Dong I. Yoon

Selective recognition of metal complexes by macrocyclic ethers: further observations on the macrocycle size dependence and the first-sphere ligand composition dependence of recognition thermodynamics

Abstract Additional studies of solution phase recognition of Ru(NH3)x(pyridine)y2+, Ru(NH3)x(2,2′-bipyridine)y2+ and Ru(NH3)4(1,10-phenantroline)2+ species by dibenzo crown ethers are reported. The factors most closely examined were crown size, ammine ligand content and ancillary ligand composition. The overall study confirms that recognition or association derives primarily from H-bond formation (ammine hydrogen/ether oxygen. Evidently opposing these interactions, however, are crown conformational rearrangements. Consequently, straight-forward correlatins between association strength and potential number of H-bond interactions are found only in selected cases. Based on comparisons of association constants for (bis) pyridine, bipyridine and phenanthroline ligand-containing species with dibenzo crowns, evidence is also found for favorable polypyridine/benzene interactions. NMR (NOE) measurements indicate that the preferred association geometrics in solution are those that make each of the benzenes of the crown coplanar (or nearly coplanar) with the ligated polypyridine.

A luminescent tricarbonylchlororhenium(I) complex featuring a flexible “crown ether” ligand. Manipulation of photoexcited state properties via binding of small cations†

A luminescent complex, [Re(CO)3(Cl)(LL)] where LL is 1,11-bis(4-pyridylcarboxy)-3,6,9-trioxaundecane, was prepared, and the crystal structures of two solvates were determined. The flexible polyether chain of the chelating ligand adopts an all gauche conformation about the aliphatic C–C bonds, and does not appear to introduce any appreciable constraints on the geometry at the octahedral metal center. The cavity formed by the “crown ether” has a diameter of ca. 7 A. Binding of cations causes a decrease of the luminescence lifetime of the ReIILL– excited state, consistent with an “energy gap” effect and with a rapid excited-state equilibrium between bound and unbound moieties. Binding constants were determined for several alkali metal ions, and for the ammonium cation. The chemical affinity of the crown-functionalized ligand is not specific for any of the cations studied, but, instead, is similar for a range of cations. Comparative studies with a complex containing ester-functionalized pyridine ligands, but lacking the polyether linkage necessary to form the crown, also showed excited state binding of small cations, indicating that the anionic ester pyridyl fragment, rather than the polyether fragment, is responsible for the binding.

Spectroscopic and photophysical studies of apparent cluster-to-organic-acceptor charge transfer in a molecular cadmium sulfide assembly

Abstract A nitrobenzene (NB) decorated cadmium sulfide cluster, [Cd 4 (SNB) 10 ][N(CH 3 ) 4 ] 2 , has been prepared and examined spectroscopically. The assembly exhibits an intense cluster-to-attached-acceptor charge-transfer band at 376 nm. Observation of back electron transfer (nitrobenzene to cluster) via time resolved luminescence yields a rate constant of ≥ 5 × 10 9 s −1 . Raman studies show that seven vibrational modes are coupled to the electron transfer reaction and that those exhibiting the greatest initial-state/final-state displacements are the CdS and NO stretches. Despite the activity of ν Cd-S , however, the electron donor is more appropriately characterized as an individual sulfur atom, rather than a delocalized assembly.

A crown-linked donor-acceptor assembly containing ReI(diimine)(CO)3Cl and nitrobenzene components

The structure of the title assembly, tricarbonylchloro[16-nitro-3,6,9,12,20,23,26,29-octaoxa-34,37-diazatetracyclo[34.3.1.114,18.131,35]dotetraconta- 1(39),14,16,18 (41),31,33,35 (42),36 (40),37-nonaene- 2,13,19,30-tetraone]rhenium(I), C35H33ClN3O17Re, has been determined via a single-crystal diffraction study. The rhenium ion is octahedrally coordinated. The bidentate bipyridine/crown ether/nitrobenzene assembly is folded such that the pyridyl rings and nitrobenzene moiety are almost coplanar.