Studies of Phosphazenes: Part II*-Reactions of Hexachlorocyclotriphosphazatriene with N-Methylaniline

823-82

Electronic phase separation in the rare earth manganates, (La1-xLnx)0.7Ca0.3MnO3 (Ln = Nd, Gd and Y)

All the three series of manganates showsaturation magnetization characteristic of ferromagnetism, with the ferromagnetic Tc decreasing with increasing in x up to a critical value of x, xc (xc = 0.6, 0.3, 0.2 respectively for Nd, Gd, Y). For x > xc, the magnetic moments are considerably smaller showing a small increase around TM, the value of TM decreasing slightly with increase in x or decrease in . The ferromagnetic compositions (x xc) show insulator-metal (IM) transitions, while the compositions with x > xc are insulating. The magnetic and electrical resistivity behavior of these manganates is consistent with the occurrence of phase separation in the compositions around xc, corresponding to a critical average radius of the A-site cation, , of 1.18 A. Both Tc and TIM increase linearly when < rA > > or x xc as expected of a homogenous ferromagnetic phase. Both Tc and TM decrease linearly with the A-site cation size disorder at the A-site as measured by the variance s2. Thus, an increase in s2 favors the insulating AFM state. Percolative conduction is observed in the compositions with > < rAc >. Electron transport properties in the insulating regime for x > xc conforms to the variable range hopping mechanism. More interestingly, when x > xc, the real part of dielectric constant (e') reaches a high value (104-106) at ordinary temperatures dropping to a very small (~500) value below a certain temperature, the value of which decreases with decreasing frequency.Comment: 27 pages; 11 figures, Submitted to J.Phys:Condens Matte

Magnetic and electron transport properties of the rare-earth cobaltates, La0.7-xLnxCa0.3CoO3 (Ln = Pr, Nd, Gd and Dy) : A case of phase separation

Magnetic and electrical properties of four series of rare earth cobaltates of the formula La0.7-xLnxCa0.3CoO3 with Ln = Pr, Nd, Gd and Dy have been investigated. Compositions close to x = 0.0 contain large ferromagnetic clusters or domains, and show Brillouin-like behaviour of the field-cooled DC magnetization data with fairly high ferromagnetic Tc values, besides low electrical resistivities with near-zero temperature coefficients. The zero-field-cooled data generally show a non-monotonic behaviour with a peak at a temperatures slightly lower than Tc. The near x = 0.0 compositions show a prominent peak corresponding to the Tc in the AC-susceptibility data. The ferromagnetic Tc varies linearly with x or the average radius of the A-site cations, (rA). With increase in x or decrease in (rA), the magnetization value at any given temperature decreases markedly and the AC-susceptibility measurements show a prominent transition arising from small magnetic clusters with some characteristics of a spin-glass. Electrical resistivity increases with increase in x, showed a significant increase around a critical value of x or (rA), at which composition the small clusters also begin to dominate. These properties can be understood in terms of a phase separation scenario wherein large magnetic clusters give way to smaller ones with increase in x, with both types of clusters being present in certain compositions. The changes in magnetic and electrical properties occur parallely since the large ferromagnetic clusters are hole-rich and the small clusters are hole-poor. Variable-range hopping seems to occur at low temperatures in these cobaltates.Comment: 23 pages including figure

X-ray structural characterization of dicyclohexylammonium chloride and its conversion to bromo-, iodo- and hexafluorophosphate derivatives

47-4

Glassy behavior in the ferromagnetic and the non-magnetic insulating states of the rare earth manganates, Ln0.7Ba0.3MnO3 (Ln = Nd or Gd)

While La0.7Ba0.3MnO3 is a ferromagnetic metal (TC = 340 K) with longrange ordering, Nd0.7Ba0.3MnO3 shows a transition around 150 K with a small increase in magnetization, but remains an insulator at all temperatures. Gd0.7Ba0.3MnO3 is non-magnetic and insulating at all temperatures. Low field dc magnetization and ac susceptibility measurements reveal the presence of a transition at around 150 K in Nd0.7Ba0.3MnO3, and a complex behavior with different ordering/freezing transitions at 62, 46 and 36 K in the case of Gd0.7Ba0.3MnO3, the last one being more prominent. The nature of the field dependence of the magnetization, combined with the slow magnetic relaxation, ageing and memory effects, suggests that Nd0.7Ba0.3MnO3 is a cluster glass below 150 K, a situation similar to that found for La_{1-x}SrxCoO3. Gd0.7Ba0.3MnO3, however, shows non-equilibrium dynamics characteristic of spin glasses, below 36 K. The difference in nature of the glassy behavior between Gd0.7Ba0.3MnO3 and Nd0.7Ba0.3MnO3 probably arises because of the larger disorder arising from the mismatch between the sizes of the A-site cations in the former. Our results on Nd0.7Ba0.3MnO3 and Gd0.7Ba0.3MnO3 suggest that the magnetic insulating states often reported for rare earth manganates of the type Ln1-xAxMnO3 (Ln = rare earth, A = alkaline earth) are likely to be associated with glassy magnetic behavior.Comment: 20 pages including figure

Multiferroic nature of charge-ordered rare earth manganites

Charge-ordered rare earth manganites Nd0.5Ca0.5MnO3, La0.25Nd0.25Ca0.5MnO3, Pr0.7Ca0.3MnO3 and Pr0.6Ca0.4MnO3 are found to exhibit dielectric constant anomalies around the charge-ordering or the magnetic transition temperatures. Magnetic fields have a marked effect on the dielectric properties, indicating the presence of coupling between the magnetic and electrical order parameters. The observation of magnetoferroelectricity in these manganites is in accord with the recent theoretical predictions of Khomskii and coworkers

Cyclic sulphur-nitrogen compounds and phosphorus reagents: Part IV1-Reactions of phosphiniminocyclotrisulphurtrinitride, (R) Ph2PN-S3N3 (R = Phenyl- and morpholino-) with Ph3P and (OC4H8N) Ph2P: six-membered to eight-membered ring (6→8) conversions

450-453Triphenylphosphine (A) reacts slowly with Ph3PN-S3N3(I) both in CH3CN and C6H6 to produce the known disubstituted eight-membered heterocycle, 1,5-(Ph3PN)2S4N4(III). The recently reported 1,5-[(OC4H8N)Ph2PN]2S4N4 (IV) is obtained in better yield (ca. 70%) from the reaction between (OC4H8N)Ph2PN-S3N3(II) and (OC4H8N)Ph2P(B) in acetonitrile. However, reactions in benzene of (I) with (OC4H8N)Ph2P and of (II) with Ph3P afford an inseparable mixture of (III) and (IV). Reaction temperature appears to be critical in the e ring transformation reactions

Cyclic sulphur-nitrogen compounds and phosphorus reagents: Part XIII¹-Reactions of cyclic sulphur-nitrogen chlorides with Ph₃P-influences of tertiary base, Et₃N and the ring size of the cyclothiazyl chloride on the product formation

961-966Similar to the reactions with S4N3Cl and S3N3Cl3,triphenylphosphine reacts with five-membered cyclic sulphur-nitrogen chlorides namely, S3N2Cl and S3N2Cl2 to give triphenylphosphiniminium chloride, Ph3P=NHCl- as the major product. Maximum yield (ca. 90%) is obtained when triphenylphosphine is reacted with S3N2Cl in acetonitrile at room temperature in 2:1 molar ratio. Analogous reactions performed in presence of triethylamine afford two cyclothiazene products containing phosphinimino substituent. The ring size of the S-N chloride seems to determine the nature of phosphiniminocyclothiazenes formed. A rationalization of the results obtained has been attempted

Studies of phosphazenes-VII: reactions of hexabromocyclotriphosphazatirene, N<SUB>3</SUB>P<SUB>3</SUB>Br<SUB>6</SUB>, with ethylamine

The reaction of hexabromocyclotriphosphazene, N3P3Br6 with ethylamine yields the derivatives N3P3Br6-n(NHEt)n [n = 1, 2(two isomers), 4 and 6]. Two hydrogen bromide adducts, N3P3Br2(NHEt)4&#183;HBr and N3P3(NHEt)6&#183;HBr have also been isolated. The 1H NMR data indicate that the bis-derivatives have nongeminal structures whereas the tetrakis-compound possesses a geminal structure. For the hydrogen bromide adducts, infrared and 1H NMR spectroscopic data suggest that protonation occurs at a ring nitrogen atom. The halogen replacement pattern is very similar to that observed in the analogous reaction of hexachlorocyclotriphosphazene, N3P3Cl6

Cyclic S-N compounds and phosphorus reagents--Part XVIll¹: Synthesis and X-ray structural characterization of phosphiniminocyclotrithiazenes with a primary amino substituent

1052-1056First examples of phosphiniminocyclotrithiazenes containing a primary amino group, (Ph)(R)(iPrNH)PN-S3N3 [R=(i) Ph. I and (ii) DCA (dicyclohexylamino), II] have been isolated from room temperature reactions of S4N4. with the corresponding phosphine in acetonitrile. Single crystal X-ray structure of compounds I and II reveal very similar endocyclic structural features, but for the deviation of tricoordinate sulphur [S(l)] from the mean plane of the ring. The primary amino group [(CH3)2CHNH]binds equally strongly in I and II, but the N-H bonds show differences in both bond length and orientation with respect to the adjacent P-N bond. Heterocycles I and II show different sensitivities for ring conversion to cyclophosphathiazene