The rapid voltage and capacity fade of the otherwise promising Ni-rich layered LiNi0.8Mn0.1Co0.1O2 (NMC811) cathode are the primary obstacles to its successful commercialization in lithium-ion batteries (LIBs). Here, in situ electrochemical electron paramagnetic resonance (EPR) spectroscopy is employed to gain insight into the cation redox behavior of the NMC811 cathode during the cell charge/discharge process. Different oxidation states of Ni ions are detected by variations in the signal of the EPR spectra. Ex situ studies of NMC811 at different SOC levels also confirm changes in the local Mn-Ni environment. A comparison of in situ studies on fresh and cycled NMC811 electrodes demonstrates that the fundamental redox processes remain unchanged upon cycling of the material. Finally, dissolved Mn and Co ions from the bulk are found using ex situ EPR characterization of the cycled cathode and separator. The dissolution of these metal ions can accelerate the degradation of the entire battery.

Photocatalytic synthesis of hydrogen peroxide (H2O2) from oxygen (O2) is a challenging process. Metal-organic framework (MOF) materials are emerging photocatalysts with potential tunable light absorption properties. Herein, we report a rhenium (Re) modified Zr-based MOF, Re10-MFM-67, in which active Re sites are incorporated into MFM-67 by partial replacement of 9,9'-bianthracene-10,10'-dicarboxylic acid (H2L1) with a [(H2L2)ReI(CO)3Cl] (H2L2 = 2,2'-bipyridine-5,5'-dicarboxylic acid) moiety. Re10-MFM-67 (10 refers to the molar percentage content of Re complex within the material) exhibits broadband light absorption with an exceptional rate of formation of H2O2 from O2 of 8.50 mmol gcat-1 h-1 and a record turnover frequency (TOF) of 28.7 h-1 under visible light irradiation (λ > 400 nm). Synchrotron powder X-ray diffraction (SPXRD) and neutron powder diffraction (NPD) confirm the structure of Re10-MFM-67, and together with extended X-ray absorption fine structure (EXAFS) analysis establish the coordination environment and binding of the [ReI(CO)3Cl] moiety within the framework structure. In situ electron paramagnetic resonance (EPR) spectroscopy suggests that photocatalytic H2O2 generation on Re10-MFM-67 occurs via a two-step oxygen reduction reaction (ORR) pathway with the superoxide anion formed as an intermediate. This study promotes the design of MOF-based photocatalysts with conjugated ligands for efficient photosynthesis.

Following electrospray ionization (ESI), it is common for analytes to enter the gas phase accompanied by an additional small ion or molecule. Although these may not be influential in solution, they often determine the charge of the entire complex and can markedly tune their properties in the gas phase. Therefore, measuring their relative influence can be used to assist our understanding of the structure and stability of the target molecule. Because these adducts are usually distinguishable by their mass, differences in the behaviour of the analyte resulting from these added species can be extracted readily. Here, we use ion mobility mass spectrometry (IM-MS), supported by density functional theory (DFT), to investigate how different charge carriers (H+, Na+, K+, Cs+) as well as water influence the disassembly, stability, and conformational landscape of the homometallic ring [Cr8F8(O2CtBu)16] and different heterometallic rotaxanes [NH2RR’][Cr7MF8(O2CtBu)16], where M = Mn, Fe, Co, Ni, Cu, Zn, and Cd. The results yield new insights on their disassembly mechanisms and support previously reported trends in cavity size and transition metal properties, demonstrating the potential of adduct ion studies for characterising metallosupramolecular complexes in general.

Understanding the fundamental reactivity of polymetallic complexes is challenging due to the complexity of their structures with many possible bond breaking and forming processes. Here we apply ion mobility mass spectrometry (IM-MS) coupled with density functional theory (DFT) to investigate the disassembly mechanisms and energetics of a family of heterometallic rings and rotaxanes with the general formula [NH2RR’][Cr7MF8(O2CtBu)16] with M = MnII, FeII, CoII, NiII, CuII, ZnII, CdII. Our results show that their stability can be tuned both by altering the d-metal composition in the macrocycle and by the end groups of the secondary ammonium cation [NH2RR’]+. Ion mobility probes the conformational landscape of the disassembly process from intact complex to structurally distinct isobaric fragments, providing unique insights to how a given divalent metal tunes the structural dynamics.

We report the synthesis of extended hybrid organic-inorganic rotaxanes based on (pyCH2NH2CH2CH2py)[TiIV 7GaIIIO8(O2CtBu)16] (1) and (pyCH2NH2CH2py)[TiIV 7GaIIIO8(O2CtBu)16] (3) building blocks, containing an anionic macrocycle and doubly pyridyl-terminated secondary ammonium threads. Reaction of 1 and 3 with [Cu(hfac)2] (hfac = 1,1,1,5,5,5-hexafluoroacetylacetonate) gives {[Cu(hfac)2]3[1]2} (2) and {[Cu(hfac)2]2[3]} (4), respectively, which are characterized by single-crystal X-ray crystallography. The products are controlled by the differing steric demands imposed by the two arms of the thread. The structure of 2 is an extended [3]rotaxane, with two molecules of 1 binding to a central [Cu(hfac)2] molecule via the longer arm of the thread, and two [Cu(hfac)2] units terminating the structure at the shorter arm. The structure of 4, where both arms of the thread are short, is an extended [2]rotaxane terminated by two molecules of [Cu(hfac)2]. The Cu…Cu…Cu fragment in 2 is linear, with the central Cu lying on an inversion center and with a separation between the terminal copper ions of 31.3 Å. Double Electron-Electron Resonance (DEER; also known as PELDOR) spectroscopy proves that the [3]rotaxane structure remains intact in solution, detecting both terminal…center and terminal…terminal Cu…Cu interactions, with orientation-selective measurements demonstrating that there is a rearrangement of the structure at the terminal positions on dissolution.

Catalytic cleavage of beta-O-4 linkages is an essential but challenging step in the depolymerization of lignin. Here, we report the templated electrosynthesis of a hydrophobic metal-organic polyhedral catalyst (Cu-MOP-e), which exhibits excellent hydrothermal stability and exceptional activity for this reaction. The oxidative cleavage of 2-phenoxyacetophenone, 1, a lignin model compound, over Cu-MOP-e at 90 degrees C for 1 h affords full conversion with yields of the monomer products phenol and benzoic acid of 99%. The reusability of Cu-MOP-e was confirmed by carrying out ten cycles of reaction. The mechanism of catalyst-substrate binding was investigated by highresolution synchrotron X-ray powder diffraction, in situ X-ray absorption spectroscopy, electron paramagnetic resonance spectroscopy, and density functional theory (DFT) calculations. The combination of optimal porosity and active Cu(II) sites provides confined binding of 2-phenoxyacetophenone, thus promoting the cleavage of beta-O-4 linkage under relatively mild conditions.

The thermostable four-coordinate divalent lanthanide (Ln) bis-amidinate complexes [Ln(Piso)2] (Ln = Tb, Dy; Piso = {(NDipp)2CtBu}, Dipp = C6H3iPr2-2,6) were prepared by the reduction of parent five-coordinate Ln(III) precursors [Ln(Piso)2I] (Ln = Tb, Dy) with KC8; halide abstraction of [Ln(Piso)2I] with [H(SiEt3)2][B(C6F5)] gave the respective Ln(III) complexes [Ln(Piso)2][B(C6F5)]. All complexes were characterized by single crystal and powder XRD, SQUID magnetometry UV-vis-NIR, ATR-IR, NMR and EPR spectroscopy, and ab initio CASSCF-SO calculations. These data consistently show that [Ln(Piso)2] formally exhibit Ln(II) centers with 4fn5dz21 (Ln = Tb, n = 8; Dy, n = 9) valence electron configurations. We show that simple assignments of the f-d coupling to either L−S or J−s schemes is an oversimplification, especially in the presence of significant crystal field splitting. The coordination geometry of [Ln(Piso)2] is intermediate between square planar and tetrahedral. Projecting from the quaternary carbon atoms of the CN2 ligand backbones shows near-linear C···Ln···C arrangements. This results in strong axial ligand fields to give effective energy barriers to magnetic relaxation of 1920(91) K for the Tb(II) analog and 1964(48) K for Dy(II), the highest values observed to date for any mononuclear Ln(II) single-molecule magnet (SMM).

Single-crystal X-ray structures of hydrated di-(2-pyridyl) ketone 4,4-dimethyl-3-thiosemicarbazone (HDpk44mT·H2O), the ternary ionic copper-(II) complexes [Cu-(Dpk-H-44mT)-(phen)]-(ClO4)2·1-(1/2)-MeOH (1·1-(1/2)-MeOH) and [Cu-(Dpk44mT)-(phen)]-ClO4 (2) (Dpk-H-44mT = zwitterionic) form of HDpk44mT; phen = 1,10-phenanthroline and the molecular dioxovanadium-(V) complex [VO2(Dpk44mT)] (3) have been determined. Additionally, the solution structures of HDpk44mT·H2O and complex 3 have been elucidated with the aid of NMR spectroscopic techniques. Coordination compounds 1·1-(1/2)-MeOH, 2 and 3 represent extremely rare examples of thiosemicarbazone complexes of their specific kind possessing a di-(2-pyridyl)-ketimine moiety. Under slightly acidic conditions, complex 1·1-(1/2)-MeOH is produced with the thiosemicarbazone ligand occurring in the zwitterionic thio-enolate form, but readily converts to complex 2 in basic medium. In the crystal lattice, these two copper-(II) complexes show vastly different patterns of π-π stacking interactions. However, they have in common the ligand-imposed distorted square-pyramidal coordination geometry exhibiting a tetragonally induced disparity between the distances of the axial-equatorial CuII-Nphen bonds. X-band EPR spectroscopy demonstrated retention of the coordination sphere (g z > g x,y > 2.00; A z > A x,y ) in frozen solution. The crystallographic asymmetric unit of [VO2(Dpk44mT)] comprises two discrete molecules, one of which exhibits π-π stacking interactions. Their coordination geometry at the vanadium-(V) center is severely distorted square pyramidal. Complexes 1·1-(1/2)-MeOH, 2 and 3 are electroactive with reduction potentials lying within the biologically accessible redox potential window. While the copper-(II) complexes are highly efficacious as antiproliferative agents against the cancer cell lines HeLa and MCF-7, the main drawback is the lack of selectivity over the normal cell line MCF-10A. In sharp contrast, [VO2(Dpk44mT)] is specifically and selectively potent toward MCF-7 over HeLa and MCF-10A cells, and may provide impetus for further in vitro antitumor investigations.

The extension of previous studies of heterometallic rings (HMRs) is described, including new synthetic chemistry and physics. These HMRs feature a ring of, typically, eight metal centers with a central charge-balancing cation. New HMRs and related molecules are described, varying the number of metals present. The eight metal HMRs have been used as components of larger supramolecular assembly, most often by making the HMRs into [2]rotaxanes or pseudo-rotaxanes, where the thread of the rotaxane is terminated by a binding group such as pyridine. This allows the formation of [n]rotaxanes, where n = 3, 4, 5,7, 13, or 1014. Mass spectrometry and NMR studies of the HMRs have given greater understanding of the host-guest chemistry of these metal analogues of crown ethers. Physical studies have included 4D-inelastic neutron scattering (INS) and continuous wave and pulsed EPR spectroscopy to measure magnetic interactions between spin components of the supramolecular assemblies. The use of the HMRs as resists for high-resolution lithography is also discussed.

Both metalloporphyrins and heterometallic {Cr7Ni} rings are of significant research interest due to their proposed roles in quantum information processing devices. In this study, we present a series of complexes in which [Cr7NiF3(Etglu)((O2CBu)-Bu-t)(15)] (N-EtgluH(5) = N-ethyl-d-glucamine) heterometallic rings are coordinated to metalloporphyrin linkers: the symmetric [M(TPyP)] for M = Cu2+, VO2+, and H2TPyP = 5,10,15,20-tetra(4-pyridyl)porphyrin; and the asymmetric [{VO}(TrPPyP)] for H-2(TrPPyP) = 5,10,15-(triphenyl)-20-(4-pyridyl)porphyrin. The magnetic interactions present in these complexes are unraveled using the continuous wave (CW) electron paramagnetic resonance (EPR) technique. The nature of the coupling between the {Cr7Ni} rings and the central metalloporphyrin is assessed by numerical simulations of CW EPR spectra and determined to be on the order of 0.01 cm(-1), larger than the dipolar ones and suitable for individual spin addressability in multiqubit architectures.

Lanthanide (Ln) silylamide chemistry is well-developed, but the corresponding silylphosphide chemistry is immature; there are only ten structurally characterized examples of Ln(II) bis(trimethylsilyl)phosphide complexes to date, and no reported derivatives with bulkier R-groups. Here we report the synthesis of the first f-block bis(triisopropylsilyl)phosphide complexes, [Ln{P(SiiPr3)2}2(THF)x] (1-Ln; Ln = Sm, Eu, x = 3; Ln = Yb, x = 2), by the respective salt metathesis reactions of parent [LnI2(THF)2] with 2 eq. of [Na{P(SiiPr3)2}]n in toluene. Complexes 1-Ln were characterized by a combination of NMR, EPR, ATR-IR, electronic absorption and emission spectroscopies, elemental analysis, SQUID magnetometry and single crystal X-ray diffraction. These data contrast with those obtained for related Ln(II) bis(trimethylsilyl)phosphide complexes due to the bulkier ligands in 1-Ln, and also with Ln(II) bis(triisopropylsilyl)amide complexes due to a combination of longer Ln–P vs. Ln–N bonds and the softer nature of P- vs. N-donor ligands.

We investigate actinide covalency effects in two [AnCp(3)(tt)] (An = Th, U) complexes recently studied with pulsed electron paramagnetic resonance spectroscopy, using the Hyperion package to obtain relativistic hyperfine coupling constants from relativistic multiconfigurational wave functions. H-1 and C-13 HYSCORE simulations using the computed parameters show excellent agreement with the experimental data, highlighting the accuracy of modern relativistic ab initio methods. The extent of covalency indicated from the calculations on [ThCp3tt] is in agreement with the original report based on traditional spectral fitting methods, while the covalency in [UCp3tt] is found to be previously overestimated. The latter is due to the paramagnetic spin-orbit effect that arises naturally in a relativistic theory of hyperfine coupling and yet was not accounted for in the original study, thus highlighting the necessity of relativistic approaches for the interpretation of magnetic resonance data pertaining to actinides.

Herein we present a series of room-temperature stable, structurally analogous rare-earth complexes of the form [M(NHAriPr6)2] (M = Sc, Y, La, Sm, Eu, Tm, Yb; NHAriPr6 = {N(H)C6H3-2,6-(C6H2-2,4,6-iPr3)2}). All seven complexes contain formal M(II) ions with close M···arene contacts. The Sc(II) and La(II) complexes display an open-book deformation (ca. 11–13°) of one metal-bound arene, while for Y(II) there are two symmetry-equivalent Y···arene interactions with smaller deformations (ca. 7°). In the case of Sc(II), Y(II), and La(II), quantum chemical calculations reveal the delocalization of a metal d-electron from M(II) into ligand π-orbitals forming δ-bonding interactions. In the case of Y(II), EPR and UV-Vis-NIR spectroscopies combined with quantum chemical calculations show a structural change in solution to the single-open-book deformation structure in common with Sc(II) and La(II). While the Sm(II), Eu(II), Tm(II), and Yb(II) complexes retain similar close M···arene contacts, their 4fn+1 valence electron configurations do not lead to δ-bonding interactions; however, NMR studies of diamagnetic 4f14 Yb(II) reveal 171Yb···1H coupling to arene ring-protons at room temperature and show that the M···arene interaction is preserved in solution across a wide temperature range. These complexes represent a rare structurally analogous M(II) series which extends from the group 3 elements into the lanthanide series and includes an extremely rare neutral formal Sc(II) complex.

Mono- and bis-salen functionalised [2]rotaxanes have been synthesised from the esterification of [2]rotaxanes containing phenol-terminated threads (salen=N,N'-bis(salicylidene)ethylenediamine). The [2]rotaxanes have general formula [RH][Cr7NiF8(O2CtBu)16], where [RH]+ is a thread with a central secondary ammonium site that templates a [Cr7NiF8(O2CtBu)16]- ring. The threads are terminated at one or both ends by carboxylic acid functionalised salen groups. The {M(salen)} groups can be free-base [M=(H+)2] or metallated [M=Cu2+, Ni2+, (VO)2+]. The [2]rotaxanes have been characterised by single crystal XRD and solid- and solution-state EPR spectroscopy. Where two paramagnetic M ions are involved [M=Cu2+ and/or (VO)2+] the [2]rotaxanes contain three electron spin S= 1 / 2 ${{ 1/2 }}$ centres, since the {Cr7Ni} ring has an S= 1 / 2 ${{ 1/2 }}$ ground state which is well isolated at low temperatures. These three-spin [2]rotaxanes have been characterised in solution by pulsed dipolar EPR spectroscopies (DEER, also known as PELDOR, and RIDME). The M⋅⋅⋅M and M⋅⋅⋅{Cr7Ni} interactions measured are consistent with dipolar interactions and also with the distances from single crystal XRD. The authors declare no competing financial interest.

AbstractThe design and preparation of efficient catalysts for ammonia production under mild conditions is a desirable but highly challenging target. Here, we report a series of single-atom catalysts [M-SACs, M = Mn(II), Fe(III), Co(II), Ni(II), Cu(II), Zn(II), Mo(II)] derived from UiO-66 containing structural defects and their application to electrochemical reduction of nitrate (NO3-) to ammonia (NH3). Cu-SAC and Fe-SAC exhibit remarkable yield rates for NH3 production of 30.0 and 29.0 mg h−1 cm−2, respectively, with a high Faradaic efficiency (FENH3) of over 96% at −1.0 V versus the reversible hydrogen electrode. Importantly, their catalytic performance can be retained in various simulated wastewaters. Complementary experiments confirmed the nature of single-atom sites within these catalysts and the binding domains of NO3- in UiO-66-Cu. In situ spectroscopic techniques, coupled with density functional theory calculations confirm the strong binding of NO3- and the formation of reaction intermediates, thus facilitating the catalytic conversion to NH3.

Whilst lanthanide (Ln) silylamide chemistry is mature, the corresponding silylphosphide chemistry is underdeveloped, with [Sm{P(SiMe3)2}{μ-P(SiMe3)2}3Sm(THF)3] being the sole example of a structurally authenticated Ln(II) silylphosphide complex. Here we expand Ln(II) {P(SiMe3)2} chemistry through the synthesis and characterization of nine novel complexes. The dinuclear ‘ate’ salt-occluded complexes [{Ln[P(SiMe3)2]3(THF)}2(μ-I)K3(THF)] (1-Ln; Ln = Sm, Eu) and polymeric ‘ate’ complex [KYb{P(SiMe3)2}3{μ-K[P(SiMe3)2]}2] (2-Yb) were prepared by the respective salt metathesis reactions of parent [LnI2(THF)2] (Ln = Sm, Eu, Yb) with 2 or 3 eq. of K{P(SiMe3)2} in diethyl ether. The separate treatment of these complexes with either pyridine or 18-crown-6 led to the formation of the mononuclear solvated adducts, trans-[Ln{P(SiMe3)2}2(py)4] (3-Ln; Ln = Sm, Eu, Yb) and [Ln{P(SiMe3)2}2(18-crown-6)] (4-Ln; Ln = Sm, Eu, Yb), with concomitant loss of K{P(SiMe3)2}. The complexes were characterized by a combination of NMR, EPR, ATR-IR, electronic absorption and emission spectroscopies, elemental analysis, SQUID magnetometry, and single crystal X-ray diffraction. We find that these complexes exhibit electronic structures that contrast with those of related Ln(II) bis(trimethylsilyl)amide complexes due to differences in ligand donor atom hardness and ligand steric requirements from Ln–P bonds being longer than Ln–N bonds.

We report the high NH3 uptake in a series of copper-carboxylate materials, namely MFM-100, MFM-101, MFM-102, MFM-126, MFM-127, MFM-190(F), MFM-170, and Cu-MOP-1a. At 273 K and 1 bar, MFM-101 shows an exceptional uptake of 21.9 mmol g-1. The presence of Cu(ii)& ctdot;NH3 interactions and changes in coordination at the [Cu2(O2CR)4] paddlewheel are analysed and discussed. High NH3 uptake is observed in a series of paddlewheel [Cu2(O2CR)4] metal-organic frameworks.

Although several Run+ (n = 2 or 3) complexes have been reported to be excellent biomimetics for the water oxidation process of photosystem II, investigation and spectroscopic characterization of the reactive intermediates such as [Ru-IV/V & boxH;O](n+) involved in the catalytic process are not only scarce but also a daunting task. Here, we report a catalyst [Ru-III(L)(PPh3)(H2O)](+) (2) found to show electrochemical water oxidation efficiency with a considerably low overpotential of 195 mV compared to other Run+ water oxidation catalysts reported in the nonaqueous media. Besides, the Schiff base ligand (L) employed in this study facilitates the stabilization of a [LRuV & boxH;O](+) species. By the use of multispectroscopic techniques (spectroelectrochemistry, electron paramagnetic resonance, and resonance Raman), we have shed light on the electronic structure of the elusive [LRuV & boxH;O](+) species. Based on the experimental results, a plausible intermolecular radical coupling (I2M) mechanism is proposed, which is corroborated by theoretical calculations.

Landmark advances in rare earth (RE) chemistry have shown that divalent complexes can be isolated with non-Aufbau 4f n {5d/6s}1 electron configurations, facilitating remarkable bonding motifs and magnetic properties. We report a series of divalent bis-tethered arene complexes, [RE(NHAriPr6 )2] (2RE; RE = Sc, Y, La, Sm, Eu, Tm, Yb; NHAriPr6 = {N(H)C6H3-2,6-(C6H2-2,4,6-iPr3)2}). Fluid solution EPR spectroscopy gives g iso < 2.002 for 2Sc, 2Y, and 2La, consistent with formal nd1 configurations, calculations reveal metal-arene δ-bonding via mixing of nd(x 2-y 2) valence electrons into arene π* orbitals. Experimental and calculated EPR and UV-Vis-NIR spectroscopic properties for 2Y show that minor structural changes markedly alter the metal d(x 2-y 2) contribution to the SOMO. This contrasts 4f n {5d/6s}1 complexes where the valence d-based electron resides in a non-bonding orbital. Complexes 2Sm, 2Eu, 2Tm, and 2Yb contain highly-localised 4f n+1 ions with no appreciable metal-arene bonding by density functional calculations. These results show that the physicochemical properties of divalent rare earth arene complexes with both formal nd1 and 4f n+1 configurations are nuanced, may be controlled through ligand modification, and require a multi-pronged experimental and theoretical approach to fully rationalise.

We report three new polymers, based on mechanically interlocked inorganic-organic rotaxanes. They are made in very mild conditions and involve pyrimidine head groups binding to copper(ii) linking units. A two-dimensional 6,3 net and a three-dimensional 10,3b net are found depending on the solvent used in the reaction. We report three new polymers, based on mechanically interlocked inorganic-organic rotaxanes.