Hf -containing monomers

Over the next few years, both the mid-infrared and the far-infrared spectra for Ar-HF and Ar-HCl were extended to numerous other bands and to other isotopic species (most importantly those containing deuterium). In 1992, Hutson [18, 39] combined all the available spectroscopic data to produce definitive potential energy surfaces that included both the angle dependence and the dependence on the HF/HCl monomer vibrational quantum number v... 

Preparation of Hf-Containing Polymers Through Polymerization of Metal-Containing Monomers (Process III)... 

Reacting HfOCI wiilli the sodium or potassium salt of acrylic or methacrylic acid, we obtained for the first time Hf(IV)-containing monomers. Hafnium oxoacrylates and methaaylates were syn-thesized according to the Scheme 10.8 (polymer 7). 

C Hg) leads to Cp elimination and the formation of HfC film at temperatures as low as 250 to 350 °C [37]. In light of this, it was expected that the thermal transformations of the Hf-containing polymers and monomers would be accompanied by the formation of refractory hafnium compounds, in particular HfC. This led us to investigate the thermolysis of the synthesized Hf-containing compounds (Scheme 10.11). 

Polymers containing Hf(TV) in the main chain or side chains can be prepared by any of the known processes for synthesis of metal-containing polymers. An attractive approach is the polycondensation of dicyclo-pentadienyl derivatives of hafnium(IV) with diols or oxygen-free diacetylenic hgands. An alternative approach is polymerization of the Hf(TV) monomers with (meth)acrylate and fumarate groups, synthesized for the first time in this study. We investigated the thermolysis of the synthesized... 

N,N-dimethylaminoethyl methacrylate) (DMAEMA) by an SPG emulsification technique [34]. The process consists of two steps - emulsification and polymerization. The oil phase containing monomers (styrene and DMAEMA), hexadecane (HD) and an initiator N.hf-azobis (2,4-dimethyl valeronitrile) (ADVN) is pressed by nitrogen gas through the SPG membrane into the aqueous phase. The aqueous phase contains stabilizer polyvinyl alcohol (PVA), surfactant sodium lauryl sulfate (SLS), electrolyte Na2S04 and water-soluble inhibitor (NaN02 or diaminopheny-lene). The emulsion obtained is then transferred to a separate reaction kettle and polymerization is started by raising the reaction temperature to 70 °G. After 24 h, microcapsules with uniform size are obtained. 

Van der Waals complexes containing monomers with large rotational constants, such as HF, HCl, H2O and NH3, undergo very wide-amplitude bending motions even in low vibrational states. These states are best understood using quantum numbers derived from a free internal rotor picture, rather than those derived from the conventional near-rigid picture. The anisotropy of the potential splits and shifts the monomer free-rotor states, but the qualitative pattern of energy levels and allowed transitions remains. 

Cerium tetrakis(acetylacetonate), a venerable compound,695 exists as a and /3 modifications. Both these contain [Ce(acac)4] monomers of D2 square antiprismatic coordination but differ in the crystal packing. In the a form,696 Ce—0 = 2.36-2.43 A with the ring angle O—Ce— 0 = 72°, while in the / form697 Ce—0 = 2.32 A and O—Ce—0 = 71.3°. The tetrakis(acetyl-acetonates) of Zr, Hf, Th, U and Pu also show dimorphism. The tetrakis(dibenzoylmethanate) [Ce(dbm)4] adopts a similar square antiprismatic structure with Ce—O = 2.299-2.363 A and O—Ce—O = 70.8° or 71,2°.698 There is some tendency for Ce3+ /J-diketonates to pass into the Ce4+ tetrakis(/3-diketonate). A series of tri- and tetra-valent cerium /3-diketonates has been examined from the point of view of the effect of additional ligands such as Ph3PO on this process, and it was found that Ce3+ /J-diketonates were stabilized by adduct formation, particularly by 1,10-phenanthroline.699... 

The water dimer adds a number of new dimensions to the problem since each water molecule contains three vibrational frequencies instead of one. The two stretching modes are labeled V, and Vji Vj refers to the symmetric bending motion. The frequencies computed for the water monomer are reported in the first three columns of Table 3.45, followed by the corresponding frequencies in the dimer. As in the case of (HF)2, the unpolarized basis sets strongly underestimate the stretching frequencies in the monomer. On the other hand, the bending frequency is computed reasonably well with all of the sets, albeit the small unpolarized sets do yield a bit of an overestimate. Rather similar patterns are evident in the dimer as well. The unpolarized sets underestimate v and Vj and yield a small overestimate, by less than 100 cm of the frequency for V2. 

The energetics of formation of the H20 --H20--HC1 complex are reported in Table 5.31, in a format comparable to that for H20"-HF"HF in Table 5.29. All data were obtained at the MP2 level and are corrected for BSSE by the counterpoise procedure. The three basis sets all contain polarization functions and yield comparable results. The binding of HCl to the pre-formed water dimer (step lb) is considerably more favorable than its binding to a water monomer, as in step 2a. This enhancement is referred to as E p in Table 5.31, and amounts to between 2 and 3 kcal/mol. (The same quantity is identically equal to the enhancement of binding of water to HjO—HCl as compared to HCl.) It is worth noting that whereas the total binding energy in the appropriate row of Table 5.31 is rather insensitive... 

On the other hand, the data in Table 1 refer to monomeric H20 and HF. The gaseous oligomers of HF and the highly hydrogen-bonded two liquids and their mixture (hydrofluoric acid) are stabilized by interactions also known (37) from crystals containing FHF-, H2OHOH2 and acidic carboxylates, and the may need auxilliary bonding to a smaller extent than the monomers. It must be noted that / = 19.9 and... 

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