摘要:
The reaction of Zn((O2CBu)-Bu-t)(2) with 4-(dimethylamino)pyridine (DMAP) in 1:2 and 1:1 mol ratios afforded [Zn((O2CBu)-Bu-t)(2)(DMAP)(2)]center dot H2O (1 center dot H2O) and [Zn-5(mu(3)-OH)(2)((O2CBu)-Bu-t)(2)(mu(2)-kappa O-1':kappa O-1'-(O2CBu)-Bu-t)(6)(DMAP)(2)] (2) in 95% and 98% yields, respectively. Complex 1 center dot H2O upon crystallization from CHCl3/n-hexane mixture at ambient temperature afforded 1 center dot CHCl3 in 77% yield. Complex 2 upon re-crystallization in a CH2Cl2/n-hexane mixture or CDCl3 at ambient condition afforded a unique pentanuclear complex, [Zn-5(mu(3)-OH)(2)((O2CBu)-Bu-t)(kappa O-2,O'-(O2CBu)-Bu-t)(mu(2)-kappa O-1:kappa O-1'-(O2CBu)-Bu-t)(6)(DMAP)(2)] (3) in 98% yield. Complex 3 upon re-crystallization in methanol transformed back to 2. The new complexes were characterized by elemental analysis, TGA/DTA/DSC analysis, FT-IR, NMR (solution H-1 and C-13, and solid state CP-MAS) spectroscopy, and selected complexes were characterized by single crystal X-ray diffraction. The molecular structures of 2 and 3 represent a crystallographic snapshot of a monodentate <-> chelating 'carboxylate shift' process. Variable temperature H-1 NMR measurements carried out on 2 in methanol-d indicated the presence of two species, possibly 2 and 3, in about a 2:1 ratio, respectively at 198 K suggesting the aforementioned 'carboxylate shift' process operating in solution. Various factors that are responsible for the 'carboxylate shift' process are discussed. (C) 2013 Elsevier Ltd. All rights reserved.