Tripod system

Ni complexes are relatively rare and are often stabilized by specialized ligands such as N-donor macrocycles and P-donor tripodal systems. Ni has a d electron configmation and its complexes are therefore paramagnetic with one unpaired electron. They show a variety of stereochemistries depending upon the ligands present, although fom or five... 

NH4 over K". Our initial calculations indicated that a benzene-based tripodal system with imidazoline arms (Fig. 34.7a) possessed vacant sites for the interaction with only one solvent molecule, while the K" " ion has three vacant sites for three solvent molecules. In order to maximize the affinity and selectivity of these receptors for NH4, it becomes important to maximize the ir-electron density of the receptor. Indeed, receptors with enhanced ir-electron density by trimethylated phenyl ring with the strong proton-withdrawing subunits exhibit much higher affinities and selectivities [129]. 

Generalized STIRAP schemes, including more than three states, for which one state is a continuum have been studied. The bound state tripod system [243, 244] has been extended to a tripod system coupled via a continuum [95], as shown in the left panel of Figure 3.16. In fhis scheme, if is possible to find laser parameters which allow for ionizafion-free partial population transfer between the discrete states within the counter-intuitive pulse order, as shown in the right panel of Figure 3.16. 

D. C. Cheng, Y. P. Niu, and S. Q. Gong. Controllable atom localization via double-dark resonances in a tripod system. Journal of Physics B Atomic Molecular and Optical Physics 2006 Oct 10 23(10) 2180-2184. 

C. Goren, A. D. Wilson-Gordon, M. Rosenbluh, and H. Friedmann. Sub-Doppler and subnatural narrowing of an absorption line induced by interacting dark resonances in a tripod system. Physical Revew A 2004 Jun 2 69(6) 063802(5). 

H. Goto and K. Ichimma. Observation of coherent population transfer in a four-level tripod system with a rare-earth-metal-ion-doped crystal. Physical Revew A 2007 Mar 15 75(3) 033404 (14). 

Various tripod systems have been synthesized with the goal of fullerene complexation (Fignre 9). One such scaffold involves a tripod with rigid linkers this system is proposed to make a supramolecnlar network wherein the net stoichiometry is expected to be 1 2 (tripod to fullerene). On the basis of an experimental analysis, it was conclnded that each fnllerene is always held by two porphyrins. These two porphyrins can be oriented snch that a U-shaped arrangement is defined between two porphyrins contained within the same molecule, 8. Or, the two porphyrins can from two separate tripods. In aU cases, the distances between the snrface of Ceo and the porphyrin plane were fonnd to range from 2.52 to 2.92 A, as wonld be expected for a system in which n-n interactions persist. 

Another tripod-type, porphyrin-based receptor is 10. This system, characterized by flexible linkers, was readily synthesized through a one-step click reaction of an azide-functionalized porphyrin with a tertiary amine functionalized with three alkynyl groups. The resulting tripod system can capture a pyridine-functionalized fullerene with 1 1 stoichiometry. The corresponding association constant, K, was found to be 9.4 x 1(1 in o-dichlorobenzene as determined from UV-vis spectroscopic titrations. The supramolecular dyad formed via this capture event was then found capable of undergoing photoinduced ET from the zinc porphyrin to the fullerene with a charge-separated lifetime of 0.5 ns. ... 

Figure 9 Recently developed tripod systems for fullerene encapsulation. 8 is a tripod on a rigid scaffold. 9 is a cyclic trimer. 10 is a trimer with flexible arms.

Instrumented tripods with flowmeters, transmissiometers, optical backscatter sensors (OBS), in situ settling cylinders, and programmable camera systems have often been used in marine environments, for example, oceanographic studies of flow conditions and suspended particle movements in the bottom nepheloid layer [37,38]. These instruments were deployed to study suspended-sediment dynamics in the benthic boundary layer and were able to collect small water samples (1-2 L) at given distances from the seafloor. An instrumented tripod system (Bioprobe), which collects water samples and time-series data on physical and geological parameters within the benthic layer in the deep sea at a maximum depth of 4000 m, has been described [39]. For biogeochemical studies, four water samples of 15 L each can be collected between 5 and 60 cm above the seafloor. Bioprobe contains three thermistor flowmeters, three temperature sensors, a transmissiometer, a compass with current direction indicator, and a bottom camera system. 

In 2006, Bernard et al. also examined centrosymmetric boron cluster-containing molecules. Although these molecules did not show second-order nonlinear optical effects because of their cen-trosymmetry, they are interesting candidates for third-order TPA nonlinear processes. Centrosymmetric materials are more suitable for TPA applications in the visible range than noncentrosymmetric ones, because of their lower coloration (Wang et al., 2001). The presence of donor substituents at each arm of tripodal systems increases the TPA properties (Brunei et al., 2001). Bernard et al. desaibed, for the first time, branched octupolar systems with three dodecaborate units (Figure 13.16). 

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