The attractive isomers of 1,1′-bis(verdazyl)ferrocene diradical on structure-property relationship

- Based on diradical 1,1′-bis(verdazyl)ferrocene (20), two isomeric 319 and 4144 are obtained by rotate about 19° and 144°.
- Three diradicals complexes displayed 2e/8c π-π (20) bonding, σ-covalent bonding (319) and non-bonding (4144), respectively.
- The 20,319 and 4144 may transform to each other with two separate radicals in different environment.

In 2006, the interesting π-stacks diradical 1,1′-bis(verdazyl)ferrocene (20) with two-electron multicenter (2e/mc) bonding were synthesized and investigated (J. Am. Chem. Soc. 2006, 128, 690-691). Based on the 20, two attractive isomeric complexes(319 and 4144) are designed by a piece of radical rotating along iron-Cp axis about 19° and 144°, respectively. Among these three diradicals, a unique two-electron eight-center (2e/8c) π-π bonding is obtained in the 20 due to the overlap of SOMOs of the two pieces of radicals, the 319 has a σ-covalent bonding, and two separate radicals are shown in the 4144. Further, the UV-visible absorption spectrum of 20 and 319 arise a new absorption feature at 566 and 530 nm, respectively, which may be assigned to π-π stacking (20) and σ-covalent (319) bonding of two pieces of radicals, although this absorption feature not exist in experimental UV-visible absorption spectrum. Fortunately, the UV-visible absorption spectrum of 4144 is similar to experimental results, which demonstrate that the 20 with 2e/8c bonding may transform to be 4144 with two separate radicals in solution. These three diradicals may transform to each other, which is beneficial to understanding their magnetic properties in solution and crystal and designing new complexes with excellent magnetic property.

Based on the interesting π-stacks diradical 1,1′-bis(verdazyl)ferrocene (20), we calculated a scan through rotational motion along iron-Cp axis, and two lower enger attractive isomeric diradicals 319 and 4144 are obtained by rotate about 19° and 144°. Interestingly, these three diradicals complexes displaed 2e/8c π-π (20) bonding, σ-covalent bonding (319) and non-bonding (4144), respectively. The 20, 319 and 4144 may transform to each other with two separate radicals in different environment.147