Summary:
In this Τhesis we report the synthesis and study with spectroscopic techniques
(UV-Vis and 31Ρ NMR) and Cyclic Voltammetry of the heterometallic complexes of
Rh(I) with tetrathiomolybdate and tetrathiotungstate and auxiliary ligands
commercially available phosphites, 1,5 cyclooctadiene (COD), phosphines and
diphosphines. The anionic complexes [L2Rh(μ-S)2MS2] were characterized with
ESI-MS measurements.
The complex [{(P(OEt)3)2Rh}2(μ-WS4)] and [{(P(OiPr)3)2Rh}2(μ-WS4)], were
characterized by X-ray diffraction analysis. Both complexes crystallize in the
same space group C2/c (Z=4) with unit cell dimensions a=17,642(3) A,
b=19.358(3) A, c=16,002(2) A and a=20,587(3) A, b=19.425(3) A, c=17,698(3) A,
respectively. The structures for both complexes show two square planar rhodium
fragments with two phosphites binding through the sulfur atoms of a tetrahedral
WS4 unit.
The detailed DFT study of the electronic structures of [(P(OPh)3)2Rh(μ-
S)2MoS2] and [(COD)Rh(μ-S)2WS2] has revealed the existence of extended
electron delocalization over the four-membered Rh(μ-S)2M (M=Mo,W) ring and
hence the possibility of electronic communication between the metal centres.
The electronic spectrum of [(COD)Rh(μ-S)2WS2] was studied with TDDFT
calculations, and the main absorption band in the visible region was assigned
to ν(Rh>W) electron transfer transition, which is actually a HOMOLUMO
transition.
For the bimetallic and trimetallic complexes of the types [L2Rh(μ-S)2MS2] and
[{L2Rh}2(μ-ΜS4)] (M=Mo,W and L=P(OPh)3, P(O-o-CH3C6H4)3, P(OMe)3, P(OEt)3,
P(OiPr)3), it was found that the measured values of the electronic transitions
ν(RhM) (M=Mo ή W) correlate linearly with the electronic parameter of Tolman,
rendering these transitions well-defined ligand electronic parameters, which
describe the net donating ability of monodentate and bidentate ligands (CO,
COD, phosphites, diphosphines).
The study of the variation of the Δδ(31P) and 1J(RhP) of the phosphite
complexes with respect to the QALE model electronic parameters χd, πp, and Ear
has succeeded in the assessment of the σ and π effects on these NMR spectral
parameters.
Keywords:
Rhodium, Tetrathiomolybdate, Tetrathiotungstate, UV-Vis Spectroscopy, 31P NMR Spectroscopy
