R. Stuart Tobias

Kinetics of the ligand exchange between organo-gold(III), -gallium(III), -thallium(III), and -tin(IV) acetylacetonates and free acetylacetone☆

Abstract The rate of the exchange of the acetylacetonate ligand between several organometallic acetylacetonates and the proton chelate, acetylacetone, have been studied using pmr spectroscopy. The order of increasing exchange rate is Cl 2 Sn(acac) 2 ⪡ (CH 3 ) 2 Au(acac) ⋍ (CH 3 )ClSn (acac) 2 ⋍ (CH 3 ) 2 Ga (acac) 6 H 5 ) 2 Sn (acac) 2 3 ) 2 Sn(acac) 2 3 ) 2 Tl(acac). Since the rate of intramolecular exchange appears to be much greater than that for intermolecular exchange, the diorgano-tin(IV) and thallium(III) chelates should be very non-rigid molecules at room temperature. The rate of exchange of acetylacetonate between (CH 3 ) 2 Sn(acac) 2 and (C 6 H 5 ) 2 Sn(acac) 2 is slower than the exchange between either complex and acetylacetone.

Nature of solutions of methylmercury(II), dimethylgold(III), and trimethylplatinum(IV) jn pyridine and liquid ammonia: ligand exchange in unsymmetrical dimethylgold(III) complexes

Summary Dimethylgold chloride dissolved in pyridine is present as [(CH 3 ) 2 AuClPy] as indicated by the Raman spectrum, but the solution gives only a single, sharp methyl proton resonance. In chloroform solution, [(CH 3 ) 2 AuClPy] exhibits classical two site exchange behavior as the temperature is increased from − 38 to 64°. The exchange is first order in pyridine, and the mechanism is probably the same as that for the process which makes both syn and anti protons equivalent in unsymmetrical π-allylpalladium(II) and -platinum(II) compounds. The iodides CH 3 HgI, [(CH 3 ) 2 AuI] 2 , and [(CH 3 PtI] 4 all react with neat pyridine to give solutions of the neutral iodo complexes which were identified by their Raman spectra. The spectrum of the cation [CH 3 HgPy] + was observed with pyridine solutions of CH 3 HgClO 4 . In contrast to their behavior in pyridine, the iodides all dissolve in liquid ammonia to yield the cationic species [CH 3 HgNH 3 ] + , [(CH 3 ) 2 Au(NH 3 ) 2 ] + , and [(CH 3 ) 3 Pt(NH 3 ) 3 ] + . Dissolution of CH 3 HgClO 4 in liquid ammonia also yields [CH 3 HgNH 3 ] + . The Raman spectra of the cations are very similar to the spectra of the corresponding aquo cations in aqueous nitrate or perchlorate solutions, although water is not a sufficiently good ligand to dissolve the iodides. Compared to the aquo complexes, the metalcarbon stretching frequencies are 12 to 19 cm −l lower in frequency as a consequence of a slightly stronger metal-nitrogen bond.

The limitations of salt cryoscopy for the study of complex species in aqueous solution

Abstract The implications and the validity of the tacit assumptions made in the theory and in the application of the salt cryoscopic method as used for the study of charged poly- and mononuclear complexes have been examined. Data obtained from salt cryoscopy are compared with results obtained from different experimental methods. On the basis of this information, it appears that the method has limited value for the study of polynuclear complexes containing more than 3 or 4 metal atoms or for the study of systems containing a series of stepwise mononuclear complexes. Results in these cases should be considered indicative rather than conclusive. The conditions necessary for the interpretation of cryoscopic and e.m.f. data are compared, particularly for the case of polynuclear complexes, and it is seen that the conditions are much better satisfied in the case of the e.m.f. measurements.

Raman spectra of dimethylgermanium dihydroxide in aqueous solution: Acidity trends in the sequence (CH3)2Ge(IV), (CH3)2Sn(IV), and (CH3)2Pb(IV)

Abstract Raman spectra have been obtained on aqueous solutions prepared from [(CH 3 ) 2 GeO] 4 . The solutions have been shown to contain tetrahedral (CH 3 ) 2 Ge(0H) 2 and vibrational assignments have been made. The equilibrium constants for the hydrolysis of dimethylgermanium, tin, and lead compounds have been compared and discussed in terms of the structures and hybridization of thespecies present in acidic aqueous solutions.

Laser Raman spectra of bis(2,4-pentanedionato)dimethyltin(IV) in oriented single crystals and solutions: the molecular structure in solution

Abstract In a study of the structure of (CH 3 ) 2 Sn(acac) 2 (Hacac = acetylacetone), Raman spectra have been recorded with benzene solutions, non-oriented crystalline samples, and with oriented single crystals. Far infrared spectra also are reported for non-oriented samples. Factor group analyses in C 2h 5 symmetry are carried out for the skeletal and ligand vibrations. The crystal spectra are assigned in terms of the factor group species and in most cases also in terms of the symmetry species of the molecular modes. The frequencies of the skeletal vibrations are almost identical for the crystal where (CH 3 ) 2 Sn(acac) 2 exists as a centrosymmetric molecule with trans methyl groups and the benzene solution. Intermolecular interactions between the two molecules in the unit cell are very weak as correlation splittings must be less than 1 cm −1 . Relative values were determined for the Raman crystal tensor components of the symmetric (SnC 2 ) stretching mode from single crystal intensity measurements. By appropriate transformation, these were used to obtain the relative values of the molecular tensor for this mode. From these data, the depolarization ratio for a non-oriented sample was computed to be p = 0.19 ± 0.02, p s = 0.10 ± 0.02. With the benzene solution, the observed values were 0.18 ± 0.02, 0.11 ± 0.01. The relative values of the components of the derived polarizability tensor are similar to those of (CH 3 ) 2 SnF 2 which also has trans methyl groups. Using the Wolkenstein approximation of bond polarizabilities, it is estimated that the decrease in anisotropy brought about by a trans to cis isomerization upon dissolution should cause a decrease in p of 38 per cent, in marked contrast to the experimental results. Both the frequency and intensity data suggest that (CH 3 ) 2 Sn(acac) 2 has the same trans structure in solution and in the crystal, although the cis structure has been assigned to the molecule in solution on the basis of dipole moment data. Possible origins of the reported orientation dipole moment of 2.95 D for the molecule in benzene solution are discussed.

Pentamethyl- and hexamethyl-platinate(IV)

Reactions of tetramethylbis(methyldiphenyl-phosphine)platinum(IV) or trimethylplatinum iodide with methyl-lithium in diethyl ether yield lithium hexamethyl platinate(IV); in the former case, pentamethyl(methyldi-phenylphosphine)platinate(IV) is observed as an intermediate.