Inorganic crystal engineering using hydrogen bonds

3 Inorganic crystal engineering using hydrogen bonds 

The central metal domain of a metal complex consists of the metal atom M, a metal hydride group, or a number of metal atoms if a metal cluster complex is considered. The ligand domain is composed of ligand atoms L directly bonded with the metal center(s). The periphery domain is the outmost part of the complex, consisting of those parts of the ligand not strongly influenced by electronic interaction with the metal center. 

Hydrogen bonding arising from donor groups (M)O-H and (M)N-H is commonly observed. The a-type coordinated ligands are hydroxy (OH), aqua (OH2), alcohol (ROH), and amines (NH3, NRH2, NR2H). Acceptors include halide-type (M-X with X = F, Cl, Br, I), hydride-type (D-H- H-M and D-H- H-E with E = B, Al, Ga) and carbonyl-type (D-H- OC-M). 

Some examples of the coordination polymers consolidated by hydrogen bonding are discussed below. 

Hydrogen-bonded chain in (a) Fe[iy5-CpCOOH]2, (b) [Ag(nicotinamide)2]+, and (c) Ru(r/s-Cp)(jj5-l-p-tolyl-2-hydroxyindenyl)l (T stands for p-tolyl group). 

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The use of coordination bonds to form networks, so-called coordination polymers, perhaps represents the most widely studied form of inorganic crystal engineering. This approach has also been examined in a number of reviews [8] and is discussed elsewhere in this volume (see Chapter 5). While coordination chemistry will have an important role to play in a number of the hydrogen-bonded systems presented in this chapter, coordination polymers will only be discussed in the context of their cross-linking or their perturbation using hydrogen bonds. 

Hydrogen bond types that are widely used in organic crystal engineering, primarily D-H A where D, A = O or N, will inevitably be important in inorganic systems since the same functional groups that form such hydrogen bonds, i.e. carboxyl, amide, oxime, alcohol, amine, etc., can be present as part of organic... 

Clearly specific to inorganic systems are hydrogen bonds that directly involve metal atoms, M-H A and D-H M, i.e. those in the Metal Domain. A survey of crystal structures has illustrated that M-H O hydrogen bonds appear to resemble C-H O hydrogen bonds, although the former are of course far less abundant. The extent to which such hydrogen bonds may be useful in crystal engineering is addressed in Section 6. 

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