It was found that perfluoropolyethers (PFPE) with carboxylic acid end groups, PFPE-COOH, and their sodium salts, PFPE-COONa, afford an anhydrous fluid medium in which the direct pair-wise interaction of these end groups may be examined. An IR study (of the carbonyl band) of these materials revealed not only the dimerization of acid units, but also the formation of salt dimers, (salt)2, and mixed dimers, (acid)(salt). The carbonyl spectra of PFPE-acid/salt mixtures exhibit temperature-dependent broadening, shift, and, in some cases, coalescence of the bands which are attributed to the pseudocoalescence phenomenon stemming from the presence of relatively low energy cation exchange passages among the three possible dimers. Examination of the corresponding CH3COOH/CH3COONa system by ab initio calculations (6-31G) yielded the heat of dimerization of ∼20, ∼50, and ∼35 kcal/mol for the acid−acid, the salt−salt, and the acid−salt dimers, respectively. The calculated dimer structures are shown and discussed. The calculations also yielded the carbonyl stretching frequencies in good accord, and in support of the analyses/postulates made for the PFPE-acid/salt system.
The interaction between Cu atoms and ammonia molecules cocondensed in argon matrices was examined by ESR. The observed spectra revealed the formation of Cu(NH3)1 - 3 complexes. The g tensors and the hyperfine coupling tensors for the Cu and N nuclei of the complexes were determined. All three complexes showed large, essentially isotropic Cu hyperfine coupling interaction corresponding to 50−60% of that observed for isolated Cu atoms. No hyperfine structures due to protons were discerned. It is thus concluded that these complexes are formed merely by the dative interaction of the NH3 lone pair electrons with vacant Cu 4s/4p valence orbitals. The unpaired electron resides in a Cu 4s/4p-hybridized orbital projected away from the ligand(s). The ESR spectrum of the monoligand complex Cu(NH3) showed reversible photoconversion to the second spectrum in accord with the photoisomerization process Cu(NH3) ↔ HCuNH2 reported in an earlier IR study. The second spectrum, though partially obscured by other signals, revealed a pattern consistent with the ionic character H-Cu2+(NH2)- where the unpaired electron resides in the Cu 3d z 2 orbital.
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