Volume 239, Issue 1-2

The intermetallic ytterbium compound Yb 2 Pd 2 Cd shows a structural phase transition at ∼150 K. The structures of the room-temperature (Mo 2 B 2 Fe type, P 4/ mbm , a = 757.07(7), c = 371.99(4) pm, wR 2 = 0.0620, 272 F 2 values, 12 variables) and low-temperature (new type, P 4/ mbm , a = 747.26(4), c = 741.46(4) pm, wR 2 = 0.0384, 511 F 2 values, 19 variables) modifications were refined from single crystal X-ray diffractometer data. The superstructure formation corresponds to an isomorphic transition of index 2. The driving force for the structural phase transition is an ytterbium charge ordering (the superstructure exhibits two crystallographically independent ytterbium sites) with a much higher degree of divalent ytterbium in the low-temperature modification. The striking structural feature concerns the ytterbium–palladium coordination with different Yb–Pd distances: longer ones for predominantly divalent Yb1 (2 × 284.7 and 4 × 296.1 pm, ∅ = 292.3 pm) and shorter ones for trivalent Yb2 (2 × 277.5 and 4 × 288.4 pm, ∅ = 284.8 pm).

The silicides Sc T 2 Si 2 ( T = Ru, Rh, Os) were synthesized by arc-melting of the elements and subsequent annealing in sealed silica ampoules. They crystallize with the rarely observed HfFe 2 Si 2 type structure, space group Pbcm . The structures of ScRu 2 Si 2 ( a = 761.64(4), b = 730.70(6), c = 521.07(6) pm, w R = 0.0314, 633 F 2 values, 31 variables) and ScOs 2 Si 2 ( a = 771.10(8), b = 736.68(7), c = 521.88(5) pm, w R = 0.0479, 623 F 2 values, 31 variables) were refined from single crystal X-ray diffractometer data. The refinements showed small degrees of Ru/Si respectively Os/Si mixing on one 4 c site, leading to the refined compositions ScRu 1.96(1) Si 2.04(1) and ScOs 1.91(1) Si 2.09(1) . The monomeric building units in both structures are two slightly distorted, crystallographically independent RuSi 5 respectively OsSi 5 square pyramids, which are condensed via common edges. The resulting densely packed [Ru 2 Si 2 ] and [Os 2 Si 2 ] networks leave voids for the scandium atoms with coordination number 18: Sc@Si 8 Ru 8 Sc 2 and Sc@Si 8 Os 8 Sc 2 . Temperature dependent magnetic susceptibility measurements of ScRu 2 Si 2 and ScOs 2 Si 2 indicate Pauli paramagnetism. Solid-state 29 Si and 45 Sc static and MAS NMR spectroscopy reveal significant Knight shifts and a strong influence of the T /Si mixing on the experimental NMR line shapes. A larger overall 29 Si magnetic shift for ScRu 2 Si 2 compared to ScOs 2 Si 2 , although with a negative sign for one of the 29 Si resonances, suggests stronger paramagnetic effects for ScRu 2 Si 2 , in agreement with the magnetic susceptibility measurements.

Solid-state carbodiimides and cyanamides are a group of compounds that generally shows motifs of layered structures, with an alternating sequence of metal cations and NCN 2− anions. A study of the relationship between the ionic sizes in the cation layer and the crystal structures found is presented using the geometric characteristics of the NCN 2− coordination environment. The results of this analysis reveal a ‘Goldilocks zone’ of cationic sizes, from Al 3+ to Tl + , that are capable of forming stable “layered” metal carbodiimide structures. Furthermore, by employing a vectorial approach a correlation between the size difference of the cations and the degree of tilting of the NCN 2− framework has been found, capable of predicting the likelihood of new phases crystallizing in such structures.

Tm 2 CrB 3 O 9 was obtained by high-pressure/high-temperature syntheses at 7.5 GPa and 850 °C. The compound crystallizes homeotypically to walstromite in the triclinic space group P 1 ¯ $P\overline{1}$ (no. 2) with the unit cell parameters a  = 5.9118(4) Å, b  = 5.9148(4) Å, c  = 8.3575(6) Å, α  = 83.64(1)°, β  = 71.19(1)°, and γ  = 79.93(1)°, and two formula units per cell. Single-crystal and powder diffraction data are accompanied by an infrared spectroscopic investigation and the structural features of this new compound are discussed in detail.

A doubly mononuclear cobalt(II) complex [Co(Hpmt) 2 (N 3 ) 2 ] 2 ( 1 ) (Hpmt = 2-(2-pyridylmethylamino)ethanesulfonic acid; N 3  = azide anion) has been synthesized and structurally characterized. Single-crystal X-ray diffraction analysis showed that 1 has crystallized in orthorhombic crystal system, Cmc 2 1 space group. In the two independent and identical complexes, the cobalt(II) centers are both hexa-coordinated in distorted CoN 6 octahedrons. The reduced Schiff base ligand Hpmt displayed a new coordination mode of bidentate chelate ( κ 2 - N , N ′). The careful comparisons between Hpmt upon coordination and as free acid form demonstrated that the conformation flexibility might be responsible for its multiple coordination modes. The N–H⋯O and C–H⋯N hydrogen bonds constructed the 3D network, and this mainly agreed with the Hirshfeld surface analysis results.

Crystal structure of a series of 1-alkylimidazole-4,5-dicarboxylic acids has been determined. It is shown that an increase in the length of the alkyl group leads to drastic changes in the crystal and molecular structures. 1-Methyl and 1-ethylimidazole-4,5-dicarboxylic acid crystallize in zwitterionic form, but 1-propyl- and 1-butylimidazole-4,5-dicarboxylic acid crystallize as rare equimolar mixture of neutral and zwitterionic tautomeric forms. The observed changes in the crystal and molecular structures are apparently associated with the steric factor, which determines both the packing method and the tautomeric composition of the unit cell.

A survey of the crystallographically determined structures of the Group 13 dithiophosphates and dithiophosphinates is presented with a focus upon both the molecular structures and supramolecular association involving the heavy element. Only small numbers of aluminium(III) (two) and gallium(III) (one) structures are known and these along with the 10 indium(III) examples have a preponderance towards homoleptic species with most coordination geometries based on an octahedron owing to the presence of symmetrically or almost symmetrically chelating phosphorodithiolato ligands; the notable exception is the gallium species which has an approximately tetrahedral geometry as two of the dithiophosphinate ligands coordinate in a monodentate mode. Diverse molecular structures are noted for the four heteroleptic examples of the lighter Group 13 elements which assemble in their crystals employing intermolecular interactions that do not involve the central element, as with the homoleptic structures. A completely different situation is evident for the thallium(I)/(III) structures which display a diverse array of coordination geometries and which usually assemble via Tl⋯S triel-bonding interactions; in the supramolecular assembly of thallium(I) crystals, Tl(lone-pair)⋯π(aryl) interactions are often observed.