Showing papers by "Milan Mazúr published in 2010"

Self-Assembled Hydrogen-Bonding Chains of Copper(II) 2-Nitrobenzoate with Nicotinamide

Abstract: The synthesis, spectral characterization and crystal structure of two new nitrobenzoatocopper(II) complexes, namely, [Cu2(2-O2Nbz)4(nia)2]·ACN (1) and [Cu2(2-O2Nbz)4(ACN)2] (2) (where 2-O2Nbz = 2-nitrobenzoate, nia = nicotinamide and ACN = acetonitrile) are reported. The complexes 1 and 2 form dinuclear units of the paddle-wheel type around the crystallographic inversion centers. The copper ions are bridged by four 2-nitrobenzoate anions and the neutral N-donor ligands, viz. nicotinamide in 1 and acetonitrile in 2, are coordinated at apical positions. Selected geometric parameters of both complexes are compared with values for related tetra-2-nitrobenzoate complexes of copper(II) as well as the other dimeric copper(II) carboxylates with apical nicotinamide and acetonitrile ligands. The molecules of 1 are linked with N–H···O and C–H···O hydrogen bonds. The π–π stacking interactions in 1 are observed between benzene rings of 2-nitrobenzoate anions and pyridine rings of nicotinamide and also between acetonitrile molecules and benzene rings of 2-nitrobenzoate anions. The C–H···O hydrogen-bonds and CH/π interactions are observed in crystal structure of 2. The synthesis, spectral characterization and crystal structure of two new nitrobenzoatocopper(II) complexes, namely, [Cu2(2-O2Nbz)4(nia)2]·ACN and [Cu2(2-O2Nbz)4(ACN)2] (where 2-O2Nbz = 2-nitrobenzoate, nia = nicotinamide and ACN = acetonitrile) are reported. The both complexes form dinuclear units of the paddle-wheel type around the crystallographic inversion centers.

Hydrogen‐Bond‐Based Magnetic Exchange Between μ‐Diethylnicotinamide(aqua)bis(X‐salicylato)copper(II) Polymeric Chains

Abstract: Polymeric salicylatocopper(II) complexes of unusual composition [Cu(X-sal)2(μ-denia)(H2O)]n [denia = diethylnicotinamide, and X-sal = 5-methylsalicylate (1), 3-methylsalicylate (2), 4-methoxysalicylate (3), 3,5-dichlorosalicylate (4) and 3,5-dibromosalicylate (5)] were synthesized and characterized. Magnetic measurements were performed in the temperature range 1.8–300 K. The structural unit of all complexes consists of a CuII atom, which is monodentately coordinated by the pair of X-salicylate anions in trans positions. Water and the diethylnicotinamide ligand occupy the other two basal plane positions of the tetragonal pyramid. The axial positions are occupied by a diethylnicotinamide oxygen atom of neighboring structural units, thus forming a spiral polymeric structure parallel to b axis. Magnetic measurements showed that all complexes 1–5 exhibit a susceptibility maximum at about 6–8 K. The obtained data fit to Bleaney–Bowers equation gave singlet-triplet energy gaps 2J = –8.60 cm–1 for 1, 2J = –6.57 cm–1 for 2, 2J = –8.57 cm–1 for 3, 2J = –6.82 cm–1 for 4, and 2J = –6.45 cm–1 for 5. The supramolecular structure based on hydrogen bonds [described by supramolecular synthons R22(10) and R22(12)] is the pathway for antiferromagnetic interactions of the magnetically coupled pairs of copper atoms of neighboring chains within the 2D supramolecular layers. The results of the magnetic measurements suggest involvement of the COO groups in the magnetic interaction pathway for all five complexes.

[Cu(X-salicylato)2(N,N-diethylnicotinamide)2(H2O)2] complexes: conformational polymorphism and its consequence in supramolecular hydrogen-bonding networks formation

Abstract: Novel copper(II) X-salicylate complexes with N,N-diethylnicotinamide (dena) of the formula [Cu(RCOO)2(dena)2(H2O)2] (RCOO = 3-methylsalicylate anion (3-Mesal, 1), 4-methylsalicylate anion (4-Mesal, 2), 5-methylsalicylate anion (5-Mesal, 3), 5-methoxysalicylate anion (5-MeOsal, 4) or 4-methoxysalicylate anion (4-MeOsal, 5)), and complex [Cu(3-MeOsal)2(dena)2(H2O)2]∙2H2O (3-MeOsal = 3-methoxysalicylate anion (6)) have been prepared in the crystalline forms and characterized by spectroscopic methods (IR, Vis–UV, EPR). All the compounds according to their composition (1–5) seem to possess octahedral copper(II) stereochemistry. The complex 1 has been prepared in two different forms. X-ray analyses of the complexes 1, 4, and 5 were carried out and they featured a tetragonal-bipyramidal geometry around the copper atoms. The tetragonal planes are created by X-salicylate anions bonded to the copper(II) atoms via unidentate carboxylate oxygen atoms and the pyridine ring nitrogen atoms of the neutral ligand N,N-diethylnicotinamide, while in axial positions are water molecules. The two forms of complex 1 present conformation polymorphs and supramolecular isomers.

EPR Study of 5-Chlorosalicylate-Cu(II)-3-Pyridylmethanol Ternary Complex Systems in Frozen Water–Methanol Solutions

Abstract: Two copper(II) ternary complex systems containing 5-chlorosalicylic acid (5-ClsalH) and different copper(II) salts with varying 3-pyridylmethanol (ron = ronicol) concentration, system I [CuSO4 (aq) +2(5-ClsalH(solv)) + xron(l)] and system II [Cu(ac)2(aq) + 2(5-ClsalH(solv)) + xron(l)], where x = 0, 2, 4, 6 and 8, were prepared and studied by electron paramagnetic resonance (EPR) spectroscopy in frozen water–methanol solutions to observe the effects of different copper(II) salts and varying neutral ligand concentration on the formation of resulting complexes in solution. The trend in g-values (g|| > g⊥ > 2.0023) indicates that the unpaired electron on the copper ion is localized in the \( d_{{x}^{\rm{2}} - {y}^{\rm{2}}} \) orbital. The detailed analysis of the second-derivative Cu(II) EPR spectra has shown well-resolved 14N superhyperfine splitting in the perpendicular part of the axially symmetric spectra. The resolution of nitrogen superhyperfine multiplet patterns increased with increase in the ronicol concentration (ligand-to-metal ratio x). The number of superhyperfine lines was found to be constant (nonet) when x > 4 for system I and x ≥ 4 for system II. This fact indicates that for these x-values four equivalent nitrogen atoms could be coordinated to the central copper atom in the equatorial plane of both systems.

One‐Dimensional and Two‐Dimensional Coordination Polymers of Copper(II) Nitrobenzoate with Bridging 3‐Pyridylmethanol Ligand

Abstract: Complexes of composition [Cu(X-NO2bz)2(μ-3PM)2]n[X-NO2bz = 2-nitrobenzoate (1), 3-nitrobenzoate (2) or 4-nitrobenzoate (3) and 3PM = 3-pyridylmethanol] were prepared and studied by elemental analysis, UV/Vis, IR and EPR spectroscopy. The molecular structures of two new complexes 1 and 3 were solved. The copper atoms of both complexes exhibit an elongated octahedral coordination environment with the equatorial positions occupied by two monodentate nitrobenzoato anions and two 3-pyridylmethanol nitrogen atoms in trans positions. The both axial positions are occupied by oxygen atoms of bridging 3-pyridylmetanol ligands The polymeric structure of complex [Cu(2-NO2bz)2(μ-3PM)2]n (1) contains two-dimensional layers. The complex 3 exhibits a polymeric chain-like structure [Cu(4-NO2bz)2(μ-3PM)2]n with copper atoms double-bridged by two 3-pyridylmethanol molecules similarly as it was found for complex 2.

Preparation, Characterization and Photoreactivity of Methyl- and Methoxysalicylatocopper(II) Complexes

Abstract: The synthesis and characterization of complexes of stoichiometry Cu(Xsal)2(H2O)2 for X = 3MeO and 4-MeO and Cu(Xsal)2(H2O) for X = 3-Me and 4-Me (where 3-MeOsal = 3methoxysalicylate, 4-MeOsal = 4-methoxysalicylate, 3-Mesal = 3-methylsalicylate and 4-Mesal = 4-methylsalicylate) are reported. The composition of all complexes has been determined by elemental analysis and their ligand coordination mode and stereochemistry have been determined by electronic, infrared and EPR spectroscopy. The photoreactivity of prepared complexes in DMSO (DMSO = dimethylsulfoxid) solutions at room temperature have been studied too. For complexes of composition Cu(4-MeOsal)2(H2O)2 and Cu(4Mesal)2(H2O) some spectral changes registered after irradiation with light (λirr = 366 nm).