Bipyridinium‐bis(carboxylate) Radical Based Materials: X‐ray, EPR and Paramagnetic Solid‐State NMR Investigations

The zwitterionic 1,1′-bis(4-carboxyphenyl)-4,4′-bipyridinium (bp4pc) has been synthesized and crystals of its hydrated form bp4pc·2H2O and of its protonated reduced form H-bp4pc have been obtained. Upon heating, bp4pc·2H2O undergoes partial dehydration, leading to bp4pc·H2O at 160 °C, together with a color change from yellow (room temperature) to green (140 °C) and finally to brown (160–180 °C). Analysis of bond lengths in the solid state reveals the expected short (d = 1.425 A) and long (d = 1.485 A) C–C central bond lengths in the all-radical salt H-bp4pc and bp4pc·2H2O, respectively, whereas the distance of 1.475 A in bp4pc·H2O does not allow a conclusion to be drawn regarding the presence of radicals in this compound. EPR and solid-state paramagnetic NMR experiments of H-bp4pc and the hydrated zwitterion bp4pc·2H2O at different temperatures, however, show that the color change of the latter upon heating is due to the presence of bipyridinium radicals, the concentration of which, although low, increases with increasing temperature. The nature of the electron donor involved in this thermal-induced electron transfer is not fully understood. Most plausible is the possibility that it is the carboxylate group with an intramolecular electron-transfer process; on the other hand it, cannot be excluded that the electron stems from the water molecule, which decomposes into O2, H+, and e– giving H-bp4pc entities.

[1]  O. Toma,et al.  Photo- and thermochromic and adsorption properties of porous coordination polymers based on bipyridinium carboxylate ligands. , 2015, Inorganic chemistry.

[2]  Gang Xu,et al.  Photochromic hybrid containing in situ-generated benzyl viologen and novel trinuclear [Bi3Cl14]5-: improved photoresponsive behavior by the π···π interactions and size effect of inorganic oligomer. , 2014, Inorganic chemistry.

[3]  Bin Tan,et al.  Auxiliary ligand-controlled photochromism and decolourization of two bipyridinium-based metal–organic hybrid materials with various water clusters , 2014 .

[4]  O. Toma,et al.  Unprecedented stacking of MV2+ dications and MV˙+ radical cations in the mixed-valence viologen salt (MV)2(BF4)3 (MV = methylviologen). , 2013, Chemical communications.

[5]  A. Kassiba,et al.  Solid-state NMR correlation experiments and distance measurements in paramagnetic metalorganics exemplified by Cu-cyclam. , 2013, Chemphyschem : a European journal of chemical physics and physical chemistry.

[6]  N. Mercier.  The Templating Effect and Photochemistry of Viologens in Halometalate Hybrid Crystals (Eur. J. Inorg. Chem. 1/2013) , 2013 .

[7]  Li‐Ming Wu,et al.  Charge-distribution-related regioisomerism of photoresponsive metal-organic polymeric chains. , 2012, Dalton transactions.

[8]  Jie Zhang,et al.  Reversible luminescence switching between single and dual emissions of bipyridinium-type organic crystals. , 2012, Chemical communications.

[9]  S. Liao,et al.  Photo- and thermally induced coloration of a crystalline MOF accompanying electron transfer and long-lived charge separation in a stable host-guest system. , 2012, Chemical communications.

[10]  S. Liao,et al.  Synthesis of a 3D photochromic coordination polymer with an interpenetrating arrangement: crystal engineering for electron transfer between donor and acceptor units , 2012 .

[11]  Q. Yao,et al.  Solvent- and anion-controlled photochromism of viologen-based metal–organic hybrid materials , 2012 .

[12]  Gang Xu,et al.  A room-temperature X-ray-induced photochromic material for X-ray detection. , 2012, Angewandte Chemie.

[13]  Shuai-Hua Wang,et al.  Photochromic metal complexes of N-methyl-4,4'-bipyridinium: mechanism and influence of halogen atoms. , 2012, Inorganic chemistry.

[14]  J. C. Barnes,et al.  Solution-phase mechanistic study and solid-state structure of a tris(bipyridinium radical cation) inclusion complex. , 2012, Journal of the American Chemical Society.

[15]  Jie Zhang,et al.  Supramolecular isomer-dependent photochromism and emission color tuning of bipyridinium salts , 2011 .

[16]  L. Sanguinet,et al.  Stable Photoinduced Separated Charge State in Viologen Halometallates: Some Key Parameters , 2011 .

[17]  Z. Li,et al.  Conformational and photosensitive adjustment of the 4,4'-bipyridinium in Mn(II) coordination complexes. , 2010, Chemical communications.

[18]  P. Auban-Senzier,et al.  Photochromism, electrical properties, and structural investigations of a series of hydrated methylviologen halobismuthate hybrids: influence of the anionic oligomer size and iodide doping on the photoinduced properties and on the dehydration process. , 2010, Inorganic chemistry.

[19]  Gang Xu,et al.  Inorganic-organic hybrid photochromic materials. , 2010, Chemical communications.

[20]  F. Rastrelli,et al.  Predicting the NMR spectra of paramagnetic molecules by DFT: application to organic free radicals and transition-metal complexes. , 2009, Chemistry.

[21]  Rosario Scopelliti,et al.  A Crystallographic Story of Snakes and Ladders: Encapsulated Water Polymers and Rigid Metal Complexes Based on Mono-N-substituted Carboxylate 4,4′-Bipyridine , 2009 .

[22]  Q. Yao,et al.  Novel polythreaded coordination polymer: from an armed-polyrotaxane sheet to a 3D polypseudorotaxane array, photo- and thermochromic behaviors. , 2009, Inorganic chemistry.

[23]  C. Tu,et al.  The formation of a hydrated homochiral helix from an achiral zwitterionic salt, spontaneous chiral symmetry breaking and redox chromism of crystals. , 2009, Chemical communications.

[24]  Gang Xu,et al.  Photochromism of a methyl viologen bismuth(III) chloride: structural variation before and after UV irradiation. , 2007, Angewandte Chemie.

[25]  E. Oldfield,et al.  Solid-state NMR of a paramagnetic DIAD-FeII catalyst: sensitivity, resolution enhancement, and structure-based assignments. , 2006, Journal of the American Chemical Society.

[26]  T. Vaid,et al.  Isolation and characterization of phenyl viologen as a radical cation and neutral molecule. , 2005, The Journal of organic chemistry.

[27]  H. Yoshikawa,et al.  Inorganic-organic hybrid molecular architectures of cyanometalate host and organic guest systems: specific behavior of the guests. , 2005, Accounts of chemical research.

[28]  E. Clennan.  Viologen embedded zeolites , 2004 .

[29]  Y. Ishii,et al.  A new approach in 1D and 2D 13C high-resolution solid-state NMR spectroscopy of paramagnetic organometallic complexes by very fast magic-angle spinning. , 2003, Journal of the American Chemical Society.

[30]  T. Ishida,et al.  Polycyano–polycadmate host clathrates including a methylviologen dication. Syntheses, crystal structures and photo-induced reduction of methylviologen dication , 2002 .

[31]  K. B. Yoon,et al.  Charge-Transfer Interaction of Methyl Viologen with Zeolite Framework and Dramatic Blue Shift of Methyl Viologen−Arene Charge-Transfer Band upon Increasing the Size of Alkali Metal Cation , 1999 .

[32]  J. Kochi,et al.  Isolation and oxidation-reduction of methylviologen cation radicals. Novel disproportionation in charge-transfer salts by x-ray crystallography , 1990 .

[33]  B. Emmert,et al.  Über chinhydron-artige Verbindungen des Dihydro-γ,γ-dipyridyls , 1924 .

[34]  H. Kamogawa,et al.  Organic solid photochromism via a photoreduction mechanism. Photochromism of viologen crystals , 1985 .