Anion binding by Ag(i) complexes of urea-substituted pyridyl ligands

Abstract

A series of Ag(I) complexes of ureidopyridyl ligands 1 and 2 have been prepared from oxo-anion salts. In all cases the new materials contain the AgL 2 + cation interacting with oxo-anions via the urea moiety. The complexes containing the para ligand 2: 5), all exhibit remarkably similar chain-like structures based around a linear Ag(I) centre, despite the change in the counter-ion. A recurring R 2 2 (8) hydrogen-bonding ring motif between the urea group and the oxo-anion is observed in almost all cases. An exception to this trend is the anhydrous nitrate structure [Ag(2)]NO 3 (6) in which the nitrate is coordinated in a bridging position between two silver centres, which adopt distorted trigonal pyramidal geometries. Structures containing the ligand 1, 10) and [Ag(1) 2 ]NO 3 Á 0.5MeOH Á 0.5MeNO 2 (11), display very different geometries, although the R 2 2 ( 8) is observed to persist throughout. The most notable of these structures are 10 and 11 in which the nitrate anion is chelated within a 'pincer' arrangement by the silver complex. The nitrate anion is situated asymmetrically within the cavity of the host complex. This discrete nitrate complex persists in solution with strong nitrate binding by the [Ag(1) 2 ] + host compared to other anions being observed.

Anion receptor coordination tripods capped by [9]ane-S3

“…Addition of between 3.5 and 4 equivalents of ligand led to a greater yield of the desired three-armed receptor complexes 5 and 6, but required removal of the excess ligand. For complex 5 this was achieved by dissolution of the crude product in acetone and addition of cold diethyl ether until the 30 complex precipitated. Complex 6 required more careful solvent balance, eventually involving a mixture of acetone, diethyl ether and ethyl acetate to remove the majority of the excess ligand by recrystallisation, although some ligand was still found to be present by 1 2+ proved difficult, as a result of steric crowding about the metal centre.…”

“…The second method relies on blocking three coordination sites of the octahedral metal centre in a facial (fac) manner such that the opposite three sites are positioned in a mutually orthogonal fashion to generate a tripodal anion binding pocket. The best method for achieving 30 such blocking is through the use of a tridentate face-capping ligand, often an arene, [14][15][16] heterocycle, 17,18 or claw-like tridentate ligand. 19,20 Such a capped metal leads to the range of complexes known as 'half-sandwich' or 'piano-stool' complexes, named for their distinctive three-legged appearance.…”

“…25 Excitation of 4 at the primary absorbance wavelength at 347 nm results in primarily emission assignable to a monomeric pyrene derivative which shares similarities to the free ligand ( Figure 5). Both free ligand and complex 4 exhibit broad bands to longer 30 wavelength assignable to pyrene excimer emission. 45 This band occurs at 511 nm for the free ligand, while the excimer band for 4 appears to involve two overlapping excimeric species, possibly intra-and intermolecular excimers.…”

“…In 25 these cases, the neighbouring pyridyl C-H signal (Hc, Figure 2) alone was followed during the titration, while for the other amine receptors (2 and 4) the N-H resonance remained sharp in the NMR spectrum and thus could be monitored. In titrations with 4, only the NH resonance was monitored, as the pyridyl CH signal 30 is obscured by the pyrene CH resonances. The NMR spectrum of 4 proved concentration dpendent and a dilution study gave a dimerization constant of 2.63(8) which was included as a constant in anion complexation titratons.…”

Studies of Synthetic Macrocyclic Complexes of Co (II) and Mn( II) in the Catalytic Oxidation of Hydroquinones

“…[3][4][5][6] The catalytic oxidation of methyl hydroquinone by tetramethyl tetraaza cobalt macrocyclic complexes has also been reported. [7][8][9][10][11][12] We carried out the autooxidation of methoxy and some other hydroquinones in presence of Co(II) and Mn(II) complexes of hexamethyl tetraaza macrocyclic ligands A and B. …”