Boron Hydrides.pptx

Anorganic

1. Boron Hydrides These form one of the most structurally diverse series of compounds. Simplest is diborane, B 2 H 6 . Similar formula to ethane, but structurally very different because it is electron deficient. Gets around the problem by forming delocalised bonds. C has 4 valence e, H has 1, so C 2 H 6 has enough electrons (8+6) for 7 2c2e bonds. B 2 H 6 only has 6+6=12 electrons. This makes an ethane-like structure impossible

2. Boranes have unusual structures and bonding Notice that there are two types of bonds in boranes :- the regular two-center 2e - bond :- a three-center 2e - bond

3. TATANAMA SENYAWA BORAN

4. Structure-bonding elements (p116) Terminal (2c –2e) boron-hydrogen bond B––H (3c –2e) hydrogen bridge bond B B (2c –2e) boron-boron bond B––B Open (3c –2e) B-B-B bond B B Closed (3c –2e) boron bond B B B H B

5. Electron Counting Just how electron deficient a borane is can be derived by counting the number of skeletal pairs of electrons. Each HB has 4 valence electrons. One pairs used for a 2c2e bond (e.g a terminal BH). The remaining 2e are used for delocalized cluster bonding. Any remaining H contribute 1e to the cluster [B 6 H 6 ] 2- write as (BH) 6 2- Each BH unit contributes 2e Plus the 2- charge gives 14 electrons 6 boron atoms in the cluster bonded with 7 pairs (6+1).

6. Dengan menggunakan Wade’s rule buktikan senyawa cluster di bawah ini memiliki bentuk seperti disebutkan : [B 9 H 9 ] 2- , closo B 6 H 10 , nido B 4 H 10 , arachno