Cooperative double deprotonation of bis(2-picolyl)amine leading to unexpected bimetallic mixed valence (M-I, MI) rhodium and iridium complexes

Cooperative reductive double deprotonation of the complex [Rh I(bpa)(cod)]+ ([4]+, bpa = PyCH 2NHCH2Py) with one molar equivalent of base produces the bimetallic species [(cod)Rh(bpa-2H)Rh(cod)] (7), which displays a large Rh -I,RhI contribution to its electronic structure. The doubly deprotonated ligand in 7 hosts the two >Rh(cod)> fragments in two distinct compartments: a >square planar compartment> consisting of one of the Py donors and the central nitrogen donor and a >tetrahedral Ï€-imine compartment> consisting of the other pyridine and an >imine C=N> donor. The formation of an >imine donor> in this process is the result of substantial electron transfer from the {bpa-2H}2- ligand to one of the rhodium centers to form the neutral imine ligand bpi (bpi = PyCH2N=CHPy). Hence, deprotonation of [RhI(bpa)(cod)] + represents a reductive process, effectively leading to a reduction of the metal oxidation state from RhI to Rh-I. The dinuclear iridium counterpart, complex 8, can also be prepared, but it is unstable in the presence of 1 mol equiv of the free bpa ligand, leading to quantitative formation of the neutral amido mononuclear compound [Ir I(bpa-H)(cod)] (2). All attempts to prepare the rhodium analog of 2 failed and led to the spontaneous formation of 7. The thermodynamic differences are readily explained by a lower stability of the M-I oxidation state for iridium as compared to rhodium. The observed reductive double deprotonation leads to the formation of unusual structures and unexpected reactivity, which underlines the general importance of >redox noninnocent ligands> and their substantial effect on the electronic structure of transition metals. © 2011 American Chemical Society.This research was supported by the MICINN/FEDER (Project CTQ2008-03860, Spain) and Gobierno de Aragón (GA, Project PI55/08, Spain), The Netherlands Organization for Scientific Research (NWO_CW VIDI project 700.55.426), the European Research Council (ERC, EU seventh framework program, grant agreement 202886-CatCIR), and the University of Amsterdam. M.P.d.R. and L.A. thank GA and MICINN/FEDER, respectively, for a fellowship.Peer Reviewe

Little exchange at the liquid/solid interface: Defect-mediated equilibration of physisorbed porphyrin monolayers

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Anticaking Activity of Ferrocyanide on Sodium Chloride Explained by Charge Mismatch

Sodium chloride crystals have a strong tendency to cake, which can be prevented by treating them with the anticaking agent ferrocyanide. Using surface X-ray diffraction, we show how the ferrocyanide ion sorbs onto the {100} face of the sodium chloride crystal where it replaces a sodium ion and five surrounding chloride ions. The coverage is about 50%. On the basis of the determined atomic structure, we propose the following anticaking mechanism. Because of the charge of the ferrocyanide ions sorbed on the surface, the crystal can only continue growing by leaving an energetically unfavorable sodium vacancy, or by desorbing the ferrocyanide ion. Therefore, the ferrocyanide effectively blocks further growth of sodium chloride crystals, thereby preventing them from agglomerating and caking

Anticaking activity of ferrocyanide on sodium chloride explained by charge mismatch

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