Vibrational studies of some mercury compounds and related systems

Abstract

This thesis deals with the vibrational study of mercury complexes with nitrogen-donor - and a few oxygen-donor-ligands, as well as the related amine-ICl complexes. A chapter of the thesis is devoted to the derivation of symmetry coordinates. The opening chapter briefly outlines two methods of interpreting solid state spectra and the application of Normal Coordinate Analysis to spectroscopic data. The set-up of the Raman instrument and the acquisition of Raman and infrared spectra are discussed. The assignments of twenty-one amine-ICl complexes are made in Chapter 2. The chosen amines are pyridine and substituted pyridines, together with a few polycyclic nitrogen bases. Simple force constant calculations are performed to allow comparison of I-N bond strengths between the various complexes. A general trend emerges correlating the stretching force constants of I-N and I-Cl bonds to the base strength of the ligand. For complexes with ring ligands, this study demonstrates that the numerical frequency of the donor-acceptor vibration is not necessarily the most temperature sensitive, as is anticipated from chemical deduction. A significant finding from the study of this series is of a new band in the vicinity of 200 cm-1 attributable to the rocking mode of the coordinated ligand. The observed frequency trends in the coordinated ligand vibrations, relative to the free ligands in amine-ICl complexes, prepare the way for the assignment of the more complicated species, CH3 HgL(ClO4)and HgnLm (ClO4)2 [L =amine; = 1 or 2; m = 2 or 4] in Chapters 3 and 4. In dimercury(I) complexes, a Raman band in the interval 100-180 cm-1 is attributed to the ν(Hg-Hg) mode, and the numerical value of this band is dependent on the ligand base strength as well as on the number of ligands. The ν(Hg-N) modes span 113-260 cm-1. Simple force constant calculations are performed for most complexes. However, no definite correlation between Hg-N force constants and the ligand base strength can be found. In common with the findings in the TCl analogues, a new band is consistently observed at 200. cm-1 and hence establishes once and for all that the band is characteristic of a coordinated ligand vibration, probably the rocking mode. Chapter 5 deals with the investigation of the nature of interaction between mercury and nitrate in dimercury(I) nitrate phases in solid and aqueous solution. An attempt has been made to confirm the chemical formula and subsequently the structure of the constituent entities of two solid phases obtainable from the recrystallization of Hg2 (NO3)22H2O in dilute nitric acid. Distinctive ν(Hg-Hg) modes occur between 172-203 cm-1 and the ν(Hg-O) modes are attributed to the bands in the interval 257-511 cm-1. Further vibrational studies on the mercury(I) and (II) complexes with very weakly basic oxygen ligands, viz. H2PO4-, Ph3PO and Ph3AsO, are treated in Chapter 6. The ν(Hg-Hg) and ν(Hg-O) modes are assigned in the intervals 170-190 and 200-270 cm-1, respectively. Finally in chapter 7, a method is presented whereby symmetry coordinates are constructed utilizing the atomic orbital symmetry associated with the point group. All the components of any degenerate representation can be obtained with equal ease. The derivation of symmetry coordinates by means of ascent in symmetry is also presented.