Coordination compounds partial decomposition

The physical and chemical properties are less well known for transition metals than for the alkaU metal fluoroborates (Table 4). Most transition-metal fluoroborates are strongly hydrated coordination compounds and are difficult to dry without decomposition. Decomposition frequently occurs during the concentration of solutions for crysta11i2ation. The stabiUty of the metal fluorides accentuates this problem. Loss of HF because of hydrolysis makes the reaction proceed even more rapidly. Even with low temperature vacuum drying to partially solve the decomposition, the dry salt readily absorbs water. The crystalline soflds are generally soluble in water, alcohols, and ketones but only poorly soluble in hydrocarbons and halocarbons. 

The mechanism of the process in terms of involved reactions is quite complex. An isolation of decomposition intermediates was possible only in few cases [16, 17]. To point up the diversity of the reaction paths that can occur during the decompositions of these compounds, two examples will be given in the following. The first is the thermal decomposition of [Fe(urea)g](NOj)j [17] compound (Scheme 3.2). After melting, a simultaneously release of nitrate and urea takes place, that subsequent suffer further transformations. The evolved gaseous medium favors besides a partial reduction of the Fe, their coordination with HO" in different hydroxyl-based complexes. On further heating, the complex intermediates are converted into various iron hydroxides and oxyhydroxides species, via successive oxidation and dehydrogenation steps. 

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