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(+)2A(2-) 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(+)2A(2-) system was synthesized by assembling D/A combinations of paddlewheel-type [Ru2(II,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 [Ru2(II,III)](+) units with weakly antiferromagnetically coupled S = 3/2 spins via diamagnetic TCNQRx(2-) 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 |(2)E1/2(A) - (1)E1/2(A)|, where (2)E1/2(A) and (1)E1/2(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 = |(2)E1/2(A) - (1)E1/2(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.