Ligand isotope vibrational spectroscopic and DFT studies of Pt(II) and Cu(I) complexes

by Medina, Gerardo Juan

Abstract (Summary)
Ligand-isotope labelling studies were performed on Zeise’s salt derivatives with pyridine N-oxide and quinoline N-oxide, their perdeuterated and O-18 isotopomers, C[subscript 2]D[subscript 4] and [superscript 13]CO, and the results of the vibrational analyses are reported. The isotopomers are modelled utilizing DFT calculations at the B3LYP level with the 6-31 G** basis set, and a pseudopotential level for the Pt atom. The calculated and observed structure and vibrational spectra correlate well. The crystal structures of [Pt(C[subscript 2]H[subscript 4])(pyO)Cl[subscript 2] and [Pt(CO)(quinO)Br[subscript 2] are reported.

The frequency for the [nu]Pt-O vibration, ambiguously assigned in the literature, is here assigned unequivocally at 400 cm[superscript (-1)]. Previously observed, but inadequately described phenomena are addressed: the [nu]N-O vibration in substituted quinoline N-oxides has been assigned previously at significantly different frequencies, depending on the nature of the substituent. This suggests that there is no specific mid-ir band associated with a high N-O character. A suitable explanation is presented for this phenomenon, showing that in low symmetry systems (eg. quinO) the N-O stretch is dispersed among several modes, whereas in high symmetry systems (eg. pyO) only a few limited modes have a high N-O character.

A theoretical study of Cu(I) carbonyl compounds with macrocyclic ligands is presented. Local and global HSAB parameters applied to the donor and Cu atoms are used to explain the observed reactivities and the available spectroscopic data. Extended to [Cu(CO){H[subscript 2]N(CH[subscript 2])[subscript n]NH(CH[subscript 2])[subscript m] NH[subscript 2]}] BPh[subscript 4] (where n = 2, m = 2, 3 and n =3, m = 3, 4) and their -d[subscript 5] and [superscript 13]CO isotopomers, subtle differences obtained experimentally for the CO stretching frequency in this series have been reproduced in the DFT calculations at the B3LYP level, using the 6-31 G* and 6-31 G** basis sets. Several properties (ligand pK[subscript a] values, [nu]CO frequencies, etc.) correlate with some HSAB descriptors.

Vibrational analyses are presented of Cu(I) carbonyl Schiff-base derivatives of N-Benzylidene-N’-[2-(benzyilidene-amino)-ethyl]-ethane-1,2-diamine, {2,2N3(C[subscript 6]H[subscript 4]R)[subscript 2]}, and their -d[subscript 5] and [superscript 13]CO isotopomers. The crystal structure of [Cu(CO){2,2N3(C[subscript 6]H[subscript 5])[subscript 2]}]BPh[subscript 4] is reported. From geometry optimizations and the HSAB descriptors, spectroscopic trends ([n]Cu-N and [nu]CO) are related to calculated global hardness and the Hammett substituent parameters, and are discussed in terms of ?-donation and ?-backbonding of Cu- CO.

Bibliographical Information:


School:Rhodes University

School Location:South Africa

Source Type:Master's Thesis



Date of Publication:01/01/2005

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