Mean Si Research Articles

NMR of albite–microcline series

The chemical bonding in silicates has been studied experimentally and theoretically1. Spinning at 54.72° yields sharp peaks in NMR patterns for 29Si and 27Al (refs 2, 3). Qualitative interpretation of the isotropic chemical shift is useful, but the interrelated effects of framework geometry, cation substitution and hydrogen bonding must be quantified for zeolites. The isotropic chemical shift for 29Si in silica polymorphs is related to the mean secant of adjacent Si–O…Si angles4, and the complex NMR patterns of tridymite and uncalcined fluoride silicalite have been interpreted quantitatively (see also refs 5, 6). In some zeolites7, the average Si–O–T (tetrahedral) angle is correlated with the isotropic chemical shift for 29Si. The proposed relationships8,9 between mean Si–O distance and the isotropic chemical shift for 29Si are poorly obeyed by silica polymorphs4, and the cation-oxygen bond strength provides a better correlation than Si–O for a wide range of silicates10. We show here that the mean secant Si–O–T provides a better guide than Si–O and bond strength for Na,K-feldspars in the series between low albite and low microcline.

Functional measurement scales of painful electric shocks.

Subjects were required to rate the combined intensities of two factorially paired shocks ranging in intensity from 1 mA through 2, 3, 4, and 5 mA. In Experiment 1, an anchored 1–20-point rating scale was used, and in Experiment 2, one of two scales, 1–15 points or 1–25 points, was provided to the subject. Data from all three conditions were fit by a weighted average model, Rij=wsi+(i−w)sj, where Rijs are mean ratings, si and sj are scale values of the first and second shocks, and w is a weight parameter. The derived psychophysical functions were linear in all three cases, and the slope increases with the number of available categories, in conformity to range-frequency theory. In a third experiment, subjects were divided according to the ratings they gave of pain elicited by the 5-mA shock. The weighted averaging model provided an appropriate integration model for both higher and lower pain raters. Higher raters tended to accord an equal weight to both shocks, whereas lower raters accorded greater weight to the second stimulus. Implications for research on analgesic procedures are discussed.

Calcium hydroxide distribution and calcium silicate hydrate composition in tricalcium silicate and β-dicalcium silicate pastes

Pastes of tricalcium silicate (C 3S) and β-dicalcium silicate (C 2S) 23 years old were studied by electron probe microanalysis. In both cases, regions consisting entirely or largely of calcium hydroxide and of CSH were distinguished on a scale of 2–50 μm. The regions high in CSH accounted for 75–80 percent of the whole in the C 3S paste and about 96 percent in the C 2S paste; these values are much higher than those initially occupied by anhydrous starting materials. Within the high CSH areas, no compositional variation was detected that could have corresponded to the so-called inner and outer hydrates. The ratio of mean Ca to mean Si in the high CSH areas was found to be 1.72 for the C 3S paste and 1.78 for the C 2S paste with an exciting beam energy of 10 keV.

The crystal structure of decaphenyl-1-oxacyclohexasilane·0.5 C 6H 6 solvate

The crystal structure of decaphenyl-1-oxacyclohexasilane·0.5 C 6H 6 solvate is reported. This is the first crystal structure determination for an example of the little known class of polycyclohexasilanes containing a heteroatom. The conformation of the molecule is close to the 1,4-boat form with the oxygen and a silicon atom on the same side of the least-squares plane of the remaining atoms. Two types of SiSi bonds were found, related by the mirror-symmetry of the ring, with mean bond lengths of 2.391(1) [(O)SiSi(Si)] and 2.373(2) Å [(Si)SiSi(Si)]. The SiOSi valence angle is 146.0(5)° and the mean SiC bond distance 1.877(3) Å.

Novel inorganic ring systems: XXXIX. A dimeric cycloalumadisilatriazane

The first cycloalumadisilatriazane system, [ClAl(NMeSiMe 2) 2NMe] 2 ( C1), has been prepared. IR and Raman spectra are reported. The molar weight of C1 in benzene and 1H, 13C, 27Al and 29Si NMR spectra are consistent with a nitrogen-bridged dimer which is stereochemically rigid on the NMR time scale near room temperature. Mass spectral evidence is also presented for the dimeric nature of C1 in the gas phase. C1 crystallizes in the triclinic space group P 1 with a 8.2262(7) Å, b 9.5147(7) Å, c 10.2552(b) Å, α 102.655(5)°, β 97.448(5)°, γ 112.088(6)° and Z = 1. The structure was refined to an R value of 0.0303 for 2487 counter-measured, observed X-ray data. The mean AlN bridging distance (1.947(8) Å) in the centrosymmetric (AlN) 2 ring is much longer than the AlN(cn3) bond (cn = coordination number), 1.803(2) Å. A smaller dependence on nitrogen valency was found for the SiN bond lengths; thus the SiN(cn 4) and mean SiN(cn 3) are 1.798(2) and 1.726(14) Å, respectively.

Refinement of a partially disordered natrolite, Na2Al2Si3O10· 2H2O

AbstractThe structure of natrolite from Zeilberg, Oberfranken, Germany, Na2Al2Si3O10· 2H2O, is orthorhombic with space groupFdd2,a= 18.319(4),b= 18.595(4),c= 6.597(1) Å,Z= 8 andDx= 2.22g cm−3, and was refined toR(unweighted) = 0.032 andR(weighted) = 0.025 using 1661 non-equivalent reflections. The structure contains [SiO4]tetrahedra (mean Si – O distance 1.629 Å), [AlO4]tetrahedra (mean Al – O distance 1.723 Å), and [NaO6]-polyhedra (mean Na – O distance 2.444 Å), and shows a partial Si/Al disorder of about 30% in all the tetrahedral sites.

Synthesis and the crystal structure of a manganoan fluoromica, K(Mg2.44Mn0.24)Si3.82Mn0.18)O10F2.

Synthesis of a manganoan fluoromica KMg3(Si3.5Mn0.5)O10F2 with Mn in fourfold coordination was tried, utilizing mixtures of KF, MgF2, MgO, SiO2 and MnC2O4 for the starting materials. Mica crystals were obtained below 1150°C after crystallization of manganoan chondrodite (Mg, Mn)5Si2O8(OH, F)2. The X-ray structure analysis revealed that the crystal has a structure of the 1 M mica with cell dimensions of a=5.285(1), b=9.157(1), c=10.190(2)A and β=99.97(2)°, and a chemical composition corresponding to K(Mg2.44Mn0.24)(Si3.82Mn0.18)O10F2. The structure refinement was carried out with the full-matrix least-squares procedure to the final R value of 0.043 for 1131 observed reflections. The (Si, Mn)–Oapical distance is 1.616A and the mean (Si, Mn)–Obasal distance is 1.638A. The mean (Si, Mn)–O distance of 1.632A is longer than the literature value of 1.625A for the mean Si–O distance in the SiO4 tetrahedra by 0.007A, supporting the conclusion that Mn atoms substituted a part of Si4+ ions at the tetrahedral sites in the present experiment. The mean octahedral cation-anion distances are 2.071A for M(1) octahedra and 2.070A for M(2). The tetrahedral rotation angle is 1.73°, and the octahedral flattening angles are 58.4° for M(1) octahedra and 58.3° for M(2).

The crystal structure of a cyclo-silazoxane, [(Me 2Si) 2ONC 6F 5] 2

Crystals of the silazoxane, [(Me 2Si) 2ONC 6F 5] 2 are triclinic with a 8.703(4), b 14.334(6), c 13.021(6) Å, α 102.05(3), β 107.43(4) and γ 105.83(4)°, space group P 1 , Z = 2. The asymmetric unit consists of two half molecules, each of which lies on a centre of symmetry. Each of the rings has a chair conformation with mean Si—N and Si—O distances of 1.747 and 1.623 Å respectively; the endocyclic angles at the silicon atoms in the asymmetric unit are different (mean values 109.6 and 106.3°) and the ring angles at oxygen and nitrogen have mean values of 147.7 and 123.2° respectively.

1388 THE INFLUENCE OF FREE FATTY ACIDS (FFA) AND GLUCOSE INFUSION (GI) ON SERUM BILIRUBIN (BIL) AND BILIRUBIN BINDING TO ALBUMIN

This report describes the risk incidence of a large group (N= 1271) of jaundiced neonates to bil toxicity through measurement of serum albumin saturation by salicylate displacement (saturation index or SI) and the role of FFA and GI in this problem. RESULTS: 12 jaundiced neonates (bil=13.9 mg/dl) with high SI (7.8±0.6%), history of poor oral intake but no hemolytic disease nor drug exposure were treated with GI at a rate of lg/kg/h for 1-2 h. After GI, there was a significant (p<0.01) fall in SI (Δ= -4.1%), bil (Δ= -0.9 mg/dl), FFA (Δ= -0.48 mEq/L) principally oleic (Δ= -6.5%) and linoleic (Δ= -3.2%) acids and a rise in serum insulin (Δ= +17.8 mcu/ml, p<0.005). These changes were not due to simple dilution since serum total protein did not significantly fall (Δ= -0.2 g/dl, p<0.10). Routine SI measured in 1271 infants with bil ≥ 10 mg/dl showed 154 (12%) infants to have SI (> 7%): 50% were fullterm, only 24% had hemolytic disease and none had exposure to drugs. GI was given to 82 of these infants (mean bil=14.7 mg/dl; mean SI=8.0%). After GI, there was a significant (p<0.01) fall in bil (Δ= -1.2 mg/dl) and SI (Δ= -3.7%) in 76/82 (93%) infants treated. No rebound to high SI occurred within 24 h after GI. CONCLUSION: Our study indicates that by routine testing, a high percentage (12%) of infants with bil ≥ 10 mgs% are at or near risk to bilirubin toxicity as indicated by a SI ≥ 7%. These infants should be identified since treatment with GI is simple and highly effective in lowering both bil and SI probably through a mechanism of insulin release. The favorable response in most cases to GI indicates that serum FFA, particularly oleic and linoleic acids, play a major role clinically in bil binding to albumin.

Crystal and molecular structure of 5-ethyl-5,10-dihydrido-10,10-diphenylphenazasiline

The structure of 5-ethyl-5,10-dihydro-10,10-diphenylphenazasiline has been determined from three-dimensional X-ray data collected by counter methods. The compound in the monoclinic space group P2 1/ b with a 10.782(5), b 22.642(9), c 8.830(4) Å and γ 74°41′(2). The observed and calculated densities ( Z = 4) are 1.22 and 1.21 g cm -3, respectively. Anisotropic(Si, N, C)-isotropic block-diagonal least squares refinement gave a conventional R factor of 3.9% for 1871 reflections with I>2σ(I). The central six-membered ring of the tricyclic system adopts a boat conformation; the dihedral angle between the benzo-group planes is 157.3°. The CSiC angle in the heterocycle is 101.1(1)°; the mean SiC bond length is 1.850(2) Å (in the cycle) and 1.862(2) Å (with Ph group). The nitrogen atom is displaced 0.05 Å from the plane of the adjacent carbon atoms; the sum of the angle about N is 359.7°.

Cirrhotic hyperglobulinemia

We have measured immunoglobulin (Ig) synthesis by circulating lymphoid cells of 20 patients with cirrhotic hyperglobulinemia (CH) and 20 age-matched controls. We used specific anti-Ig antisera to precipitate Ig synthesized from [14C] amino acid precursors in 13 controls and employed an electroimmunoassay of the "rocket" type to measure Ig elaborated by cultured cells in 4 patient-control pairs. In addition, we studied 3 patient-control pairs by absorption of elaborated Ig onto an anti-Ig-coated solid phase, bromoacetylcellulose. The synthetic index (SI; the ratio of Ig synthesis by a CH patient and a control) was elevated in every case. Mean SI by coprecipitation was 7.2 +/- 5.4 (mean +/- SD), by rocket" 7.3 +/- 3.0 for IgG and 2.2 +/- 0.8 for IgA, and by immunoabsorption 13.8 +/- 8.4 for IgG. Three cirrhotic nonhyperglobulinemic patient-control pairs showed a mean SI of 1.0 +/- 0.1. CH and control populations showed equal numbers of membrane Ig-positive B lymphocytes by immunofluorescence. We conclude that (1) peripheral blood lymphoid cells are appropriate for study of differences in Ig synthetic capacity among individuals; (2) CH is associated with increased in vitro Ig synthesis; and (3) CH lymphocytes may be an appropriate cell population for the study of control mechanisms in Ig synthesis.

The crystal and molecular structure of the molybdenum tetracarbonyl complex of 1,4-diphenyl-2,2′,3,3′5,5′,6,6′-octamethylcyclo-1,4- diphospha-2,3,5,6-tetrasilahexane

The crystal and molecular structure of the molybdenum tetracarbonyl complex of 1,4-diphenyl-2,2′,3,3′,5,5′,6,6′-octamethylcyclo-1,4-diphosph a-2,3,5,6-tetrasilahexane, (PhPSi2Me4)2Mo(CO)4, has been determined by single crystal X-ray diffraction. The crystals are monoclinic, space group P21/n, with a = 15.983(5), b = 19.316(6), c = 10.580(3) Å, β = 99.99(2)° V = 3217(2) Å3, Z = 4, and ρcalcd = 1.356 g/cm3. The structure was solved by Patterson heavy atom methods and was refined by full-matrix least-squares procedures to a final R1 of 3.3% and R2 of 4.3%, for 6342 reflections with intensities greater than 2σ. The coordination of the boat-shaped (PhPSi2Me4)2 ligand to molybdenum tetracarbonyl produces a distorted octahedral environment about the metal. The mean Si—Si (2.358(14) Å) and P—Si (2.275(19) Å) distances are not greatly altered from the values found for them in the free ligand. The structural consequences of P → Si π-bonding in the latter are therefore minimal. The relatively long P—Mo (mean length 2.592(13) Å) distances are interpreted as the result of reduced back-bonding from the metal, caused by the presence of the relatively electropositive silyl groups on phosphorus. Consistently, the equatorial Mo—C bonds, which are trans to the diphosphine ligand, are shorter (mean length 1.968(19) Å) than the corresponding bonds to the axial carbonyl groups (mean length 2.021(15) Å).

Synthese et etude structurale d'un nouveau compose du silicium: di-2,2′-bipyridine silicium

Low pressure sublimation of tri-2,2′-bipyridinesilicon(0) leads to di-2,2′-bipyridinesilicon crystals. The unit cell is orthorhombic, space group Pbca, a 21.509, b 15.995, c 10.127 », Z = 8. The crystal structure was solved using 490 reflexions recorded at room temperature and refined down to a reliability index R = 0.046. The silicon atom is surrounded tetrahedrally by the bidentate 2,2′-bipyridine ligand with a mean NSiN angle of 100° and a mean SiN bond length of 1.72 ».

Variation of mean Si–O bond lengths in silicon–oxygen tetrahedra

Variation of mean Si–O bond lengths in silicon–oxygen tetrahedra

Variation of mean SiO bond lengths in silicon-oxygen octahedra

The mean bond length SiO in silicon-oxygen octahedra is a function of the mean coordination number of the oxygen atoms ( CN) in the octahedron: (SiO) mean = 1.729 + 0.013 CN. The radius of Si in six coordination against oxygen is 0.407 Å.

The structures of 5-methyl-5-phenyl-5 H-dibenzo[ b,f] silepin and its saturated analog

The structures of 5-methyl-5-phenyl-5 H-dibenzo[ b,f] silepin (I) and 5-methyl- 5-phenyl-1O,11-dihydro-5 H-dibenzo [ b,f] silepin (II) have been determined from three-dimensional X-ray data collected by counter methods. I crystallizes in the orthorhombic space group Pnam with a 7.596(3), b 18.102(5) and c 12.190(2) Å; observed and calculated densities ( Z = 4) are 1.17 and 1.18 g cm −3, respectively. II crystallizes in the monoclinic space group P2 1 c with a 11.115(3), b 7.920(3), c 20.765(5) Å and β 111.71(2)°; observed and calculated densities ( Z = 4) are 1.17 g cm −3. Anisotropic refinement of nonhydrogen atoms, with hydrogen atoms included at fixed ideal locations, gave conventional R-factors of 4.5% (I) and 5.0% (II). Compound I exhibits the boat conformation for the tricyclic framework and is located on a crystallographically required mirror plane. Com- pound II has the expected folded boat conformation. The torsion angle about the 10,11-bond is 0.0° for I, a crystallographic symmetry requirement, and 89.9° for II. Mean SiC bond distances are 1.863 Å(I) and 1.875 Å(II). The dihedral angles between the planar benzo groups are 129.7° (I) and 137.2° (II); introduc- tion of unsaturation at the 10,11-position decreases the dihedral angle in the tri- cyclic system, i.e., the tricyclic system is more bent.

An orthrohombic superstructure of tridymite existing between about 105 and 180°C

Abstract A modification of tridymite with an orthorhombic structure exists between monoclinic low tridymite and orthorhombic high tridymite. The three unit-cell edges of this structure are parallel with the corresponding ones of orthorhombic high tridymite but the a translation is three times as long as that of the latter. The crystal structure was determined by the use of x-ray intensities at about 155°C on a crystal from refractory silica brick. The space group is P212121 and the unit cell of, dimensions a = 26.171(3), b = 4.986(4) and c = 8.196(4) Å, contains twenty-four formula units. The six-membered rings of the silica tetrahedra are distorted in a way similar to those of monoclinic low tridymite: two thirds have a ditrigonal shape and one third have an oval shape in (001). The same ring types stack on top of one another along the orthorhombic c axis (parallel with the c direction of hexagonal ideal tridymite). This is not the case in monoclinic low tridymite. The mean Si–O distance, uncorrected for thermal motion, is 1.58 Å and the mean values of the Si–O–Si angles are 170.4° for tetrahedra joined nearly parallel to c, and 153.0° for those nearly in (001).

Crystal and molecular structure of tetramethyl- N, N′-diphenylcyclodisilazane

The crystal structure of tetramethyl- N, N' -diphenylcyclodisilazane is reported. The molecule has a centre of symmetry and the phenyl groups are almost coplanar with the cyclodisilazane ring. SiN bond distances are 1.739(3) and 1.749(3) Å, the mean SiC bond length is 1.849 and the CN bond length is 1.382(4) Å, while the NSiN and SiNSi bond angles are 85.7(1) and 94.3(1)°, respectively. Considerable bathochromic shifts are found in the UV spectra of the compound compared with that of N-phenyl(hexamethyl)disilazane. Structural and spectroscopic data show enhanced delocalization. The π-bond orders calculated by the PPP method are p(CN) 0.325 and p(SiN) 0.346.

Crytal and molecular structures of γ-1-phenylsilatrane: some structural features of silatranes

γ-1-phenylsilatrane crystallizes in the monoclinic space group P2 1/ n, with a 8.475, b12.949, c 11.122 » and β 90.86°. The structure was determined by direct methods and was refined to R 0.078 for 1687 observed reflexions and 0.081 for all 1813 reflexions. The →Si bond length is 2.132(4), SiC is 1.894(5) ». The mean SiO bond distance is 1.656 Å, angle NSiC is 179.0(2)°. The average NSiO, CSiO and OSiO angles are 83.6, 96.4 and 123.5°. By use of published data for six other silatrane molecules, some structural features were established. Thus, the length of the N→Si bond is affected by the other apical substituents of the silicon atom, the number of oxygen atoms attached to it and steric effects. Increase in the length of the dative N→Si bond is accompanied by further distortion of the trigonal bipyramidal configuration and of the tetrahedron around the nitrogen atom. The relatively long SiC( sp 2) bond may be due to decrased d π  p π interaction. The crystalline modifications (α, β, ψ) of the 1-phenyl-derivative possibly result from rapid ring-inversion in solution.

The B2Si8O30 groups of tetrahedra in axinite and comments on the deformation of Si tetrahedra in silicates

Abstract The crystal structure of axinite, H(Fe,Mn)Ca2Al2BSi4O16, has been redetermined and refined from three-dimensional, equi-inclination diffractometer intensity data. The crystal used in this study came from Woodlake, California, and has an Fe:Mn ratio close to 1:1. Its unit-cell constants are: a = 7.1566(15), b = 9.1995(20), c = 8.959(2) Å, α = 91.8(8)°, β = 98.14(02)°, γ = 77.30(02)° and its space group is P[unk]. The final R value is 0.042. The most noteworthy features of the axinite structure include: (1) the B2Si8O30 group in which four pairs of Si tetrahedra are connected by two B tetrahedra into a novel group of tetrahedra; (2) the finite octahedral chains of four Al and two Fe(Mn) which are, in turn, connected by elongated Ca antiprisms into sheets; (3) the B2Si8O30 tetrahedral groups which link these octahedral sheets together; and (4) the presence of a hydrogen bond between two oxygen atoms, one of which is bonded to a silicon atom. The distortions of the Si tetrahedra in axinite are examined by plots of tetrahedral-edge length versus the mean Si–O distances of the two oxygen atoms of the edge. The edges between bridge and nonbridge oxygen atoms were found to be invariably the shortest. Similar charts were prepared for several pyrosilicates, pyroxenoids, clinopyroxenes and clinoamphiboles. The relationship between the ratios of (O–O):(Si–O) length and types of oxygen is discussed as measures of tetrahedral distortion.