Mononuclear and Dinuclear Ruthenium Complexes of cis- and trans

Article pubs.acs.org/IC

Cite This: Inorg. Chem. XXXX, XXX, XXX−XXX

Mononuclear and Dinuclear Ruthenium Complexes of cis- and transThioindigo: Geometrical and Electronic Structure Analyses Madhumita Chatterjee,† Sudipta Mondal,‡ Prabir Ghosh,† Wolfgang Kaim,*,‡ and Goutam Kumar Lahiri*,† †

Department of Chemistry, Indian Institute of Technology Bombay, Powai, Mumbai 400076, India Institut für Anorganische Chemie, Universität Stuttgart, Pfaffenwaldring 55, D-70550 Stuttgart, Germany

‡

Inorg. Chem. Downloaded from pubs.acs.org by UNIV OF SOUTH DAKOTA on 09/10/18. For personal use only.

S Supporting Information *

ABSTRACT: The compounds [Ru(acac)2(L)] (1) and [Ru2(acac)4(μ-L)] (2) with acac− = acetylacetonato and L = thioindigo were characterized crystallographically with a cisconfigurated L and O,O′-coordinated metal in 1 and with trans-configurated L and two S,O-coordinated bridged ruthenium centers for 2. The electronic structures of 1 and 2 were confirmed by spectroscopy and density functional theory calculations, suggesting considerable metal-to-ligand electron transfer resulting in the formation of the thioindigo radical anion and oxidized metal(s). UV−Vis−Near-IR and IR (spectro)electrochemistry was used to investigate charged forms 1n (n = 1+, 1−) and 2n (n = 1+, 1−, 2−), which reveal electron transfer activity of both the metal and the thioindigo ligand as well as sizable orbital mixing. An intense near-IR absorption is observed for 2− at 2180 nm. The remarkable ligand properties of thioindigo are being discussed in connection to related coordination compounds of indigo derivatives such as dehydroindigo and corresponding (“Nindigo”) diimines.

■

INTRODUCTION The interest in indigo and its derivatives such as thioindigo, L, has continued after the dye application phase1 because of the recognition of useful electronic properties for materials science.2,3 However, the coordination chemistry remained underdeveloped, and the variety of metal complexes of noninnocent and ambidentate forms of deprotonated indigo were studied systematically only recently.4,5 With thioindigo, a fluorescent and photostable molecule,6 even fewer metal compounds were described.7 The availability of several charge forms of Ln (n = 0, 1−, 2−) was reported7 in 2017, and the bis(bidentate) bridging capacity was shown for a bis-phenylimino derivative of thioindigo in 2018 (Figure 1).8 Our present report uses unaltered L as a chelate and bischelate ligand for the {Ru(acac)2} complex fragment (acac− = acetylacetonato) to allow for a structural and electronic comparison with complexes of related indigoid ligands.9−11 The compounds obtained were 1 and 2 (Figure 2), and the methods for study included experimental techniques (X-ray diffraction, electrochemistry, UV−vis−NIR−IR (NIR = nearinfrared) spectroelectrochemistry, electron paramagnetic resonance (EPR)) and computations (time-dependent (TD) density functional theory (DFT)).

(2), were obtained from the same reaction mixture involving [RuII(acac)2(CH3CN)2] and L in refluxing tetrahydrofuran (THF) under a dinitrogen atmosphere. The complexes 1 and 2 were separated on a neutral alumina column using 3:1 and 1:2 petroleum ether (60−80°)−dichloromethane mixtures, respectively. Attempts to obtain the cis-configurated O,O′;S,S′ bonded dinuclear complex or the trans-configurated O,S;S,O bonded 2 from the mononuclear counterpart 1 were unsuccessful, which prevents further speculation on the mechanisms leading to the observed product isomers. The complexes 1 and 2 exhibited the expected microanalytical and mass spectral data (Figure S1, Supporting Information and Experimental Section). The well-resolved 1H NMR spectra (Figures S2 and S3 in Supporting Information and Experimental Section) of 1 and 2 displayed the calculated number of four distinct protons (two doublets and two triplets from L) as well as one/two CH and two/four CH3 singlet signals from acac, corresponding to half of the molecule due to the symmetry in each case. For compound 2 this result suggests the presence of only one diastereomer as confirmed by X-ray crystallography. Bis-chelate complexes of doubly bidentate indigoid ligands can occur in meso (ΔΛ) and rac (ΔΔ,ΛΛ) configurations.5,8−11 The ν(C−O) frequencies of coordinated L in the IR spectra for KBr disks of 1 or 2

■

RESULTS AND DISCUSSION Synthesis and General Characterization. The thioindigo-derived electrically neutral complexes, namely, mononuclear [Ru(acac)2(L)] (1) and dinuclear [{Ru(acac)2}2(μ-L)] © XXXX American Chemical Society

Received: July 2, 2018

A

DOI: 10.1021/acs.inorgchem.8b01829 Inorg. Chem. XXXX, XXX, XXX−XXX

Article

Inorganic Chemistry

Figure 1. Indigoid molecules (in trans configuration).

Figure 2. Representation of the new compounds described in this article (1, 2) and of related deprotonated indigo (3) and nindigo (4) complexes reported earlier.10,11

appeared at very similar positions of 1567 or 1564 cm−1, respectively. X-ray Analysis and DFT-Supported Structure Discussion. The molecular identity of the complexes 1 and 2 was authenticated by their single-crystal X-ray structures (Figures 3

Figure 4. Perspective view of 2 in the crystal of 2·CH3CN. Ellipsoids are drawn at the 50% probability level. Hydrogen atoms and solvent molecule are omitted for clarity.

Figure 3. Perspective view of 1 in the crystal of 1·C7H8. Ellipsoids are drawn at the 50% probability level. Hydrogen atoms and solvent molecule are omitted for clarity.

reluctant to be coordinated by electron-rich metal centers,12 in contrast to carbonyl functions. This would favor O,O′ coordination over S,S′ or O,S coordination in spite of the presumably strained and unusual seven-membered chelate ring in 1. As another argument, a metal-to-thioindigo π backdonation is more feasible via the carbonyl-O acceptor functions than via electron-donating thiophene-type S atoms. For trans-thioindigo containing 2 the observed bis(βthiodiketonato) coordination13 with two edge-sharing sixmembered ring chelates is apparently preferable to a less symmetrical isomer with one O,O′-coordinated metal in a seven-membered chelate ring and one S,S′-coordinated metal in a five-membered chelate arrangement. However, a related unsymmetrical arrangement has been observed in a dinuclear deprotonated indigo complex of Ru(acac)2.11 The Ru···Ru distance at 6.47 Å in 2 is rather large for dinuclear complexes

and 4, Table 1, and Tables S1−S5). On the one hand, crystal structure analysis of the mononuclear 1 revealed the binding of {Ru(acac)2} with the O,O′ donors of cis-configurated9 thioindigo, resulting in a puckered seven-membered chelate ring (Table S6). On the other hand, trans-configurated thioindigo was found to bridge two {Ru(acac)2} metal complex fragments through the S and O donors, respectively, forming two six-membered O,S-chelates in 2 with rac (ΔΔ,ΛΛ) configuration. The distorted octahedral situation around the metal ions in 1 and 2 is evident from the cis and trans angles. Avoiding speculation on the reaction mechanism, the formulation of different configurations, cis-thioindigo in 1 and trans-thioindigo in 2, can be attributed to various factors. To start with, thiophene-type sulfur centers are typically B


Article

Inorganic Chemistry

bond lengths, (b) the presence of broken-symmetry15 singlets as ground states for 1 and 2 with relatively close-lying (417 or 1116 cm−1) broken-symmetry triplet excited states (Table S8), (c) charge distributions confirming a significant metal-toligand charge transfer (MLCT), and (d) effects of electron uptake or loss, signifying a mostly metal-centered highest occupied molecular orbital (HOMO) and a more ligand-based lowest unoccupied molecular orbital (LUMO) (Tables S9− S17). Electrochemistry. Both 1 and 2 exhibited multiple redox processes including one reversible oxidation (Ox1) and two reversible reduction (Red1, Red2) processes in CH3CN within the potential window of ±2.0 V versus saturated calomel electrode (SCE) (Figure 5, Table 2). The separations of

Table 1. Experimental and DFT-Calculated Selected Bond Lengths (Å) for 1·C7H8 and 2·CH3CN 2·CH3CNa

1·C7H8 bond

expt

DFT

bond

expt

DFT

Ru1−O1 Ru1−O2 Ru1−O3 Ru1−O4 Ru1−O5 Ru1−O6 C1−C9 O1−C2 O2−C10 S1−C1 S2−C9 S1−C8 S2−C16 C2−C1 C10−C9 C3−C2 C11−C10 C11−C16 C3−C8

1.970(6) 1.975(6) 2.022(6) 2.015(6) 2.016(6) 2.003(6) 1.398(10) 1.287(10) 1.273(10) 1.756(8) 1.754(9) 1.747(8) 1.752(8) 1.440(12) 1.433(11) 1.456(10) 1.472(11) 1.364(11) 1.375(11)

2.012 2.011 2.055 2.052 2.052 2.055 1.393 1.262 1.262 1.786 1.786 1.764 1.764 1.459 1.459 1.465 1.464 1.399 1.399

Ru1−O2 Ru2−O1 Ru1−S2 Ru2−S1 Ru1−O3 Ru1−O4 Ru1−O5 Ru1−O6 Ru2−O7 Ru2−O8 Ru2−O9 Ru2−O10 O1−C2 O2−C10 C1−C9 C10−C9 C2−C1 S2−C8 S1−C16 S2−C1 S1−C9 C11−C10 C2−C3 C11−C16 C3−C8

1.985(9) 1.991(9) 2.302(4) 2.297(4) 2.024(9) 2.031(9) 2.045(8) 2.009(8) 2.020(8) 2.022(9) 2.046(8) 2.015(9) 1.277(14) 1.303(14) 1.402(16) 1.406(17) 1.420(17) 1.786(13) 1.793(13) 1.755(13) 1.745(12) 1.472(17) 1.480(17) 1.390(17) 1.389(18)

2.058 2.053 2.372 2.371 2.057 2.074 2.059 2.067 2.073 2.057 2.058 2.067 1.262 1.261 1.384 1.455 1.454 1.784 1.784 1.777 1.776 1.466 1.466 1.402 1.402

a

Ru···Ru distance 6.470 Å.

of indigoid ligands (Table S7), a result of the larger size of S versus O or N. The two heterocyclic π systems are twisted by only 8.8° (Table S6), ensuring strong π conjugation. An important issue when discussing preferred coordination structures is the question of charge and oxidation states. It has been found that thioindigo can exist as neutral molecule L, as radical anion L·−, or as dianionic ligand L2−.7 Structural parameters indicative of effective charges have been derived7 from calculations and structure determination of {[L(μ2-O), (μ-O)Cp*Cr}2 5 and {[2,2,2]cryptand(Na+)}(L·−) 6 and can be applied here to assess the electronic structures of thioindigo in 1 and 2. Comparing the experimental CO bond lengths of ∼1.28 Å and the central CC distances of 1.40 Å (Table 1) for 1 and 2 with the literature values7 (CO: 1.21(3) Å for trans-L, 1.24−1.37 Å for cis- or trans- L·− or L·− in 6, 1.332(2) Å for L2− in 5; central CC: 1.34(3) Å for L, ∼1.40 Å for cis- or transL·− or L·− in 6, 1.445(2) Å for L2− in 5), the best fit would be with an L·− description in compounds 1 and 2. Considering the diamagnetism of the compounds, this would imply antiferromagnetic interaction between a ligand radical anion and oxidized [Ru(acac)2] complex fragments, a situation that has been previously established for mononuclear and dinuclear complexes of [Ru(acac)2].14 However, the coordination of a π back-donating entity such as [Ru(acac)2] to CO can cause a lengthening of that bond even without full metal-to-ligand electron transfer. The Ru−S bond lengths are in the expected range.8 According to DFT calculations (Table S3) they change on oxidation but not on reduction. DFT calculations of 1 and 2 (Table 1 and Tables S2−S5, Figure S4) reveal (a) reproduction of the experimental parameters, with typical overestimation of metal-element

Figure 5. Cyclic (black) and differential pulse (green) voltammograms of 1 and 2 vs SCE in CH3CN/0.1 M Et4NClO4 at 298 K. (inset) The reversible waves.

potentials between the stepwise redox processes in 1 and 2 led to comproportionation constant (Kc) values in the range from 1 × 108 to 1 × 1020 (Table 2), corresponding to varying stabilities of the intermediate redox states. Spectroelectrochemistry experiments suggested fully reversible features of Ox1 and Red1 for 1 and of Ox1 and Red1, Red2 for 2. The pertinent question of the involvement of metal and/or L based frontier orbitals in the reversible redox processes was addressed via experimental investigations in conjunction with theoretical studies. Comparison of the reduction potentials for 2 with those of free thioindigo16 reveals an anodic shift of ∼0.3 V, which signifies a rather small effect of coordination of the electronrich metal centers. The comparison of compounds 1−4 in Table 2 reveals decreasing redox potentials in that order, corresponding to facilitated oxidation and cathodically shifted reduction on replacing S through O or NPh. IR- and UV−Vis−NIR Spectroelectrochemistry and TD-DFT Analysis. The thioindigo chromophore has been investigated in detail;17 however, the response of metal coordination was studied only very recently.7 The largely reversible electron transfer as evident from cyclic voltammetry invited attempts to investigate electronic transitions and C


Article

Inorganic Chemistry Table 2. Electrochemical Dataa E°298/[V] (ΔEp/[mV])b

complex Ox2 1 2 3e 4

d

1.08 1.38(230) 0.76(70)

Kcc

Ox1

Red1

Red2

0.77 (60) 0.53(70) 0.55(220) 0.11(70)

−0.12 (60) −0.38(80) −0.52(280) −0.88(90)

−1.32 (70) −0.87(90) −1.23(240) −1.45(110)

Kc1d

Kc2d

2.1 × 10 1.2 × 1014 1.1 × 1011

× × × ×

9

1.3 3.0 1.4 6.0

Kc3d 15

10 1015 1018 1016

1.9 2.1 1.1 4.6

× × × ×

1020 108 1012 109

this work this work 11 10

a From cyclic voltammetry in CH3CN/0.1 M Et4NClO4 at 100 mV s−1. bPotential in volts versus SCE; peak potential differences ΔEp [mV] in parentheses. cComproportionation constant from RT ln Kc = nF(ΔE). Kc1 between Ox2 and Ox1; Kc2 between Ox1 and Red1 and Kc3 between Red1 and Red2. dIrreversible. eFrom cyclic voltammetry in CH2Cl2/0.1 M Bu4NClO4 at 100 mV s−1.

vibrational response of 1 and 2 in the UV−vis−NIR and IR regions. The results from optically transparent thin-layer electroysis (OTTLE)18 spectroelectrochemistry are shown in Figures 6−8 and summarized together with TD-DFT calculations data in Tables S18−S20.

Figure 6. UV−Vis−NIR spectroelectrochemical response of 1n (n = 1+, 0, 1−) in CH3CN/0.1 M Bu4NClO4.

Figure 7. UV−Vis−NIR spectroelectrochemical response of 2n (n = 1+, 0, 1−, 2−) in CH3CN/0.1 M Bu4NClO4.

The mononuclear 1 shows an absorption at 662 nm that gets hardly shifted on oxidation but is considerably diminished in intensity on reduction. TD-DFT calculations suggest an MLCT situation for that transition in 1, implying a largely metal-centered HOMO and a mostly ligand-centered LUMO (Table S9). No near-IR features were observed on electron transfer. The dinuclear compound 2 exhibits a moderately intense long-wavelength absorption at 1050 nm, which is assigned to an MLCT transition based on TD-DFT calculations (Figure 7, Table S19). Whereas oxidation to 2+ leads to a slight hypsochromic shift, the two-step reversible reduction involves a remarkable intermediate 2− (Kc ≈ 1 × 108) that exhibits intense bands in the NIR region (Figures 7 and 8). These NIR features disappear after the second reduction to 22−, and they are identified as mainly ligand-to-ligand′ charge transfer (LL′CT) transitions through ORCA analysis (Table S19). The occurrence of such conspicuous NIR features only for the

“half-reduced” dinuclear system 2n might suggest a mixedvalent contribution;19 however, radical ligands of larger conjugated π systems are also frequently distinguished by intense NIR activity.20 The CO stretching vibrations in the IR region are just slightly shifted on electron transfer in 2n (Figure 8, Table S20), in agreement with the rather marginal changes of C−O bond lengths as calculated by DFT for 1n and 2n (Tables S2 and S3). EPR Spectra and Spin Densities. The paramagnetic products of electron transfer to and from 1 and 2 were studied by EPR spectroscopy in conjunction with DFT-calculated spin densities. Large metal spin densities will result in deviations of the g factor components from ge = 2.0023 due to the high spin−orbit coupling constants of heavy elements.19 However, such high concentration of spin on the metal will also favor rapid relaxation and therefore broad lines, necessitating very low temperature to observe an EPR resonance.21 D


Article

Inorganic Chemistry

Figure 10. EPR spectrum of electrogenerated 2− in CH3CN/0.1 M Bu4NClO4 at 4.2 K. g1 = 2.16, g2 = 2.12, g3 = 1.93; Δg = 0.23; ⟨g⟩ = 2.07 (top, *signal attributed to organic decomposition product during electrolysis). EPR spectrum of electrogenerated 2+ in CH2Cl2/0.1 M Bu4NClO4 at 4.2 K with computer simulation. (g1 = 2.40, g2 = 2.24, g3 = 2.03; Δg = 0.37; ⟨g⟩ = 2.23 (bottom).

observations agree with DFT-calculated spin densities (Figure 11, Figures S5 and S6, Tables S18, S19, and S21), suggesting

Figure 8. IR spectroelectrochemical responses of 2n (n = 1+, 0, 1−, 2−) in CH3CN/0.1 M Bu4NClO4.

At 4 K useful EPR signals could be recorded for electrogenerated 1− and 2− (Figure 9 and Figure 10), while 1+ did not exhibit a signal under those conditions. Whereas 1− showed a rhombic signal with a sizable g anisotropy as typical for a low-spin d5 configuration of RuIII, the spectrum of 2− exhibits a relatively small axial splitting, which suggests larger contributions from thioindigo radical.22 These experimental

Figure 11. DFT-calculated Mulliken spin density plots for 1n and 2n.

somewhat metal-based spin for 1− but more ligand-centered spin for 2−. The absence of observable EPR signals for electrogenerated 1+ is in agreement with predominantly metalbased spin. The data for individual atoms are shown in Figures S5 and S6. In conjunction with the structural and spectroelectrochemical results the spin density information thus suggests alternative oxidation state assignments as shown in Scheme 1. On the basis of spin densities (Table S21, Figure 11) and other information from DFT calculations (Supporting Information) the following redox schemes can be constructed: Starting from the neutral mononuclear compound 1 with significant RuIII(L·−) character the one-electron oxidation to 1+ leads to a ruthenium(III) complex of L. Two alternative formulations can be considered for the reduction to 1−, because metal and ligand exhibit significant spin densities. On one side, in the dinuclear series, the oxidation of the native

Figure 9. EPR spectrum of 1− in CH2Cl2/0.1 M Bu4NClO4 at 4.2 K. g1 = 2.42, g2 = 2.18, g3 = 2.02; Δg (g1 − g3) = 0.40; ⟨g⟩ ({1/3(g12 + g22 + g32)}1/2) = 2.21. E


Inorganic Chemistry

■

Scheme 1. Experimentally Evidenced Redox Series with Oxidation State Combinations

Article

EXPERIMENTAL SECTION

Materials. The metal precursor RuII(acac)2(CH3CN)2 was prepared according to the reported procedure.24 Thioindigo (L) was purchased from TCI Chemicals. All other chemicals and reagents were of reagent grade and used without further purification. For spectroscopic and electrochemical studies high-performance liquid chromatography (HPLC) grade solvents were used. Physical Measurements. The electrical conductivities of the complexes were checked in CH3CN with autoranging conductivity meter (Toshcon Industries). 1H NMR spectra were recorded using a Bruker Avance III 400 MHz spectrometer. The elemental analysis was performed with a Thermo Finnigan (FLASH EA 1112 series) microanalyzer. Electrospray mass spectrometry was checked on a Bruker Maxis Impact (282001.00081) spectrometer. Cyclic and differential pulse voltammetric measurements were performed on a PAR model 273A electrochemistry system. A glassy carbon working electrode, a platinum wire auxiliary electrode, and an SCE were used in a standard three-electrode configuration. Tetraethylammonium perchlorate (TEAP) was used as the supporting electrolyte, and the solute concentration was ∼1 × 10−3 M. The scan rate used was 100 mV s−1. All electrochemical experiments were performed under dinitrogen atmosphere. The half-wave potential E°298 was set equal to 0.5(Epa + Epc), where Epa and Epc are anodic and cathodic cyclic voltammetry peak potentials, respectively. The EPR measurements were made in a two-electrode capillary tube25 with an X-band (9.5 GHz) Bruker system ESP300 spectrometer. UV−Vis−NIR spectroelectrochemical studies were performed in CH3CN/0.1 M Bu4NClO4 at 298 K using an OTTLE cell18 mounted in the sample compartment of a J&M TIDAS spectrophotometer. IR spectroelectrochemical measurements were recorded on a Nicolet 6700 FT-IR instrument by using an OTTLE cell. Preparation of Complexes. A mixture of the metal precursor RuII(acac)2(CH3CN)2 (100 mg, 0.262 mmol) and thioindigo (L) (38 mg, 0.13 mmol) was heated to reflux in 50 mL of THF under dinitrogen atmosphere over a period of 6 h. The solvent was then evaporated under reduced pressure, and the solid product thus obtained was purified by using a neutral alumina column. The green mononuclear complex (1) was initially eluted through 3:1 petroleum ether (60−80°)−dichloromethane, followed by the brown dinuclear complex through 1:2 petroleum ether (60−80°)−dichloromethane mixture. Evaporation of solvent under reduced pressure yielded pure 1 and 2. 1: Yield: 54.7 mg, 35%. Anal. Calcd for C26H22O6S2Ru: C, 52.25; H, 4.05; found: C, 52.18; H, 4.09%. Molar conductivity (CH3CN): (ΛM(Ω−1 cm2 M−1)) = 4. ESI-MS(+) in CH3CN, m/z calcd for {1+H}+: 596.002; found: 596.005. 1H NMR (400 MHz, (CDCl3)): δ(ppm, J(Hz)): 8.07 (t, 1H, 6.0, L), 7.55 (d, 1H, 8.0, L), 7.11 (d, 1H, 8.0, L), 7.04 (t, 1H, 6.0, L), 5.23 (s, 1H, acac), 2.92 (s, 3H, acac), 2.28 (s, 3H, acac). 2: Yield: 35.2 mg, 30%. Anal. Calcd for C36H36O10S2Ru2: C, 48.31; H, 4.05; found: C, 48.47; H, 4.19%. Molar conductivity (CH3CN): (ΛM(Ω−1 cm2 M−1)) = 3. ESI-MS(+) in CH3CN, m/z calcd for {2+H}+: 895.03; found: 895.01. 1H NMR (400 MHz, (CDCl3)): δ(ppm, J(Hz)): 7.73 (t, 1H, 6.0, L), 6.93 (d, 1H, 8.0, L), 6.47 (d, 1H, 8.0, L), 6.27 (t, 1H, 8.0, L), 4.75 (s, 2H, acac), 3.35 (s, 3H, acac), 2.01 (s, 3H, acac), 1.90 (s, 3H, acac), 1.06 (s, 3H, acac). Crystallography. Single crystals of 1 and 2 were grown by slow evaporation of their 1:1 dichloromethane−toluene and 1:1 dichloromethane−acetonitrile solutions, respectively. X-ray crystal data were collected on a RIGAKU SATURN-724+ CCD single-crystal X-ray diffractometer using Mo Kα radiation. Data collection was evaluated by using the CrystalClear-SM Expert software. The data were collected by the standard ω-scan technique and were scaled and reduced using the CrystalClear-SM Expert software. Absorption correction (numerical) was applied to the collected reflections. The structure was solved by direct methods using SHELXT-2014 program and refined by full matrix least-squares with SHELXL-2017, refining on F2.26 All non-hydrogen atoms were refined anisotropically. The hydrogen atoms were placed in geometrically constrained positions

form 2 with Ru2.5(L·−)Ru2.5 character can be envisaged to lead to a coupled three-spin situation23 of 2+ with one net spin remaining largely at the metal. On the other side, reduction to 2− is interpreted as involving mostly ligand-centered spin with a possibly low-lying mixed-valent excited state. Further reduction leads to 2 2− with conventional Ru II (L)Ru II configaration. Remarkably, all (S = 1/2) forms from Table S21 exhibit significant spin densities on the metal(s). As a result, the EPR signals show large g anisotropies. Except for 1+, the doublet species are also having significant spin densities on the thioindigo ligand, leading to considerably mixed Ru/L spin distribution.

■

CONCLUSION Two very recent articles on thioindigo7 and thioindigo diimine compounds8 stated “Despite the abundance of available literature on thioindigo, no examples of metal complexes featuring thioindigo... currently exist in the literature”8 and “in contrast to indigo, no coordination complexes of thioindigo are known”.7 The present report thus fills a gap, revealing the special properties of this bis-bidentate bridging ligand in a standard8−11 diruthenium situation. In contrast to indigo with its acidic NH functions and the resulting dehydroindigo ligand redox system the unaltered thioindigo molecule is an ambidentate bis-chelating π-acceptor ligand without basic N donor function. The present study reveals that the two neutral complexes, mononuclear 1 and dinuclear 2, use primarily the carbonyl O atoms for coordination of Ru(acac)2, whereas the thiophene-type S centers are only metal-bonded in a supporting role. The different charge states available for 1n (n = +, −) and 2n (n = +, −, 2−) show electron transfer activity of both the metal and the thioindigo ligand. Considerable metal/ligand mixing in the singly occupied molecular orbitals (MOs) is observed for 1− and 2n (n = +, −). Taken together this report establishes a remarkable coordinative potential of the commercially available thioindigo as an unconventional versatile ligand. F


Inorganic Chemistry

■

and refined with isotropic temperature factors, generally 1.2Ueq of their parent atoms. Hydrogen atoms were included in the refinement process as per the riding model. CCDC 1849899 (1) and 1849900 (2) contain the supplementary crystallographic data for this paper. Computational Details. Full geometry optimizations were performed by using the DFT method at the (R)B3LYP level for 22− and (U)B3LYP level for 1+, 1−, 12−, 22+, 2+, and 2−.27 Except ruthenium all other elements were assigned the 6-31G* basis set. The LANL2DZ basis set with effective core potential was employed for the ruthenium atom.28 The broken-symmetry formalism29 was applied for 1 and 2. The stability of the UKS ((U)B3LYP) solution was checked by stability analysis. The BS(m, n) notation was adopted in that regard, where m(n) denoted the number of spin up (spin down) electrons at the two interacting fragments. Full geometry optimization (opt) was performed for the broken-symmetry calculation of 1 and 2. The vibrational frequency calculations were performed to ensure that the optimized geometries represented the local minima, and there were only positive eigenvalues. All calculations were performed with Gaussian09 program package.30 Vertical electronic excitations based on (R)B3LYP/(U)B3LYP optimized geometries were computed for 1n (n = +1, 0, −1) and 2n (n = +1, 0, −1, −2) using the TD-DFT formalism31 in acetonitrile using conductor-like polarizable continuum model (CPCM).32 Chemissian 1.733 was used to calculate the fractional contributions of various groups to each molecular orbital. All calculated structures were visualized with ChemCraf t.34 Electronic spectra were calculated using the SWizard program.35,36 The ORCA 3.0.0 program37,38 was used for calculating NIR electron transitions.

■

ASSOCIATED CONTENT

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.inorgchem.8b01829. Mass spectra, NMR, DFT-optimized structures, spin density plots, crystal data table, structural parameters, energy, MO compositions, TD-DFT data table, IR data table, Mulliken spin densities data (PDF) Accession Codes

CCDC 1849899−1849900 contain the supplementary crystallographic data for this paper. These data can be obtained free of charge via www.ccdc.cam.ac.uk/data_request/cif, or by emailing [email protected], or by contacting The Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: +44 1223 336033.

AUTHOR INFORMATION

Corresponding Authors

*E-mail: [email protected]. (G.K.L.) *E-mail: [email protected]. (W.K.) ORCID

Wolfgang Kaim: 0000-0002-8404-4929 Goutam Kumar Lahiri: 0000-0002-0199-6132 Notes

The authors declare no competing financial interest.

■

REFERENCES

(1) (a) Zollinger, H. Color Chemistry; Wiley-VCH: Weinheim, 2003. (b) Hartough, H. D.; Meisel, S. L. Thioindigo and Related Dyes. In Chemistry of Heterocyclic Compounds: Compounds with Condensed Thiophene Rings; Wiley: New York, 2008; Vol. 7, pp 175−224. (2) Glowacki, E. D.; Voss, G.; Sariciftci, N. S. A 25th Anniversary Article. Progress in chemistry and applications of functional indigos for organic electronics. Adv. Mater. 2013, 25, 6783−6800. (3) (a) Fukushima, K.; Nakatsu, K.; Takahashi, R.; Yamamoto, H.; Gohda, K.; Homma, S. Crystal Structures and Photocarrier Generation of Thioindigo Derivatives. J. Phys. Chem. B 1998, 102 (31), 5985−5990. (b) Petermayer, C.; Dube, H. Indigoid Photoswitches: Visible Light Responsive Molecular Tools. Acc. Chem. Res. 2018, 51, 1153−1163. (4) Nawn, G.; Oakley, S. R.; Majewski, M. B.; McDonald, R.; Patrick, B. O.; Hicks, R. G. Redox-active, near-infrared dyes based on ’Nindigo’ (indigo-N,N′-diarylimine) boron chelate complexes. Chem. Sci. 2013, 4, 612−621. (5) Chatterjee, M.; Mondal, P.; Beyer, K.; Paretzki, A.; Kaim, W.; Lahiri, G. K. A structurally characterised redox pair involving an indigo radical: indigo based redox activity in complexes with one or two [Ru(bpy)2] fragments. Dalton Trans. 2017, 46, 5091−5102. (6) Kirsch, A. D.; Wyman, G. M. Excited state chemistry of indigoid dyes. 5. The intermediacy of the triplet state in the direct photoisomerization and the effect of substituents. J. Phys. Chem. 1977, 81, 413−420. (7) Konarev, D. V.; Khasanov, S. S.; Shestakov, F.; Fatalov, A. M.; Batov, M. S.; Otsuka, A.; Yamochi, H.; Kitagawa, H.; Lyubovskaya, R. N. cis-Thioindigo (TI) - a new ligand with accessible radical anion and dianion states. Strong magnetic coupling in the {[TI-(μ2-O),(μO)] Cp*Cr}2 dimers. Dalton Trans. 2017, 46, 14365−14372. (8) Boice, G. N.; Garakyaraghi, S.; Patrick, B. O.; Sanz, C. A.; Castellano, F. N.; Hicks, R. G. Diastereomerically Differentiated Excited State Behavior in Ruthenium(II) Hexafluoroacetylacetonate Complexes of Diphenyl Thioindigo Diimine. Inorg. Chem. 2018, 57, 1386−1397. (9) (a) Mondal, P.; Plebst, S.; Ray, R.; Mobin, S. M.; Kaim, W.; Lahiri, G. K. Uncommon cis Configuration of a Metal-Metal Bridging Noninnocent Nindigo Ligand. Inorg. Chem. 2014, 53, 9348−9356. (b) Mondal, P.; Chatterjee, M.; Paretzki, A.; Beyer, K.; Kaim, W.; Lahiri, G. K. Non-innocence of Indigo: Dehydroindigo Anions as Bridging Electron-Donor Ligands in Diruthenium Complexes. Inorg. Chem. 2016, 55, 3105−3116. (10) Mondal, P.; Ehret, E.; Bubrin, M.; Das, A.; Mobin, S. M.; Kaim, W.; Lahiri, G. K. A Diruthenium Complex of a “Nindigo” Ligand. Inorg. Chem. 2013, 52, 8467−8475. (11) Chatterjee, M.; Ghosh, P.; Beyer, K.; Paretzki, A.; Fiedler, J.; Kaim, W.; Lahiri, G. K. Isomeric Diruthenium Complexes Bridged by Deprotonated Indigo in cis and trans Configuration. Chem. - Asian J. 2018, 13, 118−125. (12) (a) Angelici, R. J. Structural aspects of thiophene coordination in transition metal complexes. Coord. Chem. Rev. 1990, 105, 61−76. (b) Rauchfuss, T. B. The Coordination Chemistry of Thiophenes. Prog. Inorg. Chem. 2007, 39, 259−329. (13) Livingstone, S. E. Monothio-β-diketones and their metal complexes. Coord. Chem. Rev. 1971, 7, 59−80. (14) (a) Maji, S.; Sarkar, B.; Mobin, S. M.; Fiedler, J.; Urbanos, F. A.; Jimenez-Aparicio, R.; Kaim, W.; Lahiri, G. K. Valence-State Alternatives in Diastereoisomeric Complexes [(acac)2Ru(μ-QL)Ru(acac)2]n (QL2‑ = 1,4-Dioxido-9,10-anthraquinone, n = + 2, + 1, 0, −1, −2). Inorg. Chem. 2008, 47, 5204−5211. (b) Kar, S.; Sarkar, B.; Ghumaan, S.; Roy, D.; Urbanos, F. A.; Fiedler, J.; Sunoj, R. B.; Jimenez-Aparicio, R.; Kaim, W.; Lahiri, G. K. A New Coordination Mode of the Photometric Reagent Glyoxalbis(2-hydroxyanil) (H2gbha): Bis-Bidentate Bridging by gbha2‑ in the Redox Series {(μ-gbha)[Ru(acac)2]2}n (n = − 2, − 1, 0, + 1, + 2), Including a Radical-Bridged Diruthenium(III) and a RuIII/RuIV Intermediate. Inorg. Chem. 2005, 44, 8715−8722.

S Supporting Information *

■

Article

ACKNOWLEDGMENTS

Financial support received from the Science and Engineering Research Board (Dept. of Science and Technology), Council of Scientific and Industrial Research (fellowship to M.C.) New Delhi (India) and from the Land Baden-Wü rttemberg (Germany) is gratefully acknowledged. G


Article

Inorganic Chemistry

74, 5737−5743. (b) Noodleman, L.; Norman, J. G.; Osborne, J. H.; Aizman, A.; Case, D. Models for Ferredoxins: Electronic Structures of Iron-Sulphur Clusters with One, Two, and Four Iron Atoms. J. Am. Chem. Soc. 1985, 107, 3418−3426. (c) Noodleman, L.; Davidson, E. R. Ligand Spin Polarization and Antiferromagnetic Coupling in Transition Metal Dimers. Chem. Phys. 1986, 109, 131−143. (d) Noodleman, L.; Peng, C. Y.; Case, D. A.; Mouesca, J. M. Orbital Interactions, Electron Delocalization and Spin Coupling in Iron-Sulfur Clusters. Coord. Chem. Rev. 1995, 144, 199−244. (30) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb, M. A.; Cheeseman, J. R.; Scalmani, G.; Barone, V.; Mennucci, B.; Petersson, G. A.; Nakatsuji, H.; Caricato, M.; Li, X.; Hratchian, H. P.; Izmaylov, A. F.; Bloino, J.; Zheng, G.; Sonnenberg, J. L.; Hada, M.; Ehara, M.; Toyota, K.; Fukuda, R.; Hasegawa, J.; Ishida, M.; Nakajima, T.; Honda, Y.; Kitao, O.; Nakai, H.; Vreven, T.; Montgomery, J. A., Jr.; Peralta, J. E.; Ogliaro, F.; Bearpark, M.; Heyd, J. J.; Brothers, E.; Kudin, K. N.; Staroverov, V. N.; Kobayashi, R.; Normand, J.; Raghavachari, K.; Rendell, A.; Burant, J. C.; Iyengar, S. S.; Tomasi, J.; Cossi, M.; Rega, N.; Millam, J. M.; Klene, M.; Knox, J. E.; Cross, J. B.; Bakken, V.; Adamo, C.; Jaramillo, J.; Gomperts, R.; Stratmann, R. E.; Yazyev, O.; Austin, A. J.; Cammi, R.; Pomelli, C.; Ochterski, J. W.; Martin, R. L.; Morokuma, K.; Zakrzewski, V. G.; Voth, G. A.; Salvador, P.; Dannenberg, J. J.; Dapprich, S.; Daniels, A. D.; Farkas, O.; Foresman, J. B.; Ortiz, J. V.; Cioslowski, J.; Fox, D. J. Gaussian 09, Revision A.02; Gaussian, Inc.: Wallingford, CT, 2009. (31) (a) Bauernschmitt, R.; Ahlrichs, R. Treatment of Electronic Excitations within the Adiabatic Approximation of Time Dependent Density Functional Theory. Chem. Phys. Lett. 1996, 256, 454−464. (b) Stratmann, R. E.; Scuseria, G. E.; Frisch, M. J. An Efficient Implementation of Time-Dependent Density-Functional Theory for the Calculation of Excitation Energies of Large Molecules. J. Chem. Phys. 1998, 109, 8218−8225. (c) Casida, M. E.; Jamorski, C.; Casida, K. C.; Salahub, D. R. Molecular Excitation Energies to High-Lying Bound States from Time-Dependent Density Functional Response Theory: Characterization and Correction of the Time-Dependent Local Density Approximation Ionization Threshold. J. Chem. Phys. 1998, 108, 4439−4450. (32) (a) Barone, V.; Cossi, M. Quantum Calculation of Molecular Energies and Energy Gradients in Solution by a Conductor Solvent Model. J. Phys. Chem. A 1998, 102, 1995−2001. (b) Cossi, M.; Barone, V. Time-dependent density functional theory for molecules in liquid solutions. J. Chem. Phys. 2001, 115, 4708−4718. (c) Cossi, M.; Rega, N.; Scalmani, G.; Barone, V. Energies, Structures, and Electronic Properties of Molecules in Solution with the C-PCM Solvation Model. J. Comput. Chem. 2003, 24, 669−681. (33) Leonid, S.; Chemissian 1.7; 2010. Available at http://www. chemissian.com (accessed March 12, 2018). (34) Zhurko, G. A.; Zhurko, D. A.: ChemCraft 1.6; Plimus: San Diego, CA. Available at http://www.chemcraftprog.com (accessed June 4, 2018). (35) Gorelsky, S. I. SWizard program, http://www.sg-chem.net/ (accessed June 6, 2018). (36) Gorelsky, S. I.; Lever, A. B. P. Electronic structure and spectra of ruthenium diimine complexes by density functional theory and INDO/S. Comparison of the two methods. J. Organomet. Chem. 2001, 635, 187−196. (37) (a) Neese, F. ORCA, an ab initio, DFT, and Semiempirical Electronic Structure Package, Version 3.0.0.; Institut für Physikalische und Theoretische Chemie, Universität Bonn: Bonn, Germany, 2010. (b) Neese, F. Wiley Interdiscip. Rev.: Comput. Mol. Sci. 2012, 2, 73−78. (38) Sinnecker, S.; Rajendran, A.; Klamt, A.; Diedenhofen, M.; Neese, F. Calculation of Solvent Shifts on Electronic g-Tensors with the Conductor-Like Screening Model (COSMO) and Its SelfConsistent Generalization to Real Solvents (Direct COSMO-RS). J. Phys. Chem. A 2006, 110, 2235−2245.

(15) (a) Noodleman, L.; Case, D. A.; Aizman, A. J. Broken Symmetry Analysis of Spin Coupling in Iron-Sulfur Clusters. J. Am. Chem. Soc. 1988, 110, 1001−1005. (b) Lu, C. C.; Bill, E.; Weyhermü ller, T.; Bothe, E.; Wieghardt, K. Neutral Bis(αiminopyridine)metal Complexes of the First-Row Transition Ions (Cr, Mn, Fe, Co, Ni, Zn) and Their Monocationic Analogues: Mixed Valency Involving a Redox Noninnocent Ligand System. J. Am. Chem. Soc. 2008, 130, 3181−3197. (c) Sinha, V.; Pribanic, B.; de Bruin, B.; Trincado, M.; Gruetzmacher, H. Ligand- and Metal-Based Reactivity of a Neutral Ruthenium Diolefin Diazadiene Complex: The Innocent, the Guilty and the Suspicious. Chem. - Eur. J. 2018, 24, 5513−5521. (d) Das, A.; Ghosh, P.; Priego, J. L.; Jimenez-Aparicio, R.; Lahiri, G. K. Unsymmetric (μ-oxido)/(μ-pyrazolato) and Symmetric (μpyrazolato)2 Bridged Diosmium Frameworks: Electronic Structure and Magnetic Properties. Inorg. Chem. 2016, 55, 8396−8406. (e) Mandal, A.; Kundu, T.; Ehret, F.; Bubrin, M.; Mobin, S. M.; Kaim, W.; Lahiri, G. K. Varying Electronic Structural Forms of Ruthenium Complexes of Non-innocent 9,10-phenanthrenequinonoid Ligands. Dalton Trans. 2014, 43, 2473−2487. (16) Boice, G.; Patrick, B. O.; McDonald, R.; Bohne, C.; Hicks, R. Synthesis and Photophysics of Thioindigo Diimines and Related Compounds. J. Org. Chem. 2014, 79, 9196−9205. (17) Jacquemin, D.; Preat, J.; Wathelet, V.; Fontaine, M.; Perpete, E. A. Thioindigo dyes: Highly accurate visible spectra with TD-DFT. J. Am. Chem. Soc. 2006, 128, 2072−2083. (18) Krejcik, M.; Danek, M.; Hartl, F. Simple construction of an Infrared Optically Transparent Thin-layer Electrochemical cell: Applications to the Redox Reactions of Ferrocene, Mn2(CO)10 and Mn(CO)3(3,5-di-t-butyl-catecholate). J. Electroanal. Chem. Interfacial Electrochem. 1991, 317, 179−187. (19) Kaim, W.; Lahiri, G. K. Unconventional Mixed-Valent Complexes of Ruthenium and Osmium. Angew. Chem. 2007, 119, 1808−1828; Angew. Chem., Int. Ed. 2007, 46, 1778−1796. (20) Kaim, W. Concepts for metal complex chromophors absorbing in the near infrared. Coord. Chem. Rev. 2011, 255, 2503−2513. (21) Kaim, W. ESR Spectroscopy of Inorganic and Organometallic Radicals. In Electron Transfer in Chemistry; Balzani, V., Ed., WileyVCH: Weinheim, Germany, 2001; Vol. 2, pp 976−1002. (22) Gerson, F.; Huber, W. Electron Spin Resonance Spectroscopy of Organic Radicals; Wiley-VCH: Weinheim, Germany, 2003. (23) Paretzki, A.; Hübner, R.; Ye, S.; Bubrin, M.; Kämper, S.; Kaim, W. Electronic, charge and magnetic interactions in three-centre systems. J. Mater. Chem. C 2015, 3, 4801−4809. (24) Kobayashi, T.; Nishina, Y.; Shimizu, K. G.; Satô, G. P. Diacetonitrilebis(β-Diketonato) ruthenium(II) Complexes. Their Preparation and Use as Intermediates for the Synthesis of Mixedligand β-Diketonato Ruthenium(III) Complexes. Chem. Lett. 1988, 17, 1137−1140. (25) Kaim, W.; Ernst, S.; Kasack, V. ESR of Homo- and Heteroleptic Mono- and Dinuclear tris(α-diimine) Ruthenium Radical Complexes. J. Am. Chem. Soc. 1990, 112, 173−178. (26) (a) Sheldrick, G. M. A short history of SHELX. Acta Crystallogr., Sect. A: Found. Crystallogr. 2008, A64, 112−122. (b) Program for Crystal Structure Solution and Refinement; University of Goettingen: Goettingen, Germany, 1997. (c) Sheldrick, G. M. Crystal Structure Refinement with SHELXL. Acta Crystallogr., Sect. C: Struct. Chem. 2015, C71, 3−8. (27) Lee, C.; Yang, W.; Parr, R. G. Development of the ColicSalvetti Correlation-Energy Formula into a Functional of the Electron Density. Phys. Rev. B: Condens. Matter Mater. Phys. 1988, 37, 785− 789. (28) (a) Andrae, D.; Haeussermann, U.; Dolg, M.; Stoll, H.; Preuss, H. Energy-adjusted ab intio Pseudopotentials for the Second and Third Row Trasition Elements. Theor. Chim. Acta 1990, 77, 123−141. (b) Fuentealba, P.; Preuss, H.; Stoll, H.; von Szentpaly, L. A Proper Account of Core-Polerizantion with Pseudopotentials: Single ValanceElectron Alkali Compounds. Chem. Phys. Lett. 1982, 89, 418−422. (29) (a) Noodleman, L. Valence Bond Description of Antiferromagnetic Coupling in Transition Metal Dimers. J. Chem. Phys. 1981, H


Mononuclear and Dinuclear Ruthenium Complexes of cis- and trans

Recommend Documents