Hydrides - Swiss rhododendron

This refers to a binary compound of hydrogen in which hydrogen is the electronegative component. In a broader sense, it refers to all compounds of hydrogen and other elements, including cases in which hydrogen is the electropositive component, such as H ₂ S and NH _3. They are classified as follows: [ I ] Nonmetallic hydrides: Hydrides of boron and elements in groups 14 to 17 of the periodic table. Most are covalently bonded molecules, and many are gaseous at room temperature, with low melting and boiling points. However, hydrocarbons with large molecular weights and bonds between carbon atoms are an exception. In cases where hydrogen bonds exist between molecules, such as water and ammonia, the melting and boiling points may be higher than expected. In hydrides of elements of the same group (in the broad sense), the lower the electronegativity of the element, the more unstable it is. For example, HI is less stable than HCl, and H ₂ Te is less stable than H ₂ S. [ II ] Metallic hydrides:
(1) Salt-type hydrides: The H in hydrides (M ^I H, M ^II H ₂ ) with alkali metals and alkaline earth metals with an electronegativity of around 1 forms an ionic bond as the hydride ion H- ^. Hydrides of Be and Mg, which have a small ionic radius, have strong covalent bonds.
(2) Interstitial hydrides (see alternative terms) - Interstitial compounds: In hydrides of transition metals with intermediate electronegativity, H atoms or ^H- are inserted into the gaps of the metal lattice. They are often non-stoichiometric compounds. Pd, FeTi, and LaNi ₅ alloys, for example, can reversibly absorb large amounts of hydrogen, and are therefore used in hydrogen purification and as hydrogen storage alloys.
(3) Hydride complexes: Ligand hydride ^H- is coordinated to a central metal atom either alone (e.g. ^, _BH4- , _AlH4- ⁾ , or together with other ligands as mixed complexes.

Source: Morikita Publishing "Chemical Dictionary (2nd Edition)" Information about the Chemical Dictionary 2nd Edition

水素の二元化合物で，水素が陰性成分となるものをいう．広義には，H₂S，NH₃など水素が陽性成分となる場合も含め，水素とほかの元素との化合物すべてをいう．次のように分類される．【Ⅰ】非金属水素化物：ホウ素および周期表14～17族元素の水素化物．多くは共有結合性分子で，常温で気体のものも多く，融点，沸点も低い．ただし，炭素原子間の結合がある分子量の大きい炭化水素は例外である．水，アンモニアなど，分子間に水素結合が存在する場合は，予想より高い融点，沸点を示すこともある．同族元素の水素化物(広義)では，その元素の電気陰性度が低いほうがより不安定である．たとえば，HIはHClより，H₂TeはH₂Sより不安定である．【Ⅱ】金属水素化物：
(1)塩型水素化物；電気陰性度が1前後のアルカリ金属，アルカリ土類金属との水素化物(M^ⅠH，M^Ⅱ H₂)のHは，水素化物イオン H^－ となってイオン結合している．イオン半径の小さいBe，Mgの水素化物は共有結合性が強い．
(2)侵入型水素化物([別用語参照]侵入型化合物)；電気陰性度が中間的な遷移金属の水素化物では，H原子または H^－ が金属格子のすきまに入っている．不定比化合物となることが多い．Pd，FeTi，LaNi₅合金などは大量の水素を可逆的に吸収するので，水素精製や水素吸蔵合金として使われる．
(3)ヒドリド錯体；配位子ヒドリド H^－ が単独でBH₄^－，AlH₄^－などのように，または混合錯体としてほかの配位子とともに中心金属原子に配位したもの．

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