Biomedical subjects

R Kniep

Publications and source records attributed to R Kniep.

7 recordsLinked to original sources

PubMed2002

Speciation of nitrogen - [N(3-)] and [N(2)(2-)] - in binary compounds.

The nitrogen content of the binary compounds SrN = Sr(4)[N](2)[N(2)], Sr[N(2)], and Ba[N(2)] (prepared by high-pressure syntheses) was determined analytically by using the carrier gas hot extraction method. For handling of the air- and moisture-sensitive samples, a transfer chamber was constructed to protect the compounds against decomposition before being analyzed. Additionally, it was necessary to develop a method allowing controlled and variable heating of the electrode furnace to get analytical results with high precision and accuracy. By means of a suitable temperature program it was possible not only to verify the existence but also to quantify the two different nitrogen species ([N(3-)] and [N(2)(2-)]), and thus confirm the results of recent neutron diffraction studies.

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PubMed2002

Large orbital moments and internal magnetic fields in lithium nitridoferrate(I).

The iron nitridometalates Li2[(Li(1-x)Fe(I)(x))N] display ferromagnetic ordering and spin freezing. Large magnetic moments up to 5.0mu(B)/Fe are found in the magnetization. In Mössbauer effect studies huge hyperfine magnetic fields up to 696 kOe are observed at specific Fe sites. These extraordinary fields and moments originate in an unusual ligand field splitting for those Fe species leading [within local spin density approximation (LSDA)] to a localized orbitally degenerate doublet. Including spin-orbit interaction and strong intra-atomic electron correlation (LDA+SO+U) gives rise to a large orbital momentum.

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PubMed2001

Li24[MnN3]3N2 and Li5[(Li1-xMnx)N]3, two intermediates in the decomposition path of Li7[MnN4] to Li2[(Li1-xMnx)N]: an experimental and theoretical study.

The crystal structure of Li7[Mn(V)N4] was re-determined. Isolated tetrahedral [Mn(V)N4](7-) ions are arranged with lithium cations to form a superstructure of the CaF2 anti-type (P4bar3n, No. 218, a = 956.0(1) pm, Z = 8). According to measurements of the magnetic susceptibility, the manganese (tetrahedral coordination) is in a d(2) S = 1 state. Thermal treatment of Li7[Mn(V)N4] under argon in the presence of elemental lithium at various temperatures leads to Li24[Mn(III)N3]3N2, Li5[(Li1-xMnx)N]3, and Li2[(Li1-xMn(I)x)N], respectively. Li24[Mn(III)N3]3N2 (P3bar1c, No. 163, a = 582.58(6) pm, c = 1784.1(3) pm, Z = 4/3) crystallizes in a trigonal unit cell, containing slightly, but significantly nonplanar trigonal [MnN3](6-) units with C3v symmetry. Measurements of the magnetic susceptibility reveal a d(4) S = 1 spin-state for the manganese (trigonal coordination). Nonrelativistic spin-polarized DFT calculations with different molecular models lead to the conclusion that restrictions in the Li-N substructure are responsible for the distortion from planarity of the [Mn(III)N3](6-). Li5[(Li1-xMnx)N]3 (x = 0.59(1), P6bar2m, No. 189, a = 635.9(3) pm, c = 381.7(2) pm, Z = 1) is an isotype of Li5[(Li1-xNix)N]3 with manganese in an average oxidation state of about +1.6. The crystal structure is a defect variant of the alpha-Li3N structure type with the transition metal in linear coordination by nitrogen. Li2[(Li1-xMn(I)x)N] (x = 0.67(1), P6/mmm, No. 191, a = 371.25(4) pm, c = 382.12(6) pm, Z = 1) crystallizes in the alpha-Li3N = Li2[LiN] structure with partial substitution of the linearly nitrogen-coordinated Li-species by manganese(I). Measurements of the magnetic susceptibility are consistent with manganese (linear coordination) in a low-spin d(6) S = 1 state.

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PubMed2001

Preparation, crystal structure, and properties of barium pernitride, BaN(2).

Stoichiometric barium pernitride, BaN(2), was prepared from the elements under N(2) pressure of 5600 bar in an autoclave at 920 K. The compound is isotypic to ThC(2) (space group C2/c, Z = 4) according to powder X-ray (neutron) diffraction data with a = 7.1712(1), b = 4.3946(1), c = 7.2362(1) A, and beta = 104.864(1) degrees (a = 7.1745(1), b = 4.3963(1), c = 7.2393(1) A, beta = 104.876(1) degrees ). The N-N distance of 1.221(4) A (based on the neutron diffraction data) is indicative of a double bond in the N(2)(2-) dumbbells. BaN(2) is metallic according to magnetic susceptibility measurements and TB-LMTO band structure calculations.

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PubMed2001

NaZn(H2O)2[BP2O8].H2O: a novel open-framework borophosphate and its reversible dehydration to microporous sodium zincoborophosphate N.

Crystals of NaZn(H2O)2[BP2O8].H2O were grown under mild hydrothermal conditions at 170 degrees C. The crystal structure (solved by X-ray single-crystal methods: hexagonal, P6(1)22 (no. 178), a = 946.2(2), c= 1583.5(1) pm, V= 1227.8(4).10(6) pm3, Z = 6) exhibits a chiral octahedral-tetrahedral framework related to the CZP topology and contains helical ribbons of corner-linked borate and phosphate tetrahedra. Investigation of the thermal behavior up to 180 degrees C shows a (reversible) dehydration process; this leads to the microporous compound Na[ZnBP2O8].H2O, which has the CZP topology. The crystal structure of Na[ZnBP2O8].H2O was determined by X-ray powder diffraction by using a combination of simulated annealing, lattice-energy minimization, and Rietveld refinement procedures (hexagonal, P6(1)22 (no. 178), a = 954.04(2), c = 1477.80(3) pm, V= 164.88(5).10(6) pm3, Z = 6). The essential structural difference caused by the dehydration concerns the coordination of Zn2- changing from octahedral to tetrahedral arrangement.

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PubMed2000

Crystal structures of two polymorphs of Ca3[Al2N4].

Green transparent single crystals of alpha-Ca3[Al2N4] (monoclinic, P2(1)/c, No. 14, a = 957.2(3) pm, b = 580.2(3) pm, c = 956.3(5) pm, beta = 111.62(3) degrees; Z = 4) were obtained from reactions of mixtures of the representative metals with nitrogen above temperatures of 1000 degrees C. beta-Ca3[Al2N4] (monoclinic, C2/c, No. 15, a = 1060.6(2) pm, b = 826.0(2) pm, c = 551.7(1) pm, beta = 92.1(1) degrees; Z = 4) was formed as a byproduct of a reaction of calcium with alumina under nitrogen at T = 930 degrees C in form of colorless crystals. The crystal structures of the two polymorphs contain edge- and corner-sharing AlN4 tetrahedra, leading to different layered anionic partial structures: infinity 2[AlN2/2N2/3)2(AlNN2/2N1/3)6/3(12-)] in the alpha-phase and infinity 2[Al2N2N4/2(6-)] in the beta-polymorph.

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PubMed1999

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Tetrahedral framework structures with topologies that show close relationships to the feldspar group or to gismondine are formed by the zincoborophosphates A[ZnBP(2)O(8)] (see picture). The compounds are readily accessible under mild hydrothermal conditions (T(max)=170 degrees C) and are thermally remarkably stable (for example, 940 degrees C for A=Cs). Metalloborophosphates are a new class of compounds, which are expected to provide access to zeolite-like microporous systems.

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