Bifurcated Hydrogen Bonds as a Key Feature in the Solid State Organization of Paramagnetic Dithiolene Complexes

The synthesis and X-ray crystal structures of the HNMe3+ and pyridinium (PyH+) salts of the
paramagnetic anionic nickel dithiolene complexes [Ni(mnt)2]•- (with four CN groups) and [Ni(edtCN)2]•- (with two
CN groups) are described and analyzed to evaluate the ability of the nitrile groups of such dithiolene complexes to
act as hydrogen bond (HB) acceptors. Single NH···N⋮C hydrogen bonds are identified in [HNMe3]2[Ni(mnt)2] and
[HNMe3][Ni(mnt)2] where the number of CN groups largely exceeds that of the N−H ones. On the other hand, with
only two nitrile substituents, the [Ni(edtCN)2]•- complexes in [HNMe3][Ni(edtCN)2] associate into dianionic dyads
stabilized by bifurcated NH···N⋮C hydrogen bonds to form an original tetramolecular [HNMe3]2[Ni(edtCN)2]2
motif. Another bifurcated motif is found in the pyridinium salt of [Ni(edtCN)2]•-. Finally, in [PyH][Ni(mnt)2], and
despite the presence of four CN groups for only one pyridinium N−H moiety, bifurcated hydrogen bonds are still
found to control the structural organization. They indeed involve not only the N−H but also the activated Cpara−H
groups of the pyridinium cation. The structural requirements imposed by these hydrogen bond motifs reflect in the
magnetic properties of the salts, leading either to noninteracting or to strongly dimerized, singlet−triplet activated
systems, as determined from SQUID magnetic susceptibility measurements.