Electron transport and magnetic properties of some mixed-valent alkalithiocuprates

Electrical transport properties of some two-dimensional isostructural compounds KCu4S3, RbCu4S3, and CsCu4S3 and a one dimensional conductor Na3Cu4S4 have been investigated. Conductivities have been measured on pelletized materials in the temperature range 300 to 150 K. All of them behave as metallic conductors. The room temperature conductivities of these compounds are KCu4S3, 1600 Ω-1 cm-1; RbCu4S3, 1400 Ω-1 cm-1; CsCu4S3, 1250 Ω-1 cm-1; Na3Cu4S4, 700 Ω-1 cm-1. The observed trend in conductivities among the isostructural compounds may be rationalized either on the basis of shortest Cu---Cu distances or on the carrier charge concentrations per unit volume. All of these compounds behave as Pauli paramagnetic materials

Mono- and dinuclear oxovanadium (IV) compounds containing VO(ONS) basic core: synthesis, structure and spectroscopic properties

Reaction of [VO(acac)2] with S-methyl 3-(2-hydroxyphenyl) methylenedithiocarbazate (H2L1) and its nitro- (H2L2) and bromo derivatives (H2L3) as tridentate heterodonor (ONS)2− ligands offers a basic VO(ONS) core. In the presence of bidentate (N,N′) donor ancillar ligands, various mono- and dinuclear oxovanadium(IV) complexes [VOL(2,2′-bipy)] (1–3), [VOL(Phen)] (4, 5) and [LOV(μ-4,4′-bipy)VOL] (4, 5) and [LOV(μ-4,4′-bipy)VOL] (6–8) were obtained. The compounds have been characterized by EPR, electronic and FAB mass spectroscopic studies. The X-ray crystal structure of a representative compound [VOL2(2,2′-bipy)] (2) is reported and shows the presence of the tridentate ONS ligand occupying the meridional sites leading to distorted octahedral geometry. The nitrogen donor, occupying an apical position has a trans-labilizing influence, resulting in elongation of the V=O terminal bond. Magnetic susceptibility and EPR spectral studies indicate non-interacting nature ( vbJ vb ≈ 0) of the vanadium(IV) unpaired electrons in the dinuclear complexes (6–8).Subodh Kanti Dutta, Edward R. T. Tiekink and Muktimoy Chaudhur

Copper(II)-induced methanolysis of a stable enediol: isolation and crystallographic characterization of chloro(methylpicolinato-N,O)(picolinato-N,O)-copper(II)

Mallika Bhar, Muktimoy Chaudhury and Edward R. T. Tiekin

Metal complexes of sulphur-nitrogen chelating agents: Part 11 - Synthesis, characterisation, and thermodynamics of nucleophilic substitution reactions of monohalogeno nickel(II) complexes of tridentate ligands of the type SNN in solution and the solid state

Square-planar nickel(II) complexes [NiLX](X = Cl, Br, I, or SCN) have been obtained through deprotonation of the ligands methyl 2-(β-aminoethylamino)cyclopent-1-enedithiocarboxylate (HL1), methyl 2-(β-aminoisopropylamino)cyclopent-1-enedithiocarboxylate (HL2), and methyl 2-(β-diethylaminoethylamino)cyclopent-1-enedithiocarboxylate (HL3). Diamagnetic complexes of composition [NiL(MeCN)][ClO4](L = L1-L3) and [Ni2L2(HL)][ClO4]2(L = L1 or L2) have also been synthesised. The equilibrium constants for the nucleophilic substitution reaction [NiL2X]+ B ⇌[NiL2(B)]++ X-(X = Cl, Br, or I; B = pyridine and its methyl-substituted derivatives) have been determined spectrophotometrically in the temperature range 25-50 ¯C. A linear correlation has been obtained between the ΔH⊖ and ΔS⊖ values. The enthalpy changes (ΔH2) and activation energies (Ea*) for the thermal dissociation [NiL2(B)]X(s)→[NiL2X](s)+ B(g) have been determined. A linear correlation has been found between the (ΔS2) and Ea* values

Tri- and Tetranuclear Nickel(II) Inverse Metallacrown Complexes Involving Oximato Oxygen Linkers: Role of the Guest Anion (Oxo versus Alkoxo) in Controlling the Size of the Ring Topology

A trinuclear oximato complex, [(NiHL1)3( μ3-O)]ClO4 (1), with inverse metallacrown 9-MC-3 topology has been synthesized using a Schiff-base ligand (H2L1) formed by condensation of ethanolamine (Hea) and diacetylmonoxime (Hdamo). The diamagnetic compound has been characterized by electrospray ionization mass spectrometry as well as by single-crystal X-ray diffraction analysis. In the solid state, the alcoholic OH group in this molecule stays away from coordination. Surprisingly in a similar chemical reaction, when intact Hea and Hdamo have been used as ligands instead of their Schiff-base forms, the product obtained is a 12-MC-4-type metallacrown, (Et3NH)[Ni4(damo)4(Hea)2(ea)2](ClO4)3 (2), with a larger cavity size needed to accommodate a pair of hydrogen-bonded (O-H3 3 3 O)- anions. Unlike in 1, the alcoholic OH groups in 2 take part in metal coordination. Compound 2 on being refluxed with lithium hydroxide inmethanol is converted to 1 in almost quantitative yield. This appears to be a novel reaction type, leading to contraction of a metallacrown ring size. A family of 12-MC-4 Ni4 metallacrowns in inverse topology, viz., [Ni4(damo)4(H2dea)2(Hdea)2](ClO4)2 3 2H2O (3), [Ni4(dpko)4(Hea)2(ea)2](ClO4)2 3 4H2O (4), and [Ni4(mpko)4(Hmea)2(mea)2](ClO4)2 (5), have been synthesized following a methodology similar to that adopted for 2, using different combinations of free oximes [viz., dipyridylketonoxime (Hdpko) and methylpyridylketonoxime (Hmpko)] and amin alcohols [viz., diethanolamine (H2dea), and N-methylethanolamine (Hmea)]. Crystal and molecular structures of 3-5 have been reported, each involving either a quasi (in 3) or a perfect (in 4 and 5) square plane (S4 symmetry) with four octahedral Ni centers occupying the corners, and serve as a backbone of puckered metallacrown rings that accommodate a pair of hydrogenbonded (O-H3 3 3 O)- anions. Antiferromagnetic interactions within the [Ni4] core [J/kB ≈ -20 to -27 K based on the following spin Hamiltonian: H=-2J(S1 3 S2þ S2 3 S3þ S3 3 S4þ S4 3 S1)] lead to an ST=0 ground state for these complexes. Introduction Metallacrowns are a type of metallacycle that can be considered as inorganic analogues of crown ethers because of the similarities they have both in structure and in function.1 These compounds usually have a combination of a transition-metal ion and a heteroatom (usually nitrogen

Tetra-, Tri-, and Mononuclear Manganese(II/III) Complexes of a Phenol-Based N2O2 Capping Ligand: Use of Carboxylates as Ancillary Ligands in Tuning the Nuclearity of the Complexes

Manganese(II/III) complexes of a phenol-based tetradentate ligand L2- [H2L ) N,N′-dimethyl-N,N′-bis(2-hydroxy- 3,5-dimethylbenzyl)-ethylenediamine], namely, [Mn4(L)2(PhCOO)6] (1), [Mn3(L)2(CH3CH2COO)2(OMe)2] · H2O (2), and [Mn(L){(CH3)3CCOO}(CH3OH)] · CH3OH (3), have been synthesized. The basicity and steric congestion provided by the carboxylate moiety used as an ancillary ligand have profound influence on tuning the nuclearity of these compounds. Results of X-ray crystallography, electronic spectroscopy, and variable-temperature (1.8-300 K) magnetic measurements have been used to characterize these compounds. Complex 1 has a very interesting centrosymmetric structure that involves two crystallographically equivalent binuclear [MnII-MnIII] units, connected together by a pair of syn-anti bridging benzoates to generate a “dimer of dimers” structural motif. Compound 2 with propionate as the ancillary ligand, on the other hand, has a nearly linear MnIII-MnII-MnIII core with antiferromagnetically coupled (J ) -0.13 cm-1) metal centers. Compound 1 has an ST ) 9 spin ground state with ferromagneticlly coupled metal centers (Jwb) 2.8(1) and Jbb ) 0.09(2) cm-1) that failed to function as a single molecule magnet due to the presence of low-lying excited states with smaller spin values and a weak magnetic anisotropy. The electron paramagnetic resonance spectrum of 1 in the frozen solution (12 K) displays two signals in the g ) 2 and g ) 4 regions, each split into six lines due to 55Mn (I ) 5/2) superhyperfine couplings. The use of bulky pivalate as a replacement for benzoate provides enough steric bulk to generate a mononuclear species [Mn(L){(CH3)3CCOO}(CH3OH)] · CH3OH (3). The lone manganese(III) center in this compound has an octahedral geometry, completed by the tetradentate ligand L2- together with an axially coordinated methanol molecule and a monodentate pivalate. The latter two are connected by a hydrogen bond, thus stabilizing the monodentate carboxylate moiety. Redox behaviors (CV) of 1 and 3 are grossly similar, each undergoing a quasi-reversible reduction process at E1/2 ) -0.03 and -0.11 V, respectively, versus a Ag/AgCl reference