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Comparison of the Coordination of B12F12^2-^, B12Cl122-, and B12H12^2-^ to Na+ in the Solid State: Crystal Structures and Thermal Behavior of Na2(B12



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


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 K and 295 K NPD), and Na2(H2O)6(B12Cl12) (100 K SC-XRD) are reported. The compound Na2(H2O)4(B12F12) contains [(Na(υ-H2O)2Naυ-H2O)2)]2+}∞ infinite chains; the compound Na2(H2O)6(B12Cl12) contains discrete [(H2O)2Na(υ-H2O)2Na(H2O)2]2+ cations with OH&#8226&#8226&#8226O 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 B12F122−, B12H122−, and B12Cl122− towards 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 Na(H2O)4X2 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, Cl, and H hydrated compounds, respectively, demonstrating that the relative coordinating ability by this criterion is B12Cl122− << B12H122− < B12F122−. This conclusion must be tempered by the fact that two of the four H2O ligands in Na2(H2O)6(B12Cl12) are terminal and two bridge pairs of Na+ ions, whereas all four H2O ligands bridge pairs of Na+ ions in Na2(H2O)4(B12F12) and Na2(H2O)4(B12H12). 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 experiments demonstrate 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 complete dehydration to Na2(B12F12) and Na2(B12Cl12) within minutes at 150 and 75 °C, respectively. In appropriately modified forms, the anhydrous, halogenated closo-borane compounds may find utility as component materials for fast-ion-conducting solid electrolytes in future energy-storage devices.
Inorganic Chemistry


closo-boranes, crystallography, density functional theory, hydrates, neutron powder diffraction, phase transitions, single-crystal x-ray diffraction, sodium closo-borates, structure


Bukovsky, E. , Peryshkov, D. , Wu, H. , Zhou, W. , Tang, W. , Jones, W. , Stavila, V. , Udovic, T. and Strauss, S. (2017), Comparison of the Coordination of B<sub>12</sub>F<sub>12</sub>^2-^, B<sub>12</sub>Cl<sub>12</sub><sup>2-</sup>, and B<sub>12</sub>H<sub>12</sub>^2-^ to Na<sup>+</sup> in the Solid State: Crystal Structures and Thermal Behavior of Na<sub>2</sub>(B<sub>12</, Inorganic Chemistry, [online], (Accessed April 14, 2024)
Created April 5, 2017, Updated October 12, 2021