Goran A. Bogdanović

Evidence Based on Crystal Structures and Calculations of a C−H···π Interaction Between an Organic Moiety and a Chelate Ring in Transition Metal Complexes

Structural and computational evidence is given for a special type of C−H···π interaction where the C−H group interacts with the π-system of a six-membered chelate ring. An investigation of crystal structures shows that these interactions take place in quite a number of metal complexes, including organometallic compounds; in the CSD we found over 1200 structures with these interactions. These interactions exist in complexes of different metals and various chelate rings. DFT calculations on three model systems show that the energy of these interactions is about 1 kcal/mol. (© Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002)

Stacking vs. CH–π interactions between chelate and aryl rings in crystal structures of square-planar transition metal complexes

The crystal structures of square-planar transition-metal complexes from the Cambridge Structural Database (CSD) with close contacts between planar chelate rings and aryl rings containing six carbon atoms (C6-aryl) were analyzed. Most of the chelate rings in these structures are fused with aromatic or other π-delocalized chelate rings. The results show that planar chelate rings can be involved in stacking and CH–π interactions with organic aryl rings. However, the number of stacking interactions is a few times larger than the number of CH–π interactions. The analysis also shows that in almost all cases CH–π interactions are formed only when stacking interactions are prevented by voluminous substituents. Hence, between planar chelate rings and C6-aryl rings stacking interactions are preferred to CH–π interactions.

Reaction of copper(II) with 1-carboxamide-3,5-dimethylpyrazole, 1-carboxamidine-3,5-dimethylpyrazole, 4-acetyl-3-amino-5-methylpyrazole and 5-amino-4-carboxamide-1-phenylpyrazole ☆

Abstract Complex formation of copper(II) bromide and acetate with 1-carboxamide-3,5-dimethylpyrazole (HL3) and copper(II) bromide with 5-amino-4-carboxamide-1-phenylpyrazole (L2), 4-acetyl-3-amino-5-methylpyrazole (HL4) and 1-carboxamidine-3,5-dimethylpyrazole (HL5), was studied. The obtained compounds, CuBr2(L2)2, Cu(L3)2, CuBr2(HL4)2, CuBr2(HL5)2 and [CuBr(HL1)(L3)]2 (HL1 denotes the 3,5-dimethylpyrazole), are characterized by elemental analysis, FT-IR spectrometry, molar conductivity, TG-MS and DSC. The X-ray structure of [CuBr(HL1)(L3)]2 and Cu(L3)2 is discussed. For [CuBr(HL1)(L3)]2 a dimeric penta-co-ordinated structure has been found; the co-ordination around the metal in Cu(L3)2 is trans-square planar. To CuBr2(L2)2 and CuBr2(HL4)2 a nearly tetrahedral, while for CuBr2(HL5)2 an octahedral geometry may be assumed. It means that the geometry of the compounds in the first place depends on the ligand substituents. The course of the complex formation reaction is anion-dependent and may be explained on the basis of Pearsons theory, taking into account the steric factors. A low stability intermediate formation was observed in the thermal decomposition of Cu(L3)2.

Mixed ligand Co(II), Ni(II) and Cu(II) complexes containing terephthalato ligands. Crystal structures of diaqua(2,2′-dipyridylamine)(terephthalato)metal(II) trihydrates (metal=cobalt or nickel)

Abstract A series of nine ternary Co(II), Ni(II) and Cu(II) complexes with some aromatic diamines and dianion of terephthalic acid (tpht) have been synthesized and characterized by elemental analysis, magnetic susceptibility measurements, IR and diffuse-reflectance spectroscopy. All compounds were obtained as microcrystalline solids, stable in air and insoluble in common solvents. Two of them, [M(tpht)(dipya)(H 2 O) 2 ]·3H 2 O [M=Co(II), Ni(II); dipya=2,2′-dipyridylamine], were obtained as single crystals and their crystal structures have been determined by X-ray structure analysis. Both structures consist of discrete [M(tpht)(dipya)(H 2 O) 2 ] 2+ complex units with two H 2 O molecules in the trans position. Three additional H 2 O molecules together with coordinated H 2 O and O atoms from COO groups make a three-dimensional network of hydrogen bonds. Terephthalato ligands are coordinated by only one COO group, which acts as a chelating ligand. Central metal ions are in a distorted octahedral environment. Based on the above-mentioned analysis and known crystal structures, the possible structures and geometry of the complexes are discussed. All Co(II) and Ni(II) complexes are pseudooctahedral and mononuclear, with only one of the tpht COO groups coordinated in a chelate mode. Cu(II) complexes have probably distorted octahedral geometry with bridging role of tpht ions and monodentate or strongly asymmetric coordination of COO groups.

Synthesis, characterization and antitumor activity of polymeric copper(II) complexes with thiosemicarbazones of 3-methyl-5-oxo-1-phenyl-3-pyrazolin-4-carboxaldehyde and 5-oxo-3-phenyl-3-pyrazolin-4-carboxaldehyde.

New polymeric copper(II) complexes with two tridentate ONS thiosemicarbazone ligands containing substituted pyrazolone moiety were synthesized and characterized by means of spectroscopic, electrochemical and crystallographic techniques. While both ligands exist as different tautomers in the solid state and DMSO-d(6) solution, Cu(II) ion coordinates the ligands from the same tautomeric form with square-pyramidal geometry around each Cu atom. In the crystal structures, the copper(II) complex cation forms polymeric chains {[Cu(L)Cl](+)}(n) with a bridging chlorine atom. One of the complexes was found to have a significantly higher cytotoxic potential in comparison with cisplatin in inhibition of several cell lines (HL60, REH, C6, L929 and B16). The results obtained on the basis of flow cytometry indicated that apoptosis could be possible mechanism of cell death.

Transition metal complexes with thiosemicarbazide-based ligands. Part XLI. Two crystal structures of cobalt(III) complexes with salicylaldehyde S-methylisothiosemicarbazone and theoretical study on orientations of coordinated pyridines

Abstract Two compounds, [CoIII(L)(py)3][CoII(py)Cl3]·EtOH and [CoIII(L)(py)3]I3 (H2L=salicylaldehyde S-methylisothiosemicarbazone, py=pyridine), were synthesized and the crystal structures determined by single-crystal X-ray diffraction. In both structures the geometries of the cation are very similar to a thiosemicarbazide-based ligand coordinated in the mer configuration. The axial pyridines are in mutual perpendicular orientation, the angles between the planes being 85.3(2) and 82.5(2)°. The plane of the equatorial pyridine is tilted with respect to the equatorial plane by about 40°. The orientations of the pyridines were studied in model systems by quantum chemistry calculations. It was shown that the interactions between axial and equatorial pyridines are responsible for the orientation of pyridines in the complex cation; consequently, there are very similar geometries of the complex cation in both crystal structures. The compounds were also characterized by elemental analysis, molar conductivity, magnetic susceptibility and electronic absorption spectra.

Disodium hexaaquacobalt(II) bis[dihydrogen 1,2,4,5-benzenetetracarboxylate(2 –)] tetrahydrate

The title structure, Na 2 [Co(H 2 O) 6 ](C 10 H 4 O 8 ) 2 .4H 2 O, consists of [Co(H 2 O) 6 ] 2+ and Na + cations, dihydrogen 1,2,4,5-benzenetetracarboxylate(2-) (H 2 btc) anions and water of crystallization. The [Co(H 2 O) 6 ] 2+ and H 2 btc ions, as well as the water molecules, are linked together by a three-dimensional network of hydrogen bonds. A short symmetrical intramolecular hydrogen bond between the COO and COOH groups is found to exist in the H 2 btc ions.

Electronic features and hydrogen bonding capacity of the sulfur acceptor in thioureido-based compounds. Experimental charge density study of 4-methyl-3-thiosemicarbazide

Sulfur atom is generally considered as a weak hydrogen bonding acceptor which is mostly explained by its low electronegativity. This is a background, and motivation, for this study that aims to provide additional insight into electronic features of the sulfur acceptor. The analysis of sulfurs electronic features uses high-resolution, low-temperature X-ray diffraction datasets on 4-methyl-3-thiosemicarbazide (MeTSC) and salicylaldehyde thiosemicarbazone (SalTSC). The total electron density distribution was modeled using Hansen–Coppens multipole model. The fact that MeTSC crystallizes with two crystallographically independent (but chemically equivalent) molecules, engaging in partly different D–H⋯S interactions, has, quite conveniently, enabled the examination of fine effects of the D–H⋯S interactions on the lone pairs electron density of the two S acceptors. The deformation density distribution, topological analysis of the total experimental charge density ρ(r) and its Laplacian (∇2ρ(r)), and, finally, electrostatic potential all point to the great flexibility of the S acceptor and its ability to adjust to the spatial distribution of the interacting donor groups. Toroidal accumulation of the S lone pairs electron density, strong value of the negative electrostatic potential even at a distance of 3.1 A from the S nucleus, and interpenetration of the van der Waals spheres for the donor and S acceptor atoms are all an indication of sulfurs capacity to simultaneously engage in a greater number of interactions than conventional acceptors such as O and N.

Different intermolecular interactions in azido[2-(diphenylphosphino)benzaldehyde semicarbazonato-kappa2P,N1,O]nickel(II).

The title compound, [Ni(C(20)H(17)N(3)OP)(N(3))], is the first complex with a semicarbazide-based ligand having a P atom as one of the donors. The influence of the P atom on the deformation of the coordination geometry of the Ni(II) ion is evident but less expressed than in the cases of complexes with analogous seleno- and thiosemicarbazide ligands. The torsion angles involving the two bonds formed by the P atom within the six-membered chelate ring have the largest values [C-P-Ni-N = 24.3 (2) degrees and C-C-P-Ni = -24.2 (4) degrees ], suggesting that the P atom considerably influences the conformation of the ring. Two types of N-H...N hydrogen bond connect the complex units into chains.

Aerosol synthesis of pure and Pt-doped ZnO particles using nitrate and pdda-Pt(IV) complex solutions

Pure and Pt-doped ZnO nanophase particles were synthesized by ultrasonic spray pyrolysis. The particles were obtained through the decomposition of zinc nitrate and with a newly developed Pt(IV) complex with 1,3-propylenediamine- N,N ′-diacetate tetradentate class ligand (pdda). The complex was characterized by elemental analysis, electronic absorption and infrared spectroscopy. The form of the determined complex structure { trans- [Pt(pdda)Br 2 ]·H 2 O} implies that Pt(IV) ion has a distorted octahedral coordination due to intramolecular N–H···Br interaction. The results of structural refinement (cell parameters, bond lengths, and ion occupancy) of ultrasonically derived pure and Pt-doped ZnO particles suggest either the formation of Zn i interstitials or platinum ion incorporation into the ZnO lattice in octahedral interstitial positions, respectively. A well-crystallized hexagonal wurtzite structure of ZnO was pronounced in all investigated samples [JCPDS card 36-1415, Joint Committee on Powder Diffraction Standards, defined by International Centre for Diffraction Data (www.icdd.com)]. Phase determination also indicated the presence of a nitrate hydroxide hydrate phase (JCPDS card 24-1460), as a result of incomplete precursor decomposition and a spinel Zn 2 PtO 4 phase (below 1.0 wt%) located in the boundary region for a Pt-doped ZnO sample. Based on x-ray diffraction, scanning electron microscopy, and energy-dispersive spectroscopy analyses, it was shown that the different particle growingmorphologies, which were either spheroidally or pyramidally shaped, were influenced by the precursor chemistry, processing parameters and the presence of platinum ions. The composite internal particle structure revealed by transmission electron microscopy and selected area electron diffraction analyses, implied that the secondary particles represent an assembly of primary particles sized under 60 nm aroused during the processes of nucleation, growth and aggregation. Both hexagonal and spheroidal shape of primary particles was evident. The particle morphology, primarily particle size and the mechanism of Pt 4+ ion introduction into the ZnO cell was discussed based on the structural refinement and selected area electron diffraction analysis.