Isostructural crystals

A number of other phosphate-based glass-ceramic systems have been investigated. Fine-grained glass-ceramics based on crystals isostructural with NZP (NaZt O ) can be prepared from certain transition-metal orthophosphate and silicophosphate glasses (27). The extensive solid solution possible in the NZP phase provides for a wide range in thermal expansion, with coefficients ranging from —20 to 60 x 10-7 /°C. 

In its precipitation reactions ameiicium(IIl) is very similar to the other tripositive actinide elements and to the rare earth elements. Thus the fluonde and the oxalate are insoluble and the phosphate and iodate are only moderately soluble in acid solution, whereas the nitrates, halides, sulfates, sulfides, and perchlorates are all soluble. Americium(VI) can be precipitated with sodium acetate giving crystals isostructural with sodium uranyl acetate,... 

Crystal isostructurality refers to identical or nearly identical packing arrays of chemically distinct compounds and is inversely related to the phenomenon of polymorphism, which, instead, refers to the ability of a single compound to crystallize in different packing arrays. A series of isostructural inclusion compounds is typically based on a common host framework with voids that may be occupied by different guest molecules. The constant guest environment provided by such a series is a factor that facilitates interpretation of the mechanisms of processes such as thermal decomposition and guest exchange. 

In the vapour phase As is known to exist as tetrahedral Asa molecules with (As-As 243.5 pm) and when the element is sublimed, a yellow, cubic modification is obtained which probably also contains Asa units though the structure has not yet been determined because the crystals decompose in the X-ray beam. The mineral arsenolamprite is another polymorph, e-As it is possibly isostructural with metallic orthorhombic P. 

The spectra of Pu3+ LaCl3 (29) and isostructural PUCI3 (30) have been examined and the energy-level analysis has been refined using extensive crystal-field data. Consequently, the results included in Table IV are well established. As already indicated, they serve as one basis for estimating parameters for higher-valent species. 

The reports about the crystal structure of Mn(Et2cftc)2, determined by means of X-ray powder diagrams are contradictory. According to Fackler and Holah (18) this compound is isomorphous with Cu(Et2rftc)2, but Lahiry and Anand (44) state the complex to be isostructural with Ni(Et2 tc)2- EPR data (g = 1.92 and g = 4.11) and magnetic susceptibility measurements (4.1 BM at room temperature) show the compound to be the first Mn(II) complex with a quartet ground state (44). 

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