Synthesis and characterisation of new N1-alkyl-3,5-dipyridylpyrazole derived ligands. Study of their reactivity with Pd(II) and Pt(II)

Two new pyrazole-derived ligands, 1-ethyl-3,5-bis(2-pyridyl)pyrazole (L¹) and 1-octyl-3,5-bis(2-pyridyl)pyrazole (L²), both containing alkyl groups at position 1 were prepared by reaction between 3,5-bis(2-pyridyl) pyrazole and the appropriate bromoalkane in toluene using sodium ethoxide as base.The reaction between L¹, L² and [MCl₂(CH₃CN)₂] (M = Pd(II), Pt(II)) resulted in the formation complexes of formula [MCl₂(L)] (M = Pd(II), L = L¹ (1); M = Pd(II), L = L² (2); M = Pt(II), L = L¹ (3); M = Pt(II), L = L² (4)). These complexes were characterised by elemental analyses, conductivity measurements, infrared, ¹H, ¹³C{¹H} NMR and HMQC spectroscopies. The X-ray structure of the complex [PtCl₂(L²)] (4) was determined. In this complex, Npyridine and Npyrazole donor atoms coordinate the ligand to the metal, which complete its coordination with two chloro ligands in a cis disposition.     

Synthesis, X-ray crystal structures and properties of complex salts and sterically crowded heteroleptic complexes of group 10 metal ions with aromatic sulfonyl dithiocarbimates and triphenylphosphine ligand

Two new complex salts of the form (Bu₄N)₂[Ni(L)₂] (1) and (Ph₄P)₂[Ni(L)₂] (2) and four heteroleptic complexes cis-M(PPh₃)₂(L) [M = Ni(II) (3), Pd(II) (4), L = 4-CH₃OC₆H₄SO₂NCS₂] and cis-M(PPh₃)₂(L′) [ M = Pd(II) (5), Pt(II) (6), L′ = C₆H₅SO₂NCS₂] were prepared and characterized by elemental analyses, IR, ¹H, ¹³C and ³¹P NMR and UV-Vis spectra, solution and solid phase conductivity measurements and X-ray crystallography. A minor product trans-Pd(PPh₃)₂(SH)₂, 4a was also obtained with the synthesis of 4. The NiS₄ and MP₂S₂ core in the complex salts and heteroleptic complexes are in the distorted square-plane whereas in the trans complex, 4a the centrosymmetric PdS₂P₂ core is perforce square planar. X-ray crystallography revealed the proximity of the ortho phenyl proton of the PPh₃ ligand to Pd(II) showing rare intramolecular C-H?Pd anagostic binding interactions in the palladium cis-5 and trans-4a complexes. The complex salts with σ_rt values ∼10⁻⁵ S cm⁻¹ show semi-conductor behaviors. The palladium and platinum complexes show photoluminescence properties in solution at room temperature.     

Synthesis and in vitro evaluation of palladium(II) salicylaldiminato thiosemicarbazone complexes against Trichomonas vaginalis

Eight mononuclear Pd(II) complexes containing salicylaldiminato thiosemicarbazones (saltsc-R; where R = H (1), 3-OMe (2), 3-^tBu (3) and 5-Cl (4)) as dinegative tridentate ligands were prepared by the reaction of the corresponding thiosemicarbazone with the precursor Pd(L)₂Cl₂ (L = phosphatriazaadamantane or 4-picoline) in the presence of a weak base. These complexes (9-16) were characterised by a range of spectroscopic and analytical techniques including NMR spectroscopy and X-ray diffraction. These complexes along with four other Pd(II) analogues (5-8) were screened for activity in vitro against the Trichomonas vaginalis parasite. Preliminary results show that the type of ancillary ligand as well as the substituents on the aromatic ring of the salicylaldiminato thiosemicarbazone ligand influences the antiparasitic activity of these complexes.     

Synthesis, characterization and in vitro cytotoxicity of the first palladium(II) oxalato complexes involving adenine-based ligands

The first [Pd(Lⁿ)₂(ox)] xH₂O oxalato(ox) complexes involving 2-chloro-N6-(benzyl)-9-isopropyladenine (L¹; complex 1), 2-chloro-N6-(4-methoxybenzyl)-9-isopropyladenine (L²; 2), 2-chloro-N6-(2,3-dimethoxybenzyl)-9-isopropyladenine (L³; 3), 2-chloro-N6-(2,4-dimethoxybenzyl)-9-isopropyladenine (L⁴; 4), and 2-chloro-N6-(4-methylbenzyl)-9-isopropyladenine (L⁵; 5) have been synthesized by the reactions of potassium bis(oxalato)palladate(II) dihydrate, [K₂Pd(ox)₂]·2H₂O, with the mentioned organic compounds (H₂ox = oxalic acid; x = 0 for 1-3 and 5 or 2 for 4). Elemental analyses (C, H, N), FTIR, Raman and NMR (¹H, ¹³C, ¹⁵N) spectroscopies, conductivity measurements and thermal studies (thermogravimetric and differential thermal analyses, TG/DTA) have been used to characterize the prepared complexes. The molecular structures of [Pd(L²)₂(ox)] (2) and [Pd(L⁵)₂(ox)]·L⁵·Me₂CO (5·L⁵·Me₂CO) have been determined by a single crystal X-ray analysis. The geometry of these complexes is slightly distorted square-planar with two appropriate Lⁿ (n = 2 or 5) molecules mutually arranged in the head-to-head (2) or head-to-tail (5) orientation. The Lⁿ ligands are coordinated to the central Pd(II) ion via the N7 atoms. The same conclusions regarding the binding properties of L¹-L⁵ ligands can be made based on multinuclear NMR spectra. In vitro cytotoxicity of the complexes 1-5 has been evaluated against human chronic myelogenous leukaemia (K562) and human breast adenocarcinoma (MCF7) cancer cell lines. Significant cytotoxicity has been determined for the complexes 3 (IC₅₀ = 6.2 μM) and 5 (IC₅₀ = 6.8 μM) on the MCF7 cell line, which is even better than that found for the well-known and widely-used platinum-bearing antineoplastic drugs, i.e. oxaliplatin and cisplatin.     

High catalytic activities in the norbornene polymerization with neutral palladium complexes containing N4-type tetradentate chelating ligands

Norbornene polymerization catalyzed by new Pd(II) complexes bearing N4-type tetradentate ligands obtained from the reaction between a 6-methyl-2-picolinic acid or picolinic acid and appropriate diamines has been studied. A class of new palladium complexes, [Pd(X¹X²bpb)] and [Pd(X¹X²-6-Me₂bpb)] (X¹ = Me, X² = Me (1 and 4); X¹ = H, X² = H (2 and 5); X¹ = H, X² = NO₂ (3 and 6); bpb = N,N′-(o-phenylene)bis(pyridine-2-carboxamidate); 6-Me₂bpb = N,N′-(o-phenylene)bis(6-methylpyridine-2-carbox-amidate)) were synthesized and characterized. The molecular structure of Pd complex 5 was determined by X-ray crystallography, showing distorted square planar configurations. Using modified methylaluminoxanes (MMAO) as an activator, the palladium complexes exhibited high catalytic activities for the polymerization of norbornene. The catalytic activities up to 4.0 × 10⁶ g of PNBEs/mol_Pd·h and M_w up to 8.34 × 10⁵ g/mol with PDI < 2.53 were observed. Amorphous polynorbornenes (PNBEs) were obtained with good solubility in halogenated aromatic solvents. Interestingly, the structural modification with the methyl groups of pyridyl rings and the strong electron-withdrawing substituents induced improvement in solubility, thermal stability and catalytic activity. FT-IR, ¹H, and ¹³C NMR analyses of the polymers suggest that the catalytic polymerization occurs via vinyl addition mechanism.     

Syntheses and characterization of titanium malonato and amino acid complexes: [Ti(cp)2(OOCCH2NMe2)] - The first structurally characterized α-amino acid titanium(III) complex

The reaction of [Ti(cp^∗)₂(BTMSA)] (1) (cp^∗ = η⁵-C₅Me₅, BTMSA = bis(trimethylsilyl)acetylene) with malonic acids ((HOOC)₂CR₂, R = H, Me) and N,N-dimethylglycine resulted in the formation of titanium(IV) dicarboxylato complexes [Ti(cp^∗)₂{(OOC)₂CR₂}] (R = H, 2; R = Me, 3) and an α-amino acid titanium(III) complex [Ti(cp^∗)₂(OOCCH₂NMe₂)] (4). The identities of complexes 2-4 were confirmed by microanalysis, ¹H and ¹³C NMR spectroscopy (2, 3), ESI-MS and CID experiments (2, 3) as well as by ESR and magnetic measurements (μ_eff = 1.81, 298 K) for 4. Single X-ray diffraction analyses of 2 and 4 exhibited monomolecular complexes in which the titanium atom is distorted tetrahedrally coordinated by two η⁵-C₅Me₅ rings and by the chelating bound malonato-κ²O,O′ (2) and N,N-dimethylglycinato-κ²O,O′ ligand (4).     

Syntheses, crystal structure, spectroscopic characterization and antifungal activity of new N-R-sulfonyldithiocarbimate metal complexes

Five new compounds with the general formula of (Bu₄N)₂[M(RSO₂NCS₂)₂], where Bu₄N = tetrabutylammonium cation, (M = Ni, R = 4-FC₆H₄) (1), (M = Zn, R = 4-FC₆H₄, 4-ClC₆H₄, 4-BrC₆H₄, 4-IC₆H₄), (2), (3), (4) and (5), respectively, were obtained by the reaction of the appropriate potassium N-R-sulfonyldithiocarbimate (RSO₂NCS₂K₂) with nickel(II) chloride hexahydrate or zinc(II) acetate dihydrate in metanol:water 1:1. The elemental analyses and the IR data are consistent with the formation of the expected bis(dithiocarbimato)metal(II) complexes. The ¹H and ¹³C NMR spectra showed the signals for the tetrabutylammonium cation and the dithiocarbimate moieties. The compounds 1, 2 and 5 were also characterized by X-ray diffraction techniques. The nickel(II) is coordinated by two N-4-fluorophenylsulphonyldithiocarbimato(2-) ligands forming a planar coordination. The zinc(II) exhibits distorted tetrahedral configuration in compounds 2 and 5 due to the chelation effect of two sulfur atoms of the N-R-sulfonyldithiocarbimate ligands. The antifungal activities of the compounds were tested in vitro against Colletotrichum gloeosporioides, an important fungus that causes the plant disease known as anthracnose in fruit trees. All the complexes were active.     

Synthesis and characterisation of palladium(II) and platinum(II) compounds containing pyrazole-derived ligands: crystal structure of [PdCl2(HL)] (HL = 3-phenyl-5-(2-pyridyl)pyrazole)

Reaction of the ligands 3-phenyl-5-(2-pyridyl)pyrazole (HL¹), 3,5-bis(2-pyridyl)pyrazole (HL²), 3-methyl-5-(2-pyridyl)pyrazole (HL³) and 3-methyl-5-phenylpyrazole (HL⁴) with [MCl₂(CH₃CN)₂] (M = Pd(II), Pt(II)) or [PdCl₂(cod)] gives complexes with stoichiometry [PdCl₂(HL)₂] (HL = HL¹, HL², HL³), [Pt(L)₂] (L = L¹, L², L³) and [MCl₂(HL⁴)₂] (M = Pd(II), Pt(II)). The new complexes were characterised by elemental analyses, conductivity measurements, infrared and ¹H NMR spectroscopies. The crystal and molecular structure of [PdCl₂(HL¹)] was resolved by X-ray diffraction, and consists of monomeric cis-[PdCl₂(HL¹)] molecules. The palladium centre has a typical square planar geometry, with a slight tetrahedral distortion. The tetra-coordinated metal atom is bonded to one pyridine nitrogen, one pyrazolic nitrogen and two chloro ligands in a cis disposition. The ligand HL¹ is not completely planar.     

Synthesis, structures and luminescent properties of new heterobimetallic Zn-4f Schiff base complexes

A series of new 3d-4f heterobimetallic Schiff base complexes of the general formula [Zn(μ-L²)Ln(NO₃)₃(H₂O)_n] (Ln = La 1, Nd 2, Gd 3, Er 4 and Yb 5; n = 1 or 2; H₂L² = N,N′-bis(3-methoxy-5-p-tolylsalicylidene)ethylene-1,2-diamine) are synthesized and characterized. Complexes 1, 2, 4 and 5 are structurally characterized by X-ray crystallography. The photophysical properties of these complexes are also investigated. At room temperature, complexes 1-5 exhibit similar solution absorption and emission spectra in the UV-Vis region. Furthermore, compounds 2, 4 and 5 exhibit solution emission corresponding to the lanthanide(III) ion in the near-infrared region at room temperature. The triplet state emission of the 3d-4f bimetallic complexes without energy transfer is also determined through the photophysical study of complex 3.     

Rigid-rod structured palladium complexes

Mononuclear and homobimetallic palladium complexes of structural type [trans-(Me(O)CS-4-C₆H₄)(Ph₃P)₂Pd(N^∩N)]OTf (8a, N^∩NC₄H₄N₂; 8b, N^∩NC₅H₄N-4-CN) and {[trans-(Me(O)CS-4-C₆H₄)(Ph₃P)₂Pd]₂N^∩N}(OTf)₂ (9a, N^∩N = 4,4′-bipyridine (=bipy); 9b, N^∩N = C₆H₄-1,4-(CN)₂; 9c, N^∩N = (C₆H₄-4-CN)₂) are accessible by the reaction of trans-(Ph₃P)₂Pd(C₆H₄-4-SC(O)Me)(OTf) (6) with 1 or 0.5 equivalents of the Lewis-bases N^∩N (7a, N^∩N = C₄H₄N₂; 7b, N^∩N = C₅H₄N-4-CN; 7c, N^∩N = bipy; 7d, N^∩N = C₆H₄-1,4-(CN)₂; 7e, N^∩N = (C₆H₄-4-CN)₂) in high yield. Complex 6 can be prepared in a two-step synthesis procedure. Oxidative addition of I-1-C₆H₄-4-SC(O)Me (2) to Pd(PPh₃)₄ (3) gives trans-(Ph₃P)₂Pd(C₆H₄-4-SC(O)Me)(I) (4), which further reacts with [AgOTf] (5) to afford 6.The formation of 8 and 9 strongly depends on the size of the Lewis-bases N^∩N. It is obvious that the co-ordination of the second N-ligated site of 8a or 8b to a further bulky[(PPh₃)₂Pd(C₆H₄-4-SC(O)Me)]⁺ unit is not possible. In contrast, more extended N^∩N species such as 7c-7e will result in the formation of linear structured homobimetallic 9a-9c.The solid-state structures of 4 and 4 · CH₂Cl₂ are reported. Complex 4 is packed in the orthorhombic space group Pbca. The assembly of dichloromethane into the crystal lattice breaks the symmetry, whereby 4 · CH₂Cl₂ crystallises in the triclinic space group . In both modifications a square-planar palladium(II) ion is present, with the iodo atom and the Me(O)CS-C₆H₄ unit trans-positioned. The different crystal packing has no significant influence onto the geometry around the d⁸-configurated palladium atoms.     

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.     

Cu(II) complexes with square pyramidal (N2S)CuCl2 chromophore: Jahn-Teller distortion and subsequent effect on spectral and structural properties

One monomeric neutral Cu(II) complex [(pmtpm)CuCl₂] (1) is reported by Lindoy and Livingstone [8]. Two new complexes namely, μ-Cl bridged binuclear Cu(II) complex [{(pmtpm)Cu(Cl)}₂ μ-Cl](ClO₄) (2) and a bis μ-Cl bridged binuclear Cu(II) complex [{(pmtpm)Cu}₂(μ-Cl)₂](ClO₄)₂ (3) derived from a tridentate Schiff base ligand, 2-pyridyl-N-(2′-methylthiophenyl)methyleneimine (pmtpm) were synthesized and characterized by various spectroscopic methods and by X-ray crystallography. (N₂S)CuCl₂ chromophore(s) of distorted square pyramidal coordination geometries around Cu(II) ion(s) have been observed for all the complexes 1-3. The equatorial sites of the square plane comprise two N and a thioether S donor atoms of the pmtpm ligand as well as one Cl⁻ ion (terminal in 1 and 2, and bridging in 3) while the remaining axial site is occupied by a terminal Cl⁻ ion (for 1) or a bridging Cl⁻ ion (for 2 and 3). The equatorial Cu-Cl distances are much shorter [1: 2.2511(4) Å, 2: 2.2307(12) Å, 3: 2.2513(12) Å] than the axial Cu-Cl distances [1: 2.4394(4) Å, 2: 2.5597(9) Å, 3: 2.7037(12) Å]. The correlation of an axial Cu-Cl bond elongation with a lower g_|| value in the solid state EPR spectrum and a blue shifted ligand field transition in the solid and solution phase absorption spectrum has been observed.     

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.     

Diffusion NMR studies on neutral and cationic square planar palladium(II) complexes

Diffusion NMR investigations were carried out in CD₂Cl₂ for a series of neutral (1-7) and cationic (8-10) square planar palladium complexes. Diffusion data were elaborated through a modified Stokes-Einstein equation that takes into account the size and shape of molecules. The hydrodynamic volume at infinite dilution of all complexes was found to be similar to the crystallographic volume and always much larger than the van der Waals volume. The self-aggregation tendency of [Pd(N,C⁻)(N,N)][PF₆] ionic complexes [(N,C⁻) = (C₆H₄-(Ph)C(O)-CN-Et); 8, (N,N) = 2,2′-bipirydine; 9, (N,N) = (2,6-(iPr)₂-C₆H₃)NC(Me)-C(Me)N(2,6-(iPr)₂-C₆H₃); 10, (N,N) = (2,6-(iPr)₂-C₆H₃)NC(R′)-C(R′)N(2,6-(iPr)₂-C₆H₃), R′₂ = naphthalene-1,8-diyl] was investigated by performing ¹H and ¹⁹F diffusion experiments as a function of the concentration. Clear evidence for the formation of ion triples containing two cationic units was obtained for 8, most likely due to the establishment of a weak Pd?O interaction. The tendency to form ion triples was much reduced in 9 and 10, having an increased steric hindrance in the apical positions. While 9 showed the usual tendency to afford a mixture of free ions and ion pairs, solvated ions were the predominant species in the case of 10 even at high concentration values (approaching 100 mM).     

Structures, magnetic properties, and XPS of one-dimensional cyanide-bridged Cu-Ni/Pt bimetallic assembly complexes

Synthesis, crystal structures, and spectroscopic and magnetic properties of new one-dimensional cyano-bridged bimetallic complexes, [Cu^II(N-Eten)₂][M^II(CN)₄] (N-Eten = N-ethylethylenediamine; M^II = Ni^II (1) and Pt^II (2)), have been reported. Both complexes consist of one-dimensional alternate chains of Cu^II and M^II moieties. The Pt-C bond distances of 1.997(3) and 2.001(3) Å for 2 are considerably longer than the Ni-C bond lengths of 1.866(3) and 1.872(3) Å for 1. Because of pseudo Jahn-Teller distortion, the axial Cu-N bond distances of 2.554(2) and 2.550(3) Å for 1 and 2 are longer than those of equatorial ones of 2.008(2) and 2.056(2) Å for 1 and 2.010(2) and 2.054(2) Å for 2. In contrast to M^II-C bond distances, the Cu-N ones of 1 are similar to those of 2 regardless of element-substitution. These complexes indicate weak antiferromagnetic interactions with Weiss constants = − 4.68 and −3.95 K for 1 and 2, respectively. The emission spectrum of 2 (λ_ex = 360 nm) exhibits a broad band with peaks at 22 800 and 24 000 cm⁻¹ at 298 K. The Cu 2p_1/2 and 2p_3/2 peaks of XPS spectra are compared systematically to various copper(II) complexes showing different bridging features or distorted coordination geometries as models for excited structures induced by external physical conditions. The spectroscopic properties are discussed from the viewpoint of magneto-optical properties.     

Hybrid scorpionate/cyclopentadienyl titanium and zirconium complexes with alkoxide and imido ligands

The reactivity of hybrid scorpionate/cyclopentadienyl ligand-containing trichloride zirconium complexes [ZrCl₃(bpzcp)] (1) [bpzcp = 2,2-bis(3,5-dimethylpyrazol-1-yl)-1,1-diphenylethylcyclopentadienyl] and [ZrCl₃(bpztcp)] (2) [bpztcp = 2,2-bis(3,5-dimethylpyrazol-1-yl)-1-tert-butylethylcyclopentadienyl] toward several lithium alkoxides has been carried out. Thus, alkoxide-containing complexes [ZrCl₂(OR)(bpzcp)] (R = Me, 3; Et, 4; ⁱPr, 5; (R)-2-Bu, 6), [ZrCl₂(OR)(bpztcp)] (R = Me, 7; Et, 8; ⁱPr, 9; (R)-2-Bu, 10) and [Zr(OR)₃(bpztcp)] (R = Et, 11; ⁱPr, 12) were prepared by deprotonation of the appropriate alcohol group with BuⁿLi followed by reaction with 1 or 2. In addition, the imido-complex [Ti(N^tBu)Cl(bpztcp)(py)] (13) were also prepared. The structures of these complexes have been proposed on basis of spectroscopic and DFT methods.     

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.     

Nickel(II) complexes of terdentate or symmetrical tetradentate Schiff bases: Evidence of the influence of the counter anions in the hydrolysis of the imine bond in Schiff base complexes

Two sets of ligands, set-1 and set-2, have been prepared by mixing 1,3-diaminopentane and carbonyl compounds (2-acetylpyridine or pyridine-2-carboxaldehyde) in 1:1 and 1:2 ratios, respectively, and employed for the synthesis of complexes with Ni(II) perchlorate, Ni(II) thiocyanate and Ni(II) chloride. Ni(II) perchlorate yields the complexes having general formula [NiL₂](ClO₄)₂(L = L¹ [N³-(1-pyridin-2-yl-ethylidene)-pentane-1,3-diamine] for complex 1 or L²[N³-pyridin-2-ylmethylene-pentane-1,3-diamine] for complex 2) in which the Schiff bases are monocondensed terdentate, whereas Ni(II) thiocyanate results in the formation of tetradentate Schiff base complexes, [NiL(SCN)₂] (L = L³[N,N′-bis-(1-pyridin-2-yl-ethylidine)-pentane-1,3-diamine] for complex 3 or L⁴ [N,N′-bis(pyridin-2-ylmethyline)-pentane-1,3-diamine] for complex 4) irrespective of the sets of ligands used. Complexes 5 {[NiL³(N₃)₂]} and 6 {[NiL⁴(N₃)₂]} are prepared by adding sodium azide to the methanol solution of complexes 1 and 2. Addition of Ni(II) chloride to the set-1 or set-2 ligands produces [Ni(pn)₂]Cl₂, 7, as the major product, where pn = 1,3-diaminopentane. Formation of the complexes has been explained by the activation of the imine bond by the counter anion and thereby favouring the hydrolysis of the Schiff base. All the complexes have been characterized by elemental analyses and spectral data. Single crystal X-ray diffraction studies confirm the structures of three representative members, 1, 4 and 7; all of them have distorted octahedral geometry around Ni(II). The bis-complex of terdentate ligands, 1, is the mer isomer, and complexes 4 and 7 possess trans geometry.     

Cyanato bridged binuclear nickel(II) and copper(II) complexes with pyridylpyrazole ligand: Synthesis, structure and magnetic properties

Binuclear cyanate bridged nickel(II) complex [Ni(L)(NCO)]₂(PF₆)₂ (1) and copper(II) complex [Cu(L)(NCO)]₂(PF₆)₂ (2), where L is N,N-bis(3,5-dimethylpyrazol-1-ylmethyl)aminomethylpyridine, a tetradentate N₄-coordinated ligand have been synthesized and characterized by physicochemical method. The structures of complexes 1 and 2 have been studied by single crystal X-ray diffraction analysis. The structure analysis reveals that both nickel(II) and copper(II) center are coordinated in distorted octahedral fashion and coordination mode of cyanate ligand is end-to-end (μ-1,3) for complex 1 but it is double end-on (μ-1,1) mode for complex 2. The variable temperature magnetic susceptibility data, measured from 2 to 300 K, show weak antiferromagnetic interaction with J value −6.2(1) cm⁻¹ for complex 1, whereas complex 2 has very weak ferromagnetic interaction with J value +0.5(1) cm⁻¹.     

Insights into electronic and structural properties of novel Pd(II) salen-type complexes

Novel palladium(II) complexes with salen-type ligands based on 3-methylsalicyladehyde and a set of aliphatic diamines (C1 to C4) have been synthesised and characterized by spectroscopic techniques (UV-Vis and FTIR), Density Functional Theory (DFT) calculations and single-crystal X-ray diffraction for C1 and C4. X-ray diffraction analysis of these complexes was focused on coordination sphere and supramolecular arrangements. In the two compounds, the molecules form dimers, being the most relevant intermolecular interactions the hydrogen bonds of the type C-H?O, C-H?π and π?π stacking interactions between the six-membered metallocycles.Electronic spectra of all Pd(II) complexes are dominated by charge transfer and intraligand bands at λ < 400 nm. DFT calculations showed that the HOMO is ligand-dominated, with the metal contribution being ∼18% for all complexes. This suggests that the structural/electronic differences between the ligands do not influence significantly the participation of metal orbitals in HOMO. All the complexes exhibit dipole moments with the same direction, from the aldehyde moiety towards the imine bridge with C2 and C3 showing quite similar values, μ_C2 = 5.49 and μ_C3 = 5.54 D, whereas complexes C1 and C4 show slightly higher values: μ_C1 = 5.79 and μ_C4 = 6.17 D. The magnitude of bond lengths and angles predicted by DFT calculations are comparable to those determined by X-ray crystallography.The experimental vibrational frequencies of the Pd(II) complexes were correlated with the values estimated by DFT calculations. The good agreement between the experimental and theoretical vibrational data allowed the assignment of relevant IR bands to molecular vibration modes.