Unmasking the constitution and bonding of the proposed lithium nickelate “Li3NiPh3(solv)3”: revealing the hidden C6H4 ligand

More than four decades ago, a complex identified as the planar homoleptic lithium nickelate “Li₃NiPh₃(solv)₃” was reported by Taube and co-workers. This and subsequent reports involving this complex have lain dormant since; however, the absence of an X-ray diffraction structure leaves questions as to the nature of the Ni–PhLi bonding and the coordination geometry at Ni. By systematically evaluating the reactivity of Ni(COD)₂ with PhLi under different conditions, we have found that this classical molecule is instead a unique octanuclear complex, [{Li₃(solv)₂Ph₃Ni}₂(μ-η²:η²-C₆H₄)] (5). This is supported by X-ray crystallography and solution-state NMR studies. A theoretical bonding analysis from NBO, QTAIM, and ELI perspectives reveals extreme back-bonding to the bridging C₆H₄ ligand resulting in dimetallabicyclobutane character, the lack of a Ni–Ni bond, and pronounced σ-bonding between the phenyl carbanions and nickel, including a weak σ_C–Li → s_Ni interaction with the C–Li bond acting as a σ-donor. Employing PhNa led to the isolation of [Na₂(solv)₃Ph₂NiCOD]₂ (7) and [Na₂(solv)₃Ph₂(NaC₈H₁₁)Ni(COD)]₂ (8), which lack the benzyne-derived ligand. These findings provide new insights into the synthesis, structure, bonding and reactivity of heterobimetallic nickelates, whose prevalence in organonickel chemistry and catalysis is likely greater than previously believed.

We disclose the actual octanuclear nature of the major compound from reacting Ni(COD)₂ and PhLi, assigned for more than four decades as ‘Li₃NiPh₃(solv)₃’. We provide a thorough bonding analysis and discuss its potential implications in catalysis.     

DFT insight into asymmetric alkyl–alkyl bond formation via nickel-catalysed enantioconvergent reductive coupling of racemic electrophiles with olefins

A DFT study has been conducted to understand the asymmetric alkyl–alkyl bond formation through nickel-catalysed reductive coupling of racemic alkyl bromide with olefin in the presence of hydrosilane and K₃PO₄. The key findings of the study include: (i) under the reductive experimental conditions, the Ni(ii) precursor is easily activated/reduced to Ni(0) species which can serve as an active species to start a Ni(0)/Ni(ii) catalytic cycle. (ii) Alternatively, the reaction may proceed via a Ni(i)/Ni(ii)/Ni(iii) catalytic cycle starting with a Ni(i) species such as Ni(i)–Br. The generation of a Ni(i) active species via comproportionation of Ni(ii) and Ni(0) species is highly unlikely, because the necessary Ni(0) species is strongly stabilized by olefin. Alternatively, a cage effect enabled generation of a Ni(i) active catalyst from the Ni(ii) species involved in the Ni(0)/Ni(ii) cycle was proposed to be a viable mechanism. (iii) In both catalytic cycles, K₃PO₄ greatly facilitates the hydrosilane hydride transfer for reducing olefin to an alkyl coupling partner. The reduction proceeds by converting a Ni–Br bond to a Ni–H bond via hydrosilane hydride transfer to a Ni–alkyl bond via olefin insertion. On the basis of two catalytic cycles, the origins for enantioconvergence and enantioselectivity control were discussed.

The enantioconvergent alkyl–alkyl coupling involves two competitive catalytic cycles with nickel(0) and nickel(i) active catalysts, respectively. K₃PO₄ plays a crucial role to enable the hydride transfer from hydrosilane to nickel–bromine species.     

Ligand-field transition-induced C–S bond formation from nickelacycles

Photoexcitation is one of the acknowledged methods to activate Ni-based cross-coupling reactions, but factors that govern the photoactivity of organonickel complexes have not yet been established. Here we report the excited-state cross-coupling activities of Ni(ii) metallacycle compounds, which display ∼10⁴ times enhancement for the C–S bond-forming reductive elimination reaction upon Ni-centered ligand-field transitions. The effects of excitation energy and ancillary ligands on photoactivity have been investigated with 17 different nickelacycle species in combination with four corresponding acyclic complexes. Spectroscopic and computational electronic structural characterizations reveal that, regardless of coordinated species, d–d transitions can induce Ni–C bond homolysis, and that the reactivity of the resulting Ni(i) species determines the products of the overall reaction. The photoactivity mechanism established in this study provides general insights into the excited-state chemistry of organonickel(ii) complexes.

d–d excitations can accelerate C–S reductive eliminations of nickelacycles via intersystem crossing to a repulsive ³(C-to-Ni charge transfer) state inducing Ni–C bond homolysis. This homolytic photoreactivity is common for organonickel(ii) complexes.     

Nickel Phosphinidene Molecular Clusters from Organocyclophosphine Precursors

We report a new family of nickel phosphinidene molecular clusters synthesized from the reaction of bis(1,5-cyclooctadiene)nickel(0) ([Ni(cod)₂]) with organocyclophosphine and trialkylphosphine. We found that [Ni(cod)₂] cleaves the organocyclophosphine P−P bonds to generate phosphinidene groups, establishing the cyclic molecules as valuable precursors for making charge-neutral molecular clusters passivated by two-electron donor capping ligands. The formation of the cluster core structure is controlled by the bulkiness of the precursor and of the capping ligand. As a demonstration of this new cluster-forming reaction, we describe three clusters with different core nuclearity and degree of ligation: Ni₁₂(PMe)₁₀(PEt₃)₈, Ni₈(PMe)₆(PMe₃)₈, and Ni₈(PiPr)₆(PMe₃)₆. In addition, we show that the larger cluster, Ni₁₂(PMe)₁₀(PEt₃)₈, can be used as a low temperature single-source molecular precursor to the catalytically active nickel phosphide phase Ni₂P.     

Conformational Effects of [Ni2(μ‐ArS)2] Cores on Their Electrocatalytic Activity

Two nickel complexes supported by tridentate NS₂ ligands, [Ni₂(κ‐N,S,S,S′‐N^Ph{CH₂(MeC₆H₂R′)S}₂)₂] ( 1 ; R′=3,5‐(CF₃)₂C₆H₃) and [Ni₂(κ‐N,S,S,S′‐N^iBu{CH₂C₆H₄S}₂)₂] ( 2 ), were prepared as bioinspired models of the active site of [NiFe] hydrogenases. The solid‐state structure of 1 reveals that the [Ni₂(μ‐ArS)₂] core is bent, with the planes of the nickel centers at a hinge angle of 81.3(5)°, whereas 2 shows a coplanar arrangement between both nickel(II) ions in the dimeric structure. Complex 1 electrocatalyzes proton reduction from CF₃COOH at ?1.93 (overpotential of 1.04 V, with i_cat/i_p≈21.8) and ?1.47 V (overpotential of 580 mV, with i_cat/i_p≈5.9) versus the ferrocene/ferrocenium redox couple. The electrochemical behavior of 1 relative to that of 2 may be related to the bent [Ni₂(μ‐ArS)₂] core, which allows proximity of the two Ni???Ni centers at 2.730(8) Å; thus possibly favoring H⁺ reduction. In contrast, the planar [Ni₂(μ‐ArS)₂] core of 2 results in a Ni???Ni distance of 3.364(4) Å and is unstable in the presence of acid.     

Multicentered bonding and quasi-aromaticity in metal-chalcogenide cluster chemistry

On the basis of the localized molecular orbital (LMO) theory, the bonding schemes for the following types of cluster compounds are briefly reviewed in this paper; the linear [Et₄N][Cl₂FeS₂MoS₂Cu(PPh₃)₂] cluster, triangular trinuclear [M ₃(₃–X)(–Y ₃]⁴⁺ (M = Mo, W;X = O, S;Y = O, S, Se) clusters, triangulated polyhedral clusters: closo-boranes B _n H _n ^2–, octahedral [Co₆(CO)₁₄]^4–, [Ni₂Co₄(CO)₁₄]^2– and [Co₆(₃ –X ₈ ·L ₆ ⁿ⁺ (X = S, Se;L = PPh₃, PEt₃, CO;n = 0,1) as well as quasi-aromatic cluster ligands in cubane-type [Mo₃S₄ ·ML _n ^{(4 +q) +} (M = Mo, W, Fe, Ni, Cu, Sn, Sb;L = Ligand and sandwich-type [Mo₃S₄ ·M · S₄Mo₃]⁸⁺ (M = Mo, Sn, Hg). We put emphasis upon the characteristics of multicentered bonding in these cluster molecules, and, especially, point out existence of a novel species of quasi-aromatic cluster compounds.     

Three Heterometallic Mo–M′ Cubane-Like Tetranuclear Cluster Compounds (M′=Cu, Pb, Sb): Synthesis, Structure and Third-Order NLO Property

Three new heterometallic tetranuclear cluster compounds with a [Mo₃YS₃M] cubane-like cluster core (M=Cu, Pb, Sb; Y=O, S), [Mo₃OS₃(CuI)(-OAc)₂(dtp)₂(DMF)] (1), (dtp=S₂P(OC₂H₅)^– ₂), [Mo₃OS₃(PbI₃)(dtc)₃(py)₃] (2) (dtc=S₂CN(C₂H₅)^– ₂), [Mo₃S₄(SbI₃)(dtcpyr)₄(py)]·2H₂O (3) (dtcpyr=S₂CNC₄H^– ₈) have been synthesized and structurally characterized by IR, Raman, UV–Vis, ¹H NMR, ¹³C NMR spectroscopies and single-crystal X-ray diffraction studies. Their structure and bonding features are discussed. Compounds 1 and 2 show a good third-order optical nonlinearity, as measured by degenerate four-wave mixing technique.     

Hexanuclear Pt complexes composed of two cyclic triplatinum units connected with 1,4-diphenylene and 1,1′-ferrocenylene spacer

1,4-Bis(dimethylsilyl)benzene reacted with [Pt₃H(PEt₃)₃(μ-PPh₂)₃] at room temperature to yield trinuclear Pt complex [Pt₃(SiMe₂C₆H₄SiMe₂H)(PEt₃)₂(μ-PPh₂)₃] (1a). Heating a solution containing an equimolar mixture of [Pt₃H(PEt₃)₃(μ-PPh₂)₃] and 1a at 60 °C produced a hexanuclear Pt complex [(PEt₃)₂(μ-PPh₂)₃Pt₃(SiMe₂C₆H₄SiMe₂)Pt₃(PEt₃)₂(μ-PPh₂)₃] (2a). Complex 1a was characterized by X-ray crystallography and NMR spectroscopy, while the structure of 2a was determined by X-ray crystallography of single crystals containing 2a and [Pt₃H₂(PEt₃)₂(μ-PPh₂)₄] in 1:1 ratio. [Pt₃(SiMe₂fcSiMe₂H)(PEt₃)₂(μ-PPh₂)₃] (fc = Fe(η⁵-C₅H₄)₂) (1b) and [(PEt₃)₂(μ-PPh₂)₃Pt₃(SiMe₂fcSiMe₂)Pt₃(PEt₃)₂(μ-PPh₂)₃] (2b) were obtained similarly from the reactions of 1,1′-bis(dimethylsilyl)ferrocene with [Pt₃H(PEt₃)₃(μ-PPh₂)₃] and characterized by NMR spectroscopy and elemental analyses.     

Synergetic stability enhancement with magnesium and calcium ion substitution for Ni/Mn-based P2-type sodium-ion battery cathodes

The conventional P2-type cathode material Na_0.67Ni_0.33Mn_0.67O₂ suffers from an irreversible P2–O2 phase transition and serious capacity fading during cycling. Here, we successfully carry out magnesium and calcium ion doping into the transition-metal layers (TM layers) and the alkali-metal layers (AM layers), respectively, of Na_0.67Ni_0.33Mn_0.67O₂. Both Mg and Ca doping can reduce O-type stacking in the high-voltage region, leading to enhanced cycling endurance, however, this is associated with a decrease in capacity. The results of density functional theory (DFT) studies reveal that the introduction of Mg²⁺ and Ca²⁺ make high-voltage reactions (oxygen redox and Ni⁴⁺/Ni³⁺ redox reactions) less accessible. Thanks to the synergetic effect of co-doping with Mg²⁺ and Ca²⁺ ions, the adverse effects on high-voltage reactions involving Ni–O bonding are limited, and the structural stability is further enhanced. The finally obtained P2-type Na_0.62Ca_0.025Ni_0.28Mg_0.05Mn_0.67O₂ exhibits a satisfactory initial energy density of 468.2 W h kg⁻¹ and good capacity retention of 83% after 100 cycles at 50 mA g⁻¹ within the voltage range of 2.2–4.35 V. This work deepens our understanding of the specific effects of Mg²⁺ and Ca²⁺ dopants and provides a stability-enhancing strategy utilizing abundant alkaline earth elements.

A synergetic effect involving Mg and Ca can reduce the adverse impact on redox reactions related to Ni–O bonding in Mg and Ca co-doped P2-Na_0.67Ni_0.33Mn_0.66O₂ material, leading to better overall properties than its singly-doped counterparts.     

Heterostructured FeNi hydroxide for effective electrocatalytic oxygen evolution

Hydrogen production technology by water splitting has been heralded as an effective means to alleviate the envisioned energy crisis. However, the overall efficiency of water splitting is limited by the effectiveness of the anodic oxygen evolution reaction (OER) due to the high energy barrier of the 4e⁻ process. The key to addressing this challenge is the development of high-performing catalysts. Transition-metal hydroxides with high intrinsic activity and stability have been widely studied for this purpose. Herein, we report a gelatin-induced structure-directing strategy for the preparation of a butterfly-like FeNi/Ni heterostructure (FeNi/Ni HS) with excellent catalytic performance. The electronic interactions between Ni²⁺ and Fe³⁺ are evident both in the mixed-metal “torso” region and at the “torso/wing” interface with increasing Ni³⁺ as a result of electron transfer from Ni²⁺ to Fe³⁺ mediated by the oxo bridge. The amount of Ni³⁺ also increases in the “wings”, which is believed to be a consequence of charge balancing between Ni and O ions due to the presence of Ni vacancies upon formation of the heterostructure. The high-valence Ni³⁺ with enhanced Lewis acidity helps strengthen the binding with OH⁻ to afford oxygen-containing intermediates, thus accelerating the OER process. Direct evidence of FeNi/Ni HS facilitating the formation of the Ni–OOH intermediate was provided by in situ Raman studies; the intermediate was produced at lower oxidation potentials than when Ni₂(CO₃)(OH)₂ was used as the reference. The Co congener (FeCo/Co HS), prepared in a similar fashion, also showed excellent catalytic performance.

A butterfly-like FeNi/Ni HS featuring a “torso” of Ni-doped FeOOH and two “wings” of Ni₂(CO₃)(OH)₂ showed excellent activity in electrocatalytic oxygen evolution reaction attributable to the increase of higher-valance Ni³⁺ in the heterostructure.     

Synthesis,crystal structures and physical properties of two terephthalate-bridged copper(II) and nickel(II) complexes

Two ₂-terephthalate (tp) bridged complexes, [Cu₂(tp)(pren)₄](ClO₄)₂ (pren = 1,3-diaminopropane) (1) and [Ni₂(tp)(pren)₄(Him)₂](ClO₄)₂ (Him = imidazole) (2), have been synthesized and characterized by X-ray single-crystal structural analysis. In the discrete dinuclear [Cu₂(tp)(pren)₄]²⁺ cation of complex (1), each Cu^II atom has a square-pyramidal geometry, being coordinated by four nitrogen atoms (avg. 2.031 Å) from two pren ligands at the basal plane and one oxygen atom [2.259(3) Å] from a bis-monodentate tp group at the axial position. In the discrete dinuclear [Ni₂(tp)(pren)₄(Him)₂]²⁺ cation of complex (2), each Ni^II center is coordinated by five nitrogen atoms [Ni—N 2.069(3)–2.109(2) Å] from one Him group and two pren groups, and completed by one oxygen atom [Ni—O 2.138(3) Å] from a bis-monodentate tp group to furnish a distorted octahedron. Magnetic susceptibility studies show that the pair of metal atoms, although being separated by >11.5 Å, exhibit weak intramolecular antiferromagnetic interactions in complexes (1) (g = 2.07 and J = –3.4 cm^–1) and (2) (g = 2.10 and J = –0.7 cm^–1). The electrochemical behaviors of the complexes have also been studied by cyclic voltammogram processes.     

Synthesis,structure and physical properties of trinuclear M3tdt3(PEt3)3 (M = Fe,Co) clusters containing metal–metal bonds

Trinuclear M₃tdt₃(PEt₃)₃ (M = Fe^II for I, Co^II for II) clusters have been synthesized from the reaction between M(PEt₃)₂Cl₂ and Na₂tdt (tdt = toluene-3,4-dithiolate) in MeCN. Both complexes have been characterized by elemental analyses, FT-IR, UV–Vis, FAB-MS, ¹H NMR and cyclic voltammetry. Structures of Fe₃tdt₃(PEt₃)₃ (I) and Co₃tdt₃(PEt₃)₃ (II) were determined by single crystal X-ray crystallography. The Fe₃ triangular core of the 48-electron complex I, with an isosceles triangular geometry, showed very short Fe–Fe distances of 2.4014(13) and 2.4750(12) Å, which are comparable to the extensive M–M frameworks found in the FeMo-cofactor in nitrogenase. The isostructural Co₃tdt₃(PEt₃)₃ (II), with an analogous Co₃ coordination geometry, showed short Co–Co distances of 2.4442(9) and 2.5551(10) Å. The slightly longer M–M distances in complex II were explained by a total valence electron counting argument. Cyclic voltammetry of Fe₃tdt₃(PEt₃)₃ (I) showed robust reduction waves compared to Co₃tdt₃(PEt₃)₃ (II). Temperature-dependent effective magnetic moment measurements of I and II showed both clusters behave similarly and the magnetic property of the M₃ equilateral triangle core with extensive metal–metal interactions was characterized as degenerate frustration.     

Nickel complexes of 1-methylimidazoline-2(3H)-thione: crystal structures of trans-dichlorotetrakis(1-methylimidazoline-2(3H)-thione)nickel(II) and tetrakis[1-methylimidazoline-2(3H)-thione]nickel(II) tetrafluoroborate

Summary Crystal structures have been determined for two nickel complexes of the monodentate S-donating ligand 1-methyl imidazoline-2(3H)-thione (mimtH). The parainagnetic trans-octahedral complex, [Ni(mimtH)₄Cl₂], crystallises in an orthorhombic unit cell (a=12.459(1),b=13.078(1),c=15.406(1)Å, V=2510.24ų,Z=4, space group Pbca). Final conventional R from 1848 observed data [F>4(F)] is 0.0273. The Ni–Cl distance is. 2.537(1) Å and the mean Ni–S distance is 2.479 Å.The diamagnetic complex, [Ni(mimtH)₄](BF₄)₂, contains a distorted square-planar cation which is H-bonded. to [BF₄]^– anions. The complex crystallises in an orthorhombic unit cell [a=9.810(1),b=14.585(1),c=20.120(2)Å, V=2878.8ų,Z=4, space group Pbcn]. Final conventional R from 1756 observed data [F>4(F)] is 0.0629. The average Ni–S distance is 2.216Å.     

Nickel-mediated N–N bond formation and N2O liberation via nitrogen oxyanion reduction

The syntheses of (DIM)Ni(NO₃)₂ and (DIM)Ni(NO₂)₂, where DIM is a 1,4-diazadiene bidentate donor, are reported to enable testing of bis boryl reduced N-heterocycles for their ability to carry out stepwise deoxygenation of coordinated nitrate and nitrite, forming O(Bpin)₂. Single deoxygenation of (DIM)Ni(NO₂)₂ yields the tetrahedral complex (DIM)Ni(NO)(ONO), with a linear nitrosyl and κ¹-ONO. Further deoxygenation of (DIM)Ni(NO)(ONO) results in the formation of dimeric [(DIM)Ni(NO)]₂, where the dimer is linked through a Ni–Ni bond. The lost reduced nitrogen byproduct is shown to be N₂O, indicating N–N bond formation in the course of the reaction. Isotopic labelling studies establish that the N–N bond of N₂O is formed in a bimetallic Ni₂ intermediate and that the two nitrogen atoms of (DIM)Ni(NO)(ONO) become symmetry equivalent prior to N–N bond formation. The [(DIM)Ni(NO)]₂ dimer is susceptible to oxidation by AgX (X = NO₃⁻, NO₂⁻, and OTf⁻) as well as nitric oxide, the latter of which undergoes nitric oxide disproportionation to yield N₂O and (DIM)Ni(NO)(ONO). We show that the first step in the deoxygenation of (DIM)Ni(NO)(ONO) to liberate N₂O is outer sphere electron transfer, providing insight into the organic reductants employed for deoxygenation. Lastly, we show that at elevated temperatures, deoxygenation is accompanied by loss of DIM to form either pyrazine or bipyridine bridged polymers, with retention of a BpinO⁻ bridging ligand.

Deoxygenation of nitrogen oxyanions coordinated to nickel using reduced borylated heterocycles leads to N–N bond formation and N₂O liberation. The nickel dimer product facilitates NO disproportionation, leading to a synthetic cycle.     

[Et3PH][W4O3Cl7(PEt3)3]. A 12-electron tetrahedral tungsten cluster with an interesting arrangement of ligands

From the reaction between W₂Cl₆(PEt₃)₂ and H₂O in tetrahydrofuran the dark green crystalline compound [Et₃PH][W₄O₃Cl₇(PEt₃)₃] was obtained and characterized by X-ray crystallography. At –155° the cell dimensions werea=b=c=20.392(3) Å,Z=8,d _calcd=2.36 g cm^–3 in the space group I23. The compound is a triethylphosphonium salt of the [W₄O₃Cl₇(PEt₃)₃]^– anion. The latter contains a tetrahedron of tungsten atoms with W–W=2.61 Å (ave) and may be viewed as a W₃(-Cl)₃Cl₃(PEt₃)₃ cluster capped by ad ⁰-[WO₃Cl]^– unit and this has proved useful in examining the bonding within the cluster by use of the M.O. calculational method of Fenske and Hall. The cluster anion has crystallographically imposed C_3v symmetry. Theoxo-groups bridge the tungsten atoms in a notably asymmetric manner W–O=1.87(2) Å and 2.04(2) Å with the shorter distances being involved with the capping [WO₃Cl]^– unit. The W–P bonds lie in the W₃(₃-Cl)₃ plane and the three terminal W–Cl bonds are trans to theoxo-bridges.     

Synthesis,structure, FAB mass spectrum,and magnetic property of a dodecanuclear cluster complex of chromium with hydrido ligands [Cr12S16(H)2(PEt3)10]

A dodecanuclear cluster complex of chromium [Cr₁₂S₁₆(H)₂(PEt₃)₁₀] was prepared by the reaction of a hexanuclear cluster complex [Cr₆S₈(H)(PEt₃)₆] with elemental sulfur, and characterized by the FAB mass spectroscopy and single-crystal X-ray structure analysis. Crystallographic data: [Cr₁₂S₁₆(H)₂(PEt₃)₁₀] · 2CH₂Cl₂ (207 K), triclinic, P1, a = 14.697(6) Å, b = 14.733(5) Å, c = 14.238(5) Å, α= 96.60(3)°, β= 109.77(3)°, γ= 65.69(3)°, Z= 1. This complex contains two octahedral Cr₆S₈ cluster cores linked by a Cr-Cr and two Cr-S bonds, and each core holds an interstitial hydrogen atom. The intercluster bonding mode is similar to those in the superconducting Chevrel-Sergent phases. The paramagnetic moment of the dodecanuclear cluster decreases remarkably at lower temperatures showing the antiferromagnetic coupling between the paramagnetic cluster centers.     

Synthesis of a heterobimetallic actinide nitride and an analysis of its bonding

Reaction of [K(DME)][Th{N(R)(SiMe₂CH₂)}₂(NR₂)] (R = SiMe₃) with 1 equiv. of [U(NR₂)₃(NH₂)] (1) in THF, in the presence of 18-crown-6, results in formation of a bridged uranium–thorium nitride complex, [K(18-crown-6)(THF)₂][(NR₂)₃U^IV(μ-N)Th^IV(NR₂)₃] (2), which can be isolated in 48% yield after work-up. Complex 2 is the first isolable molecular mixed-actinide nitride complex. Also formed in the reaction is the methylene-bridged mixed-actinide nitride, [K(18-crown-6)][K(18-crown-6)(Et₂O)₂][(NR₂)₂U(μ-N)(μ–κ²-C,N–CH₂SiMe₂NR)Th(NR₂)₂]₂ (3), which can be isolated in 34% yield after work-up. Complex 3 is likely generated by deprotonation of a methyl group in 2 by [NR₂]⁻, yielding the new μ-CH₂ moiety and HNR₂. Reaction of 2 with 0.5 equiv. of I₂ results in formation of a U^V/Th^IV bridged nitride, [(NR₂)₃U^V(μ-N)Th^IV(NR₂)₃] (4), which can be isolated in 42% yield after work-up. The electronic structure of 4 was analyzed with EPR spectroscopy, SQUID magnetometry, and NIR-visible spectroscopy. This analysis demonstrated that the energies of 5f orbitals of 4 are largely determined by the strong ligand field exerted by the nitride ligand.

The heterobimetallic actinide nitride [(NR₂)₃U^V(μ-N)Th^IV(NR₂)₃] (R = SiMe₃) has an m_J = 5/2 ground state and its highest energy 5f excited state is primarily 5f-N_nitride σ-antibonding in character.     

Novel Type of Tetranitrosyl Iron Salt: Synthesis,Structure and Antibacterial Activity of Complex [FeL’2(NO)2][FeL’L”(NO)2] with L’-thiobenzamide and L”-thiosulfate

In this work a new donor of nitric oxide (NO) with antibacterial properties, namely nitrosyl iron complex of [Fe(C₆H₅C-SNH₂)₂(NO)₂][Fe(C₆H₅C-SNH₂)(S₂O₃)(NO)₂] composition (complex I), has been synthesized and studied. Complex I was produced by the reduction of the aqueous solution of [Fe₂(S₂O₃)₂(NO)₂]²⁻ dianion by the thiosulfate, with the further treatment of the mixture by the acidified alcohol solution of thiobenzamide. Based on the structural study of I (X-ray analysis, quantum chemical calculations by NBO and QTAIM methods in the frame of DFT), the data were obtained on the presence of the NO…NO interactions, which stabilize the DNIC dimer in the solid phase. The conformation properties, electronic structure and free energies of complex I hydration were studied using B3LYP functional and the set of 6–31 + G(d,p) basis functions. The effect of an aquatic surrounding was taken into account in the frame of a polarized continuous model (PCM). The NO-donating activity of complex I was studied by the amperometry method using an “amiNO-700” sensor electrode of the “inNO Nitric Oxide Measuring System”. The antibacterial activity of I was studied on gram-negative (Escherichia coli) and gram-positive (Micrococcus luteus) bacteria. Cytotoxicity was studied using Vero cells. Complex I was found to exhibit antibacterial activity comparable to that of antibiotics, and moderate toxicity to Vero cells.     

Observation of “de Vries-like” properties in bent-core molecules

“de Vries” liquid crystals, defined by a maximum layer shrinkage of ≤1% from the smectic A to C phase transition, are an integral component of ferroelectric liquid crystal (FLC) displays. Bona fide de Vries materials described in the literature are primarily perfluorinated, polysiloxane and polysilane-terminated rod-like (or calamitic) LCs. Herein, for the first time, we report a series of newly designed achiral unsymmetrical bent-core molecules with terminal alkoxy chains exhibiting similar properties to “de Vries” LCs. The new molecular structure is based on the systematic distribution of four phenyl rings attached via ester and imine linkers having 3-amino-2-methylbenzoic acid as the central core with a bent angle of 147°. Detailed microscopic investigations in differently aligned (planar as well as homeotropic) cells along with SAXS/WAXS studies revealed that the materials exhibited a SmA–SmC phase sequence along with the appearance of the nematic phase at higher temperatures. SAXS measurements divulged the layer spacings (d-spacings) and hence, the layer shrinkage was calculated ranging from 0.19% to 0.68% just below the SmA–SmC transition. The variation of the calculated molecular tilt angle (α) derived from the temperature-dependent SAXS data, followed the power law with exponent values 0.29 ± 0.01 and 0.25 ± 0.01 for compounds 1/10 and 1/12, respectively. The experimental values obtained were very close to the theoretically predicted values for the materials with de Vries-like properties. The analysis of temperature-dependent birefringence studies based on the prediction of the Landau theory, showed a dip across the SmA–SmC phase transition typical of compounds exhibiting the de Vries characteristics. The collective results obtained suggest “de Vries” SmA as a probable model for this bent-core system which may find applications in displays.

A simple molecular design of unsymmetrical bent-core molecules exhibiting low layer shrinkage and a dip in the birefringence at the SmA–SmC phase transition, typical characteristics of “de Vries” liquid crystals.