Alireza Azhdari Tehrani

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

In this study, N-(3-halophenyl)-2-pyrazinecarboxamide ligands, L(3-F), L(3-Cl), L(3-Br), and L(3-I), carrying a different halogen atom on the phenyl meta-position and N-phenyl-2-pyrazinecarboxamide ligand, L(H), have been employed for the synthesis of 12 mercury(II) complexes, [HgCl2(L(H))]n, 1, [HgCl2(L(3-Cl))]n, 2, [Hg2Cl4(L(3-Br))2], 3, [Hg2Cl4(L(3-I))2], 4, [Hg2Br4(L(H))2], 5, [HgBr2(L(3-F))], 6, [HgBr2(L(3-Cl))], 7, [HgBr2(L(3-Br))], 8, [HgBr2(L(3-I))], 9, [Hg2I4(L(H))2], 10, [HgI2(L(3-Br))], 11, and [HgI2(L(3-I))]n, 12. Interestingly, structural analysis clearly shows that, by the replacing of coordinated anions from chloride with bromide and iodide in each series containing the same ligand, the coordination geometry and structural motif of the resulting compounds have been dramatically affected. One of the common features in the crystal structures of these complexes is that there is a strong tendency to form halogen bonding synthons between adjacent halophenyl and pyrazine rings. The influence of these halogen bonding interactions on the supramolecular assemblies has been discussed with the help of geometrical analysis and theoretical calculations. The X···N halogen bonding distances are 2.5-9.4% shorter than the sum of the van der Waals radii of nitrogen and halogen atoms. Theoretical methods also show the halogen bonding energies within a range of -27.86 to -46.15 kJ·mol(-1). In all complexes synthesized here, the pyrazine ring is coordinated to the mercury(II) ion through the N atom syn to the carbonyl. Therefore, the second common feature of the crystal structures for complexes studied here is the selectivity of the metal ion coordination site. The halogen bond synthon repetitivity across these compounds and selectivity in the mercury(II) ion coordination site further point to application in the coordination crystal engineering research field.

Urea-containing metal-organic frameworks as heterogeneous organocatalysts

Two novel pillared metal-organic frameworks (MOFs) containing a urea-functional group are introduced. Herein, the urea functional group was incorporated into the MOF backbone by preparing a urea-ditopic ligand. These frameworks (TMU-18 and TMU-19) were fabricated using the synthesized urea-containing ligand, 4,4′-bipyridine (bipy) and 1,2-bis(4-pyridyl)ethane (bpe), and using zinc nitrate as the metal source. Subsequently, TMU-18 and TMU-19 were characterized by X-ray diffraction, IR spectroscopy, elemental analysis, scanning electron microscopy (SEM) and thermogravimetric analysis. Furthermore, their potential efficiency as organocatalysts was evaluated in the regioselective methanolysis of epoxides.

Urea Metal–Organic Frameworks for Nitro-Substituted Compounds Sensing

Urea groups are known to form strong hydrogen bonds with molecules containing atom(s) that can act as hydrogen bond acceptor(s). Thus, urea is a particularly interesting building block for designing receptors for neutral or charged guests. In the quest for new sensors with enhanced performance for the detection of nitro-substituted compounds, two pillared metal-organic frameworks containing urea functional groups were synthesized and structurally characterized. The sensing properties of these frameworks toward nitro-analytes were investigated and compared to each other. The study clearly reveals the importance of urea groups orientation inside the pore cavity of MOFs, as well as the supramolecular interactions between the interpenetrated networks. This work is interesting as it represents the first example of urea-functionalized MOFs for nitro-analytes recognition.

Mechanochemical synthesis of isoreticular metal–organic frameworks and comparative study of their potential for nitrobenzene sensing

A series of halogen containing isoreticular metal–organic frameworks (IRMOFs) were synthesized via a liquid-assisted grinding method. The luminescence properties of these frameworks were described for nitrobenzene sensing. This investigation revealed the prominent roles of frontier molecular orbital energies of the linkers, substitution polarizability and structural parameters in the ability of IRMOFs to sense nitrobenzene.

Synthon crossover between halogen⋯π and halogen⋯halogen interaction

The synthon crossover between the halogen⋯π interaction and halogen bonding in a series of N-(4-halophenyl)-2-naphthamide and N-(4-halophenyl)quinoline-2-carboxamide has been investigated by different methods. The results indicate that the heteroatom substitution in the aromatic ring leads to a change in the iodine bonding acceptor site from the iodine atom in N-(4-iodophenyl)-2-naphthamide, naph-I, to the π-electron cloud in N-(4-iodophenyl)quinoline-2-carboxamide, quin-I.

Effect of halogen bonding interaction on supramolecular assembly of halogen-substituted phenylpyrazinamides

A series of halogen-substituted phenylpyrazinamides have been synthesized and crystallographically characterized in order to investigate the effect of halogen bonding interaction on supramolecular assembly of N-phenylpyrazine-2-carboxamide derivatives. The notable feature in crystal structures of meta- and para-iodinated, brominated and chlorinated compounds is that there is a tendency to form a halogen bonding synthon between adjacent halophenyl and prazine/halophenyl rings. Influence of these halogen bonding interactions on supramolecular assemblies have been discussed with the help of geometrical analysis and theoretical calculations. The X⋯N halogen bonding distances are 2.2–7.7% shorter than the sum of the van der Waals radii of the nitrogen and halogen atoms. Also, theoretical methods show the N⋯X halogen bonding energies within a range of −9.43 to −23.67 kJ mol−1. Our studies show that the selection of halogen atom as well as the position of substitution on phenylpyrazinamide compound may be important for crystal design based on halogen bonding.

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

A series of four new manganese(II) complexes based on the L4-X ligand, where L is N-(4-halo)phenyl picolinamide ligands, have been synthesized, characterized and their supramolecular crystal structures were studied by geometrical analysis and theoretical calculation. Our study reveals the role of weak intermolecular interactions involving halogens, such as C–H⋯X hydrogen bonds (in the cases of 1 and 2) and C–X⋯X′–M halogen bonds (in the cases of 3 and 4), in the structural changes of supramolecular assemblies of coordination compounds. This study could provide further insight into discovering the role of weak intermolecular interactions in the context of metallosupramolecular assembly.

Two pillared metal–organic frameworks comprising a long pillar ligand used as fluorescent sensors for nitrobenzene and heterogeneous catalysts for the Knoevenagel condensation reaction

Two new pillared zinc and cadmium–organic frameworks were synthesized by incorporating two different organic linkers, namely 2-aminoterephthalic acid as an oxygen-donor linker and N4,N4′-bis(pyridin-4-ylmethylene)-biphenyl-4,4′-diamine as a long pillaring strut. The structures of these two frameworks were analyzed using X-ray crystallography, FT-IR spectroscopy, thermogravimetric and elemental analyses. Their structural features as well as their stability were studied. These two MOFs having the same organic composition and the same network topology but different inorganic nodes differ in their chemical stability. Also, these two frameworks respond differently to nitrobenzene when they are used as fluorescent sensors. Furthermore, the catalytic behavior of one of these frameworks toward the Knoevenagel condensation reaction was investigated.

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

A series of new Ru(II) half-sandwich complexes with the general formula [(arene)Ru(L)Cl2], where L is a monodentate amine ligand and arene is a p-cymene or benzene ring, were synthesized and characterized and their supramolecular structures were analyzed. The crystal packing of these compounds was studied using geometrical analysis, Hirshfeld surface analysis and theoretical calculations. Our study reveals the importance of three common hydrogen bonding motifs as the primary factor controlling the supramolecular architecture of this series of complexes. Furthermore, the role of an amine ligand substituent could be different depending on the type of interactions that occurs between functional groups. Interestingly, homomeric self-complementary intermolecular interactions are formed when the ancillary ligand contains benzyl cyanide or alkyl 4-aminobenzoate. These non-conventional interactions could be promising for the design of organometallic supramolecular arrays.

Halogen bonding synthon crossover in conformational polymorphism

Two concomitant conformational polymorphs of N-(3-bromophenyl)-2-pyrazinecarboxamide have been discovered and characterized. The synthon crossover between Br⋯Br and Br⋯N “halogen bonding” on the formation of these polymorphs has been investigated by Hirshfeld surface analysis, halogen bonding interaction energy, lattice energy calculations and calorimetric analysis. From our results, it can be seen that different halogen bonding synthons, along with other intermolecular interactions, namely hydrogen bonding and π–π stacking interactions, result in the formation of different conformational polymorphs.