# Crystal Structure Elucidation of the Novel Molecular-Inorganic Polymer $\mathrm{K_{2}SeO_{4}\cdot H_{2}SeO_{3}}$

## TL;DR

This study determined the detailed crystal structure of a novel molecular-inorganic polymer, K2SeO4·H2SeO3, revealing its polymeric chain formation and the influence of potassium ions on molecular arrangement.

## Contribution

The paper reports the first elucidation of the orthorhombic crystal structure of K2SeO4·H2SeO3, highlighting its unique polymeric chain structure and detailed atomic interactions.

## Key findings

- Polymeric chain formed along the c axis via hydrogen bonds.
- Potassium ions influence the orientation of selenate and selenous acid.
- High-quality crystal structure data with low R-factors.

## Abstract

The orthorhombic crystal structure of the novel molecular-inorganic polymer $\mathrm{K_{2}SeO_{4}\cdot H_{2}SeO_{3}}$ was elucidated using single-crystal X-ray diffraction with MoK$\alpha$ radiation ($\lambda$= 0.71073 {\AA}), performed at 100 and 298.15 K. The reported data is at 100 K since there were no structural differences as compared to the room temperature. The technique revealed $\mathrm{K_{2}SeO_{4}\cdot H_{2}SeO_{3}}$ crystals to have space group $Pbcm$ with unit cell dimensions $a =$ 8.8672(17) {\AA}, $b =$ 7.3355(14) {\AA}, $c =$ 11.999(2) {\AA} and $Z =$ 4. The unit cell volume obtained was $V =$ 780.5(3) {\AA}$^3$ with a calculated density $D_{c} = 2.980 Mg/m^3$. In $\mathrm{K_{2}SeO_{4}\cdot H_{2}SeO_{3}}$, the selenate anions and selenous acid molecules form an infinite polymeric chain along the \textit{c} axis, through strong hydrogen bonds. That is to say; there are two distinctive species forming a polymeric sequence extended along the \textit{c} axis with an alternating molecule-anion-molecule $\mathrm{(SeO_{4}^{2-}-H_{2}SeO_{3})_{n}}$, defined as a Molecular Inorganic Polymer (MIP). The $\mathrm{K^{+}}$ cations influence the orientation of the $\mathrm{SeO_{4}^{2-}}$ anions, and these consequently affect the arrangement of the $\mathrm{H_{2}SeO_{3}}$ molecules within the structure. The crystal packing forces are governed by ionic and dipole-dipole interaction. Full-matrix least-square refinement method on $F^2$ provide final Reliability indices of $R_{1}$ = 0.0150, and $wR_{2}$ = 0.0377, and a Goodness-of-fit = 1.140; at 0.75 {\AA} resolution, where $R_{int}$ = 0.0230, and $F(000)$ = 656 for 1014 independent reflections ($I>2\sigma(I)$), from a total of 8,576 reflections collected.