Synthesis, structure and the dehydrogenation mechanism of calcium amidoborane hydrazinates

The calcium amidoborane hydrazinates, Ca(NH2BH3)(2)center dot nN(2)H(4), were firstly synthesized by reacting different molar ratios of Ca(NH2BH3)(2) and N2H4. In particular, Ca(NH2BH3)(2) and N2H4 with a molar ratio of 1: 2 crystallizes into the orthorhombic symmetry P2(1)2(1)2(1) space group with the lattice parameters of a = 6.6239(4) angstrom, b = 13.7932(6) angstrom, c = 4.7909(2) angstrom. The dehydrogenations of calcium amidoborane hydrazinates are two-step reactions, exhibiting superior dehydrogenation properties compared with those of pristine Ca(NH2BH3)(2). For Ca(NH2BH3)(2)-1/2N(2)H(4), approximately 4.6 equiv. hydrogen (or 7.9 wt% hydrogen) can be released at 150 degrees C. Kinetic analysis shows that the activation energies for the two steps of hydrogen desorption from Ca(NH2BH3)(2)center dot 2N(2)H(4), are much lower than those of pristine Ca(NH2BH3)(2), suggesting an improvement in the dehydrogenation kinetics of Ca(NH2BH3)(2) after coordinating with N2H4. Isotopic labeling results show that the driving force for the dehydrogenation of calcium amidoborane hydrazinates is the combination mechanism of protonic hydrogen and hydridic hydrogen (H-delta+ and H delta-). In addition, initial H-2 release from calcium amidoborane hydrazinates originates from the interaction of [-BH3] and N2H4, rather than [-BH3] and [-NH2] (in [-NH2BH3]).