Crystal structure of a water oxidation catalyst solvate with composition (NH4)2[FeIV(L-6H)]·3CH3COOH (L = clathrochelate ligand)

Maksym O Plutenko; Sergii I Shylin; Sergiu Shova; Aleksander V Blinder; Igor O Fritsky

doi:10.1107/S2056989023010514

Crystal structure of a water oxidation catalyst solvate with composition (NH₄)₂[Fe^IV(L-6H)]·3CH₃COOH (L = clathrochelate ligand)

Acta Crystallogr E Crystallogr Commun. 2024 Jan 1;80(Pt 1):25-28. doi: 10.1107/S2056989023010514.

Authors

Maksym O Plutenko¹, Sergii I Shylin², Sergiu Shova³, Aleksander V Blinder⁴, Igor O Fritsky^{1

4}

Affiliations

¹ Department of Chemistry, Taras Shevchenko National University of Kyiv, 01601 Kyiv, Ukraine.
² Department of Chemistry - Ångström Laboratory, Uppsala University, 75335, Uppsala, Sweden.
³ "Petru Poni" Institute of Macromolecular Chemistry, Department of Inorganic, Polymers, 700487 Iasi, Romania.
⁴ Innovation Development Center ABN, Pirogov Str. 2/37, 01030 Kyiv, Ukraine.

Abstract

The synthetic availability of mol-ecular water oxidation catalysts containing high-valent ions of 3d metals in the active site is a prerequisite to enabling photo- and electrochemical water splitting on a large scale. Herein, the synthesis and crystal structure of di-ammonium {μ-1,3,4,7,8,10,12,13,16,17,19,22-dodeca-aza-tetra-cyclo-[8.8.4.1^3,17.1^8,12]tetra-cosane-5,6,14,15,20,21-hexa-onato}ferrate(IV) acetic acid tris-olvate, (NH₄)₂[Fe^IV(C₁₂H₁₂N₁₂O₆)]·3CH₃COOH or (NH₄)₂[Fe^IV(L-6H)]·3CH₃COOH is reported. The Fe^IV ion is encapsulated by the macropolycyclic ligand, which can be described as a dodeca-aza-quadricyclic cage with two capping tri-aza-cyclo-hexane fragments making three five- and six six-membered alternating chelate rings with the central Fe^IV ion. The local coord-ination environment of Fe^IV is formed by six deprotonated hydrazide nitro-gen atoms, which stabilize the unusual oxidation state. The Fe^IV ion lies on a twofold rotation axis (multiplicity 4, Wyckoff letter e) of the space group C2/c. Its coordination geometry is inter-mediate between a trigonal prism (distortion angle φ = 0°) and an anti-prism (φ = 60°) with φ = 31.1°. The Fe-N bond lengths lie in the range 1.9376 (13)-1.9617 (13) Å, as expected for tetra-valent iron. Structure analysis revealed that three acetic acid mol-ecules additionally co-crystallize per one iron(IV) complex, and one of them is positionally disordered over four positions. In the crystal structure, the ammonium cations, complex dianions and acetic acid mol-ecules are inter-connected by an intricate system of hydrogen bonds, mainly via the oxamide oxygen atoms acting as acceptors.

Keywords: cage complex; clathrochelate; crystal structure; high-valent iron; template synthesis.

Grants and funding

This work was supported by the Ministry of Education and Science of Ukraine through grant No. 22BF03–03, the European Union’s Horizon 2020 Research and Innovation Programme under the Marie Skłodowska-Curie grant agreement No. 778245, and the Swedish Foundation for Strategic Research.