Linear Trichromium Complexes with Direct Cr to Cr Contacts. 2. Compounds with Cr₃(dipyridylamide)₄³⁺ Cores

Seven compounds having in common a Cr₃(dpa)₄³⁺ core (dpa = di(2-pyridyl)amide ion) have been prepared and all shown to have an unsymmetrical chain of three Cr atoms. This chain can be described as a pair of quadruply bonded Cr^II atoms to which a Cr^III atom is attached. No symmetrical chain has been found, contrary to a previous preliminary report. The seven compounds have been well characterized crystallographically, and their short and long Cr to Cr distances (Å, in parentheses) are:  1 [Cr₃(dpa)₄Cl₂]Cl·2CH₂Cl₂·THF (2.12, 2.47), 2 [Cr₃(dpa)₄Cl₂]AlCl₄·CH₂Cl₂ (2.011, 2.555), 3 [Cr₃(dpa)₄Cl₂]FeCl₄·CH₂Cl₂ (2.009, 2.562), 4 [Cr₃(dpa)₄Cl₂]I₃·THF·2H₂O (2.08, 2.49), 5 [Cr₃(dpa)₄Cl₂]PF₆·2CH₂Cl₂ (2.08, 2.48), 6 [Cr₃(dpa)₄(BF₄)F]BF₄·2CH₂Cl₂ (1.900, 2.595), 7 [Cr₃(dpa)₄ClF]BF₄·CH₂Cl₂·C₆H₁₄ (2.039, 2.507). Magnetic susceptibility measurements on 1 and 2 reveal μ_eff = 3.85 ± 0.05 μ_B from 10 to 300 K.