZ level of calculation.The results obtained indicate that the geometries in which the hydrogen/halogen atom is bonded at the N atom are more stable than those where it is bonded at the O/S atom,and that it is the molecular electrostatic potential(MEP)-not the electronegativity-that determines the stability of the hydrogen/halogen bond.For the same electron donor(N or O/S) in the triatomic radical and the same X atom in XY,the bond strength decreases in the order Y = F > Cl > Br.In the hydrogen/halogen bond formation process for all of the complexes studied in this work,transfer of spin electron density from the electron donor to the electron acceptor is negligible,but spin density rearranges within the triatomic radicals,being transferred to the terminal atom not interacting with XY.     

Anion-directed self-assembly in coordination networks: architectural control via cooperative noncovalent interactions

The self-assembly of a new flexible tritopic pyrazine-pyridine ligand (pz-3-py) with HgX(2) (X = Cl, Br) was investigated. The results show that coordinated chloride and bromide anions play different roles, and two architecturally different coordination polymers were obtained with the anions used. Where X = Cl, in [Hg(μ(3)-pz-3-py)Cl(2)](n) (1), the 2D network is isolated, while for X = Br, in [Hg(μ-pz-3-py)Br(2)](n) (2), a 1D zigzag chain is constructed. Our results show that noncovalent interactions such as hydrogen bond, halogen···halogen, and halogen···π interactions, when acting cooperatively, are driving forces for the selection of different structures.     

Synthesis of 1,2,3-triazole derivatives and in vitro antifungal evaluation on Candida strains

1,2,3-Triazoles have been extensively studied as compounds possessing important biological activities. In this work, we describe the synthesis of ten 2-(1-aryl-1H-1,2,3-triazol-4-yl)propan-2-ols via copper catalyzed azide alkyne cycloaddition (CuAAc or click chemistry). Next the in vitro antifungal activity of these ten compounds was evaluated using the microdilution broth method against 42 isolates of four different Candida species. Among all tested compounds, the halogen substituted triazole 2-[1-(4-chlorophenyl)-1H-(1,2,3)triazol-4-yl]propan-2-ol, revealed the best antifungal profile, showing that further modifications could be done in the structure to obtain a better drug candidate in the future.     

Preorganization: A Powerful Tool in Intermolecular Halogen Bonding in Solution

Preorganization is a powerful tool in supramolecular chemistry which has been utilized successfully in intra- and intermolecular halogen bonding. In previous work, we had developed a bidentate bis(iodobenzimidazolium)-based halogen bond donor which featured a central trifluoromethyl substituent. This compound showed a markedly increased catalytic activity compared to unsubstituted bis(iodoimidazolium)-based Lewis acids, which could be explained either by electronic effects (the electron withdrawal by the fluorinated substituent) or by preorganization (the hindered rotation of the halogen bonding moieties). Herein, we systematically investigate the origin of this increased Lewis acidity via a comparison of the two types of compounds and their respective derivatives with or without the central trifluoromethyl group. Calorimetric measurements of halide complexations indicated that preorganization is the main reason for the higher halogen bonding strength. The performance of the catalysts in a series of benchmark reactions corroborates this finding.     

Communication: Competition between π···π interaction and halogen bond in solution: a combined 13C NMR and density functional theory study

Competition between π···π interaction and halogen bond in solution has been investigated by using carbon nuclear magnetic resonance spectroscopy ((13)C NMR) combined with density functional theory calculation. Both experimental and theoretical results clearly show that there are no C-Cl···π or C-Br···π halogen bonds and only the π···π interactions exist in the binary liquid mixtures of C(6)D(6) with C(6)F(5)Cl and C(6)F(5)Br, respectively. The case is totally different for the binary liquid mixtures of C(6)D(6) with C(6)F(5)I in which the C-I···π halogen bonds not the π···π interactions are present. The important role of entropy in the competition between π···π interaction and halogen bond in solution was also discussed.     

2-Iodo-imidazolium receptor binds oxoanions via charge-assisted halogen bonding

A detailed (1)H-NMR study of the anion binding properties of the 2-iodo-imidazolium receptor 1 in DMSO allows to fully attribute the observed affinities to strong charge-assisted C-I···X(-) halogen bonding (XB). Stronger binding was observed for oxoanions over halides. Phosphate, in particular, binds to 1 with an association constant of ca. 10(3) M(-1), which is particularly high for a single X-bond. A remarkably short C-I···O(-) contact is observed in the structure of the salt 1·H(2)PO(4)(-).     

Synthesis, reactions, and applications of fluorine-containing multifunctional carbon compounds

The chemistry of compounds containing a carbon atom bearing three or four different labile functional groups has received little attention. These compounds should be of considerable significance in theoretical and synthetic organic chemistry. Among the compounds with multifunctional structures, those having both carbonyl and halogen groups in addition to other heteroatom groups seem especially valuable from a synthetic viewpoint. Their potential use as probes in pure and applied synthetic chemistry has not been exploited, presumably because of structural instability and a paucity of synthetic approaches. Keeping this background in mind, we focused on the synthesis of a new class of multifunctional carbon compounds in which ester carbonyl, halogen, and other heteroatom-derived functional groups are directly attached to the central carbon atom. Fluorine was chosen as the halogen because of the inherent stability of the CF bond and because of the fundamental chemical and biological interest in fluorine-containing compounds. The synthesis, reactions, and some applications of various fluorine-containing multifunctional carbon compounds are described.     

The halogen bond made visible: experimental charge density of a very short intermolecular Cl···Cl donor-acceptor contact

[ZnCl(2)(3,4,5-trichloropyridine)(2)] features short intermolecular Cl···Cl contacts between halogen atoms of different nature, and a charge density study provides experimental evidence for the accepted model of the halogen bonds: an arene-bonded Cl atom acts as a donor of electron density towards the "sigma hole" of a chlorido ligand attached to a neighbouring Zn(II) cation.     

Investigation of Intermolecular C-H···Halogen Hydrogen Bonded Supramolecular Assemblies in Three Copper(Ⅰ) Complexes Formed by 3,3'-Dimethoxy-6,6'-dimethyl-2,2'-bipyridine Ligand

Three new crystalline compounds 1-3 were successfully obtained by the reactions of 3,3'-dimethoxy-6,6'-dimethyl-2,2'-bipyridine ligand(dmbp) with the corresponding Cu(Ⅰ) salts.Crystal data for 1:orthorhombic Pbca,a = 18.5858(12),b = 8.1821(5),c = 20.6066(13) ,V = 3133.7(3) 3,Z = 8,Dc = 1.843 g/cm3,F(000) = 1696,μ = 3.366 mm-1,the final R = 0.0223 and wR = 0.0542.Crystal data for 2:Orthorhombic Pbca,a = 18.7883(16),b = 8.3249(7),c = 19.0294(17) ,V = 2976.4(4) 3,Z = 8,Dc = 1.731 g/cm3,F(000) = 1552,μ = 4.154 mm-1,the final R = 0.0279 and wR = 0.0680.Crystal data for 3:monoclinic P21/c,a = 13.812(10),b = 9.910(7),c = 23.444(17) ,β = 104.3350(10)°,V = 3090(4) 3,Z = 4,Dc = 1.476 g/cm3,F(000) = 1408,μ = 1.588 mm-1,the final R = 0.0479 and wR = 0.1081.The results of X-ray crystallographic analysis revealed that C14H16ICuN2O2(1) and C14H16BrCuN2O2(2) are isostructural compounds with the dimers connected by C-H···halogen hydrogen bonds to generate a three-dimensional(3D) supramolecular network in 1 and a two-dimensional(2D) sheet structure in 2,respectively,while the mononuclear complex C28H32Cl2Cu2N4O4(3) is ionic.In 3,the [Cu(dmbp)2]+ cations and [ClCuCl]-anions are connected by C-H···Cl hydrogen bonds to form a one-dimensional(1D) chain along the a axis.Therefore,in the three complexes,the C-H···halogen hydrogen bonds dominate their crystal structures.Additionally,The UV luminescent properties of complexes 1-3 were investigated.     

Fluorine-fluorine interactions in the solid state: an experimental and theoretical study

The solid state structures of three compounds that contain a perfluorinated chain, CF(3)(CF(2))(5)CH(2)CH(CH(3))CO(2)H, CF(3)(CF(2))(5)(CH(2))(4)(CF(2))(5)CF(3) and {CF(3)(CF(2))(5)CH(2)CH(2)}(3)P═O have been compared and a number of C-F···F-C and C-F···H-C interactions that are closer than the sum of the van der Waals radii have been identified. These interactions have been probed by a comprehensive computational chemistry investigation and the stabilizing energy between dimeric fragments was found to be 0.26-29.64 kcal/mol, depending on the type of interaction. An Atoms-in-Molecules (AIM) study has confirmed that specific C-F···F-C interactions are indeed present, and are not due simply to crystal packing. The weakly stabilizing nature of these interactions has been utilized in the physisorption of a selected number of compounds containing long chain perfluorinated ponytails onto a perfluorinated self-assembled monolayer, which has been characterized by IRRAS (Infrared Reflection Absorption Spectroscopy).     

Organic fluorine compounds: a great opportunity for enhanced materials properties

Interactions of "organic fluorine" have gained great interest not only in the context of crystal engineering, but also in the systematic design of functional materials. The first part of this tutorial review presents an overview on interactions known by organic fluorine. This involves π-π(F), C-F···H, F···F, C-F···π(F), C-F···π, C-F···M(+), C-F···C=O and anion-π(F) interactions, as well as other halogen bonds. The effect of the exchange of H vs. F is discussed by means of several examples and a short introduction to the young field of "fluorous" chemistry is given. The second part is dedicated to numerous applications of fluorine and fluorous interactions. It is shown how application of fluorination is used to enable a number of reactions, to improve materials properties and even open up new fields of research.     

Existence of both blue-shifting hydrogen bond and Lewis acid-base interaction in the complexes of carbonyls and thiocarbonyls with carbon dioxide

In this study, 16 gas phase complexes of the pairs of XCHZ and CO(2) (X = F, Cl, Br; Z = O, S) have been identified. Interaction energies calculated at the CCSD(T)/aug-cc-pVTZ//MP2/aug-cc-pVTZ level including both BSSE and ZPE corrections range from -5.6 to -10.5 kJ mol(-1) for XCHOCO(2) and from -5.7 to -9.1 kJ mol(-1) for XCHS···CO(2). Substitution of one H atom by one halogen in formaldehyde and thioformaldehyde reduces the interaction energy of XCHZ···CO(2), while a CH(3) substitution increases the interaction energy of both CH(3)CHO···CO(2) and CH(3)CHS···CO(2). NBO and AIM analyses also point out that the strength of Lewis acid-base interactions decreases going from >C1=S3···C6 to >C1=O3C6 and to >C1-X4···C6. This result suggests the higher capacity of solubility of thiocarbonyl compounds in scCO(2), providing an enormous potential application for designing CO(2)-philic materials based on the >C=S functional group in competition with >C=O. The Lewis acid-base interaction of the types >C=S···C, >C-Cl···C and >C-Br···C is demonstrated for the first time. The contribution of the hydrogen bonding interaction to the total interaction energy is larger for XCHS···CO(2) than for XCHO···CO(2). Upon complexation, a contraction of the C1-H2 bond length and a blue shift of its stretching frequency have been observed, as compared to the isolated monomer, indicating the existence of a blue-shifting hydrogen bond in all complexes examined. Calculated results also lend further support for the viewpoint that when acting as proton donor, a C-H bond having a weaker polarization will induce a stronger distance contraction and frequency blue shift upon complexation, and vice versa.     

Weak interactions between hypohalous acids and dimethylchalcogens

The complexes formed between dimethylchalcogens X(CH(3))(2) (X = S, Se, and Te) and hypohalous acids YOH (Y = F, Cl, Br, and I) have been studied at the MP2/aug'-cc-pVTZ computational level, five minima structures being located. Two of them correspond to hydrogen bonds (HB), another two to halogen bonds (XB) with the chalcogen acting as an electron donor, the last one showing a C-H···O contact. The most stable complexes of IOH and BrOH acids present halogen···chalcogen interactions with interaction energies, E(i), up to -49 kJ mol(-1). In the case of the ClOH and FOH molecules, the hydrogen bonded complexes are more stable with interaction energies between -27 and -34 kJ mol(-1). Linear correlations between the molecular electrostatic potential (MEP) stationary points at the van der Waals surface and the interaction energy have been found. The contribution of the different energy terms to the total interaction energy was analyzed by means of the DFT-SAPT theory finding that the electrostatic attractive term is dominant in the complexes with HB and XB, excepting a few cases in which the dispersion and induction terms become more important than the electrostatic one.     

Competition between Halogen,Hydrogen and Dihydrogen Bonding in Brominated Carboranes

Halogen bonds are a subset of noncovalent interactions with rapidly expanding applications in materials and medicinal chemistry. While halogen bonding is well known in organic compounds, it is new in the field of boron cluster chemistry. We have synthesized and crystallized carboranes containing Br atoms in two different positions, namely, bound to C‐ and B‐vertices. The Br atoms bound to the C‐vertices have been found to form halogen bonds in the crystal structures. In contrast, Br atoms bound to B‐vertices formed hydrogen bonds. Quantum chemical calculations have revealed that halogen bonding in carboranes can be much stronger than in organic architectures. These findings open new possibilities for applications of carboranes, both in materials and medicinal chemistry.     

卤代对苝醌类光敏剂光敏活性影响的量子化学研究

Taking hypomycin B（HMB）as the model compound,HF / 6-31G and TD-B3LYP / 6-31G methods have been employed to explore the effect of chlorine,bromine and iodine substitutions on molecular properties and photosensitization of perylenequinonoid photosensitizer（PQP）. It was found firstly that,the halogen substitutions lowered the EHOMO and ELUMO,and the ΔE. From chlorine,bromine to iodine substitutes,the EHOMO and ELUMO increased,while the corresponding ΔE decreased. Secondly,the halogen substitutions increased the molecular triplet-generating quantum yields and lowered the molecular lowest lying triplet energies,which resulted in the substitutes’similar 1O2 yields with their parent compounds. After halogen substitutions,the molecular adiabatic electron affinities increased,which made the substitutes possess lower O2· - -generating abilities than their parent compounds. Finally,the halogen substitutions lowered the intramolecular hydrogen bond energies,while enhancing the intramolecular proton transfer（IPT）barriers of cis isomers and lowering those of trans isomers on the ground state.     

Concerted halogen and hydrogen bonding in [RuI2(H2dcbpy)(CO)2]···I2···(CH3OH)···I2···[RuI2(H2dcbpy)(CO)2

A new type of concerted halogen bond-hydrogen bond interaction was found in the solid state structure of [RuI(2)(H(2)dcbpy)(CO)(2)]···I(2)···(MeOH)···I(2)···[RuI(2)(H(2)dcbpy)(CO)(2)]. The iodine atoms of the two I(2) molecules interact simultaneously with each other and with the OH group of methanol of crystallization. The interaction was characterized by single crystal X-ray measurements and by computational charge density analysis based on DFT calculations.     

Halogen bonded complexes between volatile anaesthetics (chloroform, halothane, enflurane, isoflurane) and formaldehyde: a theoretical study

The structures and intermolecular interactions in the halogen bonded complexes of anaesthetics (chloroform, halothane, enflurane and isoflurane) with formaldehyde were studied by ab initio MP2 and CCSD(T) methods. The CCSD(T)/CBS calculated binding energies of these complexes are between -2.83 and -4.21 kcal mol(-1). The largest stabilization energy has been found for the C-Br···O bonded halothane···OCH(2) complex. In all complexes the C-X bond length (where X = Cl, Br) is slightly shortened, in comparison to a free compound, and an increase of the C-X stretching frequency is observed. The electrostatic interaction was excluded as being responsible for the C-X bond contraction. It is suggested that contraction of the C-X bond length can be explained in terms of the Pauli repulsion (the exchange overlap) between the electron pairs of oxygen and halogen atoms in the investigated complexes. This is supported by the DFT-SAPT results, which indicate that the repulsive exchange energy overcompensates the electrostatic one. Moreover, the dispersion and electrostatic contributions cover about 95% of the total attraction forces, in these complexes.     

Theoretical study on the interactions of halogen‐bonds and pnicogen‐bonds in phosphine derivatives with Br2, BrCl,and BrF

The MP2 ab initio quantum chemistry methods were utilized to study the halogen‐bond and pnicogen‐bond system formed between PH₂X (X = Br, CH₃, OH, CN, NO₂, CF₃) and BrY (Y = Br, Cl, F). Calculated results show that all substituent can form halogen‐bond complexes while part substituent can form pnicogen‐bond complexes. Traditional, chlorine‐shared and ion‐pair halogen‐bonds complexes have been found with the different substituent X and Y. The halogen‐bonds are stronger than the related pnicogen‐bonds. For halogen‐bonds, strongly electronegative substituents which are connected to the Lewis acid can strengthen the bonds and significantly influenced the structures and properties of the compounds. In contrast, the substituents which connected to the Lewis bases can produce opposite effects. The interaction energies of halogen‐bonds are 2.56 to 32.06 kcal·mol^?1; The strongest halogen‐bond was found in the complex of PH₂OH???BrF. The interaction energies of pnicogen‐bonds are in the range 1.20 to 2.28 kcal·mol^?1; the strongest pnicogen‐bond was found in PH₂Br???Br₂ complex. The charge transfer of lp(P) ? σ*(Br? Y), lp(F) ? σ*(Br? P), and lp(Br) ? σ*(X? P) play important roles in the formation of the halogen‐bonds and pnicogen‐bonds, which lead to polarization of the monomers. The polarization caused by the halogen‐bond is more obvious than that by the pnicogen‐bond, resulting in that some halogen‐bonds having little covalent character. The symmetry adapted perturbation theory (SAPT) energy decomposition analysis showes that the halogen‐bond and pnicogen‐bond interactions are predominantly electrostatic and dispersion, respectively.