Ligand Tris Research Articles

Terminal NiII−OH/−OH2 complexes in trigonal bipyramidal geometries derived from H2O

The preparation and characterization of two NiII complexes are described, a terminal NiII–OH complex with the tripodal ligand tris[(N)-tert-butylureaylato)-N-ethyl)]aminato ([H3buea]3−) and a terminal NiII–OH2 complex with the tripodal ligand N,N′,N″-[2,2′,2″-nitrilotris(ethane-2,1-diyl)]tris(2,4,6-trimethylbenzenesulfonamido) ([MST]3−). For both complexes, the source of the –OH and –OH2 ligand is water. The salts K2[NiIIH3buea(OH)] and NMe4[NiIIMST(OH2)] were characterized using perpendicular-mode X-band electronic paramagnetic resonance, Fourier transform infrared, UV–vis spectroscopies, and its electrochemical properties were evaluated using cyclic voltammetry. The solid state structures of these complexes determined by X-ray diffraction methods reveal that they adopt a distorted trigonal bipyramidal geometry, an unusual structure for 5-coordinate NiII complexes. Moreover, the NiII–OH and NiII–OH2 units form intramolecular hydrogen bonding networks with the [H3buea]3− and [MST]3− ligands. The oxidation chemistry of these complexes was explored by treating the high-spin NiII compounds with one-electron oxidants. Species were formed with S=1/2 spin ground states that are consistent with formation of monomeric NiIII species. While the formation of NiIII–OH complexes cannot be ruled out, the lack of observable O–H vibrations from the putative Ni–OH units suggest the possibility that other high valent Ni species are formed.

A new synthetic route to the electron-deficient ligand tris(3,4,5-tribromopyrazol-1-yl)phosphine oxide.

The anionic tris(pyrazolyl)borates, or scorpionates, have proven to be extremely useful ligands. Neutral tris(pyrazolyl)methane ligands, however, are difficult to prepare and require numerous purification steps for a number of substitution patterns. We have previously outlined two different routes for accessing neutral tris(pyrazolyl) ligands. We describe here an adaptation of the previously published procedures for the synthesis of the electron-poor ligand tris(3,4,5-tribromopyrazol-1-yl)phosphine oxide, C9Br9N6OP. Similar electron-deficient ligands have been proven to unlock unique chemistry for the anionic scorpionates. The title perbrominated tris(pyrazolyl)phosphine oxide displays a network of halogen bonds in the solid state. All the bonds in the pyrazole ring are rather similar to the reported borate analogues, which makes this molecule promising as a ligand for applications where very electron-poor metal complexes are required.

Cobalt(II) tris(2-pyridylmethyl)amine complexes [Co(TPA)X]+ bearing coordinating anion (X = Cl−, Br−, I− and NCS−): synthesis and application for carbon dioxide reduction

Four cobalt(II) complexes supported by the tripodal ligand tris(2-pyridylmethyl)amine (TPA) and ancillary coordinated anion (X), [Co(TPA)X]+ (X=Cl−, Br−, I− and NCS−) (1–4), have been prepared. Magnetic susceptibility measurement and electronic spectroscopy indicate that they are five-coordinated high spin cobalt(II) complexes. The structures of 2–4 have been determined by X-ray crystallography. Reduction of CO2 to CO has been observed upon irradiation of complexes 1–4 in the presence of fac-Ir(ppy)3 (ppy=C-deprotonated 2-phenylpyridine anion) and under CO2 atmosphere using blue LEDs. All of these Co complexes were found to be efficient and stable CO2 reduction catalyst with TON(CO)>1000 and CO selectivity>90% under 65h of irradiation. Among them, [Co(TPA)Br]+ showed the best performance in CO2 reduction with TON(CO)>1400 after 65h. The coordinated anion X played an important role in the photo-catalysis. Density functional theory (DFT) calculation has also been performed to examine the mechanism and role of coordinated anion X in visible-light induced CO2 reduction.

ESI-MS studies of the non-covalent interactions between biologically important metal ions and N-sulfonylcytosine derivatives.

The aim of this report is to present the electrospray ionization mass spectrometry results of the non-covalent interaction of two biologically active ligands, N-1-(p-toluenesulfonyl)cytosine, 1-TsC, 1 and N-1-methanesulfonylcytosine, 1-MsC, 2 and their Cu(II) complexes Cu(1-TsC-N3)2 Cl2 , 3 and Cu(1-MsC-N3)2 Cl2 and 4 with biologically important cations: Na+ , K+ , Ca2+ , Mg2+ and Zn2+ . The formation of various complex metal ions was observed. The alkali metals Na+ and K+ formed clusters because of electrostatic interactions. Ca2+ and Mg2+ salts produced the tris ligand and mixed ligand complexes. The interaction of Zn2+ with 1-4 produced monometal and dimetal Zn2+ complexes as a result of the affinity of Zn2+ ions toward both O and N atoms. Copyright © 2016 John Wiley & Sons, Ltd.

Construction of Noninterpenetrating and Interpenetrating (4-Fold and 8-Fold) 3-D Cd(II) Networks with Tris(1,2,4-triazol-4-yl)phenyl)amine Modulated by Aromatic Dicarboxylate Coligands

Three Cd(II)-based coordination polymers 1–3 with unique structures and topologies have been successfully constructed under solvothermal conditions by use of a newly designed N-containing rigid triangular ligand tris(4-(4H-1,2,4-triazol-4-yl)phenyl)amine (TTPA-4), wherein the structural interpenetration can be modulated by aromatic dicarboxylate coligands including thiophene-2,5-dicarboxylic acid (TDA) and terephthalic acid (TPA). Without using coligands, a noninterpenetrating porous 3-D network of 1 with nia topology was obtained. With the aid of the V-shaped TDA coligand, a 4-fold interpenetrating 3-D network of 2 resulted that is built from (2,3,7)-connecting (42.6)(44.6.88.104.124)(4)2 net. In the presence of the linear TPA auxiliary ligand, an 8-fold interpenetrating 3-D network of 3 was produced that is assembled by 3-connecting uninodal srs net. Particularly, compound 1 displays interesting dual function as the result of its unique structural attributes, which not only shows superb sensitivity for ...

Silver(I) Polymer of Tripodal Amine: Synthesis, Structure and Photoluminescence

Starting from tripodal ligand tris-(methyl-imidazole) amine (1) the colourless complex tris-(methyl-imidazole)aminesilver(I)perchlorate (2) has been synthesized, characterized by IR, UV/Vis and 1HNMR spectroscopic studies and finally solid state structure has been established by single crystal X-ray diffraction studies. A single crystal X-ray structure determination revealed the formation of coordination polymer. The crystal structure possesses weak d10–d10 ‘argentophilic’ interactions with Ag–Ag separation (3.348 A). The weak luminance at 375 nm may be this Ag–Ag weak interaction. The molecule possesses weak H-bonding with C2 and C4H of imidazole with oxygen of ClO4.

Two actinide-organic frameworks constructed by a tripodal flexible ligand: Occurrence of infinite {(UO2)O2(OH)3}4n and hexanuclear {Th6O4(OH)4} motifs

Two new actinide metal-organic frameworks were constructed by using a tripodal flexible ligand tris (2-carboxyethyl) isocyanurate (H3tci) under hydrothermal condition. The combination of H3tci and uranyl nitrate hexahydrate in aqueous solution leads to the isolation of [(UO2)2(H2O)4]0.5(tci)2(UO2)4(OH)4·18H2O (1), which contains two distinct UO22+ coordination environments. Four uranyl cations, linked through μ3-OH respectively, result in the edge-sharing ribbons. Then, the layer structure is constructed by U-O clusters linked through other eight-coordinated uranyl unions, giving rise to a porous structure in the space. Topological analysis reveals that complex 1 belongs to a (4, 8)-connected net with a schläfli symbol of (34.26.3)2(34.46.56.68.73.8). Th3(tci)2O2(OH)2(H2O)3·12H2O (2) generated by the reaction of H3tci and thorium nitrate tetrahydrate, possesses nine-fold coodinated Th(IV) centers with a monocapped square antiprismatic geometry. The hexamers “Th6O4(OH)4” motifs are connected together by the carboxylate groups, showing a three-dimensional structures. Complex 2 takes on an 8-connected architecture and the point symbol is (424.64).

Facile preparation of a three-coordinate copper(I) complex: Steric hindrance, supramolecular structure, optical property and TD-DFT study

GRAPHICAL ABSTRACT

Tris(rhenium fac-tricarbonyl) Polypyridine Functionalized Cyclotriguaiacylene Ligands with Rich and Varied Emission

Trinuclear rhenium fac-tricarbonyl bromide complexes have been synthesized coordinated to the host ligands tris(4-[4-methyl-2,2′-bipyridyl]methyl)cyclotriguaiacylene (L1), tris(4-[4-methyl-2,2′-bipyridoyl])cyclotriguaiacylene (L2), and tris(4-[2,2′,6′,2″-terpyridyl]benzyl)cyclotriguaiacylene (L3). The structure of L1 and complexes [{Re(CO)3Br}3(L1)] (1) and [{Re(CO)3Br}3(L3)] (3) have been elucidated through X-ray single-crystal diffraction, with complex 3 crystallizing as a conglomerate. The steady-state luminescent properties and time-resolved fluorescence studies of the complexes have been conducted and revealed an unusual dual-emission phenomenon for complex 2. Complexes 1 and 2 show red-shifted emission wavelengths in comparison with those typical of monometallic Re(CO)3-bipy-Br complexes, while complex 3 showed an unusual excitation-dependent variation of emission wavelength.

Tuning the Magnetoluminescence Behavior of Lanthanide Complexes Having Sphenocorona and Cubic Coordination Geometries

The reaction of the tripodal fluorophoric ligand tris(benzimidazol‐2‐ylmethyl)amine (ntbi) with two different lanthanide salts [Ln(NO3)3 and LnCl3 (Ln = Dy, Ho, Tb)] afforded two new classes of mononuclear complexes. The class 1 complexes [{Ln(ntbi)(NO3)3}2·3CH3OH; Ln = Dy (1) and Ho (3)] exhibit very rare “sphenocorona” coordination geometries around the Ln centers, whereas the class 2 complexes [{Ln(ntbi)2}5·15Cl·xH2O; Ln = Dy, x = 18 (2) and Ln = Tb, x = 27 (4)] show “cubic” coordination geometries, as revealed by single‐crystal X‐ray diffraction studies. The class 2 complexes also exhibit a unique “double‐propeller”‐type structural feature. Owing to the significant difference in the coordination geometries around the Ln centers, prominent variations in the slow magnetic relaxation behaviors as well as the luminescence intensities are observed by alternating current magnetic susceptibility and solid‐state luminescence studies, respectively.

Polynuclear copper(II) complexes bridged by polycarboxylates of aromatic and N-heterocyclic compounds

Two categories of polynuclear Cu(II) complexes bridged by multicarboxylate compounds 2,5-pyridine dicarboxylic acid (H2Py2,5-dc), 2,4-pyridine dicarboxylic acid (H2Py2,4-dc), 2,3-pyrazine dicarboxylic acid (H2Pyaz2,3-dc) and terephthalic acid (H2tp) have been isolated with the tripod N4-donor ligands tris(2-pyridylmethyl)amine (TPA) and tris(2-isopropyl-2-aminoethyl)amine (iptren). The trinuclear bridged-carboxylato species were obtained with TPA: [(TPA)Cu-(μ2-Py2,4-dc)2Cu(H2O)2-Cu(TPA)](ClO4)2·2H2O (1), [Cu(TPA)-Cu(μ2-Py2,5dc)2-Cu(TPA)](ClO4)2 (2) and [(TPA)Cu-(μ2-Pyaz2,3-dc)2Cu(ClO4)2-Cu(TPA)][Cu(TPA)(H2O)]2(ClO4)4·4H2O (3), and the dinuclear species [Cu2(iptren)2(tp)](ClO4)2 (4) and [Cu2(iptren)2(Pyaz2,5-dc)](ClO4)2·H2O (5) with iptren. The synthesized complexes were characterized by elemental microanalyses, conductivity measurements, IR and UV–Vis spectroscopic techniques as well as by single crystal X-ray crystallography. The nature of polycarboxylate compounds used and the coligands skeletal structure play crucial role in adopting certain carboxylate-bonding mode and the nuclearity of the coordination product.

Thioarsenate anions acting as ligands: Solvothermal syntheses, crystal structures and characterizations of transition metal complexes of thioarsenate and polyethyleneamine ligands

New members of transition metal complexes with thioarsenate ligands, [Co(peha)][Co(As3S3)2] (peha=pentaethylenehexamine) (1), [Co(trien)(AsS3)] (2), [Cr(trien)(AsS3)] (trien=triethylenetetramine) (3) and [Cr(en)2(AsS3)] (en=ethylenediamine) (4) were prepared by solvothermal reactions in polyamines. In 1, two As3S3 units coordinate to a Co2+ ion with both As- and S-donor atoms in the 1κ2As1,As2:1κS1-As3S3 coordination mode to form the novel [Co(As3S3)2]2− anionic cluster, in which CoAs2, CoAs2S2, and CoAs3S2 rings are formed. Another Co2+ ion is coordinated by a hexadentate peha ligand to form a octahedral [Co(peha)]2+ complex cation. Both Co3+ and Cr3+ ions are coordinated by a tetradentate trien ligand and a bidentate chelating ligand [AsS3]3−, and neutral complexes [Co(trien)(AsS3)] (2) and [Cr(trien)(AsS3)] (3) are formed. The Cr3+ is coordinated by two en ligands and a bidentate chelating ligand [AsS3]3− to form neutral complex Cr(en)2(AsS3)] (4). Complexes 2–4 represent the first examples of TM–thioarsenate complexes with polyethyleneamine coligands. Compounds 1–4 are potential semiconductors with narrow well-defined optical band gaps in the range of 1.45–1.74eV. Thermal properties of 1–4 were investigated via thermogravimetric analyses.

Syntheses and structures of discrete copper(II) and cadmium(II) supramolecular complexes based on 1,4-diacylthiosemicarbazone ligands.

Thiosemicarbazides and their metal complexes have attracted considerable interest because of their biological activities and their flexibility, which allows the ligands to bend and rotate freely to accommodate the coordination geometries of various metal centres. Discrete copper(II) and cadmium(II) complexes have been prepared by crystallization of N-[2-(2-hydroxybenzoyl)hydrazinecarbonothioyl]propanamide (H3L) with Cu(CH3COO)2 or Cd(NO3)2 in a dimethylformamide/methanol mixed-solvent system at room temperature, affording the complexes di-μ-acetato-bis{μ4-1-[(2-oxidophenyl)carbonyl]-2-(propanamidomethanethioyl)hydrazine-1,2-diido}tetracopper(II) dimethylformamide disolvate, [Cu4(C11H10N3O3S)2(C2H3O2)2]·2C3H7NO, (I), and bis{μ2-[(2-hydroxyphenyl)formamido](propanamidomethanethioyl)azanido}bis[(4,4'-bipyridine)nitratocadmium(II)] dihydrate, [Cd2(C11H12N3O3S)2(NO3)2(C10H8N2)2]·2H2O, (II). Complex (I) consists of four Cu(II) cations, two μ4-bridging trianionic ligands and two μ2-bridging acetate ligands, while complex (II) is composed of two Cd(II) cations, two μ2-bridging monoanionic ligands, two nitrate ligands and two 4,4'-bipyridine ligands. These discrete complexes are connected by hydrogen bonds and van der Waals interactions to form a three-dimensional supramolecular architecture. Compared with (I), the phenolic hydroxy group and hydrazide N atom of the thiosemicarbazide ligand of (II) are not involved in coordination and lead to a binuclear Cd(II) complex. This different coordination mode may be attributed to the larger ionic radius of the Cd(II) ion compared with the Cu(II) ion.

Reconstitution of Heme Enzymes with Artificial Metalloporphyrinoids.

An important strategy used in engineering of hemoproteins to generate artificial enzymes involves replacement of heme with an artificial cofactor after removal of the native heme cofactor under acidic conditions. Replacement of heme in an enzyme with a nonnatural metalloporphyrinoid can significantly alter the reactivity of the enzyme. This chapter describes the design and synthesis of three types of artificial metalloporphyrinoid cofactors consisting of mono-, di-, and tri-anionic ligands (tetradehydrocorrin, porphycene, and corrole, respectively). In addition, practical procedures for the preparation of apo-hemoproteins, incorporation of artificial cofactors, and characterization techniques are presented. Furthermore, the representative catalytic activities of artificial enzymes generated by reconstitution of hemoproteins are summarized.

Redox flexibility of iron complexes supported by sulfur-based tris(o-methylenethiophenolato)amine relative to its tripodal oxygen-based congener.

Tripodal ligands designed to generate a local C3 symmetry have resulted in novel types of metal complexes that feature unusual bonding and electronic properties. However, most complexes reported to date are characterised by strong field ligands that enforce low or intermediate-spin states for the metal centres. Moreover, anionic sulfur-based tripodal ligands are particularly scarce due to their challenging synthesis. In this context, we herein report the synthesis, spectral characterization, structural, and electronic properties of an iron complex supported by the tripodal, trianionic ligand [N(CH2ArS)3](3-) as the trigonal-bipyramidal complexes [Fe{N(CH2ArS)3}(X)] ((X), X = DMSO, THF). The solid-state structures reveal local C3v symmetry around the Fe(3+) ions, while electron spin resonance measurements established a high-spin state (S = 5/2). Electrochemical studies demonstrate the redox flexibility of the FeS3 fragment by direct comparison with the oxygen-based analogue N(CH2ArOH)3, which displays an irreversible reduction; in contrast, (THF) has a reversible Fe(3+)/Fe(2+) redox process at -0.83 V (relative to the ferrocenium/ferrocene redox couple). The high spin and redox properties of (THF) are attributable to the weak ligand field provided by the NS3 fragment, as confirmed by the electronic structure calculated by density functional theory, which reveals substantial electronic delocalisation and covalency of the Fe-S bonds in (X).

Single-Crystal to Single-Crystal Linker Substitution, Linker Place Exchange, and Transmetalation Reactions in Interpenetrated Pillared-Bilayer Zinc(II) Metal-Organic Frameworks.

A twofold interpenetrated pillared-bilayer framework, {[Zn3 (L)2 (L2 )(DMF)]⋅(18DMF)(6H2 O)}n (1), has been synthesized from the ligands tris(4'-carboxybiphenyl)amine (H3 L) and 1,2-bis(4-pyridyl)ethylene (L2 ). The structure contains [Zn3 (COO)6 ] secondary building units (SBUs), in which three Zn(II) ions are almost linear with carboxylate bridging. This framework undergoes reversible pillar linker substitution reactions at the terminal Zn(II) centers with three different dipyridyl linkers of different lengths to afford three daughter frameworks, 2-4. Frameworks 2-4 are interconvertible through reversible linker substitution reactions. Also, competitive linker-exchange experiments show preferential incorporation of linker L3 in the parent framework 1. The larger linker L5 does not undergo such substitution reactions and framework 5, which contains this linker, can be synthesized solvothermally as a twofold interpenetrated structure. Interestingly, when framework 5 is dipped in a solution of L3 in DMF, linker substitution takes place as before, but linker L5 now moves and diagonally binds two Zn(II) centers to afford 6 as a nonpenetrated single framework. This linker place exchange reaction is unprecedented. All of these reactions take place in a single-crystal to single-crystal (SC-SC) manner, and have been observed directly through X-ray crystallography. In addition, each 3D framework undergoes complete copper(II) transmetalation.

Electron Hopping through Double-Exchange Coupling in a Mixed-Valence Diiminobenzoquinone-Bridged Fe2 Complex.

The ability of a benzoquinonoid bridging ligand to mediate double-exchange coupling in a mixed-valence Fe2 complex is demonstrated. Metalation of the bridging ligand 2,5-di(2,6-dimethylanilino)-3,6-dibromo-1,4-benzoquinone (LH2) with Fe(II) in the presence of the capping ligand tris((6-methyl-2-pyridyl)methyl)amine (Me3TPyA) affords the dinuclear complex [(Me3TPyA)2Fe(II)2(L)](2+). The dc magnetic measurements, in conjunction with X-ray diffraction and Mössbauer spectroscopy, reveal the presence of weak ferromagnetic superexchange coupling between Fe(II) centers through the diamagnetic bridging ligand to give an S = 4 ground state. The ac magnetic susceptibility measurements, collected in a small dc field, show this complex to behave as a single-molecule magnet with a relaxation barrier of U(eff) = 14(1) cm(-1). The slow magnetic relaxation in the Fe(II)2 complex can be switched off through one-electron oxidation to the mixed-valence congener [(Me3TPyA)2Fe2(L)](3+), where X-ray diffraction and Mössbauer spectroscopy indicate a metal-centered oxidation. The dc magnetic measurements show an S = 9/2 ground state for the mixed-valence complex, stemming from strong ferromagnetic exchange coupling that is best described considering electron hopping through a double-exchange coupling mechanism, with a double-exchange parameter of B = 69(4) cm(-1). In accordance with double-exchange, an intense feature is observed in the near-infrared region and is assigned as an intervalence charge-transfer band. The rate of intervalence electron hopping is comparable to that of the Mössbauer time scale, such that variable-temperature Mössbauer spectra reveal a thermally activated transition from a valence-trapped to detrapped state and provide an activation energy for electron hopping of 63(8) cm(-1). These results demonstrate the ability of quinonoid ligands to mediate electron hopping between high-spin metal centers, by providing the first example of an Fe complex that exhibits double-exchange through an organic bridging ligand and the largest metal-metal separation yet observed in any metal complex with double-exchange coupling.

ChemInform Abstract: Metal Complexes of Carbaporphyrinoid Systems

AbstractReview: [142 refs.

Two-dimensional assemblies in f-element ion (UO22+, Yb3+) complexes with two cyclohexyl-based polycarboxylates

Three complexes of f-element metal cations, uranyl and ytterbium(III), with either Kemp’s triacid (H3L1) or 1,2,3,4,5,6-cyclohexanehexacarboxylic acid (H6L2) were obtained under solvo-hydrothermal conditions. The trianionic ligand in [H2NMe2][UO2(L1)] (1) is in the very unusual boat conformation, with two equatorial and one axial carboxylate groups. In contrast to the all-axial chair conformation, this ligand geometry is not conducive to the formation of a closed species, and a honeycomb 2D network is formed instead. Adopting the chair conformation, this ligand reacts with ytterbium(III) to give the complex [Yb(L1)(H2O)2] (2), which crystallizes as a 2D network. All-cis H6L2 undergoes isomerization into its all-trans form under the conditions used, with all functional groups equatorial. In the presence of additional nickel(II) nitrate, the complex [Ni(H2O)6][(UO2)2(L2)]·1.5H2O (3) is obtained, in which the unusual coordination mode of the hexa-anionic ligand leads to the formation of a 2D assembly.

Approaching 'Kit-Type' Labelling with (68)Ga: The DATA Chelators.

The DATA chelators are a novel class of tri-anionic ligands based on 6-amino-1,4-diazepine-triacetic acid, which have been introduced recently for the chelation of (68)Ga. Compared with macrocyclic chelators based on the cyclen scaffold (i.e., DOTA, DO3A, and DO2A derivatives), DATA chelators undergo quantitative radiolabelling more rapidly and under milder conditions. In this study, a systematic evaluation of the labelling of four DATA chelators--DATA(M), DATA(P), DATA(Ph), and DATA(PPh)--with (68)Ga is presented. The results highlight the extraordinary potential of this new class of chelators for application in molecular imaging using (68)Ga positron emission tomography (PET).