Reactions of
[Rh
III
Cl
2
Ph(SbPh
3
)
3
]
1 with an excess of purine-6-thione
(C
5
H
4
N
4
S) or 1,3-thiazole
(C
3
H
3
NS) in absolute ethanol gave crystalline
[Rh
III
Cl
2
Ph(C
5
H
4
N
4
S)(SbPh
3
)] 2 (S trans to Sb),
[Rh
III
Cl
2
Ph(SbPh
3
)(C
3
H
3
NS)
2
] 3 and
[Rh
III
Cl
2
Ph(SbPh
3
)
2
(C
3
H
3
NS)] 4. The crystal structure of complex
2 has been determined. Two different rotamers, which differ in
the orientation of the phenyl ligand around the Rh–C bond axis,
are present. The co-ordination geometry of both molecules is
pseudo-octahedral and the neutral, N
1
and N
9
protonated, purine ligand behaves as bidentate through S and
N
7
. The Rh–N
7
bonding interaction is much
weakened [average 2.262(7) Å] by the high trans
influence of the phenyl ligand. The H
8
atom of both purine
systems points towards the centre of a phenyl ring of SbPh
3
.
The geometrical parameters of the SbPh
3
molecules show that
an attractive interaction between H
8
and the phenyl ring is
operative for each rotamer. The
1
H NMR spectrum of
2, in DCON(CD
3
)
2
, shows an upfield shift
of 1.37 ppm for H
8
, consistent with a shielding effect from a
phenyl ring of SbPh
3
. Therefore, the
H
8
· · · Ph(Sb)
attractive interaction exists also in solution. The crystal structure of
3 has also been determined. The co-ordination geometry is
pseudo-octahedral, the metal being linked to two trans chloride
ions, one antimony donor from SbPh
3
, one carbon atom from the
phenyl ligand and two nitrogen atoms from thiazole ligands, one of which
is trans to Ph [Rh–N 2.245(5) Å]. The
1
H NMR spectrum shows that the solid-state structure is
maintained in CDCl
3
solution. The signals of the
H
2
and H
5
protons of the thiazole ligands are
shifted downfield by 0.65 and 0.63 and 0.45 and 0.45 ppm for the
molecules trans and cis to the C donor, respectively,
upon complexation. The
1
H HMR spectrum of 4 is in
agreement with the presence of a thiazole ligand trans to Ph.
An interaction between the chloride ligands and some protons of the
phenyl rings of SbPh
3
is resposible for a downfield chemical
shift of about 0.2 ppm for the relevant
1
H NMR signals in
compounds 1–4. Molecular mechanics analysis
based on the crystal structures of 2 and 3 made it
possible to set up force-field parameters suitable for this class of
molecules. In the case of 3 the rotation of the
SbPh
3
molecule around the Rh–Sb bond is highly
hindered; the lowest barrier between minima is higher than 125 kJ
mol
-1
. The rotations of the thiazole ligands have
minima consistent with the crystal structure.
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