Irradiation of dibenzyl diselenide BnSeSeBn with X‐ray or UV‐light cleaves the Se−C and the Se−Se bonds, inducing stable and metastable radical states. They are inevitably important to all natural and life sciences. Structural changes due to X‐ray‐induced Se−C bond‐cleavage could be pin‐pointed in various high‐resolution X‐ray diffraction experiments for the first time. Extended DFT methods were applied to characterize the solid‐state structure and support the refinement of the observed residuals as contributions from the BnSeSe⋅ radical species. The X‐ray or UV‐irradiated crystalline samples of BnSeSeBn were characterized by solid‐state EPR. This paper provides insight that in the course of X‐ray structure analysis of selenium compounds not only organo‐selenide radicals like RSe⋅ may occur, but also organo diselenide BnSeSe⋅ radicals and organic radicals R⋅ are generated, particularly important to know in structural biology.

Irradiation of dibenzyl diselenide BnSeSeBn with X-ray or UV-light cleaves the SeÀ C and the SeÀ Se bonds, inducing stable and metastable radical states. They are inevitably important to all natural and life sciences. Structural changes due to X-ray-induced SeÀ C bond-cleavage could be pin-pointed in various highresolution X-ray diffraction experiments for the first time. Extended DFT methods were applied to characterize the solid-state structure and support the refinement of the observed residuals as contributions from the BnSeSe * radical species. The X-ray or UV-irradiated crystalline samples of BnSeSeBn were characterized by solid-state EPR. This paper provides insight that in the course of X-ray structure analysis of selenium compounds not only organo-selenide radicals like RSe * may occur, but also organo diselenide BnSeSe * radicals and organic radicals R * are generated, particularly important to know in structural biology.