Ternary transition metal complex hydrides

Three transition metal complex hydrides Mg NiH, Mg CoHj and Mg FeH have been extensively studied, especially from the standpoint of their synthesis to nanos-tructured hydrides by ball milling. 

They suggested that in the first stage of hydrogenation hydrogen dissolves in the Mg Ni phase to the extent that the ratio of H/(Mg + Ni)=0.1 according to the reaction 

The standard enthalpy (AH) and entropy (A5) of formation at 298 K was -64.5 kJ/molH and -122.3 J/molH K, respectively. It is to be noted that the enthalpy of formation/decomposition of Mg NiH is slightly lower than that of MgH (Sect. 2.1) which allows the former to desorb at slightly lower temperatures than MgH.  

Reilly and Wiswall reported that the polycrystalline form of Mg Ni produced by a conventional ingot metallurgy still required activation by short cycling at 300°C. 

In the past few years there still have been some research efforts focused on Mg NiH. The Akiyama s group in Japan [20-22] has developed a hydriding combustion synthesis technique for the direct fabrication of Mg NiH. The results showed that the product of Mg NiH from the hydriding combustion synthesis absorbed the maximum (3.4-3.6 wt%) near the theoretical value just after synthesis without any activation process. 

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In ternary transition metal complex hydrides, Mg2FeHg, has a considerably higher hydrogen content ( 5.5 wt%) than that of Mg2NiH4 (3.6 wt%), and a high volumetric density (150 kg/m ). 

This volume summarizes recent results of some of the leading investigators in trahsition metal hydride research. Readers interested in more extensive background material are urged to consult some of the many excellent books on the subject, such as Transition Metal Hydrides edited by E. L. Muetterties (Marcel Dekker, Inc., New York, 1971), which covers covalent metal hydride complexes, and Metal Hydrides edited by W. M. Mueller, J. P. Blackledge, and G. G. Libowitz (Academic, New York, 1968), which comprehensively covers work in binary and ternary metal hydrides. Also available in the covalent metal hydride area are excellent reviews by Ginsberg [Transition Metal Chemistry (1965) 1,112], and Kaesz and Saillant [Chemical Reviews (1972) 72, 231]. In this book we have not tried to be comprehensive rather, our purpose is to update recent developments in both major areas of metal hydride research. 

M. Kritikos D. Nordus (1991). J. Solid State Chem., 93,256-262. Synthesis and characterization of ternary alkaline-earth transition-metal hydrides containing octahedral [Ru(II)H5] and [Os(II)H6] complexes. 

Table 6.3 Metal hydride complexes in ternary and quaternary 3d transition metal hydrides, as of May 2007...

The decomposition pathways of binary and ternary metal tetrahydroborates are often highly complex and differ significantly from one system to the next, e.g., LiBHt [45], Mg(BH4)2 [46], and LiZn(BFl4)3 [47], and the formed products can even depend on the details of the desorption conditions. Certain compounds form transition metal hydrides [48], others form transition metal borides [49], di-, deca-, or dodeca-boranes [50], and others again, e.g., Cr, Cd, Mn, and Zn(BH4)2 decompose to the elements [51,52,112]. 

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