Doping Effect in Three-dimensional Donor–Acceptor Magnet: Percolated Magnetic Pathways Dominated by Local Electron Transfers

Abstract

In an electron-donor (D)electron-acceptor (A) three-dimensional assembly series with a D 2 A formulation, their magnetic properties were tuned by doping another D unit with a stronger electron-donating ability capable of reducing A ¹ to A 2¹ . The magnetic-phase-transition temperature (T c ) of doped compounds nonlinearly decreases with increasing doping rate.The control of magnetic behavior in a flexible framework of materials is an important topic of materials science, which has been carried out not only by physical stimuli such as temperature, 1 pressure, 2 electric field, 3 and photoirradiation 3b,4 but also by chemical techniques. 5,6 One of the chemical techniques is based on hostguest chemistry that has recently attracted much attention in the field of molecular porous materials, 7 in which the adsorptiondesorption of guest molecules such as crystallization solvents and common gas molecules reversibly tunes the magnetism of materials without the collapse of frameworks; 5,6 they are often called "magnetic sponge;" 8 another technique involves the use of chemical doping of, for example, alternate metal ions, elements, and organic functional groups.9,10 The former is a serendipitous technique, while the latter is a strategic one. However, the chemical doping in molecular materials is not easy to perform in a framework of materials because molecular materials relatively flexibly vary their frameworks in reflections of steric hindrance and the variation of bonding geometry around dopants. Hence, not many cases are known in which the effect of chemical doping has been systematically investigated for tuning magnetism in molecular materials.Here, we report doped magnetic materials whose magnetism is closely associated with the electron transfer around dopants in a framework. ) are paramagnetic species with S = 1 and S = 3/2, respectively, and the one-electron-reduced BTDA-TCNQ (i.e., BTDA-TCNQ•¹ as A ¹ ) is a radical with S = 1/2, providing a ferrimagnet with a magnetic-phase-transition temperature, T c = 107 K.12 Meanwhile, a similar D 2 A-type three-dimensional compound using m- 4 } 2x (BTDA-TCNQ)] (x = 0.1, 10%; 0.125, 12.5%; 0.15, 15%). They are still magnets, but interestingly, T c nonlinearly decreases on increasing the doping rate x and is rather abruptly reduces at lower temperatures in compounds with over 10% doping. This behavior can well be described using the percolation theory for their magnetic superexchange pathways.It is not easy to accurately characterize the doping rate of the doped compounds because of the difference between F and Me groups in [Ru 2 ] units; therefore, the doping rate given as 10%, 12.5%, and 15% implies the mixing ratio in the synthetic procedure. Nevertheless, the doping nature can be seen in the IR spectra. The doped compounds 10%, 12.5%, and 15% have characteristic two vibrational modes of¯(C¸N) for the BTDA-TCNQ moiety at 2198 and 2136 cm (Figure 2a). Meanwhile, thē (C¸N) peak at ca. 2196 cm ¹1 broadens with increasing doping rate, and a broad weak peak newly appear...

Magnetic Sponge Behavior via Electronic State Modulations

“…A clear distinction between the solvated and desolvated groups was found in local bond lengths in parts of [Ru 2 ] and TCNQMe 2 units, which clearly reflect the oxidation states of units demonstrated in previous work. ,− ,− For the [Ru 2 ] unit, Ru–O eq (O eq = carboxylate oxygen atom), bond distances were quite sensitive to the oxidation state of the [Ru 2 ] unit: 2.06–2.07 Å for [Ru 2 II,II ] and 2.01–2.03 Å for [Ru 2 II,III ] + . The Ru–O eq distances in 1 , 1-dry , 2 , and 2-dry are summarized in Table S2.…”

Fully Electron-Transferred Donor/Acceptor Layered Frameworks with TCNQ2–

“…Compounds 1 – 5 were synthesized using a method similar to that previously used to synthesize other [Ru 2 ] 2 TCNQ materials . The method allowed the slow mixing of two solutions by diffusion.…”

“…We found these charge/electron transfer mechanisms in D/A systems of metal–organic frameworks (we call these materials D/A-MOFs) constructed from the metal complex donors of carboxylate-bridged paddlewheel diruthenium(II, II) complexes (abbreviated as [Ru 2 II,II ] or [Ru 2 4+ ]) and organic polycyano acceptors such as TCNQ derivatives with x substitutions of R moieties (later abbreviated to TCNQR x ) and N , N ′-dicyanoquinonediimine (DCNQI) derivatives, ,− while several metal–TCNQR x high-dimensional frameworks have been known. − These D/A combinations allowed the production of D 2 A , and DA , multidimensional systems based mainly on TCNQR x and DCNQIR x , respectively. Summarizing the results of these studies, we successfully obtained a linear relationship that could be used to predict charge/electron transfer in systems with different D/A combinations from an ionization plot of Δ E H–L (DA) against Δ E 1/2 (DA), where Δ E H–L (DA) is the energy gap between the HOMO level of the [Ru 2 II,II ] unit and the LUMO level of the TCNQR x /DCNQIR x unit conventionally estimated by DFT studies, and Δ E 1/2 (DA) is the difference between the first redox potentials of the [Ru 2 II,II ] and TCNQR x /DCNQIR x units.…”

Energy Efficiency: Towards the End of Demand Growth. Edited by Fereidoon P. Sioshansi

“…Accompanying this freezing of χ ′, a χ ′′ peak was also observed, in which the initial rise of χ ′′ was observed at 82 K on cooling, giving a phase transition temperature ( T C ) 13. This T C value is relatively high compared to those for previously reported molecule‐based magnets 4b,d,e–g,m. 13 Furthermore, the long‐range ordering enabled a spontaneous magnetization, that is, ferrimagnetic ordering, because of the insertion of the intercalating paramagnetic [FeCp* 2 ] + species between the layers.…”