Ion Pair Charge‐Transfer Complexes of Dithiolene Metalates with Diquaternary 2,2′‐Biimidazoles

Abstract

Cycloalkylated biimidazolium dications (A") of reduction potentials from -0.4 to -1.4 V form ion pair charge-transfer complexes (A2+[M(mnt)z]2-) with dithiolene metalates, M = Zn, Ni, Pd, Pt, mnt2-= maleonitrile-2,3-dithiolate. X-ray analyses of (PzBBImZf[Ni(mnt)2]2-) [P2BBImZ+ = 1,1',3,3'-bis(propane-l,3-diyl)bibenzimidazolium] and (B2BIm2+ [Pd(mnt)2]2-) [B2BImZ+ = 1,1',3,3'-bis(butane-l,4-diyl)biimidazolium] reveal that the solid-state structure is largely determined by the geometry of the acceptor. When the latter is strongly twisted, the usually observed mixed donor-acceptor columns are modified to a chain-like arrangement. In the case of the bibenzimidazolium dication P2BBIm2+ the otherIon-pair charge-transfer (IPCT) complexes consisting of redox-active components provide ideal conditions for the systematic investigation of supramolecular CT interact i o n~ [~,~] .The combination of dianionic transition metal dithiolenes [ML2I2-with organic dicationic bipyridinium compounds (A2+) leads to IPCT complexes of the type (A[ML2]} showing an IPCT band in their UV-Vis-NIR spectraL41. Application of the "Hush model" affords thermodynamic and kinetic data about the relation between optical and thermal electron transfer in Flash photolysis reveals the formation of the primary redox products A+' and [ML2]-followed by a fast back-electron transferr61. Moreover, on the basis of the redox potential differences of the components the solid-state electrical conductivity can be quantitatively tunedL71.In the course of our previous investigations only bipyridinium compounds and closely related systems were used as acceptors. The first reduction potentials of these are found in the range of -0.4 to -0.8 V (MeCN, vs SCE). In the following we report on the chemical, structural, and spectroscopic properties of IPCT complexes containing biimidazolium acceptors R2BIm2+ which have unusually low first reduction potentials from -1.1 down to -1.4 V. These potentials qualify them as excellent candidates in photoreduction reactions including the photoreduction of water. Ad-

Nickel Dithiolenes Revisited: Structures and Electron Distribution from Density Functional Theory for the Three-Member Electron-Transfer Series [Ni(S2C2Me2)2]0,1-,2-

“…Any previous assessment of monoanion-dianion structural trends has been restricted to [Ni(S 2 C 2 (CN) 2 ) 2 ] 1-,2because of the stability of the dianion afforded by the electronegative ring substituent. Examination of data from the more recent and accurate structures of the monoanion [34][35][36][37][38] and dianion 34,[39][40][41][42] indicates that the bond length trends in Table 2 are followed with few exceptions. Indeed, the trend is evident from the first comparative determination of anion structures.…”

Consequences of the One‐Electron Reduction and Photoexcitation of Unsymmetric Bis‐imidazolium Salts

“…These characteristics are typically observed in bis-imidazolium salts. However, in the bridged systems [A5] 2 + , [60] [A4]2 + , [50] and [A2] 2 + [7] (Table 1), the twist angle q is dramatically reduced due to the tethers (Scheme 1).…”

Charge - Transfer Complexes of Metal Dithiolenes XXIV: Ion Pairs of the Tetrakis(dimethylamino)ethene Dication with Dithiolene Metalate Dianions

“…For apparatus em ployed see ref. [10]. Samples for diffuse reflectance spec tra were obtained by spreading the complexes onto corun dum plates (Hoechst CeramTech) which also served as reflectance standard.…”

“…The compound contains 2 x 0.33 molecules of acetone per platinum atom, disordered along the crystallographic z-axis. General procedures and listings of the programs used were given previously [10]. …”