No abstract

No abstract

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

The introduction of nitrate groups in the derivatives of the Tl “1201” structure is shown for the first time. A new superconducting oxycarbonitrate (Tl5/6Cr1/ 6)Sr4(CO3)1/2(NO3)1/2O7 is isolated. It crystallizes in a tetragonal cell with a = 3.8320(1) Å and c = 16.4112(5) Å and a P-type lattice. This compound contains, like the superconducting oxycarbonate (Tl2/ 3Cr1/3)Sr4Cu2(CO3)O7, hexavalent chromium, but it differs fundamentally from the latter by its structure. The (Tl5/6Cr1/6)Sr4Cu2(CO3)1/2(NO3)1/2O7 structure consists of a single intergrowth of the “1201” and S2CC (Sr2CuO2CO3) structures, whereas (Tl2/3Cr1/ 3)Sr4Cu2(CO3)O7 is a (110)-sheared structure derived from the latter by a shearing mechanism every five CuO6 octahedra. The transition between the two structures is discussed in terms of a size mismatch between Cr and Tl species. The critical temperature of the oxycarbonitrate is close to 65 K. The relations of this new compound with the 77 K superconducting oxycarbonate (Tl2/3Cr1/ 3)Sr4Cu2(CO3)O7 and the 34 K superconducting oxychromate Tl3(CrO4)Sr8Cu4O16 are discussed.

A New Superconducting Oxycarbonitrate:(Tl 5/6 Cr 1/6 )Sr 4 Cu 2 (CO 3 ) 1/2 (NO 3 ) 1/2 O 7 .-The novel title compound (I) is isolated in the course of attempts to introduce NO 3 groups into derivatives of the Tl "1201" structure. According to the powder XRD data, (I) (tetragonal, P4/mmm) contains Cr(VI) similar to the 77 K superconductor (Tl 2/3 Cr 1/3 ) Sr 4 Cu 2 (CO 3 )O 7 (II), but consists of an intergrowth of a "1201"-type layer [Tl 5/6 Cr 1/6 Sr 2 CuO 5 ] with one S 2 CC-type [Sr 2 CuO 2 (CO 3 ) 1/2 (NO 3 ) 1/2 ] layer, whereas (II) derives from the (1201) 1 (S 2 CC) 1 intergrowth by a shearing mechanism transversal to Cu layers along the (110) planes. Structural transitions between (I) and (II) are attributed to the decrease of the Cr content in the structure. (I) exhibits a Tc of 65 K. -(BARNABE, A.; LETOUZE, F.; PELLOQUIN, D.; MAIGNAN, A.; HERVIEU, M.; RAVEAU, B.; Chem. Mater. 9 (1997) 10, 2205-2211; Lab. Cristallogr. Sci. Mater., CNRS, Inst. Sci. Matiere Rayonnem., Univ. Caen, F-14050 Caen, Fr.; EN)