Noninnocence of Indigo: Dehydroindigo Anions as Bridging Electron

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Noninnocence of Indigo: Dehydroindigo Anions as Bridging Electron-Donor Ligands in Diruthenium Complexes Prasenjit Mondal,† Madhumita Chatterjee,† Alexa Paretzki,‡ Katharina Beyer,‡ 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

‡

S Supporting Information *

ABSTRACT: Complexes of singly or doubly deprotonated indigo (H2Ind) with one or two [Ru(pap)2]2+ fragments (pap = 2-phenylazopyridine) have been characterized experimentally [molecular structure, voltammetry, electron paramagnetic resonance (EPR), and UV−vis−near-IR spectroelectrochemistry] and by time-dependent density functional theory calculations. The compound [Ru(pap)2(HInd−)]ClO4 ([1]ClO4) was found to contain an intramolecular NH---O hydrogen bond, whereas [{Ru(pap)2}2(μ-Ind2−)](ClO4)2 ([2](ClO4)2), isolated as the meso diastereoisomer with near-IR absorptions at 1162 and 991 nm, contains two metals bridged at 6.354 Å distance by the bischelating indigo dianion. The spectroelectrochemical study of multiple reversible reduction and oxidation processes of 2n (n = 4+, 3+, 2+, 1+, 0, 1−, 2−, 3−, 4−) reveals the stepwise addition of electrons to the terminal π-accepting pap ligands, whereas the oxidations occur predominantly at the anionic indigo ligand, producing an EPR-identified indigo radical intermediate and revealing the suitability of deprotonated indigo as a σ- and π-donating bischelating bridge.

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variant,7 there have been other such examples reported involving β-diketonates8 and β-diketiminates.9 Electroactive bridging ligands are of interest, e.g., for fundamental studies of metal− metal interaction10 and for the construction of functional coordination polymers, including metal−organic frameworks.11 In this Article, we describe combinations [Ru(pap)2(HInd−)]ClO4 ([1]ClO4) and [{Ru(pap)2}2(μ-Ind2−)](ClO4)2 ([2](ClO4)2) between singly or doubly deprotonated indigo and the complex fragments [Ru(pap)2]2+ (pap = 2-phenylazopyridine). While the indigo anions will be investigated for their potential to donate π electrons, form radical intermediates, and mediate interactions between transition metals in dinuclear complexes, the pap terminal ligands are known as strong π acceptors, which tend to accept electrons easily12 and stabilize the II+ oxidation state of ruthenium.12 Both the reduction and oxidation behavior of the complex systems 1n (n = 2+, 1+, 0, 1−, 2−, 3−) and 2n (n = 4+, 3+, 2+, 1+, 0, 1−, 2−, 3−, 4−) will be described in eq 1. Indigo can be stepwise reduced under protonation to the leuco form; however, oxidation under deprotonation to dehydroindigo is also possible (eq 2).13 The latter form has been studied spectroscopically and computationally in connection with its reported occurrence in Maya Blue pigments.13a As an intermediate in the stepwise

INTRODUCTION Indigo, as a natural or industrial product1,2 with a unique colorproducing electronic structure, has received relatively little attention in terms of its metal binding capability, despite the presence of strategically placed heteroatoms for chelation under single or double six-membered ring formation by β-ketiminato functions after deprotonation. Early presumption3a−c of metalion-chelate formation was followed by crystallographic evidence for mono- and dinuclear palladium(II) complexes of the indigo monoanion and bridging octahydroindigo dianion in 1989 by Beck and co-workers.3d Furthermore, the electronic feature of the coordinated indigo has been addressed just recently in one hexarhenium carbonyl complex bridged by the doubly deprotonated trans-configured indigo.3e,f However, the structural characterization of a complex with μ-Ind2− and the electronic functional potential of indigo as a noninnocent ligand4 capable of bridging electroactive complex fragments remained underexplored. The recent interest in the coordination chemistry of nindigo = indigobis(N-arylimine) ligands as potentially noninnocent5,6 bridges has prompted us to reinvestigate the coordination potential of indigo itself. In contrast to the nindigo ligands with four basic N-donor atoms, the presence of two O-atom functions in indigo requires deprotonation in order to ensure sufficient basicity for metal binding. Both nindigo and indigo are capable of bischelation forming edge-sharing six-membered chelate rings. Although six-membered chelate ring formation is less common among noninnocent ligands than the five-membered chelate ring © XXXX American Chemical Society

Received: January 7, 2016

A

DOI: 10.1021/acs.inorgchem.6b00038 Inorg. Chem. XXXX, XXX, XXX−XXX

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exist in rac and meso diastereomeric forms, the selective formation of one particular form has been evidenced by thinlayer chromatography. The identities of [1]ClO4 and [2](ClO4)2 have been established by standard analytical methods (molar conductivity and microanalytical data) and mass spectrometry (Figures S1 and S2), 1H NMR (Figure S3), and IR (Figures S4 and S5) spectral data (see the Experimental Section) in addition to their single-crystal X-ray structures. Diamagnetic [1]ClO4 and [2](ClO4)2 exhibit partially overlapping 1H NMR resonances over the chemical shift range 6−9 ppm in (CD3)2SO (Figure S3). The free NH proton of HInd− in [1]ClO4 appears as a sharp singlet at 10.6 ppm. The dinuclear [2](ClO4)2 displays 22 aromatic proton resonances corresponding to the half-molecule expected for the meso diastereomeric form. [1]ClO4 and [2](ClO4)2 exhibit distinct IR spectral features with respect to the CO groups associated with deprotonated indigo (Figures S4 and S5). The free and coordinated CO vibrations of HInd− in [1]ClO4 appear at 1692 and 1625 cm−1, respectively, while the vibration for the coordinated CO of Ind2− in [2](ClO4)2 occurs at 1597 cm−1. Crystal Structure. The structures of [1]ClO4 and [2](ClO4)2 are shown in Figures 1 and 2, respectively. Selected crystallographic

oxidation of Ind2−, a radical-state Ind•− (eq 3) can be formulated.14

When the particular properties of the indigo/dehydroindigo chromophore,2,13 the metal-to-ligand charge-transfer (MLCT) capacity of divalent ruthenium,15 and the potential for metal− metal interaction in dinuclear complexes as mediated by conjugated bridges were combined,10 the experimental (spectroelectrochemical) and computational investigations were assumed to provide clues as to the possible extended uses of indigo in coordination chemistry.

Figure 1. Perspective view of the cationic part of [1]ClO4. H atoms are omitted for clarity (except the N2−H2 hydrogen).

and bond parameters are listed in Tables 1 and 2 and S1−S4, respectively. The crystal structures of [1]ClO4 and [2](ClO4)2 confirm the trans configuration of the deprotonated indigo (HInd− and Ind2−) with respect to its CO groups as well as retention of the tc form (tc = trans and cis with respect to the pyridine and azo N-atom donors of pap) of the precursor {Ru(pap)2}. The HInd− and Ind2− ligands in [1]ClO4 and [2](ClO4)2 are slightly twisted with torsional angles of 8.3° and 10.7°, respectively, with regard to the ring-connecting C1−C9 bond. The C1−C9 distance of 1.379(5) or 1.393(6) Å in [1]ClO4 or [2](ClO4)2, respectively, is slightly longer than that in H2Ind [1.359(3) Å17] because of the effect of chelation. The average cis ([1]ClO4, 81.51°; [2](ClO4)2, 80.77°) and trans ([1]ClO4, 170.79°; [2](ClO4)2, 170.06°) angles around the metal ions point to slightly distorted octahedral situations.

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RESULTS AND DISCUSSION Synthesis and General Characterization. The mononuclear {[RuII(pap)2(HInd−)]ClO4 ([1]ClO4)} and dinuclear {[{RuII(pap)2}2(μ-Ind2−)](ClO4)2 ([2](ClO4)2)} complexes incorporating partially and fully deprotonated indigo (H2Ind), respectively, have been obtained by the reaction of the precursor ctc-[RuII(pap)2(EtOH)2]2+ (ctc = cis−trans−cis with respect to ethanol (EtOH), pyridine, and azo N atoms of unsymmetrical pap)16 with H2Ind in refluxing EtOH and in the presence of NaOH base under a dinitrogen atmosphere, followed by chromatographic separation using a neutral alumina column. Although the dinuclear complex 22+ can, in principle, B

DOI: 10.1021/acs.inorgchem.6b00038 Inorg. Chem. XXXX, XXX, XXX−XXX

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Table 2. Selected Experimental and DFT-Calculated Bond Lengths (Å) for [1]ClO4·C7H8 and [2](ClO4)2·CH2Cl2 1+ Ru1−O1 Ru1−N1 Ru1−N3 Ru1−N5 Ru1−N6 Ru1−N8 Ru2−O2 Ru2−N2 Ru2−N9 Ru2−N11 Ru2−N12 Ru2−N14 O1−C10 O2−C2 N1−C1 N1−C8 N2−C9 N2−C16 N4−N5 N7−N8 N10−N11 N13−N14 C1−C2 C1−C9 C2−C3 C3−C8 C9−C10 C10−C11 C11−C16 N2···O2

Figure 2. Perspective view of the cationic part of [2](ClO4)2. H atoms are omitted for clarity.

Table 1. Selected Crystallographic Data for [1]ClO4·C7H8 and [2](ClO4)2·CH2Cl2 empirical formula fw cryst syst space group a (Å) b (Å) c (Å) α (deg) β (deg) γ (deg) V (Å3) Z μ (mm−1) T (K) Dcalcd (g cm−3) F(000) θ range (deg) data/restraints/param R1, wR2 [I > 2σ(I)] R1, wR2 (all data) GOF on F2 largest diff peak/hole (e Å−3)

[1]ClO4·C7H8

[2](ClO4)2·CH2Cl2

C45H35ClN8O6Ru 920.33 triclinic P1̅ 13.346(3) 13.673(4) 13.733(3) 65.766(15) 62.937(14) 77.553(18) 2033.7(9) 2 0.512 100(2) 1.503 940 3.07−25.00 7127/0/551 0.0482, 0.1061 0.0597, 0.1152 1.054 0.699/−0.717

C61H46Cl4N14O10Ru2 1479.06 monoclinic P21/c 14.805(3) 20.504(4) 20.065(5) 90 92.677(4) 90 6084(2) 4 0.744 100(2) 1.615 2984 3.06−25.00 10667/12/820 0.0608, 0.1502 0.0672, 0.1555 1.046 2.319/−1.676

22+

X-ray

DFT

X-ray

DFT

2.069(2) 2.088(3) 2.046(3) 2.036(3) 2.035(3) 1.988(3)

2.101 2.139 2.096 2.099 2.084 2.063

1.296(4) 1.214(4) 1.350(4) 1.433(4) 1.402(4) 1.368(4) 1.282(4) 1.299(4)

1.282 1.227 1.354 1.422 1.393 1.374 1.275 1.284

1.519(5) 1.379(5) 1.458(5) 1.398(5) 1.431(5) 1.431(5) 1.407(5) 2.854(4)

1.518 1.384 1.458 1.415 1.442 1.438 1.423 2.791

2.052(3) 2.091(4) 2.034(4) 1.989(4) 2.050(4) 2.033(4) 2.067(3) 2.061(4) 2.041(4) 2.063(4) 2.054(4) 1.962(4) 1.266(6) 1.272(6) 1.376(6) 1.401(6) 1.367(6) 1.405(6) 1.301(6) 1.280(6) 1.281(6) 1.302(6) 1.466(6) 1.393(6) 1.421(7) 1.412(7) 1.465(7) 1.422(7) 1.405(7)

2.087 2.140 2.085 2.066 2.099 2.113 2.087 2.140 2.099 2.114 2.085 2.066 1.268 1.268 1.382 1.399 1.382 1.399 1.284 1.275 1.275 1.284 1.478 1.396 1.427 1.423 1.478 1.427 1.423

distances {[1]ClO4, 2.012(3) Å (average); [2](ClO4)2, 2.011(4) Å (average)} relative to the RuII−N(pyridine) distances of pap {[1]ClO4, 2.040(3) Å (average); [2](ClO4)2, 2.047(4) Å (average)}. The stronger π-accepting properties of pap relative to HInd− or Ind2− in [1]ClO4 or [2](ClO4)2, respectively, are also indicated by the longer Ru−N (HInd− or Ind2−) bond distance {[1]ClO4, 2.088(3) Å; [2](ClO4)2, 2.076(4) Å} compared to the Ru−N(pyridine, pap) distances. The trans-oriented monodeprotonated HInd− develops a sixmembered chelate ring with the Ru ion through its N,O-atom donors (β-ketiminato) in [1]ClO4, leaving the free indoline NH proton and CO group at the back side. The bond length of 1.296(4) Å for coordinated C10−O1 is expectedly longer than the bond distance of 1.214(4) Å for uncoordinated C2−O2. The pendant NH proton of HInd− in [1]ClO4 forms an intramolecular N2−H2···O2 hydrogen bond with the free CO group at an N···O distance of 2.854 Å. Further, the free indoline N−H proton develops an intermolecular N2−H2···O3 hydrogen bond to the nearby ClO4− ion at an N···O distance of 3.056 Å (Tables 2 and S1 and Figure S6). The dinuclear complex ([2](ClO4)2) contains two approximately coplanar edge-sharing six-membered chelate rings, involving the β-ketiminato functions. The intramolecular Ru---Ru distance is 6.354 Å, which is longer than the g||, the reverse is valid after pap-centered reduction. (iv) Although EPR signals for higher oxidized or reduced states with S > 1/2 were not observed, the calculated spin densities in Table 4 and Figure 4 reveal consequential steps, especially continued stepwise reduction of the pap coligands in system 2n. UV−vis−NIR Spectroelectrochemistry and TimeDependent DFT (TD-DFT) Calculations. The absorption spectra of the isolated compounds [1]ClO4 and [2](ClO4)2 and of the electrochemically accessible oxidized and reduced

Table 4. DFT-Calculated Mulliken Spin-Density Values for 1n and 2n complex

Ru

pap

HInd/Ind

12+ (S = 1/2) 1 (S = 1/2) 23+ (S = 1/2) 2+ (S = 1/2) 2 (S = 1) 2− (S = 3/2) 22− (S = 2) 23− (S = 5/2) 24− (S = 2)

0.090 −0.177 0.120 −0.150 −0.354 −0.386 0.462 0.823 0.842

−0.008 1.170 −0.012 1.152 2.343 2.812 3.532 3.131 2.090

0.917 0.002 0.894 −0.010 0.004 0.568 0.008 1.054 1.075

from the room temperature spectra reveals metal isotope (99,101Ru) coupling (12+) and 14N hyperfine structure (23+). The detailed spin-density information for 23+ (Figure 4) confirms that the unpaired electron is largely concentrated on the N atoms of the dehydroindigo anion-radical ligand (Figure S11). E

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Figure 5. EPR spectra of [1]ClO4 after in situ oxidation (top) and reduction (bottom) in CH2Cl2/0.1 M Bu4NPF6.

Figure 6. EPR spectra of [2](ClO4)2 after in situ oxidation (top) and reduction (bottom) in CH2Cl2/0.1 M Bu4NPF6.

Table 5. EPR Data of Paramagnetic Intermediatesa 2+

1 giso (298 K) g1 (120 K) g2 g3 ⟨g⟩f Δgg

2.002b 2.020 2.006 1.976 2.000 0.044

1 no 2.011 1.995 1.979 1.995 0.032

2

3+

1.994c 2.013d 1.999d 1.977d 1.996 0.036

forms in acetonitrile/0.1 M Bu4NPF6 are displayed in Figures 7 and 8. The values for the observed absorption bands (Table S22) are compared with the TD-DFT calculation results in Tables 6 and 7 (Table S23 and Figure S12). Compared to indigo itself (λmax = 610 nm and ε = 22140 M−1 cm−1 in N,N-dimethylformamide),2b the isolated complex containing singly deprotonated 1+ exhibits weaker intraindigo absorption features in the long-wavelength visible region, at 780 and 532 nm (ε = 5070 and 5600 M−1 cm−1). Oxidation, which is indigo-based according to EPR, causes shifts of these features to 1042 and 814 nm and further intensity reduction. The papcentered reduction, on the other hand, produces bands at 819 and 632 nm, which involve some MLCT contributions.

+

2

no 2.010e 1.996e 1.995e 2.000 0.015

a

From in situ electrolysis in CH2Cl2/0.1 M Bu4NPF6. bA(99,101Ru) = 22 G; 99Ru, 12.7% natural abundance, I = 5/2; 101Ru, 17.0%, I = 5/2. c Insufficiently resolved hyperfine structure. d5 K. e125 K. fAverage g. g g1−g3. F

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Figure 7. UV−vis−NIR spectroelectrochemistry of 1n (n = 2+, 1+, 0) in CH3CN/0.1 M Bu4NPF6.

Figure 8. UV−vis−NIR spectroelectrochemistry of 2n (n = 4+, 3+, 2+, 1+, 0, 1−, 2−) in CH3CN/0.1 M Bu4NPF6.

energy (in the visible region) are attributed to MLCT processes. Upon oxidation to the indigo radical intermediate 23+, three NIR bands emerge, of which only one is reproduced by TD-DFT calculations and assigned to intraligand/MLCT transitions (Table 7). It is possible that aggregation of the radical forms 23+ causes some of the additional NIR absorption features. After the second, indigo-based oxidation, these three weaker NIR bands diminish and a strong absorption at 900 nm

Further electron addition is no longer reversible, as is evident from the lack of isosbestic points, presumably involving protonation of highly reduced basic forms. The dinuclear 22+ with a doubly deprotonated indigo bridge exhibits long-wavelength (NIR) bands at 1162 and 991 nm (ε = 7150 and 7010 M−1 cm−1), which are attributed to ligandto-ligand charge transfer (LLCT) from the strongly donating Ind2− to the pap acceptors. More intense transitions at higher G

DOI: 10.1021/acs.inorgchem.6b00038 Inorg. Chem. XXXX, XXX, XXX−XXX

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Inorganic Chemistry Table 6. TD-DFT (B3LYP/CPCM/CH3CN)-Calculated Electronic Transitions for 1n λ/nm for expt (DFT) 780 532 532 355 299 257

(712) (543) (466) (349) (280) (238)

ε/M−1 cm−1 ( f) 5070 (0.15) 5600 (0.04) 5600 (0.09) 17150 (0.26) 18560 (0.22) 15180 (0.11)

1042 (1125) 814 (785)

1270 (0.02) 3380 (0.09)

707 (692)

3900 (0.10)

500 (514) 366 (388) 307 (286)

7650 (0.03) 14530 (0.21) 17960 (0.24)

819 (775)

4070 (0.11)

632 518 352 297 261

4260 (0.04) 4900 (0.04) 16180 (0.27) 14950 (0.08) 14530 (0.09)

(577) (473) (349) (308) (286)

transition

character

1+ (S = 0) HOMO → LUMO+2 (0.68) HOMO−1 → LUMO+2 (0.63) HOMO−4 → LUMO (0.37) HOMO−5 → LUMO+2 (0.49) HOMO−1 → LUMO+12 (0.58) HOMO−8 → LUMO+5 (0.36) 12+ (S = 1/2) HOMO(β) → LUMO(β) (0.93) HOMO(α) → LUMO(α) (0.60) HOMO−1(β) → LUMO(β) (0.35) HOMO−3(β) → LUMO(β) (0.47) HOMO−4(β) → LUMO(β) (0.42) HOMO−9(β) → LUMO(β) (0.55) HOMO−5(α) → LUMO+2(α) (0.31) HOMO(β) → LUMO+5(β) (0.47) 1 (S = 1/2) HOMO(β) → LUMO(β) (0.55) HOMO−1(α) → LUMO+1(α) (0.37) HOMO−1(β) → LUMO(β) (0.62) HOMO−1(β) → LUMO(β) (0.72) HOMO−10(β) → LUMO(β) (0.59) HOMO−1(β) → LUMO+3(β) (0.51) HOMO−3(α) → LUMO+2(α) (0.46)

HInd(π) → HInd(π*) HInd(π) → HInd(π*) Ru(dπ)/pap(π)/HInd(π) → pap(π*) HInd(π) → HInd(π*) HInd(π) → HInd(π*) pap(π) → HInd(π*) HInd(π) → HInd(π*) HInd(π) → HInd(π*) Ru(dπ)/pap(π)/HInd(π) → HInd(π*) pap(π)/Ru(dπ) → HInd(π*) pap(π)/Ru(dπ) → HInd(π*) HInd(π) → HInd(π*) pap(π) → pap(π*) pap(π) → HInd(π*) HInd(π)/Ru(dπ) → HInd(π*) HInd(π)/Ru(dπ) → pap(π*)/Ru(dπ) Ru(dπ)/pap(π)/HInd(π) → HInd(π*) Ru(dπ)/HInd(π)/pap(π) → HInd(π*) HInd(π) → HInd(π*) Ru(dπ)/pap(π)/HInd(π) → pap(π*)/HInd(π*) HInd(π)/Ru(dπ)/pap(π) → pap(π*)/HInd(π*)

(ε = 19970 M−1 cm−1) emerges. This conspicuous transition involves transitions from various components of the complex to the dehydroindigo ligand bridge μ-Ind (eq 2), a strong π acceptor. Metal oxidation is not observed or calculated, ruling out the occurrence of RuII → RuIII intervalence charge transfer (IVCT) in a mixed-valent situation. Reduction of 22+ to 2+ and beyond involves the terminal pap ligands (Table 7). Weak pap-based NIR absorptions12 are thus observed and reproduced by calculations; only the fourth electron addition to yield symmetrical 22− is distinguished by a stronger such band at 1055 nm.

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intervalence transitions, while deprotonation of indigo suppresses the typical absorptions of the indigo chromophore.2 However, new long-wavelength bands attributed to (donor) ligand-to-(acceptor) ligand transitions do occur. Thus, with different terminal ligation, it may be further possible to obtain stepwise reduction at the bridge in the direction of the deprotonated leuco forms (μ-Ind•3− and μ-Ind4−), leading to both coordination and electron-transfer dimensions to the properties of that historically and electronically fascinating molecule.1,2

CONCLUSION According to the structural, electrochemical, and spectroscopic studies presented here, both isolated compounds [1]ClO4 and [2](ClO4)2 contain singly and doubly deprotonated forms of indigo, respectively. The dinuclear complex represents a crystallographically characterized coordination compound containing resonance-stabilized μ-Ind2−. DFT calculations confirm that the oxidation state assignment typically includes a short central CC bond based on structure A in eq 4; both oxidation in the direction of dehydroindigo and reduction to the leuco form would result in a lengthening of the central CC bond, as displayed in eq 2. While spectroelectrochemistry of the mononuclear complex 1+ is affected by the presence of intramolecular hydrogenbonded acidic NH, the dinuclear system 2n+ exhibits a noninnocent behavior of the deprotonated indigo bridge, μ-Ind2− → μ-Ind•− → μ-Ind0 (Scheme 1) with significant spin concentration at the N centers of μ-Ind•− (Figure S11). The strongly π-accepting pap terminal ligands do not only stabilize the RuII state, thus preventing mixed valency and directing the oxidation to the Ind2− bridge; they are also preferentially reduced in a stepwise fashion (Scheme 1). The RuII-stabilizing effect of the pap ligand precludes metal-based

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EXPERIMENTAL SECTION

Materials. The precursor complex ctc-Ru(pap)2Cl2 was prepared according to the literature procedure.26 Indigo (H2Ind) was purchased from Sigma-Aldrich. Other chemicals and solvents were of reagent grade and were used as received. HPLC-grade solvents were used for spectroscopic and electrochemical studies. Physical Measurements. The electrical conductivities of the solutions were checked by using an autoranging conductivity meter (Toshcon Industries, India). 1H NMR spectra were recorded on a Bruker Avance III 500 MHz spectrometer. The EPR measurements were made in a two-electrode capillary tube24 with an X-band (9.5 GHz) Bruker ESP300 spectrometer. Cyclic and differential-pulse voltammetric measurements of the complexes were done using a PAR model 273A electrochemistry system under a dinitrogen atmosphere. A glassy-carbon H

DOI: 10.1021/acs.inorgchem.6b00038 Inorg. Chem. XXXX, XXX, XXX−XXX

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Inorganic Chemistry Table 7. TD-DFT (B3LYP/CPCM/CH3CN)-Calculated Electronic Transitions for 2n λ/nm for expt (DFT)

ε/M−1 cm−1 ( f)

1162 (1237) 991 (939) 642 (585)

7150 (0.03) 7010 (0.09) 8340 (0.02)

540 (523)

23280 (0.20)

333 (376) 269 (306)

62470 (0.48) 46960 (0.41)

1626 1493 1228 (1256)

4280 3960 6190 (0.03)

904 (1051) 635 (599)

6240 (0.08) 14410 (0.10)

496 (507)

24530 (0.12)

359 (382) 314 (365)

52650 (0.38) 50560 (0.21)

1182 (1122) 900 (890)

3620 (0.02) 19970 (0.07)

598 (619) 478 (475) 367 (423)

18440 (0.15) 28490 (0.16) 55420 (0.89)

1480 (1491)

3370 (0.004)

1065 (998)

5470 (0.07)

573 (532) 440 (436)

25200 (0.06) 17660 (0.08)

317 (393)

59230 (0.09)

b (2271)

b (0.03)

1184 (1350)

5290 (0.03)

1184 (1041)

5290 (0.06)

585 (592)

19670 (0.09)

348 (360) 268 (339)

62000 (0.37) 53000 (0.06)

1482 (1645)

3260 (0.04)

918 (808)

5340 (0.04)

591 (543) 547 (533) 348 (375)

22720 (0.08) 19720 (0.06) 58900 (0.10)

348 (362) 323 (361)

58900 (0.22) 59490 (0.08)

transition 22+ (S = 0) HOMO → LUMO (0.69) HOMO → LUMO+4 (0.66) HOMO−2 → LUMO+2 (0.35) HOMO−3 → LUMO+3 (0.32) HOMO−1 → LUMO+3 (0.31) HOMO−2 → LUMO+4 (0.53) HOMO−2 → LUMO+2 (0.33) HOMO−12 → LUMO+2 (0.34) HOMO−1 → LUMO+9 (0.63) 23+ (S = 1/2) a a HOMO(α) → LUMO(α) (0.71) HOMO(β) → LUMO(β) (0.68) HOMO(β) → LUMO(β) (0.68) HOMO−6(β) → LUMO(β) (0.71) HOMO−8(β) → LUMO(β) (0.41) HOMO−5(α) → LUMO(α) (0.58) HOMO−1(β) → LUMO+3(β) (0.41) HOMO−7(α) → LUMO+1(α) (0.35) HOMO−15(β) → LUMO+3(β) (0.72) 24+ (S = 0) HOMO → LUMO (0.59) HOMO−2 → LUMO (0.51) HOMO−11 → LUMO (0.32) HOMO−14 → LUMO (0.67) HOMO−16 → LUMO (0.64) HOMO−5 → LUMO+3 (0.37) 2+ (S = 1/2) HOMO−1(α) → LUMO+1(α) (0.74) HOMO(β) → LUMO+1(β) (0.64) HOMO(β) → LUMO+2(β) (0.68) HOMO−1(α) → LUMO+2(α) (0.74) HOMO−3(β) → LUMO+2(β) (0.52) HOMO−8(α) → LUMO+2(α) (0.46) HOMO−7(β) → LUMO+1(β) (0.42) HOMO−12(α) → LUMO+1(α) (0.46) 2 (S = 1) HOMO(α) → LUMO(α) (0.71) HOMO−1(α) → LUMO+1(α) (0.56) HOMO−2(α) → LUMO+2(α) (0.69) HOMO−1(α) → LUMO+1(α) (0.30) HOMO(β) → LUMO(β) (0.66) HOMO(β) → LUMO+2(β) (0.35) HOMO−2(β) → LUMO(β) (0.73) HOMO−4(α) → LUMO(α) (0.50) HOMO−11(α) → LUMO+2(α) (0.68) HOMO−21(α) → LUMO(α) (0.33) 2− (S = 3/2) HOMO−3(α) → LUMO+1(α) (0.58) HOMO(β) → LUMO+4(β) (0.27) HOMO−4(α) → LUMO(α) (0.58) HOMO−3(α) → LUMO+1(α) (0.29) HOMO(α) → LUMO+2(α) (0.71) HOMO−2(β) → LUMO+2(β) (0.64) HOMO−9(β) → LUMO+2(β) (0.42) HOMO−8(β) → LUMO+3(β) (0.32) HOMO(α) → LUMO+15(α) (0.33) HOMO−17(α) → LUMO+1(α) (0.35)

I

character Ind(π) → pap(π*) Ind(π) → pap(π*)/Ru(dπ)/Ind(π*) Ru(dπ)/pap(π*) → Ind(π*)/pap(π*) Ru(dπ)/pap(π*) → pap(π*)/Ru(dπ) Ind(π)/Ru(dπ) → pap(π*)/Ru(dπ) Ru(dπ)/pap(π*) → pap(π*)/Ru(dπ)/Ind(π*) Ru(dπ)/pap(π*) → Ind(π*)/pap(π*) pap(π) → Ind(π*)/pap(π*) Ind(π)/Ru(dπ) → Ind(π*)

Ind(π)/Ru(dπ) → Ind(π*) Ind(π)/Ru(dπ) → Ind(π*) Ind(π)/Ru(dπ) → Ind(π*) pap(π) → Ind(π*) pap(π)/Ru(dπ) → Ind(π*) pap(π) → Ind(π*) Ru(dπ)/pap(π) → pap(π*) pap(π) → pap(π*) Ind(π) → pap(π*) pap(π) → Ind(π*)/Ru(dπ) pap(π) → Ind(π*)/Ru(dπ) Ru(dπ)/pap(π) → Ind(π*)/Ru(dπ) Ind(π)/Ru(dπ)/pap(π) → Ind(π*)/Ru(dπ) Ind(π)/pap(π) → Ind(π*)/Ru(dπ) pap(π) → pap(π*) Ind(π) → Ind(π*)/pap(π*)/Ru(dπ) Ind(π)/Ru(dπ) → pap(π*) Ind(π)/Ru(dπ) → pap(π*) Ind(π) → pap(π*)/Ru(dπ) Ru(dπ)/pap(π) → pap(π*) Ru(dπ)/pap(π)/Ind(π) → pap(π*)/Ru(dπ) Ru(dπ)/pap(π)/Ind(π) → pap(π*) pap(π) → Ind(π*)/pap(π*)/Ru(dπ) pap(π) → Ind(π*)/pap(π*) pap(π) → pap(π*)/Ru(dπ) Ind(π)/Ru(dπ) → Ind(π*)/pap(π*)/Ru(dπ) pap(π) → pap(π*)/Ru(dπ) Ind(π)/Ru(dπ) → Ind(π*) Ind(π)/Ru(dπ) → pap(π*) Ru(dπ)/pap(π) → Ind(π*) Ru(dπ)/pap(π) → Ind(π*)/pap(π*) pap(π) → Ind(π*)/pap(π*)/Ru(dπ) Ind(π)/pap(π) → Ind(π*)/pap(π*) Ind(π)/pap(π) → Ind(π*)/pap(π*)/Ru(dπ) Ind(π)/Ru(dπ) → pap(π*)/Ru(dπ) Ind(π)/Ru(dπ) → pap(π*)/Ru(dπ) Ind(π)/pap(π) → Ind(π*)/pap(π*)/Ru(dπ) pap(π)/Ind(π)/Ru(dπ) → pap(π*) Ind(π)/Ru(dπ) → Ind(π*)/pap(π*) pap(π) → Ind(π*)/pap(π*) pap(π) → pap(π*) pap(π)/Ind(π)/Ru(dπ) → pap(π*)/Ru(dπ) Ind(π) → Ind(π*)/pap(π*)/Ru(dπ)

DOI: 10.1021/acs.inorgchem.6b00038 Inorg. Chem. XXXX, XXX, XXX−XXX

Article

Inorganic Chemistry Table 7. continued λ/nm for expt (DFT)

a

ε/M−1 cm−1 ( f)

1055 (1073)

13670 (0.06)

626 (695)

13520 (0.18)

520 (546)

16440 (0.08)

354 (369) 256 (337)

80010 (0.30) 61450 (0.05)

transition

character

22− (S = 2) HOMO−4(α) → LUMO(α) (0.75) HOMO(β) → LUMO(β) (0.62) HOMO−4(β) → LUMO(β) (0.73) HOMO−6(α) → LUMO(α) (0.47) HOMO(α) → LUMO+4(α) (0.53) HOMO(α) → LUMO+4(α) (0.39) HOMO−3(α) → LUM+14(α) (0.28) HOMO−3(α) → LUMO+9(α) (0.28)

Ind(π)/pap(π)/Ru(dπ) → Ind(π*)/pap(π*)/Ru(dπ) Ind(π)/Ru(dπ) → Ind(π*) Ru(dπ)/pap(π) → Ind(π*) Ru(dπ)/pap(π) → Ind(π*)/pap(π*)/Ru(dπ) pap(π)/Ru(dπ) → pap(π*) Ru(dπ)/pap(π) → pap(π*) pap(π) → Ind(π*) pap(π) → pap(π*)

Tentatively ascribed to absorption from aggregates. bNot observed.

Scheme 1. Electronic Structural Forms of 2n

The crude product was then purified by using a neutral alumina column. The mononuclear complex [1]ClO4 was initially eluted by a solvent mixture of dichloromethane/acetonitrile (50:1), followed by the dinuclear complex [2](ClO4)2, eluted by a dichloromethane/acetonitrile (1:1) solvent mixture. Evaporation of the solvent under reduced pressure yielded pure [1]ClO4 and [2](ClO4)2. [1]ClO4. Yield: 20 mg (25%). ESI-MS(+) (in CH3CN). Calcd for {[1]}+: m/z 729.13. Found: m/z 729.15. 1H NMR [500 MHz, (CD3)2SO, 298 K, TMS; J/Hz]: δ 10.60 (s, 1H, NH), 8.95 (d, 5.49, 1H), 8.68 (d, 7.93, 1H), 8.64 (d, 8.24, 1H), 8.45 (d, 6.41, 1H), 8.25 (t, 7.63, 7.93, 1H), 8.21 (t, 7.93, 7.63, 1H), 7.83 (t, 7.32, 7.02, 1H), 7.72 (t, 7.02, 7.32, 1H), 7.47 (m, 6H), 7.32 (t, 7.93, 7.63, 4H), 7.22 (d, 8.24, 2H), 7.15 (t, 8.24, 7.32, 1H), 6.97 (d, 7.32, 2H), 6.90 (t, 7.32, 7.32, 1H), 6.83 (t, 7.93, 7.93, 1H), 5.94 (d, 7.93, 1H). IR [KBr disk, ν(CO) and ν(ClO4), cm−1]: 1692, 1625 and 1090, 620. Elem anal. Calcd for C38H27ClN8O6Ru: C, 55.11; H, 3.29; N, 13.53. Found: C, 55.16; H, 2.99; N, 13.27. Molar conductivity (CH3CN): ΛM = 94 Ω−1 cm2 M−1. [2](ClO4)2. Yield: 76 mg (56%). ESI-MS(+) (in CH3CN). Calcd for {[2](ClO4)2ClO4}+: m/z 1295.13. Found: m/z 1295.20. 1H NMR [500 MHz, (CD3)2SO, 298 K, TMS; J/Hz]: δ 8.73 (d, 7.27, 1H), 8.70 (d, 7.63, 1H), 8.58 (t, 6.60, 5.50, 2H), 8.31 (t, 8.48, 7.27, 2H), 7.97 (t, 6.05, 7.27, 1H), 7.83 (t, 6.06, 7.27, 1H), 7.51 (t, 7.27, 7.27, 2H), 7.34 (t, 7.27, 8.48, 4H), 7.17 (d, 8.48, 3H), 6.95 (d, 8.48, 3H), 6.66 (t, 6.05, 7.27, 1H), 6.02 (d, 7.27, 1H). IR [KBr disk, ν(CO) and ν(ClO4), cm−1]: 1597 and 1078, 622. Elem anal. Calcd for C60H44Cl2N14O10Ru2: C, 51.69; H, 3.18; N, 14.07. Found: C, 51.62; H, 2.84; N, 13.76. Molar conductivity (CH3CN): ΛM = 185 Ω−1 cm2 M−1. Caution! Perchlorate salts are explosive and should be handled with care. Crystal Structure Determination. Single crystals of [1]ClO4 and [2](ClO4)2 were grown by slow evaporation of a 1:1 dichloromethane/n-hexane solution of [1]ClO4 and of a 2:1 dichloromethane/methanol solution of [2](ClO4)2, respectively. The X-ray crystal data were collected on a Rigaku SATURN-724 CCD single-crystal X-ray diffractometer. 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 structures were solved by direct methods using SHELXS-97 and refined by full matrix least squares with SHELXL-97, refining on F2.28 All non-H atoms were refined anisotropically. The H atoms were placed in geometrically constrained positions and refined with isotropic temperature factors, generally 1.2Ueq of their parent atoms. SQUEEZE was applied for the disordered solvent molecule in [2](ClO4)2 by the PLATON29 program. CCDC 1438042 ([1]ClO4) and 1438044 ([2](ClO4)2) contain the supplementary crystallographic data for this paper. These data can be obtained free of charge from The Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_request/cif. Computational Details. Full geometry optimizations were carried out by using the DFT method at the (R)B3LYP level for 1+, 22+, and 24+ and the (U)B3LYP level for 12+, 1, 1−, 12−, 13−, 23+, 2+, 2, 2−, 22−, 23−, and 24−.30 Except Ru, all other elements were assigned the 6-31G* basis set. The LANL2DZ basis set with the effective core potential was employed for the Ru atom.31 All calculations were performed with the Gaussian09 program package.32 Vertical electronic excitations based on

working electrode, a platinum wire auxiliary electrode, and a saturated calomel reference electrode (SCE) were used in a standard threeelectrode configuration with tetraethylammonium perchlorate as the supporting electrolyte and a scan rate of 100 mV s−1. UV−vis−NIR spectroelectrochemical experiments were performed in CH3CN/0.1 M Bu4NPF6 at 298 K using an optically transparent thin-layer electrode cell27 mounted in the sample compartment of a J&M TIDAS spectrophotometer. All spectroelectrochemical experiments were performed under a dinitrogen atmosphere. Elemental analyses were recorded on a PerkinElmer 240C elemental analyzer. IR spectra of the complexes as KBr pellets were recorded on a Nicolet spectrophotometer (PerkinElmer model 73465). Electrospray ionization mass spectrometry (ESI-MS) spectra were recorded on a Bruker Maxis Impact instrument (282001.00081). Synthesis of [(pap) 2 Ru II (HInd − )]ClO 4 ([1]ClO 4 ) and [(pap)2RuII(μ-Ind2−)RuII(pap)2](ClO4)2 ([2](ClO4)2). The precursor ctc-Ru(pap)2Cl2 (100 mg, 0.19 mmol) and AgClO4 (79 mg, 0.38 mmol) were taken in 30 mL of EtOH and refluxed for 2 h under a dinitrogen atmosphere. The precipitated AgCl was filtered off, and the ligand H2Ind (26 mg, 0.10 mmol) and NaOH (8 mg, 0.20 mmol) were added to the filtrate. This mixture was heated to reflux for 5 h under a dinitrogen atmosphere. The reaction mixture was evaporated to dryness under reduced pressure. The crude product thus obtained was dissolved in a minimum volume of acetonitrile, and 10 mL of a saturated NaClO4 solution was added. The resulting dark precipitate was filtered off, washed twice with ice-cold distilled water, and dried under vacuum. J

DOI: 10.1021/acs.inorgchem.6b00038 Inorg. Chem. XXXX, XXX, XXX−XXX

Article

Inorganic Chemistry (R)B3LYP/(U)B3LYP-optimized geometries were computed for 1n (n = 2+, 1+, 0, 1−, 2−, 3−) and 2n (n = 4+, 3+, 2+, 1+, 0, 1−, 2−) using the TD-DFT formalism33 in acetonitrile using conductor-like polarizable continuum model (CPCM).34 Chemissian 1.735 was used to calculate the fractional contributions of various groups to each molecular orbital. All calculated structures were visualized with ChemCraf t.36

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2013, 135, 14670−14678. (f) Fortier, S.; González-del Moral, O.; Chen, C.-H.; Pink, M.; Le Roy, J. J.; Murugesu, M.; Mindiola, D. J.; Caulton, K. G. Chem. Commun. 2012, 48, 11082−11084. (6) (a) Mondal, P.; Ehret, E.; Bubrin, M.; Das, A.; Mobin, S. M.; Kaim, W.; Lahiri, G. K. Inorg. Chem. 2013, 52, 8467−8475. (b) Mondal, P.; Plebst, S.; Ray, R.; Mobin, S. M.; Kaim, W.; Lahiri, G. K. Inorg. Chem. 2014, 53, 9348−9356. (7) Ehret, F.; Bubrin, M.; Hübner, R.; Schweinfurth, D.; Hartenbach, I.; Záliš, S.; Kaim, W. Inorg. Chem. 2012, 51, 6237−6244. (8) (a) Das, A.; Scherer, T. M.; Mobin, S. M.; Kaim, W.; Lahiri, G. K. Inorg. Chem. 2012, 51, 4390−4397. (b) Das, A.; Scherer, T. M.; Mondal, P.; Mobin, S. M.; Kaim, W.; Lahiri, G. K. Chem. - Eur. J. 2012, 18, 14434−14443. (9) (a) Khusniyarov, M. M.; Bill, E.; Weyhermüller, T.; Bothe, E.; Wieghardt, K. Angew. Chem. 2011, 123, 1690−1693; Angew. Chem., Int. Ed. 2011, 50, 1652−1655. (b) Mandal, A.; Schwederski, B.; Fiedler, J.; Kaim, W.; Lahiri, G. K. Inorg. Chem. 2015, 54, 8126−8135. (10) (a) Kaim, W.; Lahiri, G. K. Angew. Chem. 2007, 119, 1808− 1828; Angew. Chem., Int. Ed. 2007, 46, 1778−1796. (b) Mandal, A.; Agarwala, H.; Ray, R.; Plebst, S.; Mobin, S. M.; Priego, J. L.; JiménezAparicio, R.; Kaim, W.; Lahiri, G. K. Inorg. Chem. 2014, 53, 6082− 6093. (c) Das, A.; Scherer, T. M.; Chowdhury, A. D.; Mobin, S. M.; Kaim, W.; Lahiri, G. K. Inorg. Chem. 2012, 51, 1675−1684. (d) McKinnon, S. D. J.; Patrick, B. O.; Lever, A. B. P.; Hicks, R. G. Inorg. Chem. 2013, 52, 8053−8066. (e) Masui, H.; Freda, A. L.; Zerner, M. C.; Lever, A. B. P. Inorg. Chem. 2000, 39, 141−152. (f) Das, A.; Scherer, T. M.; Mobin, S. M.; Kaim, W.; Lahiri, G. K. Chem. - Eur. J. 2012, 18, 11007−11018. (11) Faust, T. B.; D’Alessandro, D. M. RSC Adv. 2014, 4, 17498− 17512. (12) (a) Das, D.; Mondal, T. K.; Mobin, S. M.; Lahiri, G. K. Inorg. Chem. 2009, 48, 9800−9810. (b) Kar, S.; Pradhan, B.; Sinha, R. K.; Kundu, T.; Kodgire, P.; Rao, K. K.; Puranik, V. G.; Lahiri, G. K. Dalton Trans. 2004, 1752−1760. (c) Ghumaan, S.; Mukherjee, S.; Kar, S.; Roy, D.; Mobin, S. M.; Sunoj, R. B.; Lahiri, G. K. Eur. J. Inorg. Chem. 2006, 2006, 4426−4441. (d) Santra, B. K.; Thakur, G. A.; Ghosh, P.; Pramanik, A.; Lahiri, G. K. Inorg. Chem. 1996, 35, 3050−3052. (13) (a) Rondão, R.; Seixas de Melo, J. S.; Bonifácio, V. D. B.; Melo, M. J. J. Phys. Chem. A 2010, 114, 1699−1708. (b) Bond, A. M.; Marken, F.; Hill, E.; Compton, R. G.; Hügel, H. J. Chem. Soc., Perkin Trans. 2 1997, 1735−1742. (c) Russell, G. A.; Konoka, R. J. Org. Chem. 1967, 32, 234−236. (14) Bruin, F.; Heineken, F. W.; Bruin, M. J. Org. Chem. 1963, 28, 562−564. (15) (a) Hazari, A. S.; Das, A.; Ray, R.; Agarwala, H.; Maji, S.; Mobin, S. M.; Lahiri, G. K. Inorg. Chem. 2015, 54, 4998−5012. (b) Das, A.; Ghosh, P.; Plebst, S.; Schwederski, B.; Mobin, S. M.; Kaim, W.; Lahiri, G. K. Inorg. Chem. 2015, 54, 3376−3386. (c) Mondal, P.; Agarwala, H.; Jana, R. D.; Plebst, S.; Grupp, A.; Ehret, F.; Mobin, S. M.; Kaim, W.; Lahiri, G. K. Inorg. Chem. 2014, 53, 7389−7403. (d) Kalinina, D.; Dares, C.; Kaluarachchi, H.; Potvin, P. G.; Lever, A. B. P. Inorg. Chem. 2008, 47, 10110−10126. (e) Rusanova, J.; Rusanov, E.; Gorelsky, S. I.; Christendat, D.; Popescu, R.; Farah, A. A.; Beaulac, R.; Reber, C.; Lever, A. B. P. Inorg. Chem. 2006, 45, 6246−6262. (16) Ghosh, P.; Mondal, P.; Ray, R.; Das, A.; Bag, S.; Mobin, S. M.; Lahiri, G. K. Inorg. Chem. 2014, 53, 6094−6106. (17) Kettner, F.; Hüter, L.; Schäfer, J.; Röder, K.; Purgahn, U.; Krautscheid, H. Acta Crystallogr., Sect. E: Struct. Rep. Online 2011, 67, 2867−2867. (18) Majumdar, P.; Peng, S.-M.; Goswami, S. J. Chem. Soc., Dalton Trans. 1998, 1569−1574. (19) Roy, S.; Sarkar, B.; Imrich, H.-G.; Fiedler, J.; Záliš, S.; JiménezAparicio, R.; Urbanos, F. A.; Mobin, S. M.; Lahiri, G. K.; Kaim, W. Inorg. Chem. 2012, 51, 9273−9281. (20) (a) Sarkar, B.; Patra, S.; Fiedler, J.; Sunoj, R.; Janardanan, D.; Mobin, S. M.; Niemeyer, M.; Lahiri, G. K.; Kaim, W. Angew. Chem. 2005, 117, 5800−5803; Angew. Chem., Int. Ed. 2005, 44, 5655−5658. (b) Sarkar, B.; Patra, S.; Fiedler, J.; Sunoj, R. B.; Janardanan, D.; Lahiri, G. K.; Kaim, W. J. Am. Chem. Soc. 2008, 130, 3532−3542.

ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.inorgchem.6b00038. Mass spectra (Figures S1 and S2), 1H NMR (Figure S3), IR (Figures S4 and S5), hydrogen bonding (Figure S6), bond parameters (Tables S1−S4 and Figure S7), DFToptimized geometry of 1+ and 22+ (Figures S8 and S9), spin density values of 1n and 23+ (Figures S10 and S11), UV−vis−NIR spectra of 1 n (Figure S12), MO compositions for 1n and 2n (Tables S5−S19), DFToptimized energies of 1n and 2n (Table S20), spin density values for 1n (Table S21), absorption data for 1n and 2n (Table S22), and TD-DFT data for 1n (Table S23) PDF) X-ray crystallographic file in CIF format for [1]ClO4 (CIF) X-ray crystallographic file in CIF format for [2](ClO4)2 (CIF)

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AUTHOR INFORMATION

Corresponding Authors

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

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS Financial support received from the Department of Science and Technology, Council of Scientific and Industrial Research (fellowships to P.M. and M.C.), New Delhi, India, and DAAD, FCI, and DFG (Germany) is gratefully acknowledged.

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REFERENCES

(1) Balfour-Paul, J. Indigo; British Museum Press: London, 1998. (2) (a) Zollinger, H. Color Chemistry, 3rd ed.; VHCA: Zürich, Switzerland, 2003; pp 259−268. (b) Seixas de Melo, J.; Moura, A. P.; Melo, M. J. J. Phys. Chem. A 2004, 108, 6975−6981. (3) (a) Kunz, K. Ber. Dtsch. Chem. Ges. B 1922, 55, 3688−3691. (b) Kuhn, R.; Machemer, H. Ber. Dtsch. Chem. Ges. B 1928, 61, 118− 127. (c) Machemer, H. J. Prakt. Chem. 1930, 127, 109−168. (d) Beck, W.; Schmidt, C.; Wienold, R.; Steimann, M.; Wagner, B. Angew. Chem., Int. Ed. Engl. 1989, 28, 1529−1531. (e) Wu, J.-Y.; Chang, C.-H.; Thanasekaran, P.; Tsai, C.-C.; Tseng, C.-W.; Lee, G.-H.; Peng, S.-M.; Lu, K.-L. Dalton Trans. 2008, 6110−6112. (f) Bhattacharya, D.; Chang, C.-H.; Cheng, Y.-H.; Lai, L.-L.; Lu, H.-Y.; Lin, C.-Y.; Lu, K.-L. Chem. - Eur. J. 2012, 18, 5275−5283. (4) Kaim, W. Inorg. Chem. 2011, 50, 9752−9765. (5) (a) Oakley, S. R.; Nawn, G.; Waldie, K. M.; MacInnis, T. D.; Patrick, B. O.; Hicks, R. G. Chem. Commun. 2010, 46, 6753−6755. (b) Nawn, G.; Waldie, K. M.; Oakley, S. R.; Peters, B. D.; Mandel, D.; Patrick, B. O.; McDonald, R.; Hicks, R. G. Inorg. Chem. 2011, 50, 9826−9837. (c) Nawn, G.; McDonald, R.; Hicks, R. G. Inorg. Chem. 2013, 52, 10912−10919. (d) Nawn, G.; Majewski, M.; McDonald, R.; Hicks, R. G.; Oakley, S. R.; Patrick, B. O. Chem. Sci. 2013, 4, 612−621. (e) Fortier, S.; Le Roy, J. J.; Chen, C.-H.; Vieru, V.; Murugesu, M.; Chibotaru, L. F.; Mindiola, D. J.; Caulton, K. G. J. Am. Chem. Soc. K

DOI: 10.1021/acs.inorgchem.6b00038 Inorg. Chem. XXXX, XXX, XXX−XXX

Article

Inorganic Chemistry (21) (a) Bond, A. M.; Haga, M. Inorg. Chem. 1986, 25, 4507−4514. (b) Xiaoming, X.; Haga, M.; Matsumurainoue, T.; Ru, Y.; Addison, A. W.; Kano, K. J. Chem. Soc., Dalton Trans. 1993, 16, 2477−2484. (c) Haga, M.; Ano, T.; Kano, K.; Yamabe, S. Inorg. Chem. 1991, 30, 3843−3849. (22) Creutz, C. Prog. Inorg. Chem. 1983, 30, 1−73. (23) Weil, J. A.; Bolton, J. R. Electron Paramagnetic Resonance; Wiley: New York, 1994. (24) Kaim, W.; Ernst, S.; Kasack, V. J. Am. Chem. Soc. 1990, 112, 173−178. (25) Heilmann, M.; Baumann, F.; Kaim, W.; Fiedler, J. J. Chem. Soc., Faraday Trans. 1996, 92, 4227−4231. (26) Goswami, S.; Chakravarty, A. R.; Chakravorty, A. Inorg. Chem. 1981, 20, 2246−2250. (27) Krejcik, M.; Danek, M.; Hartl, F. J. Electroanal. Chem. Interfacial Electrochem. 1991, 317, 179−187. (28) (a) Sheldrick, G. M. Acta Crystallogr., Sect. A: Found. Crystallogr. 2008, 64, 112−122. (b) Program for Crystal Structure Solution and Refinement; University of Goettingen: Goettingen, Germany, 1997. (29) van der Sluis, P.; Spek, A. L. Acta Crystallogr., Sect. A: Found. Crystallogr. 1990, 46, 194−201. (30) Lee, C.; Yang, W.; Parr, R. G. Phys. Rev. B: Condens. Matter Mater. Phys. 1988, 37, 785−789. (31) (a) Andrae, D.; Haeussermann, U.; Dolg, M.; Stoll, H.; Preuss, H. Theor. Chim. Acta 1990, 77, 123−141. (b) Fuentealba, P.; Preuss, H.; Stoll, H.; Von Szentpaly, L. Chem. Phys. Lett. 1982, 89, 418−422. (32) 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. (33) (a) Bauernschmitt, R.; Ahlrichs, R. Chem. Phys. Lett. 1996, 256, 454−464. (b) Stratmann, R. E.; Scuseria, G. E.; Frisch, M. J. J. Chem. Phys. 1998, 109, 8218−8225. (c) Casida, M. E.; Jamorski, C.; Casida, K. C.; Salahub, D. R. J. Chem. Phys. 1998, 108, 4439−4450. (34) (a) Barone, V.; Cossi, M. J. Phys. Chem. A 1998, 102, 1995− 2001. (b) Cossi, M.; Barone, V. J. Chem. Phys. 2001, 115, 4708−4718. (c) Cossi, M.; Rega, N.; Scalmani, G.; Barone, V. J. Comput. Chem. 2003, 24, 669−681. (35) Leonid, S. Chemissian 1.7, 2005−2010. Available at http://www. chemissian.com. (36) Zhurko, D. A.; Zhurko, G. A. ChemCraft 1.5; Plimus: San Diego, CA. Available at http://www.chemcraftprog.com.

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DOI: 10.1021/acs.inorgchem.6b00038 Inorg. Chem. XXXX, XXX, XXX−XXX