Electronic structure of (MePh3P)2[NiII(bdtCl2)2]·2(CH3)2SO and (MePh3P)[NiIII(bdtCl2)2] (bdtCl2 = 3,6-dichlorobenzene-1,2-dithiolate)

High-resolution X-ray diffraction experiments, theoretical calculations and atom-specific X-ray absorption experiments were used to investigate two nickel complexes, (MePh3P)2[NiII(bdtCl2)2]·2(CH3)2SO [complex (1)] and (MePh3P)[NiIII(bdtCl2)2] [complex (2)]. Combining the techniques of nickel K- and sulfur K-edge X-ray absorption spectroscopy with high-resolution X-ray charge density modeling, together with theoretical calculations, the actual oxidation states of the central Ni atoms in these two complexes are investigated. Ni ions in two complexes are clearly in different oxidation states: the Ni ion of complex (1) is formally NiII; that of complex (2) should be formally NiIII, yet it is best described as a combination of Ni2+ and Ni3+, due to the involvement of the non-innocent ligand in the Ni—L bond. A detailed description of Ni—S bond character (σ,π) is presented.

Low-temperature investigation of natural iron-rich oxoborates vonsenite and hulsite: thermal deformations of crystal structure, strong negative thermal expansion and cascades of magnetic transitions

This work is devoted to an investigation of the magnetic properties and thermal behaviour of the natural oxoborates vonsenite and hulsite in the temperature range 5–500 K. The local environment, the oxidation states of the Fe and Sn atoms, and the charge distribution were determined using Mössbauer spectroscopy and are in accordance with a refinement of the crystal structure of hulsite from single-crystal X-ray diffraction data (SCXRD) in anisotropic approximation for the first time. The magnetic properties were studied by vibrating sample magnetometry (VSM) (5 ≤ T ≤ 400 K) and are reported for the first time for iron-rich hulsite. Both oxoborates show a very complex magnetic behaviour. Cascades of magnetic transitions are revealed and the critical temperatures were determined. The sequences of magnetic transitions in both vonsenite and hulsite with increasing temperature were found to be as follows: magnetically ordered state → partial magnetic ordering → paramagnetic state. According to X-ray diffraction data (93 ≤ T ≤ 500 K), these processes are accompanied by anomalies in the unit-cell parameters and thermal expansion of the oxoborates at critical temperatures. A strong negative volume thermal expansion is observed for both oxoborates at temperatures below ∼120 K.

Oxonium trans-bis(oxalato)rhodate and related sodium salts: a rare example of crystalline complex acid

New coordination compounds trans-bis(oxalato)diaquarhodiate sodium dihydrate Na[Rh(H2O)2Ox2]·2H2O (crystallizes in two polymorphic forms NaRh-1 and NaRh-2), trans-bis(oxalato)hydroxoaquarhodiate sodium tetrahydrate Na2[Rh(H2O)(OH)Ox2]·4H2O (Na2Rh) and trans-bis(oxalato)diaquarhodic acid tetrahydrate (H3O)[Rh(H2O)2Ox2]·4H2O (HRh) are synthesized. The compounds are characterized by IR spectroscopy, elemental analysis and single crystal X-ray diffraction. NaRh-1, NaRh-2 and Na2Rh crystallize in space group P 1. Trans-bis(oxalato)diaquarhodic acid exists not only in solution, but can also crystallize as a tetrahydrate (space group C2/c). The formation of various species in solution of rhodium hydroxide in oxalic acid and their redistribution were studied using 103Rh NMR spectroscopy.

K(Na,K)Na2[Cu2(SO4)4]: a new highly porous anhydrous sulfate and evaluation of possible ion migration pathways

Alkali copper sulfates form a rapidly developing family of inorganics. Herein, we report synthesis and crystal structure, and evaluate possible ion migration pathways for a novel Na-K-Cu anhydrous sulfate, K(Na,K)Na2[Cu2(SO4)4]. The CuO7 and SO4 polyhedra share common vertices and edges to form [Cu2(SO4)4]4− wide ribbons, which link to each other via common oxygen atoms forming the host part of the structure. Four guest alkali sites are occupied by solely K+, mixture of K+ and Na+, and solely Na+, which agrees well with the size of the cavities. The crystal structure of K(Na,K)Na2[Cu2(SO4)4] contains two symmetry-independent Cu sites with [4+1+(2)] coordination environments. The overall coordination polyhedra of Cu2+ can be considered as `octahedra with one split vertex'. A similar coordination mode was observed also in some other multinary copper sulfates, mostly of the mineral world. These coordination modes were reviewed and five types of CuO7 polyhedra are identified. CuO7 polyhedra are almost restricted to copper sulfates and phosphates. It was found that a larger amount of the smaller SO4 2− and PO4 3− anions can cluster around a single Cu2+ cation; in addition, for such relatively small anions, both mono (κ1) and bidentate (κ2) coordination modes to the Cu2+ are possible. The correlation between crystallographic characteristics and bond valence energies showed that the new copper sulfate framework, [Cu2(SO4)4]4−, contains one interconnected path suitable for Na+ mobility at tolerable activation energies and that K(Na,K)Na2[Cu2(SO4)4] can be considered as a potential candidate for novel Na-ion conductors.

Crystal engineering of co-crystal of nicotinic acid and pyrogallol: an experimental and theoretical electron density analysis

Experimental electron density analysis by means of high-resolution X-ray diffraction data up to sinθ/λmax = 1.11 Å−1 at 100 (1) K has been performed to analyze the detailed structure and the strength of intermolecular interactions responsible for the formation of a new solid form of nicotinic acid (NA), cocrystallized with pyrogallol (PY). There are two NA–PY units in the asymmetric unit. The experimental results are compared with the results obtained from theoretical structure factors modeled using periodic boundary DFT calculations. Both refinements were carried out using the Hansen and Coppens multipolar formalism (in MoPro program). The non-centrosymmetric and polar nature of the crystal system rendered the multipolar refinement challenging which was addressed by involving the transferability principle. This study highlights the significance of the transferability principle in electron density modeling in non-routine situations. The 2:2 cocrystal of NA–PY exhibits a zigzag, brickwall and sheet-like layered structure in three dimensions and is stabilized by strong intra- and inter-molecular hydrogen bonding through N—H...O and O—H...O bonds, some of them due to the zwitterion nature of NA as well as weak interactions between the PY molecules. Ranking these interactions via topological analysis of the electron density shows the leading role of the NA–NA substructure which drives the organization of the cocrystals. These strong interactions between the NA zwitterions may explain why Z′ = 2.

Kilobytes of kilopascals: high-pressure depositions of the Cambridge Structural Database

The Cambridge Structural Database (CSD) is the largest repository of crystal structures of organic and metal–organic compounds, containing over 1.1 million entries. Over 3300 of the deposits are structures determined under high pressure, with the number being strongly affected by the experimental requirements of the high-pressure techniques. Nevertheless, it still presents a population sufficiently representative for statistical data mining. In this work, an in-depth analysis of this population is presented, showing where contributors of high-pressure depositions come from, which journals high-pressure structures are published in, and also providing information on some trends in high-pressure crystallography and how they have changed over the years elucidated from data collected in the CSD. The ultimate goal of this article is to bring the high-pressure crystallography content in the CSD to a wider audience of scientists.

Low-temperature phase transition and highpressure phase stability of 1H-pyrazole-1carboxamidine nitrate

The phase transition observed in a temperature-dependent experiment at 174 K is unachievable under high-pressure conditions. Negative thermal expansion for phase (II) and negative compressibility for phase (I) were observed. A new salt of 1H-pyrazole-1-carboxamidine, (HPyCA)NO3, for guanylation reaction was obtained in a crystalline form. The compound crystallizes in monoclinic space group P21/c and a phase transition at 174 K to triclinic modification P 1 was found. An unusual increase of the unit-cell volume was observed just after transition. Although the volume decreases upon cooling, it remains higher down to 160 K in comparison to the unit-cell volume of phase (I). The mechanism of the phase transition is connected with a minor movement of the nitrate anions. The triclinic phase was unreachable at room-temperature high-pressure conditions up to 1.27 GPa. On further compression, delamination of the crystal was observed. Phase (I) exhibits negative linear compressibility, whereas abnormal behaviour of the b unit-cell parameter upon cooling was observed, indicating negative thermal linear expansion. The unusual nature of the compound is associated with the two-dimensional hydrogen-bonding network, which is less susceptible to deformation than stacking interactions connecting the layers of hydrogen bonds. Infrared spectroscopy and differential scanning calorimetry measurements were used to investigate the changes of intermolecular interactions during the phase transition.