Silicon Monoxide - Gaseous (molecular) SiO

Gaseous (molecular) SiO

Silicon monoxide molecules have been trapped in an argon matrix cooled by helium. The SiO bond length determined from SiO molecules isolated in argon is between 148.9 pm and 151 pm. This bond length is similar to the Si=O double bonds (r_SiO = 148 pm) in matrix isolated linear, molecular, SiO₂ (O=S=O), indicative of the absence of a triple bond as in CO. However, the SiO triple bond has a calculated bond length of 150 pm and a bond energy of 794 kJ/mol, which are also very close to those reported for SiO. The SiO double bond structure is, notably, an exception to Lewis' octet rule for molecules composed of the light main group elements, whereas the SiO triple bond satisfies this rule. That anomaly not withstanding, the observation that monomeric SiO is short-lived and that (SiO)_n oligomers with n = 2,3,4,5 are known, all having closed ring structures in which the silicon atoms are connected through bridging oxygen atoms (i.e. each oxygen atom is singly bonded to two silicon atoms; no Si-Si bonds), suggests the Si=O double bond structure, with a hypovalent silicon atom, is likely for the monomer.

SiO condensed with F₂, Cl₂ or COS, followed by irradiation with light, the planar molecules OSiF₂,(Si-O 148 pm); OSiCl₂, (Si-O 149 pm) and linear OSiS (Si-O 149 pm, Si-S 190 pm) are produced.

SiO condensed with oxygen atoms generated by microwave discharge produces molecular SiO₂ which has a linear structure.
When metal atoms are co-deposited (i.e.: Na, Al, Pd, Ag, Au) triatomic molecules are produced with linear, (AlSiO and PdSiO), non-linear (AgSiO and AuSiO), and ring (NaSiO) structures.