Volume 231, Issue 12

Within a “homogeneous” series of (crystal-chemically) isotypic structures one and only one chemical element E of the sum formula is replaced successively by heavier elements of the same group of the periodic table. For corresponding series of “ionic” compounds, a (coarse) “expectation value” Δ V th for the unit cell volume expansion following the replacement of E ( i ) by E ( j ) (with i < j =row numbers in the periodic table) can be calculated by using the empirical formula Δ V th =56.5 ( z E Δ ρ E ( i ) E ( j ) ) – 0.80 ( z E Δ ρ E ( i ) E ( j ) ) 2 , where z E is the number of atoms E per unit cell and Δ ρ E ( i ) E ( j ) is the linear statistical size (= radius) difference for the two elements E ( i ) and E ( j ). Two hundred and twenty-eight different series have contributed to the statistical evaluation of this formula. Series for which E are elements of low valence have been excluded a priori from the calculations if the residual atoms of higher valence by themselves form an infinite framework, as it was suspected, that in structures of this kind the “natural” volume expansion caused by the E ( i ) → E ( j ) size increase is hampered by the rigidity of this framework. Application of the above formula to structures of this kind clearly supports this suspicion only, if the framework is of dimensionality three. The results derived from all other investigated structures are qualitatively compatible with the “volume increments rule” published in the 1930s. This suggests that they should be applicable also to isotypic series of crystal structures defined in a less restricted manner.

The crystal structures of two thiolato complexes of the type [Au(SR)(PPh 3 )] with SR=2-mercaptobenzoxazol-2-yl (MBOx) and SR=2-mercaptoanthraceneoxazol-2-yl (MAOx) were determined from X-ray powder diffraction data. Both complexes include η 1 -S-monodentate ligands with the nitrogen atom preferably oriented towards the gold atom. [Au(MBOx)(PPh 3 )] ( 1a ) represents a new triclinic polymorph of [Au(MBOx)(PPh 3 )], whereas [Au(MAOx)(PPh 3 )] ( 2 ) is hitherto unknown and yields information about the molecular structure of the ligand MAOx as well as the coordination geometry in 2 . The structure determinations were validated by low temperature XRPD measurements. DTA-TG and in-situ XRPD measurements revealed a monotropic phase transition of 1a at 443 K to a monoclinic phase. Additionally, solid-state DFT-D calculations using CASTEP were carried out to evaluate the experimental results.

Three variants of novel cobalt(II) complex with deprotonated mefenamic acid ( mef ) and N,N ′-donor ligand neocuproine ( neo ) are described, namely; two differently colored and shaped crystal polymorphs of complex [Co( mef ) 2 ( neo )] ( 1a and 1b ) and a pyridine solvate [Co( mef ) 2 ( neo )]· py ( 2 ). The complexes have been characterized by infrared and UV-VIS spectroscopy, elemental analysis and single-crystal X-ray structure analysis. Although the complexes 1a , 1b and 2 crystallize in different crystal systems and space groups and differ in shapes of coordination polyhedra, the crystal structures of all three complexes contain analogous neutral units with Co(II) atom hexacoordinated by two chelate bonded mefenamato ligands and one chelate bonded neocuproine ligand, yielding CoN 2 O 4 chromophore. The main structural difference between 1a , 1b and 2 is the conformation of the coordinated mef ligands, which affects the crystal packing of the complexes.

Routines to facilitate the treatment of disorder in invariom modeling have been implemented in the open-source program M olecool Q t , a visualization program for charge-density work, and I nvariom T ool , a pre-processor program. Two published structures of an amino acid and a dipeptide and the new structure of cefaclor, a cephalosporin antibiotic, provide examples with increasing amounts of disorder, which can now be successfully modeled with invarioms. Like for ordered structures, these non-spherical scattering factors predicted by density functional theory significantly improve the structural model (figures of merit and standard deviations) also in these cases. Furthermore, they allow rapid calculation and comparison of the electrostatic potential and the molecular dipole moment for the different conformers present in the crystal structures.

The molecular structures of [Zn(S 2 COR) 2 (hmta)], R=Et ( I ) and iPr ( II ), and [Zn(S 2 CNRR′) 2 (hmta)], R=R′=Et ( III ) and R=iPr, R′=CH 2 CH 2 OH ( IV ), feature chelating 1,1-dithiolate ligands and monodentate hmta molecules; hmta=hexamethylenetetramine. The resulting NS 4 donor sets are highly distorted, with tendencies towards square pyramidal. Systematic differences in the structures are related to the greater chelating ability of the dithiocarbamate ligands leading to, e.g., elongated Zn–N bond lengths in III and IV . In the molecular packing, an unusual C–H···π(chelate ring) interaction is noted in III , which is correlated with the close to symmetric Zn–S bond lengths formed by the relevant dithiocarbamate ligand and resultant greater metalloaromatic character of the resulting ZnS 2 C chelate ring, and to the greater distortion of the coordination geometry compared with literature precedents. A three-dimensional architecture found for IV is sustained by hydroxyl-O-H···O, S and N hydrogen bonding.

Abstract: We have carried out a surface X-ray diffraction (SXRD) analysis of the approximant structure related to the recently discovered two-dimensional dodecagonal oxidic quasicrystal. The structure is characterized by the 3 2 .4.3.4 Archimedean tiling, first described by Kepler in 1619. The tiling network is related to titanium atoms observed as protrusions in scanning tunneling microscopy images. All four titanium atoms within one two-dimensional unit cell (a 0 =13.1 Å, b 0 =12.9 Å, γ =90.5°) are surrounded by three oxygen atoms. The TiO 3 units are separated by barium atoms. The total stoichiometry is given by Ba 4 Ti 4 O 10 .