Charge Manipulation in a Series of π-Stacked Pillared-Layer Frameworks by Tuning Electron Donation Ability of Building Blocks

Abstract

One advantage of charge-transfer metal–organic frameworks comprising electron-donor (D) and electron-acceptor (A) units is their controllable electronic state. Herein, a new charge-ordered state with the formula Z +[D+D0A2–]− was revealed in π-stacked pillared-layer frameworks (π-PLFs), [FeCp*2][{Ru2(R x PhCO2)4}2(TCNQ)]·n(solv) (R x PhCO2 – = R-substituted benzoate with R = m-F (1), and 3,5-F2 (2); [FeCp*2]+ = decamethylferrocenium; TCNQ = 7,7,8,8-tetracyano-p-quinodimethane; solv = interstitial crystallization solvents), where [FeCp*2]+ (Z +) acts as a pillar connecting the two-dimensional [D2A]− layers of [{Ru2(R x PhCO2)4}2(TCNQ)]− in the π-stacking mode. The prototype π-PLF with R = 2,3,5,6-F4 (0) had another charge-ordered state Z +[D0 2A–], whereas the Z +[D+D0A2–]−-type charge-ordered state in 1 and 2 was achieved by significantly enhancing the electron-donating ability of the [Ru2] units compared to that in 0, inducing electron transfer from [Ru2 II,II] to TCNQ•– to produce a set of [Ru2 II,III]+ and TCNQ2– in the layer. Compounds 1 and 2 were paramagnetic because of the isolation of paramagnetic species [Ru2 II,II] (S = 1), [Ru2 II,III]+ (S = 3/2), and [FeCp*2]+ (S = 1/2) shielded by diamagnetic TCNQ2– linkers. This work demonstrates the feasibility of charge manipulation, even in the π-PLF system, by controlling the electron-donating ability of the [Ru2] unit.