Volume 229, Issue 8

The present review will give a brief overview mainly focused on studies during the past 5 years on the mineral titanite (end-member composition CaTiSiO 5 ) which could incorporate radioactive elements in its crystal structure. Aspects of investigations were the structural damage resulting from the radioactive decay, the thermally induced recrystallization process and the elastic properties of the mineral. During the radiation induced damage process, namely the metamictization, titanite becomes partially amorphous with coexisting defect enriched crystalline and aperiodic regions. Within these crystalline regions a P 2 1 / c to C 2/ c phase transition (∼ at 500 K) occurs. Resulting from radiation induced structural damage, titanite shows elastic properties close to those of titanite glass. During recrystallization on annealing an initial softening of the titanite structure takes place (up to temperature ∼950 K) resulting from the formation of soft interfaces. Thermal annealing at higher temperatures leads to increasing structural order and the hardening of the mineral.

Metamict titanite from the Cardiff uranium mine (M28696) in Ontario, Canada, has been analyzed using 29 Si magic angle spinning nuclear magnetic resonance spectroscopy (MAS NMR). A broad Gaussian shaped NMR signal at –81 ppm occurs at room temperature resulting from the mainly locally ordered metamict structural state. NMR signals were obtained at room temperature and after annealing at 600, 950, 1220 and 1470 K. Because of increasing crystallinity the full width at half maximum (FWHM) decreased from 24 ppm to 20 ppm, respectively using a pseudo-Voigt fit. For comparison highly-crystalline titanite from Rauris showed an NMR signal at –79.3 ppm with FWHM of 4.1 ppm and an almost Lorentzian profile because of its good long range order. Integrating synchrotron X-ray diffraction (XRD) signals of Cardiff titanite show an increase of the crystallographic long range order at annealing temperatures considerably lower than the local ordering seen by NMR.

Various types of aminium thiosulfates ( 1 – 6 ), including hydrates and mixed salts, have been obtained by the reaction of ammonium thiosulfate with amines. Tert -butylamine, cyclo -hexylamine and 1,6-diaminohexane gave crystals of ( t -BuNH 3 ) 2 S 2 O 3 ·H 2 O ( 1 ), ( c -C 6 H 11 NH 3 ) 2 S 2 O 3 ( 3 ) and {(NH 4 ) 2 (H 3 NC 6 H 12 NH 3 )(S 2 O 3 ) 2 } ( 6 ), respectively, which were investigated by X-ray structural analysis. Extensive hydrogen bonding of the N-H…O and N-H…S type is responsible for formation of alternating hydrophilic and hydrophobic layers in the solid-state. In the case of ( 1 ), the layers are separated by strata of weak van der Waals interactions, while ( 3 ) consists of hydrogen-bonding stabilized rods along the b direction. The structure of ( 6 ) contains 3D covalent bonding plus hydrogen bonding networks with no separable substructures. Solubility and thermal decomposition are also briefly discussed.

Three new cyano complexes, [Cu(hmp) 2 ] [Cu(hmpH) 2 Ni(μ-CN) 2 (CN) 2 ] 2 ·4H 2 O ( 1 ), [Zn 3 (hmp) 2 (hmpH) 4 Ni 2 (μ-CN) 6 (CN) 2 ]·2H 2 O ( 2 ) and [Cd 2 (H 2 O) 2 (hmpH) 2 Ni(μ-CN) 4 Ni(μ-CN) 2 (CN) 2 ] ( 3 ) (2-pyridinemethanol abbreviated to hmpH), have been synthesized and characterized by elemental analysis, vibrational spectroscopy (FT-IR and Raman), thermal and single-crystal X-ray diffraction analyses. In 1 , Cu(II) ions are connected by the tetracyanonickelate(II) anions to form one-dimensional (1D) zig-zag chains. In 2 , tetracyanonickelate(II) ions are coordinated to the neighboring three Zn(II) ions to form a one-dimensional double chain structure. In 3 , Cd(II) ions are connected by tetrakis-monodentate tetracyanonickelate(II) ions to form a one-dimensional ladder-like chain. Adjacent ladder-like chains are linked by the bis-monodentate tetracyanonickelate(II) ions to generate a 2D network. The 3D supramolecular network of the complexes constructed by intermolecular interactions such as Ni···π, C-H···Ni, π···π and hydrogen bonding interactions.

Two new metal(II) complexes formulated as [ZnI(dmae)] 4 ·2(C 7 H 8 ) 1 and CdI 2 (Hdmae) 2 2 have been synthesized by using N,N -dimethylaminoethanol, a N,O donor ligand and characterized by melting point, elemental analysis, FT-IR spectroscopy, mass spectrometry and single crystal X-ray diffraction analysis. Complex 1 crystallizes in tetragonal I4(1)/a space group with μ 2 –O bridge between zinc atoms. The zinc atom is four coordinated with Zn–O 1.9315(13) and 1.9606(14) Å. The complex 2 is mononuclear with distorted octahedral geometry around the Cd(II) and contains two bidentate chelating Hdmae ligands and two iodine atoms, with Cd–O and Cd–N distances of 2.498(2) and 2.400(2) Å, respectively, and the weak O–H···I hydrogen bonds like interactions link the molecules to generate a 1D supramolecular structure.

Two new ionic [Fe( bpy ) 3 ](ONC(CN) 2 ) 2 ·2HONC(CN) 2 ( 1 ) and [Fe( phen ) 3 ](ONC(CN) 2 ) 2 ( 2 ) complexes have been synthesized ( bpy is 2,2′-bipyridine, phen is 1,10-phenanthroline). X-ray structural analysis (( 1 ): P 2 1 / n , a =11.7294(5), b =22.0774(11), c =16.2415(8) Å, β =98.910(5)°; ( 2 ): P 2 1 / c , a =9.4951(3), b =21.6640(9), c =17.3365(6) Å, β =92.483(3)°) revealed that their structures consist of one [Fe( bpy ) 3 ] 2+ or [Fe( phen ) 3 ] 2+ complex cation and two uncoordinated nitrosodicyanomethanide, ONC(CN) 2 - counteranions; two molecules of unique nitrosodicyanomethanide acid HONC(CN) 2 were found in ( 1 ), too. In the cations, the Fe(II) atom is coordinated by six nitrogen atoms of chelate coordinated neutral ligands forming a distorted octahedron coordination geometry. Both structures are stabilized by π-π interactions and hydrogen bonds, which are very strong in ( 1 ).

The crystal structures of two ( E )-2-(2-benzylidenehydrazin-1-yl)quinoxaline derivatives, ( E )-2-(XYC 6 H 3 -CH=N-NH)-quinoxalines, 1 , namely ( 1 : X=H; Y=4-MeO or 4-O 2 N) have been determined. In both cases, the major intermolecular interactions are N – H···N(pyrazine) hydrogen bonds. While in both compounds π···π intermolecular stacking interactions are present, these involve different aromatic rings in each case and hence different structural motifs are formed. These findings – of persistent and dominant N – H···N(pyrazine) hydrogen bonds and variable π···π interactions – concur with the previous findings for other compounds 1 . The substituents, Y, in ( 1 : X=H; Y=4-MeO or 4-O 2 N) play minor roles in the overall supramolecular arrangements.