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Coordination Properties (coordination + property)
Selected AbstractsMacrocyclic Receptor Showing Improved PbII/ZnII and PbII/CaII SelectivitiesEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 17 2010Raquel Ferreirós-Martínez Abstract Herein we report on the macrocyclic receptor N,N,-bis[(6-carboxy-2-pyridyl)methyl]-1,10-diaza-15-crown-5 (H2bp15c5) and its coordination properties towards ZnII, CdII, PbII, and CaII. The stability constants of these complexes determined by pH-potentiometric titration at 25 °C in 0.1 M KNO3 vary in the following order: PbII > CdII >> ZnII > CaII. As a result, bp15c5 presents very important PbII/ZnII and PbII/CaII selectivities. These results are in contrast to those reported for the related receptor derived from 1,7-diaza-12-crown-4, which provides very similar complex stabilities for ZnII and PbII. The X-ray crystal structure of [Cd(Hbp15c5)]+ shows heptadentate binding of the ligand to the metal ion, with two oxygen atoms of the macrocyclic unit remaining uncoordinated. The 1H NMR spectra of the complexes formed with PbII, ZnII, and CaII (D2O) show very broad peaks in the region 2,5 ppm, indicating an important degree of flexibility of the crownmoiety in these complexes. On the contrary, the 1H and 13C NMR spectra recorded for the CdII complex are well resolved and could be fully assigned. A detailed conformational investigation using theoretical calculations performed at the DFT (B3LYP) level predict a minimum energy conformation for [Cd(bp15c5)] that is very similar to that observed in the solid state. Analogous calculations performed on the [M(bp15c5)] (M = Zn or Pb) systems predict hexadentate binding of the ligand to these metal ions. In the case of the PbII complex our calculations indicate that the 6s lone pair is stereochemically active, which results in a hemidirected coordination geometry around the metal ion. The minimum energy conformations calculated for the ZnII, CdII, and PbII complexes are compatible with the experimental NMR spectra obtained in D2O solution. [source] Novel Enantioselective Synthesis of Functionalized Pyridylarsanes by a Chiral Palladium Template Promoted Asymmetric Hydroarsanation ReactionEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 27 2009Fengli Liu Abstract The asymmetric hydroarsanation reactions between diphenylarsane and (E)-1-phenyl-3-(pyridin-2-yl)-2-propenone and (E)-1-methyl-3-(pyridin-2-yl)-2-propenoate have been achieved by use of the organopalladium complex containing ortho -metalated (R)-[1-(dimethylamino)ethyl]naphthalene as the chiral reaction template in high regio- and stereoselectivities under mild conditions. Hydroarsanation of (E)-1-phenyl-3-(pyridin-2-yl)-2-propenone with diphenylarsane generated two stereoisomeric products in the ratio of 3:1 as five-membered As,N bidentate chelates on the chiral naphthylamine palladium template. Using the same chiral metal template, the corresponding hydroarsanation reaction with (E)-1-methyl-3-(pyridin-2-yl)-2-propenoate gave only one product as a six-membered As,N bidentate chelate. The naphthylamine auxiliary could be removed chemoselectively by treatment with concentrated hydrochloric acid to form the corresponding optically pure neutral complexes. Subsequent ligands displacement from the palladium using aqueous potassium cyanide generated the optically pure keto- and ester-functionalized chiral pyridylarsane ligands. The absolute configuration and the coordination properties of the pyridylarsanes have been established by single-crystal X-ray analysis.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009) [source] Mono- and Dinuclear CuII and ZnII Complexes of Cyclen-Based Bis(macrocycles) Containing Two Aminoalkyl Pendant Arms of Different LengthsEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 11 2005Carmen Anda Abstract The basicity and coordination properties towards CuII and ZnII of the bis(macrocycles) L1, L2 and L3 have been investigated by means of potentiometric, 1H NMR and UV/Vis spectroscopic titrations in aqueous solutions. The synthesis of L1 and L3 is also described. The three ligands are composed of two [12]aneN4 units separated by a p- phenylene spacer and differ in the length of the aminoalkyl pendant arms linked to each macrocyclic unit. L1,L3 form mono- and dinuclear complexes in aqueous solutions; in the dinuclear species each metal ion is coordinated by one of the two identical [12]aneN4 ligand moieties, as shown by the crystal structures of the complexes [Cu2L1]Cl4·8H2O, [Zn2L2](ClO4)4 and [Zn2L3](ClO4)4·H2O. In all structures the metal ion is pentacoordinate, and is bound to the four nitrogen donors of the cyclic unit and to the amine group of the side arm. The stability of both the [ML]2+ and [M2L]4+ complexes in aqueous solution decreases in the order L1 > L2 > L3. At the same time, both the [Cu2L]4+ and [Zn2L]4+ complexes show a different ability in proton binding among the three ligands, with the [M2L1]4+ complexes displaying the highest basicity. These results are explained in terms of the decreasing number of nitrogen donors involved in CuII or ZnII binding on passing from L1 to L3; in other words, while in the L1 dinuclear complexes each metal ion is coordinated to the four amine groups of a [12]aneN4 moiety and to the amine group of the side arm, in the L3 ones the metal cations are bound only to the four donor atoms of a cyclic moiety, the aminobutyl group not being coordinated. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005) [source] A pyrazolylamine-phosphonate monoester chelator for the fac -[M(CO)3]+ core (M = Re, 99mTc): synthesis, coordination properties and biological assessmentJOURNAL OF LABELLED COMPOUNDS AND RADIOPHARMACEUTICALS, Issue 13 2007Elisa Palma Abstract Aiming to develop new strategies for the labeling of hydroxyl-containing biomolecules with the organometallic core fac -[99mTc(CO)3]+, we have prepared a new model bifunctional chelator, L4 (ethyl hydrogen (2-{[2-(3,5-dimethyl-1H -pyrazol-1-yl)ethyl]amino}ethyl)phosphonate), combining a pyrazolyl-amine chelating group and a monophosphonate ethyl ester function (,P(O)OHOEt). The phosphonate group allows metal stabilization, and, simultaneously, can be considered as a potential attachment site for a biomolecule. Reaction of L4 with the precursor [99mTc(H2O)3(CO)3]+ gave the model radiocomplex [99mTc(CO)3(k3 -L4)] (6a). This radiocomplex was identified by comparing its chromatographic profile with that of the corresponding Re analog (6) under the same conditions, also prepared and fully characterized by the usual analytical techniques. Radiocomplex 6a is moderately lipophilic (log Po/w = 1.07), presenting high stability in vitro without any measurable decomposition or ligand exchange, even in the presence of strong competing chelators such as histidine and cysteine (37°C, 24 h). Biodistribution studies of the complex in CD-1 mice indicated a rapid blood clearance, and a rapid clearance from main organs, occurring primarily through the hepatobiliary pathway. Complex 6a presents also a high robustness in vivo, demonstrated by its resistance to metabolic degradation in blood, and intact excretion into the urine, after RP-HPLC analysis of blood and urine samples. Copyright © 2007 John Wiley & Sons, Ltd. [source] | ||||||||||