Comparison of the Coordination of B12F122-, B12Cl122-, and B12H122- to Na+ in the Solid State: Crystal Structures and Thermal Behavior of Na2(B12F12), Na2(H2O)4(B12F12), Na2(B12Cl12), and Na2(H2O)6(B12Cl12)

Eric V Bukovsky; Dmitry V Peryshkov; Hui Wu; Wei Zhou; Wan Si Tang; W Matthew Jones; Vitalie Stavila; Terrence J Udovic; Steven H Strauss

doi:10.1021/acs.inorgchem.6b02920

Comparison of the Coordination of B₁₂F₁₂^2-, B₁₂Cl₁₂^2-, and B₁₂H₁₂^2- to Na⁺ in the Solid State: Crystal Structures and Thermal Behavior of Na₂(B₁₂F₁₂), Na₂(H₂O)₄(B₁₂F₁₂), Na₂(B₁₂Cl₁₂), and Na₂(H₂O)₆(B₁₂Cl₁₂)

Inorg Chem. 2017 Apr 17;56(8):4369-4379. doi: 10.1021/acs.inorgchem.6b02920. Epub 2017 Apr 6.

Authors

Eric V Bukovsky¹, Dmitry V Peryshkov^{1

2}, Hui Wu³, Wei Zhou³, Wan Si Tang^{3

4}, W Matthew Jones¹, Vitalie Stavila⁵, Terrence J Udovic³, Steven H Strauss¹

Affiliations

¹ Department of Chemistry, Colorado State University , Fort Collins, Colorado 80523, United States.
² Department of Chemistry and Biochemistry, University of South Carolina , Columbia, South Carolina 29208, United States.
³ NIST Center for Neutron Research, National Institute of Standards and Technology , Gaithersburg, Maryland 20899, United States.
⁴ Department of Materials Science and Engineering, University of Maryland , College Park, Maryland 20742, United States.
⁵ Energy Nanomaterials, Sandia National Laboratories , Livermore, California 94551, United States.

PMID: 28383911
DOI: 10.1021/acs.inorgchem.6b02920

Abstract

The synthesis of high-purity Na₂B₁₂F₁₂ and the crystal structures of Na₂(B₁₂F₁₂) (5 K neutron powder diffraction (NPD)), Na₂(H₂O)₄(B₁₂F₁₂) (120 K single-crystal X-ray diffraction (SC-XRD)), Na₂(B₁₂Cl₁₂) (5 and 295 K NPD), and Na₂(H₂O)₆(B₁₂Cl₁₂) (100 K SC-XRD) are reported. The compound Na₂(H₂O)₄(B₁₂F₁₂) contains {[(Na(μ-H₂O)₂Na(μ-H₂O)₂)]²⁺}_∞ infinite chains; the compound Na₂(H₂O)₆(B₁₂Cl₁₂) contains discrete [(H₂O)₂Na(μ-H₂O)₂Na(H₂O)₂]²⁺ cations with OH···O hydrogen bonds linking the terminal H₂O ligands. The structures of the two hydrates and the previously published structure of Na₂(H₂O)₄(B₁₂H₁₂) are analyzed with respect to the relative coordinating ability of B₁₂F₁₂^2-, B₁₂H₁₂^2-, and B₁₂Cl₁₂^2- toward Na⁺ ions in the solid state (i.e., the relative ability of these anions to satisfy the valence of Na⁺). All three hydrated structures have distorted octahedral NaX₂(H₂O)₄ coordination spheres (X = F, H, Cl). The sums of the four Na-O bond valence contributions are 71, 75, and 89% of the total bond valences for the X = F, H, and Cl hydrated compounds, respectively, demonstrating that the relative coordinating ability by this criterion is B₁₂Cl₁₂^2- ≪ B₁₂H₁₂^2- < B₁₂F₁₂^2-. Differential scanning calorimetry experiments demonstrate that Na₂(B₁₂F₁₂) undergoes a reversible, presumably order-disorder, phase transition at ca. 560 K (287 °C), between the 529 and 730 K transition temperatures previously reported for Na₂(B₁₂H₁₂) and Na₂(B₁₂Cl₁₂), respectively. Thermogravimetric analysis demonstrates that Na₂(H₂O)₄(B₁₂F₁₂) and Na₂(H₂O)₆(B₁₂Cl₁₂) undergo partial dehydration at 25 °C to Na₂(H₂O)₂(B₁₂F₁₂) and Na₂(H₂O)₂(B₁₂Cl₁₂) in ca. 30 min and 2 h, respectively, and essentially complete dehydration to Na₂(B₁₂F₁₂) and Na₂(B₁₂Cl₁₂) within minutes at 150 and 75 °C, respectively (the remaining trace amounts of H₂O, if any, were not quantified). The changes in structure upon dehydration and the different vapor pressures of H₂O needed to fully hydrate the respective Na₂(B₁₂X₁₂) compounds provide additional evidence that B₁₂Cl₁₂^2- is more weakly coordinating than B₁₂F₁₂^2- to Na⁺ in the solid state. Taken together, the results suggest that the anhydrous, halogenated closo-borane compounds Na₂(B₁₂F₁₂) and Na₂(B₁₂Cl₁₂), in appropriately modified forms, may be viable component materials for fast-ion-conducting solid electrolytes in future energy-storage devices.