Search results for " Geometry"
showing 10 items of 2294 documents
Aluminum complexes of sterically hindered tetradentate Schiff bases: Synthesis, structure, and reactivity toward ɛ-caprolactone
1997
Abstract The sterically hindered Schiff bases tbmSalenH2 [tbmSalen = N,N′-1,2-ethylenebis(3-tert-butyl-5-methylsalicylideneimine)] and tbmSalcenH2 [tbmSalcen = N,N′-trans-1,2-cyclohexanediyl-bis(3-tert-butyl-5-methylsalicylideneimine)] afforded a series of aluminum complexes of the general formulae [Al(tbmSalen)X] and [Al(tbmSalcen)X] (X = Cl, Me, Et). The molecular structure of [Al(tbmSalcen)Cl] was determined by single-crystal X-ray structural analysis which revealed a five-coordinate aluminum center with a distorted square pyramidal geometry. The alkyl complexes were found to oligomerize ɛ-caprolactone.
One‐Dimensional Coordination Polymers of Mn II , Cu II , and Zn II Supported by Carboxylate‐Appended (2‐Pyridyl)alkylamine Ligands – Structure and Ma…
2009
Four new complexes [MnII(L1OO)(H2O)][ClO4]·2H2O (1), [ZnII(L1OO)][ClO4]·2H2O (2), [CuII(L3OO)][CF3SO3]·H2O (3), and [ZnII(L3OO)][ClO4] (4) (L1OO– = 3-[(2-(pyridine-2-yl)ethyl){2-(pyridine-2-yl)methyl}amino]propionate; L3OO– = 3-[(2-(pyridine-2-yl)ethyl){(dimethylamino)ethyl}amino]propionate) have been synthesized and characterized by elemental analysis, IR, and UV/Vis spectroscopy. Structural analysis revealed that 1, 3, and 4 are one-dimensional chain-like coordination polymers. In 1 distorted octahedral MnN3O3 and in 3 square-pyramidal CuN3O2 coordination is satisfied by three nitrogen atoms and an appended carboxylate oxygen atom of the ligand, and an oxygen atom belonging to the carboxy…
A magnetic self-contained thermochromic system with convenient temperature range
2019
A new ionic liquid with sugar-based ligand has been prepared and used to coordinate cobalt(II), at low loading, in an ionic liquid solution. The system obtained reveals magnetic switching and marked thermochromism in solution/polymer films over a convenient temperature range (20–60 °C). This system is self-contained, devoid of any volatile substances, and reproducible over multiple thermal cycles. The colour change can be attributed to a change in the coordination geometry from octahedral (pink) at room temperature to tetrahedral (blue) on warming, monitored by 59Co NMR spectroscopy, which was used for the first time to study the change. This material may find applications in stimuli-respon…
Zirconium and hafnium mono(alkyl) complexes containing a tridentate linked amido-tetramethylcyclopentadienyl ligand. Molecular structure of Hf(η5:η1:…
1998
Abstract Zirconium and hafnium complexes M( η 5 : η 1 : η 1 -C 5 Me 4 SiMe 2 NCH 2 CH 2 OMe)Cl 2 (M=Zr, Hf) containing the tridentate 2-methoxyethylamido-functionalized tetramethylcyclopentadienyl ligand C 5 Me 4 SiMe 2 NCH 2 CH 2 OMe have been synthesized by the reaction of the dilithium derivative Li 2 [C 5 Me 4 SiMe 2 NCH 2 CH 2 OMe] with MCl 4 (THF) 2 . Selective monoalkylation of the dichloro complexes gave complexes of the type M( η 5 : η 1 : η 1 -C 5 Me 4 SiMe 2 NCH 2 CH 2 OMe)(R)Cl (R=CH 2 Ph, o -C 6 H 4 CH 2 NMe 2 ). The crystal structure of the hafnium dichloro complex Hf( η 5 : η 1 : η 1 -C 5 Me 4 SiMe 2 NCH 2 CH 2 OMe)Cl 2 has been determined by X-ray crystal diffraction and sho…
Interaction of Dimethyltin(IV)2+ Cation with Gly-Gly, Gly-His, and Some Related Ligands. A New Case of a Metal Ion Able To Promote Peptide Nitrogen D…
1999
Equilibrium (pH-metric) and spectroscopic (1H,13C, and 119Sn NMR and 119Sn Mossbauer) studies were performed to characterize the interaction of the dimethyltin(IV) cation with glycine, glycyl-glycine (Gly-Gly), imidazole-4-acetic acid, histamine, histidine, glycyl-histamine, glycyl-histidine (Gly-His), and β-alanyl-histidine (carnosine). For histamine and glycyl-histamine (having only nitrogen donor atoms) no complex formation was detected. The hydrolyzed species of the dimethyltin(IV) cation are always dominant over the complexes formed with the other ligands, except with Gly-Gly and Gly-His. For these two ligands, {COO-,N-,NH2} coordinated complexes are dominant in the neutral pH range wi…
Conformational studies of hexapeptides containing two dehydroamino acid residues in positions 3 and 5 in peptide chain
2008
Abstract Synthesis and structural studies of hexapeptides containing two dehydroamino acid residues in positions 3 and 5 in a peptide chain were performed. All the investigated peptides adopted bent conformations, stabilized by intramolecular hydrogen bonding, and could exist as two different conformers in solution. Only in the case of the peptide containing ΔAla residues, expected 3 10 -helical conformation was found.
Synthesis, molecular structure, spectroscopic properties and stability of (Z)-N-methyl-C-2,4,6-trimethylphenylnitrone.
2015
Abstract New N-methyl-C-2,4,6-trimethylphenylnitrone 1 has been synthesized starting from N-methylhydroxylamine and mesitaldehyde. The product was fully characterized using different spectroscopic techniques; FTIR, NMR, UV–Vis, high resolution mass spectrometry and X-ray diffraction. The relative stability and percent of population of its two possible isomers (E and Z) were calculated using the B3LYP/6-311++G(d,p) method in gas phase and in solution. In agreement with the X-ray results, it was found that Z-isomer is the most stable one in both gas phase and solution. The molecular geometry, vibrational frequencies, gauge-including atomic orbital (GIAO), and chemical shift values were also c…
Syntheses, crystal structures and magnetic properties of polynuclear 1,4,5,8,9,12-hexaazatriphenylene (hat)-bridged copper(II) complexes
2001
Three polynuclear compounds containing copper(II) and 1,4,5,8,9,12-hexaazatriphenylene (hat) as the basic building blocks have been prepared, [Cu4(hat)2Cl8]n·6nH2O 1, [Cu(hat)(H2O)2]n[NO3]2n2, and [Cu2(hat)(H2O)6]n[SO4]2n·2nH2O 3, their crystal structures determined and variable-temperature magnetic susceptibility data measured. The basic building block in 1 is the dinuclear [Cu2(hat)Cl4] entity, two such units being connected to tetranuclear units through relatively strong axial Cu–Cl bonds (out-of-plane di-μ-chloro bridges). Weaker axial Cu⋯Cl interactions link the units into a sheet structure. In 2 and 3 hat-bridged copper(II) chains extending along glide planes are present. hat serves a…
Syntheses, crystal structures and magnetic properties of one- and two-dimensional pap-containing copper(II) complexes (pap = pyrazino[2,3- f ][4,7]…
2001
Three polynuclear complexes containing copper(II) and pyrazino[2,3-f][4,7]phenanthroline (pap) as the basic building blocks have been prepared [Cu2(pap)(H2O)2(NO3)3]n[NO3]n1, [Cu4(pap)4Cl7]nCln·15nH2O 2, and [Cu4(pap)4(H2O)4(C4O4)2]n[C4O4]n[NO3]2n·12nH2O 3, and their crystal structures and variable-temperature magnetic susceptibilities determined. Compound 1 is a single stranded zigzag chain where pap and nitrate alternate as bridges between the copper atoms. The copper coordination geometry is to a first approximation distorted square pyramidal, but with an additional semi-coordinated oxygen from non-bridging nitrate groups. The bridging nitrate coordinates in the apical position to both c…
Relation between resonance energy and substituent resonance effect inP-phenols
2005
Molecular geometries of phenol and its 17 p-substituted derivatives were optimized at the B3LYP/6–311 + G** level of theory. Three homodesmotic and three isodesmotic reaction schemes were used to estimate aromatic stabilization energies (ASE) and the substituent effect stabilization energy (SESE). Other descriptors of π-electron delocalization (HOMA and NICS, NICS(1) and NICS(1)zz) were also estimated. The SESE and ASE values correlated well with one another as well as with substituent constants. Much worse correlations with substituent constants were found for other aromaticity indices. The NICS(1)zz values are the most negative for unsubstituted phenol, indicating its highest aromaticity;…