Old Donors for New Molecular Conductors: Combining TMTSF and BEDT-TTF with Anionic (TaF 6 ) 1 − x /(PF 6 ) x Alloys

: Tetramethyl-tetraselenafulvalene (TMTSF) and bis(ethylenedithio)-tetrathiafulvalene (BEDT-TTF) are flagship precursors in the field of molecular (super)conductors. The electrocrystallization of these donors in the presence of ( n -Bu 4 N)TaF 6 or mixtures of ( n -Bu 4 N)TaF 6 and ( n -Bu 4 N)PF 6 provided Bechgaard salts formulated as (TMTSF) 2 (TaF 6 ) 0.84 (PF 6 ) 0.16 , (TMTSF) 2 (TaF 6 ) 0.56 (PF 6 ) 0.44 , (TMTSF) 2 (TaF 6 ) 0.44 (PF 6 ) 0.56 and (TMTSF) 2 (TaF 6 ) 0.12 (PF 6 ) 0.88 , together with the monoclinic and orthorhombic phases δ m -(BEDT-TTF) 2 (TaF 6 ) 0.94 (PF 6 ) 0.06 and δ o -(BEDT-TTF) 2 (TaF 6 ) 0.43 (PF 6 ) 0.57 , respec-tively. The use of BEDT-TTF and a mixture of ( n -Bu 4 N)TaF 6 /TaF 5 afforded the 1:1 phase (BEDT-TTF) 2 (TaF 6 ) 2 · CH 2 Cl 2 . The precise Ta/P ratio in the alloys has been determined by an accurate single crystal X-ray data analysis and was corroborated with solution 19 F NMR measurements. In the previously unknown crystalline phase (BEDT-TTF) 2 (TaF 6 ) 2 · CH 2 Cl 2 the donors organize in dimers interacting laterally yet no organic-inorganic segregation is observed. Single crystal resistivity measurements on the TMTSF based materials show typical behavior of the Bechgaard phases with room temperature conductivity σ ≈ 100 S/cm and localization below 12 K indicative of a spin density wave transition. The orthorhombic phase δ o -(BEDT-TTF) 2 (TaF 6 ) 0.43 (PF 6 ) 0.57 is semiconducting with the room temperature conductivity estimated to be σ ≈ 0.16–0.5 S/cm while the compound (BEDT-TTF) 2 (TaF 6 ) 2 · CH 2 Cl 2 is also a semiconductor, yet with a much lower room temperature conductivity value of 0.001 to 0.0025 S/cm, in agreement with the +1 oxidation state and strong dimerization of the donors.


Introduction
In the realm of tetrathiafulvalene (TTF) precursors and materials derived thereof [1][2][3][4][5], tetramethyl-tetraselenafulvalene (TMTSF) and bis(ethylenedithio)-tetrathiafulvalene (BEDT-TTF) (Scheme 1) occupy a prominent place because they are both related to important discoveries in the field of molecular (super)conductors [6] and interest in condensed matter physics has never wavered [7,8]. Particularly relevant in the case of TMTSF are the first superconducting organic mixed valence radical cation salts (TMTSF) 2 A (A -= PF 6 -, AsF 6 -, SbF 6 -, TaF 6 -, ClO 4 -, etc.), also known as the Bechgaard salts [9][10][11][12][13]. For example, in the series (TMTSF) 2 XF 6 (X = P, As, Sb, Ta) the evolution of a superconducting transition temperature with the anion size and the applied pressure has been observed [14][15][16]. Moreover, the properties of the spin density wave state related to pinning have been investigated in the alloys (TMTSF) 2 (AsF 6 ) 1−x (SbF 6 ) x through the measurement of the dielectric constant [17,18] and (TMTSF) 2 (PF 6 ) 1−x (AsF 6 ) x by studying the non-linear conduction at a low temperature [19]. The occurrence of such alloys in the (TMTSF) 2 XF 6 series is strongly favored by the isostructurality of all of its members regardless of the size of the XF 6 anions [20]. On the other hand, BEDT-TTF afforded a large number of molecular metals and superconductors with a wide variety of anions [21,22] including most of the TTF based high T c superconductors (with a T c above 10 K) [23][24][25][26][27]. As far as the XF 6 -(X = P, As, Sb, Ta) anions series is concerned, at the difference with the isostructural Bechgaard type compounds, their salts with BEDT-TTF show different polymorphs and conducting properties. Accordingly, triclinic α-(BEDT-TTF) 2 PF 6 showing semiconducting behavior [28] and orthorhombic β-(BEDT-TTF) 2 PF 6 with a metallic character and a metal insulator transition occurring at 297 K [29] have been prepared with PF 6 -, while the same metallic orthorhombic phase β-(BEDT-TTF) 2 AsF 6 [30] together with a semiconducting monoclinic polymorph [31] have been reported with AsF 6 − . Another monoclinic polymorph β-(BEDT-TTF) 2 AsF 6 , very close structurally to the former and also described for β-(BEDT-TTF) 2 SbF 6 , has been observed as well [32]. Finally, with the largest anion in the series, i.e. TaF 6 − , monoclinic δ m -(BEDT-TTF) 2 TaF 6 and orthorhombic δ o -(BEDT-TTF) 2 TaF 6 phases showing a semiconductor-insulator transition close to room temperature [33] together with a dimer Mott insulator monoclinic κ-(BEDT-TTF) 2 TaF 6 phase [34] have been only recently reported. The δ-phases are reminiscent of the monoclinic and orthorhombic β-(BEDT-TTF) 2 AsF 6 phases, respectively. Note that, unlike TMTSF (vide supra), no BEDT-TTF salts containing alloys of XF 6 anions have been described to the best of our knowledge. In the course of our studies on TTF based conductors containing fluorotantalate anions aimed at further expanding the size of the monoanion, we have recently attempted the synthesis of the as described (TMTSF) 3 Ta 2 F 11 [35] and (BEDT-TTF) 3 Ta 2 F 11 [36,37] phases, supposedly containing the monoanion [Ta 2 F 11 ]having a double octahedron geometry. However, a careful characterization of the fluorotantalate precursors and of the resulting radical cation salts clearly demonstrated that the two compounds we obtained were in fact (TMTSF) 3 Ta 2 F 10 O and (BEDT-TTF) 3 Ta 2 F 10 O [38], thus containing the oxobis(pentafluorotantalate) [Ta 2 F 10 O] 2dianion instead of the elusive [Ta 2 F 11 ]monoanion, the former being generated by the hydrolysis of TaF 6 -, which can take place even during the electrocrystallization process. For example, beside our own observations, Nakamura et al. mentioned the unexpected formation of crystalline (TMTTF) 3 Ta 2 F 10 O during the preparation of the Fabre phase (TMTTF) 2 TaF 6 [39]. Our initial interest for using the as described [Ta 2 F 11 ]anion in radical cation salts was related to its introduction in chiral TTF based conductors [40,41] containing fluorinated anions [38]. We have indeed demonstrated that the packing and conducting properties of chiral conductors based on dimethyl-ethylenedithio-tetrathiafulvalene (DM-EDT-TTF) could be modulated with the anion size as a consequence of the involvement of the anions in the intermolecular C-H···F hydrogen bonding with the donors [42,43]. However, instead of the sought [Ta 2 F 11 ] − anion, the salts we obtained contained the [Ta 2 F 10 O] 2− dianion [38], thus prompting us to investigate more deeply the previous claims concerning the existence of (TMTSF) 3 Ta 2 F 11 [35] and (BEDT-TTF) 3 Ta 2 F 11 [36,37] salts. As the formation of (TMTSF) 3 Ta 2 F 11 was reported as serendipitously occurring upon the electrocrystallization of TMTSF in the presence of a mixture (n-Bu 4 N)(TaF 6 ) 0.8 (PF 6 ) 0.2 while for that of (BEDT-TTF) 3 Ta 2 F 11 no clear experimental details were found in the literature, we decided to undertake a systematic study on the crystalline materials obtained by the electrocrystallization of TMTSF and BEDT-TTF with (n-Bu 4 N)TaF 6 and with alloys of different compositions containing both (n-Bu 4 N)TaF 6 and (n-Bu 4 N)PF 6 . The objective of these investigations was twofold: (i) to enrich the Bechgaard family of conductors containing anionic alloys and access first examples of BEDT-TTF salts with anionic XF 6 mixtures and (ii) definitely rule out the formation of the previously claimed (TMTSF) 3 Ta 2 F 11 and (BEDT-TTF) 3 Ta 2 F 11 salts. The anionic ratio in the different radical cation salts (TMTSF) 2 (TaF 6 ) 1−x (PF 6 ) x and (BEDT-TTF) 2 (TaF 6 ) 1−x (PF 6 ) x starting from variable TaF 6 /PF 6 compositions has been precisely determined by single crystal X-ray diffraction analyses corroborated with 19 F NMR spectroscopy measurements of the bulk crystalline materials. The electron transport properties of some of the mixed anionic salts together with those of a new 1:1 BEDT-TTF/TaF 6 phase have been determined.

Electrocrystallization Experiments
In the following, the molar ratio (n-Bu 4 N)TaF 6/ (n-Bu 4 N)PF 6 used in the experiments is referred to as the nominal ratio.
(TMTSF) 2 TaF 6 : 30 mg of (n-Bu 4 N)TaF 6 (5.58 × 10 −5 mol) were dissolved in 12 mL of THF (HPLC Fisher Scientific) passed through basic alumina from Acros. This solution was divided into two parts of 6 mL each. Next, 5 mg of TMTSF (1.12 × 10 −5 mol from Acros) were added into one of the parts and sonicated for 5 min. The two solutions were poured into an electrocrystallization cell so that the cathodic compartment contained only the supporting electrolyte and the anodic one had both the supporting electrolyte and the TMTSF donor. The two chambers were degassed with argon. Electrooxidation was run by applying a constant current of 1 µA on a platinum wire electrode, diameter 1 mm, in a thermostated chamber at 20 • C for 4 days. Black needles of (TMTSF) 2 TaF 6 were obtained on the anode.
δ o -(BEDT-TTF) 2 TaF 6 : 35 mg of (n-Bu 4 N)TaF 6 (6.51 × 10 −5 mol) were dissolved in 12 mL of dichloromethane (spectrosol Carlo Erba) passed through neutral alumina from Acros. This solution was divided into two parts of 6 mL each. Next, 5 mg of BEDT-TTF (1.30 × 10 −5 mol, prepared in the laboratory) were added into one of the parts and sonicated for 5 min. The two solutions were poured into an electrocrystallization cell so that the cathodic compartment contained only the supporting electrolyte and the anodic one had both the supporting electrolyte and the BEDT-TTF donor. The two chambers were degassed with argon. Electrooxidation was run by applying a constant current of 0.5 µA on a platinum wire electrode, diameter 1 mm, in a thermostated chamber at 20 • C for 7 days. Black needles of δ o -(BEDT-TTF) 2 TaF 6 and a few black platelets of (BEDT-TTF) 3 Ta 2 F 10 O were obtained on the anode.
Single crystals of the compounds were mounted on plastic loops using a viscous cryo-protectant oil to coat the crystal and then transferred directly to a cold nitrogen stream for data collection Details about data collections and structure refinements are given in Tables S1 and S2 (ESI). X-ray data collections were performed on a Rigaku Oxford Diffraction SuperNova diffractometer equipped with an Atlas CCD detector and micro-focus Cu-K α radiation (λ = 1.54184 Å). The structures were solved by direct methods or a dual-space algorithm and refined on F 2 by full matrix least-squares techniques with SHELX programs [44,45] (SHELXS-2013 or SHELXT-2018 and SHELXL-2016-2018) using the WinGX graphical user interface [46]. All non-H atoms were refined anisotropically and the absorption was corrected by the Gaussian technique or by a multiscan empirical absorption using a CrysAlisPro program [47]. The H atoms were placed at calculated positions and refined using a riding model. For (TMTSF) 2 (TaF 6 ) 0.12 (PF 6  To measure electrical resistivity along the long axis of the needle-shaped single crystals, gold wires were glued with silver paste directly on to the crystals. Depending on the size and brittleness of the crystals, two or four in-line contacts were performed. For the conducting salts (TMTSF) 2 (Ta x P 1−x F 6 ) and δ o -(BEDT-TTF) 2 (Ta 0.2 P 0.8 F 6 )-nominal, a constant current was applied and the voltage was measured. (TMTSF) 2 (Ta 0.2 P 0.8 F 6 )nominal and δ o -(BEDT-TTF) 2 (Ta 0.2 P 0.8 F 6 )-nominal compounds were cooled down using a Quantum Design Physical Property Measurement System (PPMS) with a 10 µA DC current excitation in the temperature range 4-300 K at a rate of 0.3K/min. The resistance of the (TMTSF) 2 (Ta 0.2 P 0.8 F 6 )-nominal was measured with only two contacts when cooling down, which made it difficult to evidence a metallic behavior as the contact resistance was added to the resistance of the sample.
For the more insulating compound (BEDT-TTF) 2 (TaF 6 ) 2 ·CH 2 Cl 2 measurements were performed in two contacts at room temperature, applying a constant voltage (0.1-1 V) and measuring the current with a Keithley 487 Picoammeter/Voltage Source.

Radical Cation Salts of TMTSF
In the first set of experiments, we investigated the electrocrystallization of TMTSF with mixtures of (n-Bu 4 N)TaF 6 and (n-Bu 4 N)PF 6 of three different molar starting compositions, i.e., 0.8/0.2, 0.5/0.5 and 0.2/0.8, referred to as "nominal", keeping in mind that the use of the mixture Ta/P 0.8/0/2 was reported to provide (TMTSF) 3 Ta 2 F 11 [35]. For comparison reasons we also prepared the classical Bechgaard phase with 100% TaF 6 and reported its accurate crystal structure at room temperature and also 100 K because these data were not recorded in the CCDC. Accordingly, the electrocrystallization of TMTSF with pure (n-Bu 4 N)TaF 6 properly prepared according to our own protocol [38] provided the expected Bechgaard salt (TMTSF) 2 TaF 6 as black needles, crystallizing in the centrosymmetric triclinic space group P-1 with one independent donor and half an anion in the asymmetric unit with the Ta center being located on an inversion center. A thorough structural resolution at room temperature clearly indicated disordered fluorine atoms with site occupation factors (s.o.f.) of 0.61/0.39 A/B while the disorder was removed at 100 K ( Figure 1). Depending on the purity of the starting (n-Bu 4 N)TaF 6 and the water and oxygen content of the electrocrystallization solvent, black crystalline platelets of (TMTSF) 3 Ta 2 F 10 O [38] occasionally form in the electrocrystallization cell, confirming the observations by Nakamura et al. from their study on the Fabre salts concerning the formation of the side crystalline product (TMTTF) 3 Ta 2 F 10 O [39]. While the electrocrystallization of TMTSF with mixtures of (n-Bu 4 N)TaF 6 and (n-Bu 4 N)PF 6 of three different nominal compositions (vide supra) provided variable amounts of crystalline (TMTSF) 3 Ta 2 F 10 O as a side product and not (TMTSF) 3 Ta 2 F 11 [35], the main crystalline material consisted of black crystalline needles of the Bechgaard phase (TMTSF) 2 (TaF 6 ) 1−x (PF 6 ) x . The Ta/P ratio in the latter, accurately refined by X-ray analysis on a couple of single crystals from each batch, had the following values (two experiments were conducted for the 0.  (Figures S1-S8). As the Ta/P ratio from one crystal to another within a same batch can slightly vary because of the easy formation of solid solutions thanks to the isostructurality throughout the Bechgaard series, we estimated the actual Ta/P ratio in the bulk crystalline materials through 19 F NMR measurements of solutions prepared by dissolving small amounts of each material in DMSO-d6 ( Figures S9-S12). The integration of the signal of PF 6 -, appearing as a doublet at −70 ppm with respect to the signals of fluorine atoms connected to Ta(V) provided the ratio TaF 6 /PF 6 in the bulk material. Satisfyingly, the ratios estimated by this method were in good agreement with those obtained by the refinement of the single crystal diffraction data (Table S3). However, very precise values were difficult to obtain because although the signals of TaF 6 -(broad singlet at ≈41 ppm) and [Ta 2 F 10 O] 2-(doublet at ≈33.7 ppm for the eight equatorial F atoms) were easily attributable [38], other signals, very likely due to TaF 5 solvated species, were also observed.
The substitution of PF 6 by TaF 6 in the structure of the Bechgaard phase provoked a steady increase of the crystalline cell volume from 709.9 Å 3 for the phase 100% P [48] to 741.6 Å 3 for the phase 100% Ta. The analysis of the cell parameters showed that a and b increased only very slightly, i.e., by 0.033 and 0.062 Å, respectively, while the c parameter expanded much stronger, by 0.39 Å (Figure 2). This anisotropic variation was not unexpected as it is along c that the shortest intermolecular donor···anion distances were observed as weak CH···F hydrogen bonding interactions while along a and b anion···anion distances were much longer and thus these directions were relatively insensitive to the size of the anion. The packing throughout the whole series was typical for the Bechgaard salts with the donors stacking along a through the axial overlap and organic-inorganic segregation along c (Figure 3 and Figure S4). The values of the central C=C and internal C-Se bonds throughout the series (Table S4) were typical for the Bechgaard salts, indicating a mixed valence state of TMTSF.

Radical Cation Salts of BEDT-TTF
As mentioned before, we could not find any reliable experimental details on the preparation of the claimed (BEDT-TTF) 3 Ta 2 F 11 [36,37] salt, which, in turn, proved to be the same material as the (BEDT-TTF) 3 Ta 2 F 10 O we obtained by the electrocrystallization of BEDT-TTF with (n-Bu 4 N) 2 Ta 2 F 10 O [38]. In order to rule out any doubt on the formation of the former we decided to apply the same electrocrystallization conditions as in the case of TMTSF, namely by using alloys [(n-Bu 4 N)(TaF 6 )] 1−x /[(n-Bu 4 N)(PF 6 )] x (x = 0, 0.2 and 0.8). Furthermore, as explained in the Introduction, no mixed BEDT-TTF/XF 6 salts are known to date and the pure forms showed a variation of packing type and conducting properties, while keeping a 2:1 donor:anion stoichiometry. However, an inspection of the reported BEDT-TTF/XF 6 (X = P, Ta) salts indicated that the orthorhombic phases β-(BEDT-TTF) 2 PF 6 [29] and δ o -(BEDT-TTF) 2 TaF 6 [33] were isostructural; therefore, an orthorhombic phase with a mixed anion composition could be expected to occur. Beside the use of XF 6 -(X = Ta, P) anionic alloys, we also envisaged the addition of equimolar TaF 6 -/TaF 5 mixtures in the electrocrystallization cell, assuming that condensation might take place to provide [Ta 2 F 11 ]in situ.
When the electrocrystallization experiment was performed with pure (n-Bu 4 N)TaF 6 , the already known orthorhombic δ o -phase (BEDT-TTF) 2 TaF 6 [33], reminiscent of the orthorhombic β-(BEDT-TTF) 2 PF 6 phase [29], was obtained as black needles together with black platelets of (BEDT-TTF) 3 Ta 2 F 10 O as a side product. Curiously, the use of a nominal mixture Ta/P 0.2/0.8 provided needle-like crystals ( Figure S13) of the same orthorhombic δ o -phase in the group Pnna, formulated as δ o -(BEDT-TTF) 2 (TaF 6 ) 0.43 (PF 6 ) 0.57 , with one independent donor and half an anion in the asymmetric unit ( Figure 4). Clearly, the TaF 6 anion adapted easier than PF 6 to this structural type.  When a reversed ratio Ta/P of 0.8/0.2 was used, the monoclinic δ m -phase, group I2/a, formulated as δ m -(BEDT-TTF) 2 (TaF 6 ) 0.94 (PF 6 ) 0.06 , was collected as black platelets ( Figure S14). This polymorph had very similar structural characteristics with its orthorhombic congener with one independent donor and half an anion in the asymmetric unit ( Figure 6) and an axial overlap of the donors along a (Figure 7). The only notable difference, beside the morphology of the crystals, i.e. needles for the δ o -phase and platelets for the δ m -phase, was the inversion of the b and c axes with the organic-inorganic segregation being along c in the δ m -phase ( Figure 7). Moreover, the donors adopted a herringbone organization orientation across the organic-inorganic segregation axis b in the δ o -phase ( Figure 5) while they adopted a parallel orientation along c in the δ m -phase ( Figure 7). Remarkably, an excellent correlation was observed in the δ m -phase for the ratio Ta/P, determined by single crystal X-ray data refinement and 19 F NMR measurements of a solution obtained by dissolving the crystalline material in DMSO-d6 ( Figure S15), which in both cases reached the value 0.94:0.06 (Table S3). The analysis of the central C=C and internal C-S bond lengths (Table S5) supported the mixed valence state of the donors.
A final attempt to prepare the elusive (BEDT-TTF) 3 Ta 2 F 11 salt was done by using an equimolar mixture of (n-Bu 4 N)TaF 6 /TaF 5 in electrocrystallization with BEDT-TTF. In these conditions, an unprecedented 1:1 phase formulated as (BEDT-TTF) 2 (TaF 6 ) 2 ·CH 2 Cl 2 crystallized as black bars on the anode ( Figure S16). The compound crystallized in the triclinic system, space group P-1, with one independent donor, one independent anion and half a molecule of CH 2 Cl 2 in the asymmetric unit ( Figure 8).
The value of the central C=C bond length of 1.386(5) Å together with those of the internal C-S bonds ranging between 1.720(4) and 1.721(4) Å (Table S5) were in agreement with an oxidation state +1 of the donor. In the packing, the donors formed isolated dimers of a bond-over-ring type with intermolecular S···S distances in the range 3.66-3.92 Å (Figure 9).   The successive dimers were separated in the stacking direction by anions and solvent molecules with no organic-inorganic segregation being observed in the packing ( Figure 10). However, relatively short lateral S···S intermolecular distances of 3.67-3.80 Å were observed in the transversal direction ( Figure 10).
In conclusion, these different trials with BEDT-TTF allowed us to prepare the first salts containing mixtures of TaF 6 and PF 6 anions and a new 1:1 BEDT-TTF/TaF 6 phase. The electrical conductivity of the needle-shaped single crystals of both compositions at room temperature was estimated to σ ≈ 100 S/cm (ρ ≈ 10 mΩ.cm) as measured in a four contacts configuration.

Single Crystal Conductivity Measurements
The temperature dependence of the resistivity was measured only for the (TMTSF) 2 (Ta 0.2 P 0.8 F 6 )-nominal corresponding with (TMTSF) 2 (TaF 6 ) 0.12 (PF 6 ) 0.88 , as determined by X-ray diffraction in a two contacts configuration. Despite a small localization below 250 K due to micro-cracks in the needle and to the resistance of the contacts, the ρ (T) curve in Figure 11 clearly shows the transition towards the spin density wave ground state around 12 K as observed in pure (TMTSF) 2 PF 6 . The conductivity was measured in two contacts because of large values of resistance. At room temperature, a non-ohmic behavior was observed with resistivity values varying between 2000 and 300 Ω.cm (conductivity 0.0005 to 0.0033 S/cm) for an applied voltage varying from V = 0.1 to 1 V ( Figure S17). When cooling down, the activation energy estimated from the resistivity data (shown in Figure 12 and Figure S18) was around 1200 K (0.1 eV) for an applied voltage of 1 V and slightly increased for lower values of the applied voltage (up to 1500 K (0.13 eV) for V = 0.2 V). These values were compatible with a 1:1 phase and the non-ohmic character, which was sample dependent but only slightly temperature dependent, could be related to the quality of the contacts. The electrical conductivity of the δ o -(BEDT-TTF) 2 (Ta 0.2 P 0.8 F 6 )-nominal corresponding with δ o -(BEDT-TTF) 2 (TaF 6 ) 0.43 (PF 6 ) 0.57 at room temperature was estimated to σ ≈ 0.16-0.5 S/cm (ρ ≈ 2-6 Ω.cm) as measured in a four contacts configuration.
The temperature dependence of the resistivity ( Figure 13) showed an activated behavior at a low temperature (below 250 K) with an activation energy of 2000 K (0.17 eV). A transition between the two semiconducting phases was observed at 296 K (as determined by the maximum of the derivative of log ρ versus 1/T), which paralleled the anomaly observed around 280-300 K in the resistivity curves of the pure δ o -and δ m -(BEDT-TTF) 2 TaF 6 phases and identified as a charge ordering transition [33].

Conclusions
In the course of our study, we have clearly shown that the use of (n-Bu 4 N)TaF 6 as a source of TaF 6 counter-ions in TMTSF and BEDT-TTF based radical cation salts must be considered with great care as the formation of (TMTSF) 3 (Ta 2 F 10 O) and (BEDT-TTF) 3 (Ta 2 F 10 O) salts as side products readily occurs. The use of anionic mixtures [TaF 6 /PF 6 ]with nominal ratios of 0.8/0.2, 0.5/0.5 and 0.2/0.8 in electrocrystallization with TMTSF afforded Bechgaard type salts containing proportions of anions paralleling those of the nominal mixtures, which were precisely determined by accurate single crystal X-ray analyses corroborated with 19 F NMR measurements indicative of the actual ratio in the bulk crystalline materials. Two such alloyed mixed valence salts were also synthesized with BEDT-TTF and also a 1:1 phase, which resulted from electrocrystallization in the presence of a TaF 6 -/TaF 5 mixture. However, in the mixed Ta/P BEDT-TTF salts, the inclusion of TaF 6 was favored over that of PF 6 -. Single crystal resistivity measurements were indicative of the typical conducting behavior of Bechgaard salts and showed semiconducting properties for the BEDT-TTF based materials. The results reported herein motivate further in-depth physical measurements on these mixed anionic phases in which the Ta/P ratio can be finely tuned.

Conflicts of Interest:
The authors declare no conflict of interest. The funders had no role in the design of the study; in the collection, analyses or interpretation of data; in the writing of the manuscript or in the decision to publish the results.