Crispin Calvo

The crystal structure of Ba2V2O7

Abstract Ba2V2O7 is triclinic with a = 13.571(3), b = 7.320(2), c = 7.306(2) A, α = 90.09(1), β = 99.48(1), β = 99.48(1), γ = 87.32(1)°, V = 7.15.1 A3, Z = 4, and space group P 1 . The crystal structure was solved by Patterson and Fourier methods and refined by full-matrix least-squares analysis to a Rw of 0.034 (R = 0.034) using 2484 reflections measured on a Syntex P 1 automatic four-circle diffractometer. The structure has two unique divanadate groups that are repeated by the b and c lattice translations to form sheets of divanadate groups parallel to (100). These sheets are linked by four unique Ba atoms that lie between these sheets. Ba(1) and Ba(3) are coordinated by eight oxygens arranged in a distorted biaugmented triangular prism and a distorted cubic antiprism, respectively. Ba(2) is coordinated by 10 oxygens arranged in a distorted gyroelongated square dipyramid and Ba(4) is coordinated by nine oxygens arranged in a distorted triaugmented triangular prism. These coordination numbers are substantiated by a bond strength analysis of the structure, and the variation in 〈BaO〉 distances is compatible with the assigned cation and anion coordination numbers. Both divanadate groups are in the eclipsed configuraton with 〈VO(br)〉 bond lengths of 1.821(4) and 1.824(4) A and VO(br)V angles of 125.6(3) and 123.7(3)°, respectively. Examination of the divanadate groups in a series of structures allows certain generalizations to be made. Longer 〈VO(br)〉 bond lengths are generally associated with smaller VO(br)V angles. When VO(br)V 140°, the divanadate group is generally in a staggered configuration. Nontetrahedral cations with large coordination numbers require more oxygens with which to bond, and hence O(br) is more likely to be three coordinate, with the divanadate group in the eclipsed configuration. In the eclipsed configuration, decrease in VO(br)V promotes bonding between O(br) and nontetrahedral cations, and hence smaller nontetrahedral cations are generally associated with smaller VO(br)V angles.

Crystallographic studies on cation substitutions in the system (Na,K) (V,P)O3

Abstract Three compounds in the system (Na,K) (V,P)O3 were synthesized and their structures were refined by full matrix least squares method in the space group C2 c . Their compositions were shown by site population analysis to be Na(V0.66P0.34)O3 (I), (Na0.88K0.12)VO3 (II), and (Na0.5K0.5)VO3 (III). All are related to the structure of α-NaVO3 which in turn is related to the clinopyroxene structure characterized by infinite chains of SiO4 tetrahedra sharing vertices and two inequivalent metal cation sites M1 and M2. Both sites feature sixfold coordination in compounds I and II, while the Na and K are ordered into M1 and M2 sites, respectively in III, with the latter showing eightfold coordination. The pentavalent cations are randomly distributed in tetrahedral sites in I, and in II the K was found to occupy the M2 sites only. Changes in the α-NaVO3 structure upon cation substitution are discussed in terms of rotation and displacement of the tetrahedral chains. Parameters for measuring these chain movements are proposed and found to exhibit an almost linear relationship with the ratio 〈X−0〉 〈M2−0〉 in cases where the M1 site is exclusively occupied by Na.

Crystallographic studies and structural systematics of the C2c alkali metal metavanadates

Four compounds in the system (Li, Na)VO3 were synthesized and their structures refined in the space group C2c. Site population analysis showed that their compositions are (Na0.5Li0.5)VO3, (Na0.62Li0.38)VO3, (Na0.71Li0.29)VO3 and (Na0.84Li0.16)VO3. All have the structure of LiVO3 and α-NaVO3 which are related to the C2c silicate pyroxenes. Structural data of eight compounds in the system (K, Na, Li)VO3 were compiled, and correlations were established by multiple regression analyses between the effective ionic radii rM1 and rM2 of the alkali metal ions and various structural parameters. The size of the M2 site and the relative displacement of the (VO3)∞ chains are found to depend primarily on rM2 only. The size of the M1 site and the amount of chain rotation are affected by both rM1 and rM2. Changes in lattice parameters are related to the chain movements. The anomalous chain configuration of LiVO3 is also discussed.

Linear metaborate anions, BO2–, in apatitic phosphates

Crystals, apatite-like in structure, with composition M9+yNax(PO4)6Bx+2yO2(M = Ca or Sr) have been obtained by the direct reaction of M3P2O8 and Na2B4O7; these crystals contain O–B–O groupings with the B atom on an inversion centre and with B–O bond lengths of 1·25 ± 0·02 A;.

Structure of [Pd{C5(CO2Me)4(CO2Me)C(CO2Me)Cl}{acac}] and the intermediacy of a σ-butadienyl complex in the PdII-induced trimerisation of dimethyl acetylenedicarboxylate

The structure of the complex, [[graphic omitted] C(CO2Me)Cl}Cl]2, obtained from reaction of dimethyl acetylenedicarboxylate (dma) and Pd(PhCN)2Cl2, has been established spectroscopically and confirmed by X-ray analysis of the acetylacetonate; such complexes were also obtained by reaction of a σ-butadienyl complex with dma.

Acetylenes and noble metal compounds. Part XII. Reactions of dimethyl acetylenedicarboxylate with palladium(II) chloride and the structure of {[chloro(methoxycarbonyl)(1,2,3,4,5-pentakismethoxycarbonylcyclopenta-2,4-dienyl)-2-MeOCO]methyl}(pentane-2,4-dionato)palladium(II)

The structure of the complex [LPd(µ-Cl)2PdL][I; L =–CCl(CO2Me)·C5(CO2Me)4C(OMe):O–], obtained from cyclotrimerisation of dimethyl acetylenedicarboxylate with PdCl2, has been determined spectroscopically and with the aid of X-ray structure analysis of [PdL(acac)](IV; acac = pentane-2,4-dionato). The organic ligand contains pentakis(methoxycarbonyl)cyclopenta-2,4-diene bearing a –C(CO2Me)(Cl)Pd substituent at C(1). Two further co-ordination sites of the square-planar Pd atom are occupied by acac and the remaining one by the ester carbonyl group [O(2a)] attached to C(2). This interaction forms a non-planar six-membered ring. The bond lengths Pd–C(6)[2·038(14)], Pd–O(2a)[2·052(10)], and the Pd–acac lengths Pd–O(7)[1·995(10)] and Pd–O(9)[2·024(11)A], are normal. Thermal or aqueous-cyanide decomposition of complex (I) affords hexamethyl mellitate. Analogues of (IV) and (I), such as [XIII; L′=–CBr(CO2Me)·C5(CO2Me)4C(OMe):O–] and [L″Pd-(µ-Br)2PdL″][XIIb; L″=–CBr(CO2Me)·C5(CO2Me)2(CF3)2C(OMe):O–]. have been obtained by reaction of the σ-buta-1,3-dienyl complex [Pd{C4(CO2Me)4Br}Br]n(IX) with dimethyl acetylenedicarboxylate and hexafluorobut-2-yne respectively. Reaction of complex (XIIb) with aqueous cyanide gives 1,2,3,4-tetrakis-(methoxycarbonyl)-5,6-bis (trifluoromethyl)benzene. The structures of some degradation products from complex (I) have been reformulated as 1 -substituted pentakis(methoxycarbonyl)cyclopenta-2,4-dienes C5(CO2Me)5·C(CO2Me)(Cl)X (X = H, Cl, or Br).