A family of polyamino phenolic macrocyclic ligands. Acid-base and coordination properties towards Co(II), Ni(II), Cu(II), Zn(II), Cd(II) and Pb(II) ions

The acid-base and coordination properties towards Co(II), Ni(II), Cu(II), Zn(II), Cd(II) and Pb(II) of four polyamino-phenol macrocycles 15-hydroxy-3,6,9-triazabicyclo[9.3.1]pentadeca-11,13,1¹⁵-triene L1, 18-hydroxy-3,6,9,12-tetraazabicyclo[12.3.1]octadeca-14,16,1¹⁸-triene L2, 21-hydroxy-3,6,9,12,15-pentaazabicyclo[15.3.1]enaicosa-17,19,1²¹-triene L3 and 24-hydroxy-3,6,9,12,15,18-hexaazabicyclo[18.3.1]tetraicosa-20,22,1²⁴-triene L4 are reported. The protonation and stability constants were determined by means of potentiometric measurements in 0.15 mol dm⁻³ NMe₄Cl aqueous solution at 298.1 K. L1 forms highly unsaturated Co(II), Cu(II), Zn(II) and Cd(II) mononuclear complexes that are prone to give dimeric dinuclear species with [(MH₋₁L1)₂]²⁺ stoichiometry, in solution. L2 forms stable Co(II), Ni(II), Cu(II), Zn(II), Cd(II) and Pb(II) mononuclear complexes that can coordinate external species as OH⁻ anion, giving hydroxylated complexes at alkaline pH. L3 forms stable Co(II), Ni(II), Cu(II), Zn(II), Cd(II) and Pb(II) mononuclear complexes and Co(II), Ni(II), Cu(II) and Zn(II) dinuclear [M₂H₋₁L3]³⁺ species. L4 forms stable mono- and dinuclear Co(II), Cu(II), Zn(II) and Cd(II) complexes, but only mononuclear species with Pb(II). The effect of macrocyclic size is considered in the discussion of results.     

Synthesis and photophysical properties of dansyl-based polyamine ligands and their Zn(II) complexes

The synthesis, potentiometric studies and photophysical properties of two new polyamine ligands (L1 and L2) possessing the dansyl chromophore were studied in aqueous 0.15 M NaCl. The compounds show the absorption and emissions bands characteristic of the dansylamide fluorophore and both present intramolecular excited state proton transfer at intermediate pH ranges. One of the ligands (L2) strongly coordinates Zn(II) leading to fluorescence quenching. A model compound (L3) of the dansyl moiety was also investigated.     

Synthesis and properties of electrochemiluminescent dinuclear Ru(II) complexes assembled with ester-bridged bis(bipyridine) ligands

New bridging ligands, such as bpy-(COOCH₂)-bpy (BL1), mbpy-(CH₂)₃COOCH₂-bpy (BL2), bpy-COO(CH₂)₆OOC-bpy (BL3), and bpy-COOCH₂PhPhCH₂OOC-bpy (BL4), have been synthesized and coordinated to [RuL₂(acetone)₂](PF₆)₂ for various [Ru(L)₂(BL)Ru(L)₂](PF₆)₄-type dinuclear ruthenium complexes (where BL = BL1, BL2, BL3, BL4, and L = bpy, o-phen, DTDP). Their electrochemical redox potentials, spectroscopic properties and relative electrochemiluminescence were investigated in detail. All dinuclear Ru complexes exhibit MLCT (metal-to-ligand charge transfer) absorption and luminescence bands in the visible region. ECL intensities of dinuclear ruthenium(II) complexes were affected not only by the kind of the ligand, but also by the nature of the bridging ligand. Among the synthesized dinuclear Ru complexes, [(DTDP)₂Ru(mbpy)-(CH₂)₃COOCH₂-(bpy)Ru(DTDP)₂](PF₆)₄ exhibited enhanced ECL intensities as high as 2.9 times greater than that of the reference, [Ru(o-phen)₃](PF₆)₂.     

Pyrazolato-bridged 1-D Co(II) coordination polymer and dinuclear Ni(II) and Cu(II) complexes: Syntheses, crystal structures and magnetic properties

Three complexes of composition [Co₃(Hdcp)₂(phen)₃(H₂O)₂]_n · nH₂O (1), [Ni₂(Hdcp)₂(H₂O)₄](Im)₂ (2) and [Cu₂(Hpca)₂(H₂O)₂(Im)₂] (3) (H₃dcp = 3,5-pyrazoledicarboxylic acid, H₂pca = 1H-pyrazole-5-carboxylic acid, Im = imidazole and phen = 1,10-phenanthroline) have been synthesized via hydrothermal reactions and their structures have been characterized. Complex 1 is mainly constructed by Hdcp and ancillary ligand 1,10-phenanthroline and exhibits one-dimensional linear chain structure. Complexes 2 and 3 are pyrazolato-bridged dinuclear complexes. The ancillary imidazole ligand was not involved in the coordination and stacked to the lattice of the complex in 2. In the process of synthesis 3, imidazole ligand was coordinated to the metal centre; with one of the carboxylic group of the H₃dcp ligand was eliminated to form [Cu₂(Hpca)₂(H₂O)₂(Im)₂] (3) in situ. The results of magnetic susceptibility measurements indicate that there exist antiferromagnetic interactions between Co(II) and Ni(II) centres in compounds 1 and 2, respectively.     

Macrocyclic dinuclear Zn(II) complexes: synthesis, structure and hydrolysis of tris(p-nitrophenyl) phosphate

A series of mono- and dinuclear zinc complexes of 3,6,9,17,20,23-hexaaza-29,30-dihydroxy-13,27-dimethyl-tricyclo[23,3,1^11,15]triaconta-1(28),11,13,15(30),25,26-hexaene (H₂L or BDBPH) have been defined in solution by potentiometry. The crystal structure of [Zn₂C₂₆H₄₀N₆O₂(CH₃OH)₂]·Br₂ has been determined by X-ray. Each zinc ion is coordinated to three nitrogen atoms, a bridged-phenolic oxygen atom, and a methanolic oxygen atom, which define a six-coordinated octahedron. Bond lengths of ZnN are in the range of 2.104(3)-2.120(3) Å and distances between Zn and O (bridged-phenolic oxygen) are 2.052(2), 2.062(2) Å, respectively. The dinuclear complexes: [Zn₂L]²⁺ and [Zn₂L(OH)]⁺ play crucial roles in hydrolytic reaction of tris(4-nitrophenyl)phosphate. A possible mechanism showed that [Zn₂L(OH)]⁺ acts as a nucleophile and [Zn₂L]²⁺ stabilizes the formation of the intermediate: [Zn₂L-BNP].     

Synthesis, spectroscopic properties and X-ray crystal structures of two dinuclear alkoxo-bridged copper(II) compounds with the ligand bis(1-methyl-2-benzimidazolyl) propane. A unique alkoxo-bridged Cu(II) dinuclear compound with an additional bidentate bridging triflate anion

Based on the new ligand bis(1-methyl-2-benzimidazolyl) propane (abbreviated as mtbz) several new copper(II) coordination compounds have been prepared and characterized structurally and spectroscopically. Two representative compounds, i.e. [Cu₂(mtbz)₂(CH₃)₂- (CF₃SO₃)](CF₃SO₃) (1) and [Cu₂(mtbz)₂(CH₃O)₂](ClO₄)₂ (4) were characterized structurally by X-ray diffraction. Crystal data for 1: monoclinic, space group P2₁/c, a=13.6585(5), B=39.981(3), C=20.919(1) Å, β=125.98(1)°, Z=8. Crystal data for 4: monoclinic, space group P2₁/c, a=13.115(2), B=9.523(2), C=17.908(4) Å, β=111.71(1)°, Z=2. Structures 1 and 4 each consist of a dinuclear unit with bridging methoxo groups and one ligand linked to each copper via an N atom. Structure 1 (which consists of two dinuclear, crystallographically independent, but chemically identical units) has the two copper atoms bridged by a triflate anion, providing each copper atom a square-pyramidal coordination, while the copper atoms in structure 4 have an almost a square-planar geometry. The Cu---Cu distances (Å) within the dinuclear units are: 1, 2.9775(13), 2.9751(13); 4, 2.9872(16); the Cu---O---Cu bridging angles (°) are: 1, 101.7(3), 101.7(3), 100.9(3), 102.1(3); 4, 103.2(2). The mid-IR section focused on the vibrations of the triflate anion reveals interesting results concerning the assignments of that anion related to the v_as(S---O) band. Characteristic Cu---O vibrations in the far-IR section were found at 386 and 230 cm⁻¹ for the methoxo-bridged and 454 and 332 cm⁻¹ for the ethoxo-bridged compounds. These dinuclear species are EPR silent, and only a weak signal of monomeric impurities is observed. They also show a diamagnetic behavior below room temperature.     

Comparative studies of coordination properties of puromycin and puromycin aminonucleoside towards copper(II) ions

Protonation equilibria of puromycin (PM) and puromycin aminonucleoside (PAN) and their coordination by copper(II) ion were studied in solution by potentiometry, electronic absorption spectroscopy (UV-Vis), circular dichroism (CD), electron paramagnetic resonance (EPR) and mass spectrometry. For puromycin four mononuclear complexes were found, with stoichiometries Cu(PM)2+, CuH(-1)(PM)+, CuH(-2)(PM) and CuH(-3)(PM)(-). In each of them the Cu(II) ion was bound in the peptidic-like manner, the differences of stoichiometries are a consequence of subsequent deprotonations of the sugar C2'-OH group and the coordinated water molecule. The coordination mode for puromycin aminonucleoside was aminosugar-like. Two dimeric complexes, Cu2H(-1)(PAN)2(2+) and Cu2H(-2)(PAN)2+, and one monomeric CuH(-2)(PAN)2 were found. The N6,N6-dimethyladenine moiety of PAN was not involved in the coordination process due to steric hindrance.     

Effect of pyrazole-substitution on the structure and nuclearity of Cu(II)-pyrazolato complexes

Trinuclear Cu(II)-pyrazolates of the general formula (Bu₄N)₂[Cu₃(μ₃-Cl)₂(μ-4-R-pz)₃Cl₃] (pz=pyrazolato anion, R=Cl, Br, I, Me), 1-4, have been prepared and characterized by X-ray diffraction and/or ¹H NMR, IR, UV-Vis spectroscopy and elemental analysis. Their structure and spectroscopic properties match the ones of the parent unsubstituted complex (Bu₄N)₂[Cu₃(μ₃-Cl)₂(μ-pz)₃Cl₃], indicating that 4-substitution of the pyrazole ligands with halogen or methyl groups does not induce structural variation. In contrast, dinuclear complexes (Bu₄N)₄[Cu₂(μ-3-Me-pz)₂Cl₄]Cl₂ · 4H₂O, Cu₂(μ-Cl)(μ-3,5-Me₂-pz)(3,5-Me₂-pzH)₄Cl₂, Cu₂(μ-Cl)(μ-OH)(3-Me-5-Ph-pzH)₄Cl₂ · 3-Me-5-Ph-pzH and Cu₂(μ-Cl)₂(3,5-Ph₂-pzH)₄Cl₂, 5-8, have been prepared with 3- and 3,5-substituted pyrazoles by the same or similar synthetic protocols.     

Synthesis and structure of monoribbed-functionalized disulfide iron(II) clathrochelates and their coordination as the ligands toward platinum(II) and platinum(IV) ions

Disulfide monoribbed-functionalized clathrochelates (i.e., fuctionalization of one of the three α-dioximate fragments) with ribbed thioalkyl, S₃-thioalkyl and hydroxythioalkyl substituents have been synthesized starting from the FeBd₂(Cl₂Gm)(BF)₂ precursor (where Bd²⁻ and Cl₂Gm²⁻ are α-benzyldioxime and dichloroglyoxime dianions) using the corresponding thiol/triethylamine system in dichloromethane solution. Clathrochelate S₆-dithiol in basic media underwent the intramolecular dealkylation to yield the S₃-thiocrown etheric clathrochelate. Clathrochelates obtained have been studied as the ligands toward Pt²⁺ and Pt⁴⁺ ions. The S-demethylation reaction of the methylsulfide complex with [PtCl₄]²⁻ dianion produced the polynuclear complexes of the dianionic clathrochelate dithiolate ligand. The reaction of n-butylsulfide clathrochelate with the trans-Pt^IVCl₄(C₆H₅CH₂CN)₂ afforded the binuclear compound with the disulfide iron(II) clathrochelate as a monodentate ligand. The obtained macrobicycles, their clathrochelate derivatives, and polynuclear complexes have been characterized using elemental analysis, MALDI-TOF and PD mass, IR, UV-Vis, and NMR spectra, and X-ray crystallography. The encapsulated iron(II) ion coordination polyhedra distortion angle φ values and the main distances in the molecules of polynuclear complexes have been deduced (obtained) using ⁵⁷Fe Mössbauer parameters and EXAFS data, respectively.     

Dinuclear alkoxo-bridged copper(II) coordination polymers: Syntheses, structural and magnetic properties

The alkoxo-bridged dinuclear copper(II) complexes [Cu₂(ap)₂(NO₂)₂] (1), [Cu₂(ap)₂(C₆H₅COO)₂] (2) and [Cu₂(ap)₂μ-1,3-C₆H₄(COO)₂(dmso)₂]·dmso (3) (ap = 3-aminopropanolato and dmso = dimethyl sulfoxide) have been synthesized via self-assembly from copper(II) perchlorate, 3-aminopropanol as main chelating ligand and nitrite and isophthalate anions as spacers and benzoate anion as auxiliary ligand. Complexes 1 and 3 crystallize as 2D and 1D coordination polymers, respectively, and their structures consist of dinuclear [Cu₂(ap)₂]²⁺ units connected with nitrite and isophthalate ligands. The adjacent dinuclear units of 2 and 1D polymers of 3 are further connected by hydrogen bonds resulting in the formation of 2D layers. The variable temperature crystallographic measurements of 1 at 100, 173 and 293 K indicate the static Jahn-Teller distortion with librational disorder in the nitrite group. Experimental magnetic studies showed that complexes 1-3 exhibit strong antiferromagnetic couplings. The values of the magnetic exchange coupling constant for 1-3 are well reproduced by the theoretical calculations.     

A ratiometric fluorescent detection of Zn(II) in aqueous solutions using pyrene-appended histidine

A fluorescent chemosensor, Py-His, based on histidine was easily synthesized in solid phase synthesis. Py-His displayed a highly sensitive ratiometric response to Zn(II) with potent binding affinity (K_a = 1.17 × 10¹³ M^?2) in aqueous solutions. The detection limit of Py-His for Zn(II) was calculated as 80.8 nM. Moreover, Py-His distinguished Zn(II) and Hg(II) by different ratiometric response type; the chemosensor showed a more enhanced increase of excimer emission intensity to Zn(II) than Hg(II). Upon addition of Ag(I) and Cu(II), Py-His showed a turn-off response mainly due to the quenching effect of these metal ions. The binding stoichiometry (2:1 or 1:1) of Py-His to target metal ions played a critical role in the fluorescent response type (ratiometric and turn off response) to target metal ions. The role of imidazole group of Py-His for ratiometric detection of Zn(II) was proposed by pH titration experiments.     

Synthesis, crystal structure and spectroscopic behaviors of Co(II) and Cu(II) complexes with Salen-type bisoxime ligands

Two Salen-type ligands (H₂L¹, 4,4′-dichloro-2,2′-[(1,3-propylene)dioxybis(nitrilomethylidyne)]diphenol and H₂L², 4,4′-dinitro-2,2′-[ethylenedioxybis(nitrilomethylidyne)]diphenol) and their corresponding complexes ({[CoL¹(MeOH)]₂(OAc)₂Co} · 2MeOH and [CuL²]₂) have been synthesized and characterized by element analyses, ¹H NMR, FT-IR and UV-Vis spectra, TG-DTA and single crystal X-ray crystallography. Crystallographic data suggests the octahedral geometry for Co(II) complex and square-pyramidal geometry for Cu(II) complex. Furthermore, the fluorescence behavior of Cu(II) complex in DMSO is discussed.     

Binding abilities of dehydropeptides towards Cu(II) and Ni(II) ions. Impact of Z-E isomerization on metal ion binding

The study on the binding ability of dehydro-tri- and tetrapeptides has shown that the ,β-double bond has a critical effect on the peptide coordination to metal ions. It may affect the binding of the vicinal amide nitrogens by the electronic effect and stabilize the complex due to steric effects. The (Z) isomer is the most effective in stabilizing of the complexes formed. The presence of large side chain in the dehydroamino acid residue may also be critical for the coordination mode in the metallopeptide systems.     

Synthesis, crystal structure, and properties of supramolecular Cu, Zn, and Cd complexes with Salen-type bisoxime ligands

Three new supramolecular complexes, [Cu(L¹)H₂O]_n (1), [Zn(L²)(H₂O)₂]_n (2), and [Cd(L²)(H₂O)₂]_n (3), have been synthesized and characterized by FT-IR spectra, fluorescence spectra, and thermal analyses. And the structures of complexes 1-3 have been elucidated by X-ray analyses. Complex 1 is square pyramidal geometry with an unusually long bond (2.262 Å) from penta-coodinated Cu^II center to the oxygen atom of the apical coordinated water molecule. Molecules are linked by hydrogen bonding between the coordinated water and the phenolic oxygen atoms of adjacent molecules, thus formed a self-assembling continual zigzag chain supramolecular structure. The crystal structure of complex 2 (or 3) has indicated that the complex consists of one Zn^II (or Cd^II) atom, one L²⁻ unit and two coordinated water molecules, the coordination number of the Zn^II (or Cd^II) atom is six, and formed an infinite metal-water chain supramolecular structure by intermolecular hydrogen bonds and π-π stacking of neighboring benzene rings. Meanwhile, the thermal and photophysical properties of the resulted complexes have also been discussed.     

New dinuclear Co(II) and Mn(II) complexes of the phenol-based compartmental ligand containing formyl and amine functions: structural, spectroscopic and magnetic properties

The phenol-based compartmental ligand Hpy2ald contains a tridentate amino arm and a weak donor aldehyde group at the 2^′ and at the 6^′ positions of the phenol ring, respectively. This ligand reacts with cobalt(II) perchlorate, cobalt(II) tetrafluoroborate and manganese(II) perchlorate, yielding dinuclear complexes, where two metal ions are doubly bridged by two deprotonated cresolate moieties. The coordination environment around the metal ions is then completed to a very distorted octahedron by three nitrogen donor atoms from the pendant amino arm and the oxygen atom of the aldehyde group. The crystal structures of the complexes, their spectroscopic and magnetic properties are reported.     

Synthesis and characterization of new unsaturated macrobicyclic and bis(macrocyclic) copper(II) complexes containing N-CH2-N linkages

New copper(II) complexes [CuL²]²⁺ (L²=7,7,9-trimethyl-1,3,6,10,13-pentaazabicyclo[11,2,1^1.13]hexadec-9-ene) and [Cu₂(L³)(H₂O)₂]⁴⁺ have been prepared by the reaction of [CuL¹]²⁺ (L¹=5,5,7-trimethyl-1,4,8,11,14-pentaazatetradce-7-ene) and formaldehyde. The mononuclear complex [CuL²]²⁺ has a square-planar coordination geometry with a 5-6-5-6 chelate ring sequence and is relatively stable even in low pH at room temperature. The dinuclear complex [Cu₂(L³)(H₂O)₂]⁴⁺ consists of two unsaturated 15-membered pentaaza macrocyclic units (7,7,9-trimethyl-1,3,6,10,13-pentaazacyclopentadec-9-ene) that are linked together by a methylene group in a tilted face-to-face arrangement [Cu?Cu distance: 7.413(2) Å ]. Each macrocyclic unit of [Cu₂(L³)(H₂O)₂]⁴⁺ contains one four-membered chelate ring and has a severely distorted octahedral coordination polyhedron. The dinuclear complex is quite stable in aqueous solutions containing an excess of formaldehyde or in dry acetonitrile but is decomposed to [CuL¹]²⁺ and [CuL²]²⁺ in pure water.     

Synthesis and characterization of monomer and dimer complexes of porphyrin iron(III) with bridging phenylcyanamide ligands

Several new mono and dinuclear complexes of [(P)Fe^III(L)], in which P is the dianion of tetraphenylporphyrin(TPP) and tetramesitylporphyrin(TMP) and L is the monoanion of 4-azo(phenylcyanamido)benzene (apc) (1) and (2) or dianion 1,4-di cyanamidobenzene (dicyd) (3), (4), (7), (8) and 4,4′-azo-diphenylcyanamide (adpc) (5), (6), (9), (10) have been prepared by the reaction of [(P)Fe^IIICl] with appropriate thallium salts of phenylcyanamide derivatives. Each of the complexes has been characterized by FT-IR, UV-Vis, ¹H NMR, MALDI-TOF and EPR spectroscopic data. In non-coordinating solvents (such as toluene or chloroform) these complexes exhibit ¹H NMR spectra that are characteristic of high-spin (S = 5/2) species. The cyanamide group (NCN) of the bridging ligand is coordinated to Fe(III) ions through the nitrile-nitrogen. The iron(III) phenylcyanamide complexes are not reactive toward dioxygen, they convert into [TPPFe^IIICl] when treated with HCl. EPR and NMR have shown that in dinuclear complexes weak magnetic interactions take place between two iron(III) paramagnetic centers.     

Dinuclear terephthalato-bridged nickel(II) complexes. Structural characterization and magnetic properties

The dinuclear terephthalato-bridged nickel(II) complexes [Ni₂(cyclen)₂(μ-tp)](ClO₄)₂ (1) [Ni₂(trpn)₂(μ-tp)(H₂O)₂](ClO₄)₂ (2) and [Ni₂(3,3,3-tet)₂(μ-tp)(H₂O)₂](ClO₄)₂ · 2H₂O (3), where tp = terephthalate dianion, cyclen = 1,4,7,10-tetraazacyclododecane, trpn = tris(3-aminopropyl)amine and 3,3,3-tet = 1,5,9,13-tetraazatridecane, were synthesized and structurally characterized by X-ray crystallography. Their magnetic susceptibilities were also determined at variable temperatures over the range 2-300 K. The structures of these complexes consist of μ-tp bridging two Ni(II) centers in a bis(bidentate) bonding fashion in 1 and in bis(monodentate) bonding fashion in 2 and 3. The coordination geometry around the Ni(II) ions in these compounds has a distorted octahedral geometry with four nitrogen atoms from the amine ligand (cyclen, trpn or 3,3,3-tet) and two coordinated oxygen atoms supplied by the chelated carboxylate group of the bridged terephthalate ligand in 1, and by one tp-carboxylate-oxygen in 2 and 3. The sixth coordination site in the last two complexes 2 and 3 is achieved via an oxygen atom from a coordinated water molecule. The intradimer Ni…Ni distances in these complexes are 10.740, 11.428 and 11.537 Å for 1, 2 and 3, respectively. The electronic spectra of the complexes in aqueous solutions are in complete agreement with the assigned X-ray geometry around the Ni(II) centers. Also, the analysis of the infrared spectral data for the ν(COO⁻) stretching frequencies of the tp-carboxalato groups reveals the existence of the bis(bidentate) and bis(monodentate) coordination modes for the bridged terephthalate ligand in 1, 2 and 3, respectively. Despite the different coordination modes of the tp bridging ligand in these complexes, they all exhibit very weak antiferromagnetic coupling. The coupling constants J were found to be −2.2, −0.6 and −1.5 cm³ K mol⁻¹ for the complexes 1, 2 and 3, respectively. The structural and magnetic results of 1-3 are discussed in relation to the other related published μ-terephthalato dinuclear Ni(II) compounds.     

Synthesis, photophysical characterisation and metal ion binding properties of new ligands containing anthracene chromophores

Two new fluorescent chemosensors for heavy metal ions have been synthesised and their photophysical properties have been investigated. They present a pyridyl-thioether-based binding site and the anthracene moiety as a chromophore. In the experimental conditions used, no evidence is found for the formation of complexes with Pb²⁺, Zn²⁺, Cd²⁺, and Ag⁺ ions. On the contrary, in acetonitrile solutions both ligands strongly bind Cu²⁺ and Hg²⁺ cations according to a 1:1 and a 1:2 (metal:ligand) stoichiometry. In these complexes, the intense luminescence typical of anthracene derivatives is almost completely quenched and this phenomenon can be mainly attributed to an intraligand electron transfer process from the anthracene chromophore to the complexed pyridine. These results are of interest for the development of new chemosensors for the design of efficient electronic tongues for the detection of transition metal ions.     

Synthesis, spectroscopic properties and structural characterisation of Pd(II) and Pt(II) complexes with 1,3,5-pyrazole derived ligands. Rotation around the metal-N bond

Reactions of ligands 1-ethyl-5-methyl-3-phenyl-1H-pyrazole (L¹) and 5-methyl-1-octyl-3-phenyl-1H-pyrazole (L²) with [PdCl₂(CH₃CN)₂ and K₂PtCl₄ gave complexes trans-[MCl₂(L)₂] (L = L¹, L²). The new complexes were characterised by elemental analyses, conductivity measurements, infrared, ¹H and ¹³C{¹H} NMR spectroscopies and X-ray diffraction. The NMR study of the complex [PdCl₂(L¹)₂], in CDCl₃ solution, is consistent with a very slow rotation of ligands around the Pd-N bond, so that two conformational isomers can be observed in solution (syn and anti). Different behaviour is observed for complexes [PdCl₂(L²)₂] and [PtCl₂(L)₂] (L = L¹, L²), which present an isomer in solution at room temperature (anti). The crystal structure of [PdCl₂(L¹)₂] complex is described, where the Pd(II) presents a square planar geometry with the ligands coordinated in a trans disposition.