Bridging Coordination Mode Research Articles

Preparation, structure and properties of a novel one-dimensional erbium (III) complex

A novel one-dimensional erbium complex [ErL2(NO3)(H2O)2]n (HL = 2-picolinic acid) was synthesized by hydrothermal methods, and its crystal structure was determined by single crystal x-ray diffraction. The complex crystallize in monoclinic system, space group C2/c with a = 15.7525(5) Å, b = 11.4958(4) Å, c = 9.7977(3) Å, β = 102.862(3) º, V = 1729.72(10) Å3, C12H10ErN3O9, Mr = 507.49, Z = 4, Dc = 1.949 g•cm-3, F(000) = 972,  = 4.901 mm-1, S= 1.119, λ(MoKα) = 0.071073 nm, R = 0.0239 and wR = 0.0668. The 2-picolinic acid ligand adopts bidentate bridging coordination mode to connect adjacent erbium ions to form a one-dimensional chain structure. A series of properties of the complex were measured by solid-state photoluminescence, solid-state diffuse reflection and differential scanning calorimetry.

Plutonium and Cerium Perrhenate/Pertechnetate Coordination Polymers and Frameworks.

Spent nuclear fuel (SNF) contains transuranic and lanthanide species, which are sometimes recovered and repurposed. One particularly problematic fission product, 99TcO4-, hampers this recovery via coextraction with high valence metals, perhaps by complexation during aqueous reprocessing of SNF. There is limited molecular-level knowledge concerning the coordination chemistry between TcO4- or its well-known surrogate ReO4- and transuranic/lanthanide species. In the current study, we investigated the coordination of ReO4-/TcO4- with plutonium and cerium cations by structural and chemical characterization of a series of isolated extended solids. In this study, Ce represents both trivalent lanthanides and is considered a surrogate for Pu, respectively, in its common trivalent and tetravalent oxidation states. The structural elucidation of the seven isolated crystalline solids revealed that ReO4-/TcO4- directly connects to PuIV, PuVIO22+, CeIII, and CeIV in the terminal and bridging coordination modes, leading to 1-, 2-, and 3-dimensional frameworks. For example, ReO4- coordination to Pu(IV) formed a 1D chain or 2D framework, isostructural with previously isolated Th(IV) compounds. However, PuVIO22+ alternating with ReO4- led to a unique 1D chain, different from the prior-reported U(VI)/Np(VI)-ReO4-/TcO4- structures. Coordination of ReO4-/TcO4- with Ce(III) promotes the assembly of 3D frameworks. Finally, attempted synthesis of a Ce(IV)-ReO4- compound resulted in a 2D framework with a mixed-valence CeIII/IV. The highly acidic reaction conditions supported the reduction of both CeIV and TcVII, challenging isolation of compounds featuring these species. Only one TcO4-containing structure was obtained in this study (CeIII-TcO4 3D framework), vs the six total Ce/Pu-ReO4 compounds. Our three Pu-ReO4 crystal structures are the first reported and translated to atomic-level information about Pu-TcO4 coordination in nuclear fuel reprocessing scenarios, in addition to broadening our knowledge of bonding trends in the early, high-valence actinides.

Intensity and lifetime ratiometric luminescent thermometer based on a Tb(III) coordination polymer.

A three-dimensional terbium(III) coordination polymer of formula [Tb(bttb)0.5(2,5-pzdc)0.5]n (1) [H4bttb = 1,2,4,5-tetrakis(4'-carboxyphenyl)benzene and H2-2,5-pzdc = 2,5-pyrazinedicarboxylic acid] was obtained under hydrothermal conditions. The bttb4- tetraanion in 1 adopts the bridging and chelating-bridging pseudo-oxo coordination modes while the 2,5-pzdc2- dianion exhibits a rather unusual bis-bidentate bridging pseudo-oxo coordination mode, both ligands being responsible for the stiffness of the resulting 3D structure. Solid-state photoluminescent measurements illustrate that 1 exhibits remarkable green luminescence emission, the most intense band occurring in the region of 550 nm (5D4 → 7F5) with lifetimes at the millisecond scale. Thermometric performances of 1 reveal a maximum relative sensitivity (Sm) of 0.76% K-1 at 295 K (δT = 0.05 K), constituting a TbIII ratiometric solid luminescent thermometer over the physiological temperature range. Variable-temperature static (dc) magnetic susceptibility measurements for 1 in the temperature range 2.0-300 K show the expected behavior for the depopulation of the splitted mJ levels of the 7F7 ground state of the magnetically anisotropic terbium(III) ion plus a weak antiferromagnetic interaction through the carboxylate bridges. No significant out-of-phase magnetic susceptibility signals were observed for 1 in the temperature range 2.0-10.0 K, either in the absence or presence of a static dc magnetic field.

From an Isolable Bismolyl Anion to an Yttrium-Bismolyl Complex with μ-Bridging Bismuth(I) Centers and Polar Covalent Y-Bi Bonds.

The synthesis and first structural characterization of the [K(18-crown-6)] bismolyl Bitet (C4 Me4 Bi) contact ion pair (1) is presented. Notably, according to Natural Resonance Theory calculations, the Bitet anion of 1 features two types of leading mesomeric structures with localized anionic charge and two lone pairs of electrons at the BiI center, as well as delocalized anionic charge in the π-conjugated C4 Bi ring. The lone pairs at Bi enable a unique bridging coordination mode of the bismolyl ligand, as shown for the first rare earth metal bismolyl complex (Cptet 2 Y)2 (μ-η1 -Bitet )2 (2). The latter results from the salt metathesis reaction of KBitet with Cptet 2 Y(BPh4 ) (Cptet =C5 Me4 H). The Y-Bi bonding interaction in 2 of 16.6 % covalency at yttrium is remarkably large.

A new route for the syntheses of coordination polymers using magnetic influence: syntheses, crystal structures and fluorescence properties.

Five coordination polymers [TM1(absa)(H2O)4]n and [TM2(absa)(bipy)(H2O)]n [TM1 = Zn (1), Co (2); TM2 = Zn (3), Co (4), Cu (5); Na2absa = 5,5'-azobissalicylic acid disodium salt; bipy = 4,4'-bipyride] were synthesized by solvent evaporation under a magnetic field. It is evident that magnetic fields bring significant and noticeable changes to the absa2- ligand orientation and the component movement behaviors to construct coordination polymers. The absa2- ligands bind to the metal ions in bridging coordination mode through the carboxylate groups, in addition to the bipy molecules adopting bridging modes. Photoluminescence measurements indicate that the emissions of compounds 1-5 are at 626, 600, 632, 658 and 682 nm in the solid state, respectively.

Isocyanide Cu(I) complexes with unexpected μ2‐bridging pseudohalides: Synthesis, characterization and catalytic activity towards CuAAC

Three neutral Cu(I) complexes bearing 2,6‐dimethylphenyl isocyanide (CNXyl) and different triatomic pseudohalogens (SCN−, OCN− and N3−) as ligands were efficiently synthesized and characterized. The solid‐state structures were unambiguously determined through single‐crystal X‐ray diffraction, revealing unexpected bridging coordination modes in the case of OCN− and N3−. All the complexes were tested for azide‐alkyne cycloaddition (CuAAC), showing interesting catalytic activity towards the formation of 1,4‐disubstituted‐1,2,3‐triazoles for the cyanato and the azido Cu(I) complexes. Both species afforded yields above 90% with 0.5 mol% of catalyst at 50°C for 24 h. Several alkynes and azides were tested using the more active azido Cu(I) complex, affording the corresponding triazoles in high yields. The azido Cu(I) complex also induced the intramolecular CuAAC in the presence of dimethyl acetylenedicarboxylate and benzyl bromide/phenylacetylene.

Hydroarylation of alkynes via dual ortho-C-H functionalization of diaryl amines on a dicopper(I,I) platform.

A pyridine and morpholine-functionalized dicopper(I,I)-NHC complex (1) features both terminal and bridging coordination modes of NHC within the same molecule, and catalyzes dual ortho-C-H functionalization of diaryl amines for the hydroarylation of alkynes. A bimetallic construct in catalyst 1 allows sequential activation of ortho-C-H bonds of two aryl units to furnish a wide variety of 9,10-dihydroacridine derivatives without the explicit use of a directing group.

Sterically Hindered Tellurium(IV) Catecholate as a Lewis Acid.

Sterically hindered tellurium catecholate Te(Cat36)2 (Cat36 = 3,6-di-tert-butyl-catecholate) was synthesized with the reaction of amorphous Te with 3,6-di-tert-butyl-o-benzoquinone. Adducts of Te(Cat36)2 with various O- and N-donors were isolated and characterized by means of single-crystal X-ray diffraction along with IR, UV-vis, and NMR (1H, 13C, and 125Te) spectroscopies. In the crystal structure of the adduct with 2,2'-bipyridine (bipy), the unprecedented μ-κ2N,N':κ2N,N'-bridging coordination mode of bipy was observed. Various intermolecular interactions Te...O, Te...N, and Te...C in adducts were analyzed using density functional theory calculations and quantum theory of atoms in molecules analysis. The estimated strength for appropriate short contacts varies from 0.9 to 5.3 kcal/mol, and they are attractive and purely non-covalent.

Syntheses, crystal structures and properties of three compounds based on the dicarboxylate ligand with S-S flexible linkage

Three new compounds, [MnL(2, 2΄-bipy)2]n·1.5nH2O (1), Co(4, 4ˊ-bipy)(H2O)4·2HL (2) and 2HL·(4, 4ˊ-bipyH)·2H2O (3) (H2L = 2,2΄-dithiosalicylic acid, 2, 2΄-bipy = 2, 2΄-bipyridine, 4, 4΄-bipy = 4, 4΄-bipyridine), have been synthesized by hydrothermal and evaporation methods. Structural determination reveals that compound 1 shows a one-dimensional chain structure with L2- ligands adopting bridging coordination modes, compound 2 features a mononuclear structure with uncoordinated HL- anions, balancing the charges, compound 3 is a new inclusion compound of HL- anions and 4, 4ˊ-bipyH cation with π-π stacking interactions. In compounds 1-3, the flexible S-S linkages can make H2L ligands present different conformations of dihedral angles between the terminal benzene rings. The S-O hypervalent bonds can stabilize the conformations. Thermogravimetric analyses and fluorescent measurements of compounds 1 and 2 have been performed. Compounds 1 and 2 exhibit broad blue fluorescent emission bands at 420 nm and 424 nm, respectively.

Structural characterization, DFT studies and luminescent properties of dinuclear copper(I)-diimine complexes with the S-shape configurations

Three dinuclear Cu(I) complexes, [Cu2(pnd)(PPh3)4](BF4)2(1), [Cu2(pnd)(dppp)2] (BF4)2(2), and [Cu2(pnd)(DPEphos)2](BF4)2(3) (PPh3 = triphenylphosphine, dppp = 1, 3-bis (diphenylphosphino)propane, DPEphos = bis(2-diphenylphosphinophenyl)ether, pnd = N, N’-bis (pyridin-2-ylmethylene)naphthyl-1, 5-diimine), have been prepared and characterized by IR, 1H NMR, 31P NMR, 13C NMR, XRD, elemental analysis and X-ray crystal structure analysis. The structural analysis reveals that the flexible pnd in 1–3 acts in a trans bridging coordination mode to connect two Cu+ ions, forming a S-shape conformation, while each of Cu (I) ion is four-coordinate N2P2, adopting a distorted-tetrahedral geometry. DFT calculations show that the HOMOs of complexes 1–3 are primarily located on the copper d-orbital and the phosphine ligand, together with a specific contribution of pnd, while LUMOs are mostly composed of pnd with admixed Cu(I) d-orbital character. Corresponding calculations of atomic charges indicate that the charge of the copper atom in complexes 1–3 is below + 1, while the total charges of the coordinated atoms are 0.743–0.786. Moreover, the solid-state emission spectra of complexes 1–3 show the existence of broad emission bands at 350–550 nm.

Imparting Superhydrophobicity to Porphyrinic Coordination Frameworks Using Organotin

Imparting Superhydrophobicity to Porphyrinic Coordination Frameworks Using Organotin

Ni8(CNtBu)12][Cl]: A nickel isocyanide nanocluster with a folded nanosheet structure.

The reaction of 1.75equiv of tBuNC with Ni(1,5-COD)2, followed by crystallization from benzene/pentane, resulted in the isolation of [Ni8(CNtBu)12][Cl] (2) in low yields. Similarly, the reaction of Ni(1,5-COD)2 with 0.6equiv of [Ni(CNtBu)4], followed by addition of 0.08equiv of I2, resulted in the formation of [Ni8(CNtBu)12][I] (3), which could be isolated in 52% yield after work-up. Both 2 and 3 adopt folded nanosheet structures in the solid state, characterized by two symmetry-related planar Ni4 arrays, six terminally bound tBuNC ligands, and six tBuNC ligands that adopt bridging coordination modes. The metrical parameters of the six bridging tBuNC ligands suggest that they have been reduced to their [tBuNC]2- form. In contrast to the nanosheet structures observed for 2 and 3, gas phase Ni8 is predicted to feature a compact bisdisphenoid ground state structure. The strikingly different structural outcomes reveal the profound structural changes that can occur upon addition of ligands to bare metal clusters. Ultimately, the characterization of 2 and 3 will enable more accurate structural predictions of ligand-protected nanoclusters in the future.

The Fascinating Flexibility and Coordination Modes of a Pentamethylene Connected Macrocyclic CNC Pincer Ligand.

The coordination chemistry of an electron-rich macrocyclic CNC pincer-ligand consisting of two pentamethylene tethered N-heterocyclic carbene moieties on a carbazole backbone (bimcaC5) is investigated by mainly NMR spectroscopy and X-ray crystal structure analysis. A bridging coordination mode is found for the lithium complex. With the larger and softer potassium ion, the ligand adopts a facial coordination mode and a polymeric structure by intermolecular potassium nitrogen interactions. The facial coordination is also confirmed at a Cp*Ru fragment, while C-H activation under dehydrogenation at the alkyl chain is observed upon reaction with [Ru(PPh3)3Cl2]. In contrast, Pd(OAc)2 reacts under C-H activation at the central carbon atom of the pentamethylene tether to an alkyl-pincer macrocycle.

Synthesis, crystal structures and catalytic activity of oxidovanadium(V) complexes with tridentate ONO aroylhydrazone ligands

Two oxidovanadium(V) complexes, [VOL1(OEt)] (1) and [V2O2(L2)2(OEt)2] (2), where L1 and L2 are the anions of 2-amino-N′-(2-hydroxybenzylidene)benzohydrazide (H2L1) and N′-(2-hydroxybenzylidene)-4-hydroxybenzohydrazide (H2L2), respectively, have been synthesized and characterized by elemental analysis, infrared and electronic spectra, and 1H NMR spectra. Structures of the complexes were further confirmed by single-crystal X-ray determination. The V atom in the mononuclear complex 1 is in square pyramidal coordination, and those in the dinuclear complex 2 are in octahedral coordination. Both aroylhydrazone ligands coordinate to the V atoms through the phenolate O, imino N, and enolate O atoms. The ethanol ligand in complex 1 is in terminal coordination mode, while that in complex 2 is in bridging coordination mode. The complexes function as effective olefin epoxidation catalysts with hydrogen peroxide as terminal oxidant and sodium hydrogen carbonate as a co-catalyst.

Manganese complexes with chelating and bridging di-triazolylidene ligands: synthesis and reactivity.

New manganese complexes bearing di-triazolylidene (di-trz) ligands are described. Depending on the wingtip substituents of the triazolylidene ligand and the synthetic procedure, two different ligand coordination modes were observed, i.e, bridging and chelating. A series of Mn(i) complexes of the general type fac-[Mn(di-trzR)(CO)3Br] (R = Me, Et, Mes) with a chelating di-trz ligand were prepared via Ag-transmetalation. In contrast, the in situ deprotonation of the triazolium salts with KOBut yielded the bimetallic Mn(0) complexes [Mn2(CO)8(μ-di-trzR)] with a bridging di-trz ligand when short alkyl chains (Me, Et, i-Pr) are present as the N1 substituents of the triazolylidene ligand. The molecular structures of monometallic and bimetallic complexes were determined by X-ray diffraction studies. In addition, the cationic fac-[Mn(di-trzEt)(CO)2(PPh3)2]Br complex, a rare example of a dicarbonyl Mn(i) N-heterocyclic carbene, was obtained when fac-[Mn(di-trzEt)(CO)3Br] was irradiated with visible light in the presence of PPh3. The crystal structure revealed a slightly distorted octahedral geometry around the Mn(i) centre, with the chelating di-triazolylidene ligand situated in trans position to the two CO ligands in the equatorial plane, and the two phosphine ligands occupying the axial positions. Cyclic voltammetry studies show reversible redox processes for the monometallic Mn(i) complexes, and a quasi-reversible EC mechanism for the oxidation of the bimetallic complexes. Infrared spectroelectrochemical studies along with DFT calculations for fac-[Mn(di-trzEt)(CO)3Br] suggest that the observed two consecutive reductions both occur at the metal centre.

Triosmium Carbonyl Clusters Containing a Mixture of Dppm and Dppe Ligands

Four osmium carbonyl complexes were synthesized via microwave heating by reacting either Os3(CO)12 or Os3(CO)10( $$\mu$$ -dppm) with dppe, where dppm = bis(diphenylphosphino)methane and dppe = 1,2-bis(diphenylphosphino)ethane. Two of the complexes, Os3(µ-dppe)(CO)8(dppe) (1) and Os3(µ-dppm)(CO)8(dppe) (2), are the first examples of triangular triosmium clusters containing diphosphane ligands that exhibit both bridging and chelating coordination modes in the same molecule. Complexes 2 and [Os3(µ-dppm)(CO)9]2(µ-dppe) (3) are the first examples of triosmium clusters containing two different diphosphane ligands in the same molecule. Complexes 3 and [Os3(µ-dppe)(CO)9]2(µ-dppe) (4) are hexanuclear clusters containing two triangular Os3 units linked together by a bridging diphosphane ligand. Crystal structures for complexes 1–3 are reported. Two trinuclear cluster complexes, Os3(μ-dppe)(CO)8(dppe) (1) and Os3(μ-dppm)(CO)8(dppe) (2), and two hexanuclear cluster complexes, [Os3(μ-dppm)(CO)9]2(μ-dppe) (3) and [Os3(μ-dppe)(CO)9]2(μ-dppe) (4), were synthesized and characterized by X-ray crystal diffraction. Complexes 2 and 3 are the first examples of triangular triosmium clusters containing two different diphosphane ligands in the same molecule.

Coordination polymers driven by 2,5-dibromoterephthalic acid and chelating co-ligands: Syntheses, structures and luminescent properties

Four coordination polymers, namely, [Zn (DBT) (4,4′-dmbpy) (H2O)]n (1), [Co(DBT) (2,2′-bpy) (H2O)]n (2), [Zn (DBT) (2,2′-bpy)]n (3), [Zn (DBT)0.5 (2,2′-bpy)2·(HDBT−)]n (4) (H2DBT ​= ​2,5-dibromoterephthalic acid, 4,4′-dmbpy ​= ​4,4′-dimethyl-2,2′-bipyridyl and 2,2′-bpy ​= ​2,2′-bipyridyl) have been synthesized under solvothermal conditions and characterized by single crystal X-ray diffraction, powder X-ray diffraction, elemental analysis, IR and thermogravimetric (TG) analysis. These four compounds remained stable until 150 ​°C, and the major quality loss (83–90%) occurred between 150 and 700 ​°C. In mixed ligands system, the main ligand H2DBT exhibits monodentate or bidentate bridging coordination modes and the auxiliary ligands 4,4′-dmbpy and 2,2′-bpy both possess bidentate chelate coordination modes. An objective of this study was to investigate the pivotal role of chelating ligands in the formation of low dimensional structures. As the bipyridyl ligands occupy the coordination site, compounds 1–3 all display two dimensional structures and 4 shows 1D chains, of which compounds 1 and 2 are isomorphic. The hydrogen bonds and π-π stacking work together in the formation of 3D supramolecular structure of these four compounds. Besides, we investigated their photoluminescence properties in the solid state at room temperature. The compounds 1, 3 and 4 exhibited good fluorescence performance, and their strong emission peaks were located at 447 ​nm (λex ​= ​285 ​nm) for 1, 427 ​nm (λex ​= ​330 ​nm) for 3, and 412 ​nm (λex ​= ​310 ​nm) for 4.

A new homobimetallic cobalt(II) complex based on the tetradentate 3,5-bis(2-pyridyl)-1H-1,2,4-triazole ligand: Synthesis, crystal structure, Hirshfeld analysis, spectroscopic characterization, magnetic properties and antimicrobial activities

A novel homobimetallic cobalt(II) complex, [Co2(bpt)2(H2O)4](NO3)2·2H2O (bpt = 3,5-bis(2-pyridyl)-1,2,4-triazolate), has been synthesized and characterized by single crystal X-ray diffraction, Hirshfeld surface analysis, as well as UV–Visible and FTIR techniques. The crystal structure determination shows that the dinuclear complex crystallizes in the triclinic crystal system with the P1- space group. The (N′,N1,N2,N″)2 double bridging coordination mode is realised with a distorted octahedral N4O2-coordinated cobalt centre. The structure cohesion is ensured by different intermolecular hydrogen bonds, π–π stacking interactions and intermolecular lone-pair···π interactions. The structure consists of [Co2(bpt)2]2+ dimeric units with a cobalt-cobalt distance of 4.170(2) Å. Magnetic measurements carried out on the homobimetallic complex indicate a relatively weak antiferromagnetic interaction between the two cobalt centres. This complex exhibited antimicrobial activity against several strains of the fungal phytopathogens Verticillium dahliae and Fusarium oxysporum fsp. melonis, as well as against the phytopathogenic bacteria Agrobacterium tumefaciens, suggesting its use in crop protection.

Microstructure, dynamics and optical properties of metal-doped imidazolium-based ionic liquids

In this paper we study the complexation of Al3+ and several transition metals (Cr3+, Fe3+, Mn2+, Ni2+) in the ionic liquid 1-butyl-3-methylimidazolium thiocyanate. New insights into the structure, single-particle dynamics and electronic properties (optical absorption spectra) of these bulk mixtures are provided by molecular dynamics and density functional theory calculations, and our results are successfully compared with available experimental data. Our theoretical results reveal the existence of a bridging coordination mode between neighboring metal-ligand complexes in the polar nanoregions, and a scarce influence of the apolar nanoregions in the single-particle dynamics of the species in the mixture. Moreover, most part of the relevant features of the UV–Vis optical absorption spectra of these systems is properly explained by our density functional theory calculations for isolated complexes in the gas phase, evidencing that ionic liquid cations play only a limited role in the complex electronic properties.

Efficient Synthesis and Multisite Reactivity of a Phosphinidene-Bridged Mo-Re Complex. A Platform Combining Nucleophilic and Electrophilic Features.

The heterometallic complex [MoReCp(μ-PR*)(CO)6] (3) was prepared in 60% overall yield from syn-[MoCp(PHR*)(CO)2] via a three-step procedure involving complexes syn-[MoCp(PClR*)(CO)2] and [MoReCp(μ-PR*)(CO)7] as intermediate species (R* = 2,4,6-C6H2tBu3). The PR* ligand in 3 displays a novel asymmetric interaction with the dimetal center, involving a double bond with one atom (Mo) and a dative single bond with the other one (Re). Compound 3 underwent thermal isomerization involving a C-H bond cleavage to yield the hydride [MoReCp(μ-H){μ-P(CH2CMe2)C6H2tBu2}(CO)6] and reacted with I2 to give [MoReCpI2(μ-PR*)(CO)6], which displays a symmetrical phosphinidene bridge. Its reaction with methyl propiolate at 293 K proceeded with [2 + 2] cycloaddition of the alkyne and decarbonylation to yield the phosphapropenylidene-bridged complex [MoReCp{μ-κ2P,C:η3-PR*CHC(CO2Me)}(CO)5] as the major product, whereas its reaction with excess CN(4-C6H4OMe) at 273 K proceeded with formal [2 + 1] cycloaddition of the isocyanide and further isocyanide addition at the Re site to yield the complex [MoReCp{μ-η2P,C:κ1P-PR*CN(4-C6H4OMe)}(CO)6{CN(4-C6H4OMe)}], which displays an azaphosphaallene ligand in a novel bridging coordination mode.