Search results for "Intramolecular force"

Syntheses, crystal structures and magnetic properties of di- and trinuclear croconato-bridged copper(ii) complexes

2002

The new croconato-bridged copper(II) compounds [Cu2(terpy)2(H2O)2(C5O5)](NO3)2·H2O (1) and [Cu3(phen)5(C5O5)2](CF3SO3)2 (2) (C5O52− = croconate, dianion of 4,5-dihydroxycyclopent-4-ene-1,2,3-trione; terpy = 2,2′:6′,2″-terpyridine; phen = 1,10-phenanthroline) have been prepared, and their crystal structures and variable temperature magnetic susceptibilities determined. The structure of complex 1 consists of croconato-bridged dinuclear [Cu2(terpy)2(H2O)2(C5O5)]2+ complex ions, nitrate counter ions and water of hydration. The croconato ligand exhibits an asymmetrical bis-bidentate coordination mode through four of its five oxygen atoms. The two crystallographically independent copper atoms hav…

Syntheses, crystal structures and magnetic properties of dinuclear copper(II) complexes with pyrazino[2,3-f  ][4,7]phenanthroline (pap) as bridging l…

2000

Three dinuclear copper(II) complexes with pyrazino[2,3-f][4,7]phenanthroline (pap) as bridging ligand have been prepared; [Cu2(pap)(C2O4)2]·5H2O 1, [Cu2(pap)(H2O)7(SO4)]SO4·3H2O 2 and [Cu2(pap)(H2O)3(NO3)3]NO33. These are the first metal complexes of pap which have been characterized by X-ray crystallography and magnetic susceptibility measurements. In 1 the dinuclear complex is intercepted by a mirror plane; the bridging pap and the terminal oxalate ligands are bidentate in the equatorial plane of copper. In addition copper has weak axial interactions to oxygen atoms of oxalate in two neighbouring molecules. In 2 the two crystallograpically independent copper atoms are both six-co-ordinate…

Why betaine crystallizes in high local C s symmetry. An ab initio MO and DFT study of anhydrous betaine and betaine monohydrate

1999

A theoretical study of the structure, charge distribution, rotational barrier and fundamental vibrations of anhydrous betaine (CH3)3NCH2COO (trimethylglycine) was carried out and compared with available experimental data. Calculations were carried out at HF, MP2 and B3LYP levels using a 6-31+G(d,p) basis set. The calculated rotational barrier of the betaine carboxylic group is 40.5 kJ/mol at the MP4(SDQ)/6-311G(d,p)//HF/6-31+G(d,p) level of theory. The rotation of the carboxylic group changes the molecule from a highly symmetric (C s ) conformation into a twisted conformation resulting in shortening of the molecule by about 50 pm. Natural population analysis (NPA) indicates intramolecular i…

1977

Solutions of chain- (PS-d3) and phenyl ring (PS-d5) deuterated polystyrenes in perdeuterated PS-d8 have been investigated with 1H and 2D NMR relaxation and wide line methods. The intra- and intermolecular parts of the 1H second moments at −100°C are 3,7 G2 and 2,0 G2, respectively, for PS-d3, and 14,7 G2 and ca. 0 G2, respectively, for PS-d5. The intermolecular contribution to the 1H spin lattice relaxation rate, determined at 55 MHz between 150°C and 250°C, is about one third of the total rate in PS-d3, and negligible in PS-d5. We suggest that this contribution is caused by rotational fluctuations of the intermolecular H H vectors. The intramolecular 1H- and 2D-relaxation rates indicate th…

Unprecedented Stereoselective Synthesis of Catalytically Active Chiral Mo3CuS4 Clusters

2005

Cluster excision of polymeric {Mo3S7Cl4}n phases with chiral phosphane (+)-1,2-bis[(2R,5R)-2,5-(dimethylphospholan-1-yl)]ethane ((R,R)-Me-BPE) or with its enantiomer ((S,S)-Me-BPE) yields the stereoselective formation of the trinuclear cluster complexes [Mo3S4{(R,R)-Me-BPE}3Cl3]+ ([(P)-1]+) and [Mo3S4{(S,S)-Me-BPE}3Cl3]+ ([(M)-1]+), respectively. These complexes possess an incomplete cuboidal structure with the metal atoms defining an equilateral triangle and one capping and three bridging sulfur atoms. The P and M symbols refer to the rotation of the chlorine atoms around the C3 axis, with the capping sulphur atom pointing towards the viewer. Incorporation of copper into these trinuclear c…

Unprecedented intramolecular pancake bonding in a {Dy2} single-molecule magnet

2020

The first example of unique coordination induced intramolecular pancake bonding was achieved through the reduction of two bis(pyrazolyl)-tetrazine ligands, affording [MIII2(μ-(bpytz)2)(THMD)4](M = Dy, Y; bpytz = 3,6-bis(3,5-dimethyl-pyrazolyl)-1,2,4,5-tetrazine; TMHD = 2,2,6,6-tetramethyl-3,5-heptanedionate). To provide a cohesive magneto-structural correlation, the mono bis(pyrazolyl)-tetrazine bridged congener [DyIII2(μ-bpytz)(THMD)6]·4(C6H6) was also isolated. Both metal complexes exhibit single-molecule magnet behaviour under an applied dc field.

Enhanced β-turn conformational stability of tripeptides containing Δphe in cis over trans configuration

2013

Conformations of three pairs of dehydropeptides with the opposite configuration of the Delta Phe residue, Boc-Gly-Delta(Z/E)Phe-Phe-p-NA (Z- p -NA and E- p -NA), Boc-Gly-Delta(Z/E)Phe-Phe-OMe (Z-OMe and E-OMe), and Boc-Gly-Delta(Z/E)Phe-Phe-OH (Z-OH and E-OH) were compared on the basis of CD and NMR studies in MeOH, TFE, and DMSO. The CD results were used as the additional input data for the NMR-based calculations of the detailed solution conformations of the peptides. It was found that Z- p -NA, E- p -NA, Z-OMe, and Z-OH adopt the beta-turn conformations and E-OMe and E-OH are unordered. There are two overlapping type III beta-turns in Z- p -NA, type II' beta-turn in E- p -NA, and type II …

Influence of solvents on conformation of dehydropeptides

2013

Abstract Structural investigations of dehydropeptides containing (Z)-dehydrophenylalanine in solvents characterized by different polarity are discussed. The conformational analysis are based on spectroscopic methods (NMR, CD), molecular modeling techniques and in case of the tripeptide, ab initio methods. The results of temperature experiment indicate, that the only conformation of the investigated hexapeptide 3 is stabilized by intramolecular hydrogen bonds. Depending on the length of the peptide chain, the polarity of solvent influences on arrangement of the side chain of the amino acids or of the main chain of the peptide.

Heterometallic CoII-CoIII-MII alkoxido-bridged heptanuclear motifs (M = Cu, Zn). Syntheses, crystal structures and magnetic properties

2018

Two new alkoxido-bridged heterometallic complexes of formula [CoIICoIII 3CuII 3(dea)6(CH3COO)3](ClO4)0.75(CH3COO)1.25 (1) and [CoII 2CoIII 2ZnII 3(tea)2(piv)6(CH3O)2(OH)2(CH3OH)2]·H2O 2 (H2dea=diethanolamine, H3tea=triethanolamine and Hpiv=pivalic acid) have been assembled using aminoalcohol ligands. The cationic core in 1 possesses a threefold crystallographic axis, and it exhibits a set of three copper(II), one cobalt(II) and three cobalt(III) ions arranged as a hexagon of alternating copper(II) and cobalt(III) ions around the central cobalt(II) ion. Each edge of the hexagon is defined by a double alkoxido bridge, the outer one being bis-monodentate with copper(II)-cobalt(III) pair wherea…

A methylenediphosphonate bridged copper(II) tetramer: Synthesis, structural, thermal, and magnetic characterization of [Cu4(H2O)2(phen)4(μ-P2O6CH2)2]…

2019

Abstract A novel tetracopper(II) complex namely, [Cu4(H2O)2(phen)4(μ-P2O6CH2)2]·21H2O (1) was synthesized by using copper(II) chloride, 1,10-phenanthroline (phen), and methylene diphosphonic acid (MDP). The structure of 1 was characterized by single crystal X-ray diffraction and spectroscopy. Compound 1 crystallizes in the triclinic system, P 1 ¯ space group and its crystal structure consists of neutral centrosymmetric tetranuclear copper(II)-methylene diphosphonate units where each peripheral {Cu(phen)(P2O6CH2)}2− fragment adopts the bidentate(Oeq-P-Oeq)/monodentate (Oax) bridging mode towards each of the two inner {Cu(phen)}2+ entities resulting in a “clamshell”-like orientation. The two …