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Lewis Acid/Base Interaction Matrix Database

Type 21 Lewis Acid/Base Complexation Chemistry

Heavy Metal Hydrides
  • Metallic or interstitial hydrides are formed by many d-block and f-block elements when heated with hydrogen under pressure. The hydrides tend to be non-stoichiometric and they may be of variable composition.
  • There is a hydride gap where elements do not form hydrides. This roughly maps to the siderophile elements.
  • Intermediate hydrides have properties between metallic and covalent.

Metallic properties and non-stoichiometric compositions are common. The bonded hydrogen may be mobile. In various models the hydrogen may be present as H+ with the lost electrons going to the metal’s d-orbitals. In other models the hydrogen is assumed to have acquired electrons from the metallic conduction band and so be present as H.

Note that even though a metal may not form a hydride, it can still form a hydride complex ion, for example rhenium:

Re7+    +   9H      →     [ReH9]

Charge: Complexes may be negatively charged or they may be neutral.

Hydride and hydrogen donors. Transition metal hydrides, MHn, can sometimes be formed by ‘dissolving’ hydrogen gas into a bulk metal to from a metal/hydride phase. This phase is the active ‘hydrogenating agent’ employed during catalytic hydrogenation. Palladium metal is able to absorb 900 times its own volume of hydrogen gas.

Transition metal/hydride coordination complexes can be formed by nucleophilic displacement of a halogen (or other nucleofugal ligand) by hydride ions supplied by LiAlH4 or NaBH4:

Metallic hydrides materials are usually dark powders or brittle solids. The bonding mechanism is important because heavy metal hydrides are being actively considered as hydrogen storage materials for hydrogen powered automobiles.

Congeneric Series: Few series.
Type 21 Lewis acid/base complex (generic)
Chlorohydrobis(triethylphosphine) platinium(II)

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Iron titanium hydride

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Lanthanum nickel hydride

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Magnesium nickel hydride

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Palladium hydride

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Rhenium nonahydride ion

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Scandium(II) hydride

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Interactions and reactions classified as:
      2 +1 2
      1 +9 1
      1 +1 +2 +1 1
      1 +6 1
      1 +4 1
      1 +4 1

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Poster Nucleophiles & Bases

© Mark R. Leach 1999 –

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