Showing papers by "Enrique J. Baran published in 2018"
Abstract: The term ‘organic minerals’ means naturally occurring crystalline organic compounds including metal salts of formic, acetic, citric, mellitic, methanesulfonic and oxalic acids. As for the rest of t...
14 citations
TL;DR: In this paper, a triclinic replica of Ca2(C2O4)Cl2·7H2O has been shown to have the same properties as the original Ca2C2C4.
Abstract: Synthetic novgorodovaite analog Ca2(C2O4)Cl2·2H2O is identical to its natural counterpart. It crystallizes in the monoclinic I2/m space group with a = 6.9352(3), b = 7.3800(4), c = 7.4426(3) A, β = 94.303(4)°, V = 379.85(3) A3 and Z = 2. The heptahydrate analog, Ca2(C2O4)Cl2·7H2O, crystallizes as triclinic twins in the P
$$\overline{1}$$
space group with a = 7.3928(8), b = 8.9925(4), c = 10.484(2) A, α = 84.070(7), β = 70.95(1), γ = 88.545(7)°, V = 655.3(1) A3 and Z = 2. The crystal packing of both calcium oxalate–chloride double salts favors the directional bonding of oxalate, C2O4
2−, ligands to calcium ions as do other related calcium oxalate minerals. The π-bonding between C and O atoms of the C2O4
2− oxalate group leaves sp
2-hydridised orbitals of the oxygen atoms available for bonding to Ca. Thus, the Ca–O bonds in both calcium oxalate–chloride double salts are directed so as to lie in the plane of the oxalate group. This behavior is reinforced by the short O···O distances between the oxygens attached to a given carbon atom, which favors them bonding to a shared Ca atom in bidentate fashion. Strong bonding in the plane of the oxalate anion and wide spacing perpendicular to that plane due to repulsion between oxalate π-electron clouds gives rise to a polymerized structural units which are common to both hydrates, explaining the nearly equal cell constants ~7.4 A which are defined by the periodicity of Ca-oxalate chains in the framework (monoclinic b ≈ triclinic a). When compared with novgorodovaite, the higher water content of Ca2(C2O4)Cl2·7H2O leads to some major differences in their structures and ensuing physical properties. While novgorodovaite has a three-dimensional framework structure, in the higher hydrate, the highly polar water molecules displace chloride ions from the calcium coordination sphere and surround them through OwH···Cl hydrogen bonds. As a result, polymerization in Ca2(C2O4)Cl2·7H2O solid is limited to the formation of two-dimensional Ca2(C2O4)(H2O)5 slabs parallel to (001), inter-layered with hydrated chloride anions. This layered structure accounts for (001) being both a perfect cleavage and a twin interface plane. The infrared and Raman spectra of both salts are also briefly discussed.
4 citations
TL;DR: Baran et al. as discussed by the authors presented the Centro de Quimica Inorganica "Dr. Pedro J. Aymonino". Universidad Nacional de La Plata.
Abstract: Fil: Baran, Enrique Jose. Facultad de Ciencias Exactas, Universidad Nacional de la Plata; Argentina. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnologico Conicet - La Plata. Centro de Quimica Inorganica "Dr. Pedro J. Aymonino". Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Centro de Quimica Inorganica "Dr. Pedro J. Aymonino"; Argentina
2 citations
TL;DR: The phenomenon of spontaneous resolution of enantiomers occurs during the crystallization of the sodium and rubidium double salts of the transition metal complex tris(oxalato)ferrate(III).
Abstract: We show here that the phenomenon of spontaneous resolution of enantiomers occurs during the crystallization of the sodium and rubidium double salts of the transition metal complex tris(oxalato)ferrate(III), namely sodium pentarubidium bis[tris(oxalato)ferrate(III)], NaRb5[Fe(C2O4)3]2. One enantiomer of the salt crystallizes in the cubic space group P4332 with Z = 4 and a Flack absolute structure parameter x = −0.01 (1) and its chiral counterpart in the space group P4132 with x = −0.00 (1). All metal ions are at crystallographic special positions: the iron(III) ion is on a threefold axis, coordinated by three oxalate dianions in a propeller-like conformation. One of the two independent rubidium ions is on a twofold axis in an eightfold coordination with neighbouring oxalate oxygen atoms, and the other one on a threefold axis in a sixfold RbO6 coordination. The sodium ion is at a site of D3 point group symmetry in a trigonal–antiprismatic NaO6 coordination.