Kinetics study of the substitution reaction of fac-[Fe(CN)2(CO)3I] with PPh3

Substitution reaction of fac-[Fe^II(CN)₂(CO)₃I]⁻ with triphenylphosphine (PPh₃) produced mono phosphine substituted complex cis-cis-[Fe^II(CN)₂(CO)₂(PPh₃)I]⁻. Crystal structure of the product showed that carbonyl positioned trans- to iodide was replaced by PPh₃. The substitution reaction was monitored by quantitative infrared spectroscopic method, and the rate law for the substitution reaction was determined to be rate = k[[Fe^II(CN)₂(CO)₂(PPh₃)I]⁻][PPh₃]. Transition state enthalpy and entropy changes were obtained from Eyring equation k = (k_BT/h)exp(−ΔH^≠/RT + ΔS^≠/R) with ΔH^≠ = 119(4) kJ mol⁻¹ and ΔS^≠ = 102(10) J mol⁻¹ K⁻¹. Positive transition state entropy change suggests that the substitution reaction went through a dissociative pathway.     

Reactions of the fac-[Re(CO)3] and [ReO] moieties with substituted benzothiazoles

The reaction of 2-(2-aminophenyl)benzothiazole (Habt) with [Re(CO)₅Br] led to the isolation of the rhenium(I) complex fac-[Re(Habt)(CO)₃Br] (1). With trans-[ReOCl₃(PPh₃)₂], the ligand Habt decomposed to form the oxofree rhenium(V) complex [Re(itp)₂Cl(PPh₃)] (2) (itp = 2-amidophenylthiolate). From the reaction of trans-[ReOBr₃(PPh₃)₂] with 2-(2-hydroxyphenyl)benzothiazole (Hhpd) the complex [Re^VOBr₂(hpd)(PPh₃)] (3) was obtained. Complexes 1-3 are stable and lipophilic. ¹H NMR and infrared assignments, as well as the X-ray crystal structures, of the complexes are reported.     

1-D coordination chains of Cu(hfac)2 and Mn(hfac)2 bridged by phenyl-nitronylnitroxide derivatives

Two alternating 1-D metal-radical linear [L:Cu(hfac)₂]_n and zig-zag [L:Mn(hfac)₂]_n chains (where L = 4-trimethylsilylethynyl-1-(4,4,5,5-tetramethyl-3-oxylimidazoline-1-oxide)benzene) and hfac = hexafluoroacetylacetonate) are described and characterized by X-ray diffraction of their crystals. Bulk magnetic measurements of L:Cu(hfac)₂ indicated a ferromagnetic interaction with J = 6 cm⁻¹ and L:Mn(hfac)₂ yielded ferrimagnetic interactions with J = −95 cm⁻¹. For the latter, a strong increase of their magnetic moment at lowest temperatures was observed only at very low static magnetic field, while for H_dc > 0.05 T saturation effect led to a downward slope after reaching a maximum.     

Syntheses, crystal structures, and magnetic properties of two cyclic dimer M2L2 complexes constructed from a new nitronyl nitroxide ligand and M(hfac)2 (M = Cu, Mn)

Two new binuclear radical complexes derived from a new long nitronyl nitroxide ligand, 2-[4-(5-pyrimidyl)phenyl]-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (4-NITPhPyrim), and M(hfac)₂ (M²⁺ = Cu²⁺, Mn²⁺; hfac⁻ = hexafluoroacetylacetonato), [Cu(hfac)₂(4-NITPhPyrim)]₂ · 4H₂O (1) and [Mn(hfac)₂(4-NITPhPyrim)]₂ · 4H₂O (2), were synthesized as well as characterized structurally and magnetically. X-ray analysis indicates that 1 and 2 are rectangle-like centrosymmetric dimer M₂L₂ complexes. Magnetic measurements indicate that there are two types of magnetic exchanges in 1: the ferromagnetic (FM) exchange between the Cu(II) ion and the directly bonded nitroxide unit (J₁ = 24.20 cm⁻¹) and the weak FM exchange of Cu-NIT through the pyrimidine and phenyl rings (J₂ = 0.62 cm⁻¹). Besides the strong antiferromagnetic (AFM) coupling between the Mn(II) ion and the directly bonded nitroxide unit (J = −87.61 cm⁻¹), there is a weak FM interaction between the two Mn-NIT pairs (θ = 0.39 K) in 2.     

Mechanistic studies on monodentate-ligand substitution of five-coordinate trigonal-bipyramidal platinum (II) complexes with tris[2-(diphenylphosphino)ethyl]phosphine

Reaction of the five-coordinate trigonal-bipyramidal platinum(II) complex, [Pt(pt)(pp₃)](BF₄) (pt = 1-propanethiolate, pp₃ = tris[2-(diphenylphosphino)ethyl]phosphine), with I⁻ in chloroform gave the five-coordinate square-pyramidal complex with a dissociated terminal phosphino group and an apically coordinated iodide ion in equilibrium. The thermodynamic parameters for the equilibrium between the trigonal-bipyramidal and square-pyramidal geometries, [Pt(pt)(pp₃)]⁺ + I⁻ ? [PtI(pt) (pp₃)], and the kinetic parameters for the chemical exchange were obtained as follows: , ΔH⁰ = − 10 ± 2.4 kJ mol⁻¹, ΔS⁰ = − 36 ± 10 J K⁻¹ mol⁻¹, , ΔH^‡ = 34 ± 4.7 kJ mol⁻¹, ΔS^‡ = − 50 ± 21 J K⁻¹ mol⁻¹. The square-planar trinuclear platinum(II) complex was formed by bridging reaction of one of the terminal phosphino groups of trigonal-bipyramidal [PtCl(pp₃)]Cl with trans-[PtCl₂(NCC₆H₅)₂] in chloroform. From these facts, ligand substitution reactions of [PtX(pp₃)]⁺ (X = monodentate anion) are expected to proceed via an intermediate with a dissociated phosphino group. The rate constants for the chloro-ligand substitution reactions of [PtCl(pp₃)]⁺ with Br⁻ and I⁻ in chloroform approached the respective limiting values as concentrations of the entering halide ions are increased. These kinetic results confirmed the preassociation mechanism in which the square pyramidal intermediate with a dissociated phosphino group and an apically coordinated halide ion is present in the rapid pre-equilibrium.     

Encapsulation of [Mn(bpy)3] cations in 2D [Mn(dca)3] sheet: Synthesis, X-ray structure and EPR study

The reaction of Mn(NO₃)₂ · 4H₂O, 2,2′-bipyridine (bpy) and sodium dicyanamide (dca) in aqueous medium yielded the {[Mn(bpy)₃][Mn(dca)₃]₂}_n (1). The single-crystal X-ray analysis of 1 revealed that the anionic part of the complex, [Mn(dca)₃]⁻, features infinite 2D sheets with a honeycomb-like porous structure having a void space of ca. 12 Å in which [Mn(bpy)₃]²⁺ cations are encapsulated to yield a fascinating molecular assembly. Mn^II ions possess an octahedral geometry both in the anionic and cationic components of complex 1. In the anionic component, each Mn^II ion is bridged by three pairs of dicyanamide anions in an end-to-end fashion with two other Mn^II ions from adjacent [Mn(dca)₃]⁻ moieties. This type of linking propagates parallel to the bc crystallographic plane to form 2D sheets. [Mn(bpy)₃]²⁺ is found to have somewhat “squeezed” upon encapsulation. No measurable magnetic interaction was evidenced through variable temperature magnetic susceptibility measurements. However, in addition to the broad g ≈ 2 resonance typical of magnetically diluted [Mn(bpy)₃]²⁺ cations, EPR spectroscopy evidenced exchange narrowing of the [Mn(dca)₃]⁻ resonance at g ≈ 2 thus indicating operation of weak magnetic interactions extended over the whole 2D network through the dca⁻ bridges.     

Bimetallic sheet and 3D threefold interpenetrating diamond-like network constructed by chelate Cu cations and Mn dicyanamide polymeric chains. Synthesis, crystal structure, and magnetism of [Cu(L)2][Mn(dca)4] (L=ethylenediamine or 1,3-diaminopropane; dca=dicyanamide N(CN)2)

Two novel bimetallic coordination polymers, [Cu(en)₂][Mn(dca)₄] (1) and [Cu(pn)₂][Mn(dca)₄] (2) (en, ethylenediamine; pn, 1,3-diaminopropane; dca, dicyanamide N(CN)₂⁻), have been synthesized and characterized. Both of them consist of Mndca anionic chains and chelate cations of copper. 1 has a sheet like architecture built by the [Cu(en)₂]²⁺ cations and the homoleptic trans-[Mn(dca)₄ ²⁻]_n chains. 2 shows unusual 3-D threefold interpenetrating diamond-like structure constructed by [Cu(pn)₂]²⁺ cations and the homoleptic cis-[Mn(dca)₄ ²⁻]_n chains. The magnetic susceptibilities obey the Curie-Weiss law with weak antiferromagnetic interactions.     

Synthesis, structures and magnetic properties of oxamido-bridged trinuclear Cu(II)-Mn(II)-Cu(II) complexes

Based on self-assembly of the dissymmetrical mononuclear entity CuL(CH₃OH) [H₂L = (E)-N¹-(2-((2-aminocyclohexydiimino)(phenyl)methyl)-4-chlorophenyl)-N²-(2-benzyl-4-chlorophenyl)oxalamide] with Mn(II), two trinuclear complexes were prepared. They are of the formula [(LCuN₃)₂Mn(CH₃OH)₂] · 2CH₃OH · 2H₂O (1) and [(LCuSCN)₂Mn(H₂O)₂] · 4CH₃OH (2). Their magnetic properties were studied by susceptibility versus temperature measurement, the best fitting of the experimental data led to J = −14.40 cm⁻¹ for 1 and J = −15.48 cm⁻¹ for 2. Hydrogen bonds help complex 1 to produce a novel S type one-dimensional chain-like supramolecular structure. In complex 2, Cl?Cl interaction also results in the formation of a one-dimensional structure.     

[60]Fullerene displacement from fac-(dihapto-[60]fullerene)(dihapto-1,2-bis-(1,10-phenanthroline) tricarbonyl tungsten(0)

The Lewis bases triphenyl phosphine and tricyclohexyl phosphine (L) displace [60]fullerene (C₆₀) from fac-(η²-C₆₀)(η²-phen)W(CO)₃ (phen=1,10-phenanthroline) to produce fac-(η²-phen)(η¹-L)W(CO)₃. Under flooding conditions, the reactions were first order with respect to fac-(η²-C₆₀)(η²-phen)W(CO)₃. The order with respect to C₆₀ and L depends on the reaction conditions i.e., whether [C₆₀]/[L] ≈ 0 or 0?It [C₆₀]/[L] ≈ 1. Two limiting cases of an interchange displacement of [60]fullerene from fac-(η²-C₆₀)(η²-phen)W(CO)₃, whose relative contributions to the overall mechanism depend on the nature of the solvent, are proposed based on the rate law and on the activation parameters. The mechanism involves an initial [60]fullerene dissociation to produce (i) the electronically unsaturated intermediate (η²-phen)W(CO)₃ for the dissociative displacement and (ii) the solvated intermediate fac-(solvent)(η²-phen)W(CO)₃ for the solvent-assisted [60]fullerene dissociation. The W-C₆₀ bond energy in fac-(η²-C₆₀)(η²-phen)W(CO)₃ was estimated to be in the vicinity of 105 kJ/mol based on the enthalpy of activation of the step where presumably [60]fullerene dissociates from fac-(η²-C₆₀)(η²-phen)W(CO)₃ to produce (η²-phen)W(CO)₃.     

Synthesis, crystal structure and magnetic properties of new dinuclear Mn(III) compounds with 4-ClC6H4COO and 4-BrC6H4COO bridges

Four new dinuclear Mn(III) compounds have been synthesised: [{Mn(bpy)(H₂O)}₂(μ-4-ClC₆H₄COO)₂(μ-O)}](ClO₄)₂ (1), [{Mn(EtOH)(phen)}₂(μ-O)(μ-4-ClC₆H₄COO)₂](ClO₄)₂ (2), [{Mn(bpy)(EtOH)}(μ-4-BrC₆H₄COO)₂(μ-O){Mn(bpy)(ClO₄)](ClO₄) (3) and [{Mn(H₂O)(phen)}₂(μ-4-BrC₆H₄COO)₂(μ-O)](ClO₄)₂ (4). The crystal structures of 2 and 3 are evidence for the tendency of the ethanol and the perchlorate to act as ligands. Due to the coordination of these groups, the environment of the manganese ions is elongated in the monodentate ligand direction, and this distortion is more important when this ligand is the perchlorate. The magnetic properties of the four compounds have been analysed: compounds 1, 3 and 4 show antiferromagnetic behaviour, with J = −6.33 cm⁻¹ for 1, J = −6.76 cm⁻¹ for 3 and J = −3.08 cm⁻¹ for 4 (H = −JS₁·S₂), while compound 2 shows a very weak ferromagnetic coupling. For this compound, at low temperature the most important effect on the χ_MT data is the zero-field splitting of the ion, and the best fit was obtained with |D_Mn| = 2.38 cm⁻¹ and |E_Mn| = 0.22 cm⁻¹.     

Kinetic studies of tris(2,2′-bipyridine)iron(III) perchlorate with cobaloxime, [Co(dmgBF2)2(H2O)2]

The kinetics of the reduction of by Co(dmgBF₂)₂(H₂O)₂ in 0.041 M HNO₃/NaNO₃ was found to be first-order in both the oxidizing and reducing agents and the second-order rate constant is given by k_obs = k₁ + k₂K[Cl⁻], with k₁=1.59 × 10⁶ M⁻¹ s⁻¹and k₂K = 1.83 × 10⁸ M⁻² s⁻¹, at 25 °C. The term that is first-order in [Cl⁻] is attributed to the formation of an ion-pair between and Cl⁻. For k₁, the activation parameters ΔH* and ΔS* are 2.22 ± 0.02 kcal mol⁻¹ and −22.7 ± 0.8 cal mol⁻¹ K⁻¹, respectively. The self-exchange rate constant of k₂₂ ≈ 8.7 × 10⁻³ M⁻¹ s⁻¹ for was estimated using Marcus theory and the known self-exchange rate constant for .     

Three Mn(II) supramolecular coordination complexes containing carboxylate-tetrazolate ligands

Three novel complexes [Mn(atza)₂(H₂O)₄] (1), [Mn(nptza)₂(CH₃OH)₄] (2), and [Mn(a4-ptz)₂(H₂O)₂]_n · 2nH₂O] (3) [atza = 5-aminotetrazole-1-acetato, nptza = 5-[(4-nitryl)phenyl] tetrazole-1-acetato, a4-ptz = 5-[N-acetato(4-pyridyl)] tetrazole] containing carboxylate-tetrazolate ligands have been synthesized and characterized by element analysis. X-ray crystallography shows that complexes 1 and 2 both contain mononuclear structure. The complex 3 is a 1D polymeric chain structure. Compounds 1-3 are self-assembled to form supramolecular structures through hydrogen bonds interactions.     

Intramolecular exchange of coordinated and dangling phosphines in pentacarbonyl group 6 complexes of 1,1,2-tris(diphenylphosphino)ethane

The linkage isomers, (OC)₅M[κ¹-PPh₂ CH₂CH(PPh₂)₂] 1 and (OC)₅M[κ¹-PPh₂ CH(PPh₂)CH₂PPh₂] 2 (M = Cr, Mo and W) exist in equilibrium at room temperature. Equilibrium constants for 1Cr ? 2Cr, 1Mo ? 2Mo and 1W ? 2W at 25 °C in CDCl₃ are 2.61, 5.0 and 4.74, respectively. Enthalpy favors the forward reaction (ΔH = −13.5, −12 and −12.2 kJ mol⁻¹, respectively) while entropy favors the reverse reaction (ΔS = −37.6, −28 and −28.2 J K⁻¹ mol⁻¹, respectively). Isomerization is much faster than chelation with 1Mo ? 2Mo ? 1W ? 2W > 1Cr ? 2Cr. Enthalpies of activation for 1Cr ? 2Cr and 1W ? 2W are 119.0 and 92.6 kJ mol⁻¹, respectively, and entropies of activation are 1.4 and −28.2 J K⁻¹ mol⁻¹, respectively. Isomerization is 10⁴ times faster for these complexes than for (OC)₅M[κ¹-PPh₂CH₂CH₂P(p-tolyl)₂]. A novel mechanism is proposed to account for the rate differences. The X-ray crystal structure of 2W shows that the phosphorus atom of the short phosphine arm lies very close to a carbon atom of the W(CO)₄ equatorial plane (3.40 Å) which could allow “through-space” coupling, accounting in part for the observation of long-range J_PC and J_PW coupling. The X-ray structure of (OC)₅W[κ¹-PPh₂ C(CH₂)PPh₂] 5W has been determined for comparison to 2W.     

Modulation of trans-to-cis photoisomerization and photoluminescence of 1,2-bis(4-pyridyl)ethylene or 4-styrylpyridine coordinated to fac-tricarbonyl(5-chloro-1,10-phenathroline)rhenium(I)

Photochemical and photophysical properties of fac-[Re(CO)₃(Clphen)(trans-L)]⁺ complexes, Clphen = 5-chloro-1,10-phenathroline and L = 1,2-bis(4-pyridyl)ethylene, bpe, or 4-styrylpyridine, stpy, were investigated to complement the understanding of intramolecular energy transfer process in tricarbonyl rhenium(I) complexes having an electron withdrawing group attached to polypyridyl ligands. These new compounds were synthesized, characterized and the photoisomerization quantum yields were accurately determined by ¹H NMR spectroscopy. The true quantum yields for fac-[Re(CO)₃(Clphen)(trans-bpe)]⁺ were constant (Φ = 0.55) at all investigated irradiation wavelengths. However, for fac-[Re(CO)₃(Clphen)(trans-stpy)]⁺, similar true quantum yields were observed only at higher energy irradiation (Φ_{313 nm} = 0.53 and Φ_{365 nm} = 0.57), but it decreased significantly at 404 nm (Φ = 0.41). These results indicated different deactivation pathways for the trans-stpy complex photoisomerization. Quantum yields decreased as the ³IL_trans-L and ³MLCT_Re→NN excited states become closer and the behavior was discussed in terms of the excited state energy gaps. Additionally, luminescence properties of photoproducts, fac-[Re(CO)₃(Clphen)(cis-L)]⁺, were also investigated in different environments to analyze the relative energy of the ³MLCT_Re→Clphen excited state for each compound.     

Ultrafast excited-state dynamics of photoisomerizing complexes fac-[Re(Cl)(CO)3(papy)2] and fac-[Re(papy)(CO)3(bpy)] (papy = trans-4-phenylazopyridine)

The character and dynamics of low-lying electronic excited states of the complexes fac-[Re(Cl)(CO)₃(papy)₂] and fac-[Re(papy)(CO)₃(bpy)]⁺ (papy = trans-4-phenylazopyridine) were investigated using stationary (UV-Vis absorption, resonance Raman) and ultrafast time-resolved (visible, IR absorption) spectroscopic methods. Excitation of [Re(Cl)(CO)₃(papy)₂] at 400 nm is directed to ¹ππ^∗(papy) and Re → papy ¹MLCT excited states. Ultrafast (?1.4 ps) intersystem crossing (ISC) to ³nπ^∗(papy) follows. Excitation of [Re(papy)(CO)₃(bpy)]⁺ is directed to ¹ππ^∗(papy), ¹MLCT(papy) and ¹MLCT(bpy). The states ³nπ^∗(papy) and ³MLCT(bpy) are then populated simultaneously in less then 0.8 ps. The ³MLCT(bpy) state decays to ³nπ^∗(papy) with a 3 ps time constant. ³nπ^∗(papy) is the lowest excited state for both complexes. It undergoes vibrational cooling and partial rotation around the -NN- bond, to form an intermediate with a nonplanar papy ligand in less than 40 ps. This species then undergoes ISC to the ground state potential energy surface, on which the trans and cis isomers are formed by reverse and forward intraligand papy rotation, respectively. This process occurs with a time constant of 120 and 100 ps for [Re(Cl)(CO)₃(papy)₂] and [Re(papy)(CO)₃(bpy)]⁺, respectively. It is concluded that coordination of papy to the Re center accelerates the ISC, switching the photochemistry from singlet to triplet excited states. Comparison with analogous 4-styrylpyridine complexes (M. Busby, P. Matousek, M. Towrie, A. Vl?ek Jr., J. Phys. Chem. A 109 (2005) 3000) reveals similarities of the decay mechanism of excited states of Re complexes with ligands containing -NN- and -CC- bonds. Both involve sub-picosecond ISC to triplets, partial rotation around the double bond and slower ISC to the trans or cis ground state. This process is about 200 times faster for the -NN- bonded papy ligand. The intramolecular energy transfer from the ³MLCT-excited ^∗Re(CO)₃(bpy) chromophore to the intraligand state of the axial ligand occurs for both L = stpy and papy with a comparable rate of a few ps.     

Synthesis of monoamine derivatives of [Ir4(CO)12]. X-ray crystal structure of [Ir4(CO)11(4-picoline)]

The mono-substituted amine derivatives [Ir₄(CO)₁₁L] (L = pyridine (1), 4-methylpyridine (2), 4-ter-butyl pyridine (3), 3,5-dimethylpyridine (4), 3,4-dimethylpyridine (5)) were obtained by the reaction of [Ir₄(CO)₁₁Br]⁻ with the corresponding aromatic amine. In the solid state, cluster 2 has an approximate C_s symmetry with all terminal ligands as shown by an X-ray analysis. In solution, this unbridged structure is in dynamic equilibrium with two other isomeric forms having three edge-bridging CO’s on a common basal face and the amine ligand coordinated in axial or in radial position relative to this face.     

Synthesis and crystal structure of bis{di-μ-hydroxobis[fac-tribromoaquotin(IV)]} heptahydrate

A product isolated from a reaction mixture of Br₂ and Ph₃ Sn(CH₂)₁₃CH₃ (3:1 mole ratio) in CHCl₃ solution in air was bis{di-μ-hydroxobis[fac-tribromoaquotin(IV)]} heptahydrate, 2[Br₃ (H₂O)Sn(μ-OH)₂ Sn(O₂H)Br₃] · 7H₂O, 2[fac-(1: X = Br)] · 7H₂O. Previous reports had indicated that the tin complexes, [fac-(1: X = Cl or Br)], had been obtained in various solvated forms from hydrolysis or oxidation/hydrolysis of appropriate tin(IV) or tin(II) halides. The crystal structure determination, reported here, provides an improved refinement of the core, i.e., [fac-(1: X = Br)], of 2[fac-(1: X = Br)] · 7H₂O compared to previous attempts. The solid state structure consists of a central rhomboidal planar Sn₂O₂ ring. The tin centres have distorted octahedral geometries, with each Br ligand trans to an O atom. The Br ligands, trans to the aqua ligands, form longer bonds to tin at 2.5556(7) and 2.5544(6) Å, than those trans to the bridging OH ligands, between 2.5021(7) and 2.5127(7) Å. The Br, OH and H₂O ligands as well as the solvate water molecules are all involved in an extensive hydrogen bonding system in 2[fac-(1: X = Br)] · 7H₂O.     

A new series of iodocarbonyl ruthenium (II) complexes with unsymmetrical phosphine-phosphine sulfide ligands of the type Ph2P(CH2)nP(S)Ph2, n = 1-4: Isolation and structural investigation

Hexa-coordinated chelate complex cis-[Ru(CO)₂I₂(P∩S)] (1a) {P∩S = η²-(P,S)-coordinated} and penta-coordinated non-chelate complexes cis-[Ru(CO)₂I₂(P∼S)] (1b-d) {P∼S = η¹-(P)-coordinated} are produced by the reaction of polymeric [Ru(CO)₂I₂]_n with equimolar quantity of the ligands Ph₂P(CH₂)_nP(S)Ph₂ {n = 1(a), 2(b), 3(c), 4(d)} in dichloromethane at room temperature. The bidentate nature of the ligand a in the complex 1a leads to the formation of five-membered chelate ring which confers extra stability to the complex. On the other hand, 1:2 (Ru:L) molar ratio reaction affords the hexa-coordinated non-chelate complexes cis,cis,trans-[Ru(CO)₂I₂(P∼S)₂] (2a-d) irrespective of the ligands. All the complexes show two equally intense terminal ν(CO) bands in the range 2028-2103 cm⁻¹. The ν(PS) band of complex 1a occurs 23 cm⁻¹ lower region compared to the corresponding free ligand suggesting chelation via metal-sulfur bond formation. X-ray crystallography reveals that the Ru(II) atom occupies the center of a slightly distorted octahedral geometry. The complexes have also been characterized by elemental analysis, ¹H, ¹³C and ³¹P NMR spectroscopy.     

Complexes of [Re(CO)3Cl] with different oxidation states of the polyfunctional bmtz/H2bmtz ligand system (bmtz=3,6-bis(2-pyrimidyl)-1,2,4,5-tetrazine)

Combining fac-[Re(CO)₃Cl] with components of the ligand redox system bmtz/bmtz⁻/H₂bmtz/H₂bmtz⁻ (bmtz=3,6-bis(2-pyrimidyl)-1,2,4,5-tetrazine) has led to the isolation of the complexes (H₂bmtz)Re(CO)₃Cl, (μ-H₂bmtz)[Re(CO)₃Cl]₂ and (μ-bmtz)[Re(CO)₃Cl]₂. Other species characterized were (bmtz)Re(CO)₃Cl (UV/Vis, IR), [(H₂bmtz)Re(CO)₃Cl]⁻ (UV/Vis, IR, EPR), {(μ-H₂bmtz)[Re(CO)₃Cl]₂}⁻ (UV/Vis, IR, EPR) and {(μ-bmtz)[Re(CO)₃Cl]₂}⁻ (UV/Vis, IR, X band and high-field EPR). The results confirm bmtz as very strong and H₂bmtz as moderate π acceptor ligand versus one or two chelate-bonded low-valent metal centers. Reactivity is observed in terms of oxidative proton and reductive chloride dissociation.     

Trinuclear-based coordination compounds of Mn(II) and Co(II) with 4-amino-3,5-dimethyl-1,2,4-triazole and azide and thiocyanate anions: Synthesis, structure and magnetic properties

A 2D layer complex 1 and a linear trinuclear complex 2 with mixed ligands have been synthesized and characterized by elemental analyses, IR and single-crystal X-ray diffraction. In 1, the Mn(II) ions are six-coordinated and lie in distorted octahedron coordination environments. Complex 1 is connected into a 2D layer structure based on a linear trinuclear Mn₃(admtrz)₄(N₃)₆ (admtrz = 4-amino-3,5-dimethyl-1,2,4-triazole) building unit with either (6,3) topology when Mn1 cations as three-connected nodes or (4,4) network when the coordination trinuclear units being regarded as four connected nodes. In 2, the Co(II) ions are in slightly distorted octahedron coordination geometries. The magnetic behaviors are investigated in the temperature range 1.8-300 K. The magnetic susceptibility measurements show that the Mn(II) ions of complex 1 are weakly antiferromagnetically coupled with g = 1.98(1), J1 = −6.31(5) cm⁻¹ and J2 = −1.88(1) cm⁻¹. There is dominant zero field splitting (ZFS) effects with g values, g_// = 2.38(2) and g_⊥ = 4.96(4), indicated a significant presence of the spin-orbit coupling and magnetization experiment reveals large, uniaxial zero-field splitting parameters of D = −29.55 cm⁻¹ for 2.