Trigonal Bipyramidal Complexes Research Articles

Synthesis, structure and magnetic properties of copper(II) complexes of 2-amino-5-trifluoromethylpyridine (5-TFMAP): (5-TFMAP)2CuX2 (X = Cl or Br), (5-TFMAP)3CuBr2 and [(5-TFMAP)2CuBr2](5-TFMAPH)Br

Reaction of 2-amino-5-trifluoromethylpyridine (5-TFMAP) with copper halides in water or alcohol solvents produced four coordination complexes: (5-TFMAP)2CuX2, (X=Cl (1) or Br (2)), (5-TFMAP)3CuBr2 (3) and [(5-TFMAP)2CuBr2](5-TFMAPH)Br (4). In all compounds, the 5-TFMAP ligands are coordinated to the Cu(II) ion through the pyridine nitrogen atom in a trans-geometry and a nearly square planar environment is observed in 1, 2 and 4. In 3, coordination of an additional 5-TFMAP ligand results in a distorted trigonal bipyramidal complex. All complexes are characterized by single-crystal X-ray diffraction. Compound 1 crystalizes as a chain structure via pairs of long Cl…Cu contacts between molecules and the temperature dependent magnetic susceptibility data has been fit to an alternating chain model, resulting in J=−5.97(1)K and J′=−0.95(4)K. Compound 2 exhibits weaker antiferromagnetic interactions, also via the bihalide superexchange pathway, resulting in J=−3.02(2)K from a fit to the uniform chain model. The structure of compound 3 also exhibits a uniform antiferromagnetic chain, but via the two-halide pathway (short Br…Br contacts) and susceptibility data exhibit significantly stronger interactions (J=−31.05(5)K). Compound 4 is not stable in air and loses a molecule of 5-TFMAP from the crystal lattice upon standing.

Pushing the limits of magnetic anisotropy in trigonal bipyramidal Ni(ii).

Monometallic complexes based on 3d transition metal ions in certain axial coordination environments can exhibit appreciably enhanced magnetic anisotropy, important for memory applications, due to stabilisation of an unquenched orbital moment. For high-spin trigonal bipyramidal Ni(ii), if competing structural distortions can be minimised, this may result in an axial anisotropy that is at least an order of magnitude stronger than found for orbitally non-degenerate octahedral complexes. Broadband, high-field EPR studies of [Ni(MDABCO)2Cl3]ClO4 (1) confirm an unprecedented axial magnetic anisotropy, which pushes the limits of the familiar spin-only description. Crucially, compared to complexes with multidentate ligands that encapsulate the metal ion, we see only a very small degree of axial symmetry breaking. 1 displays field-induced slow magnetic relaxation, which is rare for monometallic Ni(ii) complexes due to efficient spin-lattice and quantum tunnelling relaxation pathways.

Synthesis, characterization, and reactivity of iron(III) complexes supported by a trianionic ONO(3-) pincer ligand.

Synthetic and characterization results of a new family of Fe(III) compounds stabilized by a trianionic [CF3-ONO](3-) pincer-type ligand are reported. The ligand possesses three negatively charged donors constrained to the meridional positions that provide sufficient electron density to stabilize high-valent metal complexes. Using the redox-insulated [CF3-ONO](3-), pentacoordinated square-pyramidal {[CF3-ONO]FeCl2}{LiTHF2}2 (3), dimeric μ-DME{[CF3-ONO]FeDME}2 (4), trigonal bipyramidal [CF3-ONO]Fe(bpy) (5), and octahedral [CF3-ONO]Fe(bpy)H2O (5·H2O) complexes are synthesized. An interesting feature of the [CF3-ONO](3-) pincer-type ligand is its ability to coordinate the metal center in both the more common meridional positions or occupying a face of a trigonal bipyramidal complex. The molecular structure of 3 contains structural features similar to those of a rare square-planar high-spin Fe(II) complex, and the important role of the counterions in stabilizing a square-plane is emphasized. SQUID magnetometry measurements of 3 reveal its high-spin character, and cyclic voltammetry measurements indicate high oxidation state species are unstable. However, all compounds can be reduced, and in particular 5 displays a reversible reduction event at -2255 mV versus ferrocene (Fc(+)/Fc) that can be assigned to either the Fe(I)/Fe(0) couple or 2,2'-bipyridine reduction.

Mono- and polynuclear vanadium(IV) and -(V) compounds with 2-substituted phenyl/pyridyl heterocyclic chelates

In this account, we report the isolation of novel vanadium(IV) and -(V) compounds with 2-substituted phenyl/pyridyl heterocyclic chelates. The 1:2molar reaction between NH4VO3 and 2-hydroxyphenylbenzothiazole (Hobs) led to the formation of a polynuclear vanadium(IV) compound, [VO(obs)2]n (1). A trigonal bipyramidal mononuclear complex, cis-[VO2(obz)py] (2) was formed from the reaction of NH4VO3 and 2-hydroxyphenylbenzimidazole (Hobz) in the presence of pyridine. The novel octahedral vanadium(IV) complex, [VO(Hpbyz)2SO4] (3).H2O was afforded from the 2:1molar reaction between 2-pyridylbenzimidazole (Hpybz) and VOSO4. These metal compounds were characterized by means of conductance measurements, UV–Vis, Emission, EPR, IR, 51V- and 1H NMR spectroscopy as well as single crystal X-ray diffraction. The difference between the electronic properties of the respective metallic compounds are emphasized by the intense intra-ligand (π–π∗) relaxations observed in the emission spectra of 1 (at 466nm) and 2 (469nm) while no emission spectrum could be attained for 3. The X-ray studies revealed that in 1 and 2, the chelating moieties act as monoanionic bidentate chelators (i.e. obs or obz) through the deprotonated phenolic oxygens and neutral heterocyclic nitrogens whereas a Npy,Nbz-coordination mode of the neutral Hpbyz chelators are observed in 3.

Synthesis and Structural Characterization of Ruthenium Carbonyl Cluster Complexes Containing Platinum with a Bulky N-Heterocyclic Carbene Ligand

The reaction of Ru3(CO)12 with Pt(IMes)2 in benzene solvent at room temperature afforded the monoplatinum-triruthenium cluster complex Ru3Pt(IMes)2(CO)11, 1, in 21% yield and the trigonal bipyramidal cluster complex Ru3Pt2(IMes)2(CO)12, 2, in 26% yield. The reaction of Ru(CO)5 with Pt(IMes)2 in benzene solvent at 0 °C yielded two trinuclear cluster complexes, the monoplatinum-diruthenium Ru2Pt(IMes)(CO)9, 3, and the monoruthenium-diplatinum cluster complex RuPt2(IMes)2(CO)6, 4. The reaction of 2 with hydrogen at 80 °C afforded the tetrahydrido-tetraruthenium complex Ru4(IMes)(CO)11(μ-H)4, 5, and the dihydrido-diruthenium-diplatinum complex Ru2Pt2(IMes)2(CO)8(μ-H)2, 6. All six compounds were structurally characterized by single-crystal X-ray diffraction analyses.

Theoretical study of the magnetic anisotropy and magnetic tunnelling in mononuclear Ni(ii) complexes with potential molecular magnet behavior

Magnetic molecules that present a slow decay of their magnetization (molecular magnets) are very interesting both from a fundamental and applied points of view. While many approaches focus strongly on finding systems with strong magnetic anisotropy giving rise to large spin-reversal barriers, less is known on the behavior of magnetic tunnelling, which is also a fundamental component of molecular magnet behavior. In this work, we propose a model to describe both the spin-reversal barrier and magnetic tunnelling in Ni(II) trigonal bipyramidal complexes, which could be easily extended to other transition-metal systems. Based on this model, we show the criteria that lead to the optimal complexes to find molecular magnet behavior. We test our proposal with multi-reference configuration-interaction (MRCI) and ligand-field-density-functional-theory (LF-DFT) first-principles calculations applied over several families of mononuclear Ni(II) complexes. As a salient result, we find that the complex [NiCl3(Hdabco)2]+ (dabco is 1,4-diazabicyclo[2.2.2]-octane) displays both a very large magnetic anisotropy energy, 524 cm−1, and a small tunnelling splitting, 0.2 cm−1, when compared to other systems containing the same metal. We expect molecular magnet behaviour to be observed when small magnetic fields are employed to disrupt tunnelling. These values are reached due to the choice of ligands that favor a complete destruction of the Jahn–Teller distortions through spin–orbit coupling and an unquenched orbital momentum.

Z-Selective Ring-Opening Metathesis Polymerization of 3-Substituted Cyclooctenes by Monoaryloxide Pyrrolide Imido Alkylidene (MAP) Catalysts of Molybdenum and Tungsten

Ring-opening metathesis polymerization of a series of 3-substituted cyclooctenes (3-MeCOE, 3-HexCOE, and 3-PhCOE) initiated by various Mo and W MAP complexes leads to cis,HT-poly(3-RCOE) polymers. The apparent rate of polymerization of 3-HexCOE by W(N-t-Bu)(CH-t-Bu)(Pyr)(OHMT) (1c; Pyr = pyrrolide; OHMT = O-2,6-Mesityl2C6H3) is greater than the rate of polymerization by Mo(N-t-Bu)(CH-t-Bu)(Pyr)(OHMT) (1b), but both gave the same cis,HT polymer structures. Formation of HT-poly(3-RCOE) employing 1c takes place via propagating species in which the R group (methyl, hexyl, or phenyl) is on C2 of the propagating alkylidene chain, a type of intermediate that has been modeled through the preparation of W(N-t-Bu)(CHCHMeEt)(Pyr)(OHMT). The rate of ROMP is exceedingly sensitive to steric factors: e.g., W(N-t-Bu)(CH-t-Bu)(Me2Pyr)(OHMT), the dimethylpyrrolide analogue of 1c, essentially did not polymerize 3-HexCOE at 22 °C. When a sample of W(N-t-Bu)(CHCHMeEt)(Pyr)(OHMT) and 3-methyl-1-pentene in CDCl3 is cooled to −20 °C, the alkylidene resonances for W(N-t-Bu)(CHCHMeEt)(Pyr)(OHMT) disappear and resonances that can be ascribed to protons in a synα/synα′ disubstituted trigonal bipyramidal metallacyclobutane complex appear. 3-Methyl-1-pentene is readily lost from this metallacycle on the NMR time scale at room temperature.

Facile synthesis of a rare example of an iron(III) iodide complex, [FeI3(AsMe3)2], from the reaction of Me3AsI2 with unactivated iron powder

The reaction of Me3AsI2 with unactivated iron powder provides a synthetic entry into the coordination chemistry of iron(III) iodide, which is inaccessible by traditional routes due to the low stability of the parent halide FeI3. The reaction of iron powder with Me3AsI2 results in the formation of a trigonal bipyramidal complex, [FeI3(AsMe3)2], which features the iodide ligands in the equatorial positions, and the Me3As groups occupying the axial positions. This complex is a rare example of an iron(III) iodide complex, and is the first iron(III) complex of a monodentate tertiary arsine ligand. The preparation of [FeI3(AsMe3)2] via the direct oxidation of iron powder further demonstrates that complexes of “soft” donor ligands can be prepared with “hard” transition metal centres, such as iron(III), in direct contravention of the HSAB principle. The structure of [FeI3(AsMe3)2] is isomorphous with all previously reported [MX3(EMe3)2] (M=main group or transition metal, X=halide, E=N, P, As) trigonal bipyramidal structures.

Reprint of Bis(phosphinomethyl)phenylamines and bis(phosphinomethyl)sulfides and their reaction with d8-platinum group precursors

The potentially tridentate phosphines R2PCH2XCH2PR2 [X=NPh, R=Ph (1), tBu (2), Cy (3), X=S, R=Ph (4), tBu (5)] were treated with different Pd(II), Pt(II) as well as Rh(I) and Ir(I) complex precursors. All new palladium and platinum compounds are formed as cis bisphosphine complexes. This is also the case if the sterically demanding phosphines 2 and 3 are treated with MCl(CO)(PPh3)2 while the comparable reaction with 1 generates trigonal bipyramidal complexes. In contrast to this the reaction of 5 with Ir(CO)2Cl(p-TolNH2) forms the macrocycle 5b. All new compounds have been characterized by 1H, 13C, 31P NMR and IR spectroscopy. Single crystal X-ray analysis has been performed from most of the compounds as well.

Conversion of Fe–NH2 to Fe–N2 with release of NH3

Tris(phosphine)borane ligated Fe(I) centers featuring N(2)H(4), NH(3), NH(2), and OH ligands are described. Conversion of Fe-NH(2) to Fe-NH(3)(+) by the addition of acid, and subsequent reductive release of NH(3) to generate Fe-N(2), is demonstrated. This sequence models the final steps of proposed Fe-mediated nitrogen fixation pathways. The five-coordinate trigonal bipyramidal complexes described are unusual in that they adopt S = 3/2 ground states and are prepared from a four-coordinate, S = 3/2 trigonal pyramidal precursor.

Synthesis, characterization, cytotoxicity and antimicrobial studies on bis(N-furfuryl-N-(2-phenylethyl)dithiocarbamato-S,S′)zinc(II) and its nitrogen donor adducts

[Zn(fpedtc)2] (1), [Zn(fpedtc)2(py)] (2), [Zn(fpedtc)2(1,10-phen)] (3) and [Zn(fpedtc)2(2,2′-bipy)] (4) (where fpedtc = N-furfuryl-N-(2-phenylethyl)dithiocarbamate, py = pyridine, 1,10-phen = 1,10-phenanthroline and 2,2′-bipy = 2,2′-bipyridine) were synthesized. Characterization of the complexes were achieved by IR and NMR (1H and 13C) spectra and in addition, for 2 and 3, by X-ray crystallography. Single crystal X-ray structural analysis of 2 and 3 showed that complex 2 is almost half way between trigonal bipyramidal and square pyramidal and complex 3 has a distorted octahedral geometry. Zn–N distances in 2 is shorter than that found in a six coordinate complex 3 due to the change in coordination number. These complexes were also screened for in vitro antibacterial and antifungal activities and significant activities have been found. In vitro cytotoxic activity of all the synthesized complexes was evaluated on HeLa cell line. Complex 1 exhibits maximum inhibitory effect at a concentration of 40 μg mL−1 on HeLa cell line.

ChemInform Abstract: Unexpected Formation of Stannolanes and Trigonal Bipyramidal Tin Complexes by Radical Cyclization Reaction.

AbstractThe radical cyclization of chiral aza‐Morita—Baylis—Hillman adducts (I) with Bu3SnH yields bicyclic stannolanes (III) with high diastereoselectivity.

Manganese Nitride Complexes in Oxidation States III, IV, and V: Synthesis and Electronic Structure

The synthesis and characterization of a series of manganese nitrides in a tripodal chelating tris(carbene) ligand framework is described. Photolysis of [(TIMEN(xyl))Mn(N(3))](+) (where TIMEN(xyl) = tris[2-(3-xylylimidazol-2-ylidene)ethyl]amine) yields the isolable molecular Mn(IV) nitride, [(TIMEN(xyl))Mn(N)](+). Spectroscopic and DFT studies indicate that this Mn(IV) d(3) complex has a doublet electronic ground state. The metal-centered one-electron oxidation of this Mn(IV) species results in formation of the pentavalent Mn(V) nitride, [(TIMEN(xyl))Mn(N)](2+). Unlike previously reported, tetragonal Mn(V) nitrides with a d(2), nonmagnetic S = 0 ground state, this trigonal bipyramidal complex has a triplet ground state S = 1. One-electron reduction of [(TIMEN(xyl))Mn(N)](+) produces the neutral, nonmagnetic trivalent [(TIMEN(xyl))Mn(N)] species with a d(4) low-spin, S = 0, ground state.

Metavanadate at the Active Site of the Phosphatase VHZ

Vanadate is a potent modulator of a number of biological processes and has been shown by crystal structures and NMR spectroscopy to interact with numerous enzymes. Although these effects often occur under conditions where oligomeric forms dominate, the crystal structures and NMR data suggest that the inhibitory form is usually monomeric orthovanadate, a particularly good inhibitor of phosphatases because of its ability to form stable trigonal-bipyramidal complexes. We performed a computational analysis of a 1.14 Å structure of the phosphatase VHZ in complex with an unusual metavanadate species and compared it with two classical trigonal-bipyramidal vanadate-phosphatase complexes. The results support extensive delocalized bonding to the apical ligands in the classical structures. In contrast, in the VHZ metavanadate complex, the central, planar VO(3)(-) moiety has only one apical ligand, the nucleophilic Cys95, and a gap in electron density between V and S. A computational analysis showed that the V-S interaction is primarily ionic. A mechanism is proposed to explain the formation of metavanadate in the active site from a dimeric vanadate species that previous crystallographic evidence has shown to be able to bind to the active sites of phosphatases related to VHZ. Together, the results show that the interaction of vanadate with biological systems is not solely reliant upon the prior formation of a particular inhibitory form in solution. The catalytic properties of an enzyme may act upon the oligomeric forms primarily present in solution to generate species such as the metavanadate ion observed in the VHZ structure.

Bis(phosphinomethyl)phenylamines and bis(phosphinomethyl)sulfides and their reaction with d8-platinum group precursors

The potentially tridentate phosphines R2PCH2XCH2PR2 [X=NPh, R=Ph (1), tBu (2), Cy (3), X=S, R=Ph (4), tBu (5)] were treated with different Pd(II), Pt(II) as well as Rh(I) and Ir(I) complex precursors. All new palladium and platinum compounds are formed as cis bisphosphine complexes. This is also the case if the sterically demanding phosphines 2 and 3 are treated with MCl(CO)(PPh3)2 while the comparable reaction with 1 generates trigonal bipyramidal complexes. In contrast to this the reaction of 5 with Ir(CO)2Cl(p-TolNH2) forms the macrocycle 5b. All new compounds have been characterized by 1H, 13C, 31P NMR and IR spectroscopy. Single crystal X-ray analysis has been performed from most of the compounds as well.

Different geometries of novel cobalt(II) compounds with 2-hydroxy-benzophenones and neocuproine: Crystal and molecular structures of [Co(2-hydroxy-benzophenone)2(neoc)], [Co(2-hydroxy-4-methoxybenzophenone)(neoc)Br] and [Co(neoc)Br2]·CH3OH·H2O

Ten mixed-ligand Co(II) compounds with 2-hydroxy-benzophenones(ketones) and neocuproine(neoc) were synthesized and characterized by physicochemical and spectral (IR, UV–Vis) data. The cyclic voltammetry study in CH3CN gave all the expected waves for the redox processes of the metal Co(II) and the studied ligands. The X-ray diffraction study of two representative compounds proved the two different geometries, octahedral for [Co(2-hydroxy-benzophenone)2(neoc)] (3) and trigonal bipyramidal for [Co(2-hydroxy-4-methoxybenzophenone)(neoc)Br] (10). Additionally, the precursor compound [Co(neoc)Br2]·CH3OH·H2O (11) was proved by (X-ray) to posses tetrahedral geometry. The molecular structure and the possible isomers of the trigonal bipyramidal complex 10 were studied by means of density functional calculations (DFT). The thermal stability was investigated by means of simultaneous TG/DTG–DTA technique in nitrogen atmosphere up to 1000°C, where metallic cobalt was found as the solid residue.

Synthesis and structural characterization of bis[(4S,5R)-4-methoxycarbonyl-5-methyl-1,3-oxazolidine]copper(II) dichloride and bis[(4S,5R)-4-methoxycarbonyl-5-methyl-2-oxazoline]-[(4S,5R)-4-methoxycarbonyl-5-methyl-1,3-oxazolidine]ruthenium(III) trichloride

In the reaction of N,N′-methylenebis[(4S,5R)-4-methoxycarbonyl-5-methyloxazolidine] (1) with CuCl2 or RuCl3 in alcoholic solvents novel complexes, bis[(4S,5R)-4-methoxycarbonyl-5-methyl-1,3-oxazolidine]copper(II) dichloride (2) and bis[(4S,5R)-4-methoxycarbonyl-5-methyl-2-oxazoline]-(4S,5R)-4-methoxycarbonyl-5-methyl-1,3-oxazolidineruthenium(III) trichloride (3), respectively, were isolated and fully characterized by X-ray crystallography. In these reactions, which occurred under mild conditions, ligand 1 was cleaved at the bridging aminal position and degraded to (4S,5R)-4-methoxycarbonyl-5-methyl-1,3-oxazolidine 5. The trigonal bipyramidal Cu complex 3 contains two such oxazolidine ligands coordinated in different ways. One is bonded in a monodentate fashion via the nitrogen atom of the five-membered ring, the other binds as a bidentate ligand, additionally using the carbonyl oxygen of the ester group. In the octahedral Ru complex 4 there are one oxazolidine ligand 5 and two oxazoline ligands 6. Thus, in the synthesis of 4 the carbon atom between oxygen and nitrogen in the oxazolidine ring was partly oxidized from the half-aminal status to the carboxamide status.

Unexpected formation of stannolanes and trigonal bipyramidal tin complexes by radical cyclization reaction

Optically active stannolanes and trigonal bipyramidal pentacoordinated tin complexes were readily prepared by radical cyclization of N-propargylated chiral aza-Morita-Baylis-Hillman adducts induced by Bu(3)SnH. A translocated radical through the cyclization attacked the Bu(3)Sn group in an S(H)2 manner.

Facile synthesis of rhodium and iridium complexes bearing a [PEP]-type ligand (E = Ge or Sn) via E–C bond cleavage

Rhodium and iridium complexes bearing a tridentate [PEP] type ligand ([PEP] = {o-(Ph(2)P)C(6)H(4)}(2)E(Me); E = Ge or Sn) were synthesized through the phosphine exchange reaction accompanied by selective E-C bond cleavage. The ligand precursors {o-(Ph(2)P)C(6)H(4)}(2)EMe(2) (E = Ge or Sn) were readily obtained in excellent yields by treating {o-(Ph(2)P)C(6)H(4)}(2)Li with 0.5 equivalents of Me(2)ECl(2). Tris(triphenylphosphine)rhodium(I) carbonyl hydride M(H)(CO)(PPh(3))(3) (M = Rh, Ir) cleaved one of the E-Me bonds of {o-(Ph(2)P)C(6)H(4)}(2)EMe(2) exclusively to afford the trigonal bipyramidal (TBP) complexes, [PEP]M(CO)(PPh(3)). Square-planar rhodium complexes [PEP]Rh(PPh(3)) were also prepared from the reactions of tetrakis(triphenylphosphine)rhodium(I) hydride Rh(H)(PPh(3))(4) with {o-(Ph(2)P)C(6)H(4)}(2)EMe(2). Further, the trans influence of group 14 elements E (E = Si, Ge, Sn) in [PEP]Rh(PPh(3)) is discussed in terms of the (1)J(Rh-P) coupling constants, indicating that E exhibited a stronger trans labilizing effect in the order Sn < Ge < Si.

Oxo iron(iv) as an oxidative active intermediate of p-chlorophenol in the Fenton reaction: a DFT study

Debate continues over which active species plays the role of oxidative agent during the Fenton reaction-the HO˙ radical or oxo iron [Fe(IV)O](2+). In this context, the present study investigates the oxidation of p-chlorophenol by [Fe(IV)O(H(2)O)(5)](2+) using DFT calculations, within gas-phase and micro-solvated models, in order to explore the possible role of oxo iron as a reactant. The results show that the chlorine atom substitution of p-chlorophenol by oxo iron is a highly stabilising step (ΔH = -83 kcal mol(-1)) with a free energy barrier of 5.8 kcal mol(-1) in the micro-solvated model. This illustrates the high oxidising power of the [Fe(IV)O(H(2)O)(5)](2+) complex. On the other hand, the breaking of the Fe-O bond, leading to the formation of hydroquinone, is observed to be the rate-determining step of the reaction. The rather large free energy barrier corresponding to this bond cleavage amounts to 10.2 and 9.3 kcal mol(-1) in the gas-phase and micro-solvated models, respectively. Elsewhere, the lifetime of the HO˙ radical has previously been shown to be extremely small. These facts, combined with observations of oxo iron under certain experimental conditions, suggest that oxo iron is a highly plausible oxidative species of the reaction. In addition, a trigonal bipyramidal iron complex, coordinated either by hydroxyl groups and/or by water molecules, has been found in all described mechanisms. This structure appears to be a stable intermediate; and to our knowledge, it has not been characterised by previous studies.