Supporting Information for “ A Hydride Composite Featuring Mutual Destabilisation and Reversible Boron Exchange : Ca ( BH 4 ) 2-Mg 2 NiH 4 ”

Please do not adjust margins a. Institute of Materials Research, Materials Technology, Helmholtz-Zentrum Geesthacht GmbH, Max-Planck-Straße 1, D-21502, Geesthacht, Germany b.Pavia Hydrogen Lab, CSGI and Università di Pavia, Dipartimento di Chimica, Sezione di Chimica Fisica, Viale Taramelli, 16, 27100, Pavia, Italy c.Department of Physics, University of Helsinki, Gustaf Hällströmin katu 2 P.O. Box 64, Helsinki, Finland d.ISIS Facility, Rutherford Appleton Laboratory, Chilton, Didcot, Oxfordshire OX11 0QX, United Kingdom e.Servei de Ressonància Magnètica Nuclear, Universitat Autònoma de Barcelona, Cerdanyola del Vallès, Spain f.Department of Chemistry and NIS Centre, University of Torino, Via P. Giuria 7, Torino, Italy g.Departament de Física, Facultat de Ciències, Universitat Autònoma de Barcelona, E-08193 Bellaterra, Cerdanyola del Vallès, Barcelona, Spain h.Helmut Schmidt University, Institute of Materials Technology, Hamburg, Germany Received 00th January 20xx, Accepted 00th January 20xx