Molecular-Engineered Biradicals Based on the Y III-Phthalocyanine Platform

A mixed-ligand phthalocyanine/porph y r i n yttrium(III) radical double-decker complex (DD) was synthesized using the custom-made 5,10,15-tris(4-methoxyphenyl)-20-(4-((trimethylsilyl)ethynyl)phenyl)porphyrin. The trimethylsilyl func-tionality was then used to couple two such complexes into biradicals through rigid tethers. Glaser coupling was used to synthesize a short-tethered biradical (C1) and Sonogashira coupling to synthesize longer-tethered ones (C2 and C3). Field-swept echo-detected (FSED), saturation recov e r y , and spin nutation-pulsed electron paramagnetic resonance experiments revealed marked similarities of the magnetic properties of DD with those of the parent [Y(pc)2]center dot complex, both in the solid state and in CD2Cl2/CDCl 3 4:1 frozen glasses. FSED experiments on the biradicals C2 and C3 revealed a spectral broadening with respect to the spectra of DD and [Y(pc)2]center dot assigned to the effect of dipola r interactions in solution. Apart from the main resonance, satellite features were also observed, which were simulated with dipole- dipole pairs of shortest distances, suggesting spin delocalization on the organic tether. FSED experiments on C1 yielded spect r a l line shapes that could not be simulated as the integration of the off-resonance echoes was complicated by field-dependent modulations. While, for all dimers, the on-resonance spin nutation experiments yielded Rabi oscillations of the same frequencies, off-resonance nutations on C1 yielded Rabi oscillations that could be assigned to a M S = -1 to MS = 0 transition within a S = 1 multiplet. The DFT calculations showed that the trans conformation of the complexes was significantly more stable than the cis one and that it induced a marked spin delocalization over the rigid organic tether. This spin leakage was most pronounced for the shortest biradical C1.

Automated summary

A mixed-ligand phthalocyanine/porphyrin yttrium(III) radical double-decker complex (DD) was synthesized using a custom-made 5,10,15-tris(4-methoxyphenyl)-20-(4-((trimethylsilyl)ethynyl)phenyl)porphyrin. Rigid tethers were used to couple two such complexes into biradicals through the trimethylsilyl functionality. The magnetic properties of DD were found to be similar to those of the parent [Y(pc)2]center dot complex in both the solid state and frozen glasses.