Complexation of Tetraanisolyl–Anthraquinodimethanes With Alkali Metal Ions: A Combined Mass Spectrometric and Computational Study

Abstract

In this work, we investigated a group of tetranisolyl-functionalized anthraquinodimethane (TAAQ) derivatives in terms of their binding properties with alkali metal cations (Li⁺, Na⁺, K⁺, Rb⁺, and Cs⁺). These anthraquinodimethane extended tetrathiafulvalenes (TTFAQs) feature preorganized multiple ether groups, enabling them to bind with alkali metal cations in a manner analogous to crown ethers or spherands. The resulting guest–host complexes, M⁺(TAAQ), were analyzed by mass spectrometry through sustained off-resonance irradiation collision-induced dissociation (SORI-CID) to determine their fragmentation behavior in the gas phase. Our findings revealed that, with the exception of Li⁺(TAAQ) and Na⁺(o-TAAQ), all complexes lost the neutral TAAQ moiety, leaving alkali metal cations as fragments. By combining experimental data and density functional theory (DFT) modeling, we deduced the possible dissociation pathways for Li⁺(TAAQ) and Na⁺(o-TAAQ). Furthermore, energy-resolved (ER) SORI-CID analysis allowed for a comparative study of the relative gas-phase stability of M⁺(TAAQ), revealing a stability trend that aligns with the binding energies computed based on the lowest energy structures for these complexes. Through the approach of natural energy decomposition analysis (NEDA), electrostatic interactions (ES) were identified as the key driving force behind the assembly of M⁺(TAAQ).