Extraordinary structural complexity of ilmajokite: a multilevel hierarchical framework structure of natural origin.

Andrey A Zolotarev,Elena Sokolova,Fernando Cámara,Frank Hawthorne,Luca Bindi,Sergey V Krivovichev,Elena S Zhitova

doi:10.1107/s2052252519016622

Abstract

The crystal structure of ilmajokite, a rare Na-K-Ba-Ce-titanosilicate from the Khibiny mountains, Kola peninsula, Russia, has been solved using single-crystal X-ray diffraction data. The crystal structure is based on a 3D titanosilicate framework consisting of trigonal prismatic titanosilicate (TPTS) clusters centered by Ce3+ in [9]-coordination. Four adjacent TPTS clusters are linked into four-membered rings within the (010) plane and connected via ribbons parallel to 101. The ribbons are organized into layers parallel to (010) and modulated along the a axis with a modulation wavelength of csinβ = 32.91 Å and an amplitude of ∼b/2 = 13.89 Å. The layers are linked by additional silicate tetrahedra. Na+, K+, Ba2+ and H2O groups occur in the framework cavities and have different occupancies and coordination environments. The crystal structure of ilmajokite can be separated into eight hierarchical levels: atoms, coordination polyhedra, TPTS clusters, rings, ribbons, layers, the framework and the whole structure. The information-based analysis allows estimation of the complexity of the structure as 8.468 bits per atom and 11990.129 bits per cell. According to this analysis, ilmajokite is the third-most complex mineral known to date after ewingite and morrisonite, and is the most complex mineral framework structure, comparable in complexity to paulingite-(Ca) (11 590.532 bits per cell).

Highlights

Minerals constitute a distinct group of crystalline materials formed by natural geochemical or biogeochemical processes without any anthropogenic influence
As has been noted previously [see, e.g. Makovicky (1997); Ferraris et al (2004); Hawthorne (2014)], 126 Zolotarev et al Extraordinary structural complexity of ilmajokite research papers measures recently proposed by Krivovichev (2012, 2013, 2014)
The total value of Shannon information places ilmajokite as the third-most complex mineral known to date after ewingite, Mg4Ca4(UO2)12(CO3)15O2(OH)6Á69H2O [23 477.507 bits per cell with Hcorrection and 12 684.86 bits per cell without H-correction ($46% of total complexity is due to H atoms); Olds et al (2017)] and morrisonite, Ca11(As3+V24+V150+As65+O51)2Á78H2O [13 588.350 bits per cell with H-correction and 7553.229 bits per cell after H-correction (H atoms are responsible for $44% of structural complexity); Kampf et al (2016)]

Summary

Introduction

Minerals constitute a distinct group of crystalline materials formed by natural geochemical or biogeochemical processes without any anthropogenic influence. 5500 different mineral species are known today with more than 100 new species discovered every year. Many of these minerals have their synthetic counterparts, but there are many minerals that have no artificial analogs (Khomyakov, 1994). Their existence and formation under natural conditions represent a serious challenge for both mineralogists and material scientists looking for new structural architectures with interesting physical and chemical properties. The crystal structures of charoite and denisovite are based on different kinds of silicate nanotubules (Rozhdestvenskaya et al, 2009, 2010, 2017), and ewingite (Olds et al, 2017) and morrisonite (Kampf et al, 2016) contain novel types of nanoscale heteropolyhedral clusters

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