Redox-Induced Interconversion and Ligand-Centered Hemilability in

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

Redox-Induced Interconversion and Ligand-Centered Hemilability in NiII Complexes of Redox-Noninnocent Azo-Aromatic Pincers Siuli Das,† Suman Sinha,† Upasona Jash,† Rina Sikari,† Anannya Saha,‡ Suman K. Barman,‡ Paula Brandaõ ,§ and Nanda D. Paul*,† †

Department of Chemistry, Indian Institute of Engineering Science and Technology, Shibpur, Botanic Garden, Howrah 711103, West Bengal, India ‡ Department of Chemical Sciences, Indian Institute of Science Education and Research Kolkata, Mohanpur 741246, India § Departamento de Química, CICECO-Instituto de Materiais de Aveiro,Universidade de Aveiro, 3810-193 Aveiro, Portugal S Supporting Information *

ABSTRACT: A series of nickel(II) complexes, namely, [NiII(La−c)2Cl2] (1a−c), [NiII(La,b)3](X)2 {([2a](X)2, [2b](X)2) (X = ClO4, I3)}, [NiII(Lc)2(OH2)2](ClO4)2 ([3](ClO4)2) and [NiII{(La,b)·−}2] (4a, 4b) featuring the redox-active tridentate azo-aromatic pincer ligand 2-(arylazo)-1,10-phenanthroline (L) were synthesized. The coordinated azo-aromatic ligand showed reversible hemilability depending on its formal oxidation state. On the one hand, in its native state, the unreduced ligand L shows bidentate coordination; the 1,10-phenanthroline moiety binds the central Ni(II) atom in a bidentate fashion, while the azo-chromophore remains pendent. On the other hand, the one-electron reduced ligand [L]·− binds the nickel(II) atom in a tridentate fashion. In complexes 1, [2]2+, and [3]2+, the 1,10-phenanthroline moiety of the neutral unreduced azo-aromatic ligand L binds the central nickel(II) atom in a bidentate fashion, while the azo-chromophore remains pendent. The complex 4 is a singlet diradical species, where two monoanionic azo-anion radical ligands [L]·− are bound to the central nickel(II) center in a tridentate fashion. Redox-induced reversible hemilability of the coordinated azo-aromatic ligand L was revealed from the interconversion of the synthesized complexes upon reduction and oxidation. Complex 1 upon reduction transformed to complex 4 with the loss of two chlorido ligands, whereas the complex 4 upon oxidation in the presence of excess chloride (LiCl) source transformed back to 1. Similarly, the complexes [2]2+ and 4 were also found to be interconvertible upon reduction and oxidation, respectively. Thorough experimental and density functional theory studies were performed to unveil the electronic structures of the synthesized complexes, and attempt was made to understand the redox-induced hemilability of the coordinated azo-aromatic ligand L.

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INTRODUCTION

In this regard, the chemistry of transition-metal complexes of redox-active ligands has gained immense attention over the years because of its multidimensional possibilities ranging from its applications in catalysis/small molecule activation to molecular electronics.5−7 Various redox noninnocent ligands were employed over the years to synthesize numerous transition-metal complexes to study their structure−bonding relationship and to explore their possible applications.8−11 In 2017, we reported the synthesis and characterization of some iron complexes of redox-active tridentate azo-aromatic ligands, 2-(arylazo)-1,10-phenanthroline (L).12 Among the several Fe(II)-complexes reported, some of them showed promising catalytic activity in dehydrogenation of alcohols, where both metal and ligand have been argued to participate in a cooperative manner. In continuation of our ongoing research to explore the chemistry of some chosen redox-active ligands,

The term hemilability refers to the ability of a polydentate ligand to reversibly coordinate to a metal center by one of the available donor/binding sites in a fluxional process.1 Hemilabile ligands have drawn considerable attention over the years particularly in the field of synthetic coordination chemistry and catalysis due to their unique capability to furnish vacant sites at the metal center during a chemical reaction, which are otherwise unavailable at the ground state. However, the control of hemilability beyond equilibrium is always challenging.2 Use of hybrid ligands containing significantly different chemical donor functions, such as hard and soft donor atoms or groups, is one of the possible ways of controlling such hemilability.1−3 The next way is to control the oxidation state of the metal ion, which may indeed prefer different coordination numbers and geometries.4 The coordination behavior can even be controlled by controlling the redox events of the coordinated ligands, provided the ligand is redoxnoninnocent.3,5,6 © XXXX American Chemical Society

Received: January 26, 2018

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DOI: 10.1021/acs.inorgchem.8b00231 Inorg. Chem. XXXX, XXX, XXX−XXX

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Inorganic Chemistry

reaction of La−c (0.314 mmol; 2.0 equiv) with hydrated NiCl2 (0.157 mmol; 1.0 equiv) afforded the new brown colored neutral complexes [Ni(La−c)2Cl2] (1a−c) in nearly 90% yield (Scheme 1). Similarly, when La,b (0.314 mmol; 3.0 equiv) was

herein we report the synthesis, isolation, and crystallographic characterization of some new octahedral nickel(II) complexes [Ni II (L a−c ) 2 Cl 2 ] (1a−c), [Ni II (L a,b ) 3 ](X) 2 {([2a](X) 2 , [2b](X)2) (X = ClO4, I3)}, [NiII(Lc)2(OH2)2](ClO4)2 ([3](ClO4)2), and [NiII{(La,b)·−}2] (4a, 4b), respectively, of redoxactive azo-aromatic ligands, 2-(arylazo)-1,10-phenanthroline (L). Depending upon the formal oxidation state, the coordinated ligand L shows reversible hemilability; a switching between a bidentate to a tridentate coordination was observed keeping the overall distorted octahedron geometry around the Ni(II) centers intact. On the one hand, in complexes 1, [2]2+, and [3]2+ the 1,10-phenanthroline moiety of the neutral unreduced azo-aromatic ligand L binds the central nickel(II) atom in a bidentate fashion, while the azo-chromophore remains pendent. On the other hand, the complex 4 is a singlet diradical species, where two of the coordinated azo-aromatic ligands are found to be reduced by one electron each offering tridentate coordination to the nickel(II) center. The coordinated azo-aromatic ligands showed reversible hemilability depending on its formal oxidation state as revealed by reversible interconversion of these complexes upon reduction and oxidation. Complex 1 upon reduction transformed to complex 4 with the loss of two chlorido ligands, whereas the complex 4 upon oxidation in the presence of excess chloride (LiCl) source transformed back to 1. Similarly, the complexes [2]2+ and 4 were also found to be interconvertible upon reduction and oxidation, respectively. Thorough experimental and density functional theoretical (DFT) calculations were performed to unveil the electronic structures of all the synthesized complexes, and attempt was made to understand the redox-induced hemilability of the coordinated azo-aromatic ligand L.

Scheme 1. Synthetic Scheme for Complexes 1−4

reacted with hydrated Ni(ClO4)2 (0.105 mmol; 1.0 equiv), the dicationic red colored complexes [Ni(La,b)3](ClO4)2 ([2a, 2b](ClO4)2 were isolated in nearly 85% yield. However, a dicationic red colored complex [Ni(Lc)2(H2O)2](ClO4)2 ([3](ClO4)2 was isolated from the reaction of Ni(ClO4)2·6H2O (0.157 mmol; 1.0 equiv) with Lc (0.314 mmol; 2.0 equiv) in nearly 85% yield. Reaction of La,b (0.314 mmol) with a lowvalent nickel(0) precursor, Ni(COD)2 (0.157 mmol), produced homoleptic neutral complexes [Ni(La,b)2] (4a, 4b) in nearly quantitative yield. Characterization of the isolated complexes using elemental analysis and positive-ion electrospray ionization (ESI) mass spectrometry fully matches with their formulations (see the Supporting Information). The complexes 1a−c, [2a,b](ClO4)2, and [3](ClO4)2 are paramagnetic with roomtemperature (RT) magnetic moment μeff values of 3.01, 3.05, 2.95 (for 1a−c); 3.12, 3.10 (for [2a,b](ClO4)2), and 3.10 μB (for [3](ClO4)2), indicating high-spin electronic configuration of the Ni(II) ions. Complexes 4a and 4b are found to be diamagnetic (S = 0 ground state). Sharp 1H NMR signals are observed in the range of 7.55−9.28 ppm for both complexes 4a and 4b. The spectral pattern reveals that the coordinated ligands are magnetically equivalent on the NMR time scale (see Supporting Information). On the one hand, IR spectroscopy of 1a, [2a](ClO4)2, and [3](ClO4)2 showed absorption bands (ν(N−N) = 1400 cm−1) in the region comparable with those observed for the uncoordinated ligands (1415 cm−1).12 On the other hand, the N−N stretching frequencies ν(N−N) of 4a and 4b were found to be considerably decreased (1325 cm−1), indicating the coordination of azo-N donor atom as well as the possibility of accumulation of negative charge on the azo-group as were reported with transition-metal complexes with azoanion radical ligands.11 X-ray Crystallography. The ligand Lc and the nickel complexes 1b, [2b](ClO4) 2, [3](ClO4)2, and 4b were characterized by single-crystal X-ray diffraction. ORTEP view of the molecular structures of Lc, 1b, [2b](ClO4)2, [3](ClO4)2, and 4b with partial atom numbering scheme is displayed in Figures 2−6, respectively. Crystallographic details are given in Table S1, and selected experimental bond lengths and angles are compared with the DFT-optimized structural parameters in Table S2. Unlike La,b, the dichloro-substituted free base ligand Lc is solid at room temperature. We succeeded to obtain single crystals of Lc via slow evaporation of its dichloromethane (DCM)−hexane (3:1) solution. Unlike the solid-state structure

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RESULT AND DISCUSSION Synthesis. Three tridentate N,N,N-donor azo-aromatic pincer ligands, La, Lb, and Lc, bearing different substituents on the phenyl ring, were used in this work (Figure 1). These

Figure 1. Azo-aromatic ligands used in this study.

ligands offer tridentate coordination with one nitrogen donor site from the azo chromophore and two nitrogen donor sites from 1,10-phenanthroline moiety. All these ligands were synthesized following a known literature method.12 The synthesis, characterization, and coordination behavior of La and Lb with FeCl2 and hydrated Fe(ClO4)2 were reported; however, the ligand Lc, having two chloro substituents at the ortho positions of the phenyl ring, was synthesized for the first time particularly for this work. Our present work begins with the reactions of hydrated nickel chloride with the azo-aromatic scaffolds La−c with an aim to synthesize coordinatively unsaturated Ni-complexes. The B


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Inorganic Chemistry

Figure 2. ORTEP view of Lc. Ellipsoids are drawn at 50% probability. Hydrogen atoms are omitted for clarity.

Figure 5. ORTEP view of [Ni(Lc)2(H2O)2](ClO4)2 ([3](ClO4)2). Ellipsoids are drawn at 50% probability. The ClO4− counterions and hydrogen atoms are omitted for clarity.

Figure 3. ORTEP view of [Ni(Lb)2Cl2] (1b). Ellipsoids are drawn at 50% probability. Hydrogen atoms are omitted for clarity.

Figure 6. ORTEP view of [Ni(Lb)2] (4b). Ellipsoids are drawn at 50% probability. Hydrogen atoms are omitted for clarity.

[3](ClO4)2), respectively. Two chlorido and H2O ligands occupy the remaining two coordination sites in complexes 1b and [3](ClO4)2, respectively. Unlike [2b](X)2 (X = ClO4, I3), in case of [3](ClO4)2 presence of two chlorides at the ortho positions of the phenyl ring of the two coordinated ligands makes the environment around the nickel center crowded, which possibly averts the coordination of the third ligand, Lc. As expected the N−N distances (1.258(3)Å (for 1b); 1.246(6), 1.197(9), and 1.258(7)Å (for [2b](ClO4)2); and 1.276(8)Å (for [3](ClO4)2)) are found to be comparable with those of the HLa and Lc. Single crystals of 4b, suitable for X-ray diffraction, were grown by slow evaporation of its dichloromethane−hexane solution under argon environment. Complex 4b is hexacoordinated; two tridentate ligands Lb coordinate the central nickel ion in a meridional fashion. Unlike complexes 1b, [2b](ClO4)2, and [3](ClO4)2, in 4b both the 1,10-phenanthroline moiety and the azo-chromophore of Lb coordinate the nickel center in a tridentate mode. The complex 4b has a C2 (noncrystallographic) axis, which makes one-half of the molecule identical to the other half as observed during 1H NMR analysis. The most important observation in the structure of 4b is the significant elongation of the N−N bonds (1.349(4)

b

Figure 4. ORTEP view of [Ni(L )3](ClO4)2 ([2b](ClO4)2). Ellipsoids are drawn at 50% probability. The ClO4− counterions and hydrogen atoms are omitted for clarity.

of HLa, the geometry around the diaza chromophore in Lc is cis (Figure 2). The N−N distance is 1.249(2) Å. Single crystals of 1b were obtained via slow evaporation of its methanol solution, whereas the single crystals of complexes [2b](ClO4)2 and [3](ClO4)2 were grown via slow evaporation of their dichloromethane−heptane and dichloromethane− hexane solutions, respectively. The coordination environment around the central nickel ion in complexes 1b, [2b](ClO4)2, and [3](ClO4)2 is distorted octahedral. Interestingly, the tridentate azoaromatic ligands (two Lb for 1b, three Lb for [2b](ClO4)2, and two Lc for [3](ClO4)2) are bound to the nickel(II) center in a bidentate coordination mode. The 1,10-phenanthroline moiety of the azo-aromatic ligands is coordinated to the nickel(II) center, whereas the azo-chromophores remain pendent. The averaged nonbonding distances of the azo-chromophores are 3.357(2)Å (for 1b), 2.917(4) Å (for [2b](ClO4)2), and 3.355(3) Å (for C


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Inorganic Chemistry Å) compared to HLa and Lc.12 This indeed points to the possibility that the two coordinated ligands Lb in 4b are reduced.11 In view of the observed diamagnetism of 4b, the elongated N−N bond leads to three different limiting electronic structure possibilities, namely, [Ni0(Lb)2], [NiI{(Lb)}·−)(Lb)], and [NiII{(Lb)·−}2. Thorough DFT studies were performed to unveil the most plausible electronic structure description of the above three possibilities. Cyclic Voltammetry and EPR Spectroscopy. Cyclic voltammetry of Lc, 1a−c, [2a,b](ClO4)2, and [3](ClO4)2 was performed in CH3CN, and that of 4a and 4b were performed in CH2Cl2 solutions containing 0.1 M [Bu4N]ClO4 as the supporting electrolyte at 25 °C. The potentials are referenced to the saturated Ag/AgCl electrode. The results are collected in Table 1; the voltammogram of 4b is shown in Figure 7, and those of 1b, [2b](ClO4)2, and [3](ClO4)2 are shown in Supporting Information.

the cyclic voltammogram of [3](ClO4)2. The complex 4b showed two successive reversible oxidations at −0.185 and 0.0925 V, respectively, and two irreversible reductions at −1.0 and −1.28 V, respectively. The oxidative nature of the redox responses at −0.185 and 0.0925 V were confirmed by exhaustive electrolysis. Notably, the observed peak potential separation (ΔE = Ep,ox − Ep,red) for the first reversible oxidation wave at −0.185 V is 127 mV, whereas it is 63 mV for the second oxidation wave at 0.0925 V. It is worth to mention here that, under the identical experimental conditions the ΔE = Ep,ox − Ep,red observed for the ferrocenium/ferrocene couple is 65 mV. This indeed points to the possibility of two-electron transfer process at −0.185 V.9d On the basis of the DFT studies, all the redox responses observed for 1a−c, [2a,b]2+, and [3]2+ and the two-electron oxidative wave observed for 4a and 4b are assigned as ligand-centered events. All the nickel(II) complexes 1a−c, [2a,b](ClO4)2, [3](ClO4)2, 4a, and 4b were found to be electron paramagnetic resonance (EPR) silent. However, electrochemically generated oxidized and reduced complexes were studied by EPR spectroscopy at 77 K to have a closer look on the electronic levels associated with the reversible redox couples. As expected, the one-electron-reduced species [Lc]·−, obtained via bulk electrolysis of Lc at −1.15 V, showed an isotropic single-line EPR spectrum at g = 2.005 indicating the formation of ligandcentered radical. Exhaustive electrolysis of 4b was performed under nitrogen environment at −0.05 V to characterize the two-electron oxidation couple at −0.185 V. Interestingly, after exhaustive electrolysis at −0.05 V, instead of [4b]2+ we end up with the EPR-silent [2b]2+ as was observed during oxidation of 4b using I2 as the oxidant. Redox-Induced Interconversion and Reversible Hemilability of the Coordinated Azo-Aromatic Ligands. The azo-aromatic ligands La−c are redox-active, and their iron complexes, reported recently,12 undergo reduction producing azo-anion radicals even in the presence of KOtBu as a reductant. The complexes 1a−c, [2a,b](ClO4)2, [3](ClO4)2, 4a, and 4b also showed multiple reductions and oxidations in their corresponding cyclic voltammograms. Therefore, to explore the possibility of redox-induced interconversion of all these complexes under reducing and oxidizing conditions, several control reactions were performed (Scheme 2). The mixed-ligand complexes [Ni(La,b)2Cl2] (1a, 1b) when reduced using excess KOtBu in dichloromethane under inert conditions afforded the homoleptic octahedral neutral complexes [Ni(La,b)2] (4a, 4b) in nearly 85% yields. The same result was observed when cobaltocene was used as the reducing agent. To gain insight into these KOtBu-mediated transformations of 1a and 1b to 4a and 4b, respectively, the reaction of 1b with KOtBu was followed by UV−vis spectroscopy. Upon addition of KOtBu to a solution of 1b in dichloromethane, the characteristic peaks at 328 and 375 nm gradually disappeared, and formation of a new peak was observed at 350 nm (Figure 8a). A gradual rise in absorption was also observed at 518 and 660 nm indicating the formation of 4b. The electronic spectra of pure 1b, [2b](ClO4)2, [3](ClO4)2, and 4b are displayed in Figure S14. The corresponding absorbance values are summarized in Table S3. Similarly, when 4b was exposed to air in the presence of excess chloride (Cl−) source like LiCl, the peak at 350 nm gets blue-shifted to 328 nm, and the peak at 390 nm also blueshifted to 378 nm, while the peak at 513 nm and the two

Table 1. Electrochemical Dataa of Lc, 1a-c, [2a](ClO4)2, [2b](ClO4)2, [3](ClO4)2, 4a, and 4b compound

oxidation (ΔEp, mV)

reduction (ΔEp, mV)

−0.180 (125), 0.0920 (63) −0.185 (127), 0.0925 (62)

−1.02 (76), −1.30 −0.25, −0.77 −0.23, −0.72 −0.26, −1.07 −0.25, −0.57, −0.85, −1.1 −0.23, −0.54, −0.84, −1.0 −0.32, −1.05 −1.10, −1.30 −1.0, −1.28

c

L 1a 1b 1c [2a](ClO4)2 [2b](ClO4)2 [3](ClO4)2 4a 4b a

Conditions: solvent: CH3CN for Lc, 1a−c, [2a,b](ClO4)2, and [3](ClO4)2; CH2Cl2 for 4a and 4b. Supporting electrolyte: [Bu4N]ClO4 (0.1 M). Reference electrode: saturated Ag/AgCl. Solute concentration: 1 × 10−3 M. ΔEp = Epa − Epc. Scan rate = 50 mV s−1.

Figure 7. Cyclic voltammogram of 4b in CH2Cl2.

The cyclic voltammogram of Lc showed two irreversible reductions at −1.02 and −1.30 V, respectively. Two reductive waves at −0.23 and −0.72 V, respectively, were observed in the cyclic voltammogram of the mixed-ligand complex 1b. The irreversibility observed in the cyclic voltammogram of 1b may be attributed to the loss of chlorido ligands upon reduction as was observed during the formation of 4b from 1b upon addition of a reducing agent (cf. below). The complex [2b](ClO4)2 showed four irreversible reductions at −0.23, −0.54, −0.84, and −1.0 V, respectively. Two irreversible reductions at −0.32 and −1.05 V, respectively, were observed in D


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Inorganic Chemistry Scheme 2. Redox-Induced Interconversion and Reversible Hemilability of Coordinated Azo-Aromatic Ligandsa

a

Conditions: (i)excess KOtBu, solvent-deoxygenated EtOH, RT, 1 h, under argon atmosphere. (ii)Excess LiCl dissolved in minimum amount of propan-2-ol, solvent DCM, RT, 1 h, under aerial conditions. (iii)Excess I2 solution in DCM, solvent DCM, RT, 1 h, under aerial conditions. (iv)Excess AgClO4, solvent ethanol, RT, 1 h, under aerial conditions.

of the complexes 4a and 4b. However, dechlorination followed by reduction under argon atmosphere afforded 4a and 4b. After repeated trials we were successful to crystallize the dechlorinated complex of [Ni(Lc)2Cl2] (1c) as [Ni(Lc)2(H2O)2] ([3](ClO4)2). These experimental observations indeed confirm that even if there are vacant coordination sites available, the 1,10-phenanthroline moiety of the tridentate azo-aromatic ligand (La,b) prefers to bind the nickel(II) center in a bidentate fashion, the azo-chromophore remains pendent, and the tridentate coordination was preferred only when the azoaromatic ligand undergoes one-electron reduction to form the azo-anion radical. Upon reduction, the negative charge accumulates at the N-donor atoms of the azo-chromophore, which possibly enhances its coordination ability, and hence in one-electron reduced azo-anion radical oxidation state, the azoaromatic ligands bind the nickel(II) center in a tridentate fashion. Electronic Structures and DFT Studies. DFT studies were performed to unveil the electronic structures of the synthesized compounds as well to understand the redoxinduced interconversion and ligand-centered hemilability. The optimized structures match quite well with the experimental data (see Table S2). Geometry optimizations were performed on the free ligand Lc and its one- and two-electron reduced counterparts [Lc]·− and [Lc]2−. As expected, the monoanionic [Lc]·− has a doublet ground state, whereas the dianionic [Lc]2− possesses a singlet S = 0 ground state. A gradual increase in the N−N distance was observed on going from the native ligand [Lc]0 (N−N = 1.274 Å) to its monoanionic [Lc]·− (N−N = 1.333 Å) and dianionic

humps at 598 and 660 nm gradually vanishes indicating the formation of 1b (Figure 8b). Interestingly, when a dichloromethane solution of the hexacoordinated complex [2b]2+ was stirred in the presence of excess KOtBu under inert conditions, the complex 4b was obtained in 80% yield from the reaction mixture after 1.0 h. When KOtBu was added to a dichloromethane solution of [2b]2+, the characteristic peaks at 330 and 370 nm gradually disappears, and formation of a new peak was observed at 350 nm (Figure 8c). Formation of a new peak at 518 nm and gradual development of a hump at 660 nm was also observed, indicating the conversion of [2b]2+ to 4b. Upon oxidation of 4b in the presence of ferrocenium cation (Fc+), the peaks at 350 and 390 nm shifted to 340 and 372 nm, respectively, while the peak at 513 nm and the two humps at 594 and 667 nm gradually vanishes with time. Our attempt to isolate the product obtained after chemical oxidation using iodine as the oxidant produced the hexacoordinated complex [2b](I3)2, in 60% isolated yield. An increase in the yield of [Ni(Lb)2](I3)2 ([2b](I3)2) was observed in the presence of added excess ligand Lb (Figure S11). It is noteworthy to mention here that the coordinated azoaromatic ligand shows reversible hemilability in complexes 1a, 1b, [2a](ClO4)2, [2b](ClO4)2, 4a, and 4b. To confirm that the observed hemilabile behavior of the azo-aromatic ligands in these nickel(II) complexes is only redox-induced and not because of the unavailability of vacant coordination sites, complexes 1a,b were subjected to dechlorination reactions in the presence of AgClO4. Interestingly, even after the dechlorination of 1a and 1b we did not observe the formation E


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Inorganic Chemistry

Figure 8. (a) Redox-induced conversion of 1b to 4b in the presence of KOtBu as the reductant. (b) Conversion of 4b to 1b in the presence of oxygen as the oxidant and LiCl as chloride ion source. (c) Conversion of 2b to 4b in presence of KOtBu as the reductant. (d) Oxidation of 4b in the presence of Fc+.

Figure 9. Spin-density plot for [NiII(Lb)2Cl2] (1b) (I); [NiII(Lb)3]2+ ([2b]2+) (II); [NiII(Lc)2(OH2)2]2+ ([3c]2+) (III); and [NiII{(Lb)·−}2] (4b) (IV).

[Lc]2− (N−N = 1.386 Å) form, respectively. Similar to La, the lowest unoccupied molecular orbitals (LUMOs) of Lc are mainly localized on the azo-chromophore. Spin density plot for [Lc]·−is displayed in Figure S18. The complexes 1b, [2b](ClO4)2, and [3](ClO4)2 were found to be open-shell triplet (S = 1). The electronic structures of these complexes can be best described as [NiII(Lb)2Cl2] (1b), [NiII(Lb)3](ClO4)2 ([2b](ClO4)2), and [NiII(Lc)2(OH2)2] ([3](ClO4)2), respectively. In 1b and [3](ClO4)2, 1,10-

phenanthroline moieties of two neutral tridentate azo-aromatic ligands (SL = 0), Lb and Lc, respectively, are bound to a highspin NiII (SNi= 1) center in a bidentate fashion, while the azochromophores remain pendent. Two chlorido (for 1b) and two H2O (for [3](ClO4)2) molecules coordinate the two remaining coordination sites. In [2b](ClO4)2, 1,10-phenanthroline moieties of three neutral tridentate azo-aromatic ligands (SL = 0), Lb are bound to the high-spin NiII (SNi = 1) center in a bidentate fashion, and the azo-chromophores remain pendent. F


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Inorganic Chemistry

respectively. Calculated bond lengths were compared with the experimental ones in Table S2, and the molecular orbitals (MOs) are displayed in Figure S26. Analysis of the magnetic orbitals reveals that two unpaired electrons are mainly metalbased for 1b, [2b]2+, and [3]2+ (see Supporting Information), which supports the oxidation state of nickel as Ni(II). For 4b, 172α and 173α are metal-centered, whereas 172β and 173β are ligand-based (azo-anion radical; Figure 10). The observed diamagnetism (S = 0) may be attributed to the antiferromagnetic coupling of two ferromagnetically coupled S = 1 ligand spin state with the metal S = 1 spin state. MO analysis shows that the LUMOs of 1b, [2b]2+, [3]2+, and 4b are primarily ligand-based (see Supporting Information) indicating ligandcentered reduction as observed in the cyclic voltammograms. DFT studies were also performed to explore the redoxinduced interconversion of all these complexes and to understand the reversible hemilability shown by the coordinated azo-aromatic ligands (L) upon reduction and oxidation as was discussed above. To start with we chose the experimentally observed redoxinduced conversion of the tris-ligated complex [NiII(Lb)3]2+ ([2b]2+) to the bis-ligated complex [NiII{(Lb)·−}2] (4b) over the simple two-electron reduction of [2b]2+ to [NiII(Lb){(Lb)·−}2] ([2b′]) having three azo-aromatic ligands bound in bidentate fashion with one pendent azo-chromophores from each of the ligands (Scheme 3). In agreement with our experimental findings, the complex 4b, where two of the oneelectron reduced azo-chromophores are coordinated to the central Ni(II)-center, was found to be stabilized by −3.69 kcal mol−1 compared to [NiII(Lb){(Lb)·−}2] ([2b′]), where the azochromophores are pendent (here optimized energy of [NiII(Lb){(Lb)·−}2] ([2b′]) is compared with optimized energy of [NiII{(Lb)·−}2] (4b) and that of the dissociated ligand Lb). Therefore, upon reduction, dissociation of one of the coordinated ligands is favored, and azo-anion radical ligands thus formed prefer tridentate coordination over the bidentate coordination as observed experimentally. The two-electron reduction of [NiII(Lb)2Cl2] (1b) to [NiII{(Lb)·−}2] (4b) over a four-coordinate species where the

Complex 4b was found to be a singlet diradical. Broken symmetry density functional calculations (BS(2,2)) reveal that high-spin NiII center is coordinated to two one-electron reduced open-shell, π-radical monoanions (L·−). Spin density analysis shows that the nickel center contains +1.76 spin population and that each of the ligands has −0.88 spin population mainly localized on the azo-chromophore. Two ferromagnetically coupled S = 1 ligand spin state couples with the metal S = 1 spin state to give the observed S = 0 ground state. This BS(2,2) state was found to be stabilized by −40.36 kcal/mol than the corresponding closed-shell configuration. The alternative electronic structure description, [NiII{(Lb)·−}2], containing a low-spin NiII (SNi = 0) center coordinated to two antiferromagnetically coupled azo-anion radical ligands (Lb)·− (SL = 1/2) was calculated to be destabilized by +15.39 kcal mol−1 compared to the BS(2,2) state. All attempts to locate the other alternative, having S = 0 ground state with [NiI{(Lb)·−}{Lb}] electronic structure description, leads to +0.84 spin population on one ligand and −0.84 spin population on the other ligand with 0.0 spin population on the nickel center (Figure S19). Spin-density plot for 4b and the corresponding magnetic orbitals are displayed in Figures 9IV and 10,

Figure 10. Qualitative representation of magnetic-orbitals for [NiII(Lb)2] (4b) (BS (2,2)).

Scheme 3. Possibility of Two-Electron Reductive Conversion of [NiII(Lb)3]2+ ([2b]2+) to [NiII{(Lb)·−}2] (4b) and [NiII(Lb){(Lb)·−}2] (2b′)

G


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Inorganic Chemistry

Scheme 4. Possibility of Two-Electron Reductive Conversion of [NiII(Lb)2Cl2]2+ (1b) to [NiII{(Lb)·−}2] (4b) and [NiII{(Lb)·−}2] (4b′)

synthesized complexes as well as to understand the unusual redox-induced hemilability shown by the coordinated azoaromatic ligand.

azo-chromophores are pendent (Scheme 4) was also explored theoretically. The complex 4b, having two azo-anion radical ligands bound in a tridentate fashion, was found to be stabilized by −41.87 kcal mol−1 than the tetra-coordinated complex 4b′ having two one-electron reduced ligands bound in bidentate fashion with one pendent azo-chromophore from each ligand. These results are also in line with the experimental results. Similarly, upon two-electron oxidation, the Ni(II)−N(azo) bond lengths in complex 4b increase substantially to 2.331 Å.

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EXPERIMENTAL SECTION

Materials. NiCl2, Ni(ClO4)2, and Ni(COD)2 were obtained from Sigma-Aldrich. All other reagents, chemicals, and solvents were obtained from available commercial suppliers and used without further purifications. Solvents were dried following the standard procedures and distilled prior to use. Tetrabutylammonium perchlorate was synthesized following a known literature method.13 Caution! Perchlorates must be handled with care and appropriate safety precautions. Physical Measurements. A PerkinElmer 240C elemental analyzer was used to perform elemental analyses (C, H, N). A micromass QTOF mass spectrometer (serial no. YA 263) was used to record the mass spectra. A Jasco spectrometer was used to record the UV−vis spectra. 1H NMR spectra were recorded on Bruker Avance 300/400/ 500 MHz and JEOL 400 MHz spectrometers, and SiMe4 was used as the internal standard. All electrochemical experiments were performed using a personal computer (PC)-controlled AUT.MAC204 electrochemical workstation under nitrogen atmosphere. Ag/AgCl was used as the reference electrode, a Pt disk was used as the working electrode, and a Pt wire was used as the auxiliary electrode. [Bu4N]ClO4 (0.1 M) was used as the supporting electrolyte in dichloromethane or acetonitrile solvents. During exhaustive electrolysis a Pt wire gauge was used as the working electrode. Gouy balance (Sherwood Scientific) was used to record the room-temperature magnetic moments of 1, [2]2+, and [3]3+, respectively. X-band EPR spectra were recorded in a JEOL JES-FA200 spectrometer.

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CONCLUSION In summary, we have reported an unusual redox-controlled interconversion of a series of NiII-complexes featuring redoxactive tridentate azo-aromatic pincer ligands La−c. The ligands 2-(arylazo)-1,10-phenanthroline (La,b) showed redox-induced hemilabile coordination. In its native state, the unreduced ligand L shows bidentate coordination; the 1,10-phenanthroline moiety binds the central Ni(II) atom in a bidentate fashion, while the azo-chromophore remains pendent. On the contrary, the monoanionic azo-anion ligand {(La,b)·−) coordinates the NiII ion in a tridentate mode. On the one hand, in complexes 1, [2]2+, and [3]2+, the 1,10-phenanthroline moiety of the neutral unreduced azo-aromatic ligands L binds the central nickel(II) atom in a bidentate fashion, while the azo-chromophore remains pendent. On the other hand, the complex 4 is a singlet diradical species, where both the 1,10-phenanthroline moiety and the azo chromophores of the azo-aromatic ligands (La/b) are bound to the NiII center in a tridentate coordination mode. Depending upon the formal oxidation state of the coordinated azo-aromatic ligands, the complexes 1a,b, 2a,b, 4a, and 4b undergo interconversion. Complexes 1a,b; [2a]2+, [2b]2+ upon reduction transformed to complex 4a and 4b, respectively, with the loss of two chlorido ligands (for 1a, 1b) and one La/b (for [2b]2+), whereas the complex 4a,b upon oxidation in the presence of excess chloride (LiCl) source transformed back to 1a,b. Thorough experimental and DFT calculations were performed to unveil the electronic structures of all the

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SYNTHESIS Synthesis of Azo-Aromatic Ligands La−c. The azoaromatic ligands La−c were prepared following a literature procedure.12 Characterization data of Lc: UV/vis: λmax/nm (ε, M−1 cm−1), 224(28 336), 287(19 224), 342(7735), 447(609). IR (KBr cm−1): 1575 (ν, CN), 1420 (ν, NN). 1H NMR (400 MHz, CDCl3): δ 9.27−9.24 (m, 1H), 8.48−8.43 (m, 1H), 8.32−8.29 (m, 1H), 8.12 (t, J = 8, 1H), 7.92 (t, J = 8, 2H), 7.71−7.68 (m, 1H), 7.46 (d, J = 8, 1H), 7.28−7.24 (m, 2H). H


Article

Inorganic Chemistry

dichloromethane/hexane (10:2) under argon environment. Yield 95%. UV/vis: λmax/nm (ε, M−1 cm−1), 346(27 524), 518(11 459), 592(7163), 650(3622). IR (KBr cm−1): 1635 (ν, CN), 1335 (ν, NN). Elemental Analysis: C36H24N8Ni: calcd: C, 68.93; H, 3.86; N, 17.86. Found: C, 68.99; H, 3.95; N, 17.92%. 1H NMR:(300 MHz,CDCl3) δ 9.28 (d, J = 2.7 Hz,1H), 8.43 (d, J = 8.4 Hz, 1H), 8.30 (d, J = 7.5 Hz, 1H), 8.17 (d, J = 8.4 Hz, 3H), 7.88 (s, 2H), 7.69 (d, J = 3.6 Hz, 1H), 7.57 (s, 3H). Synthesis of [Ni(Lb)2] (4b). Same synthetic procedure as described above for 4a was followed to prepare the complex 4b. Yield 90%. UV/vis: λmax/nm (ε, M−1 cm−1), 350(10 696), 518(6926), 591(3245), 660(2253). IR (KBr cm−1): 1620 (ν, CN), 1325 (ν, NN). Elemental Analysis: C36H22Cl2N8Ni: calcd: C, 62.11; H, 3.19; N, 16.09. Found: C, 62.16; H, 3.27; N, 16.04%. 1H NMR:(300 MHz,CDCl3) δ 9.28 (s, 1H), 8.45 (d, J = 6.6 Hz, 1H), 8.32 (d, J = 7.2 Hz, 1H), 8.16 (s, 3H), 7.91 (s, 2H), 7.71 (s, 1H), 7.56 (d, J = 7.8 Hz, 2H). Redox-Induced Interconversion. Conversion of 1a to 4a. To obtain 4a from 1a, 100 mg (0.130 mmol) of the complex [Ni(La)2Cl2] (1a) was dissolved in deoxygenated ethanol, and excess KOtBu was added to it under argon atmosphere. Upon addition of KOtBu the brown colored solution instantly changes to deep violet. The reaction was continued for 1 h. The resultant solution was filtered, and the violet color precipitate, thus obtained, was recrystallized from dichloromethane/hexane (1:5). Yield 85%. Conversion of 1b to 4b. Same synthetic procedure as described for 1a was followed to achieve this conversion. Yield 85%. Conversion of 4a to 1a. To obtain 1a from 4a, 100 mg (0.143 mmol) of the complex [Ni(La)2] (4a) was dissolved in dichloromethane, and to it excess LiCl dissolved in minimum amount of propan-2-ol was added dropwise under aerial conditions. The brown colored solution instantly changed to yellowish-brown. The reaction was continued for 1 h. The resultant solution was filtered, and the brown color precipitate, thus obtained, was recrystallized from methanol/ether (1:5). Yield 90%. Conversion of 4b to 1b. Same synthetic procedure as described for 4a was followed to achieve this conversion. Yield 90%. Conversion of [2a](ClO4)2 to 4a. To obtain 4a from [2a](ClO4)2, 100 mg (0.082 mmol) of the complex [Ni(La)3](ClO4)2 ([2a] (ClO4)2) was dissolved in ethanol, and excess KOtBu was added to it under argon atmosphere. Upon addition of KOtBu the red colored solution instantly changes to deep violet. The reaction was continued for 1 h. The resultant solution was filtered, and the violet color precipitate, thus obtained, was recrystallized form dichloromethane/hexane (1:5). Yield 80%. Conversion of [2b](ClO4)2 to 4b. Same synthetic procedure as described for 4a was followed to achieve this conversion. Yield 80%. Conversion of 4a to [2a](I3)2. To obtain [2a](I3)2 from 4a, 100 mg (0.143 mmol) of the complex [Ni(La)2] (4a) was dissolved in dichloromethane, and to it dichloromethane solution of iodine was added dropwise. The color of the solution changed gradually from violet to red. Then the reaction mixture was concentrated, and excess iodine was washed off with hexane. The product was recrystallized from dichloromethane/hexane (1:5). Yield 60%.

Elemental Analysis for C18H10Cl2N4: calcd: C, 61.21; H, 2.85; N, 15.86. Found: C, 61.14; H, 2.97; N, 15.93%. Synthesis of [Ni(La)2Cl2] (1a). In a 100 mL round-bottom flask, 100 mg (0.314 mmol) of the ligand La was allowed to dissolve in ethanol. Then, on addition of 37.3 mg (0.157 mmol) of NiCl2·6H2O to it, the orange colored solution instantly changes to dark red, and gradually brown precipitation occurs. The reaction was continued for 6 h in a magnetic stirrer. The resultant solution was then filtered, and the precipitate thus obtained was recrystallized from methanol/ether (1:5). Yield 90%. UV/vis: λmax/nm (ε, M−1 cm−1), 315(49 803), 360(32 931). IR (KBr cm−1): 1650 (ν, CN), 1410 (ν, N N). μeff(RT): 3.01 μB. Anal. Calcd for C36H24Cl2N8Ni: C, 61.93; H, 3.46; N, 16.05. Found: C, 62.02; H, 3.57; N, 16.12%. Synthesis of [Ni(Lb)2Cl2] (1b). Same synthetic procedure as described above for 1a was followed to prepare the complex 1b. Yield 90%. UV/vis: λmax/nm (ε, M−1 cm−1), 328(31 293), 375(29 235) IR (KBr cm−1): 1625 (ν, CN), 1400 (ν, N N). μeff(RT): 3.05 μB. Elemental Analysys: C36H22Cl4N8Ni: calcd: C, 56.36; H, 2.89; N, 14.61. Found: C, 56.27; H, 2.97; N, 14.55%. Synthesis of [Ni(Lc)2Cl2] (1c). Same synthetic procedure as described above for 1a was also followed to prepare the complex 1c. Yield 90%. UV/vis: λmax/nm (ε, M−1 cm−1), 304(29 340), 343(15 271), 483(2242). IR (KBr cm−1): 1620 (ν, CN), 1395 (ν, NN). μeff(RT): 2.95 μB. Elemental Analysis: C36H20Cl6N8Ni: calcd: C, 51.72; H, 2.41; N, 13.40. Found: C, 51.64; H, 2.51; N, 13.46%. Synthesis of [Ni(La)3](ClO4)2 ([2a](ClO4)2). In a 100 mL round-bottom flask, 100 mg (0.314 mmol) of the ligand, La was allowed to dissolve in ethanol. Then on addition of 38.4 mg (0.105 mmol) of Ni(ClO4)2·6H2O the orange colored solution instantly changes to deep red. The reaction was continued for 6 h in a magnetic stirrer. The resultant solution was then filtered, and the red color precipitate thus obtained was recrystallized from dichloromethane/hexane (1:5). Yield 85%. UV/vis: λmax/nm (ε, M−1 cm−1), 316(32 893), 362(21 898). IR (KBr cm−1): 1650 (ν, CN), 1410 (ν, NN). μeff(RT): 3.12 μB. Elemental Analysis: C54H36Cl2N12NiO8: calcd: C, 58.40; H, 3.27; N, 15.14. Found: C, 58.46; H, 3.37; N, 15.19%. Synthesis of [Ni(Lb)3](ClO4)2 ([2b](ClO4)2). Same synthetic procedure as described above for [2a](ClO4)2 was followed to prepare the complex [2b](ClO4)2. Yield 85%. UV/vis: λmax/nm (ε, M−1 cm−1), 330(9224), 367(7692). IR (KBr cm−1): 1625 (ν, CN), 1400 (ν, NN). μeff(RT): 3.10 μB. Elemental Analysis: C54H33Cl5N12NiO8: calcd: C, 53.43; H, 2.74; N, 13.85. Found: C, 53.37; H, 2.83; N, 13.78%. Synthesis of [Ni(Lc)2(H2O)2](ClO4)2 ([3](ClO4)2). Same synthetic procedure as described above for [2a](ClO4)2 was also followed to prepare the complex [3](ClO4)2. Yield 85%. UV/vis: λmax/nm (ε, M−1 cm−1), 305(33 443), 348(16 393), 483(2426). IR (KBr cm−1): 1625 (ν, CN), 1400 (ν, NN). μeff(RT): 3.10 μB. Elemental Analysis: C36H24Cl6N8NiO10: calcd: C, 43.24; H, 2.42; N, 11.20. Found: C, 43.30; H, 2.56; N, 11.16%. Synthesis of [Ni(La)2] (4a). In an oven-dried Schlenk tube 100 mg (0.314 mmol) of the ligand (La) and 43.0 mg (0.157 mmol) Ni(COD)2 were added under argon atmosphere. The Schlenk was then fitted with a Teflon screw cap, vacuum evaporated, and backfilled with argon. Deoxygenated dichloromethane was added to it and allowed to stir for 6 h. Once the reaction was complete, the solvent was evaporated to dryness and crystallized by fast evaporation of its solution in I


Article

Inorganic Chemistry Conversion of 4b to [2b](I3)2. Same synthetic procedure as described above for 4a was used to prepare [2b](I3)2 from 4b. Yield 60%. X-ray Crystallography. We succeeded to obtain good quality single crystals, suitable for X-ray diffraction, of Lc and [3](ClO4)2 via slow evaporation of their dichloromethane− hexane solvent mixture. Single crystals of 1b were obtained by slow evaporation of its methanol solution, and that of [2b](ClO4)2 were grown via slow evaporation of its dichloromethane−heptane solution. Dichloromethane−hexane solution of 4b was evaporated under argon atmosphere to obtain good quality single crystals of 4b, suitable for X-ray diffraction. Single-crystal X-ray diffraction data of Lc, 1b, [2b](ClO4)2, [3](ClO4)2, and 4b were collected with monochromated Mo Kα radiation (λ = 0.710 73 Å) on a Bruker SMART Apex II diffractometer equipped with a CCD area detector. The thermal parameters of some carbons in the single-crystal structure of [2b](ClO4)2 showed high values, suggesting that these carbons were disordered. In these circumstances, several trial models with additional disorder were tried in the structure refinement without success. In the single-crystal structure of [3](ClO4)2 the hydrogen atoms bonded to O6 of water solvent molecule were not discernible from the last final difference Fourier map, and consequently their positions were not considered. The SAINT-NT software package was used for the data reduction.14 With SADABS program, multiscan absorption correction was applied to all intensity data.15 The structures were solved by a combination of direct methods with subsequent difference Fourier syntheses and refined by fullmatrix least-squares on F2 using the SHELX-2013 suite.16 In all the cases, the non-hydrogen atoms were treated anisotropically. The crystal data together with refinement details are given in Table S1. Computational Details. All the electronic structures were assigned by DFT calculations using the Gaussian 09 program17 with PBE0 hybrid functional (G09/PBE0).18,19 Within the calculations the quasi-relativistic effective core pseudo potential proposed by Hay and Wadt, LANL2DZ pseudo potential,20a and the corresponding optimized set of basis function has been employed for Ni. For nitrogen, oxygen, and chlorine, a valence double-ζ polarized basis set, 6-311+G(d),20b was used, while the atomic orbitals of all other atoms are described by 631G(d,p)20c basis set. Broken-symmetry formalism as introduced by Noodleman23 was used to achieve the spin-polarized symmetry-broken21,22 solutions. The symmetry-broken wave functions were obtained by employing “guess = mix” option. By BS(2,2) it means two unpaired electrons on metal center and two electrons on ligands (one on each ligand).17 Molecular orbitals and spin-density plots were built using the Chemcraft24 Visualization program.

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ing [email protected], or by contacting The Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: +44 1223 336033.

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. ORCID

Nanda D. Paul: 0000-0002-8872-1413 Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS The research was supported by DST (Project No. YSS/2015/ 001552). S.D. is thankful to UGC, S.S. is thankful to IIESTS, U.J. is thankful to DST-Inspire, and R.S. is thankful to UGCRGNF for providing fellowship. We thank IIEST, Shibpur, for financial assistance. SAIF, IIESTS is duly acknowledged for providing single-crystal X-ray facility. P.B. thanks CICECOAveiro Institute of Materials, POCI-01-0145-FEDER-007679 (FCT Ref No. UID/CTM/50011/2013), financed by national funds through the FCT/MEC and when appropriate cofinanced by FEDER under the PT2020 Partnership Agreement. This paper is dedicated to Professor R. N. Mukherjee of Department of Chemistry, Indian Institute of Technology, Kanpur, on the occasion of his 65th birth anniversary.

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REFERENCES

(1) (a) Slone, C. S.; Weinberger, D. A.; Mirkin, C. A. The transition metal coordination chemistry of hemilabile ligands. Prog. Inorg. Chem. 2007, 48, 233. (b) Braunstein, P.; Naud, F. Hemilability of Hybrid Ligands and the Coordination Chemistry of Oxazoline-Based Systems. Angew. Chem., Int. Ed. 2001, 40, 680−699. (c) Rosen, M. S.; Spokoyny, A. M.; Machan, C. W.; Stern, C. L.; Sarjeant, A. A.; Mirkin, C. A. Chelating Effect as a Driving Force for the Selective Formation of Heteroligated Pt(II) Complexes with Bidentate Phosphino-Chalcoether Ligands. Inorg. Chem. 2011, 50, 1411−1419. (d) Peris, E. Smart N-Heterocyclic Carbene Ligands in Catalysis. Chem. Rev., DOI: 201710.1021/acs.chemrev.6b00695. (2) (a) Steinborn, D. Fundamentals of Organometallic Catalysis; Wiley-VCH: Weinheim, Germany, 2012; p 155. (b) Wang, D.; Weinstein, A. B.; White, P. B.; Stahl, S. S. Ligand-Promoted PalladiumCatalyzed Aerobic Oxidation Reactions. Chem. Rev., DOI: 2018118263610.1021/acs.chemrev.7b00334. (c) Crabtree, R. H. Dihydrogen Complexation. Chem. Rev. 2016, 116, 8750−8769. (d) Machan, C. W.; Lifschitz, A. M.; Stern, C. L.; Sarjeant, A. A.; Mirkin, C. A. Crystallographic Snapshots of the Bond-Breaking Isomerization Reactions Involving Nickel(II) Complexes with Hemilabile Ligands. Angew. Chem. 2012, 124, 1498−1501. (e) Jeffrey, J. C.; Rauchfuss, T. B. Metal Complexes of Hemilabile Ligands. Reactivity and Structure of Dichlorobis(0- (diphenylphosphino)anisole)ruthenium(II). Inorg. Chem. 1979, 18, 2658−2666. (3) (a) Paretzki, A.; Bubrin, M.; Fiedler, J.; Zàliš, S.; Kaim, W. Correlated Coordination and Redox Activity of a Hemilabile Noninnocent Ligand in Nickel Complexes. Chem. - Eur. J. 2014, 20, 5414−5422. (b) Lindner, R.; van den Bosch, B.; Lutz, M.; Reek, J. N. H.; van der Vlugt, J. I. Tunable Hemilabile Ligands for Adaptive Transition Metal Complexes. Organometallics 2011, 30, 499−510. (c) Hübner, R.; Weber, S.; Strobel, S.; Sarkar, B.; Zàliš, S.; Kaim, W. Reversible intramolecular single-electron oxidative addition involving a hemilabile noninnocent ligand. Organometallics 2011, 30, 1414−1418. (d) van der Vlugt, J. I.; Pidko, E. A.; Vogt, D.; Lutz, M.; Spek, A. L.; Meetsma, A. T-Shaped Cationic CuI Complexes with Hemilabile PNPType Ligands. Inorg. Chem. 2008, 47, 4442−4444. (e) Ye, S.; Sarkar, B.; Lissner, F.; Schleid, Th.; van Slageren, J.; Fiedler, J.; Kaim, W.

ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.inorgchem.8b00231. Characterization data, ORTEP, FMOs, and Cartesian coordinates of the optimized structures (PDF) Accession Codes

CCDC 1819614−1819619 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 emailJ


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Inorganic Chemistry

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