Tetrahalocatecholate Rare Earth Complexes: Dinuclear Motifs with Intramolecular RE···XC(Ar) Interactions

The reaction of yttrium or cerium nitrate and tetrachloro- or tetrabromocatecholate (X4Cat2– with X = Cl or Br) has afforded the compounds (Et3NH)2[{Y­(Cl4Cat)­(H2O)2}2(μ-Cl4Cat)2]·2MeOH·2H2O (1-Cl), (Et3NH)2[{Y­(Br4Cat)­(H2O)2}2(μ-Br4Cat)2]·1.5MeCN (1-Br), (Et3NH)4[(Cl4Cat)­(H2O)2Y­(μ-Cl4Cat)2Y­(Cl4Cat)2]·2.5MeOH·3.5H2O (2-Cl), (Et3NH)4[{Y­(Cl4Cat)­(Cl4CatH)­(H2O)}2(μ-Cl4Cat)2]·4H2O (3-Cl), (Et3NH)7[{CeIV(Cl4CatH)­(NO3)­(μ2-Cl4Cat)3}2CeIII]­(NO3)2 (4-Cl), and (Et3NH)4[CeIV(X4Cat)4] (5-X with X = Cl, Br). Small variations of the reaction stoichiometry and crystallization methods allow the isolation of dinuclear yttrium complexes with four, five, and six tetrachlorocatecholate ligands in 1-Cl, 2-Cl, and 3-Cl, respectively. Single crystal X-ray diffraction studies of these compounds reveal a conserved tetrachlorocatecholate-bridged dinuclear yttrium core in each case, but with different peripheral ligation. A key feature of the core unit is Y···ClC­(Ar) intramolecular interactions with a catecholate chloro substituent ortho to one of the coordinating oxygen atoms. The tetrabromocatecholate analogue 1-Br has also been obtained. Applying similar methods to redox-active cerium, rather than yttrium, instead affords an unusual mixed-valence trinuclear {CeIIICeIV2} complex in 4-Cl, as well as two mononuclear cerium­(IV) complexes in 5-Cl and 5-Br. Density functional theory calculations confirm the [CeIV(Cl4Cat)4]4– charge distribution for 5-Cl.