Influence of Halogen Bonding Interaction on Supramolecular Assembly of Coordination Compounds; Head-to-Tail N···X Synthon Repetitivity

H-bond engineering as a general strategy for inhibiting twisted intramolecular charge transfer in donor-acceptor fluorescent probes: Reshaping the pre-twisting method

Twisted intramolecular charge transfer (TICT) is a fluorescence quenching mechanism that occurs in donor-acceptor (D‒A) molecules. Chemical engineering research into TICT regulation over the past 50 years has primarily focused on manipulating steric factors by introducing alkyl groups at the D-A junction (pre-twisting). Herein, we report a significant advance in TICT-based probes through the introducing of H-bond as an efficient strategy for suppressing TICT. Accordingly, ortho-Cl installation in the N-phenylpyrazine-2-carboxamide (PPC) platform can achieve complete reversal from the quenching mode to the light-up mode. This specific H-bonding (N-H⋯Cl) effectively blocks N-C(Ar) bond rotation, leading to fluorescence-ON. This suggested that TICT inhibition may be involved. Therefore, in a sharp contrast to the general nature of the pre-twisting method in rotor molecules, which involves incorporating steric hindrance at either the donor or acceptor moiety to enhance intramolecular rotation (promotion TICT), the ortho-H bonding strategy completely freezes D‒A bond twisting (suppression TICT), resulting in improved fluorescent intensity. Furthermore, the fluorophores were evaluated for Hg2+ detection and in vivo bio-imaging. Notably, Hg-complexation induced another fluorescence inversion (OFF-ON) by imposing spatial constraints on twisting freedom in 3,4-Cl-PPC. Taken together, this work provides a valid and generalizable tactic for the development of high-performance sensing fluorophores through inhibition of TICT.

The Halogen Bond in Weakly Bonded Complexes and the Consequences for Aromaticity and Spin-Orbit Coupling

The halogen bond complexes CF3X⋯Y and C2F3X⋯Y, with Y = furan, thiophene, selenophene and X = Cl, Br, I, have been studied by using DFT and CCSD(T) in order to understand which factors govern the interaction between the halogen atom X and the aromatic ring. We found that PBE0-dDsC/QZ4P gives an adequate description of the interaction energies in these complexes, compared to CCSD(T) and experimental results. The interaction between the halogen atom X and the π-bonds in perpendicular orientation is stronger than the interaction with the in-plane lone pairs of the heteroatom of the aromatic cycle. The strength of the interaction follows the trend Cl < Br < I; the chalcogenide in the aromatic ring nor the hybridization of the C−X bond play a decisive role. The energy decomposition analysis shows that the interaction energy is dominated by all three contributions, viz., the electrostatic, orbital, and dispersion interactions: not one factor dominates the interaction energy. The aromaticity of the ring is undisturbed upon halogen bond formation: the π-ring current remains equally strong and diatropic in the complex as it is for the free aromatic ring. However, the spin-orbit coupling between the singlet and triplet π→π* states is increased upon halogen bond formation and a faster intersystem crossing between these states is therefore expected.

Semiconducting crystalline inorganic-organic hybrid metal halide nanochains

One-dimensional (1D) inorganic-organic metal halide hybrids at the molecular level, which can be considered as arrays of nanochains isolated by organic components, have shown remarkable optical and electric properties. This review summarizes their reported structural types and shows how to modify their band gaps and optical and electric properties.

Coordination chemistry of mercury(ii) halide complexes: a combined experimental, theoretical and (ICSD & CSD) database study on the relationship between inorganic and organic units

The coordination sphere can be influenced by many factors of inorganic and organic units. Despite the predominant role of inorganic unit in coordination sphere determination, organic unit can change it via one major or cooperativity of minor effects.

The combination of halogen and hydrogen bonding: a versatile tool in coordination chemistry

4-Iodo-N-(4-pyridyl)benzamide (INPBA) and four derived coordination complexes were synthesized in order to explore the combination of halogen and hydrogen bonding interactions in coordination chemistry.

Is Gelation Behavior Predictable through a Crystal Engineering Approach? A Case Study in Four Similar Coordination Compounds

In this paper, a detailed study on the gelation properties of a series of terpyridine and dipyrazine-pyridine ligands in the presence of metal salts is reported. To reveal the driving forces for the self-assembly of the metallogelators, their crystal structure is scrutinized. Inspired by the gelation of CuCl₂[Terpy- nCN], where "Terpy- nCN" is 4'-( n-cyanophenyl)-2,2',6',2″-terpyridine, to look into the aggregation behavior of the related analogues, synthesis of CuCl₂[Dipyz-py- nCN] derivatives, where "Dipyz-py- nCN" is 4-( n-cyanophenyl)-2,6-di-pyrazin-2-yl-pyridine, with the same cyano groups is performed. We then find that the Dipyz-py counterpart forms crystals when the molecules are stacked in an alternating way, instead of the unidirectional one required for gel formation. A crystal engineering approach is applied to determine the interactions that are favorable for fabricating a fiber network that is likely to be present in both crystalline and gel states and to find the interaction that disturbs this delicate balance between gelation and crystallization in coordination compounds; then, we conclude that the subtle balance between the molecular shape and intermolecular interactions is the origin of the gelation and crystallization of the current molecular system. This enables us to find the mutual connection among the structure of molecules, assembly behavior, and intermolecular interactions. With our experiments, a deep understanding of the balance among solution, gelation, and crystallization with subtle molecular diversions is provided.

The role of π-π stacking and hydrogen-bonding interactions in the assembly of a series of isostructural group IIB coordination compounds

The supramolecular chemistry of coordination compounds has become an important research domain of modern inorganic chemistry. Herein, six isostructural group IIB coordination compounds containing a 2-{[(2-methoxyphenyl)imino]methyl}phenol ligand, namely dichloridobis(2-{(E)-[(2-methoxyphenyl)azaniumylidene]methyl}phenolato-κO)zinc(II), [ZnCl2(C28H26N2O4)], 1, diiodidobis(2-{(E)-[(2-methoxyphenyl)azaniumylidene]methyl}phenolato-κO)zinc(II), [ZnI2(C28H26N2O4)], 2, dibromidobis(2-{(E)-[(2-methoxyphenyl)azaniumylidene]methyl}phenolato-κO)cadmium(II), [CdBr2(C28H26N2O4)], 3, diiodidobis(2-{(E)-[(2-methoxyphenyl)azaniumylidene]methyl}phenolato-κO)cadmium(II), [CdI2(C28H26N2O4)], 4, dichloridobis(2-{(E)-[(2-methoxyphenyl)azaniumylidene]methyl}phenolato-κO)mercury(II), [HgCl2(C28H26N2O4)], 5, and diiodidobis(2-{(E)-[(2-methoxyphenyl)azaniumylidene]methyl}phenolato-κO)mercury(II), [HgI2(C28H26N2O4)], 6, were synthesized and characterized by X-ray crystallography and spectroscopic techniques. All six compounds exhibit an infinite one-dimensional ladder in the solid state governed by the formation of hydrogen-bonding and π-π stacking interactions. The crystal structures of these compounds were studied using geometrical and Hirshfeld surface analyses. They have also been studied using M06-2X/def2-TZVP calculations and Bader's theory of `atoms in molecules'. The energies associated with the interactions, including the contribution of the different forces, have been evaluated. In general, the π-π stacking interactions are stronger than those reported for conventional π-π complexes, which is attributed to the influence of the metal coordination, which is stronger for Zn than either Cd or Hg. The results reported herein might be useful for understanding the solid-state architecture of metal-containing materials that contain MIIX2 subunits and aromatic organic ligands.

Solid-state supramolecular architectures of a series of Hg(ii) halide coordination compounds based on hydroxyl-substituted Schiff base ligands

Herein, six Hg(ii) coordination compounds containing Schiff base ligands were synthesized, characterized and studied using geometrical and Hirshfeld analyses as well as theoretical calculations.

Lone pair⋯π interaction versus σ-hole appearance in metal-bonded halogens

Three complexes of N-(2,5-diluorophenyl)-2-pyrazine carboxamide and ZnX₂ have been synthesized. The crystal structures reveal that in all three coordination compounds, metal-bound halides have interacted with π systems through a negative electrostatic region.

Sonochemical synthesis, characterization, and effects of temperature, power ultrasound and reaction time on the morphological properties of two new nanostructured mercury(II) coordination supramolecule compounds

Two new mercury(II) coordination supramolecular compounds (CSCs) (1D and 0D), [Hg(L)(I)₂]_n (1) and [Hg₂(L')₂(SCN)₂]·2H₂O (2) (L=2-amino-4-methylpyridine and L'=2,6-pyridinedicarboxlic acid), have been synthesized under different experimental conditions. Micrometric crystals (bulk) or nano-sized materials have been obtained depending on using the branch tube method or sonochemical irradiation. All materials have been characterized by field emission scanning electron microscope (FESEM), scanning electron microscopy (SEM), powder X-ray diffraction (PXRD) and FT-IR spectroscopy. Single crystal X-ray analyses on compounds 1 and 2 show that Hg²⁺ ions are 4-coordinated and 5-coordinated, respectively. Topological analysis shows that the compound 1 and 2 have 2C1, sql net. The thermal stability of compounds 1 and 2 in bulk and nano-size has been studied by thermal gravimetric (TG), differential thermal analyses (DTA) for 1 and differential scanning calorimetry (DSC) for 2, respectively. Also, by changing counter ions were obtained various structures 1 and 2 (1D and 0D, respectively). The role of different parameters like power of ultrasound irradiation, reaction time and temperature on the growth and morphology of the nano-structures are studied. Results suggest that increasing power ultrasound irradiation and temperature together with reducing reaction time and concentration of initial reagents leads to a decrease in particle size.

Influences of temperature, power ultrasound and reaction time on the morphological properties of two new mercury(II) coordination supramolecular compounds

Nanoparticles of two new coordination compounds, [Hg₂(L)₂(Br)₄]_n (1) and [Hg(L')(SCN)₂] (2), (L=2-amino-4-methylpyridine, L'=2,6-pyridinedicarboxlic acid), have been synthesized by use of a sonochemical process and characterized by scanning electron microscopy (SEM), field emission scanning electron microscopy(FESEM), X-ray powder diffraction (XRPD), Fourier transform infrared spectroscopy (FTIR) spectroscopy and elemental analyses. The single crystal X-ray data of compounds 1 and 2 imply that the Hg(II) ions are four and five coordinated, respectively. Topological analysis shows that 1D and 0D coordination networks of 1 and 2 can be classified as underlying nets of topological types 2C1 and 1,3M4-1, respectively. The thermal stability of compounds has been studied by thermal gravimetric (TG) and differential thermal analyses (DTA). The role of temperature, reaction time and ultrasound irradiation power on the size and morphology of "nano-structures" 1 and 2, has been investigated. Results claim that an increase of temperature, sonication power and decrease in reaction time leads to a decrease of particle size.

Trimethyl-, triethyl- and trimethoxybenzene-based tripodal compounds bearing pyrazole groups: conformations and halogen-/hydrogen-bond patterns in the crystalline state

X-ray analyses of a series of benzene-based tripodal molecules1–9provide interesting insights into the molecular recognition phenomena and give information about the different conformations which adopt the molecules in the solvent-free crystals and in solvates.

Conformational variety of flexible mono-dentate ligands in coordination compounds: influence of π-involving interactions

The effect of intermolecular interactions on the conformational variety of flexible mono-dentate ligands in coordination compounds has been investigated through the preparation of two series of mercury(ii) complexes. In this regard, the molecular and structural architecture of eight complexes, [HgCl2(L(amide-Cl))2] (), [HgCl2(L(amide-Br))2] (), [HgBr2(L(amide-Br))2] (), and [HgI2(L(amide-Br))2] (), as the first series and [HgBr2(L(imine-Cl))2] (), [HgBr2(L(imine-Br))2] (), [HgI2(L(imine-Cl))]n (), and [HgI2(L(imine-Br))]n (), as the second series, using two kind of flexible ligands, N-(1-halonaphthalen-4-yl)nicotinamide, L(amide-X), and 4-halo-N-((pyridin-3-yl)methylene)naphthalen-1-amine, L(imine-X), has been studied. Inspection of the packing of these compounds clearly shows the presence of conformational changes in the arrangement of the ligands in each series. Although there are slight differences between the crystal packing of these compounds, it seems that π-involving intermolecular interactions including πnaphπnaph in the first series and πimineπpy/naph in the second series with the cooperation of Hgπpy can lock the ligand conformational variety to a single conformer.

The first phosphoramide-mercury(II) complex with a Cl2Hg-OP[N(C)(C)]3 segment

Mercury(II) exhibits a strong preference for linear coordination which has been attributed to relativistic effects splitting the 6p orbitals and promoting sp hybridization. If the two ligands attached to the mercury(II) ion are weak donors, the metal ion can act as a good Lewis acid and expand its coordination number. Moreover, mercury has a special affinity for softer bases, such as S and N atoms, and has much less affinity for hard bases, such as those including an O atom. The asymmetric unit of dichlorido[tris(piperidin-1-yl)phosphane oxide-κO]mercury(II)-dichloridomercury(II) (2/1), [HgCl2{(C5H10N)3PO}]2·[HgCl2], is composed of one HgCl2{(C5H10N)3PO} complex and one half of a discrete HgCl2 entity located on an inversion centre. The coordination environment around the Hg(II) centre in the complex component is a distorted T-shape. Bond-valence-sum calculations confirm the three-coordination mode of the Hg(II) atom of the complex molecule. The noncovalent nature of the Hg...Cl and Hg...O interactions in the structure are discussed.

The Halogen Bond

The halogen bond occurs when there is evidence of a net attractive interaction between an electrophilic region associated with a halogen atom in a molecular entity and a nucleophilic region in another, or the same, molecular entity. In this fairly extensive review, after a brief history of the interaction, we will provide the reader with a snapshot of where the research on the halogen bond is now, and, perhaps, where it is going. The specific advantages brought up by a design based on the use of the halogen bond will be demonstrated in quite different fields spanning from material sciences to biomolecular recognition and drug design.

The role of intermolecular interactions involving halogens in the supramolecular architecture of a series of Mn(ii) coordination compounds

This study reveals the role of halogen-involving interactions in structural changes of supramolecular assemblies of manganese(ii) complexes including N-(4-halo)phenyl picolinamide ligands.

Ultrasonic-assisted synthesis and structural characterization of two new nano-structured Hg(II) coordination polymers

Two new Hg(II) coordination polymers containing N,N'-Bis-pyridin-3-ylmethylene-naphtalene-1,5-diamine ligand were synthesized by conventional and sonochemical methods, characterized by spectroscopic techniques (FT-IR and elemental analysis), and their X-ray crystallographic structures were determined. The crystal packing and supramolecular features of these coordination polymers were studied using geometrical analysis and Hirshfeld surface analysis. The crystal structure analysis revealed that H⋯H contacts, C-H⋯π and C-H⋯X (X = Cl for 1 and X = Br for 2) hydrogen bonding interactions are strong enough to govern the supramolecular architecture. The BFDH analysis helps us to compare the predicted morphology to that obtained under ultrasonication. This study may provide further insight into discovering the role of weak intermolecular interactions in the context of nano-supramolecular assembly.

Theoretical insight into the interplay between lithium and halogen–hydride bonds: An ab initio study

Quantum chemical calculations have been performed to analyze the intermolecular interactions in the ternary NCLi ⋯ NCX ⋯ HMgY complexes ( X = F , Cl , Br ; Y = H , F , Cl , Br , Li ). A cooperative effect is observed between the lithium and halogen–hydride bonds in these complexes. The cooperative energy ranges from -1.81 kJ/mol to -5.21 kJ/mol, -3.59 kJ/mol to -9.86 kJ/mol and -4.77 kJ/mol to -14.27 kJ/mol for X = F , Cl and Br , respectively (at MP2/6-311++G(d,p) level). The geometrical and interaction energies analysis reveal that the lithium bond has a greater enhancing effect on the halogen–hydride bond. The results of many-body analysis indicate that two- and three-body interaction energies have a positive contribution to the total interaction energy. The electronic characteristics of the complexes have been analyzed through molecular electrostatic potential (MEP), atoms in molecules (AIM), electron localization function (ELF) and natural bond orbital (NBO) methodologies.

The role of weak hydrogen and halogen bonding interactions in the assembly of a series of Hg(ii) coordination polymers

A series of eight new Hg(ii) complexes based on the L^4-X ligands, where L is (E)-4-halo-N-(pyridin-4-ylmethylene)aniline, were synthesized and characterized and their supramolecular crystal structures were studied by different geometrical and theoretical methods.

Influence of N-heteroaromatic π–π stacking on supramolecular assembly and coordination geometry; effect of a single-atom change in the ligand

A study on how the polarization of aromatic systems, through the introduction of a nitrogen heteroatom, affects the π–π interactions and crystal packing of mercury coordination compounds.

Structures and trends of one-dimensional halide-bridged polymers of five-coordinate cadmium(ii) and mercury(ii) with benzopyridine and -pyrazine-type N-donor ligands

Structural trends in halide-bridged polymers of d¹⁰ metals, which showcase the templating effect introduced by benzopyridine-type N-donor ligands, are reported.

Complexes between hypohalous acids and phosphine derivatives. Pnicogen bond versus halogen bond versus hydrogen bond

The complexes of HOBr:PH2Y (Y=H, F, Cl, Br, CH3, NH2, OH, and NO2), HOCl:PH2F, and HOI:PH2F have been investigated with ab initio calculations at the MP2/aug-cc-pVTZ level. Four types of structures (1, 2, 3a, and 3b) were observed for these complexes. 1 is stabilized by an O⋯P pnicogen bond, 2 by a P⋯X halogen bond, 3a by a H⋯P hydrogen bond and a P⋯X pnicogen bond, and 3b by H⋯P and H⋯Br hydrogen bonds. Their relative stability is related to the halogen X of HOX and the substituent Y of PH2Y. These structures can compete with interaction energy of -10.22∼-29.40 kJ/mol. The HO stretch vibration shows a small red shift in 1, a small irregular shift in 2, but a prominent red shift in 3a and 3b. The XO stretch vibration exhibits a smaller red shift in 1, a larger red shift in 2, but an insignificant blue shift in 3a and 3b. The PY stretch vibration displays a red shift in 1 but a blue shift in 2, 3a, and 3b. The formation mechanism, stability, and properties of these structures have been analyzed with molecular electrostatic potentials, orbital interactions, and non-covalent interaction index.

The effects of halogen bonding and molecular design on the self-assembly of coordination polymers of Mn(iii)-tetraarylporphyrin with axial bridging ligands

Two new coordination polymers of Mn(iii)-tetra(iodophenyl)porphyrin with isonicotinate and pyrimidine-5-carboxylate linkers have been synthesized. The effect of halogen-bonding interactions on their self-assembly in the crystalline bulk and on a graphite surface has been discussed.

Temperature-dependent halogen⋯halogen synthon crossover in coordination compounds

The crossover between type I and type II Br⋯Br synthons on the formation of coordination compounds has been investigated for the first time.

Stepwise formation of heteronuclear coordination networks based on quadruple-bonded dimolybdenum units containing formamidinate ligands

The first 2D and 3D heteronuclear coordination networks based on quadruple-bonded dimolybdenum units containing formamidinate ligands are reported.

Supramolecular assemblies of Ru(ii) organometallic half-sandwich complexes

Extended hydrogen bonding network in [(arene)Ru(para-substituted amine ligand)Cl₂].

Strengthening N⋯X halogen bonding via nitrogen substitution in the aromatic framework of halogen-substituted arylpyrazinamides

The importance of N⋯X halogen bonding in a series of N-(5-halo-2-pyridinyl)pyrazine-2-carboxamides has been investigated by different methods.

Exploring supramolecular assembly and luminescent behavior in a series of RE-p-chlorobenzoic acid-1,10-phenanthroline complexes

Eleven new rare earth (RE)-p-chlorobenzoic acid-1,10-phenanthroline complexes have been synthesized and their structural, supramolecular and luminescent properties have been explored.

Enhancing effects of electron-withdrawing groups and metallic ions on halogen bonding in the YC6F4X···C2H8N2 (X = Cl, Br, I; Y = F, CN, NO2, LiNC+, NaNC+) complex

Halogen-bonding interactions are highly directional intermolecular interactions that are often important in crystal engineering. In this work, the second-order Møller-Plesset perturbation theory (MP2) calculations and the quantum theory of "atoms in molecules" (QTAIM) and noncovalent interaction (NCI) studies were carried out on a series of X···N halogen bonds between substituted haloperfluoroarenes C6F4XY (X = Cl, Br, I; Y = F, CN, NO2) as bond donors and 1,2-diaminoethane as bond acceptor. Our research supports earlier work that electron-withdrawing substituents produce an enhancement effect on the size of the σ-hole and the maximum positive electrostatic potentials (VS,max), which further strengthens the halogen bonding. The metallic ion M(+) (M(+) = Li(+), Na(+)) has the ability to enhance the size of both the σ-hole and VS,max value with the formation of [MNCC6F4X](+), resulting in more electronic charge transfer away from the halogen atom X and an increase in the strength of the halogen bond. It is found that the values of V(S,max) at the σ-holes are linear in relation to the halogen-bonded interaction energies and the halogen-bonding interaction distance, indicating that the electrostatic interaction plays a key role in the halogen-bonding interactions. The values of V(S,max) at the σ-holes are also linear in relation to the electron density ρ(b), its Laplacian nabla(2)ρb, and -Gb/Vb of XB, indicating that the topological properties (ρb, nabla(2)ρb) and energy properties (Gb, Vb) at the BCPs are correlated with the electrostatic potentials.