Powdered graphite (either finely broken HOPG or Union Carbide SP1) interacts with 1:1 SiF4/F2 mixture (∼50 atmospheres) at 40°, to yield a second-stage compound (a0 = 2.46(1), c0 = 11.29(1) Å) of composition C∼24SiF5. This product interacts with excess PF5 with quantitative displacement of SiF4 to yield a first-stage fluorophosphate (a0 = 2.46(1); c0 = 7.65(1) A ̊) according to the equation: C24SiF5 + 2PF5 → C24PF6. PF5 + SiF4. The first-stage fluorophosphate falls to a second-stage salt (a0 = 2.46(1); c0 = 10.87 A ̊) under vacuum: C24PF6.PF5 20° → C24PF6 + PF5. This is identical to that prepared directly: 24C + PF5 + 1 2 F2 → C24PF6. Extensive reduction of C24PF6, at ≈20° : 2C24PF6 + PF3 → 48C + 3PF5 to graphite of crystallinity comparable to that of the starting graphite establishes that the initial C24SiF5 does not involve extensive fluorination of the graphite. The ease of displacement of SiF4 by superior fluoroacids indicates that C24SiF5 can be a valuable precursor for other graphite salts. Ready formation of a first-stage fluoroborate, C7BF4, Ic = 7.70(1) A ̊ contrasts with the failure to prepare similarly a first-stage SiF5- salt.
All Science Journal Classification (ASJC) codes
- Electronic, Optical and Magnetic Materials
- Condensed Matter Physics
- Mechanics of Materials
- Mechanical Engineering
- Metals and Alloys
- Materials Chemistry