16.
In view of immense importance of silylenes and the fact that their properties undergo significant changes on substitution with halogens, here, we have used B3LYP/6-311++G** level of theory to access the effects of 1–4 halogens (X = F, Cl, Br, and I) on four unprecedented sets of cyclopentasilylene-2,4-dienes; with the following formulas: SiC
4H
3X ( 1
X ), SiC
4H
2X
2 ( 2
X ), SiC
4HX
3 ( 3
X ), and SiC
4X
4 ( 4
X ). In going down from F to I, the singlet (s)-triplet (t) energy gap (ΔE
s-t, a possible indication of stability), and band gap (ΔE
H-L) decrease while nucleophilicity (
N), chemical potential (
μ), and proton affinity (PA) increase. The overall order of
N,
μ, and PA for each X is 2
X > 1
X > 3
X > 4
X . Precedence of 2
X over 1
X is attributed to the symmetric cross conjugation in the former. The highest and lowest
N are shown by 2
I and 4
F . The trend of divalent angle () for each X is 4
X > 1
X > 3
X > 2
X . The results show that in going from electron withdrawing groups (EWGs) to electron donating groups (EDGs), the ΔE
s-t and ΔE
H-L decrease while
N,
μ, and PA increase. Also, rather high
N of our scrutinized silylenes may suggest new promising ligands in organometallic chemistry.
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