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

Seven compounds having in common a Cr 3 (dpa) 4 3+ 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 [Cr 3 (dpa) 4 Cl 2 ]Cl·2CH 2 Cl 2 ·THF (2.12, 2.47), 2 [Cr 3 (dpa) 4 Cl 2 ]AlCl 4 ·CH 2 Cl 2 (2.011, 2.555), 3 [Cr 3 (dpa) 4 Cl 2 ]FeCl 4 ·CH 2 Cl 2 (2.009, 2.562), 4 [Cr 3 (dpa) 4 Cl 2 ]I 3 ·THF·2H 2 O (2.08, 2.49), 5 [Cr 3 (dpa) 4 Cl 2 ]PF 6 ·2CH 2 Cl 2 (2.08, 2.48), 6 [Cr 3 (dpa) 4 (BF 4 )F]BF 4 ·2CH 2 Cl 2 (1.900, 2.595), 7 [Cr 3 (dpa) 4 ClF]BF 4 ·CH 2 Cl 2 ·C 6 H 14 (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.