T. Peppel et al. / Polyhedron 52 (2013) 482–490
489
and quin). In 4, with L = PPh3 the Ni coordination is NiBr3P, respec-
tively. The average Ni–Br and the Ni–N/Ni–P bond distances fall in
their expected regions (see Table 2). In 1 and 2 with the principally
similar ligands NMIm and NMBIm the values are almost identical.
The Ni–Br distance in 3 (quin ligand) compares also well with the
ones of the former two compounds, but the Ni–N distance is
slightly longer. To the best of our knowledge crystal structure data
of nickel complex salts with ligands comparable to those of 1,2, or
3 exist in the literature so far only for (nBu4N)[NiBr3(quin)] [20].
The structural parameters of this compound compare well with
those of 3. Also, the bond lengths of the anion of 4 are in the same
range as those of (Ph4As)[NiBr3(PPh3)] [21].
In all four title compounds the average Br–Ni–Br angles are lar-
ger than the ideal tetrahedral value, whereas the average Br–Ni–N/
P angles are smaller than 109.47°, as expected from the different
atom radii (see Table 2).
The salts 1 and 2 crystallize in the monoclinic crystal system, 1
with space group P21/n and 2 with P21/c, both with four ion pairs in
the unit cell. 3 and 4 crystallize triclinic (P1) with two formula
units in the unit cell. In all four structures the atoms of the ion
pairs of the asymmetric unit are located on general positions.
Therefore, none has higher point symmetry than identity. Figs. 3–
6 show ORTEP plots of one ion pair of the four title compounds.
The arrangement of ions in the unit cells of 1–4 is shown in
Figs. 7–10.
N atoms (H at C5 (1), C9 (2), C10 (3), and C19 (4)). All these H
atoms have rather short distances to Br atoms of neighboring com-
plex anions. They range from 2.779 Å in 2 to 3.002 Å in 4. Unfortu-
nately, the trend of these increasing hydrogen bond lengths does
not reflect any reasonable trend of melting points of these
compounds.
4. Conclusion
Results of detailed investigations about new compounds with
pseudo-tetrahedral Nickel(II) complex anions of the type [NiBr3
(L)]ꢀ with L = organic ligand N ligands (three examples) and one
example with a P ligand is presented. Information about the syn-
thesis, single-crystal X-ray structures, spectroscopy, thermal
behavior and magnetic properties of (EMIm)[NiBr3(L)] with L = N-
methylimidazole, N-methylbenzimidazole, quinoline, and triphen-
ylphosphane; EMIm = 1-ethyl-3-methylimidazolim is given. They
all contain pseudo-tetrahedrally coordinated Nickel ions. The
materials are paramagnetic and thermally stable up to 200 °C. They
have relatively low melting points, and might be useful as molten
salts.
Acknowledgment
Support from the Deutsche Forschungsgemeinschaft (SPP 1191)
is gratefully acknowledged.
In crystals of 1 the cations and anions are alternatively stacked
along the crystallographic a direction in such a way that the planar
imidazolium rings, which are present in both the cation and the
anion are arranged almost parallel. Even though, the distance of
Appendix A. Supplementary data
this planar units is short at 3.87 Å,
p-stacking interactions are
not expected to be present to a larger extend, because the five-
membered ring of the cation is shifted away from that of the anion
in a direction parallel to the ring plane, see Fig. 7. Also, the ring
plane of the cation is tilted by 4° relative to that of the anion.
In the salt with the N-methylbenzimidazole ligand the arrange-
ment of ions can also be described in such a way that rows of ions
exist. But different to the arrangement in 1, where rows of alternat-
ing cations and anions exist, here rows of only cations neighboring
CCDC 878295, 878294, 878293 and 878296 contains the sup-
plementary crystallographic data for compounds 1–4. These data
Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: (+44) 1223-
336-033; or e-mail: deposit@ccdc.cam.ac.uk.
References
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