A Novel Heterometallic Ring {Cr₅Ni₃} and New {Cr₆Co₂} and {Cr₆Zn₂} Rings

A new heterometallic ring, [Me₄N][(Me₄N)₂Cr₅Ni₃F₈(BTFB)₁₆] (BTFB = 3,5-bis(trifluoromethyl)benzoate) is reported, templated about tetramethylammonium (Me₄N)⁺. This ring features five Cr(III) centers and three Ni(II) centers at the vertices of an octagon. Each edge of the octagon is bridged by internal fluoride and two external BTFB ligands. In the crystal structure, two of the three ammonium cations are at the center of the octagonal ring, while the third cation is outside. X-ray single crystal diffraction does not distinguish between five possible isomers, but a single isomer, with nickel sites at the 1, 3, and 6 positions of the octagon, can be deduced by a combination of collision-induced dissociation mass spectrometry (CID-MS), and EPR spectroscopy and magnetometry, which show a ground state spin of ¹/₂. The same reaction carried out with cobalt(II) or zinc(II) in place of nickel(II) leads to ordered [(Me₄N)₂Cr₆M₂F₈(BTFB)₁₆] (M = Co or Zn) in which the divalent metals are placed at the 1,5-positions in the metal octagon.