Lewis Acid/Base Interaction Matrix Database


Type 5 Lewis Acid/Base Complexation Chemistry
Saline Hydrides

               Li+      +    H       LiH
               Mg2+   +   2H     MgH2

Bonding:

Group I & II alkali and alkaline earth hydrides exist as ionic lattice solids. However, molecular 1:1 (LiH) and 1:2 (MgH2) complexes are formed in the vapor phase, although with difficulty as the compounds are liable to decompose back to elemental form.

LiH is a much theoretically studied diatomic species. Studies show that bonding involves more than just s-LUMO/s-HOMO overlap. In valence bond (VB) terminology, the lithium’s 2s-LUMO mixes with (ie hybridizes with) a higher energy empty 2p orbital (ie the LUMO + 1 MO) to generate a directional sp hybrid bond.

MO calculations show that the bonding in LiH involves 66% Li 2s/H1s overlap and 34% Li 2p/H 1s overlap.

Charge:

The charge on a Type 5 complex is always neutral.

Chemistry:

Saline hydride complexes either act as strong proton abstracting Bases or as donors of nucleophilic hydride ion. Organic chemists employ saline hydride complexes as proton abstracting Bases, with H2 being the conjugate Brønsted acid.

Sodium hydride readily abstracts a proton from dimethyl sulfoxide (DMSO), pKa 35, to form sodium dimsyl:

Inorganic chemists are more likely to use saline hydride reagents as a source of nucleophilic (and reducing) hydride ion, for example in the synthesis of sodium borohydride:

Congeneric Series:

     

              LiH             NaH              KH               RbH              CsH
              BeH2          MgH2            CaH2            SrH2              BaH2

Type 5 Lewis acid/base complex (generic)
Barium hydride

more here
Beryllium hydride

more here
Calcium hydride

more here
Cesium hydride

more here
Lithium hydride

more here
Magnesium hydride

more here
Potassium hydride

more here
Rubidium hydride

more here
Sodium hydride

more here
Strontium hydride

more here


Interactions and reactions classified as:
Type 5 Lewis Acid/Base Complexation Chemistry
      1 +1 1
       +
      1 +1 1
      1 +1 1
      1 +1 1
      1 +1 1
      1 +2 1
      1 +2 1
      1 +2 1
      1 +2 1
      1 +2 1



Poster
Nucleophiles & Bases

© Mark R. Leach 1999-


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