Ru@MOF

In order to study the stabilizing property of MOF-5 in comparison to the surfactant approach in non aqueous colloid chemistry of metal particles, the system Ru MOF-5 was selected as a target [64], The synthesis and characterization of Ru colloids starting from [Ru(cod)(cot)] in solution is well reported in the literature [77-79],... 

Rg. 12 TEM pictures of Ru MOF-5 with a corresponding SAED pattern for the embedded Ru nanoparticles. Reproduced with permission from [64]. Copyright 2008 American Chemical Society... 

D reconstruction (Fig. 13b) shows that most of the particles are in fact located at the outer domains of the investigated MOF-5 specimens with a maximum penetration of 20 mn, and only some particles are located in the core of the MOF-5 crystallites. This is in contrast to the results from the tomographical TEM measurements of Pd MOF-5 (Fig. 11), where a more or less uniform particle distribution was observed. Obviously, the preparation technique has a great impact on the particles distribution. The photolytically synthesized Pd MOF-5 shows a more uniform particle distribution than the material Ru MOF-5, which was obtained by thermally activated hydrogenolysis over a long period of time. In the case of Ru MOF-5,... 

Fig. 15 XANES (left) and EXAFS (right) of (a) Ru MOF-5, (b) [Ru(cod)(cot) MOF-5, (c) Ru-ox MOF-5, (d) Ru foil and (e) RuOj. AU data were recorded at Uquid nitrogen temperature. Reproduced with permission [64], Copyright 2008 American Chemical Society...

With a similar approach, Fischer and coworkers entrapped Ru nanoparticles inside porous [Zn40(BDC)3] (MOF-5) by hydrogenolysis of the adsorbed volatile ruthenium species [Ru(COD)(COT)] (COD — 1,5-cyclooctadiene, COT = 1,3,5-cyclooctatriene) [17]. The included Ru nanoparticles had a size range of 1.5-1.7 nm, and the intact framework of MOF-5 was cmifirmed by different spectroscopic methods. The resulting solid Ru MOF-5 was tested for oxidation of benzyl alcohol however, only a modest conversion of 25% to benzyl aldehyde was obtained, and the XRD revealed the breakdown of the structure of MOF-5 as well as the loss of framework porosity. In contrast, the crystallinity of Ru(S>MOF-5 remained when it was used to catalyze the hydrogenation of benzene to cyclohexane with 25% conversion under 3 bar H2 at 75°C (Scheme 8). 

Scheme 8 Schematic for the formation of Ru MOF-5 and its applications on alcohol oxidation...

The introduction of Ru nanoparticles with retaining the MOF of MOF-5 was carried out in Ref. [120]. After the introduction of Ru in the form of [Ru(cod)(cot)]3j MOF-5 into the framework, hydrogenolysis is carried out, which results in the formation of Ru nanoparticles inside the cavities with the formation of the Ru MOF-5 material. This catalytic system shows a moderate activity in the oxidation of benzyl alcohol to benzaldehyde (Reaction 5) ... 

Mixed-valence Ru"-Ru" paddlewheel carboxylate complexes also have potential for oxidation reactions after incorporation in a microporous lattice with porphyrinic ligands. This MOF can be used for oxidation of alcohols and for hydrogenation of ethylene. Both the porosity of the lattice and the abihty of the diruthenium centers to chemisorb dioxygen are essential for the performance of the catalyst [62, 64]. 

The M(VI) oxidation state is represented in the 4d series by the hexafluorides, MFg, of the elements Mo, Tc, Ru, and Rh. All are obtained by direct fluorination of the metal and are unstable powerfully oxidising species — once again the instability seems most marked at the end of the series. Unfortunately hardly any electronic spectral data exist. The first charge-transfer band of the d°MoF(s has been located at 54 kK. (42), and a study of the vibrational spectrum of RuF6 (43) revealed electronic bands at 1.95 and 1.4 kK., which are probably the F2, r5 Ti, and /13,... 

The RuF5-t q)e elucidated by Holloway, Peacock and SmaU (150) is a distorted version of the MoFs-stracture. The tetramere units Me4F2o are maintained the 4-membered ring of Ru-atoms is distorted to form a rhombus, however, and the Ru—F—Ru-bridges are no longer hnear (127° and 137° resp.). Similarly tilted rings are found in the stracture of the trifluoride RuFa (139), only that they are further poljmierized to form a three-dimensional framework (page 39). 

Since the initial report of CuBF4[Cu(TPyP)] , several other TPyP MOFs have appeared wherein the pyridyl moieties are coordinated to nodes that consist of simple metal ions. The metal ion nodes have included Fe (119), Ag (120), Cd " (121), Pb (121), and Ru (122). In many cases, the secondary metal nodes bear additional hgands, for example as coordinated solvent molecules or counterions. Thus, the coordination geometries about the metal nodes and the resulting topologies are partly determined by the availability of pyridyl coordination sites and the geometric preferences of the metal nodes. 

Finally, electrode potential and acidity data were used by Ng et al. to study ligand effects on CpM(PR3)2H2 and TpM(PPh3)2(// -H2)+ (M = Ru, Os) complexes under similar conditions [31] these data are included in Table 3. The Ru-H BDE determined by Ng for CpRu(PPh3)2H2+ (Table 3, entry 19 289 kJ mol" ) is in near perfect agreement with that of Angelici (Table 2, entry 25 286 kJ mol ) but somewhat different from the value derived from Morris data (Table 3, entry 1 303 kJ moF ). The source of the discrepancy might partly be the assumptions and conversions made to align the pXa and electrochemical reference scales of the different solvents used. 

Oxidation of cyclohexane was also studied using homogeneous complex of Ru(lll) with 1,2 DAP under similar condition (Table 8). However for convenience same quantity of catalyst could not be used as the same quantity of unbound catalyst gave immeasurable oxygen uptake. Inspite of using larger amount ofRu (III), a lower reaction rate was observed as compared to polymer supported catalyst. Effect of various parameters such as concentration of substrate and catalyst, temperature, amount and nature of solvent is seen and the results are summerised in Table 8. The energy of activation was found to be 7.04 Kcal mof. 

Fig. 14 Images of millimeter-sized MOF-5 crystals after loading with [Ru(cod)(cot)] before (Jeft) and after (right) treatment with Hj. The presented crystals on the left and the right side stem from the same loading experiment. One of them (right) was then treated with In order to show the macroscopicaUy uniform distribution of the precursor and the Ru nanoparticles after hydrogenol-ysis, the crystals were cut (middle) and turned to examine the cross section (bottom). Reproduced with permission from [64]. Copyright 2008 American Chemical Society...

In contrast, TEM and PXRD data of Au MOE-5 show polydispersed Au particles in a size range of 5-20 nm (see Fig. 17), with a metal loading in Au MOF-5 determined to be 48 wt%. The gold particles appear to interact more weakly with the host matrix than the Pd, Ru and Cu particles and thus larger agglomerates are formed possibly by diffusion of the particles to the outer surface. 

Enantioselective exchange of chiral cations has also been achieved in homochiral MOF systems. The 2D framework POST-1, described in Section 1.2.1.1.2, contains ID homochiral pores within which both enantioselective guest exchange and catalysis occurs. Upon suspension of L-POST-1 in a methanol solution of racemic [Ru(2,2 -bpy)3]Cl2 (2,2 -bpy = 2,2 -bipyridine), 80 % of the exchangeable protons are exchanged with the propeller-type cation, with ee = 66 % in favour of the D form. 

BINAP) groups [40]. This combined the structural stability of the MOF with the excellent enantioselective performance of homogeneous Ru and Rh-BINAP complexes [41]. 

The ability of Ru(ii) tris(2,2 -bipyridine) cations to template two new MOF structures from Zn(ii) ions and l,3,5-tris(4-carbo yphenyl)benzene tribenzoic acid has been exploited. Ru(ii) complexes encapsulated in each of the two new MOFs exhibit biphasic MLCT emission decay lifetimes consistent with two distinct environments in the structure that modulate the excited-state properties of the complexes. ... 

Recently Kent et al. studied the classic Ru to Os ET process in isomorphous metal-organic frameworks (MOFs) based on [M[4,4 -(H02C)2-bpy]2bpy] " building blocks (where M is Ru or Os). Thanks to the crystalline nature... 

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