Synthesis, characterization, and magnetic properties of new homotrinuclear bis(oxamato) copper(II) complexes with an asymmetric central N,N′-bridge

The new mononuclear bis(oxamato) complex [n-Bu₄N]₂[Cu(obbo)] (1) (obbo=o-benzyl-bis(oxamato)) has been synthesized as a precursor for trinuclear oxamato-bridged transition metal complexes. Starting from 1 the homotrinuclear complexes [Cu₃(obbo)(pmdta)₂(NO₃)](NO₃)·CH₂Cl₂·H₂O (2) and [Cu₃(obbo)(tmeda)₂(NO₃)₂(dmf)] (3) have been prepared, where pmdta = N,N,N′,N″,N″-pentamethyldiethylenetriamine, tmeda = N,N,N′,N′-tetramethylethylenediamine and dmf = dimethylformamide. The crystal structures of 1-3 were solved. The magnetic properties of 2 and 3 were studied by susceptibility measurements versus temperature. For the intramolecular J parameter values of −111 cm⁻¹ (2) and −363 cm⁻¹ (3) were obtained.     

N,N′-Bis(3-methoxysalicylidene)propane-1,2-diamine mononuclear 4f and heterodinuclear Cu-4f complexes: Synthesis, crystal structure and electrochemical properties

Reactions of H₂L [H₂L = N,N′-bis(3-methoxysalicylidene)propane-1,2-diamine] and Ln(NO₃)₃ · 6H₂O give rise to two different mononuclear 4f complexes, namely, {[(H₂L)La(NO₃)₃(MeOH)] · H₂O}_n (1) and [(H₂L)Nd(NO₃)₃] (2). Further additions of Cu(Ac)₂ · H₂O to the mononuclear 4f complexes yield expected heterodinuclear Cu-4f complexes [LCu(Me₂CO)Ln(NO₃)₃] (3, Ln = Nd; 4, Ln = Eu; 5, Ln = Dy). Complex 1 is a unique 1D polymeric chain structure, and 2 is one of the few structurally characterized discrete hexadentate salen-type mononuclear 4f complexes. Complexes 3-5 are similar to their analogues. However, they are prepared by a reversed synthetic route in contrast to their isomorphic complexes. Electrochemical behavior of heterodinuclear Cu-4f complexes 3-5 has been examined by cyclic voltammetry in acetonitrile. The redox potential of heterodinuclear Cu-4f complexes 3-5 shows significant anodic shift comparing to that of mononuclear copper complex (LCu). A tendency of anodic shift was observed in a sequence of 3 < 4 < 5. This results from the modulating effect of coordination geometry around Cu(II) ion on redox potential.     

Synthesis and structure of dichloropalladium(II) complexes of heteroleptic N,S- and N,Se-donor ligands based on the 2-organochalcogenomethylpyridine motif, and Mizoroki-Heck catalysis mediated by complexes of N,S-donor ligands

Ligands containing the 2-organochalcogenomethylpyridine motif with substituents in the 4- or 6-position of the pyridyl ring, R⁴,R⁶-pyCH₂ER¹ [R⁴ = R⁶ = H, ER¹ = SMe (1), SeMe (2), SPh (6), SePh (7); R⁴ = Me, R⁶ = H, ER¹ = SMe (3), SPh (8), SePh (9); R⁴ = H, R⁶ = Me, ER¹ = SMe (4), SPh (10), SePh (11); R⁴ = H, R⁶ = Ph, ER¹ = SMe (5), SPh (12), SePh (13)] are obtained on the reaction of R⁴,R⁶-pyMe with LiBuⁿ followed by R¹EER¹. On reaction with PdCl₂(NCMe)₂, the ligands with a 6-phenyl substituent form cyclopalladated species PdCl{6-(o-C₆H₄)pyCH₂ER¹-C,N,E} (5a, 12a, 13a) with the structure of 13a (ER¹ = SePh) confirmed by X-ray crystallography; other ligands form complexes of stoichiometry PdCl₂(R⁴,R⁶-pyCH₂ER¹). Complexes with R⁶ = H are monomeric with N,E-bidentate configurations, confirmed by structural analysis for 3a (R⁴ = Me, ER¹ = SMe), 7a (R⁴ = H, ER¹ = SePh) and 9a (R⁴ = Me, ER¹ = SePh). Two of the 6-methyl substituted complexes examined by X-ray crystallography are oligomeric with trans-PdCl₂(N,E) motifs and bridging ligands, trimeric [PdCl₂(μ-6-MepyCH₂SPh-N,S)]₃ (10a) and dimeric [PdCl₂(μ-6-MepyCH₂SePh-N,Se)]₂ (11a). This behaviour is attributed to avoidance of the Me···Cl interaction that would occur in the cis-bidentate configuration if the pyridyl plane had the same orientation with respect to the coordination plane as observed for 3a, 7a and 9a [dihedral angles 8.0(2)-16.8(2)°]. When examined as precatalysts for the Mizoroki-Heck reaction of n-butyl acrylate with aryl halides in N,N-dimethylacetamide at 120 °C, the complexes exhibit the anticipated trends in yield (ArI > ArBr > ArCl, higher yield for electron withdrawing substituents in 4-RC₆H₄Br and 4-RC₆H₄Cl). The most active precatalysts are PdCl₂(R⁴-pyCH₂SMe-N,S) (R = H (1a), Me (3a)); complexes of the selenium containing ligands exhibit very low activity. For closely related ligands, the changes SMe to SPh, 6-H to 6-Me, and 6-H to 6-Ph lead to lower activity, consistent with involvement of both the pyridyl and chalcogen donors in reactions involving aryl bromides. The precatalyst PdCl₂(pyCH₂SMe-N,S) (1a) exhibits higher activity for the reaction of aryl chlorides in Buⁿ₄NCl at 120 °C as a solvent under non-aqueous ionic liquid (NAIL) conditions.     

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.     

The use of trans-4-cotininecarboxylate to construct a polymeric copper(II) azido complex: Hydro(solvo)thermal synthesis, structure and magnetic properties

A new pyridyl-carboxylate ligand, the anion of trans-4-cotininecarboxylic acid, HL, 1, has been used to prepare a new polymeric copper(II) complex, [CuLN₃]_2n, 2, based on a [CuLN₃]₂ dimeric building block. The single crystal structures of both 1 and 2 have been determined and 1 has been found to be in its zwitterionic configuration. The structure of 2 is a one-dimensional tape-like polymeric structure based on an end-on azido-bridged binuclear [Cu₂N₃]₂ backbone moiety. Magnetic studies reveal that 2 is close to paramagnetic from 2 to 300 K with a Curie constant of 1.094 emu K/mol, a Weiss temperature of 0.73 K and a corresponding μ_eff of 2.09 μ_B. A fit of χ_MT for 2 with S₁ = S₂ = ½, yields g = 2.441(6), J = −0.49(3) cm⁻¹, zJ = −0.38(2) cm⁻¹ and N(α) = 0.00053(12) emu/mol, a fit that indicates the presence of both very weak intramolecular intrachain antiferromagnetic exchange coupling within the one-dimensional tape-like chains and very weak interchain antiferromagnetic exchange coupling between these chains.     

Rhenium(IV) cyanate complexes: Synthesis, crystal structures and magnetic properties of NBu4[ReBr4(OCN)(DMF)] and (NBu4)2[ReBr(OCN)2(NCO)3]

Two new rhenium(IV) mononuclear compounds of formula NBu₄[ReBr₄(OCN)(DMF)] (1) and (NBu₄)₂[ReBr(OCN)₂(NCO)₃] (2) (NBu₄ = tetrabutylammonium cation, OCN = O-bonded cyanate anion, NCO = N-bonded cyanate anion and DMF = N,N-dimethylformamide) have been synthesized and their crystal structures determined by single-crystal X-ray diffraction. 1 crystallizes in the monoclinic system with the space group P2₁/n, whereas 2 crystallizes in the triclinic one with as space group. In both complexes the rhenium atom is six-coordinated, in 1 by four Br atoms in the equatorial plane, and two trans-oxygen atoms, one of a DMF molecule and another one from a cyanato group, while in 2 by one bromide anion and five cyanate ligands, two of which are O-bonded and three N-bonded, forming a somewhat distorted octahedral surrounding. Magnetic susceptibility measurements on polycrystalline samples of 1 and 2 in the temperature range 1.9-300 K are interpreted in terms of magnetically isolated spin quartets with large values of the zero-field splitting (|2D| is ca. 41.6 and 39.2 cm⁻¹ for 1 and 2, respectively).     

Interaction of Pt(II) and Pd(II) complexes of terpyridine with 1-methylazoles: A combined experimental and density functional study

The synthesis and characterization of several complexes of the composition [{M(terpy)}_n(L)](ClO₄)_m (M = Pt, Pd; L = 1-methylimidazole, 1-methyltetrazole, 1-methyltetrazolate; terpy = 2,2′:6′,2″-terpyridine; n = 1, 2; m = 1, 2, 3) is reported and their applicability in terms of a metal-mediated base pair investigated. Reaction of [M(terpy)(H₂O)]²⁺ with 1-methylimidazole leads to [M(terpy)(1-methylimidazole)](ClO₄)₂ (1: M = Pt; 2: M = Pd). The analogous reaction of [Pt(terpy)(H₂O)]²⁺ with 1-methyltetrazole leads to the organometallic compound [Pt(terpy)(1-methyltetrazolate)]ClO₄ (3) in which the aromatic tetrazole proton has been substituted by the platinum moiety. For both platinum(II) and palladium(II), doubly metalated complexes [{M(terpy)}₂(1-methyltetrazolate)](ClO₄)₃ (4: M = Pt; 5: M = Pd) can also be obtained depending on the reaction conditions. In the latter two compounds, the [M(terpy)]²⁺ moieties are coordinated via C5 and N4. X-ray crystal structures of 1, 2, and 3 are reported. In addition, DFT calculations have been carried out to determine the energy difference between fully planar [Pd(mterpy)(L)]²⁺ complexes Ip-IVp (mterpy = 4′-methyl-2,2′:6′,2″-terpyridine; L = 1-methylimidazole-N3 (I), 1-methyl-1,2,4-triazole-N4 (II), 1-methyltetrazole-N3 (III), or 3-methylpyridine-N1 (IV)) and the respective geometry-optimized structures Io-IVo. Whereas this energy difference is larger than 70 kJ mol⁻¹ for compounds I, II, and IV, it amounts to only 0.8 kJ mol⁻¹ for the tetrazole-containing complex III, which is stabilized by two intramolecular C-H?N hydrogen bonds. Of all complexes under investigation, only the terpyridine-metal ion-tetrazole system with N3-coordinated tetrazole appears to be suited for an application in terms of a metal-mediated base pair in a metal-modified oligonucleotide.     

Structural chemistry of dihalogenopalladium(II) and platinum(II) complexes of heteroleptic N,S- and N,Se-donor ligands based on the 2-organochalcogenomethylpyridine motif

The structural chemistry of dihalogenopalladium(II) and platinum(II) complexes of 2-organochalcogenomethylpyridine ligands is described. Complexes with a methyl group in the 6-position of the pyridyl ring, 6-MepyCH₂ER, form dimeric complexes [trans-PdX₂(μ-6-MepyCH₂SePh-N,Se)]₂ (X = Br (1), I (2)) or mononuclear complexes trans-PdI₂(6-MepyCH₂SR-N)₂ (R = Me (5), Ph (6)). Absence of a 6-methyl substituent results in the bidentate configuration observed for PdI₂(pyCH₂SePh-N,Se) (3) and PdI₂(4-MepyCH₂SMe-N,S) (4). Related platinum(II) complexes are mononuclear including PtCl₂(6-MepyCH₂SPh-N,S) (8) as an analogue of trimeric [trans-PdCl₂(μ-6-MepyCH₂SPh-N,S)]₃. Differences between palladium and platinum appear to result from a combination of steric and electronic factors.     

Synthesis, crystal structures and characterization of three novel complexes with N-[2-(2-hydroxybenzylideneamino)ethyl]-4-methyl-benzene-sulfonamide as ligand

Reaction of the N-tosyl-ethylenediamine and salicylaldehyde forms a new sulfonamide Schiff base N-[2-(2-hydroxybenzylideneamino)ethyl]-4-methyl-benzene-sulfonamide (H₂L). Three novel complexes constructed from H₂L, namely, [M(HL)₂] · xH₂O (M = Cu, x = 0 for 1, M = Ni, x = 0 for 2 and M = Zn, x = 1 for 3) have been prepared and characterized via X-ray single-crystal diffraction, elemental analysis, X-ray powder diffraction (XRPD), FT-IR, UV-Vis, TGA and photoluminescence measurements. Complex hydrogen bonds, C-H···π and π-π stacking interactions lead 1-3 to present 1-D, 2-D and 3-D supramolecular architectures, respectively.     

Structural comparison of (pentamethylcyclopentadienyl)iridium(III) azido complexes containing potentially N,S-bidentate N-heterocyclic thiolates: 2- or 8-quinolinethiolate and benzimidazole-2-thiolate

The crystal structures of mononuclear (azido)(pentamethylcyclopentadienyl)iridium(III) complexes bearing 2- or 8-quinolinethiolate (n-Sqn⁻), [Cp^∗Ir(N₃)(n-Sqn)] {n = 2 (1) or 8 (2); Cp^∗ = η⁵-C₅Me₅} have been determined by X-ray analysis. The 2-Sqn complex, 1, acquires severe steric strains in the four-membered κ²N,S chelate ring, while the 8-Sqn isomer, 2, forms a strain-free five-membered planar κ²N,S chelate ring. It has also been revealed that the corresponding benzimidazole-2-thiolate (Hbimt⁻) complex, which was obtained similarly to the above n-Sqn complexes from [Cp^∗Ir(N₃)₂]₂ and Na(Hbimt), takes an unsymmetrical dinuclear structure bridged by two Hbimt⁻ ligands with different bonding modes, [Cp^∗Ir(N₃){μ(S:N¹)-Hbimt}{μ(S:S)-Hbimt}Ir(N₃)Cp^∗] · MeOH (3).     

Exploring the coordination chemistry and reactivity of hemilabile N-alkylaminopyrazole ligands towards Pd(II)

Reaction of the N-alkylaminopyrazole (NN′N) ligands bis[(3,5-dimethyl-1-pyrazolyl)methyl]ethylamine (bdmae) and bis[(3,5-dimethyl-1-pyrazolyl)methyl]isopropylamine (bdmai) with [PdCl₂(CH₃CN)₂] in a 1:1 M/L ratio in CH₂Cl₂ produces cis-[PdCl₂(NN′N)] (NN′N = bdmae (1), bdmai (2)). The solid state structure of complex 1 was determined by X-ray diffraction studies. The bdmae ligand is coordinated through the two N_pz atoms to the metal atom, which completes its coordination with two chlorine atoms in a cis disposition.Treatment of the corresponding ligand with [PdCl₂(CH₃CN)₂] in 1:1 M/L ratio in the presence of AgBF₄ and metathesis with NaBPh₄ in CH₂Cl₂/CH₃OH (3:1) gave [PdCl(bdmae)](BPh₄) (3), and in the presence of NaBPh₄ in CH₂Cl₂/CH₃CN (3:1) gave [PdCl(bdmai)](BPh₄) (4). Complexes 1 and 2 were again obtained when complexes 3 and 4 were heated under reflux in a solution of Et₄NCl in acetonitrile. These Pd(II) compounds were characterised by elemental analyses, conductivity measurements, IR, ¹H and ¹³C{¹H} NMR, HMQC and NOESY spectroscopies. The NMR studies of the complexes prove the rigid conformation of the ligands when they are complexed.     

Synthesis and characterization of gallium complexes bearing N-arylmethylenethiobenzahydrazone ligands; crystal structure of diethyl[N-(4-N,N-dimethylamino)benzylidene thiobenzahydrazonato]gallium

Five diethylgallium complexes of type Et₂GaL [(L = N-(4-methoxy) benzylidenethiobenzahydrazonato (1), N-(3,4-dimethoxy)benzylidenethio benzahydrazonato (2), N-(4-N,N-dimethylamino)benzylidenethiobenza hydrazonato (3), N-(2-naphthyl)methylenethiobenzahydrazonato (4), N-(9-anthryl)methylenethiobenzahydrazonato (5)] have been synthesized by the reaction of triethylgallium with appropriate N-arylmethylene thiobenzahydrazones. The compounds obtained have been characterized by elemental analysis, ¹H NMR, IR and mass spectroscopies, respectively. The solid structure of 3 has been determined by X-ray single crystal analysis, in which Ga atom is four coordinate. The photoluminescent property of complex 1 was studied. The maximum emission wavelength is 475 nm upon radiation by UV light.     

Synthesis and reactivity of osmium (VI) nitrido complexes containing pyridine-carboxylato ligands

A series of osmium(VI) nitrido complexes containing pyridine-carboxylato ligands Os^VI(N)(L)₂X (L = pyridine-2carboxylate (1), 2-quinaldinate (2) and X = Cl (a), Br (1b and 2c) or CH₃O (2b)) and [Os^VI(N)(L)X₃]⁻ (L = pyridine-2,6-dicarboxylate (3) and X = Cl (a) or Br (b)) have been synthesised. Complexes 1 and 2 are electrophilic and react readily with various nucleophiles such as phosphine, sulfide and azide. Reaction of Os^VI(N)(L)₂X (1 and 2) with triphenylphosphine produces the osmium(IV) phosphiniminato complexes Os^VI(NPPh₃)(L)₂X (4 and 5). The kinetics of nitrogen atom transfer from the complexes Os^VI(N)(L)₂Br (2c) (L = 2-quinaldinate) with triphenylphosphine have been studied in CH₃CN at 25.0 °C by stopped-flow spectrophotometric method. The following rate law is obtained: −d[Os(VI)]/dt = k₂[Os(VI)][PPh₃]. Os^VI(N)(L)₂Cl (L = 2-quinaldinate) (2a) reacts also with [PPN](N₃) to give an osmium(III) dichloro complex, trans-[PPN][Os^III(L)₂Cl₂] (6). Reaction of Os^VI(N)(L)₂Cl (L = 2-quinaldinate) (2a) with lithium sulfide produces an osmium(II) thionitrosyl complex Os^II(NS)(L)₂Cl (7). These complexes have been structurally characterised by X-ray crystallography.     

One-dimensional silver(I) and mercury(II) complexes with 1,4-bis(1-benzyl-benzimidazol-2-yl)cyclohexane (N-BBzBimCH)

The crystal structures of four Ag(I) and Hg(II) complexes of the ligand 1,4-bis(1-benzyl-benzimidazol-2-yl)cyclohexane (N-BBzBimCH) have been described, that is, [Hg₂(N-BBzBimCH)Cl₄] (1), [Hg(N-BBzBimCH)Br₂] (2), [Ag(N-BBzBimCH)](NO₃)(H₂O) (3) and [Ag₂(N-BBzBimCH)(CF₃OCO)₂] (4). All these compounds show 1D polymeric structures in the solid state. In complexes 1 and 4, the chloride ions and the trifluoroacetate groups bridge the [Hg₂(N-BBzBimCH)Cl₂] and [Ag₂(N-BBzBimCH)] fragments, respectively, to generate 1D polymers. While the bromide ions in complex 2 and nitrate groups in complex 3 are only serving as terminal ligands to suffice the coordination geometry of the metal centers. In all cases, weak intermolecular interactions such as C-H?X (X = Cl, Br) contacts, hydrogen bonds, π-π interactions and C-H?π stacking play important roles to extend the 1D chain structures to 2D network. Solid state fluorescence of these compounds was also studied.     

Synthesis, characterization and magnetic properties of new homotrinuclear copper(II) complexes

Two new mononuclear bis(oxamato) complexes with the formula [nBu₄N]₂[M(nabo)] M = Ni (4), Cu (5), with nabo = 2,3-naphthalene-bis(oxamato) have been synthesized as precursors for trinuclear oxamato-bridged transition metal complexes. Starting from 5 the homo-trinuclear complex [Cu₃(nabo)(pmdta)₂(BF₄)](BF₄) · MeCN · Et₂O (7), with pmdta = N,N,N′,N″,N″-pentamethyldiethylenetriamine, has been prepared. The central N,N′-2,3-naphthalene bridge of 7 is so far the most extended π-conjugated bridge of trinuclear bis(oxamato) type transition metal complexes. The goal of this work was to verify the N,N′-2,3-naphthalene bridge of 7 on its magnetic properties in comparison to the N,N′-o-phenylene bridge of the related homo-trinuclear complex [Cu₃(opba)(pmdta)₂(NO₃)](NO₃) · 2MeCN (6) (opba = o-phenylene-bis(oxamato)). The crystal structures of 4-7 were solved. The magnetic properties of 6 and 7 were studied by susceptibility measurements versus temperature. For the intramolecular J parameter, values of −89 cm⁻¹ (6) and −113 cm⁻¹ (7) were obtained. The different J values are discussed based on the crystal structures of 6 and 7.     

Mono, di and polynuclear Cu(II)-azido complexes incorporating N,N,N reduced schiff base: syntheses, structure and magnetic behavior

Three kinds of copper(II) azide complexes have been synthesised in excellent yields by reacting Cu(ClO₄)₂ · 6H₂O with N,N-bis(2-pyridylmethyl)amine (L¹); N-(2-pyridylmethyl)-N′,N′-dimethylethylenediamine (L²); and N-(2-pyridylmethyl)-N′,N′-diethylethylenediamine (L³), respectively, in the presence of slight excess of sodium azide. They are the monomeric Cu(L¹)(N₃)(ClO₄) (1), the end-to-end diazido-bridged Cu₂(L²)₂(μ-1,3-N₃)₂(ClO₄)₂ (2) and the single azido-bridged (μ-1,3-) 1D chain [Cu(L³)(μ-1,3-N₃)]_n(ClO₄)_n (3). The crystal and molecular structures of these complexes have been solved. The variable temperature magnetic moments of type 2 and type 3 complexes were studied. Temperature dependent susceptibility for 2 was fitted using the Bleaney-Bowers expression which led to the parameters J = −3.43 cm⁻¹ and R = 1 × 10⁻⁵. The magnetic data for 3 were fitted to Baker’s expression for S = 1/2 and the parameters obtained were J = 1.6 cm⁻¹ and R = 3.2 × 10⁻⁴. Crystal data are as follows. Cu(L¹)(N₃)(ClO₄): Chemical formula, C₁₂H₁₃ClN₆O₄Cu; crystal system, monoclinic; space group, P2₁/c; a = 8.788(12), b = 13.045(15), c = 14.213(15) Å; β = 102.960(10)°; Z = 4. Cu(L²)(μ-N₃)(ClO₄): Chemical formula, C₁₀H₁₇ClN₆O₄Cu: crystal system, monoclinic; space group, P2₁/c; a = 10.790(12), b = 8.568(9), c = 16.651(17) Å; β = 102.360(10)°; Z = 4. [Cu(L³)(μ-N₃)](ClO₄): Chemical formula, C₁₂H₂₁ClN₆O₄Cu; crystal system, monoclinic; space group, P2₁/c; a = 12.331(14), b = 7.804(9), c = 18.64(2) Å; β = 103.405(10)°; Z = 4.     

Structure, magnetic properties and nuclease activity of pyridine-2-carbaldehyde thiosemicarbazonecopper(II) complexes

New complexes of formulae [Cu(HL²)(H₂O)(NO₃)](NO₃) (1), [{Cu(L¹)(tfa)}₂] (2), [{Cu(L¹)}₂(pz)](ClO₄)₂ (3) and {[{Cu(L¹)}₂(dca)](ClO₄)}_n (4), where HL¹ = pyridine-2-carbaldehyde thiosemicarbazone, HL² = pyridine-2-carbaldehyde 4N-methylthiosemicarbazone, Htfa = trifluoroacetic acid (CF₃COOH), pz = pyrazine (C₄H₄N₂) and dca = dicyanamide [N(CN)₂]⁻, have been synthesized and characterized. The crystal structures of these compounds are built up of monomers (1), dinuclear entities with the metal centers bridged through the non-thiosemicarbazone coligand (2 and 3) and 1D chains of dimers (4). In all the cases, square-pyramidal copper(II) ions are present, except for the square-planar ones in 3. Magnetic measurements show antiferromagnetic couplings in 2, 3 and 4. The susceptibility data were fitted by the Bleaney-Bowers’ equation for copper(II) dimers derived from H = -2JS₁S₂ being the obtained J/k values −4.8, −4.3 and −5.1 K for compounds 2-4, respectively. The magnetic susceptibility of the already known [{Cu(HL¹)(tfa)}₂](tfa)₂ compound has been also measured for the first time. The J/k value is -0.3 K, lower than that in 2. The nuclease activity of 3 and 4 has been analyzed.     

Binuclear manganese(III) complexes of an unsymmetric pyrazolate-based compartmental ligand with hard donor set

The synthesis, crystal structure and magnetic properties of manganese(III) binuclear complexes [Mn^III₂(L-3Н)₂(CH₃ОH)₄]·2CH₃ОH (1) and [Mn^III₂(L-3Н)₂(Py)₄]·2Py (2) (L = 3-[(1E)-N-hydroxyethanimidoyl]-4-methyl-1H-pyrazole-5-carboxylic acid) are reported. The ligand contains two distinct donor compartments formed by the pyrazolate-N and the oxime or the carboxylic groups. The complexes were characterized by X-ray single crystal diffraction, revealing that both 1 and 2 consist of dinuclear units in which the two metal ions are linked by double pyrazolate bridges with a planar {Mn₂N₄} core. Cryomagnetic measurements show antiferromagnetic interaction with g = 1.99, J = −3.6 cm⁻¹, Θ = −2.02 K for 1 and g = 2.00, J = −3.7 cm⁻¹, Θ = 1.43 K for 2.     

Cleavage of a RNA analog containing uridine by a bifunctional dinuclear Zn(II) catalyst

The macrocyclic ligand, 1,4-bis((1-oxa-4,7,10-triazacyclododecan-7-yl)methyl)benzene (L1) is prepared. L1 binds two Zn(II) ions at neutral pH to form Zn₂(L1) as studied by using pH-potentiometric titrations. Zn₂(L1) binds two uridines at pH 7.0, I = 0.100 M (NaCl) and the mononuclear analog Zn(L2) (L2 = 1-oxa-4,7,10-triazacyclododecane) binds a single uridine; dissociation constants for both complexes are in the millimolar range. Both complexes promote the cleavage of a simple RNA analog lacking a nucleobase (HpPNP = 2-hydroxypropyl-4-nitrophenylphosphate), and a uridine containing RNA analog UpPNP (uridine-3′-4-nitrophenylphosphate). Plots of the first-order rate constant for cleavage of HpPNP as a function of Zn(L2) concentration from 0.5 mM to 20.0 mM are linear, consistent with weak complexation to substrate K_d > 20 mM. In contrast, first-order rate constants for cleavage of UpPNP by Zn(L2) or Zn₂(L1) over similar concentration ranges exhibit a downward curvature, consistent with the formation of a complex between catalyst and UpPNP. Comparison of second-order rate constants (k₂ = k_cat/K_d) shows that the dinuclear complex Zn₂(L1) is a better catalyst than Zn(L2) for both HpPNP and UpPNP cleavage.     

fac-/mer-[RuCl3(NO)(P-N)] (P-N = [o-(N,N-dimethylamino)phenyl]diphenylphosphine): Synthesis, characterization and DFT calculations

Complex fac-[RuCl₃(NO)(P-N)] (1) was synthesized from the reaction of [RuCl₃(H₂O)₂(NO)] and the P-N ligand, o-[(N,N-dimethylamino)phenyl]diphenylphosphine) in refluxing methanol solution, while complex mer,trans-[RuCl₃(NO)(P-N)] (2) was obtained by photochemical isomerization of (1) in dichloromethane solution. The third possible isomer mer,cis-[RuCl₃(NO)(P-N)] (3) was never observed in direct synthesis as well as in photo- or thermal-isomerization reactions. When refluxing a methanol solution of complex (2) a thermally induced isomerization occurs and complex (1) is regenerated.The complexes were characterized by NMR (³¹P{¹H}, ¹⁵N{¹H} and ¹H), cyclic voltammetry, FTIR, UV-Vis, elemental analysis and X-ray diffraction structure determination. The ³¹P{¹H} NMR revealed the presence of singlet at 35.6 for (1) and 28.3 ppm for (2). The ¹H NMR spectrum for (1) presented two singlets for the methyl hydrogens at 3.81 and 3.13 ppm, while for (2) was observed only one singlet at 3.29 ppm. FTIR Ru-NO stretching in KBr pellets or CH₂Cl₂ solution presented 1866 and 1872 cm⁻¹ for (1) and 1841 and 1860 cm⁻¹ for (2). Electrochemical analysis revealed a irreversible reduction attributed to Ru^II-NO⁺ → Ru^II-NO⁰ at −0.81 V and −0.62 V, for (1) and (2), respectively; the process Ru^II → Ru^III, as expected, is only observed around 2.0 V, for both complexes.Studies were conducted using ¹⁵NO and both complexes were isolated with ¹⁵N-enriched NO. Upon irradiation, the complex fac-[RuCl₃(NO)(P-N)] (1) does not exchange ¹⁴NO by ¹⁵NO, while complex mer,trans-[RuCl₃(NO)(P-N)] (2) does. Complex mer,trans-[RuCl₃(¹⁵NO)(P-N)] (2′) was obtained by direct reaction of mer,trans-[RuCl₃(NO)(P-N)] (2) with ¹⁵NO and the complex fac-[RuCl₃(¹⁵NO)(P-N)] (1′) was obtained by thermal-isomerization of mer,trans-[RuCl₃(¹⁵NO)(P-N)] (2′).DFT calculation on isomer energies, electronic spectra and electronic configuration were done. For complex (1) the HOMO orbital is essentially Ru (46.6%) and Cl (42.5%), for (2) Ru (57.4%) and Cl (39.0%) while LUMO orbital for (1) is based on NO (52.9%) and is less extent on Ru (38.4%), for (2) NO (58.2%) and Ru (31.5%).