Crystallographic study reveals direct equatorial chloride coordination in uranyl peroxide stabilized by potassium, suggesting new actinide phase behavior in chloride-rich nuclear waste environments.
Uranyl peroxide chemistry has traditionally been limited to natural phases─studtite and metastudtite─or to synthetic uranyl peroxide complexes and clusters in which the uranyl equatorial plane is generally oxygen-coordinated. Herein, we report the first uranyl peroxide chloride compound of K(UO 2 )O 2 (H 2 O)Cl·2H 2 O, featuring chloride directly coordinated within the uranyl equatorial plane, a structural motif unprecedented in natural or synthetic uranyl peroxide materials. Structural and spectroscopic analyses combined with theoretical modeling reveal a distinctive studtite-like chain structure in which Cl – coordinates directly in the equatorial plane of uranyl. K + occupies interstitial positions and engages in both K + –Cl – contacts and coordination to framework oxygen atoms. Compared with studtite, K(UO 2 )O 2 (H 2 O)Cl·2H 2 O displays elongated U═O yl bonds and twisted uranyl–peroxide chains, arising from K–O interactions. Notably, substitution with Li +, Na +, or Cs + chlorides failed to yield analogous structures, demonstrating the size-specific role of K + . K(UO 2 )O 2 (H 2 O)Cl·2H 2 O exhibited enhanced thermal stability, which was attributed to the interlayer water bound to K + . This work establishes a new topology in uranyl peroxide chemistry and demonstrates how anion incorporation and size-selective cation templating can stabilize unprecedented actinide phases relevant to chloride-rich nuclear waste environments.
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