Carboxylate linkers

Hyun et al. [345] prepared PbS Q-dots in a suspension and tethered them to Ti02 nanoparticles with a bifunctional thiol-carboxyl linker molecule. Strong size dependence due to quantum confinement was inferred from cyclic voltammetry measurements, for the electron affinity and ionization potential of the attached Q-dots. On the basis of the measured energy levels, the authors claimed that pho-toexcited electrons should transfer efficiently from PbS into T1O2 only for dot diameters below 4.3 nm. Continuous-wave fluorescence spectra and fluorescence transients of the PbS/Ti02 assembly were consistent with electron transfer from small Q-dots. The measured charge transfer time was surprisingly slow ( 100 ns). Implications of this fact for future photovoltaics were discussed, while initial results from as-fabricated sensitized solar cells were presented. 

NaOH or KOH MeOH Carboxyl linker Carboxylic acids... 

Metal-organic frameworks (MOFs) based upon pyridine-carboxylate linkers... 

Figure 32 Metal organic framework (MOF) integrated with catenanes (a) structure of [2]catenane unit used in MOF-1011 and (b) schematic of 2D layer of MOF-1011—the catenane units reside above and below the 2D layer containing MOF-lOll s backbone of Cu(I) ions and acetylene/carboxylate linkers.

In many ways the electronic coupling in both the neutral and the mixed-valence compounds can be reduced to the simple orbital diagram depicted in Fig. 7 [26]. In the neutral complex only the MLCT transition is observed, but for the singly oxidized radical cations three electronic transitions are possible the LMCT, the IVCT (in a fully delocalized compound this is better described as charge resonance transition), and an LMCT. For carboxylate linkers the LMCT is not observed because the CO2 Tt orbitals are too low in energy, but substitution of O by S or NR raises the energy of this filled n orbital. 

Owing to the oxophilicity of Al + ions all Al-MOFs contain Al-O bonds. In contrast to the large number of microporous zeolites in which the aluminmn ion in the framework is exclusively tetrahedrally surrounded, only octahedrally coordinated A1 atoms have been observed in Al-MOFs until now. The majority of the limited number of reported Al-MOFs is based on poly-carboxylic linker molecules although a few examples of porous aluminum phosphonates have been described in the literature. " The stability and the small number of Al-based MOFs stems from the same factors the high charge (-1-3) of the metal ion and the small ionic radius (r(CN = 6) 0.675 A). Hence dissolution of these MOFs in water is often kinetically hindered and at the same time they are almost... 

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