Methyl-transfer reaction to alkylthiol catalyzed by a simple vitamin B12 model complex using zinc powder

The catalytic methyl-transfer reaction from methyl tosylate to 1-octanethiol was carried out in the presence of a simple vitamin B₁₂ model complex, [Co(III){(C₂C₃)(DO)(DOH)pn}Br₂], with zinc powder as the reducing reagent at 50 °C. Such a catalytic reaction proceeded via the formation and dissociation of a cobalt-carbon bond in the simple vitamin B₁₂ model complex under non-enzymatic conditions. The mechanism for the methyl-transfer reaction was investigated by electronic and mass spectroscopies. The Co(I) species, which is generated from the reduction of the catalyst by the zinc powder, and its methylated CH₃-Co complex were found to be indispensable intermediates.     

Synthesis and electrochemistry of Co(III) and Co(I) complexes having C5Me5 auxiliary

The synthesis and electrochemistry of half-sandwich type of Co(III) complexes [(C₅Me₅)Co(bidentate)(CH₃CN)](BF₄)₂ {bidentate = dppe (1,2-bis(diphenylphosphino)ethane), dppp (1,3-bis(diphenylphosphino)propane), bpy (2,2′-bipyridine), en (ethylenediamine)) are reported. Cyclic voltammograms of [(C₅Me₅)Co(bidentate)(CH₃CN)](BF₄)₂ in CH₃CN s showed two redox couples assignable to Co(II)/Co(III) and Co(I)/Co(II). The Co(I) complex having C₅Me₅ and dppe was also prepared. Two redox couples of this Co(I) complex, (C₅Me₅)Co(dppe), in CH₃CN coincided with those of [(C₅Me₅)Co(dppe)(CH₃CN)](BF₄)₂ in spite of the structural change around the metal center.     

Rh and Ir dibenzo[a,e]cyclooctatetraene complexes: Chloro, hydroxo, and mixed Au oxo complexes

New and improved procedures are reported for the synthesis of [M(DBCOT)(μ-Cl)]₂ (M = Rh, Ir; DBCOT = dibenzo[a,e]cyclooctatetraene) from MCl₃(H₂O)_x or [M(COD)(μ-Cl)]₂ and DBCOT. Treatment of [M(DBCOT)(μ-Cl)]₂ with [(LAu)₃(μ-O)]BF₄(L = PPh₃, P^tBu₃) yields the mixed-metal oxo complexes [M(DBCOT)(μ⁴-O)(AuL)₂]₂(BF₄)₂. Dimeric [Rh(DBCOT)(μ-OH)]₂ is obtained from the reaction of [M(DBCOT)(μ-Cl)]₂ with KOH in EtOH/H₂O. All complexes except [Rh(DBCOT)(μ-Cl)]₂ have been structurally characterized by single crystal X-ray diffraction.     

Syntheses and crystal structures of the first iridium complexes with m- and p-terphenyl (tp). {[Ir2(p-tp)(cod)2](BF4)2 · 2CH2Cl2}3 and [Ir(m-tp)(η-C5Me5)](BF4)2

Novel two iridium terphenyl complexes were prepared and their structures were characterized crystallographically. The reaction of [Ir(cod)₂]BF₄ with p-terphenyl (p-tp) in CH₂Cl₂ was carried out to afford dinuclear Ir(I) complex {[Ir₂(p-tp)(cod)₂](BF₄)₂ · 2CH₂Cl₂}₃ (cod=1,5-cyclooctadiene) (1 · 2CH₂Cl₂), whereas the reaction of the intermediate [Ir(η⁵-C₅Me₅)(Me₂CO)₃]³⁺ in Me₂CO with m-terphenyl (m-tp) was done to provide mononuclear Ir(III) complex [Ir(m-tp)(η⁵-C₅Me₅)](BF₄)₂ (2). In complex 1 · 2CH₂Cl₂, two Ir atoms are η⁶-coordinated to both sides of terminal benzene rings from the upper and lower sides in the p-tp ligand, while one Ir atom is η⁶-coordinated to one side of the terminal benzene ring in the m-tp ligand in complex 2. Each crystal structure describes the first coordination mode found in metal complexes with the m- and p-tp ligands.     

Synthesis of dimethylcobalt(III) complexes containing trimethylphosphine and 2-formyl-phenolato- or 2-formyl-enolato(O:O) ligands

Substituted salicylaldehydes [C₆HR¹R²R³(CHO)(OH)] react with CoMe₃(PMe₃)₃ to afford 6-coordinate (cis-dimethyl)(2-formyl-phenolato)trans-bis(trimethylphosphine)cobalt(III) compounds Co[C₆HR¹R²R³(CHO)(O)Me₂](PMe₃)₂ (1: R¹ = H; R² = Me; R³ = tert-Bu; 2: R¹, R² = C₆H₄; R³ = H). Accordingly, substituted enolated malonic dialdehydes (CHO-CR⁴CR⁵-OH) react with CoMe₃(PMe₃)₃ to afford 6-coordinate (cis-dimethyl)(2-formyl-enolato)trans-bis(trimethylphosphine)cobalt(III) compounds Co[(CHO-CR⁴CR⁵-O)(Me)₂](PMe₃)₂ (3: R⁴, R⁵ = (CH₂)₂C₆H₄; 4: R⁴ = R⁵ = C₆H₅). In the molecular structure of 4, the cobalt atom is centred in an octahedral coordination geometry brought about by a six-membered chelate ring (O:O-ligand), cis-dimethyl and trans-trimethylphosphine groups. A reaction mechanism is suggested.     

Two new 4′,4′′-disubstituted dipyrazolylpyridine derivatives, and the structures and spin states of their iron(II) complexes

Reaction of 2 equiv of the sodium salt of ethyl pyrazole-4-carboxylate, with 1 equiv of 2,6-dibromopyridine, in diglyme at 130 °C for 5 days yields 2,6-di[4-(ethylcarboxy)pyrazol-1-yl]pyridine (L¹), with 2-bromo-6-[4-(ethylcarboxy)pyrazol-1-yl]pyridine (L²) as a significant byproduct. Reduction of L¹ with excess NaBH₄ in thf affords 2,6-di[4-(hydroxymethyl)pyrazol-1-yl]pyridine (L³) in low yield. The crystalline complex [Fe(L¹)₂][BF₄]₂ · 2CF₃CH₂OH is low-spin at 150 K, while bulk samples with this formula are approximately 10% high-spin and 90% low-spin at room temperature. This ratio does not vary significantly on cooling from its magnetic susceptibility, suggesting that the material might be contaminated by a second, minor high-spin phase. Single crystals of [Fe(L³)₂][BF₄]₂·1.4CH₃CN have a mixed spin-state population, with the low-spin state predominating at 150 K. The [Fe(L³)₂(BF₄)]⁺ moieties in the lattice associate into 1-D chains through intermolecular O-H?O and O-H?F hydrogen bonding. Bulk samples of [Fe(L³)₂][BF₄]₂ · H₂O are fully low-spin below 200 K, but the magnetic data imply the onset of a gradual thermal spin-transition centred above room temperature. DSC and TGA measurements imply that this transition is centred at 322 K, and involves loss of lattice water. Both complexes undergo spin-crossover in (CD₃)₂CO solution, with transition midpoints near 250 K.     

Structural and equilibrium studies on mixed ligand complexes of Co(II), Ni(II), Cu(II) and Zn(II) with N-(2-benzimidazolyl)methyliminodiacetic acid and typical N, N donor ligands

Mixed ligand complexes: [Co(L)(bipy)] · 3H₂O (1), [Ni(L)(phen)] · H₂O (2), [Cu(L)(phen)] · 3H₂O (3) and [Zn(L)(bipy)] · 3H₂O (4), where L²⁻ = two -COOH deprotonated dianion of N-(2-benzimidazolyl)methyliminodiacetic acid (H₂bzimida, hereafter, H₂L), bipy = 2,2′ bipyridine and phen = 1,10-phenanthroline have been isolated and characterized by elemental analysis, spectral and magnetic measurements and thermal studies. Single crystal X-ray diffraction studies show octahedral geometry for 1, 2 and 4 and square pyramidal geometry for 3. Equilibrium studies in aqueous solution (ionic strength I = 10⁻¹ mol dm⁻³ (NaNO₃), at 25 ± 1 °C) using different molar proportions of M(II):H₂L:B, where M = Co, Ni, Cu and Zn and B = phen, bipy and en (ethylene diamine), however, provides evidence of formation of mononuclear and binuclear binary and mixed ligand complexes: M(L), M(H₋₁L)⁻, M(B)²⁺, M(L)(B), M(H₋₁L)(B)⁻, M₂(H₋₁L)(OH), (B)M(H₋₁L)M(B)⁺, where H₋₁L³⁻ represents two -COOH and the benzimidazole N₁-H deprotonated quadridentate (O⁻, N, O⁻, N), or, quinquedentate (O⁻, N, O⁻, N, N⁻) function of the coordinated ligand H₂L. Binuclear mixed ligand complex formation equilibria: M(L)(B) + M(B)²⁺ ? (B)M(H₋₁L)M(B)⁺ + H⁺ is favoured with higher π-acidity of the B ligands. For Co(II), Ni(II) and Cu(II), these equilibria are accompanied by blue shift of the electronic absorption maxima of M(II) ions, as a negatively charged bridging benzimidazolate moiety provides stronger ligand field than a neutral one. Solution stability of the mixed ligand complexes are in the expected order: Co(II) < Ni(II) < Cu(II) > Zn(II). The Δ log K_M values are less negetive than their statistical values, indicating favoured formation of the mixed ligand complexes over the binary ones.     

Syntheses and structural characterization of mononuclear Rh-Cp* and Ir-Cp* complexes with η-phenanthrene, η-pyrene and η-triphenylene

Four novel mononuclear Rh-Cp* and Ir-Cp* complexes with polycyclic aromatic hydrocarbons (PAHs), [M(Cp*)(η⁶-PAHs)](BF₄)₂ (M = Rh and Ir; Cp* = η⁵-C₅Me₅; PAHs = phenanthrene (phn), pyrene (pyr) and triphenylene (triph)), were prepared by the reactions of the intermediate [M(Cp*)(Me₂CO)₃]²⁺ with appreciable PAHs. Their structures were characterized by a single crystal X-ray analysis, ¹H, ¹³C {¹H} NMR and 2D NMR techniques. The X-ray crystallographic studies showed that the [M(Cp*)]²⁺ fragment is η⁶-coordinated to one terminal benzene ring in each PAH. In particular, it is interesting to note that the partial π/π/π/π interaction was formed in the Ir-pyr complex [Ir(Cp*)(η⁶-pyr)](BF₄)₂. The 1D and 2D NMR studies described that the Rh-Cp* and Ir-Cp* complexes with PAHs gave unique ¹H and ¹³C {¹H} NMR spectra with positive coordination shifts (Δδ(¹H, ¹³C)) in (CD₃)₂CO at 23 °C, which are likely induced by the local effect and the non-local effect on the coordination of the [M(Cp*)]²⁺ fragment to PAHs. The decreasing of the coupling constants (³J_H-H) in the η⁶-coordinated benzene ring is also induced, with no changes in the uncoordinated benzene rings. The time-course of ¹H NMR spectra showed that Rh-Cp* and Ir-Cp* complexes with PAHs are partially dissociated to [M(Cp*)(Me₂CO)₃]²⁺ and metal-free PAHs in (CD₃)₂CO at 23 °C. It was demonstrated that their stabilities are in the order of Ir-triph, Ir-phn, Ir-pyr and Rh-triph complexes in (CD₃)₂CO.     

Synthesis, characterisation and substitution kinetics of unusually labile trans-[Co(tmen)(diamine)Cl2] complexes

The mixed diamine complexes trans-[Co(tmen)(diamine)Cl₂]⁺ have been synthesised (tmen = NH₂C(Me)₂C(Me)₂NH₂; diamine = en = NH₂(CH₂)₂NH₂, and ibn = NH₂C(Me)₂CH₂NH₂). Replacement of one en ligand in trans-[Co(en)₂Cl₂]⁺ by one tmen ligand engenders an enormous rate enhancement (2000-fold) for acid hydrolysis. Solvolysis rates have been measured in Me₂SO and DMF for these complexes and also trans-[Co(tmen)₂Cl₂]⁺ which is more reactive again (10⁴-fold). The measured reactivities in DMF at 2 °C establish that the kinetic effect of replacing each en by tmen is incremental, and the extreme base catalysed racemisation rate for (+)-[Co(tmen)₃]³⁺ can now be explained on this basis.     

Syntheses and structural characterizations of novel mono- and dinuclear iridium hydrido complexes with polydentate nitrogen donor ligands

New five mono- and dinuclear Ir hydrido complexes with polydentate nitrogen ligands, [Ir(H)₂(PPh₃)₂(tptz)]PF₆ (1), [Ir₂(H)₄(PPh₃)₄(tptz)](PF₆)₂ · 2H₂O (2 · 2H₂O), [Ir(H)₂(PPh₃)₂(tppz)]BF₄ (3), [Ir₂(H)₄(PPh₃)₄(tppz)](BF₄)₂ (4) and [Ir₂(H)₄(PPh₃)₄(bted)](BF₄)₂ · 6CHCl₃ (5 · 6CHCl₃), were systematically prepared by the reactions of the precursor Ir hydrido complex [Ir(H)₂(PPh₃)₂(Me₂CO)₂]X (X=PF₆ and BF₄) with 2,4,6-tris(2-pyridyl)-1,3,5-triazine (tptz), 2,3,5,6-tetrakis(2-pyridyl)pyrazine (tppz) and 1,4-bis(2,2^′:6^′,2″-terpyridine-4^′-yl)benzene (bted), and their structures and properties were characterized in the solid state and in solution. Each of the Ir hydrido complexes with polydentate nitrogen ligands crystallographically described a unique coordination mode. Their ¹H NMR spectra demonstrated unusual ¹H NMR chemical shifts of pyridyl rings that are likely induced by the ring current effect of neighboring ligands.     

[S2], [S3], and [N3] coordination modes of hydrotris(thioxotriazolyl)borato. Zinc, nickel, cobalt, and bismuth complexes

The ligand hydrotris(1,4-dihydro-3-methyl-4-phenyl-5-thioxo-1,2,4-triazolyl)borato (Tr^Ph,Me) was synthetized as natrium salt and the complexes [Zn(Tr^Ph,Me)₂] · 7.5H₂O · 1.5CH₃CN (2a), [Zn(Tr^Ph,Me)₂] · 8DMF (2b), [Co(Tr^Ph,Me)₂] · 8DMF (3a), [Ni(Tr^Ph,Me)₂] · H₂O · 6DMSO (4a), [Bi(Tr^Ph,Me)₂]NO₃ (5), have been isolated and structurally characterized by X-ray diffraction. In the zinc derivatives the ligand adopts different denticity and coordination modes, η² and [S₂] for 2a and η³ and [N₃] for 2b, depending on the crystallization solvent, giving rise to tetrahedral and octahedral geometry, respectively. In the octahedral cobalt and nickel complexes the ligand is η³ and [N₃] coordinated whereas in the bismuth complex the η³ and [S₃] coordination is exhibited.     

Synthesis, structure and electronic spectra of new three-coordinated copper(I) complexes with tricyclohexylphosphine and diimine ligands

Three new copper(I) complexes with tricyclohexylphosphine (PCy₃) and different diimine ligands, [Cu(phen)(PCy₃)]BF₄ (1) (phen = 1,10′-phennanthroline), [Cu(bpy)(PCy₃)₂]BF₄ (2) (bpy = 2,2′-bipyridine) and [Cu(MeO-CNN)(PCy₃)]BF₄ (3) (MeO-CNN = 6-(4-methoxyl)phenyl-2,2′-bipyridine), have been synthesized and characterized. X-ray structure reveals that complexes 1 and 3 are three-coordinated with trigonal geometry, while complex 2 adopts distorted tetrahedron geometry. Complexes 1 and 3 exhibit ligand redistribution reactions in chloromethane solution by addition of excess amount of PCy₃, in which three-coordinated 1 changes into four-coordinated [Cu(phen)(PCy₃)₂]⁺, and 3 leads to form [Cu(PCy₃)₂]BF₄ and CNN-OMe. All the three complexes display yellow ³MLCT emissions in solid state at room temperature with λ_max at 558, 564 and 582 nm for 1, 2 and 3, respectively, and red-shift to 605, 628 and 643 nm at 77 K in dichloromethane solution.     

Synthesis, characterization, crystal structures, and photophysical properties of a series of room-temperature phosphorescent copper(I) complexes with oxadiazole-derived diimine ligand

In this paper, we report four phosphorescent Cu(I) complexes of [Cu(OP)(PPh₃)₂]BF₄, [Cu(Me-OP)(PPh₃)₂]BF₄, [Cu(OP)(POP)]BF₄, and [Cu(Me-OP)(POP)]BF₄ with oxadiazole-derived diimine ligands, where OP = 2-(5-phenyl-[1,3,4]oxadiazol-2-yl)-pyridine, Me-OP = 2-(5-p-tolyl-[1,3,4]oxadiazol-2-yl)-pyridine, POP = bis(2-(diphenylphosphanyl)phenyl) ether, and PPh₃ = triphenylphosphane, including their synthesis, crystal structures, photophysical properties, and electronic nature. The Cu(I) center has a distorted tetrahedral geometry within the Cu(I) complexes. Theoretical calculation reveals that all emissions originate from triplet metal-to-ligand-charge-transfer excited state. It is found that the inter-molecular sandwich structure triggered by inter- and intra-molecular pi-stacking within solid state Cu(I) complexes is highly effective on restricting the geometric relaxation that occurs in excited states, and thus greatly enhances the photoluminescence (PL) performances, including PL quantum yield improvement, PL decay lifetime increase, and emission blue shift.     

A bulky platinum triamine complex that reacts faster with guanosine 5′-monophosphate than with N-acetylmethionine

A bulky platinum triamine complex, [Pt(Me₅dien)(NO₃)]NO₃ (Me₅dien = N,N,N′,N′,N′′-pentamethyldiethylenetriamine) has been prepared and reacted in D₂O with N-acetylmethionine (N-AcMet) and guanosine 5′-monophosphate (5′-GMP); the reactions have been studied using ¹H NMR spectroscopy. Reaction with 5′-GMP leads to two rotamers of [Pt(Me₅dien)(5′-GMP-N7)]⁺. Reaction with N-AcMet leads to formation of [Pt(Me₅dien)(N-AcMet-S)]⁺. When a sample with equimolar mixtures of [Pt(Me₅dien)(D₂O)]²⁺, 5′-GMP, and N-AcMet was prepared, [Pt(Me₅dien)(5′-GMP-N7)]⁺ was the dominant product observed throughout the reaction. This selectivity is the opposite of that observed for a similar reaction of [Pt(dien)(D₂O)]²⁺ with 5′-GMP and N-AcMet. To our knowledge, this is the first report of a platinum(II) triamine complex that reacts substantially faster with 5′-GMP than with N-AcMet; the effect is most likely due to steric clashes between the methyl groups of the Me₅dien ligand and the N-AcMet.     

Tris(trimethylsilyl)stannyl alkali derivatives: Syntheses and NMR spectroscopic properties

Starting from tetrakis(trimethylsilyl)stannane, the tris(trimethylsilyl)stannyl alkali derivatives (Me₃Si)₃SnM, (M = Li, Na, K, Rb, Cs) were prepared in excellent yields. Reaction with MgBr₂ · Et₂O afforded bis[tris(trimethylsilyl)stannyl]magnesium. Reaction products were investigated by means of multinuclear NMR spectroscopy. At low temperatures, coupling of ⁷Li and ¹¹⁹Sn between [(Me₃Si)₃Sn]⁻ and [Li · 3THF]⁺ (337 Hz) or [Li · 12Cr4]⁺ (275 Hz), was observed. NMR chemical shifts and coupling constants of the stannyl anions exhibit a strong dependency on the nature of the cation, solvent system, concentration and temperature. In addition, the molecular structure of tris(trimethylsilyl)stannyl sodium · 15Cr5 was determined by X-ray crystallography. The [Na · 15Cr5]⁺ and [(Me₃Si)₃Sn]⁻ units are joined by a direct Sn-Na contact, 3.0775(18) Å in length.     

Substituent dependent dimensionalities in cobalt isophthalate supramolecular complexes and coordination polymers containing dipyridylamine ligands

Hydrothermal synthesis has afforded cobalt 5-substituted isophthalate complexes with 4,4′-dipyridylamine (dpa) ligands, showing different dimensionalities depending on the steric bulk and hydrogen-bonding facility of the substituent. [Co(tBuip)(dpa)(H₂O)]_n (1, tBuip = 5-tert-butylisophthalate) is a (4,4) grid two-dimensional coordination polymer featuring 2-fold parallel interpenetration. [Co(MeOip)₂(Hdpa)₂] (2, MeOip = 5-methoxyisophthalate) is organized into 3-fold parallel interpenetrated (4,4) grids through strong N-H⁺?O⁻ hydrogen bonding. {([Co(OHip)(dpa)(H₂O)₃])₃·2H₂O}_n (3, OHip = 5-hydroxyisophthalate) possesses 1-D chain motifs. The 5-methyl derivative {[Co(mip)(dpa)]·3H₂O}_n (4, mip = 5-methylisophthalate) has a 3-D 6⁵8 cds topology. {[Co(H₂O)₄(Hdpa)₂](nip)₂·2H₂O} (5, nip = 5-nitroisophthalate) and {[Co(sip)(Hdpa)(H₂O)₄]·2H₂O} (6, sip = 5-sulfoisophthalate) are coordination complexes. Antiferromagnetic superexchange is observed in 1 and 4, with concomitant zero-field splitting. Thermal decomposition behavior of the higher dimensionality complexes is also discussed.     

Reactivity of [PdCl(μ-med)]2 with monodentate or bidentate ligands. Structure of the dinuclear complexes [Pd(μ-med)(PPh3)]2(BF4)2 and [Pd(μ-med)(bpy)]2(BF4)2. [Hmed=N-(2-mercaptoethyl)-3,5-dimethylpyrazole]

Treatment of the ligand N-(2-mercaptoethyl)-3,5-dimethylpyrazole with [Pd(CH₃COO)₂]₃ and reaction of [PdCl(μ-med)]₂ with pyridine (py) or triphenylphosphine (PPh₃) in the presence of AgBF₄ produced the following complexes: [Pd(CH₃COO)(μ-med)]₂, [Pd(μ-med)(py)]₂(BF₄)₂ and [Pd(μ-med)(PPh₃)]₂(BF₄)₂. Similar reactions carried out with 2,2^′-bipyridine (bpy) or 1,3-bis(diphenylphosphino)propane (dppp) produced [Pd(μ-med)(bpy)]_x(BF₄)_x (x=1 or 2) and [Pd(μ-med)(dppp)]_x(BF₄)_x (x=1 or 2). Treatment of [Pd(μ-med)(bpy)]_x(BF₄)_x with [PdCl₂(CH₃CN)₂] produced [Pd₃Cl₂(μ-med)₂(bpy)₂](BF₄)₂. Treatment of [Pd(μ-med)(dppp)]_x(BF₄)_x with [PdCl₂(CH₃CN)₂] produced a mixture of [Pd(μ-Cl)(dppp)]₂(BF₄)₂ and [Pd(μ-med)₂(dppp)]²⁺. X-ray crystal structures of [Pd(μ-med)(PPh₃)]₂(BF₄)₂ · 2CH₃CN and [Pd(μ-med)(bpy)]₂(BF₄)₂ · 0.5CH₃OH are presented.     

Preparation, crystal structures and spectroscopic properties of novel [MCl3 − n(P)3 + n] (M = Co, Rh; n = 0, 1, 2 or 3) series of complexes containing tripodal tridentate phosphine, 1,1,1-tris(dimethylphosphinomethyl)ethane

Cobalt(III) and rhodium(III) complexes of the series of [M^IIICl_3 − n(P)_3 + n]ⁿ⁺ (M = Co or Rh; n = 0, 1, 2 or 3) have been prepared with the use of 1,1,1-tris(dimethylphosphinomethyl)ethane (tdmme) and mono- or didentate phosphines. The single-crystal X-ray analyses of both series of complexes revealed that the M-P and M-Cl bond lengths were dependent primarily on the strong trans influence of the phosphines, and secondarily on the steric congestion around the metal center resulting from the coordination of several phosphine groups. In fact, the M-P(tdmme) bonds became longer in the order of [MCl₃(tdmme)] < [MCl₂(tdmme)(PMe₃)]⁺ < [MCl(tdmme)(dmpe)]²⁺ (dmpe = 1,2-bis(dimethylphosphino)ethane) < [M(tdmme)₂]³⁺ for both Co^III and Rh^III series of complexes, while the M-Cl bond lengths were shortened in this order (except for [M(tdmme)₂]³⁺). Such a steric congestion around the metal center can also account for the structural and spectroscopic characteristics of the series of complexes, [MCl(tdmme)(dmpm, dmpe or dmpp)]²⁺ (dmpm = bis(dimethylphosphino)methane, dmpp = 1,3-bis(dimethylphosphino)propane). The X-ray analysis for [CoCl(tdmme)(dmpm or dmpe)](BF₄)₂ showed that all Co-P bonds in the dmpm complex were shorter by 0.03-0.04 Å than those in the dmpe complex. Furthermore, the first d-d transition energy of the Co^III complexes and the ¹J_Rh-P(tdmme) coupling constants observed for the Rh^III complexes indicated an unusual order in the coordination bond strengths of the didentate diphosphines, i.e., dmpm > dmpe > dmpp.     

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.     

Synthesis, characterization and properties of iron(II) complexes with a series of tripodal ligands based on the parent ligand tris(2-pyridylmethyl)amine

Iron(II) complexes of the type [Fe(L)(NCS)₂] with the tripodal ligand apme (apme = N¹-(2-aminoethyl)-N¹-(2-pyridyl-methyl)-1,2-ethanediamine) as well as with its derivatives were prepared and structurally characterized. The bond distances thus obtained showed that all complexes investigated were high-spin at the respective temperature. Furthermore [Fe(Me₄apme)(NCS)₂] was analyzed using Mößbauer spectroscopy that showed that this complex remains in its high-spin state over the entire temperature range.