Atash V. Gurbanov

Chelate ring stacking interactions in the supramolecular assemblies of Zn(II)and Cd(II) coordination compounds: a combined experimental and theoretical study

The self-assembly of Zn(II) and Cd(II) ions with two isomeric tetradentate ligands, 2-pyridyl-isonicotinoylhydrazone (HL1) and 2-benzoylpyridyl-picolinoylhydrazone (HL2), was studied by elemental analysis, FT-IR spectroscopy and single-crystal X-ray diffraction. The reaction of zinc(II) and cadmium(II) salts with HL1 and HL2 in methanol under solvothermal conditions produced six monomer and one tetranuclear zinc(II) complexes, namely, Zn(HL1)Br2 (1), Zn(HL1)Cl2 (2), [Cd(HL1)2](NO3)2·H2O (3), Cd(HL2)Br2(4), Zn(HL2)Cl2 (5), Zn(HL2)Br2 (6) and [Zn4(L2)4I2][ZnI4]·2H2O (7). The structure of 7 includes a cationic tetranuclear cluster of four zinc ions, four ligands, and two anions, counterbalanced by ZnI42− ions. However, the reaction of zinc(II) and cadmium(II) salts with HL1 under the same conditions produced monomer compounds. Herein, the ligand effects on the complex structures were studied. Hirshfeld surface analysis and fingerprint plots facilitate the comparison of intermolecular interactions in compounds 1–7, which are crucial in building supramolecular architectures.

Halogen-bonded tris(2,4-bis(trichloromethyl)-1,3,5-triazapentadienato)-M(III) [M = Mn, Fe, Co] complexes and their catalytic activity in the peroxidative oxidation of 1-phenylethanol to acetophenone

One-pot template condensation of CCl3CN with ammonia on a metal source [MnCl2·4H2O, FeCl3·6H2O or Co(CH3COO)2·4H2O] in DMSO led to the formation of tris{2,4-bis(trichloromethyl)-1,3,5-triazapentadienato}-M(III) complexes, [M{NHC(CCl3)NC(CCl3)NH}3]·n(CH3)2SO [M = Mn, n = 1 (1); M = Fe, n = 2 (2); M = Co, n = 2 (3)], which were characterized using elemental analysis, and IR, ESI-MS and single-crystal X-ray analysis. The role of inter- and intramolecular non-covalent halogen and hydrogen bonds in the synthesis of 1–3 is discussed. It is shown that the crystal ionic radii of the metal ions [68.5 (Co) 3.155 (2) > 3.133 (1) A]. Compounds 1–3 and the related di(triazapentadienato)-Cu(II) complex [Cu{NHC(CCl3)NC(CCl3)NH}2]·2(CH3)2SO (4) act as catalyst precursors for the additive-free microwave (MW) assisted homogeneous oxidation of 1-phenylethanol with tert-butylhydroperoxide (TBHP), leading to the formation of acetophenone with yields up to 99% and TONs up to 5.0 × 103 after 1 h of low power (10 W) MW irradiation.

Pb⋯X (X = N, S, I) tetrel bonding interactions in Pb(II) complexes: X-ray characterization, Hirshfeld surfaces and DFT calculations

Four new Pb(II) complexes of nicotinoylhydrazone and picolinoylhydrazone-based ligands and three different anionic co-ligands (acetate, thiocyanate and iodide) have been synthesized and characterized by structural, analytical and spectroscopic methods. The ligands coordinate to the Pb(II) metal center in a tridentate fashion via two nitrogen and one oxygen donor atoms either in mono-deprotonated or in neutral forms. Single-crystal X-ray crystallography reveals that the molecular complexes aggregate into larger entities depending upon the anion coordinated to the metal centre. The Pb(II) center is hemidirectionally coordinated and, consequently, it is sterically ideal for establishing tetrel bonding interactions. Consequently, in the crystal structures of all the complexes, the Pb participates in short contacts with nitrogen, iodide or sulphur atoms. These contacts are shorter than the sums of the van der Waals radii and larger than the sums of the covalent radii, therefore they can be defined as non-covalent tetrel bonding interactions. They interconnect the covalently bonded units (monomers or dimers) into supramolecular assemblies (1D infinite chains and 3D structures). Hirshfeld surface analysis and fingerprint plots have been used to analyse the contribution of contacts involving the Pb atom. We have analysed the interesting supramolecular assemblies observed in the solid state of all four complexes by means of DFT calculations and characterized them using Baders theory of atoms-in-molecules.

The role of unconventional stacking interactions in the supramolecular assemblies of Hg(II) coordination compounds

In this study, nine mercury(II) complexes of the composition [Hg(Ln)(X)2] (X = Cl, Br and I, n = 1–3), (L1 = 2-pyridine piconyl hydrazone); L2 = (2-acetylpyridine piconyl hydrazone) and L3 = (2-phenylpyridine piconyl hydrazone) are synthesized and spectroscopically characterized. Single-crystal X-ray crystallography showed that the molecular complexes can aggregate into larger entities depending upon the anion coordinated to the metal centre. Moreover, Hirshfeld surface (HS) analyses were employed to gain additional insight into interactions responsible for the packing of complexes 1–9. Quantitative examination of 2D fingerprint plots revealed, among others, the dominating participation of H⋯H and H⋯X interactions in the molecular packing. Moreover, C–H⋯X hydrogen bonds, π–π, and chelate-ring–π interactions are described and analysed by means of density functional theory (DFT) calculations since they play an important role in the construction of three-dimensional supramolecular frameworks. The influence of the halide on the energetic features of the assemblies has been also studied.

Cyanosilylation of Aldehydes Catalyzed by Iron(iii) Arylhydrazone-β-Diketone Complexes

Two known iron(iii) complexes, [Fe(H2O)3(L1)]·xH2O (x = 4 (1), 5 (2)) and [Fe(H2O)3(L2)]·3H2O (3), bearing the basic forms of 5-chloro-3-(2-(4,4-dimethyl-2,6-dioxocyclohexylidene)hydrazinyl)-2-hydroxybenzenesulfonic acid (H3L1) and 3-(2-(2,4-dioxopentan-3-ylidene)hydrazinyl)-2-hydroxy-5-nitrobenzenesulfonic acid (H3L2), were prepared and used as homogeneous catalysts for cyanosilylation of a variety of aldehydes with trimethylsilyl cyanide leading to the corresponding cyanohydrin trimethylsilyl ethers. High yield (up to 98 %) was observed in the reaction catalyzed by 3 at room temperature in methanol.

One-pot insertion of chalcones into the benzoylacetone backbone

Interaction of 1-phenylbutane-1,3-dione and chalcones in the presence of a base gives, in one step, good to high yields cyclic and unusual acyclic insertion products in ratios which depend on substrate, catalyst, and reaction conditions. All the synthesized compounds are characterized using IR, 1H and 13C NMR spectroscopies, ESI–MS, and single-crystal X-ray diffraction (for one compound) analysis.

2-[2-(4-Meth­oxy­phen­yl)-4,5-diphenyl-1H-imidazol-1-yl]ethanol

In the title compound, C24H22N2O2, the central imidazole ring makes dihedral angles of 49.45 (8), 88.94 (9) and 19.43 (8)° with the benzene ring and the two phenyl rings, respectively. The dihedral angle between the phenyl rings is 77.86 (9)°, and they form dihedral angles of 49.06 (9) and 67.31 (8)° with the benzene ring. In the crystal, molecules are linked by O—H⋯N hydrogen bonds, forming chains along the b axis. These chains are connected by C—H⋯O hydrogen bonds, forming a two-dimensional network parallel to (100). In addition, C—H⋯π interactions are also observed. The terminal C and O atoms of the ethanol group are disordered over two sets of sites with an occupancy ratio of 0.801 (5):0.199 (5).

10-(2-Hy-droxy-eth-yl)-9-(2-hy-droxy-phen-yl)-3,3,6,6-tetra-methyl-1,2,3,4,5,6,7,8,9,10-deca-hydro-acridine-1,8-dione.

The dihydropyridine ring in the title compound, C25H31NO4, adopts an envelope conformation with the methine C atom representing the flap. The cyclohexenone rings also adopt envelope conformations with the C atoms bearing the methyl C atoms representing the flaps. The phenolic hydroxy group forms an intramolecular hydrogen bond to one of the two keto O atoms. The hydroxy group of the N-bonded alkyl chain forms an intermolecular hydrogen bond to the other keto O atom of an adjacent molecule. The latter hydrogen bond leads to the formation of a helical chain running along the b axis.

Extended lead(II) architectures engineered via tetrel bonding interactions

The evaluation of N′-(pyridin-2-ylmethylene)nicotinohydrazide (HLI) and N,N′′′-bis(1-(pyridin-2-yl)-ethylidene)carbazide (H2LII) as linker precursors in the synthesis of novel PbII extended structures is described. An equimolar one-pot reaction of PbX2 (X = NO3−, CH3COO−) salts with HLI and H2LII in MeOH at 60 °C in a branched tube apparatus leads to heteroleptic complexes [Pb(HLI)(NO3)2]n (1), [Pb(LI)(CH3O)]n (2), [Pb2(H2LII)(NO3)4] (3) and [Pb2(HLII)(CH3COO)3]n (4), respectively. The nature of the anion in the parent PbII salt also influences the final structure. In all complexes, the PbII center exhibits a hemidirected coordination geometry with all the covalent bonds being concentrated on one hemisphere of the coordination sphere. The sterically available PbII ion participates in Pb⋯O/N tetrel bonding or Pb⋯Cg interaction as evidenced from the detailed structural and topological analysis of the described complexes. As a result of these interactions, the structures of all four compounds can be extended to a higher dimensional framework, which is further stabilized by hydrogen N–H⋯O/C–H⋯O and dihydrogen C–H⋯H–C bonds and/or π⋯π stacking interactions. The complementary Hirshfeld surface analysis of the discrete complex 3, considering covalent bonds, showed that the structure is highly dominated by H⋯X (X = O, H and C) and O⋯Y (Y = O, Pb, C and N) contacts, of which the O⋯Pb/H/N/C contacts are highly favoured. DFT based charge and energy decomposition (ETS-NOCV) calculations are performed in order to shed light on the nature of the non-covalent interactions that determine the stability of the obtained structures.

Quasi-aromatic Möbius Metal Chelates

We report the design as well as structural and spectroscopic characterizations of two new coordination compounds obtained from Cd(NO3)2·4H2O and polydentate ligands, benzilbis(pyridin-2-yl)methylidenehydrazone (LI) and benzilbis(acetylpyridin-2-yl)methylidenehydrazone (LII), in a mixture with two equivalents of NH4NCS in MeOH, namely [Cd(SCN)(NCS)(LI)(MeOH)] (1) and [Cd(NCS)2(LII)(MeOH)] (2). Both LI and LII are bound via two pyridyl-imine units yielding a tetradentate coordination mode giving rise to the 12 π electron chelate ring. It has been determined for the first time (qualitatively and quantitatively), using the EDDB electron population-based method, the HOMA index, and the ETS-NOCV charge and energy decomposition scheme, that the chelate ring containing CdII can be classified as a quasi-aromatic Möbius motif. Notably, using the methyl-containing ligand LII controls the exclusive presence of the NCS- connected with the CdII atom (structure 2), while applying LI allows us to simultaneously coordinate NCS- and SCN- ligands (structure 1). Both systems are stabilized mostly by hydrogen bonding, C-H···π interactions, aromatic π···π stacking, and dihydrogen C-H···H-C bonds. The optical properties have been investigated by diffused reflectance spectroscopy as well as molecular and periodic DFT/TD-DFT calculations. The DFT-based ETS-NOCV analysis as well as periodic calculations led us to conclude that the monomers which constitute the obtained chelates are extremely strongly bonded to each other, and the calculated interaction energies are found to be in the regime of strong covalent connections. Intramolecular van der Waals dispersion forces, due to the large size of LI and LII, appeared to significantly stabilize these systems as well as amplify the aromaticity phenomenon.