Biomedical subjects

S T Norberg

Publications and source records attributed to S T Norberg.

3 recordsLinked to original sources

PubMed2001

Crucial influence of solvent and chirality-the formation of helices and three-dimensional nets by hydrogen-bonded biimidazolate complexes.

Deprotonation and recrystallisation of racemic [Co(2,2'-biimidazole)3][NO3]3 by ammonia in water/dimethylformamide solutions gave crystals of [Co(Hbiim)3] x 0.8H2O x 0.5DMF (2: Hbiim = monoanion of 2,2'-biimidazole, DMF = dimethylformamide), a porous material that contains fourfold interpenetrating (10.3) three-dimensional nets formed by neutral, hydrogen-bonded [Co(Hbiim)3] units, with DMF molecules in the narrow channels. Recrystallisation of [delta-Co(2,2'-biimidazolate)3] gave helices instead of the expected (10,3)-a net. These results are discussed in the light of additional density functional theory and molecular mechanics calculations and the X-ray structure of [Co(H2biim)3][NO3]3.

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PubMed2001

KSbO(Ge0.32Si0.68)O4, a KTP isomorph.

A structural model of potassium antimony germanate/silicate (0.32/0.68), KSbO(Ge(0.32)Si(0.68))O(4), has been determined at room temperature. KSbO(Ge(0.32)Si(0.68))O(4) belongs to the KTiOPO(4) (KTP) isomorphic family and is composed of SbO(6) octahedra (site symmetry -1 and 2) arranged in helical chains bridged by (Ge/Si)O(4) tetrahedra. Germanium and silicon have a similar distribution in the crystallographically independent tetrahedra (site symmetry 2). The structure contains large cavities occupied by the K atom. Two partially occupied potassium positions have been identified 1.273 (8) A apart, with an indication of a third potassium position between them. At room temperature, KSbO(Ge(0.32)Si(0.68))O(4) crystallizes in the paraelectric phase of space group Pnan. This phase is found at elevated temperatures for almost all KTiOPO(4) isomorphic compounds and KSbO(Ge(0.32)Si(0.68))O(4) is the second isomorph that is paraelectric at room temperature.

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PubMed2001

A TiP(2)O(7) superstructure.

A room-temperature structural model of titanium pyrophosphate, TiP(2)O(7), has been determined from synchrotron X-ray data. The structure consists of TiO(6) octahedra and PO(4) tetrahedra sharing corners in a three-dimensional network. The PO(4) tetrahedra form P(2)O(7) groups connecting the TiO(6) octahedra. The 3 x 3 x 3 superstructure differs substantially from the parent AB(2)O(7) structure. The P--O--P bonding angles of the pyrophosphate group are between 141.21 (12) and 144.51 (13) degrees for those groups not located on the threefold axis. The individual TiO(6) octahedra and PO(4) tetrahedra are somewhat distorted.

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