New Directions for Higher Boranes Bjarne R. S. Hansen

Introduction Molecular boranes have been known for 100 years! -First borane correctly identified (B4H10) in 1912 by A. Stock Molecular boranes have a rich history in rocket fuel applications -Boranes (B-H) 70,000 kJ/kg -Alkanes (C-H) 42,000 kJ/kg Metal borohydrides first reported in 1940 by Schlesinger, Brown & Burg: Al(BH4)3, Be(BH4)2, LiBH4 F. M. Hawthorne synthesized the B12H122- anion in 1960 Nobel Prize in Chemistry 1976: W. N. Lipscomb for his studies on the structure of boranes illuminating problems of chemical bonding Nobel Prize in Chemistry 1979: H. C. Brown for boron compounds as reducing agents in organic chemistry

Borane Anions Closo BnHn Nido BnHn+4 Arachno BnHn+6 5 6 7 8 9 10 11 12 10.1016/j.ccr.2015.12.003

Metal Borane Synthesis Hansen et al. Coord Chem Rev, 2016, 10.1016/j.ccr.2015.12.003

B10H102- and B12H122- compounds and derivatives NH4+ Table available here: Hansen et al. Coord Chem Rev, 2016 10.1016/j.ccr.2015.12.003 Often hydrates or solvates!

Closo-borane applications Ion conductors PCCP, 2013,15, 15825-15828 Carborane-containing amino acids Medicine (BNCT) – Cancer Therapy NH3/H2 storage J. Mater. Chem., 2010, 20, 2743-2745 Li2B12H12∙7NH3 Org. Lett., 2006, 8 (8), 1713–1716 Light Nano-Car Texas, USA Polym. Chem., 2011, 2, 2122 Polymers/Ceramics Luminescence J. Mater. Chem. A, 2015, 3, 22853

Solid-State Ion Conductivity Hansen et al. Coord Chem Rev, 2016, 10.1016/j.ccr.2015.12.003

Silver Boranes: Synthesis λ = 0.9938 Å Hydroxides, metals, nitrates or oxides can also be used instead of carbonates Muetterties, Chemistry of Boranes VIII, salts and acids of B10H102- and B12H122-,1964 Paskevicius et al. Nature Energy, 2016, submitted

Silver Boranes: Structures β-Ag2B12H12 α-Ag2B12H12 Fm-3m Pa-3 50% 12.5% Paddlewheel mechanism B12H122- anion highly dynamic Ag+ in partially occupied sites with much closer jumps Only certain Ag-sites are permitted for particular B12H122- orientations (Ag-H distance) Boron, Silver Paskevicius et al. Nature Energy, 2016, submitted

Silver Boranes: Ion Conductivity Au Sample Electrochemical Impedance Spectroscopy Mark Paskevicius Silver boranes, worth their weight in gold? Tuesday, Room 3 Paskevicius et al. Nature Energy, 2016, submitted

Aim is to study structures and decomposition mechanism NH3 storage in closo-boranes Or indirect H storage MB12H12 M = Li2, Na2, Ca Flask placed in cooling bath λ = 1.5406 Å Aim is to study structures and decomposition mechanism Hansen et al. J. Phys. Chem. C, 2016, to be submitted

NH3 storage in closo-boranes Na2B12H12∙2NH3 Trigonal, P-3m1 (no. 164) a = 7.1672(1) Å , c = 7.1574(2) Å, In situ SR-PXD of ammoniated Na2B12H12 HT-Na2B12H12 LT-Na2B12H12 Na2B12H12∙4NH3 Monoclinic, P21/n (no. 14) a = 8.6875(2)Å , b = 9.4168(3) Å, c = 9.9096(3) Å, β = 98.3296(18)° Boron, Sodium, Nitrogen, Hydrogen Na2B12H12∙xNH3 λ = 0.7750 Å Hansen et al. J. Phys. Chem. C, 2016, to be submitted

NH3 storage in closo-boranes λ = 1.5406 Å Na2B12H12 CaB12H12 Compound NH3 content (wt%) H content from NH3 (wt%) Total H content (wt%) Li2B12H12∙7NH3 43.36 7.70 12.10 Na2B12H12∙4NH3 26.62 4.73 9.45 CaB12H12∙6NH3 35.97 6.39 10.64 Thermal and chemical stability advantageous No formation of BN Reversible Hansen et al. J. Phys. Chem. C, 2016, to be submitted

NH3 storage in closo-boranes Reversible NH3 storage Thermal and chemical stability advantageous No formation of BN Reversible Hansen et al. J. Phys. Chem. C, 2016, to be submitted

Conclusions Revisit old methods to make new materials Extensive research foundation in the literature on metal boranes New materials lead to ‘new’ and exciting properties Ag2B10H10 and Ag2B12H12 are excellent ion conductors and have interesting structures Ammine metal closo-boranes can be useful for reversible NH3/H2 storage or as DeNOX catalysts There are large number of metal boranes to be explored for a broad number of applications GO AND EXPLORE NOW!

Thank you for your attention! Acknowledgements Funding: HAPPY BIRTHDAY (…Yesterday) Mark Paskevicius Torben R. Jensen Mark Paskevicius Bo Richter Mathias Jørgensen Anders S. Jacobsen Hai-wen Li Etsuo Akiba Nikolay Tumanov Yaroslav Filinchuk Antonio Santoru Claudio Pistidda Martin Dornheim Thank you for your attention!