1570
J.A.S. Bomfim et al. / Polyhedron 22 (2003) 1567Á1573
/
By far the most interesting results are those dealing
with the structural data, given by the X-ray diffraction.
Table 4 gives the most important bond lengths and bond
angles of the complexes, and Figs. 1 and 2 show the
molecular structures of complexes IÁVI. The structures
/
of complexes I [7,8,15] and II [7] are known and will be
given here for comparison. All other structures are being
reported for the first time.
All six complexes present an approximately square
planar environment around the Ni atom. Complex VI is
the only one to show Pꢀ
/
Niꢀ
/
P and Xꢀ
/
Niꢀ/X angles close
to 908, as expected. The ligand dppp has a longer chain
and can be accommodated in the chelate structure
without causing any great strain. All other complexes
present an Xꢀ
/
Niꢀ
/
X angle considerably greater than
908, and a PꢀNiꢀ
/
/
P angle below 908, which in the case of
complex III is dramatically lowered to only 75.628. This
reflects the considerable strain posed by the four-
membered ring which the Ni atom is constrained to
form by dppm. The bond distance data also show a
marked difference between VI, on the one hand, and the
other complexes, on the other. If one compares the
complexes with the Clꢂ ligand, the Niꢀ
show only slight variations. Now if we take the Niꢀ
distances, those found for VI, 2.1791 A, are higher than
those for all other complexes. The longer carbon chain
in dppp is likely to make this ligand to accept less p
backbonding from the Ni atom than the other dipho-
/
Cl distances
/P
˚
sphines, hence the longer Niꢀ
/
P distances in VI. In
complex IV, the NꢀC and CꢀS distances are quite in
/
/
accordance with expected values for the N-bonded
isothiocyanate ligand, and also in agreement with the
results shown by the IR results given in Table 1.
It is quite interesting to look at the crystal arrange-
Fig. 1. Molecular structures of complexes I (top) and II (bottom).
ments of complexes IÁVI. In spite of a certain regularity
/
namely [Ni(dppe)Cl2] [8]. Table 1 shows that when one
goes from the free ligands to the complexes the chemical
shifts undergo a notable increase. Complexation de-
shields the phosphorus atoms considerably, due to a
shift in the electron cloud to the region between
phosphorus and the metal. It is interesting to note that
the phosphorus nuclei in complex VI show a lesser
chemical shift variation compared to the free ligand
than the situation prevailing in the other complexes.
This is likely to be related to the decreased strain and
less p backbonding present in this complex, as the
discussion of the molecular structures will show. The
dppm complex, III, on the other hand, is the only one in
which a decrease in d was observed in solution as well as
in the solid state on going from the free ligand to the
complex. Our NMR data follow a trend similar to what
has been observed in diphosphine organo-platinum
complexes, in which the ring formed by the metal and
the diphosphine greatly affects the phosphorus chemical
in their molecular structures, their packing in the
crystalline state varies considerably, and is given in
Figs. 3 and 4. These figures show the dppe and dppen
complexes, i.e. I, II, IV and V, to form layered
structures, whereas III forms lump-like clusters. The
most interesting structure is that of VI, in which the
layers present tubular arrangements for the phenyl rings.
The molecular structure of the monoclinic complex
[Ni(dppe)Cl2], I, shows that the dihedral angle between
rings a and b is 70.428, whereas that between rings c and
d is 63.538. The presence of a solvent molecule is likely
to contribute to this asymmetry, which is absent in the
analogous [Ni(dppe)(NCS)2] complex, IV. In the latter,
the angles between the phenyl rings on each phosphorus
is 59.468. The crystal structure of the two complexes
shows this difference markedly. Whereas I forms
monoclinic crystals, the crystals of IV are trigonal.
The two dppen complexes, [Ni(dppen)Cl2], II, and
[Ni(dppen)I2], V, are both monoclinic, but whereas II
presents a higher molecular symmetry, with an angle of
59.468 between both sets of phenyl rings, V, possibly
shift values: [Me2Pt(dppm)], d ꢂ
/
40.0; [Me2Pt(dppe)], d
54.5; [Me2Pt(dppp)], d 3.3 [14].
Bomfim, Jo?o A.S.
