Unusual π–π interactions directed by the [{(C6H6)Ru}2W8O30(OH)2]6− hybrid anion

Abstract

The [{(C₆H₆)Ru}₂W₈O₃₀(OH)₂]⁶⁻ hybrid (organometallic–POM) anion was used as a pH-tunable building block to create special conditions for realizing π–π interactions in the crystal structure. Changing the pH of an aqueous solution of Na₆[{(C₆H₆)Ru}₂W₈O₂₈(OH)₂]·16H₂O (1) results in isolation of a series of new compounds with different Na⁺/H⁺ ratios in the cationic composition: Na_5.5H_0.5[{(C₆H₆)Ru}₂W₈O₂₈(OH)₂]·15H₂O (2), Na₅H[{(C₆H₆)Ru}₂W₈O₂₈(OH)₂]·22H₂O (3), Na₄H₂[{(C₆H₆)Ru}₂W₈O₂₈(OH)₂]·24H₂O (4), Na₃H₃[{(C₆H₆)Ru}₂W₈O₂₈(OH)₂]·23H₂O (5), and NaH₅[{(C₆H₆)Ru}₂W₈O₂₈(OH)₂]·9H₂O (6). All complexes were characterized by single crystal X-ray diffraction (SCXRD) analysis and ICP-AES. The presence of π–π stacking was detected for moderate-to-highly protonated 3–6. The energy of such interactions was calculated to increase in the following order: 6 (5.0 kJ mol⁻¹) < 5 (7.6 kJ mol⁻¹) < 3 (10.0 kJ mol⁻¹). 1 was studied for its electrochemical behavior in 0.5 M Li₂SO₄ and as a paste electrode component in methanol. Catalytic activity in methanol oxidation was detected.