The crystal structure of kurnakovite: a refinement

Abstract

The crystal structure of kurnakovite, Mg[B3Oa(OH)5] (H20)4.H20, was refined to R=0-051 from 2057 X-ray reflexions (Cu K~ radiation). Crystals are triclinic, space group P], with a= 8.3479, b= 10.6068, c=6.4447/~ (all +_0"0001 /~), ~=98-846, fl= 108.891, 7= 105-581 ° (all +_0-001°); D,,= 1.847 and D~,= 1.855 g cm -3 for Z= 2. The structure contains discrete [B3Oa(OH)5] 2-groups. These share OH groups with Mg(OH)2(HzO)4 octahedra, with which they alternate in the c direction to form chains. The fifth water molecule occurs between these chains; a network of hydrogen bonds provides the inter-chain links, as well as a few intra-chain ones. Hydrogen atoms were located and their parameters refined. The H-bonding system explains the observed cleavages.

Thermal and compressional behavior of the natural borate kurnakovite, MgB3O3(OH)5·5H2O

“…The experimental X-ray diffraction patterns collected at ambient conditions were compatible with the space group P1 and the unit-cell parameters of kurnakovite reported by Corazza [29].…”

“…Recently, Gatta et al [19], using single-crystal neutron diffraction data, provided a full anisotropic structural refinement, including even all the H atoms, and a comprehensive chemical analysis, by means of a multi-methodological approach, which surveyed the presence of 50 chemical elements, yielding a composition of the studied compound very close to the kurnakovite nominal formula. According to the model refined by Corazza [29] and later confirmed by Gatta et al [19], the neutral Mg(H2O)4B3O3(OH)5-units are organized in chains running along the [001] direction (Fig. 1).…”

“…Inderite has a monoclinic unit-cell (space group P21/c) and the Mg(H2O)4B3O3(OH)5-units are organized in independent groups, whereas kurnakovite has a triclinic unit-cell (space group P1 ) and its structure is characterized by the presence of chains. The first structural information about kurnakovite were given by Petch et al [27] and later the crystal structure was solved by Razmanova et al [28] and refined by Corazza [29], by means of single-crystal X-ray diffraction data collected with a Weissenberg camera. Recently, Gatta et al [19], using single-crystal neutron diffraction data, provided a full anisotropic structural refinement, including even all the H atoms, and a comprehensive chemical analysis, by means of a multi-methodological approach, which surveyed the presence of 50 chemical elements, yielding a composition of the studied compound very close to the kurnakovite nominal formula.…”

Ultrahigh-Field 25Mg NMR and DFT Study of Magnesium Borate Minerals

“…The retention of the unit cell parameters from room-temperature XRD experiments versus a default thermal relaxation to 0 K was intended to facilitate direct comparison with data obtained from room-temperature NMR spectra . Calculations using the optimized structures of inderite and kurnakovite yielded significantly more accurate C Q and η values than those calculated from the original XRD structures in our previous study, hence results from this research were performed with XRD crystal structures − ,,,− that underwent a full optimization of atom positions while the unit cell parameters were kept constant. Calculations were performed on the Grex SGI Altix XE 1300 cluster, which consists of 316 compute nodes, each with two 6-core Intel Xeon X5650 2.66 GHz processors (Westgrid, Compute Canada, University of Manitoba).…”

“…Magnesium, as a strongly lithophilic element, combines readily with oxygen to form diverse minerals (e.g., borates, carbonates, oxides/hydroxides, silicates, and sulfates) on Earth’s surface. For example, magnesium borates are common minerals in salt spring deposits and evaporites and are known to feature great structural diversity arising from the complex linkages of [3] B and [4] B groups and from the presence of different Mg coordination environments. − …”