Fully Electron-Transferred Donor/Acceptor Layered Frameworks with TCNQ^2–

In a series of two-dimensional layered frameworks constructed by two electron-donor (D) and one electron-acceptor (A) units (a D2A framework), two-electron transferred systems with D+2A2– were first synthesized as [{Ru2(R-PhCO2)4}2(TCNQRx)]·n(solv) (R = o-CF3, Rx = H2 (1), R = o-CF3, Rx = Me2 (2), R = o-CF3, Rx = F4 (3), R = o-Me, TCNQRx = BTDA-TCNQ (4), R = p-Me, TCNQRx = BTDA-TCNQ (5), where TCNQ is 7,7,8,8-tetracyano-p-quinodimethane and BTDA-TCNQ is bis­[1,2,5]­dithiazolotetracyanoquinodimethane). The D+2A2– system was synthesized by assembling D/A combinations of paddlewheel-type [Ru2II,II(R-PhCO2)4] complexes and TCNQRx that possibly caused a large gap between the HOMO of D and the LUMO of A (ΔEH–L(DA)). All compounds were paramagnetic because of quasi-isolated [Ru2II,III]+ units with weakly antiferromagnetically coupled S = 3/2 spins via diamagnetic TCNQRx2– and/or through the interlayer space. The ionic states of these compounds were determined using the HOMO/LUMO energies and redox potentials of the D and A components in the ionization diagram for ΔEH–L(DA) vs ΔE1/2(DA) (= E1/2(D) – E1/2(A); E1/2 = first redox potential) as well as by previously reported data for the D2A and DA series of [Ru2]/TCNQ, DCNQI materials. The boundary between the one-electron and the two-electron transferred ionic regimes (1e–I and 2e–I, respectively) was not characterized. Therefore, another diagram for ΔEH–L(DA) vs |2E1/2(A) – 1E1/2(A)|, where 2E1/2(A) and 1E1/2(A) are the second and first redox potentials of TCNQRx, respectively, was used because the 2e–I regime is dependent on on-site Coulomb repulsion (U = |2E1/2(A) – 1E1/2(A)|) of TCNQRx. This explained the oxidation states of 1–5 and the relationship between ΔEH–L(DA) and U and allowed us to determine whether the ionic regime was 1e–I or 2e–I. These diagrams confirm that a charge-oriented choice of building units is possible even when designing covalently bonded D2A framework systems.