Redox-active TTF carboxylate as an axial bridging ligand for dirhenium metal–metal bonded complexes

Inorganica Chimica Acta 425 (2015) 233–238

Contents lists available at ScienceDirect

Inorganica Chimica Acta journal homepage: www.elsevier.com/locate/ica

Redox-active TTF carboxylate as an axial bridging ligand for dirhenium metal–metal bonded complexes Bradley W. Smucker a,⇑, John Bacsa b, Jitendra K. Bera c, Eric W. Reinheimer d,1 a

Department of Chemistry, Austin College, Sherman, TX 75092, USA Department of Chemistry, Emory University, Atlanta, GA 30322, USA c Department of Chemistry, Indian Institute of Technology, Kanpur 208016, India d Department of Chemistry, Texas A&M University, P.O. Box 30012, College Station, TX 77842, USA b

a r t i c l e

i n f o

Article history: Received 24 July 2014 Received in revised form 1 October 2014 Accepted 4 October 2014 Available online 14 October 2014 Keywords: Tetrathiafulvalene monocarboxylate Dirhenium compounds Redox properties X-ray crystal structures

a b s t r a c t Tetrathiafulvalene monocarboxylate, [TTFCO2], was used as a carboxylate bridging ligand for three new dirhenium complexes. The acetate ligands of cis-Re2(dppm)2Cl2(OAc)2, trans-Re2(dppm)2Cl4(OAc), and cis-Re2Cl4(OAc)2 are displaced by TTFCO2H to form cis-Re2(dppm)2Cl2(TTFCO2)2 (1), trans-Re2(dppm)2Cl4(TTFCO2) (2), and cis-Re2Cl4(TTFCO2)2 (3), respectively. Depending on their respective solubility, the complexes were characterized via single crystal X-ray diffraction as well as electrochemical and spectroscopic properties. Ó 2014 Elsevier B.V. All rights reserved.

1. Introduction The coordination of functionalized redox-active tetrathiafulvalene (TTF) moieties to metal complexes has attracted significant attention over the past two decades because of the interesting electronic [1], magnetic [2], photophysical [3], and chemical [4] properties engendered by the TTF radical. Coordination of TTF-containing ligands to transition metal centers is typically achieved by functionalizing TTF with nitrogen (pyridyl, dipyridyl, terpyridyl, pyrazine, amido and imino groups) or phosphorus (phosphino and chelating diphosphino ligands of tertiary phosphines) containing substituents [5]. Other groups such as oxazolyl, imidazolyl, acetylacetonate (acac) and Schiff-Base groups have also been coupled to TTF cores and incorporated into metal complexes [6]. In sharp contrast to the situation with mononuclear transition metal species, coordination of redox-active ligands, such as TTF, to metal–metal bonded compounds has received limited attention. The diversity of the structural and electronic properties of metal– metal bonded compounds and the variety of ligand types that are tolerated makes them attractive candidates for reactions with redox switchable ligands [7]. Examples of redox-active ligands that have been used to span dimetal units are TEMPO [8] ⇑ Corresponding author. Tel.:+1 903 813 2217. 1

E-mail address: [email protected] (B.W. Smucker). Current address: Rigaku Americas Corporation, The Woodlands, TX 77381, USA.

http://dx.doi.org/10.1016/j.ica.2014.10.002 0020-1693/Ó 2014 Elsevier B.V. All rights reserved.

(2,2,6,6-tetramethylpyridinyl-1-oxy), TCNE [9] (tetracyanoethylene), TCNQ [10] (7,7,8,8-tetracyanoquinodimethane) and DMDCNQI [11] (2,5-dimethyl-N,N0 -dicyanoquinonediimine). With one exception, these acceptor ligands bind to the axial positions of the M–M core [12]. One example in which the TTF molecule has been coordinated directly to a metal–metal bonded species is the work of Matsubayashi et al. who reported axial coordination of TTF to Rh2(O2CCH3)4 through the sulfur atom in 1988 [13]. More interesting, however, is coordination through equatorial sites which results in stronger electronic communication between the metal centers and redoxactive ligands. Work in this vein has concentrated primarily on incorporating pendant redox-active ferrocene units attached to mono- and di-carboxylate anions into di-molybdenum, -tungsten and -rhenium complexes [14]. Tetrathiafulvalene derivatives with carboxylic acid substituents have been used to prepare coordination complexes of transition [15] and rare-earth metals [16]. The mono-substituted TTFCO2H molecule is readily synthesized by a variety of methods and is a common precursor in organic reactions of functionalized TTF derivatives [17]. Recently there have been reports of TTF monoand tetra-substituted carboxylate molecules being employed for various anionic and supramolecular applications [18,19]. Of specific relevance to the current study is the report that TTFCO2H reacts with the dirhodium paddlewheel complex Rh2(ButCO2)4 to form the TTFCO2-bridged complexes [Rh2(ButCO2)3(TTFCO2)

234

B.W. Smucker et al. / Inorganica Chimica Acta 425 (2015) 233–238

Ph2P Cl O

Re

PPh2 PPh2 O

O

S

PPh2 Re Cl

Cl Ph2P

Re O

O

PPh2

S

Cl

PPh2 Re Cl

O

PPh2

S S

S

S

O O

S S

S S

S S

Re

S

S S

Cl

Re O

S

O

S

S

Cl

Cl

Cl

Cl

S

S

Fig. 1. Schematic representations of cis-Re2Cl2(dppm)2(TTFCO2)2 (left), trans-Re2Cl4(dppm)2(TTFCO2) (middle), and cis-Re2Cl4(TTFCO2)2 (right).

(NEt3)2], cis-[Rh2(ButCO2)2(TTFCO2)2(NEt3)2] and trans-[Rh2(ButCO2)2 (TTFCO2)2(NEt3)2]. These are the first instances of metal–metal bonded complexes with a TTF containing molecule bound in equatorial positions to the M–M core [20]. Ouahab and coworkers have further used [TTFCO2] as a ligand in a binuclear gadolinium(III) complex [16] or as an anion in a binuclear copper(II) complex [21]. Herein we report the use of [TTFCO2] as a bridging ligand for a series of multiply-bonded dirhenium complexes. The coordination of the carboxylate form of TTFCO2H to dirhenium compounds cisRe2Cl2(dppm)2(TTFCO2)2 (1), trans-Re2Cl4(dppm)2(TTFCO2) (2), and cis-Re2Cl4(TTFCO2)2 (3) (Fig. 1) as well as their respective structural and electrochemical and spectroscopic properties, depending on their respective solubilities, were investigated. 2. Experimental All operations were performed under a nitrogen atmosphere using standard Schlenk-line techniques unless otherwise indicated. Solvents were distilled prior to use from the appropriate drying agents. The dinuclear starting materials cis-Re2Cl2(dppm)2 (O2CCH3)2 [22], trans-Re2Cl4(dppm)2(O2CCH3) [23], and cis-Re2Cl4 (O2CCH3)2 [24], were synthesized from their respective literature preparations. 2.1. Physical measurements IR spectra were measured as Nujol mulls between CsI plates on a Nicolet 740 FT-IR spectrometer. UV–Vis spectra were measured in HPLC grade CH2Cl2 on a Shimadzu UV-1601pc spectrophotometer. The cyclic voltammetric studies were performed on a CH Instruments Electrochemical Analyzer in dichloromethane containing 0.1 M tetra-n-butylammonium hexafluorophosphate ([TBA][PF6], recrystallized from ethanol) as the supporting electrolyte with a scan rate of 100 mV/s. The working electrode was a BAS Pt disk electrode, the reference electrode was Ag/AgCl, and the counter electrode was a Pt wire. The Cp2Fe/Cp2Fe+ couple occurs at +0.48 V versus Ag/AgCl under the same experimental conditions.

0.167 mmol), 40 mL of EtOH, and a boiling stick. The resulting orange heterogeneous solution was refluxed for 12 h. The resulting red precipitate was isolated, by filtration, from the red/orange solution, and washed with EtOH, CH2Cl2 and Et2O to give 103.9 mg (78% yield). IR (CsI-Nujol): 1564 (w), 1545 (m), 1537 (m), 1261 (m), 1092 (m), 1024 (m), 794 (m), 786 (m), 767 (m), 750 (w), 738 (m), 735 (m), 697 (w), 688 (w), 678 (w), 527 (m), 517 (m), 508 (m), 491 (m), 476 (w), 464 (w), 415 (w), 403 (w) and 230 (w) cm1. 2.2.2. trans-Re2Cl4(dppm)2(TTFCO2), 2 A 15 mL CH2Cl2 dark yellow solution containing trans-Re2Cl4 (dppm)2(O2CCH3) (33.4 mg, 0.025 mmol) was combined with 15 mL of a brown/orange methanol solution containing TTFCO2H (8.1 mg, 0.032 mmol) to make a red solution in a 50 mL Schlenk flask. After stirring 12 h, the solution was partially condensed to 5 mL and a red solid was precipitated by the addition of 20 mL of Et2O and washed with 2  20 mL of Et2O to give 8 mg (21%) of a red product. IR (CsI-Nujol): 1618 (w), 1572 (w), 1533 (w), 1197 (w), 1150 (w), 1092 (m), 1031 (w), 1000 (w), 845 (w), 773 (m), 737 (m), 688 (m), 518 (m), 504 (m), 479 (w), 422 (w) and 325 (w) cm1. UV–Vis (CH2Cl2) kmax, nm (e = M1 cm1): 319 (8.0  103), 422 (2.8  103), and 495 (2.5  103). 2.2.3. cis-Re2Cl4(TTFCO2)2, 3 A 100 mL Schlenk flask was charged with cis-Re2Cl4(O2CCH3)2 (32.8 mg, 0.049 mmol), TTFCO2H (28.6 mg, 0.115 mmol), 40 mL of EtOH, and a boiling stick to make an orange-red solution. The solution was refluxed for 12 h giving a wine-red solution. The solution was filtered and the solvent removed in vacuo. The red–purple solid was re-dissolved in a minimal amount of EtOH and combined with a mixture of toluene and hexanes (40 mL each) and filtered to give 46.4 mg (94% yield) of a purple powder. IR (CsI-Nujol): 1565 (m), 1545 (m), 1537 (m), 1161 (w), 1092 (w), 794 (w), 784 (m), 767 (m), 750 (w), 734 (m), 697 (m), 689 (m), 677 (w), 527 (w), 517 (m), 508 (w), 491 (m), 475 (w), 465 (w), and 415 (w) cm1. UV-Vis (CH2Cl2) kmax, nm (e = M1 cm1): 250 (1.7  105), 288 (2.3  105), 314 (2.2  105), 460 (2.5  104), 510 (3.1  104) and 570 (2.1  104).

2.2. Syntheses2 2.3. X-ray crystallographic data collection and structural solutions 2.2.1. cis-Re2Cl2(dppm)2(TTFCO2)2, 1 A 100 mL Schlenk flask was charged with cis-Re2Cl2(dppm)2 (O2CCH3)2 (101.7 mg, 0.076 mmol), TTFCO2H (41.2 mg, 2 Compounds were synthesized and characterized in 2002 and were no longer available for further analysis at the time of writing.

For compounds 1 and 2, the data were collected on a BrukerAXS SMART 1000 CCD diffractometer at 110 ± 2 K with graphite monochromated Mo Ka (ka = 0.71073 Å) radiation and were corrected for Lorentz and polarization effects. Frame integration, Lorentz–polarization corrections, and final cell parameter calculations

B.W. Smucker et al. / Inorganica Chimica Acta 425 (2015) 233–238

235

were carried out using SAINT [25]. Multi-scan absorption corrections were performed using SADABS [26]. Space groups were unambiguously assigned by analysis of symmetry and systematic absences using XPREP and further verified by PLATON [27]. The structures was solved using direct methods and difference Fourier techniques. The final structural refinements included anisotropic temperature factors on all non-hydrogen atoms, with the exception of selected atoms which could not be satisfactorily refined anisotropically. Structure solution, refinement, graphics, and creation of publication material were performed using SHELXS, SHELXL and XSEED [28]. Hydrogen atoms were inserted at calculated positions and constrained with isotropic thermal parameters. The solid state structures for compounds 1 and 2 with anisotropic displacement ellipsoids at 50% probability are shown in Figs. 2 and 3. Crystallographic parameters are listed in Table 1 and any special refinement conditions are noted in the following paragraphs. 2.3.1. 1CH2Cl22CH3OH Single, red–orange platelets of Re2Cl2(dppm)2(TTFCO2)2 were grown by slow diffusion of dichloromethane and methanol solutions of Re2Cl2(dppm)2(CH3CO2)2 and TTFCO2H (respectively) in a 3 mm Pyrex tube. A single crystal from the batch was affixed to the tip of a glass fiber with Dow Corning grease and transferred to the cold N2 stream of the diffractometer. 2.3.2. 24CH2Cl2 Toluene was slowly diffused into a dichloromethane solution of 2 to afford red–orange platelets. A single crystal from the batch

Fig. 3. Thermal ellipsoid plot at the 50% level for trans-Re2Cl4(dppm)2(TTFCO2), 2, with interstitial solvent molecules omitted for the sake of clarity.

Fig. 2. Thermal ellipsoid plot at the 50% level for cis-Re2Cl2(dppm)2(TTFCO2)2, 1 (left) and packing diagram showing head to tail packing (right) (a). Closest intermolecular S  S interactions (b). Interstitial molecules have been omitted for the sake of clarity.

236

B.W. Smucker et al. / Inorganica Chimica Acta 425 (2015) 233–238

3. Results and discussion

168.08(8)° and 167.82(8)° for each dirhenium complex. The Re– Cl bond lengths are both 2.551(3) Å. The TTF backbone of the ligand is nearly planar with angles along the S(1)–S(2) and S(3)–S(4) axes of 8.3° and 1.7°, respectively, and 13.3° and 12.5° for the S(9)–S(10) and S(11)–S(12) axes, respectively, on the other dirhenium complex. The two [TTFCO2] ligands bridging the dirhenium unit are canted away from each other (Fig. 2), which is understood by examining the packing of the molecules. Since the dirhenium complexes pack in a head-to-tail fashion (Fig. 2), the [TTFCO2] ligands must curve away from each other with an intramolecular S  S distance of 8.16 Å so that they can accommodate the di-phenyl groups of the neighboring molecule. The closest intermolecular S  S distance, however, is 3.80 Å (Fig. 2), well within the range for significant p interactions [1b]. The C–C distance between the TTF and the carboxylate of 1.492(19) Å is about the same as that in the TTFCO 2 anion 1.513(13) Å [21]. The trans-dirhenium(II, III) complex, 2, crystallizes in the  as 24CH2Cl2 (Fig. 3). With a formal bond triclinic space group P1 order of 3.5, the Re–Re bond length (2.2962(9) Å) has decreased slightly from that found in the triply bonded compound 1, and is slightly shorter than the distance found in the trans-Re2Cl4 (dppm)2(O2CCH3) starting material (2.2998(4) Å) [23]. The equatorial Re–Cl bond distance (2.349(2) Å) is shorter than the axial Re–Cl bond (2.611(2) Å), which are comparable to the equatorial (2.356 (2) Å) and axial (2.598 (2) Å) Re–Cl distances in the starting material. As in compound 1, the [TTFCO2] ligand exhibits a boat conformation with bends of 13.9° and 9.9° along the S–S axes. The C–C distance between the TTF moiety and the carboxylate linker 1.469(13) Å in 2 is approximately the same C–C distance in 1. The closest intermolecular S  S distance is 3.89 Å.

3.1. Syntheses

3.3. Electrochemical and electronic spectral studies

The mono-substituted tetrathiafulvalenecarboxylic acid, TTFCO2H, was prepared by the addition of CO2 to mono-lithiated TTF and was recrystallized from benzene [17]. The facile exchange of the acetate from a dirhenium complex with the [TTFCO2] ligand involves combining solutions of Re2(O2CCH3)xLy and TTFCO2H. The red dirhenium compounds, cis-Re2Cl2(dppm)2(TTFCO2)2 (1), transRe2Cl4(dppm)2(TTFCO2) (2), and cis-Re2Cl4(TTFCO2)2 (3) were prepared in 78%, 94% and 21% yields, respectively. The acetate forms of the dirhenium starting materials are attractive starting materials because they are known to undergo substitution reactions with carboxylic acids [22] to form metallocyclophane squares [29] and polymers as well as ferrocene derivatives [14c]. Despite the solubility of both starting materials (TTFCO2H and cis-Re2Cl2(dppm)2 (TTFCO2)2) in dichloromethane, compound 1 is only slightly soluble. The number of coordinated [TTFCO2] ligands plays a role in the solubility of the complex, as evidenced by the solubility of compound 2 with only one TTF moiety attached. As expected, the axial coordination of chloride also plays a role in the solubility, as compound 3, with open axial coordination sites, is soluble despite the presence of two [TTFCO2] ligands.

The electrochemical behavior of TTFCO2H as well as dirhenium compounds 2 and 3 were analyzed using cyclic voltammetric techniques (Table 2). The electrochemical studies of 1 were unreliable due to marginal solubility. For all the compounds, only two TTFcentered oxidation processes were observed. The electrochemical properties of the TTFCO2H molecule were analyzed via cyclic voltammetry in various solvents. Consistent with previous reports, the monocarboxylic acid form of TTF exhibited one reversible (E½ = 0.50 V) and one irreversible (Ep,a = 0.90 V) oxidation in all solvents [19]. The trans-Re2Cl4(dppm)2(TTFCO2) complex, 2, exhibits two reversible oxidations at E½ = +0.56 and +0.74 V, an irreversible oxidation at Ep,a = +1.21 V (Fig. 4), and an irreversible reduction at Ep,c = 1.11 V. We assign the first and third oxidations (0.56 and 1.21 V) to the lone [TTFCO2] ligand, which is similar to the behavior of the [TTFCO2] ligands in compound 3 (Table 2). The remaining oxidation (0.74 V) and reduction (Ep,c = 1.11 V) are assigned to the ReIII,III and ReII,II 2 2 species of 2, respectively. The positive charges resulting from the oxidized [TTFCO2] ligand and

3.2. X-ray structures

Table 2 Cyclic voltammetric data for TTFCO2H and compounds 2 and 3 (V vs. Ag/AgCl, Pt disk electrode in 0.1 M [n-Bu4 N][PF6] solutions at a scan rate of 100 mV/s, Ep,a and Ep,c refers to anodic and cathodic potentials).

Table 1 Crystal data and details of data collection and structural refinement for dirhenium compounds 1 and 2. Compound

1CH2Cl22CH3OH

24CH2Cl2

Formula Formula weight Temp. (K) Crystal system Space group a (Å) b (Å) c (Å) a (°) b (°) c (°) Volume (Å3) Z Dcalc (mg/m3) l (mm1) Final R indices [I > 2r]a,b R indices (all data)a,b

C67H60Cl4O6P4Re2S8 1855.81 110(2) monoclinic P2/c 23.287(5) 10.193(2) 36.010(12) 90.00 122.23(2) 90.00 7230(3) 1 1.705 3.862 R1 = 0.0683,wR2 = 0.1821 R1 = 0.1793, wR2 = 0.2318 0.940

C61H55Cl12O2P4Re2S4 1869.97 110(2) triclinic  P1

Goodness-of-fit (GOF) on F2 a b

R1 ¼

13.776(3) 15.161(3) 18.287(4) 75.20(3) 75.49(3) 79.76(3) 3548.4(14) 2 1.750 4.109 R1 = 0.0601,wR2 = 0.1244 R1 = 0.1208, wR2 = 0.1463 0.915

P

jjF 0 j  jjF c jj=jF 0 j.    2  P   2 1=2 P wR2 ¼ w F 20  F 2c . = w F 20

was secured to the tip of a glass fiber with Dow Corning grease and transferred to the cold N2 stream of the diffractometer.

A compilation of crystal data for compounds 1 and 2 is provided in Table 1. In all structures, the non-planarity of the TTF backbone indicates that the TTF core is not oxidized [30]. The cis-Re2Cl2(dppm)2(TTFCO2)2 complex crystallizes as 1CH2Cl22CH3OH in the monoclinic space group P2/c with two unique dirhenium complexes packing in a head to tail manner (Fig. 2). The Re–Re distances are 2.3169(11) and 2.3141(11) Å, which are consistent with the bond length found in the acetate starting material (2.3151(7) Å) [22]. The axial chlorides are not linear with respect to the Re–Re bond axis, the relevant angles are

Compound (solvent)

TTF-based E½ (V)

Re2-based E½ (V)

TTFCO2H (CH3CN)

0.50 Ep,a = 0.90

trans-Re2Cl4(dppm)2(TTFCO2), 2 (CH2Cl2)

0.56 Ep,a = 1.21

0.74 Ep,c = 1.11

cis-Re2Cl4(TTFCO2)2, 3 (CH3OH)

0.52 0.88

Ep,c = 0.41

237

B.W. Smucker et al. / Inorganica Chimica Acta 425 (2015) 233–238

Table 3 Electronic spectral data for TTFCO2H and compounds 2 and 3 in dichloromethane or methanol solutions. Compound (solvent)

k (nm)

e (cm1 M1)

TTFCO2H (CH3OH)

215 301 312 433 585

7.6  103 9.0  103 9.1  103 2.2  103 3.1  102

trans-Re2(dppm)2Cl4(TTFCO2), 2 (CH2Cl2)

319 422 495

8.0  103 2.8  103 2.5  103

cis-Re2Cl4(TTFCO2)2, 3 (CH3OH)

250 288 314 460 510 570

1.7  105 2.3  105 2.2  105 2.5  104 3.1  104 2.1  104

1 µA

1.4

1.2

1

0.8

0.6

0.4

0.2

0

Potential (V) Fig. 4. Cyclic voltammogram showing all the oxidations (red) and reversible oxidations (blue) observed for trans-Re2Cl4(dppm)2(TTFCO2), 2. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)

dirhenium species lead to significant shifts in the potentials from those of TTFCO2H or the starting material, trans-Re2Cl4(dppm)2(O2CCH3) (E½ = +0.52 V and Ep,c = 0.60 V) [23]. The irreversibility of the 2nd oxidation of [TTFCO2] agrees with the electrochemical behavior of TTFCO2H and this decomposition is further substantiated by the solid-state evidence of elongation of the C–C bond between the TTF molecule and the carboxylate functional group (vide supra). The compound cis-Re2Cl4(TTFCO2)2, 3, exhibits two reversible oxidations at E½ = +0.52 and +0.88 V, and a quasi-reversible reduction at Ep,c = 0.41 V (Fig. 5). The observation of only two oxidations indicate that appreciable coupling between the TTF ligands does not occur through the CO2–M2–CO2 bridge, which agrees with earlier reports of simultaneous oxidations of both TTF ligands on a dirhodium core [20]. In other research with TTF molecules linked by a heteroatom or directly bonded to each other, electronic exchange through two bridged TTF molecules was attributed to Coulombic charge repulsions and not orbital interactions [31]. It is, therefore, no surprise that communication through an even longer bridge in these carboxylate systems does not occur. The quasi-reversible reduction of 3 occurs at a similar potential as

4 µA 1.2

1

0.8

0.6

0.4

0.2

0

Potential (V)

the cis-Re2Cl4(O2CCH3)2 starting material (E½ = 0.38 V) [24]. Remarkably, the reversibility of the second oxidation indicates that the [TTFCO2] ligand is stabilized by the ReIII,III core (Fig. 5). This 2 stabilization is appreciable considering the instability of the [TTFCO2] second oxidation as a free ligand, and the observed thermal decarboxylation of a coordinated alkynoate ligand in other dinuclear complexes [32]. Electronic spectra for TTFCO2H and complexes 2 and 3 are listed in Table 3. The transitions in 2 and 3 with kmax between 310 and 320 nm are assigned to the [TTFCO2] ligand. Additional absorption bands within the spectra of the dirhenium complexes are analogous to the electronic absorption spectra of their parent compounds. 4. Conclusions The facile exchange of acetate ligand(s) using the [TTFCO2] ligand resulted in new dirhenium complexes bridged by tetrathiafulvalene-monocarboxylate. Structural analyses showed that [TTFCO2] bridges the dimetal unit equatorially, that the TTF core remains neutral, and that long range S  S interactions persist in the solid state. Electrochemical studies via cyclic voltammetry revealed significant interactions between the ligand and dirhenium core. In complex 3, the two coordinated [TTFCO2] ligands exhibited no coupling in either of the two oxidations of the TTF moiety. Additionally, the ReIII,III core engendered an unexpected stability on the 2nd oxidation of the [TTFCO2] ligand without loss of carbon dioxide typically observed in its free form. These complexes highlight the propensity of this ligand to bind to metal–metal bonded units and that the direct coordination of redox-active organic subunits to inorganic moieties through carboxylate-bridges is a viable avenue to prepare new classes of hybrid materials. Acknowledgments

1 µA 0

-0.1 -0.2 -0.3 -0.4 -0.5 -0.6 -0.7 -0.8

Potential (V) Fig. 5. Cyclic voltammograms showing the reversible TTF-based oxidations (top) and quasi-reversible Re2-based reduction (bottom) observed for cis-Re2Cl4(TTFCO2)2, 3.

The authors thank Prof. Kim R. Dunbar and the Department of Chemistry at Texas A&M University for making this entire work possible. Funding for this research was provided by the Robert A. Welch Foundation (A-1449) and the National Science Foundation (CHE-987975). Appendix A. Supplementary material Supplementary data associated with this article can be found, in the online version, at http://dx.doi.org/10.1016/j.ica.2014.10.002.

238

B.W. Smucker et al. / Inorganica Chimica Acta 425 (2015) 233–238

References [1] (a) H. Tanaka, Y. Okano, H. Kobayashi, W. Suzuki, A. Kobayashi, Science 291 (2001) 285; (b) M. Bousseau, L. Valade, J.-P. Legros, P. Cassoux, M. Garbauskas, L. Interrante, J. Am. Chem. Soc. 1986 (1908) 108. [2] (a) A. Bencini, C. Benelli, D. Gatteschi, C. Zanchini, J. Am. Chem. Soc. 106 (1984) 5813; (b) K. Inoue, H. Iwamur, J. Am. Chem. Soc. 116 (1994) 3173; (c) A. Caneschi, A. Dei, H. Lee, D.A. Shultz, L. Sorace, Inorg. Chem. 40 (2001) 408; (d) J.M. Manriquez, G.T. Yee, R.S. McLean, A.J. Epstein, J.S. Miller, Science 252 (1991) 1415; (e) J.S. Miller, Inorg. Chem. 39 (2000) 4392; (f) H. Zhao, R.A. Heintz, R.D. Rogers, K.R. Dunbar, J. Am. Chem. Soc. 118 (1996) 12844; (g) H. Zhao, M.J. Bazile Jr., J.R. Galan-Mascaros, K.R. Dunbar, Angew. Chem., Int. Ed. Engl. 42 (2003) 1015. [3] (a) J.A. Zuleta, C.A. Chesta, R. Eisenberg, J. Am. Chem. Soc. 111 (1989) 8916; (b) W. Paw, S.D. Cummings, M.A. Mansour, M.B. Connick, D.K. Geiger, R. Eisenberg, Coord. Chem. Rev. 171 (1998) 125; (c) B.W. Smucker, J.M. Hudson, M.A. Omary, K.R. Dunbar, Inorg. Chem. 42 (2003) 4714. [4] (a) K. Wang, E.I. Stiefel, Science 291 (2001) 106; (b) M.Q. Sans, P. Belser, Coord. Chem. Rev. 229 (2002) 59; (c) H. Yersin, C. Kratzer, Coord. Chem. Rev. 229 (2002) 75; (d) S. Campagna, C. Di Pietro, F. Loiseau, B. Maubert, N. McClenaghan, R. Passalacqua, F. Puntoriero, V. Ricevuto, S. Serroni, Coord. Chem. Rev. 229 (2002) 67; (e) G. Simonneaux, P. Le Maux, Coord. Chem. Rev. 228 (2002) 43. [5] D. Lorcy, N. Bellec, M. Fourmigué, N. Avarvari, Coord. Chem. Rev. 253 (2009) 1398. [6] (a) Q. Wang, P. Day, J.-P. Griffiths, H. Nie, J.D. Wallis, New J. Chem. 30 (2006) 1790; (b) J. Massue, N. Bellec, S. Chopin, E. Levillain, T. Roisnel, R. Clérac, D. Lorcy, Inorg. Chem. 44 (2005) 8740; (c) L. Wang, B. Zhang, J. Zhang, Inorg. Chem. 45 (2006) 6860; (d) M. Chahma, N. Hassan, A. Alberola, H. Stoeckli-Evans, M. Pilkington, Inorg. Chem. 46 (2007) 3807; (e) F. Pointillart, Y. Le Gal, S. Golhen, O. Cador, L. Ouahab, Inorg. Chem. 47 (2008) 9730; (f) F. Pointillart, B. Le Guennic, O. Maury, S. Golhen, O. Cador, L. Ouahab, Inorg. Chem. 52 (2013) 1398; (g) F. Pointillart, B. Le Guennic, S. Golhen, O. Cador, O. Maury, L. Ouahab, Inorg. Chem. 52 (2013) 1610; (h) G. Cosquer, F. Pointillart, B. Le Guennic, Y. Le Gal, S. Golhen, O. Cador, L. Ouahab, Inorg. Chem. 51 (2012) 8498. [7] R.A. Walton, third ed., in: F.A. Cotton, C.A. Murillo, R.A. Walton (Eds.), Multiple Bonds Between Metal Atoms, vol. 1, Springer Science and Business Media, New York, 2005, p. 271 (chapter 8). [8] T.R. Felthouse, T.-Y. Dong, D.N. Hendrickson, H.-S. Shieh, M.R. Thompson, J. Am. Chem. Soc. 108 (1986) 8201. [9] (a) C. Campana, K.R. Dunbar, X. Ouyang, J. Chem. Soc., Chem. Commun. (1994) 2427; (b) J.M. Giraudon, J.E. Guerchais, J. Sala-Pala, L. Toupet, J. Chem. Soc., Chem. Commun. (1988) 921.

[10] S.L. Bartley, K.R. Dunbar, Angew. Chem., Int. Ed. Engl. 30 (1991) 448. [11] H. Miyasaka, C.S. Campos-Fernández, J.R. Galán-Mascarós, R. Dunbar, Inorg. Chem. 39 (2000) 5870. [12] S.E. Bell, J.S. Field, R.I. Haines, M. Moscherosch, W. Matheis, W. Kaim, Inorg. Chem. 31 (1992) 3269. [13] G. Matsubayashi, K. Yokoyama, T. Tanaka, J. Chem. Soc., Dalton Trans. (1988) 3059. [14] (a) F.A. Cotton, L.M. Daniels, C.A. Murillo, J. Am. Chem. Soc. 121 (1999) 4538; (b) R.H. Cayton, M.H. Chisholm, J.C. Juffman, E.B. Lobkovsky, J. Am. Chem. Soc. 113 (1991) 8709; (c) J.K. Bera, R. Clérac, P.E. Fanwick, R.A. Walton, J. Chem. Soc., Dalton Trans. (2002) 2168. [15] Y.-R. Qin, Q.-Y. Zhu, L.-B. Huo, Z. Shi, G.-Q. Bian, J. Dai, Inorg. Chem. 49 (2014) 7372. [16] F. Pointillart, Y.L. Gal, S. Golhen, O. Cador, L. Ouahab, Chem. Commun. (2009) 3777. [17] D.C. Green, J. Org. Chem. 44 (1979) 1476. [18] (a) C.J. Kepert, D. Hesek, P.D. Beer, M.J. Rosseinsky, Angew. Chem. 37 (1998) 3158; (b) N. Mercier, M. Giffard, G. Pilet, M. Allain, P. Hudhomme, G. Mabon, E. Levillain, A. Gorgues, A. Riou, Chem. Commun. (2001) 2722; (c) Y.-D. Huang, P. Huo, M.-Y. Shao, J.-X. Yin, W.-C. Shen, Q.-Y. Zhu, J. Dai, Inorg. Chem. 53 (2014) 3480. [19] (a) A. Dolbecq, M. Fourmigué, P. Batail, Bull. Soc. Chim. Fr. 133 (1996) 83; (b) J.N. Kreitsberga, O.J. Neiland, J. Org. Chem. USSR (1987) 2131. [20] M. Ebihara, M. Nomura, S. Sakai, T. Kawamura, Inorg. Chim. Acta 360 (2007) 2345. [21] S.V. Kolotilov, O. Cador, F. Pointillart, S. Golhen, Y. Le Gal, K.S. Gavrilenko, L. Ouahab, J. Mater. Chem. 20 (2010) 9505. [22] D.R. Derringer, E.A. Buck, S.M.V. Esjornson, P.E. Fanwick, R.A. Walton, Polyhedron 9 (1990) 743. [23] A.R. Cutler, D.R. Derringer, P.E. Fanwick, R.A. Walton, J. Am. Chem. Soc. 110 (1988) 5024. [24] A.R. Chakravarty, F.A. Cotton, A.R. Cutler, R.A. Walton, Inorg. Chem. 25 (1986) 3619. [25] SAINT, Program for area detector absorption correction, Siemens Analytical Xray Instruments Inc., Madison, WI 53719, USA, 1994–1996. [26] G.M. Sheldrick, SADABS, Program for Siemens Area Detector Absorption Correction, University of Göttingen, 1996. [27] (a) G.M. Sheldrick, XPREP, Program for Space Group Determination, University of Göttingen, Germany, 1996; (b) A.L. Spek, Acta Crystallogr., Sect. A 46 (1990) C34. PLATON; (c) PLATON: A Multipurpose Crystallographic Tool, Utrecht University, Utrecht, The Netherlands, 1998. [28] (a) G.M. Sheldrick, SHELXS-97, Program for Crystal Structure Determination, University of Göttingen, 1997; (b) G.M. Sheldrick, SHELXL-97, Program for Refining Crystal Structures, University of Göttingen, 1997; (c) L.J. Barbour, J. Supramol. Chem. 1 (2001) 189. [29] J.K. Bera, B.W. Smucker, R.A. Walton, K.R. Dunbar, Chem. Commun. 24 (2001) 2562. [30] (a) B.W. Smucker, K.R. Dunbar, J. Chem. Soc., Dalton Trans. (2000) 1309; (b) C.E. Uzelmeier, B.W. Smucker, E.W. Reinheimer, M. Shatruk, A.W. O’Neal, M. Fourmigué, K.R. Dunbar, Dalton Trans. (2006) 5259. [31] M. Fourmigué, Y.-S. Huang, Organometallics 12 (1993) 797. [32] J.K. Bera, P.E. Fanwick, R.A. Walton, J. Chem. Soc., Dalton Trans. (2001) 109.