Synthesis and characterization of platinum(IV) complexes with N,S and S,S heterocyclic ligands

The reactions of [PtMe₃(OAc)(bpy)] (4) with the N,S and S,S containing heterocycles, pyrimidine-2-thione (pymtH), pyridine-2-thione (pytH), thiazoline-2-thione (tztH) and thiophene-2-thiol (tptH), resulted in the formation of the monomeric complexes [PtMe₃(-κS)(bpy)] ( = pymt, 5; pyt, 6; tzt, 7; tpt, 8), where the heterocyclic ligand is coordinated via the exocyclic sulfur atom. In contrast, in the reactions of [PtMe₃(OAc)(Me₂CO)_x] (3, x = 1 or 2) with pymtH, pytH, tztH and tptH dimeric complexes [{PtMe₃(μ-)}₂] (μ- = pymt, 9; pyt, 10; tzt, 11) and the tetrameric complex [{PtMe₃(μ₃-tpt-κS)}₄] (12), respectively, were formed. The complexes were characterized by microanalyses, ¹H and ¹³C NMR spectroscopy and negative ESI-MS (12) measurements. Single-crystal X-ray diffraction analysis of [PtMe₃(pymt-κS)(bpy)] (5) exhibited a conformation where the pymt ligand lies nearly perpendicular to the complex plane above the bpy ligand that was also confirmed by quantum chemical calculations on the DFT level of theory.     

Preparation, properties and crystal structure of two isomers of R,R,S,S- and R,S,R,S-[chloro(1,3,10,12,16,19-hexaazatetracyclo[17,3,1,1,0]tetracosane)copper(II)]

Two isomers (R,S,R,S- and R,R,S,S-) of five coordinate complex [Cu(L)Cl]⁺ have been separated and characterised. These two isomers have significantly different spectrochemical and electrochemical properties. Absorption maximum of R,S,R,S-[Cu(L)Cl]⁺ shifts to longer wavelength and its reduction potential shifts to more positive direction comparing those of R,R,S,S-[Cu(L)Cl]⁺. R,S,R,S-[Cu(L)Cl]⁺ is significantly distorted to trigonal-bipyramidal structure, whereas R,R,S,S-[Cu(L)Cl]⁺ retains almost square-planar geometry. The average bond distance of Cu-N in basal plane of R,S,R,S-[Cu(L)Cl]⁺ is longer by 0.024 Å than that of R,R,S,S-[Cu(L)Cl]⁺, whereas the bond distance of Cu-Cl in former is shorter by 0.200 Å than that in latter. The isolated square-planar complexes of R,R,S,S- and R,S,R,S-[Cu(L)](ClO₄)₂ are converted to the R,R,S,S- and R,S,R,S-[Cu(L)Cl]⁺ by the addition of Cl⁻ in nitromethane solution with the rate constants, k=1.70 (±0.02) and 8.31 (±0.07) M⁻¹ s⁻¹, respectively.     

Synthesis, structure, and catalytic activity of chiral Cu(II) and Ag(I) complexes with (S,S)-1,2-diaminocyclohexane-based N4-donor ligands

Condensation of (S,S)-1,2-cyclohexanediamine with 2 equiv. of 2-pyridine carboxaldehyde in toluene in the presence of molecular sieves at 70 °C gives N,N′-bis(pyridin-2-ylmethylene)-(S,S)-1,2-cyclohexanediamine (S,S-1) in 95% yield. Reduction of 1 with an excess of NaBH₄ in MeOH at 50 °C gives N,N′-bis(pyridin-2-ylmethyl)-(S,S)-1,2-cyclohexanediamine (S,S-2) in 90% yield. Reaction of 1 or 2 with 1 equiv. of CuCl₂ · 2H₂O in methanol gives complexes [N-(pyridin-2-ylmethylene)-(S,S)-1,2-cyclohexanediamine]CuCl₂ (3) and [Cu(S,S-2)(H₂O)]Cl₂ · H₂O (4), respectively, in good yields. Complex 4 can further react with 1 equiv. of CuCl₂ · 2H₂O in methanol to give [Cu(S,S-2)][CuCl₄] (5) in 75% yield. The rigidity of the ligand coupled with the steric effect of the free anion plays an important role in the formation of the helicates. Treatment of ligand S,S-1 with AgNO₃ induces a polymer helicate {[Ag(S,S-1)][NO₃]}_n (6), while reaction of ligand 2 with AgPF₆ or AgNO₃ in methanol affords a mononuclear single helicate [Ag(S,S-2)][PF₆] (7) or a dinuclear double helicate [Ag₂(S,S-2)₂][NO₃]₂ · 2CH₃OH (8) in good yields, respectively. All compounds have been characterized by various spectroscopic data and elemental analyses. Compounds 1, 3-5, 7 and 8 have been further subjected to single-crystal X-ray diffraction analyses. The Cu(II) complexes do not show catalytic activity for allylation reaction, in contrast to Ag(I) complexes, but they do show catalytic activity for Henry reaction (nitroaldol reaction) that Ag(I) complexes do not.     

Synthesis, characterization and antibacterial activity of Fe, Co, Cu and Zn complexes probed by transmission electron microscopy

We synthesized iron(III), cobalt(II), copper(II) and zinc(II) complexes [Fe^III(HBPClNOL)Cl₂]·H₂O (1), [Co^II(H₂BPClNOL)Cl₂] (2), [Cu^II(H₂BPClNOL)Cl]Cl·H₂O (3), and [Zn^II(HBPClNOL)Cl] (4), where H₂BPClNOL is the ligand (N-(2-hydroxybenzyl)-N-(2-pyridylmethyl)[(3-chloro)(2-hydroxy)]propylamine). The complexes obtained were characterized by elemental analysis, IR and UV-visible spectroscopies, electrospray ionization mass spectrometry (ESI-MS), tandem mass spectrometry (MS/MS), and cyclic voltammetry. X-ray diffraction studies were performed for complexes (3) and (4) revealing the presence of mononuclear and dinuclear structures in solid state for (3). However, the zinc complex is mononuclear in solid state. Biological studies of complexes (1)-(4) were carried out in vitro for antimicrobial activity against nine Gram-positive bacteria (Staphylococcus aureus strains RN 6390B, COL, ATCC 25923, Smith Diffuse, Wood 46, enterotoxigenic S. aureus FRI-100 (SEA+), FRI S-6 (SEB+) and SEC FRI-361) and animal strain S. aureus LSA 88 (SEC/SED/TSST-1+). The following sequence of inhibition promoted by the complexes was observed: (4) > (2) > (3) > (1), showing the effect of the metal on the biological activity. To directly observe the morphological changes of the internal structure of bacterial cells after the treatment, transmission electron microscopy (TEM) was employed. For the most active complex [Zn^II(HBPClNOL)Cl] (4), granulation deposits around the genetic material and internal material leaking were clearly detected.     

Stereospecific ligands and their complexes. V. Synthesis, characterization and antimicrobial activity of palladium(II) complexes with some alkyl esters of (S,S)-ethylenediamine-N,N′-di-2-propanoic acid

Three new ligands and their palladium(II) complexes of general formula [PdCl₂(R₂-S,S-eddp)] (R = n-propyl, n-butyl and n-pentyl) have been synthesized and characterized by microanalysis, infrared and ¹H and ¹³C NMR spectroscopy. Antimicrobial activity of these ligands and complexes was tested by microdilution method and both minimal inhibitory and microbicidal concentration were determined. These tested complexes demonstrated the significant antifungal activity against pathogenic fungi Aspergillus flavus and Aspergillus fumigatus. On the other hand, these complexes demonstrated moderate antibacterial activity.     

Copper and manganese complexes with C2-multitopic ligands. X-ray crystal structure of [Cu(N,N′-bis[(S)-prolyl]phenylenediamine)H2O]. Catalytic properties

Eight mononuclear complexes with multitopic C₂-symmetry ligands, [Cu(L)]ClO₄, [Mn(L)Cl(H₂O)]PF₆, (L=N,N′-bis[(S)-prolyl]phenylenediamine (1), N,N′-bis[(S)-N-benzylprolyl]phenylenediamine (2), N,N′-bis{[(S)-pyrrolidin-2-yl]methyl}phenylenediamine (3), N,N′-bis-{[(S)-N-benzyl-pyrrolidin-2-yl]methyl}phenylenediamine (4)) have been prepared and characterised by analytical (elemental analysis, and mass spectroscopy) and FT IR, NMR and electronic spectroscopies. The data show that the ligands are neutral and coordinate to the metal in a tetradentate manner. The N,N′-bis[(S)-prolyl]phenylenediamine ligand also appears as an anionic species, (LH-2), and the single crystal structure determination of the respective complex, [Cu(1)]H₂O, is reported. This new family of Cu-complexes catalyse the cyclopropanation of styrene with ethyl and t-butyl diazoacetate to afford cis/trans 2-phenylcyclopropan-1-carboxylates with good yields and selectivity against dimerisation and low ee (<10%). On the other hand, the manganese and copper complexes also catalyse the oxidation of organic sulfides to sulfoxides with high selectivity, and moderate to low enantioselectivity. If an excess of oxidant were used the reaction yields sulfone as only product with excellent yield.     

Synthesis and transition metal complexes of 3,3-bis(1-vinylimidazol-2-yl)propionic acid, a new N,N,O ligand suitable for copolymerisation

The new N,N,O heteroscorpionate ligand 3,3-bis(1-vinylimidazol-2-yl)propionic acid (Hbvip) (5) was synthesised in five steps starting from 1-vinylimidazole. This ligand is closely related to 3,3-bis(1-methylimidazol-2-yl)propionic acid (Hbmip), but contains two vinyl linker groups which can be used for radical-induced polymerisation reactions. The κ³-N,N,O coordination behaviour of 5 was proven by the synthesis of the tricarbonyl complexes [Re(bvip)(CO)₃] (6), [Mn(bvip)(CO)₃] (7) and [Cu(bvip)₂] (8). To obtain good yields of 6, it was synthesised in water instead of THF. The ligand as well as all three complexes were characterised by X-ray crystallography. Copolymerisation of 5 with pure methyl methacrylate (MMA) or a combination of MMA and ethylene glycol dimethacrylate (EGDMA) led to the solid phases P1 and P2. Polymer-bound rhenium and manganese tricarbonyl complexes could be obtained by the reaction of deprotonated P1 with [MBr(CO)₅] (M = Re, Mn) and also by copolymerisation of 6 and 7 with MMA. In both cases, the facial tripodal binding behaviour was evidenced by IR spectra of the polymers. Furthermore, the content of metal incorporated in the polymers was determined by elemental analysis, AAS or ICP-OES measurements. Reaction of the deprotonated solid phase P1 with copper(II) chloride led to a blue solid-phase (P1-Cu). The UV-Vis absorption maximum of P1-Cu is found at 615 nm, which is almost identical to that found for 8. Thereby, it seems likely that P1 is flexible enough to form bisligand complexes with copper(II). This means that the copper centres act as a kind of crosslinking agents. In contrast, the heterogeneous reaction of P2 with copper(II) chloride yielded a lime green solid phase (P2-Cu). The bathochromic shift of the absorption maximum by 102 nm suggests one-sided bound copper centres.     

Antisymbiosis. Preferential coordination of anionic oxygen versus neutral sulfur donor atoms of methylsulfanyl- or methylsulfinyl-acetato, 2-benzoato and 2-phenolato to the cis-Pt(PPh3)2 and Pt(dppe) residues

The interaction of an excess of the title ligands L⁻ with the cis-Pt(phos)₂ moieties gives compounds a-bcis-[Pt(L-O)₂(phos)₂] (a, phos = P(Ph)₃; b, phos = 1/2 dppe), in which O- is preferred to S-coordination. Such preference is confirmed by the fact that the same products are obtained by reaction of excess of L⁻ with the previously reported a-d complexes [Pt(L-O,S)(phos)₂]⁺, (c, phos = PPh₃, d, phos = 1/2 dppe), for which chelate ring opening occurs with rupture of Pt-S rather than Pt-O bonds. Compound a can be obtained also by oxidative addition of HL to [Pt(PPh₃)₃]. The Pt-O bonds in compounds a-d are stable towards substitution by Me₂SO, pyridine and tetramethylthiourea. Substitution of L’s occurs with N,N′-diethyldithiocarbamate, which forms a very stable chelate with Pt(II). Thiourea and N,N′-dimethylthiourea also react, because they give rise to cyclometallated products [Pt(phos)₂(NRC(S)NHR)]⁺ (R = H, CH₃), with one ionised thioamido group, as revealed by an X-ray investigation of [Pt(PPh₃)₂(NHC(S)NH₂)]⁺. The preference of O versus S coordination, as well as the stability of the Pt-O bonds, are discussed in terms of antisymbiosis.     

Magnetic, spectroscopic and X-ray crystallographic structural studies on copper(II) complexes of tridentate NNS Schiff base ligands formed from 2-acetylpyrazine and S-methyl- and S-benzyldithiocarbazates

New copper(II) complexes of general empirical formula, [Cu(NNS)X] (NNS = anionic forms of the 2-acetylpyrazine Schiff bases of S-methyl- and S-benzyldithiocarbazate, Hapsme and Hapsbz) and X = Cl⁻, Br⁻, NCS⁻ and NO₃⁻ have been synthesized and characterized. X-ray crystal structures of the free ligand, Hapsbz and the complexes, [Cu(apsbz)(NO₃)]_∞, [Cu(apsme)(NCS)]₂ and [Cu(apsme)Cl]₂ have been determined. In the solid state, the Schiff base, Hapsbz remains in its thione tautomeric form with the thione sulfur atom trans to the azomethine nitrogen atom. X-ray diffraction shows that the [Cu(apsbz)(NO₃)]_∞ complex is a novel coordination polymer in which one of the nitrogen atoms of the pyrazine ring bridges two adjacent copper(II) ions. The Schiff base is coordinated to the copper(II) ion in its iminothiolate form via the thiolate sulfur atom, the azomethine nitrogen atom and one of the pyrazine nitrogen atoms, the overall geometry of each copper atom in the polymer being close to a square-pyramid. The complexes, [Cu(apsme)X]₂ (X = NCS⁻, Cl⁻) are dimers in which each copper atom adopts a five-coordinate near square-pyramidal geometry with an N₃S₂ coordination environment. The Schiff base coordinates as a uninegatively charged tridentate ligand chelating via the pyridine and azomethine nitrogen atoms and the thiolate sulfur atoms. A nitrogen atom of a unidentate thiocayanate or chloride ligand and a bridging sulfur atom from a second ligand completes the coordination sphere. Room temperature μ_eff values for the complexes in the solid state are in the range 1.70-2.0 μ_B typical of uncoupled or weakly coupled Cu(II) centres. Variable temperature susceptibility studies show that the chain complex displays weak ferromagnetic coupling across the pyrazine bridges, while the S-bridged dinuclear compounds display either weak ferromagnetic or weak antiferromagnetic coupling that relates to subtle bridging geometry differences. EPR studies of frozen DMF solutions give rather similar g and A_Cu values for all compounds indicative of Cu(d_x²-y²) ground state orbitals on the Cu centers.     

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.     

Manganese(III) complexes of N2O2 donor 5-bromosalicylideneimine ligands: Combined effects of electron withdrawing substituents and chelate ring size variations on electrochemical properties

A series of mononuclear manganese(III) complexes of formulae [Mn(L)(X)(H₂O)] (1-13) and [Mn(L)(X)] (14-17) (X = ClO₄, F, Cl, Br, I, NCS, N₃), derived from the Schiff bases of 5-bromosalicylaldehyde and different types of diamine (1,2-diaminoethane, 1,2-diaminopropane, 1,3-diaminopropane and 1,4-diaminobutane), have been synthesized and characterized by the combination of IR, UV-Vis spectroscopies, cyclic voltammetry and by X-ray crystallography. The redox properties of all the manganese(III) complexes show grossly identical features consisting of a reversible or quasireversible Mn^III/Mn^II reduction. Besides Mn^III/Mn^II reduction, the complexes 4, 5, 10, 13 and 16 also show reversible or quasireversible Mn^III/Mn^IV oxidation. A linear correlation has been found for the complexes 5, 7, 11 and 13 [Mn(L²)(X)(H₂O)] (X = F, Cl, Br, I) when E_1/2 [Mn^III/Mn^II] is plotted against Mulliken electronegativities (χ_M). The effect of the flexibility of the ligand on redox potential has been studied. It has been observed that the manganese(II) state is stabilized with increasing flexibility of the ligand environment. The crystal structure of 6 shows an octahedral geometry.     

A pyridine adduct of bis(di-iso-butyldithiocarbamato-S,S′)cadmium(II): Multinuclear (C, N, Cd) CP/MAS NMR spectroscopy, crystal and molecular structure, and thermal behaviour

Crystalline bis(N,N-di-iso-butyldithiocarbamato-S,S′)(pyridine)cadmium(II) - adduct 1 was prepared and studied by means of multinuclear ¹³C, ¹⁵N, ¹¹³Cd CP/MAS NMR spectroscopy, single-crystal X-ray diffraction and simultaneous thermal analysis (STA). In molecular structure 1, the cadmium atom coordinates with four sulphur atoms and one nitrogen atom of pyridine, forming a coordination polyhedron [CdS₄N], whose geometry is an almost ideal tetragonal pyramidal (C_4v). The coordinated py molecule is in the apical position, while two structurally non-equivalent di-iso-butyldithiocarbamate ligands, playing the same terminal S,S′-chelating function, define the basal plane. To characterise additionally the structural state of the cadmium atom in this fivefold coordination, ¹¹³Cd chemical shift anisotropy (CSA) parameters, δ_aniso and η, were calculated from experimental MAS NMR spectra that revealed an almost axially symmetric ¹¹³Cd chemical shift tensor. From a combination of TG and DSC measurements taken under an argon atmosphere, we found that the mass of adduct 1 is lost in two steps involving initial desorption of coordinated py molecules with subsequent thermal destruction of liberated cadmium(II) di-iso-butyldithiocarbamate, with yellow-orange, fine-powdered solid CdS as the final product.     

Oxime-functionalized diazamesocyclic derivates and their metal complexes: Effect of the ligand backbones and anions on the generation of novel monomeric and mono-μ-Cl dimeric Cu complexes

Two oxime-functionalized diazamesocyclic derivates, namely, N,N′-bis(acetophenoneoxime)-1,4-diazacycloheptane (H₂L¹) and N,N′-bis(acetophenonoxime)-1,5-diazacyclooctane (H₂L²), have been prepared and characterized. Both ligands (obtained in the hydrochloride form) can form stable metal complexes with Cu^II and Ni^II salts, the crystal structures of which were determined by X-ray diffraction technique. The reactions of H₂L¹ with Cu(ClO₄)₂ and Ni(ClO₄)₂ afford a penta-coordinated mononuclear complex [Cu(H₂L¹)Cl] · ClO₄ (1) and a four-coordinated monomeric [Ni(HL¹)] · ClO₄ (2), in which the ligand is monodeprotonated. The ligand H₂L² also forms a quite similar mononuclear [Ni(HL²)] · ClO₄ complex with Ni(ClO₄)₂, according to our previous work. However, reactions of different Cu^II salts [Cu(ClO₄)₂, CuCl₂ and Cu(NO₃)₂ for 3, and CuSO₄ for 4] with H₂L² in the presence of NaClO₄ yield two unusual mono-μ-Cl dinuclear Cu^II complexes [Cu₂(HL²)₂Cl] · (ClO₄) (3), and [Cu₂(H₂L²)(HL²)Cl] · (ClO₄)₂ · (H₂O)(4). These results indicate that the resultant Cu^II complexes (1, 3 and 4) are sensitive to the backbones of diazamesocycles and even auxiliary anions.     

Distinct Cd and Co thiocyanate coordination complexes with 2,5-bis(pyrazinyl)-1,3,4-oxadiazole: Metal-directed assembly of a 1-D polymeric chain and a 3-D supramolecular network

The reactions of 2,5-bis(pyrazinyl)-1,3,4-oxadiazole (bpzo) with Cd^II or Co^II salt in the presence of thiocyanate afford two distinct complexes, a 1-D coordination array [Cd(bpzo)₂(SCN)₂]_n (1) and a 3-D hydrogen-bonded supramolecular network [Co(bpzo)₂(SCN)₂(H₂O)₂](CH₃CN)₂(H₂O)₂ (2). X-ray single-crystal structural determination reveals that the extended networks of complexes 1 and 2 are manipulated via different directional propagating forces. In 1, the adjacent Cd^II centers are bridged by a pair of μ_1,3-SCN⁻ anions to form a 1-D array, whereas in 2, the monomeric Co^II coordination entities are hydrogen-bonded into a novel 3-D architecture in which the thiocyanate ions take the only N-binding mode. In both cases, bpzo behaves as monodentate terminals. These results indicate that the choice of metal ions does play a critical role in the supramolecular assembly. The structural and binding features of bpzo in all related compounds have also been discussed.     

Synthesis, spectroscopy and thermal behavior of new lead(II) complexes derived from S-methyl/benzyldithiocarbazates (SMDTC/SBDTC): X-ray crystal structure of [Pb(SMDTC)(NO3)2]

Lead(II) complexes of S-methyldithiocarbazate (SMDTC), [Pb(SMDTC)(NO₃)₂] (1) and S-benzyldithiocarbazate (SBDTC), [Pb(SBDTC)(NO₃)₂] (2) have been synthesized for the first time and characterized by elemental analysis, IR and TGA techniques. The complexes were obtained by addition of the appropriate ligand to an aqueous ethanolic solution of lead(II) nitrate in 1:1 molar ratio. The X-ray crystal structure of complex 1 has been determined by single crystal X-ray diffractometry. In complex 1, lead(II) is in a nine coordinated sphere with seven oxygen atoms of the nitrate groups and thione sulfur, β-nitrogen of neutral bidentate NS chelating ligand. Three nitrate groups act as bidentate chelating whereas the fourth nitrate group is coordinating to the central lead(II) and at the same time it bridges with neighboring lead(II) atom. Coordination geometry of the central lead(II) atom has a tricapped trigonal prismatic arrangement with streochemically inactive lone pair. The lead atoms are linked into polymeric chains and these chains form twin polymeric ribbons linked through bridging oxygen atoms. The N-H?O hydrogen bond network between N_SMDTC and O_nitrate atom leads to self-assembled molecular conformation and stabilizes the crystal structure. The complex 2 with similar spectral and thermal behavior is expected to have a tricapped trigonal prismatic structure. The thermal behavior studies shows that the complexes start to decompose at relatively low temperature (ca. 110 °C) to give PbS residue.     

Complexes of N-thiophosphorylthioureas RNHC(S)NHP(S)(OiPr)2 (HL) (R = pyridin-2-yl, pyridin-3-yl, 6-amino-pyridin-2-yl) with copper(I): Crystal structures of Cu(PPh3)nL (n = 1, 2)

Reaction of the potassium salts of N-thiophosphorylated thioureas of common formula RNHC(S)NHP(S)(OiPr)₂ [R = pyridin-2-yl (HL^a), pyridin-3-yl (HL^b), 6-amino-pyridin-2-yl (HL^c)] with Cu(PPh₃)₃I in aqueous EtOH/CH₂Cl₂ leads to mononuclear [Cu(PPh₃)₂L^a,b-S,S′] (1, 2) and [Cu(PPh₃)L^c-S,S′] (3) complexes. Using copper(I) iodide instead of Cu(PPh₃)₃I, polynuclear complexes [Cu_n(L-S,S′)_n] (4-6) were obtained. The structures of these compounds were investigated by IR, ¹H, ³¹P{¹H} NMR spectroscopy, ES-MS and elemental analyses. The crystal structures of Cu(PPh₃)₂L^b (2) and Cu(PPh₃)L^c (3) were determined by single-crystal X-ray diffraction.     

Probing electron transfer reactions between two azurins from Alcaligenes xylosoxidans GIFU 1051 with optically active Ru complexes as molecular recognition probes: Importance of the 43rd residue

Electron transfer reactions between optically-active Ru^II/III complexes incorporating (S)-/(R)-amino acids, and the two azurins, azurin-1 (az-1Cu) and azurin-2 (az-2Cu) isolated from Alcaligenes xylosoxidans GIFU 1051, have been studied to probe molecular recognition sites on the two azurins. The Ru^II/III complexes are K[Ru^II(L)(bpy)] and [Ru^III(L)(bpy)], and have a tripodal ligand (L) derived from the (S)-/(R)-amino acids, which are in turn exchanged for other functional substituent groups, such as (S)-/(R)-phenylalanine, -leucine, -valine, -alanine, and -glutamic acid (L = (S)-/(R)-BCMPA, -BCMLE, -BCMVA, -BCMAL, and -BCMGA). In the oxidation reaction of az-1Cu^I promoted by the Ru^III complexes, the kinetic parameters exhibited enantio- and stereo-selectivities, while the same reaction of az-2Cu^I was less enantio- and stereo-selective. These differences suggest that the processes of formation of the activated states are different for the two azurins. On the other hand, such a difference has not been observed for az-1 and az-2 with respect to the reduction reactions promoted by both azurins Cu^II by the Ru^II complexes within the experimental error. This suggests that the neutrality of the Ru complexes is important for precise molecular recognition of azurins. His117 has been proposed as the electron transfer site. The local structures in the vicinity of the His117 side chain in the two azurins, are essentially identical with the exception of the 43rd residue, Val43 and Ala43 for az-1 and az-2, respectively. Electron transfer reactions between Ru^III complexes and a mutant azurin, V43A-az-1, were also carried out. Interestingly, the activation parameters estimated were very similar to those of az-2, indicating that the 43rd residue acts as the electron transfer site in azurins and provides rationalization for the different mechanisms of az-1 and az-2 in redox reactions.     

Synthesis and characterization of [H2NC(S)NP(S)(OiPr)2] complexes of Co(II), Ni(II), Zn(II) and Cd(II)

Reaction of the potassium salt of the N-thiophosphorylthiourea H₂NC(S)NHP(S)(OiPr)₂ (HL) with Co(II), Ni(II), Zn(II) and Cd(II) cations in aqueous EtOH leads to the chelate complexes [ML₂] all showing a 1,5-S,S′-coordination formed by the CS and PS sulfur atoms of two deprotonated ligands L⁻. The structures of the resulting compounds were studied by IR, UV-Vis, ¹H, ³¹P{¹H} NMR spectroscopy and microanalysis. The metal center is found in a tetrahedral environment in [CoL₂], [ZnL₂] and [CdL₂]. According to NMR and UV-Vis spectroscopy the metal cation of [NiL₂] exhibits square planar coordination geometry in CH₂Cl₂, CHCl₃ and C₆H₆, while tetrahedral geometry is observed in acetone, DMSO and DMF. Regardless of the solvent used for the crystallization of [NiL₂], the molecular structure in the solid is always square planar as was confirmed by XRD of single crystals and magnetic measurements of the polycrystalline material. The magnetic and photoluminescent properties of all complexes are also reported.     

S-allyl-3-(2-pyridyl-methylene)dithiocarbazate ligand and its manganese(II), cobalt(III) and nickel(II) complexes

A new NNS tridentate ligand, S-allyl-3-(2-pyridyl-methylene)dithiocarbazate (HL) has been prepared. Three coordination complexes, Mn(L)₂ (1), [Co(L)₂]NO₃ (2) and Ni(L)₂ (3) (L⁻ is the deprotonated monoanionic form of HL) have been synthesized and characterized by elemental analysis, molar conductivity, FT-IR, ¹H NMR and UV-Vis spectroscopy. 1 and 3 are neutral complexes, while 2 is cationic with nitrate as the counter ion. Single crystal X-ray diffraction analysis shows that bis-chelate complexes have a distorted octahedral geometry in which two ligands in thiolate tautomeric form coordinate to the metal center through N atoms of the pyridine and imino moieties and one S atom. Molecular geometry from X-ray analysis, molecular geometry optimization, atomic charges distribution and bond analysis of the ligand and complexes have been performed using the density functional theory (DFT) with the B3LYP functional.     

Crystal structures and third-order NLO properties in DMF solution of Co(II)-bpfp coordination polymers (bpfp=N,N-bis(pyridylformyl)piperazine)

Two novel Co(II) coordination polymers {[Co(H₂O)₂(CH₃OH)₂(4-bpfp)](NO₃)₂}_n1 (4-bpfp=N,N^′-bis(4-pyridylformyl)piperazine) and [Co(NCS)₂(CH₃OH)₂(3-bpfp)]_n2 (3-bpfp=N,N^′-bis(3-pyridylformyl)piperazine) have been synthesized and characterized by single crystal X-ray diffraction. Both the polymers consist of one-dimensional chains constructed by bridging bpfp ligands and Co(II) ions. The existence of O?H-O hydrogen bond in 1 and S?H-O hydrogen bond in 2 play important roles in creating interesting supramolecular structures. Their third-order nonlinear optical (NLO) properties in DMF solution have been studied by Z-scan technique. The results reveal that polymers 1 and 2 exhibit strong NLO absorption effects (α₂=9.00×10⁻¹¹ m W⁻¹ for 1; 1.41 × 10⁻¹⁰ m W⁻¹ for 2) and self-focusing performance (n₂=3.24×10⁻¹⁶ esu for 1; 3.05 × 10⁻¹⁶ esu for 2) in DMF solutions. The corresponding effective NLO susceptibilities χ⁽³⁾ values are 3.08 × 10⁻¹² esu (1) and 4.70 × 10⁻¹² esu (2). All of the values are comparable to those of the reported good NLO materials. Additionally, the TG-DTA results of the two polymers are in agreement with the crystal structures.