Partha Chakraborty

Synthesis, structure, EPR and electrochemical studies of a μ2-phenoxo bridged manganese(II) dimer afforded by a binucleating macrocylic ligand

Abstract The reaction of 2 moles of tris(2-aminoethyl)amine and 3 moles of 4-methyl-2,6 diformyl phenol in acetonitrile solution affords a light yellow crystalline solid having composition of H 3 L, which on reacting with manganese(II) acetate tetrahydrate in alkaline methanol produced the binuclear complex [Mn II 2 L] + . This has been isolated as a perchlorate salt. The X-ray structure of [Mn II 2 L]ClO 4 ·H 2 O is reported. The lattice consists of two crystallographically independent but metrically very similar binuclear units. Manganese(II) ions are tris μ 2 -phenolato bridged and the distorted octahedral metal coordination spheres are of type MnN 3 O 3 . The frozen (77 K) EPR spectrum of the complex shows group of 11 hyperfine lines with coupling constants of 43.7 G showing that the unpaired electrons interact with both 55 Mn centres. The complex displays two successive oxidation couples with E 1 2 values 0.54 and 1.07 V vs saturated calomel electrode.

Hexacoordinated complexes of bivalent zinc incorporating thioether binding

Abstract The reaction of zinc(II) acetate dihydrate with dithiaalkyl-substituted triazene 1-oxides, [RN(O)NNHC6H4S]2(CH2)2 (H2RL; RMe, Ph) has afforded light-yellow Zn(MeL) and light-green Zn ( PhL )· 1 2 CH 2 Cl 2 , the first hexacoordinated of zinc bonded by acyclic ligands incorporating thioether sites. Spectral features ff the complexes are briefly noted. Both the complexes have been structurally characterized revealing distorted octahedral binding of the metal ion in ZnO2N2S2 coordination spheres; the ZnO, ZnN and ZnS distances lie in the ranges 2.056(7)−2.105(8), 2.005(8)−2.029(8) and 2.649(4)−2.720(3) A, respectively. Crystal data: Zn(MeL): monoclinic, space group P21/c, a = 26.529(9), b = 7.974(3), c = 19.396(8) A , β = 110.57(3)°, V = 3842(3) A 3 , Z = 8, R = 5.40%, Rw = 5.73%; Zn ( PhL )· 1 2 CH 2 Cl 2 ; orthorhombic, space group Pbcb, a = 9.540(3), b = 19.449(6), c = 29.534(8) A, V = 5480(3) A 3 , Z = 8, R = 5.65%, Rw = 5.42%.

Synthesis, structure and metal redox of a family of copper complexes derived from hexadentate ligands incorporating thioether and triazene 1-oxide functions

Abstract Hexadentate ligands of type RN(O)NN(H)C6H4S(CH2)xSC6H4(H)NN(O)NR (H2L1: R = Me, x = 2; H2L2: R = Ph, x = 2 ; H2L3: R = Me, x = 3 ; general abbreviation H2L) have afforded copper(II) complexes of type [CuL]. The X-ray structure of [CuL2] · 1 2 CH 2 Cl 2 reveals the presence of a distorted CUS2N2O2 coordination sphere which is strongly elongated along an OCuS axis. The axial and equatorial bond lengths are: CuS, 2.636(5) and 2.473(6) A Cu0, 2.222(10) and 2.039(11) A respectively. Both the CuN bonds, 1.939(13) and 1.904(12) A lie on the equatorial plane. The structure is compared with that of [ZnL2] · 1 2 CH 2 Cl 2 , which does not display the above-noted axial elongation. The findings are rationalized in terms of simple angular overlap considerations. The EPR spectrum of [CuL2] · 1 2 CH 2 Cl 2 has g|; > g⊥, showing that the hole lies in the dx2- y2 orbital. The [CuL] complexes are electroactive in dichloromethane solutions and successive quasireversible responses due to the [CuIIL]/[CuIL]− and [CuIIIL]+/[CuIIL] couples are observed, the E 1 2 values being ∼ −0.9 V and ∼ 0.8 V vs SCE, respectively. The E 1 2 of the copper(IIIcopper(II) copple lies close to that of the corresponding nickel (III)nickel(II) couple of [NiL]. A thermodynamic rationale is provided.

Mono- and tetra-nuclear manganese(III) complexes of tripodal tris[2-(salicylideneamino)ethyl]amines

The tripodal ligands N[CH2CH2NCHC6H3X(OH)-2]3(X = H, H3L1 or Cl-5, H3L2] afford the mononuclear complexes [MnIIIL]. Structural work has shown that the symmetry of the facial MnN3O3 co-ordination sphere in the two solvates [MnL2]·3H2O and [MnL2]·MeOH varies considerably as the former has C3 and the latter C1 symmetry. The implications of these differences are discussed. Reaction of [MnL] with manganese(III) acetate dihydrate in alkaline media affords the antiferromagnetic tetranuclear cations [MnIII4O2L2]2+ in high yields. X-Ray studies on [Mn4O2L12][PF6]2·4MeCN have revealed a centrosymmetric Mn4(µ3-O)28+ core, with the shortest Mn ⋯ Mn contact being 2.906(3)A. The metal co-ordination spheres are of two types: facial-MnN3O3 and MnNO5. The cyclic voltammograms of [Mn4O2L2]2+ display two successive waves due to the MnIII–MnII couples of the MnN3O3 spheres. For [MnL] only one such couple is observed. Oxidative responses due to MnIV–MnIII couples are also observed. Some preliminary work on an iron(III) analogue of [Mn4O2L2]2+ is also described.

FeCl3-catalysed Zn-mediated allylation of cyclic enol ethers in water

AbstractA mild and environment-friendly Zn-mediated allylation of dihydrofuran and dihydropyran catalysed by iron(III) chloride in water has been developed. Graphical AbstractA mild and environment friendly Zn-mediated allylation of dihydrofuran and dihydropyran catalysed by iron(III) chlorides in water has been developed.

Manganese(III)-carboxylate binding : chemistry and structure of a hydrated pyridinedicarboxylate

The reaction of Mn(CH3COO)3 2H2O with the carboxyl-rich ligand pyridine-2,6-dicarboxylic acid (H2L) in methanol affords a high-spin (S = 2) hydratedbis-complex. Structure determination has revealed the solid to be [MnIII(H2 L)(L)] [MnIIIL2] 5H2 O: space group P−1;Z = 2;a = 7.527(3)Å3,b= 14.260(4)Å,c = 16.080(6)Å,α = 91.08(3)°,β = 103.58(3)°,γ= 105.41(3)° andV= 1611.2(10)Å3. Each ligand is planar and is bonded in the tridentate O2N fashion. The MnO4N2 coordination spheres show large distortions from octahedral symmetry. The lattice is stabilised by an extensive network of O…O hydrogen-bonding involving water molecules and carboxyl functions. Upon dissolution in water, protic redistribution occurs and the complex acts as the mono-basic acid Mn(HL)(L) (pK, 4.3 ±0.05). The deprotonated complex displays high metal reduction potentials: MnIVL2-MnIIIL2−, 1.05V; MnIIIL2−MnIIL22−-, 0.28V vs. SCE