Unprecedented stacking of MV2+ dications and MV˙+ radical cations in the mixed-valence viologen salt (MV)2(BF4)3 (MV = methylviologen)

Abstract

Using a slow liquid-gas diffusion method, the mixed-valence viologen salt (MV)2(BF4)3 (1) and the radical cation salt (MV)(BF4) (2) are crystallized. Both structures contain regular stacks of MV˙(+) radical cations (2) or alternating MV˙(+) and MV(2+) entities (1). A short intrastack intermolecular separation (3.23 Å) unprecedently reveals strong interactions between MV(2+) and MV˙(+) in 1.

A fascinating multifaceted redox-active chelating ligand: introducing the N,N′-dimethyl-3,3′-biquinoxalinium “methylbiquinoxen” platform

“… 29 The g -value is similar to those reported for phosphine-based cation radicals, 30 – 32 but is slightly higher compared to the methylviologen radical cation ( g ∼ 2.003). 7 , 8 , 33 This is consistent with the extra heteroatom in the six-membered ring hosting the unpaired spin. Consequently, the 14 N hyperfine coupling is larger than for the archetypal viologens.…”

Second-order nonlinear optical switching with a record-high contrast for a photochromic and thermochromic bistable crystal

“…However, the closely packed crystal structure did not allow a large structural distortion. In addition, it has been reported that only a minor structural change happens after coloration for viologen-based photochromic compounds 31–33. So, the geometry of each component in the crystal structure of 1 was used directly for calculations of the permanent dipole moments and first hyperpolarizabilities before and after electron transfer.…”

“…The large structural change needs sufficient steric space and is usually prohibited in the crystal lattice 30. We31,32 and the Mercier group33 previously found through single-crystal X-ray diffraction analysis, that electron-transfer (ET) photochromic processes34 are only accompanied by minor structural variation, which is more adaptable to a constrained medium. These processes result in the rearrangement of charges and thus change the permanent dipole moment, which is closely related to the SHG effect of a crystal.…”

Supramolecular Open-Framework of a Bipyridinium-Carboxylate Based Copper Complex with High and Reversible Water Uptake

“…On one hand, these ligands are based on the cationic redox‐active bipyridinium moiety (also called viologen) which has strong abilities to interact with electron donors, and on the other hand, they include units anchoring to the bipyridinium cores, which bear carboxylate groups able to bind metal ions. Bipyridinium units (V 2+ ) are known to undergo a reversible one‐electron reduction, which is accompanied with a color change as well as V •+ radicals are created due to the different absorption domains of V 2+ (UV) and V •+ (visible) . In the solid state, the color change process, which can be activated by light or by heating, results from an electron transfer from electron donors such as chlorides or caboxylates, towards the electron acceptor bipyridinium units.…”