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Pentamethylantimony
Pentamethylantimony or pentamethylstiborane is an organoantimony compound containing five methyl groups bound to an antimony atom with formula Sb(CH3)5. It is an example of a hypervalent compound. The molecular shape is trigonal bipyramidal. Some other antimony(V) organometallic compounds include pentapropynylantimony (Sb(C≡C−CH3)5) and pentaphenyl antimony (Sb(C6H5)5). Other known pentamethyl-pnictides include pentamethylbismuth and pentamethylarsenic.
Pentamethylantimony can be made by reacting Sb(CH3)3Br2 with two equivalents of methyl lithium. Another production route is to convert trimethylstibine to the trimethyl antimony dichloride, and then replace the chlorine with methyl groups with methyl lithium.
Pentamethylantimony is colourless. At -143 °C it crystallizes in the orthorhombic system with space group Ccmm. Unit cell dimensions are a=6.630 Å b=11.004 Å c=11.090 Å. There are four formula per unit cell. Unit cell volume is 809.1 Å3. The trigonal bipyramid shape has three equatorial positions for carbon, and two axial positions at the peaks of the pyramids. The length of the antimony-carbon bond is around 214 pm for equatorial methyl groups and 222 pm for the axial positions. The bond angles are 120° for ∠C-Sb-C across the equator, and 90° for ∠C-Sb-C between equator and axis. The molecules rapidly change carbon atom position, so that in NMR spectrum as low as −100 °C, there is only one kind of hydrogen position.
Pentamethylantimony is more stable than pentamethylbismuth, because in lower energy trimethylbismuth, the non-bonding pair of electrons is more shielded due to the f-electrons and the lanthanoid contraction. Trimethylantimony is higher in energy, and thus less is released in a decomposition of pentamethylantimony. Pentamethylantimony can be stored as a liquid in clean glass at room temperature.
Pentamethylantimony melts at -19 °C. Although it decomposes when boiling is attempted and can explode, it has a high vapour pressure at 8 mmHg at 25 °C.
There are two absorption bands in the ultraviolet at 2380 and 2500 Å.
Pentamethylantimony reacts with methyl lithium to yield a colourless lithium hexamethylantimonate in tetrahydrofuran.
Pentamethylantimony reacts with silsesquioxanes to yield tetramethylstibonium silsesquioxanes. eg (cyclo-C6H11)7Si7O9(OH)3 yields (cyclo-C6H11)7Si7O9(OSb(CH3)4)3. The reaction happens quickly when there are more than two OH groups.
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Pentamethylantimony
Pentamethylantimony or pentamethylstiborane is an organoantimony compound containing five methyl groups bound to an antimony atom with formula Sb(CH3)5. It is an example of a hypervalent compound. The molecular shape is trigonal bipyramidal. Some other antimony(V) organometallic compounds include pentapropynylantimony (Sb(C≡C−CH3)5) and pentaphenyl antimony (Sb(C6H5)5). Other known pentamethyl-pnictides include pentamethylbismuth and pentamethylarsenic.
Pentamethylantimony can be made by reacting Sb(CH3)3Br2 with two equivalents of methyl lithium. Another production route is to convert trimethylstibine to the trimethyl antimony dichloride, and then replace the chlorine with methyl groups with methyl lithium.
Pentamethylantimony is colourless. At -143 °C it crystallizes in the orthorhombic system with space group Ccmm. Unit cell dimensions are a=6.630 Å b=11.004 Å c=11.090 Å. There are four formula per unit cell. Unit cell volume is 809.1 Å3. The trigonal bipyramid shape has three equatorial positions for carbon, and two axial positions at the peaks of the pyramids. The length of the antimony-carbon bond is around 214 pm for equatorial methyl groups and 222 pm for the axial positions. The bond angles are 120° for ∠C-Sb-C across the equator, and 90° for ∠C-Sb-C between equator and axis. The molecules rapidly change carbon atom position, so that in NMR spectrum as low as −100 °C, there is only one kind of hydrogen position.
Pentamethylantimony is more stable than pentamethylbismuth, because in lower energy trimethylbismuth, the non-bonding pair of electrons is more shielded due to the f-electrons and the lanthanoid contraction. Trimethylantimony is higher in energy, and thus less is released in a decomposition of pentamethylantimony. Pentamethylantimony can be stored as a liquid in clean glass at room temperature.
Pentamethylantimony melts at -19 °C. Although it decomposes when boiling is attempted and can explode, it has a high vapour pressure at 8 mmHg at 25 °C.
There are two absorption bands in the ultraviolet at 2380 and 2500 Å.
Pentamethylantimony reacts with methyl lithium to yield a colourless lithium hexamethylantimonate in tetrahydrofuran.
Pentamethylantimony reacts with silsesquioxanes to yield tetramethylstibonium silsesquioxanes. eg (cyclo-C6H11)7Si7O9(OH)3 yields (cyclo-C6H11)7Si7O9(OSb(CH3)4)3. The reaction happens quickly when there are more than two OH groups.