Unexpected Family of Heterometallic Rings {Cr₆M₂} with 3,5-Bis(trifluoromethyl)benzoate

Three heterometallic rings, [Pr₂NH₂][(Pr₂NH₂)Cr₆^IIIM₂^IIF₈(BTFB)₁₆] (M is Ni, Co, or Zn, BTFBH = 3,5-bis(trifluoromethyl)benzoic acid) are reported, templated about a di-<i>n</i>-propylammonium cation. The ring contains six Cr(III) ions and two M(II) ions at the corners of an octagon, with the divalent metal ions disordered around the ring. Each edge of the octagon is bridged by a fluoride and two bridging BTFB^- ligands. One of the two ammonium cations in the crystal structure is located at the center of the octagonal ring, and the other outside the ring. Two divalent metals in the ring lead to the presence of isomers, which can be seen in the magnetic and EPR studies for M^II = Ni or Zn, and ¹⁹F-NMR spectra for M^II = Co. The data are interpreted as resulting from an approximately 50:50 mixture of isomers, where the divalent ions are at the 1,5 and 1,2 positions in the ring. A different reaction was pursued, which gave [(Pr₂NH₂)][Cr₇^IIIM^IIF₈(BTFB)₁₆] rings; these could not be fully characterized by crystallography but their formation is confirmed by elemental analysis, mass spectrometry, NMR spectroscopy (for M = Co), magnetic studies, and EPR spectroscopy (for M = Ni, Zn).