Noncovalent Interactions at Lanthanide Complexes

Lanthanide complexes have attracted a widespread attention due to their structural diversity, as well as multifunctional and tunable properties. The development of lanthanide based functional materials has often relied on the design of the secondary coordination sphere of the corresponding lanthanide complexes. For instance, usually simple lanthanide salts (solvento complexes) do not catalyze effectively organic reactions or provide low yield of the expected product, whereas the presence of a suitable organic ligand with a noncovalent bond donor or acceptor centre (secondary coordination sphere) modifies the symmetry around the metal centre in lanthanide complexes which then successfully can act as catalysts in both homogenous and heterogenous catalysis. In this minireview, we discuss several relevant examples, based on X-ray crystal structure analyses, in which the hydrogen, halogen, chalcogen, pnictogen, tetrel and rare-earth bonds, as well as cation-π, anion-π, lone pair-π, π-π and pancake interactions, are used as a synthon in the decoration of the secondary coordination sphere of lanthanide complexes.

Crystal structure and Hirshfeld surface analysis of (E)-1-(2,6-di-chloro-phen-yl)-2-(2-nitro-benzyl-idene)hydrazine

In the title compound, C13H9Cl2N3O2, the 2,6-di-chloro-phenyl ring and the nitro-substituted benzene ring form a dihedral angle of 21.16 (14)°. In the crystal, face-to-face π-π stacking inter-actions occur along the a-axis direction between the centroids of the 2,6-di-chloro-phenyl ring and the nitro-substituted benzene ring. Furthermore, these mol-ecules show intra-molecular N-H⋯Cl and C-H⋯O contacts and are linked by inter-molecular N-H⋯O and C-H⋯Cl hydrogen bonds, forming pairs of hydrogen-bonded mol-ecular layers parallel to (20). The Hirshfeld surface analysis of the crystal structure indicates that the most important contributions to the crystal packing are from H⋯H (23.0%), O⋯H/H⋯O (20.1%), Cl⋯H/H⋯Cl (19.0%), C⋯C (11.2%) and H⋯C/C⋯H (8.0%) inter-actions.

Crystal structure and Hirshfeld surface analysis of (E)-4-{2,2-di-chloro-1-[(3,5-di-methyl-phen-yl)diazen-yl]ethen-yl}-N,N-di-methyl-aniline

In the title compound, C18H19Cl2N3, the planes of the benzene rings subtend a dihedral angle of 77.07 (10)°. In the crystal, mol-ecules are associated into inversion dimers via short Cl⋯Cl contacts [3.3763 (9) Å]. A Hirshfeld surface analysis indicates that the most important contact percentages for the different types of inter-actions are H⋯H (43.9%), Cl⋯H/H⋯Cl (22.9%), C⋯H/H⋯C (20.8%) and N⋯H/H⋯N (8.0%).

Crystal structure and Hirshfeld surface analysis of 4-{2,2-di-chloro-1-[(E)-(4-fluoro-phen-yl)diazen-yl]ethen-yl}-N,N-di-methyl-aniline

In the title compound, C16H14Cl2FN3, the dihedral angle between the two aromatic rings is 64.12 (14)°. The crystal structure is stabilized by a short Cl⋯H contact, C-Cl⋯π and van der Waals inter-actions. The Hirshfeld surface analysis and two-dimensional fingerprint plots show that H⋯H (33.3%), Cl⋯H/H⋯Cl (22.9%) and C⋯H/H⋯C (15.5%) inter-actions are the most important contributors towards the crystal packing.

Role of substituents on resonance assisted hydrogen bonding vs. intermolecular hydrogen bonding

Resonance assisted hydrogen bond (RAHB) ring can be weakened/opened by a strong electron-donor (ED) group.

Crystal structure and Hirshfeld surface analysis of (E)-4-{[2,2-di-chloro-1-(4-meth-oxy-phen-yl)ethen-yl]diazen-yl}benzo-nitrile

In the title compound, C16H11Cl2N3O, the 4-meth-oxy-substituted benzene ring makes a dihedral angle of 41.86 (9)° with the benzene ring of the benzo-nitrile group. In the crystal, mol-ecules are linked into layers parallel to (020) by C-H⋯O contacts and face-to-face π-π stacking inter-actions [centroid-centroid distances = 3.9116 (14) and 3.9118 (14) Å] between symmetry-related aromatic rings along the a-axis direction. A Hirshfeld surface analysis indicates that the most important contributions to the crystal packing are from Cl⋯H/H⋯Cl (22.8%), H⋯H (21.4%), N⋯H/H⋯N (16.1%), C⋯H/H⋯C (14.7%) and C⋯C (9.1%) inter-actions.

Hydrosoluble Complexes Bearing Tris(pyrazolyl)methane Sulfonate Ligand: Synthesis, Characterization and Catalytic Activity for Henry Reaction

The catalytic activity of the water-soluble scorpionate coordination compounds [Cu(-NN’O-Tpms)2] (1), [Mn(Tpms)2] (2) and Li[FeCl2(-NN’N’’-Tpms)] (3) [Tpms = tris(pyrazolyl)-methane sulfonate, O3SC(pz)3], were studied towards the (Henry) reaction between benzaldehyde and nitromethane or nitroethane in aqueous medium to afford, respectively, 2-nitro-1-phenylethanol or 2-nitro-1-phenylpropanol, the latter in the syn and the anti diastereoisomeric forms. Complex 1 exhibited the highest activity under the optimum experimental conditions and was used to broaden the scope of the reaction to include several aromatic aldehydes achieving yields up to 94%.

Ni(II)-Aroylhydrazone Complexes as Catalyst Precursors Towards Efficient Solvent-Free Nitroaldol Condensation Reaction

The aroylhydrazone Schiff bases 2-hydroxy-(2-hydroxybenzylidene)benzohydrazide and (2,3-dihydroxybenzylidene)-2-hydroxybenzohydrazide have been used to synthesize the bi- and tri-nuclear Ni(II) complexes [Ni2(L1)2(MeOH)4] (1) and [Ni3(HL2)2(CH3OH)8]· (NO3)2 (2). Both complexes have been characterized by elemental analysis, spectroscopic techniques [IR spectroscopy and electrospray ionization-mass spectrometry (ESI-MS)], and single-crystal X-ray crystallography. The coordination behavior of the two ligands is different in the complexes: The ligand exhibits the keto form in 2, while coordination through enol form was found in 1. Herein, the catalytic activity of 1 and 2 has been compared with the nitroaldol condensation reaction under various conditions. Complex 2 exhibits the highest activity towards solvent-free conditions.

Crystal structure and Hirshfeld surface analysis of (E)-3-[(4-fluoro-benzyl-idene)amino]-5-phenyl-thia-zolidin-2-iminium bromide

In the cation of the title salt, C16H15FN3S+·Br-, the phenyl ring is disordered over two sets of sites with a refined occupancy ratio of 0.503 (4):0.497 (4). The mean plane of the thia-zolidine ring makes dihedral angles of 13.51 (14), 48.6 (3) and 76.5 (3)° with the fluoro-phenyl ring and the major- and minor-disorder components of the phenyl ring, respectively. The central thia-zolidine ring adopts an envelope conformation. In the crystal, centrosymmetrically related cations and anions are linked into dimeric units via N-H⋯Br hydrogen bonds, which are further connected by weak C-H⋯Br hydrogen bonds into chains parallel to [110]. Hirshfeld surface analysis and two-dimensional fingerprint plots indicate that the most important contributions to the crystal packing are from H⋯H (44.3%), Br⋯H/H⋯Br (16.8%), C⋯H/H⋯C (13.9%), F⋯H/H⋯F (10.3%) and S⋯H/H⋯S (3.8%) inter-actions.

Crystal structure and Hirshfeld surface analysis of (E)-1-(4-chloro-phen-yl)-2-[2,2-di-chloro-1-(4-fluoro-phen-yl)ethen-yl]diazene

In the title compound, C14H8Cl3FN2, the planes of the 4-fluoro-phenyl ring and the 4-chloro-phenyl ring make a dihedral angle of 56.13 (13)°. In the crystal, mol-ecules are stacked in a column along the a axis via a weak C-H⋯Cl hydrogen bond and face-to-face π-π stacking inter-actions [centroid-centroid distances = 3.8615 (18) and 3.8619 (18) Å]. The crystal packing is further stabilized by short Cl⋯Cl contacts. The Hirshfeld surface analysis of the crystal structure indicates that the most important contributions for the crystal packing are from Cl⋯H/H⋯Cl (31.2%), H⋯H (14.8%), C⋯H/H⋯C (14.0%), F⋯H/H⋯F (12.8%), C⋯C (9.0%) and Cl⋯Cl (6.7%) inter-actions.

Arylhydrazone ligands as Cu-protectors and -catalysis promoters in the azide-alkyne cycloaddition reaction

A series of water soluble copper(ii) complexes, [Cu(κO¹O²N-H₂L¹)(H₂O)₂]·2H₂O (2), [Cu(κO-H₃L¹)₂(H₂O)₄] (3), [Cu(κO-H₄L²)₂(H₂O)₄] (5) and [Cu(H₂O)₆]·2H₂L³·2(CH₃)₂NCHO (7), were prepared by the reaction of Cu(NO₃)₂·3H₂O with sodium (Z)-2-(2-(1-amino-1,3-dioxobutan-2-ylidene)hydrazineyl)benzenesulfonate, [Na(μ₄-1:2κO¹,2κO²,3κO³,4κO⁴-H₃L¹)]_n (1; for 2 and 3), sodium (Z)-3-(2-(1-amino-1,3-dioxobutan-2-ylidene)hydrazineyl)-4-hydroxybenzene-sulfonate, [Na(μ-1κO¹,2κO²-H₄L²)]₂ (4; for 5) or sodium (Z)-2-(2-(1,3-dioxo-1-(phenylamino)butan-2-ylidene)hydrazineyl)naphthalene-1-sulfonate, [Na(μ-1κO¹O²,2κO³-H₂L³)(CH₃OH)₂]₂ (6; for 7). Compounds 1-7 were fully characterized, also by single-crystal X-ray diffraction analysis, and applied as homogeneous catalysts for the azide-alkyne cycloaddition (AAC) reaction to afford 1,4-disubstituted 1,2,3-triazoles. A structure-catalytic activity relationship has been recognized for the first time on the basis of the occurrence of resonance- and charge-assisted hydrogen bond interactions (RAHB and CAHB), in charge and ligand binding modes, enabling the catalytic activity of the compounds to be ordered as follows: Cu(NO₃)₂≪7 (complex salt with RAHB and CAHB) < 3 (with RAHB and CAHB) < 5 (with RAHB) < 2 (neither RAHB nor CAHB). Complex 2, without such non-covalent interactions, was found to be the most efficient catalyst for the AAC reaction, affording up to 98% product yield after being placed for 15 min, at 125 °C, in a water/acetonitrile mixture under low power (10 W) MW irradiation.

Crystal structure of dimethyl (3aS,6R,6aS,7S)-1H,3H,6H,7H-3a,6:7,9a-diepoxybenzo[de]isochromene-3a 1,6a-dicarboxylate, C16H16O7

C16H16O7, monoclinic, P21/n (no. 14), a = 12.830(3) Å, b = 8.1101(16) Å, c = 14.900(3) Å, β = 114.88(3)°, V = 1406.5(6) Å3, Z = 4, R gt(F) = 0.0578, wR ref(F 2) = 0.1799, T = 100(2) K.

Trinuclear (aminonitrone)ZnII complexes as key intermediates in zinc(ii)-mediated generation of 1,2,4-oxadiazoles from amidoximes and nitriles

Amidoximes react with zinc salts in undried EtOAc furnishing the trinuclear species, where amidoximes are stabilized in the aminonitrone form.

Resonance-Assisted Hydrogen Bonding as a Driving Force in Synthesis and a Synthon in the Design of Materials

Resonance-assisted hydrogen bonding (RAHB), a concept introduced by Gilli and co-workers in 1989, concerns a kind of intramolecular H-bonding strengthened by a conjugated π-system, usually in 6-, 8-, or 10-membered rings. This Review highlights the involvement of RAHB as a driving force in the synthesis of organic, coordination, and organometallic compounds, as a handy tool in the activation of covalent bonds, and in starting moieties for synthetic transformations. The unique roles of RAHB in molecular recognition and switches, E/Z isomeric resolution, racemization and epimerization of amino acids and chiral amino alcohols, solvatochromism, liquid-crystalline compounds, and in synthons for crystal engineering and polymer materials are also discussed. The Review can provide practical guidance for synthetic chemists that are interested in exploring and further developing RAHB-assisted synthesis and design of materials.

Reaction of sodium 2-(2-(2,4-dioxopentan-3-ylidene)hydrazinyl) benzenesulfonate with ethylenediamine on Cu(ii) and Ni(ii) centres: efficient Cu(ii) homogeneous catalysts for cyanosilylation of aldehydes

Reaction of sodium 2-(2-(2,4-dioxopentan-3-ylidene)hydrazinyl)benzenesulfonate with ethylenediamine on Cu(ii) and Ni(ii) centres lead to variety of metal complexes which effectively catalyse the cyanosilylation of aldehydes with trimethylsilyl cyanide.

Copper(ii) and iron(iii) complexes with arylhydrazone of ethyl 2-cyanoacetate or formazan ligands as catalysts for oxidation of alcohols

Cooperative coordination and ionic interactions assisted E/Z isomerization of arylhydrazone ligands lead to a variety of Cu^II complexes, which effectively catalyse the homogeneous oxidation of alcohols to carbonyl compounds.

Dimeric diorganotin(iv) complexes with arylhydrazones of β-diketones: synthesis, structures, cytotoxicity and apoptosis properties

The apoptosis induction of the new dimeric diorganotin(iv) complexes correlates with the cytotoxicity. The mechanism of KB cell death might occur mainly by means of early apoptosis.