Maoyu Shang

Synthesis and characterization of a neutral, low spin iron(III) complex of a hexadentate tripodal ligand containing three imidazolate arms. Use as a dinucleating agent

Abstract The iron(III) complex of the Schiff base formed from the condensation of 1 equiv. of trist(2-aminoethyl)amine (tren) and 3 equiv. of 4-methyl-5-imidazolecar☐aldehyde has been synthesized by the reaction of iron(III) methoxide, tren and 4-methyl-5-imidazolecar☐aldehyde in methanol. Fetren(meim)3 is low spin as indicated by magnetic moment, Mo¨ssbauer and ESR measurements. The crystal structure of Fetren(meim)3 was determined (space group Pna21, R1 = 0.0331 and wR2 = 0.0857). The complex is six-coordinate although the ligand is potentially heptadentate. Basicity of the three ‘backside’ imidazolate nitrogens is demonstrated in the crystal structure by H-bonding interactions and in solution by reactions with acidic metal complexes. ZnTPP and M(hfa)2 (M = Cu(II), Ni(II)), to give imidazolate bridged adducts. Products of the reaction of Fetren(meim)3 with M(hfa)2 were isolated and identified as the 1:1 adducts.

Synthesis and structural and magnetic characterization of discrete phenolato and imidazolate bridged Gd(III)–M(II) [M=Cu, Ni] dinuclear complexes

Three dinuclear complexes formed by the reaction of Gd(hfa)3 (hfa is hexafluoroacetylacetonate) with Schiff base complexes of Cu(II) and Ni(II) have been synthesized and characterized. The crystal structures of the complexes [Gd(hfa)3M(prpen)] {MCu(II (1)), Ni(II) (2)} are reported. (H2prpen is the Schiff base derived from the condensation of 2 equiv. of 2-hydroxypropiophenone and 1 equiv. of ethylenediamine.) Both 1 and 2 are discrete dinuclear complexes consisting of an eight coordinate Gd atom which is bridged to four coordinate M(II) via both phenolate oxygen atoms of the prpen ligand. The crystal structure shows there is no tendency toward dimerization between adjacent Cu(II) Schiff base units in 1. Cryomagnetic measurements show a ferromagnetic interaction between Gd(III) and Cu(II) in 1 as predicted by theory with J 1.91 cm 1 . The reaction of Gd(hfa)3 with Ni(L) (H2L is the Schiff base derived from the condensation of 1 equiv. each of 5-chlorobenzophenone, 1,2-diaminobenzene, and 5-methyl-4-imidazolecarboxaldehyde) produced Gd(hfa)3Ni(L) (3) in which imidazolate is available to bridge Gd(III) and Ni(II).

The oxidation of [Co(edta)]2− by [Co(phen)3]3+

Abstract [(Co(phen)3][(Sb(R, R)-tartrate)2] · 8H2O, C44H44N6O20CoSb2, crystallizes in the trigonal space group P3221 (No. 154) with Z = 3, a = 18.861(4), c = 11.917(3) A and R = 0.035 for 1800 reflections. The structure has been determined and the absolute configuration of (+)589-[Co(phen)3](ClO4)3 · 2H2O formed from the compound by Cl2 oxidation is confirmed as Λ. Reduction of [Co(phen)3]3+ by [Co(edta)2− is outer-sphere with a second-order rate constant of 9.6 x 10−3 M−1 s−1 at 25 °C and 0.10 M ionic strength. When Λ-[Co(phen)3]3+ is used as oxidant, chiral induction is observed and the [Co(edta)]− product shows a enantiomeric excess of 20% of the Λ isomer. This homochiral (ΛΛ) preference contrasts with the heterochiral (ΔΛ) preference found previously for reactions of [Co(edta)]2− with [Fe(phen)3]3+ and [Os(phen)3]3+. Interpretation of the results is aided by 1H NMR relaxation studies of the ion pair {[Co(phen)3]3+, [Co(edta)]−}.

Synthesis and structural characterization of copper complexes of N4 tetradentate Schiff bases derived from N-alkylated 2-aminobenzaldehyde. Effects of cyclization, oxidation, and dinucleation

Abstract The structures of the copper complexes of 7,8,15,16,17,18-hexahydro-dibenzo[e,m][1,4,8,11]tetraazacyclotetradecine (Cu(2,2 mac)) 7,8,15,18-tetrahydro-dibenzo[e,m][1,4,8,11]tetraazacyclotetradecine-16,17-dionato (Cu(2,2 oxomac)) and Cu(Nue5f8CH3 amben) and Cu(2,2 oxomac)Ni(hfa)2 are reported. The three copper complexes containing a 14-membered macrocycle are essentially square planar complexes and exhibit no short axial interactions. The analogous acyclic complex, Cu(Nue5f8CH3 amben), exhibits an average tetrahedral distortion of 34.35° which appears to be due to steric repulsion between the two methyl groups. The dinuclear complex, which exhibits a planar exchange coupled oxamido core, was prepared by reaction of Cu(2,2 oxomac) with Ni(hfa)2. The analogous complex, Cu(2,2 oxomac)Cu(hfa)2, can be prepared by the same procedure or by reaction of Cu(2,2 mac) with Cu(hfa)2. The former method is a general synthetic route while the latter is specific for Cu(hfa)2 relying on its ability to catalyze the oxidization of the ethylene unit between the anilino nitrogen atoms to the oxamide (Nue5f8CH2ue5f8CH2ue5f8Nue5f8 to Nue5f8COue5f8COue5f8Nue5f8) under ambient conditions.

Structure and magnetic properties of [Cr(en)2(ox)][Cr(en)(ox)2]·2H2O,Δ-[Cr(en)3]Δ-[Cr(ox)3] and Δ-[Co(en)3]Δ-[Cr(ox)3]

Abstract Interactions between metal ion complexes in the compounds Δ-[Cr(en)3]Δ-[Cr(ox)3] and Δ-[Co(en)3]Δ-[Cr(ox)3] have been investigated by X-ray crystallography and magnetic susceptibility measurements. Crystals of both compounds are hexagonal and are isostructural with the known Δ-[Co(en)3]Δ-[Rh(ox)3] [Inorg. Chem. 30 (1991) 4954] with chains of alternating anions and cations parallel to the crystallographic c-axis. The susceptibility behavior suggests that magnetic interactions are stronger in Δ-[Cr(en)3]Δ-[Cr(ox)3] where both anion and cation are paramagnetic than in Δ-[Co(en)3]Δ-[Cr(ox)3] where only the anion is paramagnetic. Single crystal studies with the former compound reveal that magnetic interactions along the c-axis chains, where the Cr–Cr distances are shortest, are weaker than those involving off-axis interactions. Magnetic measurements were also made on [Cr(en)2(ox)][Cr(en)(ox)2]·2H2O. The structure of this compound has been previously reported.

Effects of electronic structure on chiral induction in outer-sphere electron transfer reactions of complexes with the C3 symmetric ligand, 1,4,7-triazacyclononane-1,4,7-tris[2′(R)-2′-propionate](-3)

Abstract The ligand 1,4,7-triazacyclononane-1,4,7-tris[2′( R )-2′-propionate](-3)(( R )-tacntp 3− ), binds stereospecifically to transition metal ions. The structures of the complexes [Cr(( R )-tacntp)]·NaBr and [Fe(( R )-tacntp)]·H 2 O have been determined by X-ray crystallography. Both complexes have the Λ-configuration but the conformation of the chelate rings in Λ-[Cr(( R )-tacntp)] is (λ,λ,λ) with a geometry close to octahedral while in Λ-[Fe(( R )-tacntp)] it is (δ,δ,δ) and the geometry is closer to that of a trigonal prism. Chiral induction in the electron transfer reactions of Λ-[Co(( R )-tacntp)], Λ-[Fe(( R )-tacntp)] and Λ-[Mn(( R )-tacntp)] with [Co(( RR,SS )-chxn) 3 ] 2+ has been investigated. All three reactions are outer-sphere and four isomeric [Co(( RR,SS )-chxn) 3 ] 3+ products are identified in each case. The oxidants Λ-[Fe(( R )-tacntp)] and Λ-[Mn(( R )-tacntp)] show very similar selectivities, quite different from those of Λ-[Co(( R )-tacntp)]. Reasons for this behavior are discussed.

STEREOSELECTIVITY IN THE REDUCTION OF Λ-[1,4,7-TRIAZACYCLONONANE-1,4,7-TRIS[2′(R)-2′-PROPIONATE]COBALT(III)]

Abstract [Co((R)-tacntp)] · NaBr, C15H24BrCoNaN3O6 crystallizes in the trigonal space group R3(No. 146) with Z = 3, a = 9.843(2) A, c = 15.781(4) A and R = 0.053 for 859 reflections. The structure has been determined and the absolute configuration about the complex is M(C3) (Λ). The second-order rate constant for outer-sphere reduction of Λ-[Co((R)-tacntp)] by [Co(en)3]2+ is 6.3 × 10−2 M−1s−1 at 25.0°C and 0.10 M ionic strength. The product, [Co(en)3]3+, is formed with 11% enantiomeric excess of the ▵ isomer. The corresponding reduction of Λ-[Fe((R)-tacntp)] has a rate constant 5 × 103 M−1s−1 and results in formation of [Co(en)3]3+ which shows 3% enantiomeric excess of the ▵ isomer.

μ-Oxo-bis[(2,3,12,13-tetrabromo-5,10,15,20-tetraphenylporphyrinato)-iron(III)] bis(dichloromethane) solvate

The precise structure of the title compound, [Fe(2)O(C(44)H(24)Br(4)N(4))(2)].2CH(2)Cl(2), is reported. The Fe-N distances are non-equivalent in pairs because of the asymmetric peripheral substitution; the values are 2.098 A to the brominated rings and 2.041 A to the other two rings. The Fe-O bond distance is 1.7583 (4) A. The molecule has required twofold symmetry so that there is one unique porphyrin macrocycle and one Fe-O bond length in contrast to a previous report on the same species.

Self-assembly of a CuTIM(S2O7) polymer: synthesis and crystallographic studies

Abstract A novel self-assembled polymer of Cu(TIM)+2 (where TIM=Me4[14]1,3,8,10-tetraeneN4, a macrocyclic ligand) with disulfate bridges has been synthesized and investigated by X-ray crystallography, IR, electronic and ESR spectroscopy. The compound crystallizes in the monoclinic space group C2/c with cell parameters a=16.745(4), b=7.4288(13), c=16.657(4) A, β=115.789(19)°. The coordination geometry around the Cu(II) center is axially elongated distorted octahedral. The basal plane around the Cu center is planar with zero deviation from the weighted least square plane comprising four nitrogen atoms (N1, N2, N1′ and N2′) of the macrocyclic ligand. Two axial positions are occupied by the O atoms of the S2O7xa02− molecules. The Cu⋯Cu distance is quite long (8.328 A) along the chain. The X-band ESR spectra of a powdered solid sample of [CuTIM(S2O7)]n polymer, recorded at room temperature gives a isotropic spectrum with a g value of 2.22.

The chemistry of ruthenium complexes of 1,2-dicyanoethylene dithiolate (mnt2−). Synthesis and characterization of [RuIV/III(mnt)3]2−/3− and the derivatives trans-[RuIII(mnt)2(PPh3)2]−, trans-[RuIII(mnt)2(py)2]− and trans-[RuIV(mnt)2(Br)2]2−

The chemistry of ruthenium(III) and ruthenium(IV) complexes with 1,2-dicyanoethylene dithiolate(2−) (mnt2−) as ligand has been investigated. The tris-complex [RuIII(mnt)3]3− is readily prepared and oxidized to [RuIV(mnt)3]2−. Both complex anions are characterized by X-ray structural analysis. Ligand substitution behavior of the anions has been examined. Reactions of [RuIII(mnt)3]3− with triphenylphosphine and pyridine are sluggish while reactions of [RuIV(mnt)3]2− with these nucleophiles are complex, involving reduction by the displaced mnt2− ligand, to give trans-[RuIII(mnt)2(PPh3)2]− and trans-[RuIII(mnt)2(py)2]− respectively. A ruthenium(IV) complex, trans-[RuIV(mnt)2(Br)2]2−, is formed on treatment of [RuIV(mnt)3]2− with Br2. These three products have also been characterized by X-ray crystallography. In solution, the complexes trans-[RuIII(mnt)2(PPh3)2]− and trans-[RuIV(mnt)2(Br)2]2− both lose one axial ligand in rapidly established equilibria. The complex, [RuIV(mnt)3]2−, undergoes an unusual photochemical rearrangement in the presence of oxygen resulting in formation of [RuII(mnts)2]2− where mnts2− is a novel tridentate sulfur-bound ligand.