KAIP207 crystallizes as monoclinic crystals with a = 7. 308(8), b = 9.662(6), c = 8.025(4) A, = 106.69(7)", z = 4 and space group P2Jc. The structure was refined from 1394 observed reflections by fullmatrix least-squares method to a final R value of 0.032. The P2074-anion consists of a pair of cornersharing PO4 groups in a nearly staggered configuration. The mean bridging and terminal P-0 bond lengths are 1.607 and 1.509 A, respectively, and the P-0-P angle is 123.2". The anions lie in planes parallel to (001). The A1 ions are bonded to six oxygen atoms contributed by anions in three layers of P 2 0 7 groups. The average AI-0 bond length is 1.889 A. The potassium ion is coordinated to ten oxygen atoms lying within a spherical shell with inner and outer radii of 2.739 and 3.185 A. Can.
HOK NAM NG and CRISPIN CALVO. Can. J. Chem. 53,2064(1975. The structure of ferric phosphate at room temperature was refined on a Dauphine-twinned crystal using full-matrix least-squares methods. The final R value was 0.078 for 487 symmetry-independent reflections whose intensities were corrected for twinning. The structure was found to be isotypic with AlP04 (berlinite) with the space group P3121 and four formula units in a unit cell defined by a = 5.036(2) and c = 11.255(4) A. The structure is also closely related to that of a-quartz with a nearly doubled c-axis because of the ordering of Fe and P atoms.The PO4 tetrahedron is almost regular with a mean P-0 distance of 1.526 A. The Fe3+ ion is tetrahedrally coordinated with an average Fe-0 distance of 1.853 A. HOK NAM NG et CRISPIN CALVO. Can. J. Chem. 53,2064 (1975. On a raffine la structure du phosphate ferrique tel qu'il existe ? I la temperature de la pibce en appliquant la methode des moindres carres (matrice complbte) a un cristal Dauphine mlcl6.La valeur finale R est de 0.078 pour 487 reflexions de symetrie independantes dont l'intensite a kt6 corrigee pour le mlclage. On a trouve que la structure est isostructurale avec celle de A1Po4 (berlinite) avec un groupe d'espace P3121 et quatre molecules par maille dkfinie par a = 5.036(2) et c = 11.255(4) A. Cette structure ressemble beaucoup ? I celle de quartz a ; l'axe c est toutefois le double a cause de l'alignement des atomes de Fe et de P. Le tktrabdre PO4 est pratiquement regulier avec une distance P-0 de 1.526 A. L'ion Fe3+ est coordonne tetraedriquement avec une distance moyenne de 1.853 A.[Traduit par le journal]
MgV2O6 crystallizes in the monoclinic space group C2/m with lattice parameters a = 9.279(7), b = 3.502(2), c = 6.731(6) Å and β = 111.77(6)° with Z = 2. The structure was refined, at room temperature, utilizing 593 symmetry independent reflections, by full matrix least squares to a final R value of 0.032. The structure consists of Mg2+ lying at a site of 2/m symmetry octahedrally coordinated to oxygen atoms with a mean separation of 2.140 Å. All the remaining atoms lie in crystallographic mirror planes with the V ion coordinated to six oxygen atoms with bond distances ranging from 1.666 to 2.671 Å. The spin Hamiltonian parameters for Mn2+ were determined at room temperature and again at liquid N2 temperatures. As these values are invariant with temperature there is no indication of a phase transformation in Mg(VO3)2 to a lower symmetry space group. The spin Hamiltonian parameters are gx = 2.0042, gy = 2.0090, gz = 2.0005; D = −459 G, E = 65 G, and A = −78 G with one of the principal axes, X, parallel to the b-axis and the Z-axis at an angle of 5° to the c-axis.
HOK NAM NG and CRISPIN CALVO. Can. J. Chem. 53,1449Chem. 53, (1975. The room temperature structure of Cd2(NH4),(S04), (CAS), isotypic with the mineral langbeinite K2Mg2(S04), has been refined by full-matrix least squares methods. The structure is cubic with a = 10.362(7) A and space group P&3. There are two inequivalent sites for the cation Cd2+ and e.p.r. spectra of doped Mn2+ show that Cd2+ was substituted in both sites with preferential occupancy by Mn2+ in a 1 : 3 ratio. Refinement of X-ray data on a mixed crystal of the stoichiometry Cdo.s4Mnl.16(NH4)2(S04)3 shows that site I contains 82% Mn2+ while site I1 has 38%. The zero-field splitting parameter D was calculated for Mn2+ in two sites using a point-charge model and confirms that Mn2+ substitutes into site I with greater preference. Although a monoclinic ferroelectric phase of CAS has been suggested below 90 K, no change in space group symmetry could be detected at 80 K. The proton second moment, calculated by the van Vleck's formula, and compared with the experimental values, suggests a tunneling motion of the protons among the four vertices of the ammonium tetrahedron.HOK NAM NG et CRISPIN CALVO. Can. J. Chem. 53, 1449Chem. 53, (1975. La structure, telle qu'elle existe la temperature ambiante, de Cd2(NH4)2(S04)3 (CAS), isostructural du minkral langbeinite K2Mg2(S04),, a kt6 affinke par moindres carrks (matrice complete). La structure est cubique avec a = 10.362(7) i % et appartient au groupe d'espace Pz13. Le cation Cd2+ occupe deux sites non-kquivalents; le spectre r.p.e. du composk additionnk de traces de Mn2+ montre que Cd2+ est substituk dans les deux sites par Mn2+ avec une occupation prkfkrentielle dans le rapport de 1 : 3. L'affinement des donnks de rayons-X d'un cristal mixte de stoichiomktrie Cdo.84Mnl.16(NH4)2(S04)3 montre que le site I contient 82% de Mn2+ alors que le site I1 n'en contient que 38x. Le parametre de couplage D a champ nu1 a kt6 calculk pour Mn2+ dans chacun des sites utilisant un modele de charge ponctuelle et confirme que Mn2+ se substitue dans le site I avec une prkfkrence plus grande. Quoiqu'il a kt6 suggkrk que le CAS existe dans une phase monoclinique ferroklectrique a des temperatures infkrieures a 90 K, on n'a pas pu dktecter de changement de groupe d'espace a 80 K. Le "moment secondaire du proton", calculk par la formule de van Vleck et compare avec les valeurs expkrimentales, suggere un mouvement du i un effet tunnel des protons parmi les quatre sommets du tktraedre de I'ammonium.[Traduit par le journal]
Die Strukturverfeinerung wird an einem Dauphineer Zwillingskristall mit Hilfe eines Fehlerquadratprogramms durchgeführt.
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