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...Nequivalent toC 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...Nequivalent toC 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 C-para-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.