"NaB15": A new structural description based on X-ray and neutron diffraction, electron microscopy, and solid-state NMR spectroscopy

A boron-rich sodium boride, formerly known as NaB15, has been subjected to a comprehensive structural reinvestigation using X-ray single-crystal and p owder diffraction, low-temperature neutron and electron diffraction, high r esolution transmission electron microscopy, and Na-23 solid-state NMR spect roscopy. The results indicate that the previously published orthorhombic sp ace group is incorrect. Consistent with all of the experimental results a m odified structural description is developed in the monoclinic space group 1 1m1 (a = 555.92(3), b = 1039.92(6), c = 833.17(5) pm, beta = 90.373(5)degre es from powder data). Because one of the interstitial boron atom positions remains unoccupied, the accurate compositional formula is NaB14.5 or Na2B29 .