Correction: Distinct photodynamics of κ-N and κ-C pseudoisomeric iron(II) complexes.

Correction for 'Distinct photodynamics of κ-N and κ-C pseudoisomeric iron(II) complexes' by Philipp Dierks et al., Chem. Commun., 2021, 57, 6640-6643, https://doi.org/10.1039/D1CC01716K.

Unraveling the electrochemical and spectroscopic properties of neutral and negatively charged perylene tetraethylesters.

A detailed investigation of the energy levels of perylene-3,4,9,10-tetracarboxylic tetraethylester as a representative compound for the whole family of perylene esters was performed. It was revealed via electrochemical measurements that one oxidation and two reductions take place. The bandgaps determined via the electrochemical approach are in good agreement with the optical bandgap obtained from the absorption spectra via a Tauc plot. In addition, absorption spectra in dependence of the electrochemical potential were the basis for extensive quantum-chemical calculations of the neutral, monoanionic, and dianionic molecules. For this purpose, calculations based on density functional theory were compared with post-Hartree-Fock methods and the CAM-B3LYP functional proved to be the most reliable choice for the calculation of absorption spectra. Furthermore, spectral features found experimentally could be reproduced with vibronic calculations and allowed to understand their origins. In particular, the two lowest energy absorption bands of the anion are not caused by absorption of two distinct electronic states, which might have been expected from vertical excitation calculations, but both states exhibit a strong vibronic progression resulting in contributions to both bands.

Distinct photodynamics of κ-N and κ-C pseudoisomeric iron(II) complexes.

Two closely related FeII complexes with 2,6-bis(1-ethyl-1H-1,2,3-triazol-4yl)pyridine and 2,6-bis(1,2,3-triazol-5-ylidene)pyridine ligands are presented to gain new insights into the photophysics of bis(tridentate) iron(ii) complexes. The [Fe(N^N^N)2]2+ pseudoisomer sensitizes singlet oxygen through a MC state with nanosecond lifetime after MLCT excitation, while the bis(tridentate) [Fe(C^N^C)2]2+ pseudoisomer possesses a similar 3MLCT lifetime as the tris(bidentate) [Fe(C^C)2(N^N)]2+ complexes with four mesoionic carbenes.

Fundamental Characterization, Photophysics and Photocatalysis of a Base Metal Iron(II)-Cobalt(III) Dyad.

A new base metal iron-cobalt dyad has been obtained by connection between a heteroleptic tetra-NHC iron(II) photosensitizer combining a 2,6-bis[3-(2,6-diisopropylphenyl)imidazol-2-ylidene]pyridine with 2,6-bis(3-methyl-imidazol-2-ylidene)-4,4'-bipyridine ligand, and a cobaloxime catalyst. This novel iron(II)-cobalt(III) assembly has been extensively characterized by ground- and excited-state methods like X-ray crystallography, X-ray absorption spectroscopy, (spectro-)electrochemistry, and steady-state and time-resolved optical absorption spectroscopy, with a particular focus on the stability of the molecular assembly in solution and determination of the excited-state landscape. NMR and UV/Vis spectroscopy reveal dissociation of the dyad in acetonitrile at concentrations below 1 mM and high photostability. Transient absorption spectroscopy after excitation into the metal-to-ligand charge transfer absorption band suggests a relaxation cascade originating from hot singlet and triplet MLCT states, leading to the population of the 3 MLCT state that exhibits the longest lifetime. Finally, decay into the ground state involves a 3 MC state. Attachment of cobaloxime to the iron photosensitizer increases the 3 MLCT lifetime at the iron centre. Together with the directing effect of the linker, this potentially makes the dyad more active in photocatalytic proton reduction experiments than the analogous two-component system, consisting of the iron photosensitizer and Co(dmgH)2 (py)Cl. This work thus sheds new light on the functionality of base metal dyads, which are important for more efficient and sustainable future proton reduction systems.

A Thioether-Ligated Cupric Superoxide Model with Hydrogen Atom Abstraction Reactivity.

The central role of cupric superoxide intermediates proposed in hormone and neurotransmitter biosynthesis by noncoupled binuclear copper monooxygenases like dopamine-ß-monooxygenase has drawn significant attention to the unusual methionine ligation of the CuM ("CuB") active site characteristic of this class of enzymes. The copper-sulfur interaction has proven critical for turnover, raising still-unresolved questions concerning Nature's selection of an oxidizable Met residue to facilitate C-H oxygenation. We describe herein a model for CuM, [(TMGN3S)CuI]+ ([1]+), and its O2-bound analog [(TMGN3S)CuII(O2•-)]+ ([1·O2]+). The latter is the first reported cupric superoxide with an experimentally proven Cu-S bond which also possesses demonstrated hydrogen atom abstraction (HAA) reactivity. Introduction of O2 to a precooled solution of the cuprous precursor [1]B(C6F5)4 (-135 °C, 2-methyltetrahydrofuran (2-MeTHF)) reversibly forms [1·O2]B(C6F5)4 (UV/vis spectroscopy: λmax 442, 642, 742 nm). Resonance Raman studies (413 nm) using 16O2 [18O2] corroborated the identity of [1·O2]+ by revealing Cu-O (446 [425] cm-1) and O-O (1105 [1042] cm-1) stretches, and extended X-ray absorption fine structure (EXAFS) spectroscopy showed a Cu-S interatomic distance of 2.55 Å. HAA reactivity between [1·O2]+ and TEMPO-H proceeds rapidly (1.28 × 10-1 M-1 s-1, -135 °C, 2-MeTHF) with a primary kinetic isotope effect of kH/kD = 5.4. Comparisons of the O2-binding behavior and redox activity of [1]+ vs [2]+, the latter a close analog of [1]+ but with all N atom ligation (i.e., N3S vs N4), are presented.

Molybdenum(VI) bis-imido Complexes of Dipyrromethene Ligands.

We report the synthesis of high-valent molybdenum(VI) bis-imido complexes 1-4 with dipyrromethene (DPM) supporting ligands of the general formula (DPMR)Mo(NR')2Cl (R, R' = mesityl (Mes) or tert-butyl (tBu)). The electrochemical and chemical properties of 1-4 reveal unexpected ligand noninnocence and reactivity. 15N NMR spectroscopy is used to assess the electronic properties of the imido ligands in the tert-butyl complexes 1 and 3. Complex 1 is inert toward ligand (halide) exchange with bulky phenolates such as KOMes or amides (e.g., KN(SiMe3)2), whereas the use of the lithium alkyl LiCH2SiMe3 results in a rare nucleophilic ß-alkylation of the DPM ligand. While the reductions of the complexes occur at molybdenum, the oxidation is centered at the DPM ligand. Quantum-chemical calculations (complete active space self-consistent field, density functional theory) suggest facile (near-infrared) interligand charge transfer to the imido ligand, which might preclude the isolation of the oxidized complex [1]+ in the experiment.

When Donors Turn into Acceptors: Ground and Excited State Properties of FeII Complexes with Amine-Substituted Tridentate Bis-imidazole-2-ylidene Pyridine Ligands.

In search of new ligand motifs for photoactive iron(II) complexes with long-lived MLCT states, a series of six complexes with tridentate amine-functionalized bis-n-heterocyclic carbene (NHC)-pyridine ligands is presented. In the homoleptic complexes imidazole-, methylimidazole-, or benzimidazole-2-ylidene, NHC donors are employed in combination with pyridine, functionalized in the 4-position by dimethylamine or dibenzylamine. The effects of these different functionalities on the electronic structure of the complexes are examined through detailed ground state characterization by NMR, single crystal X-ray diffraction, as well as electrochemical and spectroscopic methods. The net influence of these different functionalities on orbital-orbital and electrostatic ligand-iron interactions is investigated thoroughly by density functional theory, and changes in the excited state behavior and lifetimes are finally examined by ultrafast optical spectroscopy. Great deviations of the initially expected effects by substitution in 4-position on the photochemical properties are observed, together with a significantly increased π-acceptor interaction strength in the benzimidazole-2-ylidene functionalized complexes.

Monoanionic Anilidophosphine Ligand in Lanthanide Chemistry: Scope, Reactivity, and Electrochemistry.

We present the synthesis of a series of new lanthanide(III) complexes supported by a monoanionic bidentate anilidophosphine ligand (N-(2-(diisopropylphosphanyl)-4-methylphenyl)-2,4,6-trimethylanilide, short PN-). The work comprises the characterization of a variety of heteroleptic complexes containing either one or two PN ligands as well as a study on further functionalization possibilities. The new heteroleptic complexes cover selected examples over the whole lanthanide(III) series including lanthanum, cerium, neodymium, gadolinium, terbium, dysprosium, and lutetium. In case of the two diamagnetic metal cations lanthanum(III) and lutetium(III), we have furthermore studied the influence of the lanthanide ion (early vs. late) on the reactivity of these complexes. Thereby we found that the radius of the lanthanide ion has a major influence on the reactivity. Using sterically demanding, multidentate ligand systems, e.g., cyclopentadienide (Cp-), we found that the lanthanum complex La(PN)2Cl (1-La) reacts well to the corresponding cyclopentadienide complex, while for Lu(PN)2Cl (1-Lu) no reaction was observed under any conditions tested. On the contrary, employing monodentate ligands such as mesitolate, thiomesitolate, 2,4,6-trimethylanilide or 2,4,6-trimethylphenylphosphide, results in the clean formation of the desired complexes for both lanthanum and lutetium. All complexes have been studied by various techniques, including multi nuclear NMR spectroscopy and X-ray crystallography. 31P NMR spectroscopy was furthermore used to evaluate the presence of open coordination sites on the complexes using coordinating and noncoordinating solvents, and as a probe for estimating the Ce-P distance in the corresponding complexes. Additionally, we present cyclic voltammetry (CV) data for Ce(PN)2Cl (1-Ce), La(PN)2Cl (1-La), Ce(PN)(HMDS)2 (8-Ce) and La(PN)(HMDS)2 (8-La) (with HMDS = hexamethyldisilazide, (Me3Si)2N-) exploring the potential of the anilidophosphane ligand framework to stabilize a potential Ce(IV) ion.

A new bis-phenolate mesoionic carbene ligand for early transition metal chemistry.

We report the synthesis of a new pincer-type triazolylidene ligand precursor H3L[Cl] with redox-active 3,5-di-tert-butylphenolate substituents on a multigram scale following a converging ten-step route. The potential of this new mesoionic carbene ligand in early transition metal chemistry is explored. This includes the synthesis of the first triazole-derived mesoionic carbene complexes of titanium, niobium and molybdenum as well as the first example of MIC imido complexes of these elements. Furthermore, the reactivity as well as the electrochemical properties of the new complexes are compared to known, comparable bis-phenolate NHC complexes.

Experimental and Theoretical High Energy Resolution Hard X-ray Absorption and Emission Spectroscopy on Biomimetic Cu2S2 Complexes.

High energy resolution fluorescence detected X-ray absorption near edge structure (HERFD-XANES) and Valence-to-Core X-ray emission (VtC-XES) spectroscopy are established as hard X-ray methods to investigate complexes that might be relevant as mimics for the biologically important CuA site. By investigation of three carefully selected complexes of the type [Cu2(NGuaS)2X2], characterized by a cyclic Cu2S2 core portion and a varying adjunct ligand nature, it is proven that the HERFD-XANES and VtC-XES measurements in combination with extensive TD-DFT calculations can reveal details of the electronic states in such complexes, including HOMO and LUMO levels and spin states. By theoretical spectroscopy, the value of this methodic combination for future in situ studies is demonstrated.

Structural dynamics upon photoexcitation-induced charge transfer in a dicopper(i)-disulfide complex.

The structural dynamics of charge-transfer states of nitrogen-ligated copper complexes has been extensively investigated in recent years following the development of pump-probe X-ray techniques. In this study we extend this approach towards copper complexes with sulfur coordination and investigate the influence of charge transfer states on the structure of a dicopper(i) complex with coordination by bridging disulfide ligands and additionally tetramethylguanidine units [CuI2(NSSN)2]2+. In order to directly observe and refine the photoinduced structural changes in the solvated complex we applied picosecond pump-probe X-ray absorption spectroscopy (XAS) and wide-angle X-ray scattering (WAXS). Additionally, the ultrafast evolution of the electronic excited states was monitored by femtosecond transient absorption spectroscopy in the UV-Vis probe range. DFT calculations were used to predict molecular geometries and electronic structures of the ground and metal-to-ligand charge transfer states with singlet and triplet spin multiplicities, i.e. S0, 1MLCT and 3MLCT, respectively. Combining these techniques we elucidate the electronic and structural dynamics of the solvated complex upon photoexcitation to the MLCT states. In particular, femtosecond optical transient spectroscopy reveals three distinct timescales of 650 fs, 10 ps and >100 ps, which were assigned as internal conversion to the ground state (Sn → S0), intersystem crossing 1MLCT → 3MLCT, and subsequent relaxation of the triplet to the ground state, respectively. Experimental data collected using both X-ray techniques are in agreement with the DFT-predicted structure for the triplet state, where coordination bond lengths change and one of the S-S bridges is cleaved, causing the movement of two halves of the molecule relative to each other. Extended X-ray absorption fine structure spectroscopy resolves changes in Cu-ligand bond lengths with precision on the order of 0.01 Å, whereas WAXS is sensitive to changes in the global shape related to relative movement of parts of the molecule. The results presented herein widen the knowledge on the electronic and structural dynamics of photoexcited copper-sulfur complexes and demonstrate the potential of combining the pump-probe X-ray absorption and scattering for studies on photoinduced structural dynamics in copper-based coordination complexes.

The Connection between NHC Ligand Count and Photophysical Properties in Fe(II) Photosensitizers: An Experimental Study.

Four homo- and heteroleptic complexes bearing both polypyridyl units and N-heterocyclic carbene (NHC) donor functions are studied as potential noble metal-free photosensitizers. The complexes [FeII(L1)(terpy)][PF6]2, [FeII(L2)2][PF6]2, [FeII(L1)(L3)][PF6]2, and [FeII(L3)2][PF6]2 (terpy = 2,2':6',2″ terpyridine, L1 = 2,6-bis[3-(2,6-diisopropylphenyl)imidazol-2-ylidene]pyridine, L2 = 2,6-bis[3-isopropylimidazol-2-ylidene]pyridine, L3 = 1-(2,2'-bipyridyl)-3-methylimidazol-2-ylidene) contain tridentate ligands of the C^N^C and N^N^C type, respectively, resulting in a Fe-NHC number between two and four. Thorough ground state characterization by single crystal diffraction, electrochemistry, valence-to-core X-ray emission spectroscopy (VtC-XES), and high energy resolution fluorescence detected X-ray absorption near edge structure (HERFD-XANES) in combination with ab initio calculations show a correlation between the geometric and electronic structure of these new compounds and the number of the NHC donor functions. These results serve as a basis for the investigation of the excited states by ultrafast transient absorption spectroscopy, where the lifetime of the 3MLCT states is found to increase with the NHC donor count. The results demonstrate for the first time the close interplay between the number of NHC functionalities in Fe(II) complexes and their photochemical properties, as revealed in a comparison of the activity as photosensitizers in photocatalytic proton reduction.

Optical response of the Cu2 S2 diamond core in Cu2II(NGuaS)2 Cl2.

Density functional theory (DFT) and time-dependent DFT calculations are presented for the dicopper thiolate complex Cu2 (NGuaS)2 Cl2 [NGuaS=2-(1,1,3,3-tetramethylguanidino) benzenethiolate] with a special focus on the bonding mechanism of the Cu2 S2 Cl2 core and the spectroscopic response. This complex is relevant for the understanding of dicopper redox centers, for example, the CuA center. Its UV/Vis absorption is theoretically studied and found to be similar to other structural CuA models. The spectrum can be roughly divided in the known regions of metal d-d absorptions and metal to ligand charge transfer regions. Nevertheless the chloride ions play an important role as electron donors, with the thiolate groups as electron acceptors. The bonding mechanism is dissected by means of charge decomposition analysis which reveals the large covalency of the Cu2 S2 diamond core mediated between Cu dz2 and S-S π and π* orbitals forming Cu-S σ bonds. Measured resonant Raman spectra are shown for 360- and 720-nm excitation wavelength and interpreted using the calculated vibrational eigenmodes and frequencies. The calculations help to rationalize the varying resonant behavior at different optical excitations. Especially the phenylene rings are only resonant for 720 nm. © 2016 Wiley Periodicals, Inc.

Crystal structure of 2,2'-({[2-(trityl-sulfan-yl)benz-yl]azane-diyl}bis-(ethane-2,1-di-yl))bis-(isoindoline-1,3-dione).

In the structure of the title compound, C46H37N3O4S, the planes of the two isoindoline units make a dihedral angle of 77.86 (3)°. The dihedral angles between the benzyl plane and the isoindoline units are 79.56 (4) and 3.74 (9)°. The geometry at the S atom shows a short [1.7748 (17) Å] S-Cbenz-yl and a long [1.8820 (15) Å] S-Ctrit-yl bond and the C-S-C angle is 108.40 (7)°. N-C bond lengths around the azane N atom are in the range 1.454 (2)-1.463 (2) Å. he crystal packing exhibts two rather 'non-classical' C-H⋯O hydrogen bonds that result in stacking of the molecules along the a as well as the b axis and give rise to columnar sub-structures.

Bis{2-[(Tri-phenyl-meth-yl)amino]-phen-yl} diselenide aceto-nitrile monosolvate.

The mol-ecular structure of the title compound, C50H40N2Se2·C2H3N, shows a syn conformation of the benzene rings bound to the Se atoms, with an Se-Se bond length of 2.3529 (6) Šand a C-Se-Se-C torsion angle of 93.53 (14)°. The two Se-bonded aromatic ring planes make a dihedral angle of 18.42 (16)°. Intra-molecular N-H⋯Se hydrogen bonds are noted. Inter-molecular C-H⋯Se inter-actions give rise to supra-molecular chains extended along [100]. One severely disordered aceto-nitrile solvent mol-ecule per asymmetric unit was treated with SQUEEZE in PLATON [Spek (2009 ▶). Acta Cryst. D65, 148-155]; the crystal data take the presence of this mol-ecule into account.

2-Benzyl-sulfanyl-N-(1,3-dimethyl-imidazolidin-2-yl-idene)aniline.

The mol-ecular structure of the title compound, C18H21N3S, shows a twisted conformation with a dihedral angle of 67.45 (4)° between the aromatic ring planes and an N-C-C-S torsion angle of -5.01 (13)°. The imidazolidine ring and the aniline moiety make a dihedral angle of 56.03 (4)° and the asscociated C-N-C angle is 125.71 (10)°. The guanidine-like C=N double bond is clearly localized, with a bond length of 1.2879 (14) Å. The C-S-C angle is 102.12 (5)° and the S-C(aromatic) and S-C bond lengths are 1.7643 (11) and 1.8159 (12) Å.

The mixed-valent copper thiol-ate complex hexa-kis-{µ3-2-[(1,3-dimethyl-imidazol-idene)amino]-benzene-thiol-ato}dicopper(II)tetra-copper(I) bis-(hexa-fluoridophosphate) acetonitrile disolvate dichloro-methane disolvate.

The mol-ecular structure of the title compound, [Cu4(I)Cu2(II)(C11H14N3S)6](PF6)2·2CH3CN·2CH2Cl2, shows a mixed-valent copper(I/II) thiol-ate complex with a distorted tetra-hedral coordination of the Cu(I) and Cu(II) cations by one guanidine N atom and three S atoms each. Characteristic features of the Cu6S6 skeleton are a total of six chemically identical µ3-thiol-ate bridges and almost planar Cu2S2 units with a maximum deviation of 0.110 (1) Šfrom the best plane. Each Cu2S2 unit then shares common Cu-S edges with a neighbouring unit; the enclosed dihedral angle is 60.14 (2)°. The geometric centre of the Cu6S6 cation lies on a crystallographic inversion centre. Cu-S bond lengths range from 2.294 (1) to 2.457 (1) Å, Cu-N bond lengths from 2.005 (3) to 2.018 (3) Šand the non-bonding Cu⋯Cu distances from 2.5743 (7) to 2.5892 (6) Å. C-H⋯F hydrogen-bond inter-actions occur between the PF6(-) anion and the complex mol-ecule and between the PF6(-) anion and the acetonitrile solvent mol-ecule.

Bis(2-{[bis-(dimethyl-amino)-methyl-idene]amino-κN}benzene-sulfonato-κN)copper(II).

The mol-ecular structure of the title compound, [Cu(C11H16N3O3S)2], shows the Cu(II) atom with a distorted square-planar coordination geometry from the N2O2 donor set of the two chelating 2-{[bis-(dimethyl-amino)-methyl-idene]amino}-benzene-sulfonate ligands. The Cu(II) atom lies 0.065 (1) Šabove the N2O2 plane and the Cu-O [2 × 1.945 (2) Å] and Cu-N bond lengths [1.968 (3) and 1.962 (3) Å] lie in expected ranges. The two aromatic ring planes make a dihedral angle of 85.48 (1)°.

2-[2-(Benzyl-sulfan-yl)phen-yl]-1,1,3,3-tetra-methyl-guanidine.

The mol-ecular structure of the title compound, C(18)H(23)N(3)S, shows it to be a derivative of an amino-thio-phenol possessing a tetra-methyl-guanidine group with a localized C=N double bond of 1.304 (2) Šand a protected thiol functional group as an S-benzyl thio-ether. The two aromatic ring planes make a dihedral angle of 67.69 (6)°.