Steric influence of the 6-methyl group on the molecular and crystal structures of copper(II) chloride complexes with 2-(N-acetylamino)-6-methylpyridine

Synthesis, Structure, and Antiproliferative Action of 2-Pyridyl Urea-Based Cu(II) Complexes

Relying on a recently suggested protocol that furnishes convenient access to variously substituted 2-pyridyl ureas, twelve hitherto unknown Cu(II) complexes have been synthesized in the present work and their structures were evaluated by elemental analysis, HRMS, IR spectroscopy, and X-ray diffraction study. Two structural motifs ([Cu(L)2Cl]+[Cl]− or (Cu(L)2Cl2) depending on the substitution pattern on the 2-pyridine fragment were revealed. In addition, antiproliferative action of the obtained compounds have been investigated against lung cancer cell lines (A549, NCI-H460, NCI-H1975), and healthy WI-26 VA4 cells were used to monitor non-specific cytotoxicity. Two nitro-group substituted complexes Cu(U3)2Cl2 (IC50 = 39.6 ± 4.5 μM) and Cu(U11)2Cl2 (IC50 = 33.4 ± 3.8 μM) demonstrate enhanced activity against the drug resistant NCI-H1975 cells with moderate selectivity toward normal WI-26 VA4 cells. The antiproliferative mechanism of cell death underlying the growth inhibitory effect of the synthesized complexes was studied via additional experiments, including the cell cycle analysis and the apoptosis induction test. Reassuringly, certain 2-pyridyl urea-based Cu(II) complexes exerted cell line-specific antiproliferative effect which renders them valuable starting points for further unveiling the anticancer potential of this class of coordination compounds.

Copper(II) bromide, nitrate and perchlorate complexes with sterically demanding N-(6-methylpyridin-2-yl)acetamide ligands

Functionalized acid amides are widely used in biology, medicine, environmental chemistry and many other areas. Among them, pyridine-substituted amides, in particular N-(pyridin-2-yl)acetamide and its derivatives, play an important role due to their excellent chelating properties. The donor properties of these ligands can be effectively modified by introducing electron-donating substituents (e.g. alkyl groups) into the heterocycle. On the other hand, substituents in the α-position of the pyridine ring can create steric hindrance, which significantly influences the coordination number and geometry. To achieve a better understanding of these effects, copper(II) complexes with sterically demanding N-(6-methylpyridin-2-yl)acetamide ligands (L) and monoanions of different size, shape and coordination ability have been chosen as model compounds. The crystal structures of three new compounds, bromidobis[N-(6-methylpyridin-2-yl-κN)acetamide-κO]copper(II) bromide, [CuBr(C₈H₁₀N₂O)]Br, (I), aquabis[N-(6-methylpyridin-2-yl-κN)acetamide-κO]copper(II) dinitrate, [Cu(C₈H₁₀N₂O)(H₂O)](NO₃)₂, (II), and aquabis[N-(6-methylpyridin-2-yl-κN)acetamide-κO]copper(II) bis(perchlorate), [Cu(C₈H₁₀N₂O)(H₂O)](ClO₄)₂, (III), have been determined by single-crystal X-ray diffraction analysis. It has been shown that the presence of the 6-methyl group results in either a distorted square-pyramidal or a distorted trigonal-bipyramidal coordination geometry around the Cu^II centres instead of the typical octahedral geometry observed when the methyl substituent is absent or occupies any other position on the pyridine ring. Moreover, due to the steric hindrance provided by the L ligands, only the bromide ligand, the smallest of the series, enters into the first coordination sphere of the Cu^II ion in (I). In (II) and (III), the vacant coordination site of the Cu^II ion is occupied by a water molecule, while the nitrate and perchlorate anions are not involved in coordination to the metal centre. The structures of (I)-(III) are characterized by the presence of one-dimensional infinite chains formed by hydrogen bonds of the types N-H...Br [in (I)], N-H...O and O-H...O [in (II) and (III)] between the amide groups of the L ligands, the coordinated water molecules and the uncoordinated anions. The hydrogen-bonded chains are further interconnected through π-π stacking interactions between the pyridine rings of the L ligands, with approximate interplanar separations of 3.5-3.6 Å.

Crystal structure of a chloride-bridged copper(II) dimer: piperazine-1,4-dium bis-(di-μ-chlorido-bis[(4-carboxypyridine-2-carboxyl-ato-κ2N,O2)chlorido-cuprate(II)]

Crystals of a new dimeric chloride-bridged cuprate(II) derived from pyridine-2,4-di-carb-oxy-lic acid were obtained solvothermally in the presence of piperazine and hydro-chloric acid. The crystal structure determination of the title salt, (C4H12N2)[Cu2(C7H4NO4)2Cl4], revealed one of the carboxyl groups of the original pyridine-2,4-di-carb-oxy-lic acid ligand to be protonated, whereas the other is deprotonated and binds together with the pyridine N atom to the CuII atom. The coordination environment of the CuII atom is distorted square-pyramidal. One of the chloride ligands bridges two metal cations to form a centrosymmetric dimer with two different Cu-Cl distances of 2.2632 (8) and 2.7853 (8) Å, whereby the longer distance is associated with the apical ligand. The remaining chloride ligand is terminal at one of the basal positions, with a distance of 2.2272 (9) Å. In the crystal, the dimers are linked by inter-molecular O-H⋯O hydrogen bonds, together with N-H⋯O and N-H⋯Cl inter-actions involving the centrosymmetric organic cation, into a three-dimensional supra-molecular network. Further but weaker C-H⋯O and C-H⋯Cl inter-actions consolidate the packing.

Preparation of Self-Assembled Spherical g-C3N4/tz-Bi(0.92)Gd(0.08)VO4 Heterojunctions and Their Mineralization Properties

A novel kind of spherical g-C3N4/tz-Bi0.92Gd0.08VO4 heterojuctions are prepared via a simple microwave hydrothermal method. The sphere self-assembled mechanism and the heterojunction photocatalytic mechanism are mainly studied in this article. The results show that the added g-C3N4 sheets first anchor on ms-BiVO4 surfaces and then polymerize to form the coating layers, generating steric effect which is competing with Gd(3+) induction effect to affect the crystal transformation (from ms-BiVO4 to tz-BiVO4) and its growth during those processes. Afterward, independent coated structures are further polymerized and assembled into g-C3N4/tz-Bi0.92Gd0.08VO4 spheres. Because ECB (-0.95 V) of g-C3N4 is more negative than ECB (-0.05 V) of tz-BiVO4, the photoelectrons of g-C3N4 can be transferred into tz-BiVO4 surfaces through the heterojunction structure, so as to promote the separation rate of electron-hole pairs. In general, the adding of g-C3N4 can introduce hydroxyl groups to catch the photoholes and can inject electrons to react with dissolved oxygen to boost the production of active groups. Depending on such an orderly cooperation, g-C3N4/tz-Bi0.92Gd0.08VO4 heterojunction catalysts exhibit high and stable mineralization properties.