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Numerous descriptions of structural isomerism in metal complexes do not list any molecular vs ionic isomers. At the same time, one of the most striking examples of structural isomerism in organic chemistry is molecular urea, which has the same atomic composition as the chemically distinct ionic ammonium cyanate. This iconic organic couple now meets its inorganic heterometallic counterpart. We introduce a new class of structural isomers, molecular vs ionic, that can be consummated in complex and coordinatively unsaturated polynuclear/heterometallic compounds. We report inorganic molecular and ionic isomers of the composition [NaCrFe (acac) 3 (hfac) 3 ] (acac = acetylacetonate; hfac = hexafluoroacetylacetonate). Heterometallic molecular [Cr III (acac) 3 -Na-Fe II (hfac) 3 ] ( 1m ) and ionic {[Cr III (acac) 3 -Na-Cr III (acac) 3 ] + [Fe II (hfac) 3 -Na-Fe II (hfac) 3 ] - } ( 1i ) isomers have been isolated in pure form and characterized. While both ions are hetero bi metallic trinuclear entities, the neutral counterpart is a hetero tri metallic trinuclear molecule. The two isomers exhibit distinctly different characteristics in terms of solubility, volatility, mass spectrometry ionization, and thermal behavior. Unambiguous assignment of the positions and oxidation/spin states of the Periodic Table neighbors, Fe and Cr, in both isomers have been made by a combination of characterization techniques that include synchrotron X-ray resonant diffraction, synchrotron X-ray fluorescence spectroscopy, Mössbauer spectroscopy, and DART mass spectrometry. The transformation between the two isomers that does take place in solutions of noncoordinating solvents has also been tested.

The phenomenon of spin crossover involves coordination complexes with switchable spin states. This spin state change is accompanied by significant geometric changes such that low and high spin forms of a complex are distinct isomers that exist in equilibrium with one another. Typically, spin-state isomers interconvert rapidly and are similar enough in polarity to prevent their independent separation and isolation. We report here the first example, to our knowledge, of cobalt(II) spin-state isomers that can be physically separated. The reaction of Mo 2 (dpa) 4 (dpa = 2,2'-dipyridylamide) with CoBr 2 produces a mixture of two heterometallic compounds with a linear, metal-metal-bonded Mo[Formula: see text]Mo-Co chain. The complexes, SC-[BrMo 2 (dpa) 4 Co]Br (SC- 2 ) and HS-[BrMo 2 (dpa) 4 CoBr] (HS- 2 ), have identical compositions (Mo 2 Co(dpa) 4 Br 2 ) but different ground spin states and coordination geometries of the Co(II) ion. In the solid state, SC- 2 undergoes incomplete spin crossover from an S = 1/2 state to an S = 3/2 state, and HS- 2 has a high spin, S = 3/2, ground state, as confirmed by SQUID magnetometry and EPR spectroscopy. Crystallographic analyses of SC- 2 and HS- 2 show that SC- 2 has an elongated Co-Br distance relative to HS- 2 and is best described as the salt [BrMo 2 (dpa) 4 Co]Br. This limits SC- 2 's solubility in nonpolar solvents and allows for the physical separation of the two isomers. Solution studies of SC- 2 and HS- 2 indicate that SC- 2 and HS- 2 interconvert slowly relative to the NMR time scale. Additional solution-state EPR and UV-vis absorption measurements demonstrate that the choice of solvent polarity determines the predominant isomer present in solution.

We report the ability to trap the dimer Au 2 (μ-dppe) 2 I 2 (dppe is 1,2-bis(diphenylphosphino)ethane) with different separations between the three-coordinate gold ions in crystalline solvates. All of these solvates ((Au 2 (μ-dppe) 2 I 2 ·4(CH 2 Cl 2 ) ( 1 ), Au 2 (μ-dppe) 2 I 2 ·2(CH 2 Cl 2 ) ( 2 ), the polymorphs α-Au 2 (μ-dppe) 2 I 2 ·2(HC(O)NMe 2 ) ( 3 ) and β-Au 2 (μ-dppe) 2 I 2 ·2(HC(O)NMe 2 ) ( 4 ), and Au 2 (μ-dppe) 2 I 2 ·4(CHCl 3 ) ( 5 )) along with polymeric {Au(μ-dppe)I} n · n (CHCl 3 ) ( 6 )) originated from the same reaction, only the solvent system used for crystallization differed. In the different solvates of Au 2 (μ-dppe) 2 I 2 , the Au···Au separation varied from 3.192(1) to 3.7866(3) Å. Computational studies undertaken to understand the flexible nature of these dimers indicated that the structural differences were primarily a result of crystal packing effects with aurophillic interactions having a minimal effect.

The catalyzed electrochemical oxidation of ammonia to nitrogen (AOR) is an important fuel-cell half-reaction that underpins a future nitrogen-based energy economy. Our laboratory has reported spontaneous chemical and electrochemical oxidation of ammonia to dinitrogen via reaction of ammonia with the metal-metal bonded diruthenium complex Ru 2 (chp) 4 OTf (chp - = 2-chloro-6-hydroxypyridinate, TfO - = trifluoromethanesulfonate). This complex facilitates electrocatalytic ammonia oxidation at mild applied potentials of -255 mV vs ferrocene, which is the [Ru 2 (chp) 4 (NH 3 )] 0/+ redox potential. We now report a comprehensive computational investigation of possible mechanisms for this reaction and electronic structure analysis of key intermediates therein. We extend this analysis to proposed second-generation electrocatalysts bearing structurally similar fhp and hmp (2-fluoro-6-hydroxypyridinate and 2-hydroxy-6-methylpyridinate, respectively) equatorial ligands, and we further expand this study from Ru 2 to analogous Os 2 cores. Predicted M 2 4+/5+ redox potentials, which we expect to correlate with experimental AOR overpotential, depend strongly on the identity of the metal center, and to a lesser degree on the nature of the equatorial supporting ligand. Os 2 complexes are easier to oxidize than analogous Ru 2 complexes by ∼640 mV, on average. In contrast to mono-Ru catalysts, which oxidize ammonia via a rate-limiting activation of the strong N-H bond, we find lowest-energy reaction pathways for Ru 2 and Os 2 complexes that involve direct N-N bond formation onto electrophilic intermediates having terminal amido, imido, or nitrido groups. While transition state energies for Os 2 complexes are high, those for Ru 2 complexes are moderate and notably lower than those for mono-Ru complexes. We attribute these lower barriers to enhanced electrophilicity of the Ru 2 intermediates, which is a consequence of their metal-metal bonded structure. Os 2 intermediates are found to be, surprisingly, less electrophilic, and we suggest that Os 2 complexes may require access to oxidation states higher than Os 2 5+ in order to perform AOR at reasonable reaction rates.

Reactions that cleave C-C bonds and enable functionalization at both carbon sites are powerful strategic tools in synthetic chemistry. Stereodefined cyclopropyl ketones have become readily available and would be an ideal source of 3-carbon fragments, but general approaches to net C-C activation / difunctionalization are unknown. Herein we demonstrate the cross-coupling of cyclopropyl ketones with organozinc reagents and chlorotrimethylsilane to form 1,3-difunctionalized, ring-opened products. A combination of experimental and theoretical studies rule out more established mechanisms and shed light on how cooperation between the redox-active terpyridine (tpy) ligand and the nickel atom enables the C-C bond activation step. The reduced (tpy •- )Ni I species activates the C-C bond via a concerted asynchronous ring-opening transition state. The resulting alkylnickel(II) intermediate can then be engaged by aryl-, alkenyl-, and alkylzinc reagents to furnish cross-coupled products. This allows quick access to products that are difficult to make by conjugate addition methods, such as β-allylated and β -benzylated enol ethers. The utility of this approach is demonstrated in the synthesis of a key (±)-taiwaniaquinol B intermediate and the total synthesis of prostaglandin D 1 .

Oligo-α-pyridylamides offer an appealing route to polyiron complexes with short Fe-Fe separations and large room-temperature magnetic moments. A derivative of tris(2-aminoethyl)amine (H 6 tren) containing three oligo-α-pyridylamine branches and 13 nitrogen donors (H 6 L) reacts with [Fe 2 (Mes) 4 ] to yield an organic nanocage built up by two tripodal ligands with interdigitated branches (HMes = mesitylene). The nanocage has crystallographic D 3 symmetry but hosts a remarkably unsymmetric hexairon-oxo core, with a central Fe 5 (μ 5 -O) square pyramid, two oxygen donors bridging basal sites, and an additional Fe center residing in one of the two tren-like pockets. Bond valence sum (BVS) analysis, density functional theory (DFT) calculations, and electrochemical data were then used to establish the protonation state of oxygen atoms and the formal oxidation states of the metals. For this purpose, a specialized set of BVS parameters was devised for Fe 2+ -N 3- bonds with nitrogen donors of oligo-α-pyridylamides. This allowed us to formulate the compound as [Fe 6 O 2 (OH)(H 3 L)L], with nominally four Fe II ions and two Fe III ions. Mössbauer spectra indicate that the compound contains two unique Fe II sites, identified as a pair of closely spaced hydroxo-bridged metal ions in the central Fe 5 (μ 5 -O) pyramid, and a substantially valence-delocalized Fe II 2 Fe III 2 unit. Broken-symmetry DFT calculations predict strong ferromagnetic coupling between the two iron(II) ions, leading to a local S = 4 state that persists to room temperature and explaining the large magnetic moment measured at 300 K. The compound behaves as a single-molecule magnet, with magnetization dynamics detectable in zero static field and dominated by an Orbach-like mechanism with activation parameters U eff / k B = 49(2) K and τ 0 = 4(2) × 10 -10 s.

A series of chiral bowl-shaped diruthenium(II,III) tetracarboxylate catalysts were prepared and evaluated in asymmetric cyclopropanations with donor/acceptor carbenes derived from aryldiazoacetates. The diruthenium catalysts self-assembled to generate C 4 -symmetric bowl-shaped structures in an analogous manner to their dirhodium counterparts. The optimum catalyst was found to be Ru 2 ( S -TPPTTL) 4 ·BAr F [ S -TPPTTL = ( S )-2-(1,3-dioxo-4,5,6,7-tetraphenylisoindolin-2-yl)-3,3-dimethylbutanoate, BAr F = tetrakis(3,5-bis(trifluoromethyl)phenyl)borate], which resulted in the cyclopropanation of a range of substrates in up to 94% ee. Synthesis and evaluation of first-row transition-metal congeners [Cu(II/II) and Co(II/II)] invariably resulted in catalysts that afforded little to no asymmetric induction. Computational studies indicate that the carbene complexes of these dicopper and dicobalt complexes, unlike the dirhodium and diruthenium systems, are prone to the loss of carboxylate ligands, which would destroy the bowl-shaped structure critical for asymmetric induction., Competing Interests: The authors declare the following competing financial interest(s): HMLD and JKS are named inventors on a patent disclosure entitled, Chiral Diruthenium Tetracarboxylate Catalysts for Enantioselective Synthesis (International PCT Application No. PCT/US2022/015912)., (© 2023 The Authors. Published by American Chemical Society.)

Metal-metal bonded complexes are promising candidates for catalyzing redox transformations. Of particular interest is the oxidation of ammonia to dinitrogen, an important half reaction for the potential utilization of ammonia as a fuel or hydrogen carrier. This work computationally explores 30 different metal-metal bonded dimers (5 different metal centers and 6 different benzoate ligand derivatives) to explore the tunability of the redox potential when ammonia is bound to the complexes as an axial ligand, modeling the first step in ammonia oxidation electrocatalysis. We calculate the redox potentials of these compounds, making reference to experimental data when appropriate, identifying two degrees of tunability: a coarse adjustment, changing the metal center, allows for a wide range of redox potentials to be accessed (from +1.0 to -2.0 V vs. ferrocene/ferrocenium in acetonitrile solution) and a fine adjustment, the para -substituent of the benzoate derivative, which affects the redox potential in a smaller range based on the electron donating/withdrawing effects of the substituent. Ruthenium and osmium tetrabenzoate catalysts are prime candidates for next generation ammonia oxidation catalysts because their redox potentials fall within the direct ammonia fuel cell "viability zone" bracketed by the thermodynamic potentials of oxygen reduction (ORR) and nitrogen reduction (NRR). Rhodium tetrabenzoate species fall above the ORR potential, suggesting ammonia oxidation promoted by Rh 2 catalysts could instead be used to facilitate hydrogen production through coupling to hydrogen evolution at a cathode. The redox potentials of rhenium and iridium tetrabenzoate catalysts fall below the NRR potential suggesting that these compounds could be further investigated in the context of electrochemical ammonia synthesis. Each redox event studied involves electron transfer from the M-M δ* orbital regardless of choice of metal or benzoate ligand derivative; this leads us to believe that the chemical reactivity of the various studied compounds will be similar in the context of ammonia oxidation.

The observation of single-molecule magnetism in transition-metal complexes relies on the phenomenon of zero-field splitting (ZFS), which arises from the interplay of spin-orbit coupling (SOC) with ligand-field-induced symmetry lowering. Previous studies have demonstrated that the magnitude of ZFS in complexes with 3d metal ions is sometimes enhanced through coordination with heavy halide ligands (Br and I) that possess large free-atom SOC constants. In this study, we systematically probe this "heavy-atom effect" in high-spin cobalt(II)-halide complexes supported by substituted hydrotris(pyrazol-1-yl)borate ligands (Tp tBu,Me and Tp Ph,Me ). Two series of complexes were prepared: [Co II X(Tp tBu,Me )] ( 1-X ; X = F, Cl, Br, and I) and [Co II X(Tp Ph,Me )(Hpz Ph,Me )] ( 2-X ; X = Cl, Br, and I), where Hpz Ph,Me is a monodentate pyrazole ligand. Examination with dc magnetometry, high-frequency and -field electron paramagnetic resonance, and far-infrared magnetic spectroscopy yielded axial ( D ) and rhombic ( E ) ZFS parameters for each complex. With the exception of 1-F , complexes in the four-coordinate 1-X series exhibit positive D -values between 10 and 13 cm -1 , with no dependence on halide size. The five-coordinate 2-X series exhibit large and negative D -values between -60 and -90 cm -1 . Interpretation of the magnetic parameters with the aid of ligand-field theory and ab initio calculations elucidated the roles of molecular geometry, ligand-field effects, and metal-ligand covalency in controlling the magnitude of ZFS in cobalt-halide complexes.

Nitrogen heterocycles are a class of organic compounds with extremely versatile functionality. Imidines, HN[C(NH)R] 2 , are a rare class of heterocycles related to imides, HN[C(O)R] 2 , in which the O atoms of the carbonyl groups are replaced by N-H groups. The useful synthesis of the imidine compounds succinimidine and glutarimidine, as well as their partially hydrolyzed imino-imide congeners, was first described in the mid-1950s, though structural characterization is presented for the first time in this article. In the solid state, these structures are different from the proposed imidine form: succinimidine crystallizes as an imino-amine, 2-imino-3,4-dihydro-2H-pyrrol-5-amine, C 4 H 7 N 2 (1), glutarimidine as 6-imino-3,4,5,6-tetrahydropyridin-2-amine methanol monosolvate, C 5 H 9 N 3 ·CH 3 OH (2), and the corresponding hydrolyzed imino-imide compounds as amino-amides 5-amino-3,4-dihydro-2H-pyrrol-2-one, C 4 H 6 N 2 O (3), and 6-amino-4,5-dihydropyridin-2(3H)-one, C 5 H 8 N 2 O (4). Imidine 1 was also determined as the hydrochloride salt solvate 5-amino-3,4-dihydro-2H-pyrrol-2-iminium chloride-2-imino-3,4-dihydro-2H-pyrrol-5-amine-water (1/1/1), C 4 H 8 N 3 + ·Cl - ·C 4 H 7 N 3 ·H 2 O (1·HCl). As such, 1 and 2 show alternating short and long C-N bonds across the molecule, revealing distinct imino (C=NH) and amine (C-NH 2 ) groups throughout the C-N backbone. These structures provide definitive evidence for the predominant imino-amine tautomer in the solid state, which serves to enrich the previously proposed imidine-focused structures that have appeared in organic chemistry textbooks since the discovery of this class of compounds in 1883., (open access.)

Background The petroclival ligament (PL) forms the roof of Dorello's canal (DC). In humans, partial and complete ossification of this ligament have been reported. When completely ossified, DC is transformed into a bony foramen for the abducens nerve and accompanying vascular structures. As this osteological finding might have an impact on skull base surgery, this anatomical study was performed. Methodology Using 100 adult human skulls, the presence of an ossified PL was noted and classified. The diameter of the resultant bony foramen and laterality were documented. Additionally, PL was evaluated histologically in 10 heads. Results Overall, 8% of the sides were found to have partial or complete ossification of the PL. Partial ossification (type I) was noted on 3% of the sides. Completely ossified PL was identified on 5% of the sides. Some ossified ligaments (2.5%) were seen as an ossified bridge (type II), and others (2.5%) were converted into small foramina (type III). Three skulls (3%) were found to have a completely ossified ligament bilaterally. The mean diameter of the underlying DC was 0.8 mm. Partially ossified ligaments were statistically more likely to be on the right sides, and the diameter of the underlying DC was statistically smaller in type III. Histologically, the PL was found to have bone within it on three skull sides. Conclusions An ossified ligament can be found on imaging of the skull base. Moreover, during surgical approaches to the petroclival region and, specifically, DC, skull base surgeons should be cognizant of this anatomical variation., Competing Interests: The authors have declared that no competing interests exist., (Copyright © 2023, Ekanem et al.)

Electrochemical C-H functionalizations are attractive transformations, as they are capable of avoiding the use of transition metals, pre-oxidized precursors, or suprastoichiometric amounts of terminal oxidants. Herein an electrochemically tunable method was developed that enabled the divergent formation of cyclic amines or imines by applying different reaction potentials. Detailed cyclic voltammetry analyses, coupled with chronopotentiometry experiments, were carried out to provide insight into the mechanism, while atom economy was assessed through a paired electrolysis. Selective C-H amidations and imidations were achieved to afford five- to seven-membered sulfonamide motifs that could be employed for late-stage modifications., (© 2022 Wiley-VCH GmbH.)

Understanding the fundamental properties governing metal-metal interactions is crucial to understanding the electronic structure and thereby applications of multimetallic systems in catalysis, material science, and magnetism. One such property that is relatively underexplored within multimetallic systems is metal-metal bond polarity, parameterized by the electronegativities (χ) of the metal atoms involved in the bond. In heterobimetallic systems, metal-metal bond polarity is a function of the donor-acceptor (Δχ) interactions of the two bonded metal atoms, with electropositive early transition metals acting as electron acceptors and electronegative late transition metals acting as electron donors. We show in this work, through the preparation and systematic study of a series of Mo 2 M(dpa) 4 (OTf) 2 (M = Cr, Mn, Fe, Co, and Ni; dpa = 2,2'-dipyridylamide; OTf = trifluoromethanesulfonate) heterometallic extended metal atom chain (HEMAC) complexes that this expected trend in χ can be reversed. Physical characterization via single-crystal X-ray diffraction, magnetometry, and spectroscopic methods as well as electronic structure calculations supports the presence of a σ symmetry 3c/3e - bond that is delocalized across the entire metal-atom chain and forms the basis of the heterometallic Mo 2 -M interaction. The delocalized 3c/3e - interaction is discussed within the context of the analogous 3c/3e - π bonding in the vinoxy radical, CH 2 CHO. The vinoxy comparison establishes three predictions for the σ symmetry 3c/3e - bond in HEMACS: (1) an umpolung effect that causes the Mo-M interactions to become more covalent as Δχ increases, (2) distortion of the σ bonding and non-bonding orbitals to emphasize Mo-M bonding and de-emphasize Mo-Mo bonding, and (3) an increase in Mo spin population with increasing Mo-M covalency. In agreement with these predictions, we find that the Mo 2 ···M covalency increases with increasing Δχ of the Mo and M atoms (Δχ Mo-M increases as M = Cr < Mn < Fe < Co < Ni), an umpolung of the trend predicted in the absence of σ delocalization. We attribute the observed trend in covalency to the decreased energic differential (Δ E ) between the heterometal d z 2 orbital and the σ bonding molecular orbital of the Mo 2 quadruple bond, which serves as an energetically stable, "ligand"-like electron-pair donor to the heterometal ion acceptor. As M is changed from Cr to Ni, the σ bonding and nonbonding orbitals do indeed distort as anticipated, and the spin population of the outer Mo group is increased by at least a factor of 2. These findings provide a predictive framework for multimetallic compounds and advance the current understanding of the electronic structures of molecular heteromultimetallic systems, which can be extrapolated to applications in the context of mixed-metal surface catalysis and multimetallic proteins.

Hakuba's triangle is a superior cavernous sinus triangle that allows for wide and relatively safe exposure of vascular and neoplastic lesions. This study provides cadaveric measurements of the borders of Hakuba's triangle and describes its neurovascular contents in order to enrich the available literature. The anatomical borders of the Hakuba's triangle (lateral, medial, and posterior borders) were defined based on Hakuba's description and identified. Then the triangle was dissected to reveal its morphology and relationship with adjacent neurovascular structures in Embalmed Caucasian cadaveric specimens. The oculomotor nerve occupied roughly one-third of the area of the triangle and the nerve was more or less parallel to its medial border. The mean lengths of the lateral border, posterior border, and medial border were 17 mm ± 0.5 mm, 12.2 mm ± 0.4 mm, and 10.6 mm ± 0.4 mm, respectively. The mean area of Hakuba's triangle was 63.9 mm 2  ± 4.4 mm 2 . In this study, we provided cadaveric measurements of the borders of Hakuba's triangle along with descriptions of its neurovascular contents., (© 2021. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

Reaction of Co(II) nitrate with 2-methylimidazole (2mIm) yields ZIF-67, the structure of which features Co(II) ions in pseudo-tetrahedral coordination geometry. Strong antiferromagnetic interactions between Co(II) ions mediated by the 2mIm ligands lead to antiferromagnetic ordering at 22 K. Postsynthetic treatment of Co(II) ZIF-67 with 5-methyltetrazole (5mT) results in the loss of crystallinity and magnetic order. The local structure of the Co(II) ions was probed by a combination of diffuse-reflectance electronic absorption spectroscopy and Co K-edge X-ray absorption spectroscopy (in the XANES and EXAFS regions). Upon reaction with 5mT, the 4 A 2 (F)- 4 T 1 (F) and 4 A 2 (F)- 4 T 1 (P) transitions at 1140 and 585 nm, respectively, of the pseudo-tetrahedral Co(II) center in ZIF-67 become less prominent and are replaced by transitions at 990 and 475 nm attributable to the 4 T 1g (F)- 4 T 2g (F) and 4 T 1g (F)- 4 T 1g (P) transitions of a pseudo-octahedral Co(II) center, respectively. Furthermore, the 1s-3d pre-edge absorption feature in the Co K-edge XANES spectrum loses intensity during this reaction, and the edge feature becomes more sharp, consistent with a change from pseudo-T d to pseudo-O h geometry. EXAFS analysis further supports the proposed change in geometry: EXAFS data for ZIF-67 are well fitted to four Co-N scatterers at 1.99 Å, whereas the data for the 5mT-substituted compound are best fitted with 6 Co-N scatterers at 2.14 Å. Our results support the conclusion that a six-coordinate, pseudo-O h geometry is adopted upon ligand substitution. The increase in coordination number directly increases the Co-N bond distances, which in turn weakens magnetic exchange interactions. No magnetic ordering is found in the 5mT-substituted materials.

Diruthenium paddlewheel complexes supported by electron-rich anilinopyridinate (Xap) ligands were synthesized in the course of the first in-depth structural and spectroscopic interrogation of monocationic [Ru 2 (Xap) 4 Cl] + species in the Ru 2 6+ oxidation state. Despite paramagnetism of the compounds, 1 H NMR spectroscopy proved highly informative for determining the isomerism of the Ru 2 5+ and Ru 2 6+ compounds. While most compounds are found to have the polar (4,0) geometry, with all four Xap ligands in the same orientation, some synthetic procedures resulted in a mixture of (4,0) and (3,1) isomers, most notably in the case of the parent compound Ru 2 (ap) 4 Cl. The isomerism of this compound has been overlooked in previous reports. Electrochemical studies demonstrate that oxidation potentials can be tuned by the installation of electron donating groups to the ligands, increasing accessibility of the Ru 2 6+ oxidation state. The resulting Ru 2 6+ monocations were found to have the expected (π*) 2 ground state, and an in-depth study of the electronic transitions by Vis/NIR absorption and MCD spectroscopies with the aid of TD-DFT allowed for the assignment of the electronic spectra. The empty δ* orbital is the major acceptor orbital for the most prominent electronic transitions. Both Ru 2 5+ and Ru 2 6+ compounds were studied by Ru K-edge X-ray absorption spectroscopy; however, the rising edge energy is insensitive to redox changes in the compounds due to the broad line shape observed for 4d transition metal K-edges. DFT calculations indicate the presence of ligand orbitals at the frontier level, suggesting that further oxidation beyond Ru 2 6+ will be ligand-centered rather than metal-centered.

Construction of nitrogen-nitrogen triple bonds via homocoupling of metal nitrides is an important fundamental reaction relevant to a potential Nitrogen Economy . Here, we report that room temperature photolysis of Ru 2 (chp) 4 N 3 (chp - = 2-chloro-6-hydroxypyridinate) in CH 2 Cl 2 produces N 2 via reductive coupling of Ru 2 (chp) 4 N nitrido species. Computational analysis reveals that the nitride coupling transition state (TS) features an out-of-plane "zigzag" geometry instead of the anticipated planar zigzag TS. However, with intentional exclusion of dispersion correction, the planar zigzag TS geometry can also be found. Both the out-of-plane and planar zigzag TS geometries feature two important types of orbital interactions: (1) donor-acceptor interactions involving intermolecular donation of a nitride lone pair into an empty Ru-N π* orbital and (2) Ru-N π to Ru-N π* interactions derived from coupling of nitridyl radicals. The relative importance of these two interactions is quantified both at and after the TS. Our analysis shows that both interactions are important for the formation of the N-N σ bond, while radical coupling interactions dominate the formation of N-N π bonds. Comparison is made to isoelectronic Ru 2 -oxo compounds. Formation of an O-O bond via bimolecular oxo coupling is not observed experimentally and is calculated to have a much higher TS energy. The major difference between the nitrido and oxo systems stems from an extremely large driving force, ∼-500 kJ/mol, for N-N coupling vs a more modest driving force for O-O coupling, -40 to -140 kJ/mol.

Among Earth-abundant catalyst systems, iron-carbene intermediates that perform C-C bond forming reactions such as cyclopropanation of olefins and C-H functionalization via carbene insertion are rare. Detailed descriptions of the possible electronic structures for iron-carbene bonds are imperative to obtain better mechanistic insights and enable rational catalyst design. Here, we report the first square-planar iron-carbene complex ( Mes PDP Ph )Fe(CPh 2 ), where [ Mes PDP Ph ] 2- is the doubly deprotonated form of [2,6-bis(5-(2,4,6-trimethylphenyl)-3-phenyl-1 H -pyrrol-2-yl)pyridine]. The compound was prepared via reaction of the disubstituted diazoalkane N 2 CPh 2 with ( Mes PDP Ph )Fe(thf) and represents a rare example of a structurally characterized, paramagnetic iron-carbene complex. Temperature-dependent magnetic susceptibility measurements and applied-field Mössbauer spectroscopic studies revealed an orbitally near-degenerate S = 1 ground state with large unquenched orbital angular momentum resulting in high magnetic anisotropy. Spin-Hamiltonian analysis indicated that this S = 1 spin system has uniaxial magnetic properties arising from a ground M S = ±1 non-Kramers doublet that is well-separated from the M S = 0 sublevel due to very large axial zero-field splitting ( D = -195 cm -1 , E / D = 0.02 estimated from magnetic susceptibility data). This remarkable electronic structure gives rise to a very large, positive magnetic hyperfine field of more than +60 T for the 57 Fe nucleus along the easy magnetization axis observed by Mössbauer spectroscopy. Computational analysis with complete active space self-consistent field (CASSCF) calculations provides a detailed electronic structure analysis and confirms that ( Mes PDP Ph )Fe(CPh 2 ) exhibits a multiconfigurational ground state. The majority contribution originates from a configuration best described as a singlet carbene coordinated to an intermediate-spin Fe II center with a (d xy ) 2 {(d xz ),(d z 2 )} 3 (d yz ) 1 (d x 2 - y 2 ) 0 configuration featuring near-degenerate d xz and d z 2 orbitals.

The electrochemical conversion of ammonia to dinitrogen in a direct ammonia fuel cell (DAFC) is a necessary technology for the realization of a nitrogen economy. Previous efforts to catalyse this reaction with molecular complexes required the addition of exogenous oxidizing reagents or application of potentials greater than the thermodynamic potential for the oxygen reduction reaction-the cathodic process of a DAFC. We report a stable metal-metal bonded diruthenium complex that spontaneously produces dinitrogen from ammonia under ambient conditions. The resulting reduced diruthenium material can be reoxidized with oxygen for subsequent reactions with ammonia, demonstrating its ability to spontaneously promote both half-reactions necessary for a DAFC. The diruthenium complex also acts as a redox mediator for the electrocatalytic oxidation of ammonia to dinitrogen at potentials as low as -255 mV versus Fc 0/+ and operates below the oxygen reduction reaction potential in alkaline conditions, thus achieving a thermodynamic viability relevant for the future development of DAFCs., (© 2021. The Author(s), under exclusive licence to Springer Nature Limited.)

Background: The blood supply to the skull base is important to surgeons and those performing interventional and diagnostic procedures in this region. However, 1 vessel with a vast distribution in this area, the dorsal meningeal artery (DMA), has had few anatomic studies performed to investigate not only its normal anatomy but also its variations. Therefore the current study aimed to analyze the DMA via cadaveric dissection., Methods: In 10 adults, latex-injected, cadaveric heads (20 sides), the DMA was dissected using a surgical microscope. This artery and its branches were documented and measured., Results: A DMA was identified on all sides. In the majority (85%), it was a branch of the meningohypophysial trunk or common stem with either the inferior hypophysial or tentorial arteries and always had branches that traversed the basilar venous plexus. Multiple branches of the DMA were identified and categorized as bony, dural, neural, and vascular., Conclusions: Surgeons operating at the skull base or clinicians interpreting imaging of this area should have a good working knowledge of the DMA and its typical and variant anatomy., (Copyright © 2021 Elsevier Inc. All rights reserved.)

Atom-efficient syntheses of the tetraethylammonium Roussin black sulfur and selenium salts ((Et 4 N)[Fe 4 E 3 (NO) 7 ], E = S, Se) as well as their 15 N-labeled counterparts are described herein. Broken-symmetry DFT calculations were conducted on both complexes to model an antiferromagnetic interaction between the apical {FeNO} 7 unit, S ap = 3/2, and the three basal {Fe(NO) 2 } 9 units, S bas = 1/2. The calculated J values are -1813 and -1467 cm -1 for the sulfur and selenium compounds, respectively. The mechanism for antiferromagnetic exchange in both compounds was deduced to be direct exchange on the basis of the partially overlapping magnetic orbitals with orbital density only residing on the Fe-centers. The obtained Mössbauer parameters are most consistent with the calculated M S = 0 broken-symmetry state for both complexes. The values for J have been determined with variable-temperature 15 N NMR experiments. Values of -1660 and -1430 cm -1 for the sulfur and selenium compounds, respectively, were obtained by fits to the variable-temperature NMR data, further validating the broken-symmetry M S = 0 model of the electronic structure.

Aneurysmal subarachnoid hemorrhage (aSAH) is an emergent condition requiring rapid intervention and prolonged monitoring. There are few recommendations regarding the management of aSAH in pregnancy. We identified all available literature and compiled management decisions as well as reported outcomes through a systematic literature review without meta-analysis to provide recommendations for management of aSAH during pregnancy. We included a total of 23 articles containing 54 cases of pregnancy-related aSAH in our review. From these reports and other literature, we evaluated information on aSAH pathophysiology, diagnosis, and management with respect to pregnancy. Early transfer to an appropriate facility with neurocritical care, a high-risk obstetric service, and a neurosurgery team available is crucial for the management of aSAH in pregnancy. Intensive monitoring and a multidisciplinary approach remain fundamental to ensure maternal and fetal health., (© 2021. The Author(s), under exclusive licence to Springer-Verlag GmbH, DE part of Springer Nature.)

Purpose: Inflammatory myofibroblastic tumor (IMT) is a rare neoplastic tumor type of intermediate biological potential, only recently distinguished from the non-neoplastic category of inflammatory pseudotumor (IP). The literature describes very few cases of IMTs arising in the central nervous system (CNS), and the distinguishing clinical, pathological, and molecular features of IMT-CNS are not well understood. Our purpose is to publish a case of an IMT-CNS with a novel DCTN1-ALK gene fusion, furthering in the literature's characterization of a rare tumor type., Methods: Review of the literature included a PubMed Database search of articles found by the following searches: "Inflammatory myofibroblastic tumor;" "Inflammatory myofibroblastic tumor central nervous system;" "ALK gene fusion;" and "DCTN1-ALK gene fusion." Inclusion of articles discovered by these search terms was determined through critical appraisal of article relevance, number of citations, cross-citation within articles of interest, and rare findings with conflicting conclusions in an effort to reduce publication bias., Results: We present a case of IMT-CNS with several distinctive molecular features including a DCTN1-ALK gene fusion, the first of its kind described in an intracranial IMT., Conclusion: IMT is an infrequent tumor type and its presentation within the CNS is exceedingly rare. The paucity of cases, along with the ambiguity of terminology in the literature, has stunted accurate clinical, pathological, and molecular characterization of IMT-CNS. Our case report improves the characterization of the recently appreciated category of IMT-CNS so that connections between phenotype and prognosis, and between genotype and treatment, can eventually be made.

Iron-based extended metal atom chains (EMACs) are potentially high-spin molecules with axial magnetic anisotropy and thus candidate single-molecule magnets (SMMs). We herein compare the tetrairon(ii), halide-capped complexes [Fe4(tpda)3Cl2] (1Cl) and [Fe4(tpda)3Br2] (1Br), obtained by reacting iron(ii) dihalides with [Fe2(Mes)4] and N2,N6-di(pyridin-2-yl)pyridine-2,6-diamine (H2tpda) in toluene, under strictly anhydrous and anaerobic conditions (HMes = mesitylene). Detailed structural, electrochemical and Mössbauer data are presented along with direct-current (DC) and alternating-current (AC) magnetic characterizations. DC measurements revealed similar static magnetic properties for the two derivatives, with χMT at room temperature above that for independent spin carriers, but much lower at low temperature. The electronic structure of the iron(ii) ions in each derivative was explored by ab initio (CASSCF-NEVPT2-SO) calculations, which showed that the main magnetic axis of all metals is directed close to the axis of the chain. The outer metals, Fe1 and Fe4, have an easy-axis magnetic anisotropy (D = -11 to -19 cm-1, |E/D| = 0.05-0.18), while the internal metals, Fe2 and Fe3, possess weaker hard-axis anisotropy (D = 8-10 cm-1, |E/D| = 0.06-0.21). These single-ion parameters were held constant in the fitting of DC magnetic data, which revealed ferromagnetic Fe1-Fe2 and Fe3-Fe4 interactions and antiferromagnetic Fe2-Fe3 coupling. The competition between super-exchange interactions and the large, noncollinear anisotropies at metal sites results in a weakly magnetic non-Kramers doublet ground state. This explains the SMM behavior displayed by both derivatives in the AC susceptibility data, with slow magnetic relaxation in 1Br being observable even in zero static field.

The molecular processes that accompany dynamic mechanical response to large deformations at high strain rate (≈1000 s -1 or higher) underlie the early stages of damage in materials, but understanding of material response in this regime is typically limited to macroscopic constitutive equations. Here, spiropyran mechanophores are embedded in very short, stress-bearing strands in silicone elastomers, and their mechanochromic response to uniaxial compression is explored in a Split Hopkinson Pressure (or Kolsky) Bar. At strain rates of 1000 s -1 , the onset of mechanochromism occurs at lower strains, but higher stresses, than in the same materials under quasi-static loading. Similar to quasi-static loading, however, a negligible effect of mechanophore structure on the critical strain for colorimetric onset is observed. The results suggest that nonequilibrium, inhomogeneous local tension distributions in the elastomers lead to greater stress in individual strands than at the same strains under equilibrium loading, but that within the regions of force concentration, mechanochromic onset is determined primarily by a limiting local strain threshold., (© 2020 Wiley-VCH GmbH.)

Coordination complexes that possess large magnetic anisotropy (otherwise known as zero-field splitting, ZFS) have possible applications in the field of magnetic materials, including single molecule magnets (SMMs). Previous studies have explored the role of coordination number and geometry in controlling the magnetic anisotropy and SMM behavior of high-spin ( S = 3/2) Co(II) complexes. Building upon these efforts, the present work examines the impact of ligand oxidation state and structural distortions on the spin states and ZFS parameters of pentacoordinate Co(II) complexes. The five complexes included in this study ( 1 - 5 ) have the general formula, [Co(Tp Ph2 )( L X,Y )] n + (X = O, S; Y = N, O; n = 0 or 1), where Tp Ph2 is the scorpionate ligand hydrotris(3,5-diphenyl-pyrazolyl)borate(1-) and L X,Y are bidentate dioxolene-type ligands that can access multiple oxidation states. The specific L X,Y ligands used herein are 4,6-di- tert -butyl substituted o -aminophenolate and o -aminothiophenolate ( 1 and 2 , respectively), o -iminosemiquinonate and o -semiquinonate radicals ( 3 and 4 , respectively), and o -iminobenzoquinone ( 5 ). Each complex exhibits a distorted trigonal bipyramidal geometry, as revealed by single-crystal X-ray diffraction. Direct current (dc) magnetic susceptibility experiments confirmed that the complexes with closed-shell ligands ( 1 , 2 , and 5 ) possess S = 3/2 ground states with negative D -values (easy-axis anisotropy) of -41, -78, and -30 cm -1 , respectively. For 3 and 4 , antiferromagnetic coupling between the Co(II) center and o -(imino)semiquinonate radical ligand results in S = 1 ground states that likewise exhibit very large and negative anisotropy (-100 > D > -140 cm -1 ). Notably, ZFS was measured directly for each complex using far-infrared magnetic spectroscopy (FIRMS). In combination with high-frequency and -field electron paramagnetic resonance (HFEPR) studies, these techniques provided precise spin-Hamiltonian parameters for complexes 1 , 2 , and 5 . Multireference ab initio calculations, using the CASSCF/NEVPT2 approach, indicate that the strongly negative anisotropies of these Co(II) complexes arise primarily from distortions in the equatorial plane due to constrictions imposed by the Tp Ph2 ligand. This effect is further amplified by cobalt(II)-radical exchange interactions in 3 and 4 .

Background: Atypical teratoid rhabdoid tumor (ATRT) is a rare, highly malignant central nervous system neoplasm classified as an embryonal grade IV neoplasm by the World Health Organization. ATRT generally occurs in children younger than 3 years, with 85 pathologically confirmed cases reported in adults. It is most commonly supratentorial, with only 9 confirmed adult cases localized to the pineal region., Case Description: The case is described of a 29-year-old man with a history of chronic migraines and a previously negative computed tomography scan of the head presenting with worsening headaches and new-onset diplopia with upward gaze palsy. Computed tomography and magnetic resonance imaging showed a hemorrhagic pineal mass with extension into the right thalamus. After resection, the immunohistochemical staining and cytogenetic profile proved consistent with ATRT, making it the ninth reported case of pineal ATRT in an adult, which was treated aggressively with good outcome., Conclusions: Adult ATRT is rare, especially in the pineal region, with only 9 cases reported. Because of the aggressiveness, ATRT must be considered in the differential diagnosis of pineal region lesions because early diagnosis and aggressive treatment are key to prolonged survival., (Copyright © 2020 Elsevier Inc. All rights reserved.)

The metastable purple [(Py5Me2)RuIII(N3)]2+ ion reacts with PPh3 at room temperature to form the phosphinimine complex [(Py5Me2)RuII(N(H)PPh3)]2+ and free [H2NPPh3]+ in a combined 23% conversion. Mechanistic studies suggest that this is the first metallo-Staudinger reaction of a late transition metal that bypasses the nitrido mechanism and instead utilizes a Ru-N[double bond, length as m-dash]N[double bond, length as m-dash]N-PPh3 phosphazide intermediate.

Background: Diffusion tensor imaging (DTI) is a magnetic resonance-based imaging technique that can provide important information about the underlying structure and integrity of the white matter in the brain. Tractography, a DTI postprocessing technique, can provide a detailed model of individual white matter fiber tracts. Knowledge of these tracts may be beneficial in the surgical planning and execution for neurosurgical patients. Case Report: We review the basic principles behind DTI and present an illustrative case in which DTI was used to delineate the relationship of eloquent white matter tracts to a cavernous malformation in a patient undergoing resection. Conclusion: The use of DTI during preoperative planning allows the neurosurgeon to understand if a lesion is disrupting, infiltrating, or altering the course of local white matter tracts. With the combined use of DTI and intraoperative neuronavigation, the neurosurgeon can better identify and avoid white matter tracts, not only in the local area of resection but also during approach to the lesion, thereby reducing the risk of damage to vital cortical pathways and subsequent functional impairment., (©2020 by the author(s); Creative Commons Attribution License (CC BY).)

This work represents an important step in the quest to make hetero multi metallic molecules featuring specific metal types and complicated metal ratios. The rational design, synthesis, and characterization of a complex hetero tri metallic single-source molecular precursor for the next generation sodium-ion battery cathode material, Na 2 Mn 2 FeO 6 , is described. A unique pentametallic platform [Mn II (ptac) 3 -Na-Mn III (acac) 3 -Na-Mn II (ptac) 3 ] ( 1 ) was derived from the known polymeric structure of [NaMn II (acac) 3 ] ∞ , through a series of elaborate design procedures, such as mixed-ligand, unsymmetric ligand, and mixed-valent approaches. Importantly, the application of those techniques results in a molecule with distinctively different transition metal positions in terms of ligand environment and oxidation states. An isovalent substitution of Fe III for the central Mn III ion forms the target hetero tri metallic precursor [Mn II (ptac) 3 -Na-Fe III (acac) 3 -Na-Mn II (ptac) 3 ] ( 3 ) with an appropriate metal ratio of Na:Mn:Fe = 2:2:1. The arrangement of metal ions and ligands in this pentametallic assembly was confirmed by single crystal X-ray investigation. The unambiguous assignment of the positions and oxidation states of the Periodic Table neighbors Fe and Mn in 3 has been achieved by a combination of investigative techniques that include synchrotron resonant diffraction, X-ray multiwavelength anomalous diffraction, X-ray fluorescence spectroscopy, Mössbauer spectroscopy, and gas-phase DART mass spectrometry. The hetero tri metallic single-source precursor 3 was shown to exhibit a clean decomposition pattern yielding the phase-pure P2-Na 2 Mn 2 FeO 6 quaternary oxide with high uniformity of metal ion distribution as confirmed by electron microscopy.

Copper(I) iodide complexes are well known for displaying a diverse array of structural features even when only small changes in ligand design are made. This structural diversity is well displayed by five copper(I) iodide compounds reported here with closely related piperidine-2,6-di-thione (SNS), isoindoline-1,3-di-thione (SNS6), and 6-thioxopiperidin-2-one (SNO) ligands: di-μ-iodido-bis-[(aceto-nitrile-κ N )(6-sulfanylidenepiperidin-2-one-κ S )copper(I)], [Cu 2 I 2 (CH 3 CN) 2 (C 5 H 7 NOS) 2 ] ( I ), bis-(aceto-nitrile-κ N )tetra-μ 3 -iodido-bis-(6-sulfanylidenepiperidin-2-one-κ S )- tetra-hedro -tetra-copper(I), [Cu 4 I 4 (CH 3 CN) 4 (C 5 H 7 NOS) 4 ] ( II ), catena -poly[[(μ-6-sulfanylidenepiperidin-2-one-κ 2 O : S )copper(I)]-μ 3 -iodido], [CuI(C 5 H 7 NOS)] n ( III ), poly[[(piperidine-2,6-di-thione-κ S )copper(I)]-μ 3 -iodido], [CuI(C 5 H 7 NS 2 )] n ( IV ), and poly[[(μ-isoindoline-1,3-di-thione-κ 2 S : S )copper(I)]-μ 3 -iodido], [CuI(C 8 H 5 NS 2 )] n ( V ). Compounds I and II crystallize as discrete dimeric and tetra-meric complexes, whereas III , IV , and V crystallize as polymeric two-dimensional sheets. To the best of our knowledge, compound III is the first instance of an extended hexa-gonal [Cu 3 I 3 ] structure that is not supported by bridging ligands. Structures I , II , and IV display weak to moderately strong Cu⋯Cu cuprophilic inter-actions [Cu⋯Cu inter-nuclear distances range between 2.5803 (10) and 2.8485 (14) Å]. All structures except III display weak hydrogen-bonding inter-actions between the N-H of the ligand and the μ 2 and μ 3 -I - atoms. Structure III contains classical N-H⋯O inter-actions between the SNO ligands that connect the mol-ecules in a three-dimensional framework. Complex V features π-π stacking inter-actions between the aryl rings of the SNS6 ligands within the same polymeric sheet. In structure IV , there were three partially occupied solvent mol-ecules of di-chloro-methane and one partially occupied mol-ecule of aceto-nitrile present in the asymmetric unit. The SQUEEZE routine [Spek (2015 ▸). Acta Cryst . C 71 , 9-18] was used to correct the diffraction data for diffuse scattering effects and to identify the solvent mol-ecules. The given chemical formula and other crystal data do not take into account the solvent mol-ecules., (© Wheaton et al. 2020.)

The unsymmetrical coordination of gold(I) by 2,2'-bipyridine (bipy) in some planar, three-coordinate cations has been examined by crystallographic and computational studies. The salts [(Ph 3 P)Au(bipy)]XF 6 (X = P, As, Sb) form an isomorphic series in which the differences in Au-N distances range from 0.241(2) to 0.146(2) Å. A second polymorph of [(Ph 3 P)Au(bipy)]AsF 6 has also been found. Both polymorphs exhibit similar structures. The salts [(Et 3 P)Au(bipy)]XF 6 (X = P, As, Sb) form a second isostructural series. In this series the unsymmetrical coordination of the bipy ligand is maintained, but the gold ions are disordered over two unequally populated positions that produce very similar overall structures for the cations. Although many planar, three-coordinate gold(I) complexes are strongly luminescent, the salts [(R 3 P)Au(bipy)]XF 6 (R = Ph or Et; X = P, As, Sb) are not luminescent as solids or in solution. Computational studies revealed that a fully symmetrical structure for [(Et 3 P)Au(bipy)] + is 7 kJ/mol higher in energy than the observed unsymmetrical structure and is best described as a transition state between the two limiting unsymmetrical geometries. The Au-N bonding has been examined by natural resonance theory (NRT) calculations using the "12 electron rule". The dominant Lewis structure is one with five lone pairs on Au and one bond to the P atom, which results in a saturated (12 electron) gold center and thereby inhibits the formation of any classical, 2 e - bonds between the gold and either of the bipy nitrogen atoms. The nitrogen atoms may instead donate a lone pair into an empty Au-P antibonding orbital, resulting in a three-center, four-electron (3 c /4e) P-Au-N bond. The binuclear complex, [μ 2 -bipy(AuPPh 3 ) 2 ](PF 6 ) 2 , has also been prepared and shown to have an aurophillic interaction between the two gold ions, which are separated by 3.0747(3) Å. Despite the aurophillic interaction, this binuclear complex is not luminescent.

Significant progress has been made in the past 10-15 years on the design, synthesis, and properties of multimetallic coordination complexes with heterometallic metal-metal bonds that are paramagnetic. Several general classes have been explored including heterobimetallic compounds, heterotrimetallic compounds of either linear or triangular geometry, discrete molecular compounds containing a linear array of more than three metal atoms, and coordination polymers with a heterometallic metal-metal bonded backbone. We focus in this Review on the synthetic methods employed to access these compounds, their structural features, magnetic properties, and electronic structure. Regarding the metal-metal bond distances, we make use of the formal shortness ratio (FSR) for comparison of bond distances between a broad range of metal atoms of different sizes. The magnetic properties of these compounds can be described using an extension of the Goodenough-Kanamori rules to cases where two magnetic ions interact via a third metal atom. In describing the electronic structure, we focus on the ability (or not) of electrons to be delocalized across heterometallic bonds, allowing for rationalizations and predictions of single-molecule conductance measurements in paramagnetic heterometallic molecular wires.

The bis(2-pyridylthio)methanidopalladium(II) pincer complex (1), containing a Pd-C bond, was obtained from the reaction of bis(2-pyridylthio)methane (H 2 L) with palladium(II) acetate in toluene under reflux. When palladium(II) trifluoroacetate was used, H 2 L reacted to generate the tetrakis(pyridine-2-thiol)palladium(II) complex (2). Complex 2 was converted to a heterobimetallic palladium(II)-iron(II) paddlewheel complex (3) upon treatment with iron(II) triflate in the presence of a base in acetonitrile at room temperature.

Novel mixed-ligand rhodium(II) paddlewheel complexes incorporating tethered axial thioether ligands have been synthesized and characterized. The thioether moiety is essential for high yields and the suppression of byproducts in cyclopropanation reactions using an electron-deficient diazoacetate. Crystal structures, UV-vis analysis, and cyclic voltammetry experiments shed light on the catalytic performance of the complexes.

The coordination chemistry of Co(ii) with the chelating dicarboxylate ligand esp (esp = α,α,α',α'-tetramethyl-1,3-benzenedipropionate) is explored. We report here the bimetallic paddlewheel-type dimer, Co2(esp)2(EtOH)2 (1), and a bowl-shaped, heptanuclear coordination cluster, Co7(OH)4(Hesp)2(esp)4(MeCN)2·4MeCN (2). Crystal structures of both complexes are reported as well as their magnetic properties, which indicate antiferromagnetic interactions among the Co(ii) ions.

Zeolitic imidazolate frameworks (ZIFs) with open-shell transition metal nodes represent a promising class of highly ordered light harvesting antennas for photoenergy applications. However, their charge transport properties within the framework, the key criterion to achieve efficient photoenergy conversion, are not yet explored. Herein, we report the first direct evidence of a charge transport pathway through node-to-node communication in both ground state and excited state ZIFs using the combination of paramagnetic susceptibility measurements and time-resolved optical and X-ray absorption spectroscopy. These findings provide unprecedented new insights into the photoactivity and charge transport nature of ZIF frameworks, paving the way for their novel application as light harvesting arrays in diverse photoenergy conversion devices.

The paddlewheel complex Ru 2 (chp) 4 Cl (1-Cl, chp = 6-chloro-2-oxypyridinate), upon reduction with Zn, has been previously shown to dimerize to [Ru 2 (chp) 4 ] 2 (2), blocking further chemistry at the Ru 2 (II,II) axial site [ Inorg. Chem. 2015 , 54 , 8571 - 8589 ]. Functionalization of the chp ligand at the 3 and 5 positions with either bromine (dbchpH = 3,5-dibromo-6-chloro-2-pyridone) or trimethylsilyl (TMS) groups (dsichpH = 6-chloro-3,5-bis(trimethylsilyl)-2-pyridone) allows for the preparation of the Ru 2 (II,II) paddlewheel complexes Ru 2 (dbchp) 4 (3) and Ru 2 (dsichp) 4 (6), respectively, neither of which shows evidence of dimerization. Though the utilization of 3 is limited due to insolubility, complex 6 is soluble even in typically non-coordinating solvents, forming a stable κ 1 -axial adduct in CH 2 Cl 2 (6-CH 2 Cl 2 ) and showing evidence of an axial interaction with n-decane. The first example of an axially free Ru 2 (II,II) complex with a 3 A ground state is observed upon crystallization of 6 from benzene (6-C 6 D 6 ). Complex 6 is accessed via Zn reduction of Ru 2 (dsichp) 4 Cl (4-Cl), which along with Ru 2 (dsichp) 4 N 3 (4-N 3 ), show similar structural and electronic properties to their non-TMS-substituted analogues, 1-Cl and 1-N 3 . Photolysis of 4-N 3 in frozen solution generates Ru 2 (dsichp) 4 N (5); no N atom transfer to PPh 3 is observed upon room temperature photolysis in fluid solution.

Clean axial ligand substitution reactions of heterometallic extended metal atom chains (HEMACs) supported by the dpa ligand (dpa = 2,2'-dipyridylamine) have been synthetically challenging due to side reactions that alter the trimetallic core. Following the hypothesis that a heterometallic core containing second-row transition metals would be more robust toward ligand substitution, we report the synthesis of three new heterotrimetallic compounds, Mo 2 Ni(dpa) 4 (OTf) 2 (1), Mo 2 Ni(dpa) 4 (NCS) 2 (2), and Mo 2 Ni(dpa) 4 (NCSe) 2 (3) that are obtained cleanly and in good yield. Compound 1 may be synthesized either directly by reaction of Ni(OTf) 2 with Mo 2 (dpa) 4 (4) or indirectly, by reaction of Mo 2 Ni(dpa) 4 Cl 2 (5) with 2 equiv of TlOTf. Axial ligand substitution on 1 via solutions containing NaNCS or KNCSe afford 2 or 3, respectively. X-ray crystal structures of 1, 2, and 3 present short Mo-Ni distances of 2.458(8)Å /2.47(1) Å, 2.548(1), and 2.546(1), respectively. Density functional theory (DFT) calculations indicate a 3-center 3-electron σ bonding interaction between the Mo 2 quadruply bonded core and the Ni in both 1 and 2. These complexes were analyzed by SQUID magnetometry, supporting the presence of a high spin Ni 2+ center with S = 1.

Palladium(II) acetate (1) and two new complexes of the ligand α,α,α',α'-tetramethyl-1,3-benzenedipropionate (esp 2- ), C s -Pd 3 (esp) 3 ( C s -2) and C 3 h -Pd 3 (esp) 3 ( C 3 h -2), are studied in the solid state and in solution. Variable-temperature NMR and DFT studies of C s -2 reveal an unusual shielding region above the Pd atoms. The compounds show a surprising quasi-reversible reduction between -880 and -1200 mV versus Fc/Fc + , and the Pd 3 (esp) 3 complexes may be cleanly reduced electrochemically. EPR spectra of reduced samples show pseudo-axial signals with 105 Pd hyperfine coupling, consistent with unprecedented, isostructural Pd 3 5+ species with a valence-trapped Pd II -Pd II -Pd I electronic structure.

The computation of nuclear second derivatives of energy, or the nuclear Hessian, is an essential routine in quantum chemical investigations of ground and transition states, thermodynamic calculations, and molecular vibrations. Analytic nuclear Hessian computations require the resolution of costly coupled-perturbed self-consistent field (CP-SCF) equations, while numerical differentiation of analytic first derivatives has an unfavorable 6 N ( N = number of atoms) prefactor. Herein, we present a new method in which grid computing is used to accelerate and/or enable the evaluation of the nuclear Hessian via numerical differentiation: NUMFREQ@Grid. Nuclear Hessians were successfully evaluated by NUMFREQ@Grid at the DFT level as well as using RIJCOSX-ZORA-MP2 or RIJCOSX-ZORA-B2PLYP for a set of linear polyacenes with systematically increasing size. For the larger members of this group, NUMFREQ@Grid was found to outperform the wall clock time of analytic Hessian evaluation; at the MP2 or B2LYP levels, these Hessians cannot even be evaluated analytically. We also evaluated a 156-atom catalytically relevant open-shell transition metal complex and found that NUMFREQ@Grid is faster (7.7 times shorter wall clock time) and less demanding (4.4 times less memory requirement) than an analytic Hessian. Capitalizing on the capabilities of parallel grid computing, NUMFREQ@Grid can outperform analytic methods in terms of wall time, memory requirements, and treatable system size. The NUMFREQ@Grid method presented herein demonstrates how grid computing can be used to facilitate embarrassingly parallel computational procedures and is a pioneer for future implementations.

The new heterometallic chain compounds Mo 2 Ni(dpa) 4 Cl 2 (1) and [Mo 2 Ni(dpa) 4 Cl 2 ]OTf (2) (dpa=2,2'-dipyridylamine) have been prepared and studied by crystallography and magnetic susceptibility, among other methods. Oxidation of 1 to 2 removes an electron from the multiply bonded Mo 2 unit, consistent with the formulation of 2 containing a (Mo 2 ) 5+ ⋅⋅⋅(Ni) 2+ core. While 1 contains an S=1, pseudo-octahedral Ni II ion, 2 has an S=3/2 ground state, in which the two Ni II unpaired electrons, one in a localized δ-orbital and one in a heavily delocalized σ nb -orbital are joined by an unpaired electron in a Mo-Mo δ-orbital. The S=3/2 ground state is persistent to 300 K, evidencing strong ferromagnetic coupling of the Mo 2 and Ni spins with J≥150 cm -1 . This ferromagnetic interaction occurs via delocalization of a σ nb -electron across all three metal atoms, forcing ferromagnetic alignment of electrons in orthogonal Ni and Mo 2 δ-symmetry orbitals. We anticipate that this new means of coupling spins can be used as a design principle for the preparation of new compounds with high spin ground states., (© 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Nitrene transfer (NT) reactions represent powerful and direct methods to convert C-H bonds into amine groups that are prevalent in many commodity chemicals and pharmaceuticals. The importance of the C-N bond has stimulated the development of numerous transition-metal complexes to effect chemo-, regio-, and diastereoselective NT. An ongoing challenge is to understand how subtle interactions between catalyst and substrate influence the site-selectivity of the C-H amination event. In this work, we explore the underlying reasons why Ag(tpa)OTf (tpa = tris(pyridylmethyl)amine) prefers to activate α-conjugated C-H bonds over 3° alkyl C(sp 3 )-H bonds and apply these insights to reaction optimization and catalyst design. Experimental results suggest possible roles of noncovalent interactions (NCIs) in directing the NT; computational studies support the involvement of π···π and Ag···π interactions between catalyst and substrate, primarily by lowering the energy of the directed transition state and reaction conformers. A simple Hess's law relationship can be employed to predict selectivities for new substrates containing competing NCIs. The insights presented herein are poised to inspire the design of other catalyst-controlled C-H functionalization reactions.