Synthesis and Crystal Structure of (18-Crown-6)(nitrato)(triphenylphosphine oxide)potassium

Abstract

A new complex (18-crown-6)(nitrato)(triphenylphosphine oxide)potassium ( I ) is synthesized, and its crystal structure is studied by X-ray diffraction analysis (space group R 3 m , a = 14.336 Å , c = 13.776 Å , Z = 3). The structure is solved by the direct method and refined by the full-matrix least-squares method in the anisotropic approximation to R = 0.034 for 1122 independent reflections (CAD4 automated diffractometer, λ Mo K α radiation). Structure I contains a complex host-guest molecule [K ( NO 3 )(18 -crown-6)( Ph 3 PO)] with crystallographic symmetry 3 m (three planes m contain three Ph rings of the Ph 3 PO ligand and all O atoms of the crown ligand). The coordination polyhedron of the K + cation is a distorted hexagonal bipyramid with all the six O atoms of the crown ligand in the base, the O atoms of the Ph 3 PO ligand, and one (or two) O atoms of a disordered ligand in the axial positions. NO 3 -

Determinants of cation transport selectivity: Equilibrium binding and transport kinetics

“…These molecules bind K + ions in a cage of oxygen atoms ∼2.8 Å in diameter, but can deform to bind to the smaller Na + ion with its optimal 2.4-Å diameter ( Fig. 4 ) ( Kilbourn et al, 1967 ; Dobler and Phizackerley, 1974 ; Neupertlaves and Dobler, 1975 ; Kauffmann et al, 1976 ; Steinrauf et al, 1982 ; Izatt et al, 1985 ; Cram and Ho, 1986 ; Chekhlov, 2005a , c ). Because many molecules change their shape depending on the bound ligand, it’s difficult to predict which ion would be optimally bound to a particular ion-binding site without knowing the equilibrium preference in advance.…”