Manifestation of diamagnetic chemical shifts of proton NMR signals by an anisotropic shielding effect of nitrate anions

A remarkable upfield shift of the py(alpha) protons of complexed 2,2'-bipyridine in [cis-Pd(bpy)(NO3)(2)] is observed which is considered to originate from the anisotropic influence of suitably positioned coordinated nitrate anions around the Pd(II) centre of the molecule. A typical complexation-induced downfield shift is observed for the NH2 protons in [cis-Pd(en)(NO3)(2)] where 'en' stands for ethylenediamine. (c) 2006 Elsevier Ltd. All rights reserved.