Spectroscopic properties of mono- and binuclear platinum(II) alkynyl complexes with phosphine ligands: A theoretical study

Based on their MP2 optimized structures in the ground states, we obtained solution absorption spectra for trans-[Pt^II(CCR)₂(PH₃)₂] (R = H (1) and Ph (2)) and trans-[Pt^II(CCH)₂(PH₂CH₂PH₂)]₂ (3) under the time-dependent density functional theory calculations. These absorptions agree with experimental observations. The unrestricted MP2 optimization performed for 3 in the lowest-energy triplet excited state shows that upon excitation the PtPt distance shortens about 0.347 Å with respect to the 3.188 Å one in the ground state. The UMP2 calculations estimated that its ³[σ^∗(d_z²)σ(p_z)] excited state produces the 531 nm emission, corresponding to the 580 nm one of trans-[Pt^II(CCPh)₂(PPh₂CH₂PPh₂)]₂ in the solid state at 298 K.     

Cobalt(II) complexes of the antibiotic sulfadiazine, the X-ray single crystal structure of [Co(C10H9N4O2S)2(CH3OH)2]

Cobalt(II) complexes of sulfadiazine formulated as [Co(C₁₀H₉N₄O₂S)₂(CH₃OH)₂] and [Co(C₁₀H₉N₄S)₂(H₂O)₂] have been synthesized and characterized by elemental analysis, infrared and UV-Vis spectroscopy and magnetic susceptibility measurements. The crystal structures of the complex [Co(C₁₀H₉N₄O₂S)₂(CH₃OH)₂] and of free sulfadiazine are also reported. The cobalt complex and the sulfadiazine ligand both crystallize in the monoclinic space group, P21/c, with sulfadiazine acting as a bidentate ligand. Cobalt is coordinated to two-sulfonamide nitrogen and the pyrimidine nitrogen of the sulfadiazine. Two molecules of methanol complete the octahedral geometry around the cobalt, with interligand hydrogen bonding between methanol and sulfadiazine. Infrared spectroscopy confirmed the presence of water molecule in the coordination sphere of [Co(C₁₀H₉N₄S)₂(H₂O)₂]. The electronic spectra and magnetic moments of both complexes were similar, indicating that both complexes have similar structure.     

A new synthetic route towards heterotrimetallic complexes. Synthesis, crystal structure and magnetic properties of a [CuMnCr] trinuclear complex

The heterotrimetallic complex, [{LCuMn(H₂O)}{Cr(phen)(C₂O₄)₂}](ClO₄) · H₂O (1), has been obtained by assembling heterobinuclear cations, [LCuMn]²⁺, with [Cr(phen)(C₂O₄)₂]⁻ ions (H₂L is the compartmental Schiff-base resulting from the stepwise condensation of 2,6-diformyl-p-cresol with ethylenediamine and diethylenetriamine). The copper(II) and manganese(II) ions are hosted into the compartments of the macrocyclic ligand. [Cr(phen)(C₂O₄)₂]⁻ acts as a ligand, being coordinated through one oxalato oxygen atom to the apical position of the square pyramidal copper(II) ion. The cryomagnetic investigation of 1 reveals an antiferromagnetic interaction between Cu^II and Mn^II within the compartmental ligand (J = −39 cm⁻¹). The interaction between Cu^II and Cr^III across the oxalato bridge is negligible. The crystal structure of [LCuPb](ClO₄)₂ · H₂O, a useful precursor in obtaining 3d-3d′ complexes, is also reported.     

Addition of protic nucleophiles to alkynyl methoxy carbene ligands in diiron complexes

Different protic nucleophiles (i.e.Ph₂CNH, PhSH, MeCO₂H, PhOH) can be added to the CC bond of [Fe₂{μ-CN(Me)(Xyl)}(μ-CO)(CO){C(OMe)CCTol}(Cp)₂][SO₃CF₃] (1), affording new diiron alkenyl methoxy carbene complexes.The additions of Ph₂CNH and MeCO₂H are regio and stereoselective, resulting in the formation of the 5-aza-1-metalla-1,3,5-hexatriene [Fe₂{μ-CN(Me)(Xyl)}(μ-CO)(CO){C_α(OMe)C_βHC_γ(Tol)(NCPh₂)}(Cp)₂][SO₃CF₃] (2), and the 2-(acyloxy)alkenyl methoxy carbene complex [Fe₂{μ-CN(Me)(Xyl)}(μ-CO)(CO){C_α(OMe)C_βHC_γ(Tol)OC(O)Me)}(Cp)₂][CF₃SO₃] (5); the E isomer of the former and the Z of the latter are formed exclusively.Conversely, the addition of PhSH is regio but not stereoselective; thus, both the E and Z isomers of [Fe₂{μ-CN(Me)(Xyl)}(μ-CO)(CO){C_α(OMe)C_βHC_γ(Tol)(SPh)}(Cp)₂][SO₃CF₃] (3) are formed in comparable amounts.Compounds 3 and 5 are demethylated upon chromatography through Al₂O₃, resulting in the formation of the acyl complexes [Fe₂{μ-CN(Me)(Xyl)}(μ-CO)(CO){C_α(O)C_βHC_γ(Tol)(SPh)}(Cp)₂] (4) and [Fe₂{μ-CN(Me)(Xyl)}(μ-CO)(CO){C_α(O)C_βHC_γ(Tol)OC(O)Me}(Cp)₂] (6), respectively, both with a Z configured C_βC_γ bond.Finally, the reaction of 1 with PhOH proceeds only in the presence of an excess of Et₃N affording the 2-(alkoxy)alkenyl acyl complex [Fe₂{μ-CN(Me)(Xyl)}(μ- CO)(CO){C_α(O)C_βHC_γ(Tol)(OPh)}(Cp)₂] (7). The crystal structures of 4 · CH₂Cl₂ and 7 · 0.5CH₂Cl₂ have been determined by X-ray diffraction experiments.     

Syntheses, structures, and properties of Co(III) complexes derived from polypyridine ligands containing one carboxamido nitrogen donor

Four cobalt(III) complexes containing the polypyridine pentadentate ligands N,N-bis(2-pyridylmethyl)amine-N′-ethyl-2-pyridine-2-carboxamide (PaPy₃H), N,N-bis(2-pyridylmethyl)amine-N′-[1-(2-pyridylethyl)acetamide (MePcPy₃H), and N,N-bis(2-pyridylmethyl)amine-N′-(2-pyridylmethyl)acetamide (PcPy₃H), have been synthesized. All three ligands bind the Co(III) center in the same fashion with the exception of loss of conjugation between the carboxamide moiety and the pyridine ring in the latter two. The structures of [(PaPy₃)Co(OH)][(PaPy₃)Co(H₂O)](ClO₄)₃ · 3H₂O (1), [(PaPy₃)Co(NO₂)](ClO₄) · 2MeCN (2), [(MePcPy₃)Co(MeCN)](ClO₄)₂ · 0.5MeCN (3), and [(PcPy₃)Co(Cl)](ClO₄) · 2MeCN (4) have been determined. These ligands with strong-field carboxamido N donor stabilize the +3 oxidation state of the Co center as demonstrated by the facile oxidation of the corresponding Co(II) complexes (prepared in situ) by H₂O₂, [Fe(Cp)₂](BF₄), or nitric oxide (NO). The Co-N_amido bond distances of 1-4 lie in the narrow range of 1.853-1.898 Å. ¹H NMR spectra of these complexes confirm the low-spin d⁶ ground states of the metal centers.     

Transition metal derivatives of 1,10-phenanthroline-5,6-dione: Controlled growth of coordination polynuclear derivatives

The synthesis and the characterization of several mono- and polymetallic derivatives of 1,10-phenanthroline-5,6,-dione (1) are presented.The reaction of 1 with M(CO)₆ (M = Cr, Mo) gives compounds of general formula M(O,O′-C₁₂H₆N₂O₂)₃, M = Cr (2), Mo (3).Compound 3 is also obtained starting from Mo(η⁶-CH₃C₆H₅)₂, whereas the reaction of Cr(η⁶-CH₃C₆H₅)₂ with 1 affords the ionic derivative [Cr(η⁶-CH₃C₆H₅)₂][C₁₂H₆N₂O₂] (4), which has been studied by EPR spectroscopy and DFT calculations.FeCl₂(N,N′-C₁₂H₆N₂O₂)₂ (6), is obtained by thermal decomposition of [Fe(N,N′-C₁₂H₆N₂O₂)₃]Cl₂ (5).Polymetallic compounds of general formula Cr[O,O′-C₁₂H₆N₂O₂-N,N′-MCl₄]₃,containing chromium and a Group 4 element M = Ti (7), Zr (8), Hf (9), are prepared from Cr(O,O′-C₁₂H₆N₂O₂)₃ and the corresponding MCl₄ or MCl₄DME. Polynuclear derivatives of iron and chromium of formula [Fe(N,N′-C₁₂H₆N₂O₂-O,O′-CrCl₂(THF)₂)₃][PF₆]₂ (10), and Cr[O,O′-C₁₂H₆N₂O₂-N,N′-FeCl₂(THF)]₃ (11), are obtained by the reaction of [Fe(N,N′-C₁₂H₆N₂O₂)₃][PF₆]₂ with three equivalents of CrCl₂(THF)₂ and from Cr(O,O′-C₁₂H₆N₂O₂)₃ and FeCl₂(THF)_1.5, respectively. Compound 11 reacts with 1 (3 equivalents in sym-C₂H₂Cl₄ or 6 equivalents in ethanol) to give Cr[O,O′-C₁₂H₆N₂O₂-N,N′-FeCl₂(N,N′-C₁₂H₆N₂O₂)]₃ (12), and [Cr(O,O′-C₁₂H₆N₂O₂-N,N′-Fe(N,N′-C₁₂H₆N₂O₂)₂)₃]Cl₆ (13), respectively.     

Conformational isomerism of the binuclear N,N-pentamethylenedithiocarbamate cadmium(II) complex, [Cd2{S2CN(CH2)5}4] on multinuclear (N, Cd) CP/MAS NMR and single-crystal X-ray diffraction data

Crystalline N,N-cyclo-pentamethylenedithiocarbamate (PmDtc) cadmium(II) complex was prepared and studied by means of ¹⁵N, ¹¹³Cd CP/MAS NMR spectroscopy and single-crystal X-ray diffraction. The unit cell of the cadmium(II) compound comprises two centrosymmetric isomeric binuclear molecules [Cd₂{S₂CN(CH₂)₅}₄], which display structural inequivalence in both ¹⁵N and ¹¹³Cd NMR and XRD data. There are pairs of the dithiocarbamate ligands exhibiting different structural functions in both isomeric molecules. Each of the terminal ligands is bidentately coordinated to the cadmium atom and forms a planar four-membered chelate ring [CdS₂C]; whereas pairs of the tridentate bridging ligands combine two neighbouring cadmium atoms forming an extended eight-membered tricyclic moieties [Cd₂S₄C₂], whose geometry can be approximated by a ‘chair’ conformation. The structural states of cadmium atoms were characterised by almost axially symmetric ¹¹³Cd chemical shift tensors. All experimental ¹⁵N resonance lines were assigned to the nitrogen structural sites in both isomeric binuclear molecules.     

Syntheses and characterization of luminescent dinuclear and polynuclear Cu(I) complexes containing 4,4′-bis(diphenylphosphino)biphenylene bridge

The dinuclear complex [Cu₂(dpbp)₂(NCMe)₄][BF₄]₂ (1) has been prepared by treating [Cu(NCMe)₄][BF₄] with 4,4′-bis(diphenylphosphino)biphenylene (abbreviated as dpbp). Reactions of 1 with 2,2′-bipyridine and 1,1′-bis(diphenylphosphino)ferrocene (abbreviated as dppf) afford [Cu₂(dpbp)₂(2,2′-bipy)₂][BF₄]₂ (2) and [Cu₂(dpbp)(dppf)₂][BF₄]₂ (3), respectively. In contrast, compound 1 reacts with tetra(2-pyridyl)ethyl-1,4-diaminobutane (abbreviated as tpyda) to produce the polymeric complex {[Cu₂(dpbp)(tpyda)][BF₄]₂}_n (4). Compounds 1-4 are photoluminescent with the emission band (λ_max) in the range 510-554 nm. The crystal structures of 1 and 4 have been determined by an X-ray diffraction study.     

Pathfinders and trailblazers: a prokaryotic targeting system for transport of folded proteins

The twin-arginine (Tat) protein translocase is a highly unusual protein transport machine that is dedicated to the movement of folded proteins across the bacterial cytoplasmic membrane. Proteins are targeted to the Tat pathway by means of N-terminal signal peptides harbouring a distinctive twin-arginine motif. In this minireview, we describe our current knowledge of the Tat system, paying particular attention to the function of the TatA protein and to the often overlooked step of signal peptide cleavage.