An entirely new class of metal-metal dimers will be described in which two nickel(II) centers are held close together by a triad of bridging pyrazolide ions. These [Cl-Ni(μ-pz)3Ni-Cl–] dimers are synthesized by direct reaction of the corresponding sodium pyrazolide and tetrachloronickelate(II) ion in DMF. This general synthetic approach has proven effective for a variety of substituted pyrazoles. These dimer salts were characterized by MALDI-TOF-MS and UV-visible electronic spectroscopy. The [PPh4][Cl-Ni(μMe2pz)3Ni-Cl] salt was characterized by single crystal XRD, confirming for the first time the formation of this novel structure. The common (fac-N3)Ni-Cl nickel(II) environment in this dimer and the well-characterized Tp*NiCl monomer invites contrasts and comparisons. For example, the new dimer (fac-N3)Ni-Cl environment is unusually unresponsive to Lewis basic DMF molecules, where Tp*NiCl binds this solvent (and other Lewis bases) immediately and reversibly. Room temperature magnetic measurements suggest each dimer possesses two independent high spin (S = 1) nickel(II) centers. While their novel architecture makes these nickel-nickel dimers interesting on their own, these discrete high spin complexes (S ~ 2) can also be molecular magnets, well-defined magnetic centers that could be incorporated into nanoscale devices.

Anionic pyrazolide bridged nickel dimers as potential molecular magnets

ACS Spring Meeting 2021

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