A re-investigation the electronic spectra of chromium(III) picolinate complexes and high yield synthesis and characterization of Cr2(μ-OH)2(pic)4•5H2O (Hpic=picolinic acid)

Chromium(III) tris(picolinate), Cr(pic)(3), is a popular nutritional supplement, although recent studies have raised concerns about its use. The mechanisms of transport and absorption of Cr(pic)(3) have not been elucidated, in part because of the lack of a suitable spectroscopic method for following the fate of the compound. Even the electronic spectrum of the complex has been a matter of debate: discrepancies in reports of these spectra have now been reexamined and resolved. Interpretation of the H-1 NMR spectrum of Cr(pic)(3) has been complicated by the presence of small amounts of a byproduct during its synthesis, Cr-2(OH)(2)(pic)(4). A high-yield synthesis of the dimer and its NMR spectrum in dimethylsulfoxide are described. Discrepancies in reports of the electronic spectrum of the dimer are also reconciled. (C) 1999 Elsevier Science Ltd. All rights reserved.