Compartmental Ligand Research Articles

DNA cleaver with improved phosphatase and cytotoxic activity of a series of N2O‐based zinc(II) complexes

Three new Zn(II) Schiff base complexes, [ZnLCl2] (1), [ZnLBr2] (2) and [ZnL(SCN)2] (3), have been synthesized by adding Zn(II) salts of chloride and bromide to a compartmental ligand with NNO donor prepared through the simple condensation of pyridine‐2‐carboxaldehyde and a substituted aniline. The complexes have been identified using standard physicochemical methods, and their solid‐state structures have been determined through single‐crystal X‐ray analysis. The phosphatase‐like activity of all three complexes has been investigated using 4‐NPP as the model substrate in a DMSO/water medium. Complex 1 exhibits the highest level of phosphatase activity. The reactivity trend shows that complex 1 > complex 2 > complex 3. A plausible mechanism and the causes underlying the activity trend have been explored through DFT study, ESI‐mass spectra and 31P experiments. Complex 1 shows promising potential for use in gene‐targeted therapeutics due to its remarkable performance in DNA digestion. The excellent DNA cleavage result of complex 1 has led to the investigation of its molecular docking interaction with the liver cancer 2 receptor to study its anti‐liver cancer activity. Furthermore, in vitro anticancer activity of complex 1 also shows excellent antiproliferative activity against hepatocellular carcinoma.

Bimodal and Highly Branched Polyethylenes Using Dual-Site Nickel Catalysts Supported on an Unsymmetrical BIAN-PI Compartmental Ligand Scaffold

Bimodal and Highly Branched Polyethylenes Using Dual-Site Nickel Catalysts Supported on an Unsymmetrical BIAN-PI Compartmental Ligand Scaffold

Insight into ferromagnetic interactions in CuII-LnIII dimers with a compartmental ligand.

In the last two decades, efforts have been devoted to obtaining insight into the magnetic interactions between CuII and LnIII utilizing experimental and theoretical means. Experimentally, it has been observed that the exchange coupling (J) in CuII-LnIII systems is often found to be ferromagnetic for ≥4f7 metal ions. However, exchange interactions at sub-Kelvin temperatures between CuII and the anisotropic/isotropic LnIII ions are not often explored. In this report, we have synthesized a series of heterobimetallic [CuLn(HL)(μ-piv)(piv)2] complexes (LnIII = Gd (1), Tb (2), Dy (3) and Er (4)) from a new compartmental Schiff base ligand, N,N'-bis(3-methoxy-5-methylsalicylidene)-1,3-diamino-2-propanol (H3L). X-ray crystallographic analysis reveals that all four complexes are isostructural and isomorphous. Magnetic susceptibility measurements reveal a ferromagnetic coupling between the CuII ion and its respective LnIII ion for all the complexes, as often observed. Moreover, μ-SQUID studies, at sub-Kelvin temperatures, show S-shaped hysteresis loops indicating the presence of antiferromagnetic coupling in complexes 1-3. The antiferromagnetic interaction is explained by considering the shortest Cu⋯Cu distance in the crystal structure. The nearly closed loops for 1-3 highlight their fast relaxation characteristics, while the opened loops for 4 might arise from intermolecular ordering. CASSCF calculations allow the quantitative assessment of the interactions, which are further supported by BS-DFT calculations.

Exploring supramolecular architectures in Mn(iii) two-compartment o-vanhd Schiff base complexes: insights from apical aqua ligands and bond valence sum analysis

Three novel Mn(iii) vanhd complexes, namely [Mn(o-vanhd)(N3−)(H2O)]·CH3OH (1), [Mn(o-vanhd)(NCS−)(H2O)]·2CH3CN (2), and [Mn(o-vanhd)(H2O)]·ClO4·H2O (3), have been successfully synthesized using compartmental ligands paired with ancillary ligands.

A novel mixed azido/phenoxido bridged 1D CuII coordination polymer containing o-vanillin-based compartmental ligand: Synthesis, magnetism, phenoxazinone synthase and catalytic activity in epoxidation of alkenes

A novel 1-D coordination polymer, formulated as [Cu2(L)(N3)3]·H2O (1), has been synthesized by reacting the Schiff base ligand, 2-methoxy-6-((2-(2-hydroxyethylamino)ethylimino) methyl)-phenol (HL), with copper(II) chloride dihydrate in the presence of sodium azide. The X-ray structural analysis shows that compound 1 consists of tetranuclear [Cu2(L)(N3)3]2 units bearing a central double asymmetric μ1,1-N3 bridge and terminal mixed µ1,1-N3/phenoxido bridges that are linked via a double µ1,1,3-N3 bridge forming a 1-D network. The magnetic properties of 1 show the presence of ferromagnetic Cu···Cu interactions through the central double μ1,1-N3 bridge (J1 = 81.7(3) cm−1) coexisting with antiferromagnetic Cu···Cu interactions through the double µ1,1-N3/phenoxido bridge (J2 = –62.3(4)cm−1). Additionally, there is a very weak antiferromagnetic interaction (zJ = –0.12(2) cm−1) through the asymmetric µ1,1,3-N3 bridge connecting the tetranuclear units. Using o-aminophenol (OAP) as a substrate, the phenoxazinone synthase-like catalytic activity of the CuII coordination polymer 1 has been studied. The compound efficiently catalyzes the aerobic oxidation of o-aminophenol in DMF medium with a turnover number Kcat = 31.69 h−1. Moreover, 1 has been used as an active catalyst for the epoxidation of cis-cyclooctene, as a model alkene, with tert-butyl hydroperoxide (TBHP), showing an excellent epoxide yield and selectivity in CHCl3 under reflux conditions. To enlarge the scope of the reaction, the efficacy of the catalytic method has also been investigated in the epoxidation of some other substituted alkenes.

Syntheses, crystal structures, Hirshfeld surface analyses and fluorescence of binuclear complexes with unsymmetrical phenol-based compartmental ligands

Two new binuclear complexes, [Ni2L(OAc)2(H2O)]ClO4·H2O·CH2Cl2 (1) and [Zn2L(OAc)2]ClO4·CHCl3·0.5C6H12 (2), have been synthesized by using 2-[N,N-di(2-pyridylmethyl)aminomethyl]-6-(2-imidazolylmethyl)aminomethyl-4-methylphenol (HL) as a ligand. Complexes 1 and 2 have been characterized by FT-IR, powder X-ray diffraction, elemental analysis and single-crystal X-ray diffraction. X-ray crystallographic analyses show that 1 crystallizes in the triclinic P-1 space group, while 2 in the monoclinic C2/c space group. Both Ni1 and Ni2 in 1 are six-coordinate octahedra with a [Ni1O3N3] and [Ni2O4N2] configuration. In 2, the six-coordinate Zn1 cation displays a distorted octahedral [Zn1O3N3] configuration, while the five-coordinate Zn2 cation has a trigonal bipyramidal [Zn2O2N3] geometry. The intermolecular interactions in 1 and 2 have been investigated by 3D Hirshfeld surface analyses and 2D fingerprint plots to show that the prominent interactions are H···H and O···H/H···O contacts in 1 and H···H and Cl···H/H···Cl contacts in 2. Notably, the fluorescence emission of 2 has larger intensity than that of the free HL.

Synthesis of a trinuclear zinc(II) cluster composed of [4.4.3.01,5]tridecane cages: a rapid detection and degradation probe for the chemical warfare agent simulant diethyl cyanophosphonate in protein-rich food products.

Diethyl cyanophosphonate (DCNP), a simulant of Tabun, is a common pollutant in pharmaceutical waste and poses a high risk to living organisms. Herein, we demonstrate a compartmental ligand-derived trinuclear zinc(II) cluster [Zn3(LH)2(CH3COO)2] as a probe for the selective detection and degradation of DCNP. It consists of two pentacoordinated Zn(II) [4.4.3.01,5]tridecane cages bridged through a hexacoordinated Zn(II) acetate unit. The structure of the cluster has been elucidated by spectrometric, spectroscopic, and single-crystal X-ray diffraction studies. The cluster shows a two-fold increased emission as compared to the compartmental ligand (at λexc = 370 nm and λem = 463 nm) due to the chelation-enhanced fluorescence effect and acts as a turn-off signal in the presence of DCNP. It can detect DCNP at nano levels up to 186 nM (LOD). The direct bond formation between DCNP and Zn(II) via the -CN group degrades it to inorganic phosphates. The mechanism of the interaction and degradation is supported by spectrofluorimetric experiments, NMR titration (1H and 31P), time of flight mass spectrometry and density functional theory calculations. The applicability of the probe has been further tested by the bio-imaging of zebrafish larvae, analysis of high-protein food products (meat and fish) and vapour phase detection by paper strips.

Utilization of diamagnetic Zn(II) ion to boost the anisotropic nature of Ln(III) ion in heterodinuclear Zn(II)–Ln(III) single‐molecule magnets

A series of dimetallic ZnII–LnIII compounds of general formulae [LnZn(L)3(NO3)2]·2CH3OH (LnIII = DyIII (1), TbIII (2), GdIII(3)) was prepared by stepwise reaction of compartmental ligand LH = ((E)‐2‐((pyridin‐2‐ylmethylene)amino)phenol) with Ln (NO3)3·xH2O and Zn (NO3)2·xH2O in the presence of triethylamine as base. The single crystal XRD analysis indicated that both metallic ions are connected to each other through phenolic oxygen atom from fully deprotonated ligand. Based on the SHAPE analysis, the DyIII ion has nine coordination numbers with distorted spherical capped square antiprism geometry, while the ZnII ion has six coordination numbers with distorted octahedral geometry. DC magnetic studies reveal the existence of antiferromagnetic interaction between the ZnII and LnIII metal centers. AC magnetic studies reveal that the complex 1 show field‐induced single‐molecule magnet (SMM) properties with an effective energy barrier of 155 K under an applied dc field of 0.1 T, whereas complex 2 does not show SMM behavior. Furthermore, we conducted DFT and ab initio CASSCF + RASSI‐SO calculations to probe the single‐ion properties of Ln(III) ions and to understand the role of the diamagnetic ZnII ion in the magnetization relaxation in order to interpret the experimental observations. Ab initio calculations predict that the gz values are strongly axial in nature in the ground state of Dy(III) ion in complex 1 and that allows the magnetic relaxation to occur via excited states with a Ucal of 380.8 K. DFT calculations discovered that the presence of the diamagnetic Zn(II) ion causes greater negative charges on the bridging oxygen atoms, which enhances the anisotropy of Dy(III) ion and thus reduces the quantum tunneling of magnetization (QTM) effects, and helps to achieve better SMM features for 1.

New Heterotrinuclear CuIILnIIICuII (Ln = Ho, Er) Compounds with the Schiff Base: Syntheses, Structural Characterization, Thermal and Magnetic Properties.

New heterotrinuclear complexes with the general formula [Cu2Ln(H2L)(HL)(NO3)2]·MeOH (Ln = Ho (1), Er (2), H4L = N,N′-bis(2,3-dihydroxybenzylidene)-1,3-diaminopropane) were synthesized using compartmental Schiff base ligand in conjugation with auxiliary ligands. The compounds were characterized by elemental analysis, ATR-FTIR spectroscopy, X-ray diffraction, TG, DSC, TG-FTIR and XRD analysis. The N2O4 salen-type ligand coordinates 3d and 4f metal centers via azomethine nitrogen and phenoxo oxygen atoms, respectively, to form heteropolynuclear complexes having CuO2Ln cores. In the crystals 1 and 2, two terminal Cu(II) ions are penta-coordinated with a distorted square-pyramidal geometry and a LnIII ion with trigonal dodecahedral geometry is coordinated by eight oxygen atoms from [CuII(H2L)(NO3)]− and [CuII(HL)(NO3)]2− units. Compounds 1 and 2 are stable at room temperature. During heating, they decompose in a similar way. In the first decomposition step, they lose solvent molecules. The exothermic decomposition of ligands is connected with emission large amounts of gaseous products e.g., water, nitric oxides, carbon dioxide, carbon monoxide. The final solid products of decomposition 1 and 2 in air are mixtures of CuO and Ho2O3/Er2O3. The measurements of magnetic susceptibilities and field dependent magnetization indicate the ferromagnetic interaction between CuII and HoIII ions 1.

Supramolecular Arrangement and DFT analysis of Zinc(II) Schiff Bases: An Insight towards the Influence of Compartmental Ligands on Binding Interaction with Protein.

We report, for the first time, a detailed crystallographic study of the supramolecular arrangement for a set of zinc(II) Schiff base complexes containing the ligand 2,6‐bis((E)‐((2‐(dimethylamino)ethyl)imino)methyl)‐4‐R‐phenol], where R=methyl/tert‐butyl/chloro. The supramolecular study acts as a pre‐screening tool for selecting the compartmental ligand R of the Schiff base for effective binding with a targeted protein, bovine serum albumin (BSA). The most stable hexagonal arrangement of the complex [Zn−Me] (R=Me) stabilises the ligand with the highest FMO energy gap (ΔE=4.22 eV) and lowest number of conformations during binding with BSA. In contrast, formation of unstable 3D columnar vertebra for [Zn−Cl] (R=Cl) tend to activate the system with lowest FMO gap (3.75 eV) with highest spontaneity factor in molecular docking. Molecular docking analyses reported in terms of 2D LigPlot+ identified site A, a cleft of domains IB, IIIA and IIIB, as the most probable protein binding site of BSA. Arg144, Glu424, Ser428, Ile455 and Lys114 form the most probable interactions irrespective of the type of compartmental ligands R of the Schiff base whereas Arg185, Glu519, His145, Ile522 act as the differentiating residues with ΔG=−7.3 kcal mol−1.

A new N2O2-donor compartmental Schiff base ligand and its cadmium(II) complex: synthesis, mesogenic and photoluminescent properties

ABSTARCT A new mesomorphic compartmental [N2O2] donor Schiff base ligand [H2L] has been synthesized and one corresponding polymeric cadmium(II) complex of the type [Cd-L]n {H2L = 4,6-bis((E)-1-(octadecylimino)ethyl) benzene-1,3-diol} is prepared by direct reaction of metal ion with ligand. Both the ligand and its Cd-complex do exhibit mesomorphic properties. The IR spectrum of the ligand clearly reveals that the ligand acts as a bi-negative tetradentate donor through the two sets of phenolate oxygen and azomethine nitrogen. Mesomorphic behavior of these compounds are investigated with the help of polarizing optical microscopy (POM) and differential scanning calorimetry (DSC). The organization of the ligand and complex molecules in the mesophase are investigated by X-ray diffraction techniques. The Schiff base ligand and its Cd-complex shows plastic columnar mesophase (Colp) at ∼82 and ∼86 °C, respectively. The polymeric Cd-complex is blue light emitter with a broad emission maximum at ∼475 nm on excitation at 380 nm.

Histamine derived dimer of µ-Chlorido-µ-Phenoxido Dicopper(II) complex as a potential enzyme mimic with catecholase activity

A new copper(II) complex, [Cu2(L1)(µ-Cl)2]2 (C1), of the binucleating 2,6-bis((2-(4′-imidazolyl)ethyl)aminomethylidene)-4-methylphenol (HL1) with N4O binding sites, has been synthesized to investigate as potential structural and functional model for catecholase activity of the dicopper(II) site. It has been characterized by spectroscopic techniques and X-ray crystallography. The complex C1 exists as chlorido bridged dimer of binuclear copper(II) units, each possessing one end-off compartmental ligand (L1) with endogenous µ-phenoxido and exogenous µ-chlorido groups leading to intermetallic distance Cu1···Cu2 of 3.129 Å and Cu1-O1(phenoxo)-Cu2 angle of 107.67(10)o. Each copper(II) center has distorted octahedral geometry with bridging by chlorides in the tetranuclear dimer. The crystal system is monoclinc with space group P21/c. Magnetic measurements reveal that C1 is strongly antiferromagnetically coupled with J = − 115.663 ± 0.82547 cm−1. The catecholase activity of the complex has been evaluated by oxidation of 3,5-di(tert-butyl)catechol and 4-methyl catechol to the corresponding quinones under aerobic conditions. A kinetic treatment on the basis of the Michaelis-Menten model has been applied for the kinetic study. The complex is found to be selective for the substrates with higher Vmax = 8.2726x10−8 M s−1 and Km = 0.0107 M for 3,5-DTBC at 30 °C as compared to Vmax = 5.0371x10−8 M s−1 and Km = 0.027 M for 4-methyl catechol at 50 °C while it is found to be practically inactive for dopamine, 2,3-dihydroxy naphthalene and pyrocatechol oxidation.

Synergistic Experimental and Theoretical Studies of Luminescent-Magnetic Ln2Zn6 Clusters.

The present work is part of our ongoing quest for developing functional inorganic complexes using unorthodox pyridyl-pyrazolyl-based ligands. Accordingly, we report herein the synthesis, characterization, and luminescence and magnetic properties of four 3d-4f mixed-metal complexes with a general core of Ln2Zn6 (Ln = Dy, Gd, Tb, and Eu). In stark contrast to the popular wisdom of using a compartmental ligand with separate islands of hard and soft coordinating sites for selective coordination, we have vindicated our approach of using a ligand with overcrowded N-coordinating sites that show equal efficiency with both 4f and 3d metals toward multinuclear cage-cluster formation. The encouraging red and green photolumiscent features of noncytotoxic Eu2Zn6 and Tb2Zn6 complexes along with their existence in nanoscale dimension have been exploited with live-cell confocal microscopy imaging of human breast adenocarcinoma (MCF7) cells. The magnetic features of the Dy2Zn6 complex confirm the single-molecule-magnet behavior with befitting frequency- and temperature-dependent out-of-phase signals along with an Ueff value of ∼5 K and a relaxation time of 8.52 × 10-6 s. The Gd2Zn6 complex, on the other hand, shows cryogenic magnetic refrigeration with an entropy change of 11.25 J kg-1 K-1 at a magnetic field of 7 T and at 2 K. Another important aspect of this work reflects the excellent agreement between the experimental results and theoretical calculations. The theoretical studies carried out using the broken-symmetry density functional theory, ORCA suite of programs, and MOLCAS calculations using the complete-active-space self-consistent-field method show an excellent synergism with the experimentally measured magnetic and spectroscopic data.

A tetra Co(II/III) complex with an open cubane Co4O4 core and square-pyramidal Co(II) and octahedral Co(III) centres: bifunctional electrocatalytic activity towards water splitting at neutral pH.

The reaction of 2,6-diformyl-4-methylphenol, 4-methoxybenzoylhydrazine and Co(OAc)2·4H2O in 1 : 2 : 2 mole ratio in methanol under aerobic conditions produced in 61% yield a tetranuclear complex having the molecular formula [CoIICoIII(μ-OAc)(μ3-OH)(μ-L)]2 where OAc- and L3- represent acetate and N',N''-(5-methyl-2-oxido-1,3-phenylene)bis(methan-1-yl-1-ylidene)bis(4-methoxybenzoylhydrazonate), respectively. The elemental analysis and the mass spectrometric data confirmed the molecular formula of the complex. It is electrically non-conducting and paramagnetic. The complex crystallized as acetonitrile solvate. The X-ray structure shows that each Co(II) centre has a distorted square-pyramidal NO4 coordination sphere, while each Co(III) centre is in a distorted octahedral NO5 environment. The four metal atoms and the four bridging O-atoms form an open cubane type Co4O4 motif. In the crystal lattice, self-assembly of the solvated complex via intermolecular O-H⋯O interaction leads to a two-dimensional network structure. The infrared and electronic spectroscopic features of the complex are consistent with its molecular structure. Cryomagnetic measurements together with theoretical calculations suggest the presence of easy-axis anisotropy for the square-pyramidal Co(II) centres. The complex is redox-active and displays metal centred oxidation and reduction responses on the anodic and cathodic sides, respectively, of the Ag/AgCl electrode. Bifunctional heterogeneous electrocatalytic activity of the complex towards O2 and H2 evolution reactions (OER and HER) in neutral aqueous medium has been explored in detail.

Binuclear Ti(IV) complex with new compartmental ligand 2,6‐(bis‐CF3‐carbinol)‐4‐tert‐butylphenol as precatalysts for ethylene polymerization and its copolymerization with propylene and 5‐ethylidene‐norbornene

AbstractThe coordination chemistry of a new compartmental ligand 2,6‐(bis‐CF3‐carbinol)‐4‐tert‐butylphenol with Ti(IV) and Zr(IV) has been studied. The structures of Al, Ti, and Zr complexes with the participation of this ligand were established by X‐ray diffraction. Upon activation with Et2AlCl or Et3Al2Cl3 and Bu2Mg, Ti(IV) complex exhibited moderate catalytic activity for ethylene polymerization. The obtained UHMWPE samples were processed into high‐strength (up to 2.7 GPa) and high‐modulus (up to 162 GPa) films through solid‐phase molding and orientation drawing. The mononuclear and binuclear Ti(IV) complexes catalyzed the ternary copolymerization of ethylene, propylene, and 5‐ethylidene‐norbornene. Tercopolymers with a content of propylene units up to 36 mol% and 5‐EBN up to 8.6 mol% were synthesized with a high activity (2.8–6.3 tons of copolymer/mol Ti h); the mechanical characteristics of elastomeric materials have been studied.

Structural Characterization of Heterodinuclear ZnII-LnIII Complexes (Ln\u2009=\u2009Pr, Nd) with a Ring-Contracted H2valdien-Derived Schiff Base Ligand

Synthesis and structural characterization of two heterodinuclear ZnII-LnIII complexes with the formula [ZnLn(HL)(µ-OAc)(NO3)2(H2O)x(MeOH)1-x]NO3 · n H2O · n MeOH [Ln = Pr (1), Nd (2)] and the crystal and molecular structure of [ZnNd(HL)(µ-OAc)(NO3)2(H2O)] [ZnNd(HL)(OAc)(NO3)2(H2O)](NO3)2 · n H2O · n MeOH (3) are reported. The asymmetrical compartmental ligand (E)-2-(1-(2-((2-hydroxy-3-methoxybenzylidene)amino)-ethyl)imidazolidin-2-yl)-6-methoxyphenol (H2L) is formed from N1,N3-bis(3-methoxysalicylidene)diethylenetriamine (H2valdien) through intramolecular aminal formation, resulting in a peripheral imidazoline ring. The structures of 1–3 were revealed by X-ray crystallography. The smaller ZnII ion occupies the inner N2O2 compartment of the ligand, whereas the larger and more oxophilic LnIII ions are found in the outer O2O2’ site.Graphic Synthesis and structural characterization of two heterodinuclear ZnII-LnIII complexes (Ln = Pr, Nd) bearing an asymmetrical compartmental ligand formed in situ from N1,N3-bis(3-methoxysalicylidene)diethylenetriamine (H2valdien) through intramolecular aminal formation are reported.

Probing the binding interaction of zinc (II) Schiff bases with bovine serum albumin: A spectroscopic and molecular docking study

Entrapping of potent Schiff base with biomimetic environment using fluorescence properties enables better understanding of their interaction for drug‐based application. A detailed photophysical study of zinc (II) Schiff bases, 2,6‐bis((E)‐((2‐(dimethylamino) ethyl)imino)methyl)‐4‐R‐phenol, where R = methyl/tertiary butyl/chloro is reported by utilizing bovine serum albumin (BSA) as the bio membrane. Steady state absorption and emission studies of Schiff base‐protein system have been found to get altered by change in the compartmental ligand. Alternation of polarity caused by such compartmental ligands is reported by comparing the fluorescence behavior of the probes in microheterogeneous environment in a mixture of dioxane and water of varying composition. Hildebrand equation accounts for negative binding constants among BSA with Schiff base with Cl (‐I) group as the compartmental ligand in contrast to the positive magnitudes with ligands exhibiting +I effect. Functionality of such compartmental ligands (intra interactions studied using Hirshfeld analyses) upon binding with the protein is also studied in terms of quenching and denaturation studies. Schiff base with Me is found to be the most favorable ligand that bound to BSA as corroborated from the binding, quenching, micropolarity, and docking studies. Molecular docking studies predict the affinity energies for suitable binding conformations to be ~ − 6 kcal mol−1 for BSA‐Schiff base (with Me ligand).

Luminescent [ZnIILnIII] complexes anchored on graphene: Synthesis and crystal structures of [ZnIIEuIII] and [ZnIITbIII] complexes decorated with pyrene groups

Two [ZnLn] heterobinuclear complexes decorated with pyrene groups, [ZnEu(valpn)(hfac)2(pb)], have been obtained, in order to be deposited on graphene (LnIIIEuIII 2a; TbIII 2b); H2valpn is the Schiff base compartmental ligand resulted from the condensation reaction between o‐vanillin and propylenediamine (Hpb = 1‐pyrenebutiric acid; Hhfac = hexafluoroacetylacetone). The two complexes have been obtained by replacing the acetato ligand in [ZnEu(valpn)(hfac)2(CH3COO)] (EuIII: 1a; TbIII: 1b) by pb− anions. The crystal structures of 1a, 2a, and 2b have been solved and described. Compounds 2a and 2b were grafted on monolayer graphene/quartz. The new hybrid materials, 2a/graphene and 2b/graphene, as well as the starting complexes are luminescent. The two hybrid materials have been characterized by Raman spectroscopy, atomic force microscopy (AFM), and scanning electron microscopy (SEM) measurements, which confirm the presence of the complexes on graphene.

Ligand Protonation Triggers H2 Release from a Dinickel Dihydride Complex to Give a Doubly “T”‐Shaped Dinickel(I) Metallodiradical

AbstractThe dinickel(II) dihydride complex (1K) of a pyrazolate‐based compartmental ligand with β‐diketiminato (nacnac) chelate arms (L−), providing two pincer‐type {N3} binding pockets, has been reported to readily eliminate H2 and to serve as a masked dinickel(I) species. Discrete dinickel(I) complexes (2Na, 2K) of L− are now synthesized via a direct reduction route. They feature two adjacent T‐shaped metalloradicals that are antiferromagnetically coupled, giving an S=0 ground state. The two singly occupied local type magnetic orbitals are oriented into the bimetallic cleft, enabling metal–metal cooperative 2 e− substrate reductions as shown by the rapid reaction with H2 or O2. X‐ray crystallography reveals distinctly different positions of the K+ in 1K and 2K, suggesting a stabilizing interaction of K+ with the dihydride unit in 1K. H2 release from 1K is triggered by peripheral γ‐C protonation at the nacnac subunits, which DFT calculations show lowers the barrier for reductive H2 elimination from the bimetallic cleft.

Ligand Protonation Triggers H2 Release from a Dinickel Dihydride Complex to Give a Doubly "T"-Shaped Dinickel(I) Metallodiradical.

The dinickel(II) dihydride complex (1K) of a pyrazolate‐based compartmental ligand with β‐diketiminato (nacnac) chelate arms (L−), providing two pincer‐type {N3} binding pockets, has been reported to readily eliminate H2 and to serve as a masked dinickel(I) species. Discrete dinickel(I) complexes (2Na, 2K) of L− are now synthesized via a direct reduction route. They feature two adjacent T‐shaped metalloradicals that are antiferromagnetically coupled, giving an S=0 ground state. The two singly occupied local dx2-y2 type magnetic orbitals are oriented into the bimetallic cleft, enabling metal–metal cooperative 2 e− substrate reductions as shown by the rapid reaction with H2 or O2. X‐ray crystallography reveals distinctly different positions of the K+ in 1K and 2K, suggesting a stabilizing interaction of K+ with the dihydride unit in 1K. H2 release from 1K is triggered by peripheral γ‐C protonation at the nacnac subunits, which DFT calculations show lowers the barrier for reductive H2 elimination from the bimetallic cleft.