Structural Model for Benzidine-Vermiculite

Self Cite

Abstract--If anilinium ions are intercalated into Llano vermiculite, the stacking order of adjacent silicate layers is increased, resulting in a relatively sharp single crystal X-ray diffraction (XRD) pattern. The packing of intercalated organic members forms a superstructure and produces bonding from layer to layer which favors the stacking order. Superlattice reflections occur which, although sharp in the a'b* plane, are streaked along c*. Apparently there is little coherence between adjacent layers of ordered organic units.A three-dimensional set of XRD reflections for a triclinic sub-cell having the following lattice parameters was measured: a = 5.326(3), b = 9.264(4), c = 14.82(5) A, a = 90.31(7),/3 = 96.70(6), and 3' = 89.55(5) ~ In this unit cell (symmetry C1), ditrigonal cavities in adjacent silicate layers are approximately opposite. Differential Fourier analyses and least-squares refinements showed that the principal axes of the anilinium ions, i.e., N-C(1)-C(4), are nearly perpendicular to the silicate layers. The planes of the aromatic rings, however, are about +_ 30 ~ to X, neither parallel nor perpendicular to that direction, as indicated by earlier studies.Inorganic cations and water molecules are also present in the interlayer; the former and some of the latter occupy sites near the middle of the layer. Anilinium-rich and anilinium-poor domains coexist. In the latter, the cation-water system predominates and apparently conforms to the superstructure. Although the cation-water structure could not be uniquely established from the reflections produced by the subcell, possible positional coordinates were obtained. From structural data for the silicate layers, no evidence was found for long-range Si/A1 ordering in the tetrahedral sites.

Section: Discussionsupporting

confidence: 65%

Section: Superstructuresupporting

confidence: 72%

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Crystal Structure of a Vermiculite-Anilinium Intercalate

Slade

Dean

Schultz

et al. 1987

Self Cite

“…The molecules were probably aligned nearly "vertically" on the surface, thereby permitting overlap between a--orbitals of the electron donor (diamine) and acceptor (diimine) as shown in Figure 6b. A similar complex between benzidine and vermiculite at high adsorption levels has been described (Slade and Raupach, 1982). The charge-transfer complex was oxidized to the same degree as the radical monomer, and involved an association of the 2-electron oxidation product (diimine) and the unoxidized diamine.…”

Section: S U M M a R Y A N D Conclusionmentioning

confidence: 67%

Surface Reactions of 3,3′,5,5′-Tetramethyl Benzidine on Hectorite

McBride

1985

Abstract--The adsorption and oxidation of 3,3',5,5'-tetramethyl benzidine (TMB) on hectorite has been investigated using X-ray powder diffraction, ultraviolet-visible spectroscopy, electron spin resonance, and infrared spectroscopy. The molecule adsorbed by cation exchange at low adsorption levels and oxidized to the monomeric radical cation (yellow). At higher adsorption levels, intercalation of TMB occurred in amounts greater than the cation-exchange capacity of the hectorite, and the ~r-~r charge-transfer complex (blue) became much more evident. The TMB monomers appeared to lie fiat in the layer silicate interlayers, whereas the molecules in the charge-transfer complexes assumed a near-vertical orientation relative to the surface. The oxidation of adsorbed TMB was probably due to diffusion of O2 to the surface, because the structural Fe 3+ content of the hectorite was too low to facilitate a significant quantity of direct Fe 3+-TMB electron transfer.

“…The Phalaborwa vermiculite also has Fe in octahedral sites. Slade and Raupach (1982) reported that the intercalation of vermiculite by benzidinium ions at pH 1.6 produces a well-ordered intercalate having a basal spacing of 19.25 ~. More recently unpublished work by one of us (P.G.S.)…”

Section: Introductionmentioning

confidence: 96%

Structural Study of a Benzidine-Vermiculite Intercalate Having a High Tetrahedral-Iron Content by ⁵⁷Fe Mössbauer Spectroscopy

Cardile

Slade

1987

Abstract-57Fe Mrssbauer spectra obtained at room temperature and 78 K for natural Mg-saturated, Casaturated, and benzidinium-intercalated vermiculite having a high tetrahedral iron content are presented. For all samples the spectra were computer-fitted with five overlapping doublets, representing Fe in both tetrahedral and octahedral sites. One doublet has parameters consistent with the weathered ilmenite known to be present as inclusions. For the intercalated vermiculite, the 6 value of the doublet assigned to the tetrahedral Fe 3+ increased with respect to the untreated sample, suggesting that the electron densities about the Fe sites had decreased following intercalation. A charge movement from the silicate layers towards the interlayer monovalent benzidinium ions is also implied. The direction of this charge movement is opposite to that found when blue monopositive radical cations form on montmorillonite surfaces. The M6ssbauer evidence suggests the absence of an interlayer-Fe 3 § complex.