1,721,065 research outputs found
Electrolyte effect on the stereochemistry of copper(II) and nickel(II) polyamine complexes. Thermodynamic considerations
No full textThe electronic spectra of some Cu(II) and Ni(II) complexes with the tetradentate polyamines 3,2,3-(tet) (1,5,8,12-tetraazadodecane), trien, (2,3,2-tet) (1,4,8,11-tetraazaundecane), (3,3,3-tet) (1,4,9,13-tetraazatridecane), en, and (tn) (trimethylenediamine) in solns. of different concns. of the inert electrolyte NaClO4 are shown. The change of the compn. of the soln. causes considerable changes in the spectral properties of these complexes: this is ascribed to a variation of the solute-solvent interactions and of the stereochemistry of the chromophore. In Cu(II) complexes, an increase in electrolyte concn. causes in increase in the tetragonal distortion of the complex. In solns. of Ni(II) complexes, a paramagnetic species and a diamagnetic species are present at equil.: an increase in the ionic strength favors markedly the formation of the diamagnetic complex
Thermodynamic behavior of complexes with 5,6-membered condensed chelate rings. 1,4,8-Triazaoctane
No full textThe enthalpies of the reactions between NH2(CH2)2NH(CH2)3NH2 and Ni2+, Cu2+, and Zn2+ in 0.5M KNO3 at 25° were detd. by direct calorimetric titrations and previously reported free energy values were used to calc. the corresponding entropy values. Complexes formed contained a system of condensed 5- and 6-membered chelate rings and had higher heats of formation than corresponding complexes of NH2(CH2)2NH(CH2)2NH2 (5,5-ring size sequence) and NH2(CH2)3NH(CH2)3NH2 (6,6-ring size sequence.). Addn. of a 2nd mol. of ligand to the complex depended on steric factors
Coordination of a fully saturated 15-membered tetraaza macrocycle. X-ray studies of 1,4,8,12-tetraazacyclopentadecanecopper(II) perchlorate
No full textThe title complex (I) was prepd. by mixing equimolar ethanolic solns. of Cu(ClO4)2.6H2O and 1,4,8,12-tetraazacyclopentadecane. The structure of I was detd. by x-ray-crystallog. anal.; the Cu atom is centered in the plane of the 4 N atoms with elongated bonds to 2 trans perchlorate groups completing the tetragonal coordination. The 5-membered chelate ring is in a gauche conformation and the 2 6-membered chelate rings have a flattened sofa conformation
Flow microcalorimetry in stepwise equilibriums of metal complexes. Reactions of N,N'- and N,N-diethylethylenediamine with hydrogen and copper(II) ions
No full textEnthalpy values assocd. with the stepwise reactions of H+ and Cu2+ with N,N'-diethylethylenediamine [111-74-0] and N,N-diethylethylenediamine [100-36-7] were detd. by flow microcalorimetry at 25° and 0.5M (NaClO4) ionic strength. Combination with reported free energy values gave appropriate entropy values. Comparison with results for ethylenediamine shows that Et substitution causes a decrease in exothermicity of protonation and complexation and leads to a larger entropy change. Generally, reactions with the sym. ligand are more exothermic than those with the asym. one
Coordination behavior of the tetraza macrocycle isocyclam
No full textA polemic in answer to R. G. Swisher et al (ibid., 1980, 19, 1336) who claim that isocyclam (1,4,7,11-tetraazacyclotetradecane) in its Ni complex, [NiL]2+, is tridentate. On the basis of the exothermicity of formation of [NiL]2+, its NMR, and its acid-base properties, the planar L is tetradentate and does not contain a free basic N atom
Melting of Group VI transition metal hexacarbonyls: thermodynamic parameters
No full textThe heats and entropies of fusion and the heats of crystn. of Cr(CO)6, Mo(CO)6, and W(CO)6 were detd. in sealed, evacuated glass ampuls by differential scanning calorimetry. The values were combined with published sublimation data to calc. the heats of vaporization (ΔHv). The solid-gas and liq.-gas phase diagrams were detd. from ΔHv and the reported heats of sublimation, and gave the b.ps. of the 3 compds
Factors affecting thermodynamic stability of metal complexes with tripodal amines. Comments
No full textComments on a review by S. G. Zipp, A. P. Zipp, and S. K. Madan (Coord. Chem. Rev. 1974, 14, 29) are given. 23 Refs
Calorimetric determination of macrocyclic enthalpy. Copper(II) and zinc(II) complexes with 1,4,8,11-tetra-azacyclotetradecan
No full textThe enthalpies of formation of the title complexes were detd. in aq. soln. at 25° by a direct calorimetric method. The enthalpies of formation of the Cu(II) and Zn(II) complexes exceed that of the most stable analogous linear system by 4.7 and 3.0 kcal/mol, resp. For the Cu(II) complex the enthalpy of formation fits the linear correlation with spectral energy previously described (F., et al., 1976) for noncyclic nitrogen ligands
Thermodynamics of complex formation with linear aliphatic tetraamines. III. Enthalpy and entropy contributions to the stability of metal complexes of 4,7-diazadecane-1,10-diamine
No full textThe enthalpies of the reactions of the title tetraamines H2N(CH2)nNH(CH2)mNH(CH2)nNH2 (I) with H, Cu(II), Ni(II), and Zn(II) ions in 0.5M KNO3 at 25° were detd. by direct calorimetric titrns. The entropy change ΔS values were calcd. from known free energy change ΔG values. The heats of formation of the complexes of I (n = 3, m = 2) which contain a system of condensed chelate rings with the ring sequence 6,5,6, i.e. II (M = Cu, Ni, Zn) were higher than those of the corresponding complexes of I (n = m = 2) (ring-size sequence 5,5,5) and of I (n = m = 3) (ring-size sequence 6,6,6). Cu(II) and Zn(II) complexes of II had a less neg. heat of formation ΔH than the complexes of I (n = 2, m = 3), which has the ring-size sequence 5,6,5
Coordinating tendencies of a 14-membered tetraaza macrocycle which forms a seven-membered chelate ring
No full text1,4,7,10-Tetraazacyclotetradecane (L) was prepd., and the basicity and stability consts. of [CuL]2+ and [Cu(HL)]3+ were detd. by potentiometry at 25° in 0.5 mol/dm3 KNO3. The heats of formation of the Cu(II) and Ni(II) complexes were detd. by batch and flow microcalorimetry, resp. The coordination of L to Cu and Ni to form a system with a (5,5,5,7) chelate ring is less exothermic than that of 1,4,8,11-tetraazacyclotetradecane and 1,4,7,11-tetraazacyclotetradecane, which form (5,6,5,6) and (5,5,6,6) chelate sequences, resp. [CuL]2+ is more stable than [Cu(trien)]2+ (trien = triethylenetetramine) due to a favorable entropy contribution. The stability of [Cu(HL)]3+ was compared to that of protonated complexes formed by other tetraaza macrocycles
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