Super‐Efficient Platinum Catalyst Derived from a Semiconducting, DMF Solvate: Structural, Spectroscopic, Electrochemical, and Catalytic Characterization

Abstract

The reaction of [(NH3)4Pt](NO3)2 with LiTCNQF4 (TCNQF4=2,3,5,6‐tetrafluoro‐7,7,8,8‐tetracyanoquinodimethane) in dimethylformamide gives the product [(NH3)4Pt](TCNQF4)2⋅(DMF)4 (1). Subtle changes in the solvent conditions, however, result in a different product, [(NH3)4Pt](TCNQF4)2⋅Et2O⋅(CH3OH)4/3 (2). Both 1 and 2 have been characterized by X‐ray crystallography, vibrational (FTIR, Raman) and UV/vis spectroscopy, thermogravimetric analysis and electrochemistry. Single crystals of 1 indicate the presence of 3 D networks supported by hydrogen bonding, whereas the structural analysis of 2 indicates a 2 D layered network, which consists of alternating TCNQF4− and [(NH3)4Pt]2+ layers. The conductivity of a single crystal of 1 at room temperature lies in the semiconducting range (≈2.5×10−6 S cm−1). Unexpectedly, 1 was found to exhibit an exceptionally high catalytic activity for the electron transfer reaction between ferricyanide and thiosulfate ions in aqueous media. Our analysis indicates that the DMF solvates were removed prior to the catalytic reaction, but no other changes that occur in the chemical composition were found. Thus, the active catalyst is [(NH3)4Pt](TCNQF4)2 (3) rather than the starting material 1.

Solvent‐, Cation‐ and Anion‐Induced Structure Variations in Manganese‐Based TCNQF4Complexes: Synthesis, Crystal Structures, Electrochemistry and Their Catalytic Properties

“…The mid-point potentials are E m1 = À0.17 mV and E m2 = 0.524 mV (vs. Ag/Ag + ), in which E m is the average of the reduction (E p red )a nd oxidation (E p ox )p eak potentials andr epresents ac lose approximation of the reversible formal potential, E 0 f .T he separation in the potentials for the two processes is 541 mV,a nd is consistentw ith data reported in the literature under similar conditions. [24] These voltammetric data imply that, upon dissolution of 1 in DMF,T CNQF 4 2À and Mn 2 + are formed. In this scan range,n o other higher oxidations pecies are observed( e.g.,Mn 3 + ).…”

“…O'Mullane et al used films derived from MTCNQ or MTCNQF 4 (M=Cu + , Ag + )t oc atalyset he otherwise very slow redox reactiono ff erricyanidea nd thiosulfate ions in aqueous solution, [21] and, more recently,B ond and co-workersd iscovered that blue crystalline [(NH 3 ) 4 Pt](TCNQF 4 ) 2 displayed super-catalytic activity and reusability,w ith respectt ot he above reactionu nder the same conditions. [24] This encouraged us to explore whether the manganese-basedn etworks 1-3 werec apable of exhibiting similar catalytic behaviour with respectt ot his redox reaction. Unfortunately,n either 1 nor 2 were stable in aqueous solution containing K 3 [Fe(CN) 6 ]a nd Na 2 S 2 O 3 .B yc ontrast, compound 3 was stable in water and was employeda saheterogeneous catalystfor the reactionindicated in Equation (3).…”

“…The performance of 3 for this redox reaction is similar to that found for the blue crystalline material[ (NH 3 ) 4 Pt](TCNQF 4 ) 2 recently reportedb yL uetal. [24] The UV/Vis spectra in the regionso fl = 600-800 and 400-450 nm weree xamined to determinew hether any reaction occurred between dissolved 5 and K 3 [Fe(CN) 6 ]d uring the catalytic reduction process. No absorptionsa re apparent in these regions, which indicatest he absence of TCNQF 4 1À in solution.…”

“…This represents exceptional,s uper-catalytic activity compared with that of most other catalysts used for this reaction, [20][21][22][23] althoughw eh ave observeds imilarh igh activity for [Pt(NH 3 ) 4 ](TCNQF 4 ) 2 under comparablereactionc onditions. [24] Results and Discussion…”

Tetrathiafulvalene–7,7,8,8‐Tetracyanoquinodimethane and Tetrathiafulvalene–2,3,5,6‐Tetrafluoro‐7,7,8,8‐tetracyanoquinodimethane Organic Charge‐Transfer Complexes: Reusable Catalysts for Electron‐Transfer Reactions

“…[6a] Martin et al [13] also demonstrated that [(NH 3 ) 4 4À ions to complete the reaction. The overall reaction scheme is illustrated in Figure 4.…”