Ligand properties terphenyl ligands

Following the initial report of 41, the first compound with a quintuple bond between two Cr centers, it was decided to explore how changes in the steric and electronic properties of the terphenyl ligand might affect the metal-metal bonding. Thus, we developed a series of ligands related to At with different electronic and steric properties (Scheme 4) and prepared a series of chromium(II) halide precursors for further study (cf Sect. 3.2). 

The photophysical properties of terphenyl-based acyclic (22a) and cyclic hemispherands (22c, 22d, see fig. 27) have been investigated in organic solvents and in KBr pellets (1 wt%) with the purpose of introducing them later in optical amplifiers (Sloofif et al., 1998). Absorption cross sections for the 1.54 pm emission, which is quite broad with fwhh = 70 nm, amount to 0.62, 1.1, and 0.93 x 10 20 cm2 for [Er(22a)], [Er(22c)] and [Er(22d)], respectively. The best photoluminescence intensities are obtained with the cyclic ligands. The optical gain of the complexes doped into a polymer channel waveguide is on the order of 1.7 dB cm-1, while the threshold power is as low as 1.4 mW. 

Shape Selectivity Molecular recognition of the solute by the stationary phase with respect to its geometrical dimension is called shape selectivity. For this test, one can employ aromatic components with identical hydrophobicity that differ only in their three-dimensional shape. The chromatographic selectivity of o-terphe-nyl/triphenylene or tetra-benzonaphthalene/benzo[a]pyrene are commonly used and show dependencies on several features of the phase, for example, pore structure, ligand type, and density. Figure 3.6 shows a chromatogram of a test mixture of uracil (to marker), n-butylbenzene, and w-pentylbenzene (to assess hydrophobic properties and efficiency), and o-terphenyl and triphenylene (to assess shape selectivity). The test mixture was chosen to provide a short analysis time and to facilitate calculation of parameters from baseline-separated peaks. 

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