DPBS

Souza DPB, Fricks AT, Alvarez HM, Salomao GC, Olsen MFtN, FiUio LC, Fernandes C, Atunes OAC (2007) Catal Commun 8 1041-1046... 

Substantial effort has been invested in understanding how the linker(s) affect the metal-metal (M-M) distances, since the capacity of a cofacial porphyrin to accommodate a bridging diatomic molecule is often thought to be critical for achieving high catalytic activity. As of May 2007, 38 X-ray diffraction structures of cofacial porphyrins in Fig. 18.13 had been reported, with the DPA, DPB, DPD, and DPX... 

Collman JP, Hutchison JE, Lopez MA, Tabard A, Guilard R, Seok WK, Ibers JA, L Her M. 1992. Synthesis and characterization of a superoxo complex of the dicobalt cofacial diporphyrin [(/u,-02)Co2(DPB)(l,5-diphenylimidazole)2][PF6], the structure of the parent dicobalt diporphyrin Co2(DPB), and a new synthesis of the free-base cofacial diporphyrin H4(DPB). J AmChemSoc 114 9869. 

Lead partition coefficients are reported by Bindeman et al. (1998), who present the following relationship between Dpb and Xp r. 

This expression is relatively imprecise because of the scarcity of data. Also, the oxidation state of Pb in these experiments is not known. However, it is interesting that for those experiments in which both Dpb and Dsr have been determined, the Dpb/Dsr ratio is consistently less than would be predicted from the 2+ lattice strain model using parameters presented above. As in the case of clinopyroxene, increasing the effective Vlll-fold ionic radius of Pb in plagioclase, to 1.38 A, does retrieve the observed ratios. Thus one can... 

The above 2 fit parameters can also be used to derive Dpb from Dsr, assuming that the proxy relationship is valid for alkali feldspar. For the Icenhower and London (1996) experiments we obtain a further linear correlation with Xor... 

Schmidt et al. (1999) report Dpb of 0.034-0.045 for two experiments with leucite lamproite melt composition for a basanitic melt composition La Tourrette et al. (1995) give Z)pb = 0.10. In all three cases Z)pb consistently falls below, by a factor of 3, the parabola defined by the other 2+ cations, as previously noted for several other minerals. Here the implication is that the effective Xll-fold ionic radius of Pb is slightly smaller than the value given in Table 2, i.e., closer in size to rsr. Upb/Usr is between 0.6 and 1.2, in these experiments. In the PIXE partition study of Ewart and Griffin (1994) for acid volcanic rocks, Z)pb ranges from 0.21 to 2.1 (3 samples), with Upb/Usr of 0.29 to 2.9. Until there are further experimental determinations of Upb, or better constraints on its ionic radius, we suggest that Z)pb = E>sr-... 

Monte Carlo simulations and energy minimization procedures of the non-bonding interactions between rigid molecules and fixed zeolite framework provide a reasonable structural picture of DPP occluded in acidic ZSM-5. Molecular simulations carried out for DPB provide evidence of DPB sorption into the void space of zeolites and the preferred locations lay in straight channels in the vicinity of the intersection with the zigzag channel in interaction with H+ cation (figure 1). 

Figure 2. Diffuse reflectance UV-visible absorption spectra recorded as a function of time after the mixing of solid DPB and H0 57ZSM-5 (a) and after of solid DPB and H6 6ZSM-5 (b)...

The second spectrum (figure 3b) displays the spectral features of DPP+ radical cation and provides evidence of DPP spontaneous ionization DPB + HZSM-5 -> DPB + HZSM-5 " (eq. 2). The third spectrum (fig. 3c) exhibits a broad band at 425 nm and is assigned to electron-hole pair formation DPB + HZSM-5 " - DPB HZSM-5 + (eq. 3). 

The EPR spectra show the characteristic features of the DPB+ spectrum superimposed on a broad signal in the 2-g range of X-band CW-EPR spectra (figure 4.a). This spectrum evolves to featureless signal upon aging. 

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