Synthesis and electrochemical aspects of group 14 iron complexes of the type (η-C5H5)Fe(L)2ER3, L2 = (CO)2, (Ph2P)2CH2; E = C, Si, Ge, Sn

The dicarbonyl and diphosphine complexes of the type (η⁵-C₅H₅)Fe(L)₂ER₃ (L₂ = (CO)₂ (a), (Ph₂P)₂CH₂ (b); ER₃ = CH₃ (1a/b); SiMe₃ (2a/b), GeMe₃ (3a/b), SnMe₃ (4a/b)) were synthesized and studied electrochemically. Cyclic voltammetric studies on the dicarbonyl complexes 1a-4a revealed one electron irreversible oxidation processes whereas the same processes for the chelating phosphine series 1b-4b were reversible. The E_ox values found for the series 1a-4a were in the narrow range 1.3-1.5 V and in the order Si > Sn ≈ Ge > C; those for 1b-4b (involving replacement of the excellent retrodative π-accepting CO ligands by the superior σ-donor and poorer π-accepting phosphines) have much lower oxidation potentials in the sequence Sn > Si ≈ Ge > C. This latter oxidation potential pattern relates directly to the solution ³¹P NMR chemical shift data illustrating that stronger donation lowers the E_ox for the complexes; however, simple understanding of the trend must await the results of a current DFT analysis of the systems.     

Synthesis and characterization of isopropylamine complexes of lanthanide(II) diiodides: Molecular structure of TmI2(PrNH2)4 and EuI2(PrNH2)4

It was found that the lanthanide diiodides LnI₂ (1) (Ln = Nd, Sm, Eu, Dy, Tm, Yb) are dissolved in isopropylamine (IPA) without redox transformations. Stability of the formed solutions decreases in a row Eu ≈ Yb > Sm > Tm > Dy > Nd. Removing of a solvent in vacuum leaves complexes LnI₂(IPA)_x (2) (Nd, x = 5; Sm, Eu, Dy, Tm, Yb, x = 4) as crystalline colored solids. Stability of 2-Nd,Dy,Tm is higher than that of known THF or DME coordinated salts. Divalent state of metal in the products is confirmed by data of UV-Vis spectroscopy, magnetic measurements and their chemical behavior. Structure of 2-Eu and 2-Tm was established by X-ray diffraction analysis. Oxidation of 2-Nd,Dy in IPA affords amine-amides (PrⁱNH)Ln(IPA)_y (3) (Nd, y = 4; Dy, x = 3). n-Propylamine also dissolves the iodides 1-Sm,Eu,Dy,Tm,Yb but stability of the solutions is significantly lower. 1-Nd vigorously reacts with PrⁿNH₂ even at −30 °C which hampers the formation of the solution.     

Synthesis and characterization of the ligand based on benzoxazole and its transition metal complexes: DNA-binding and antitumor activity

A new ligand 2-((2-((benzo[d]oxazol-2-yl)methoxy)phenoxy)methyl)benzoxazole (L) and its four transition metal complexes M(NO₃)₂L (M = Cu, Co, Ni, Zn), have been synthesized and investigated. The single crystal structures of the complexes show that all of them have similar molecular structure and the ligand exhibits good coplanarity after coordination with the metal ions. Further investigation of DNA binding indicates that both the ligand L and the complexes can bond to DNA by intercalation mode, and the latter possesses much stronger binding affinity. Antitumor activity of these compounds tested on the four cancer cell lines, follows the order: Cu-L > Ni-L ≈ Co-L > Zn-L ? L, which are thought to be related with their DNA-binding affinity.     

A series of mononuclear Co(III) complexes using tridentate N,O-donor ligands: chemical properties and cytotoxicity activity

Continuing our interest in tridentate ligands to develop new prototypes of cobalt-based metallodrugs for combating cancer, modifications in the backbone of HL1, [(2-hydroxybenzyl)(2-(pyridil-2-yl)ethyl]amine) were proposed in order to modulate the redox potential of new Co(III) complexes. Three ligands with electron withdrawing groups were synthesized: HL2: [(2-hydroxy-5-nitrobenzyl)(2-(pyridil-2-yl)ethyl]amine); HL3: [(2-hydroxybenzyl)(2-(pyridil-2-yl)ethyl]imine) and HL4: [(2-hydroxy-5-nitrobenzyl)(2-(pyridil-2-yl)ethyl]imine). They were used to obtain the respective mononuclear complexes 2, 3 and 4, which are discussed compared to the previous reported complex 1 (obtained from HL1). The new complexes were characterized and studied by several techniques including X-ray crystallography, elemental and conductimetric analysis, IR, UV-vis and ¹H NMR spectroscopies, and electrochemistry. The substitutions of the group in the para position of the phenol (HL1 and HL2) and the imine instead of the amine (HL3 and HL4), promote anodic shifts in the complexes reduction potentials. The influence of these substitutions in the biological activities of the Co(III) complexes against the murine melanoma cell line (B16F10) was also evaluated. Little effect was observed on cellular viability decrease for all free ligands, however the coordination to Co(III) enhances their activities in the following range: 1 > 4 ≈ 2 > 3. The data suggest that no straight correlation can be addressed between the reduction potential of the Co(III) center and the cell viability.     

A novel tetrabranched neurotensin(8-13) cyclam derivative: synthesis, 64Cu-labeling and biological evaluation

New macrocyclic 1,4,8,11-tetraazacyclotetradecane (cyclam) derivatives with 1, 2 and 4 neurotensin(8-13) units 4, 5 and 7 have been synthesized. Compounds 4 and 5 were prepared by the reaction of non-stabilized neurotensin(8-13) and cyclamtetrapropionic acid 2 using 1-ethyl-3-(3-dimethylaminocarbonyl)carbodiimide-hydrochloride and N-hydroxysulfosuccinimide. The tetrameric compound 7 was synthesized by Michael addition of neurotensin(8-13) acrylamide 6 and cyclam 1. The copper(II) complexation behavior of 4, 5 and 7 was investigated by UV/visible spectrophotometry and shows that the metal center resides inside the N4 chromophore with additional apical interactions established with pendant arms. The novel tetrabranched NT(8-13) cyclam 7 with nanomolar neurotensin receptor 1 binding affinity was efficiently radiolabeled with ⁶⁴Cu under mild conditions. ⁶⁴Cu ⊂ 7 showed slow transchelation in the presence of a large amount of cyclam as competing ligand, while it completely remains intact in the presence of EDTA. The in vivo behavior of ⁶⁴Cu ⊂ 7 was studied in rats and mice. The metabolic stability in rodent models was high with a half-life of intact ⁶⁴Cu ⊂ 7 in plasma of 34 min in rats and 60 min in the mice, respectively. The binding affinity was high enough to demonstrate in vivo binding of ⁶⁴Cu ⊂ 7 to NTR1 overexpressing HT-29 tumor xenotransplants in nude mice. Regarding elimination, ⁶⁴Cu ⊂ 7 showed a substantial renal and reticuloendothelial accumulation. On the other hand, metabolization of the compound in vivo with a resulting metabolite—postulated to be the ⁶⁴Cu-cyclam-tetraarginine complex—also showed long retention in the circulating blood, preventing a better contrast of tumor imaging.     

Syntheses, crystal structures, and luminescence properties of lanthanide complexes with 5-carboxy-1-carboxymethyl-2-oxidopyridinium

Five new lanthanide complexes Ln(HL)₃(H₂O)₅ · 3H₂O (H₂L = 5-carboxy-1-carboxymethyl-2-oxidopyridinium, Ln = La (1), Sm (2), Eu (3),Tb (4), Dy (5)) have been synthesized and characterized by elemental analyses, FT-IR spectra and X-ray single crystal diffraction. All crystals are isostructural and crystallize in the triclinic space group . The metal center is nine-coordinated completely by two phenol O atoms, two chelating carboxylic O atoms from three HL ligands and five water molecules with a distorted tri-capped trigonal prismatic geometry. Photoluminescence studies revealed that complexes 2-4 exhibit strong fluorescent emission bands in the solid state at room temperature. The transition intensity varies in the order of Tb³⁺ > Dy³⁺ > Eu³⁺ > Sm³⁺.     

A preparative study of some coronands and their complexation of silver(I), zinc(II), cadmium(II) and lead(II)

A study of the complexation of heavy metal ions by the coronands 3,12,20,29-tetraoxa-35,36-diazapentacyclo[29.3.1.1.^14,18.0^5,10.0^22,27]-hexatriaconta-1(35),5(10),6,8,14,16,18(36),22(27),23,25,31,33-dodecaene (1); 2,3,11,12-bis (4^′-methylbenzo)-1,4,10,13-tetrathia-7,16-dioxacyclo-octadeca-2,11-diene (2); 7,16-diaza-1,4,10,13-tetraoxa-2,3,11,12-dibenzocyclooctadeca-2,11-diene (3); 2-[19-(2-hydroxy-2-phenylethyl)-7,8,9,10, 18,19,20,21-octahydro-6H,17H-dibenzo[b,k][1,4,10,13,7,16]tetraoxadiazacyclooctadecin-8-yl]-1-phenyl-1-ethanol (4); 1,4,10,13-tetraoxa-7,16-diazacyclo-octadecane (5); and 2-[16-(2-hydroxy-2-phenylethyl)-1,4,10,13-tetraoxa-7,16-diazacyclo-octadecanyl]-1-phenyl-1-ethanol (6) is described. Coronands 1 and 3 were prepared by literature methods, improved methods were used to prepare 2, and 4 and 6 were prepared from 3 and 5 (obtained commercially), respectively. Potentiometric studies in N,N-dimethylformamide yielded (logK/dm³ mol⁻¹)=5.50, 6.49, 9.42 and 7.52 for [Ag · 1]⁺, [Ag · 2]⁺, [Ag · 5]⁺ and [Ag · 6]⁺, respectively; <2, <2, 4.30 and <2 for [Zn · 1]²⁺, [Zn · 2]²⁺, [Zn · 5]²⁺ and [Zn · 6]²⁺, respectively, <2, <2, 5.92 and >7.52 for [Cd · 1]²⁺, [Cd · 2]²⁺, [Cd · 5]²⁺, and [Cd · 6]²⁺, respectively, and 2.62, 2.38, 6.71 and >7.52 for [Pb · 1]²⁺, [Pb · 2]²⁺, [Pb · 5]²⁺, and [Pb · 6]²⁺, respectively. ESI-MS studies of the interactions of 1-6 with Ag⁺, Zn²⁺, Cd²⁺ and Pb²⁺ are also reported.     

Solution and solid state study of copper(II) ternary complexes containing amino acids of interest for brain biochemistry - 1: Aspartic or glutamic acids with methionine or cysteine

Four new ternary complexes of Cu(II) containing aspartic or glutamic acids and methionine or cysteine as ligands were studied both in solution and in solid state. The solution study was performed using potentiometry, UV-Vis spectroscopy, electron paramagnetic resonance (EPR) spectroscopy, and electrochemistry. The stability constants of the ternary complexes were determined by potentiometry. The order of the values for the stability constants was CuGluMet (complex 4) < CuAspMet (complex 2) < CuGluCys (complex 3) < CuAspCys (complex 1), with complex 1 ≈ complex 3 ? complex 2 ≈ complex 4. This behavior was confirmed by the electronic spectra, EPR parameters and cyclic voltammetry. The compounds were synthesized in the solid state and characterized by thermogravimetry as well as vibrational and EPR spectroscopy. The results found in solid state are in agreement with the data found in solution studies where methionine, aspartic and glutamic acids coordinate to the copper(II) ion using the nitrogen atom of the amino group and one oxygen atom of the carboxylate group and cysteine coordinates through the nitrogen and sulfur atoms. The EPR data suggest that the complexes are square planar and that the complexes with cysteine as one of the ligands have some distortion.     

Syntheses, structures, and magnetic properties of 3d-4f heterometallic complexes constructed from pyrazole-bridged CuLn dinuclear units

A series of pyrazole-bridged heterometallic 3d-4f complexes, [CuDy(ipdc)₂(H₂O)₄] · (2H₂O)(H₃O⁺) (1) and [CuLn(pdc)(ipdc)(H₂O)₄] · H₃O⁺ (Ln = Ho (2), Er (3), Yb (4); H₃ipdc = 4-iodo-3,5-pyrazoledicarboxylic acid; H₃pdc = 3,5-pyrazoledicarboxylic acid), {[Cu₃Ln₄(ipdc)₆(H₂O)₁₆] · xH₂O}_n (Ln = Sm (5), x = 8.5; Ln = Eu (6), x = 7; Ln = Gd (7), Tb (8), x = 9), have been synthesized and structurally characterized. Ligand H₃ipdc was in situ obtained by iodination of ligand H₃pdc. Complexes 1-4 are pyrazole-bridged heterometallic dinuclear complexes, and 2-4 are isostructural. Complexes 5-8 are isostructural and comprised of an unusual infinite one-dimensional tape-like chain based on pyrazole-bridged heterometallic dinuclear units. The magnetic properties of compounds 1-4, 7 and 8 have been investigated through the magnetic measurement over the temperature range of 1.8-300 K.     

Palladium(II), platinum(II), ruthenium(II) and mercury(II) complexes of potentially tridentate Schiff base ligands of (E, N, O) type (E = S, Se, Te): Synthesis, crystal structures and applications in Heck and Suzuki coupling reactions

Schiff bases of 2-hydroxybenzophenone (HBP) (C₆H₅)(2-HOC₆H₄)CN(CH₂)_nEAr (L1/L2: E = S, Ar = Ph, n = 2/3; L3/L4: E = Se, Ar = Ph, n = 2/3; L5/L6: E = Te, Ar = 4-MeOC₆H₄, n = 2/3) and their complexes [PdCl(L-H)] (L = L1−L6; 1, 2, 3, 5, 7, 11), [PtCl(L3-H/L5-H)] (4/8), [PtCl₂(L4/L6)₂] (6/12), [(p-cymene)RuCl(L5/L6)]Cl (9/13) and [HgBr₂(L5/L6)₂] (10/14) have been synthesized and characterized by proton, carbon-13, selenium-77 and tellurium-125 NMR, IR and mass spectra. Single crystal structures of L1, 1, 3, 4, 5 and 7 were solved. The Pd-E bond distances (Å): 2.2563(6) (E = S), 2.3575(6)−2.392(2) (E = Se); 2.5117(5)−2.5198(5) (E = Te) are near the lower end of the bond length range known for them. The Pt-Se bond length, 2.3470(8) Å, is also closer to the short values reported so far. The Heck and Suzuki reaction were carried out using complexes 1, 3, 5 and 7 as catalysts under aerobic condition. The percentage yields for trans product in Heck reaction were found upto 85%.     

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.     

Substituted imidazole derivatives as novel cardiovascular agents

A series of novel substituted imidazole derivatives were synthesized and have been screened in vivo for their hypotensive and acute toxicity activities. Out of seventeen compounds eight compounds (2b, 2c, 3b, 3c, 3f, 4a, 4b and 4c) have shown good hypotensive and bradycardiac responses. Compounds 3b, 3c, 3f and 4c have shown better activity than reference drug clonidine. All the compounds have shown ALD50 >1000 mg/kg with maximum in 2e and 4c (>1200 mg/kg).     

Synthesis, structure, and catalytic ethylene oligomerization of nickel(II) and cobalt(II) complexes with symmetrical and unsymmetrical 2,9-diaryl-1,10-phenanthroline ligands

A series of nickel(II) and cobalt(II) complexes, NiX₂L (X = Cl, Br; 1-6) and CoCl₂L (7-9), with 2,9-diaryl-1,10-phenanthroline ligands (L¹-L³) have been synthesized and characterized by elemental analysis, UV-Vis, IR spectroscopy, and X-ray crystal structural study (for 1, 4-7, 9). The solid-state structures of 1, 5-7 and 9 show four-coordinate, slightly flattened tetrahedral geometry at the Ni(II) or Co(II) center, while 4 is five-coordinated (square-pyramidal), containing a THF molecule as an auxiliary ligand. The title complexes (1-9) display good catalytic activities in ethylene oligomerization when activated with methylaluminoxane (MAO). While the Co(II) precatalysts produce primarily C₄ isomers, the Ni(II) complexes give ethylene dimers and trimers at normal pressure. The activities and yields of linear α-olefins increase with increasing ethylene pressure for the Ni(II) complexes, leading to more high-molar-mass products (C₈-C₁₈). Complex 6 displays the best catalytic activity among the complexes studied (up to 1518 kg/mol[Ni] h at 10 atm).     

Synthesis, structures and DNA binding of ternary transition metal complexes M(II)L with the 2,2-bipyridylamine (L = p-HB, M = Co, Ni, Cu and Zn)

New ternary transition metal complexes of formulations [Co(bpa)(p-HB)₂](bpa = 2,2′-bipyridylamine, p-HB = p-hydroxybenzenecarboxylic acid) (1), [Ni(bpa)(p-HB)(H₂O)₂]⁺(NO₃)⁻ · H₂O (2), , [Cu(bpa)(p-HB)Cl] (4) and [Zn(bpa)(p-HB)₂]₂ · 0.5H₂O (5) are prepared, their structural features are characterized by crystal structural studies, and their DNA binding propensity has been evaluated by fluorescence method. The molecular structure of complex 1 shows the six coordinate octahedral geometry with one bpa and two p-HB ligands, complex 2 is the cationic complex and has the six coordinate octahedral structure with one bpa, one p-HB and two aqua ligands, complex 3 is also the cationic complex of octahedral coordination with two bpa and one p-HB ligands, complex 4 is five coordinate distorted square pyramidal with one bpa, one p-HB and chloride ligands and complex 5 has the distorted octahedral coordination with two p-HB and one bpa ligands. In all of the complexes, both bpa and p-HB act as the bidentate N and O-donor ligands, respectively. The intermolecular H-bond networks, together with π-π interaction in their solid state are also described. The complexes show the competitive inhibition of ethidium binding to DNA, and the DNA binding propensity can be reflected as the relative order: 3 > 2 > 1 > 5 > 4, in which the cationic charged Ni(II) complexes 2 and 3 show the most effective inhibition ability.     

Synthesis, characterization and olefin metathesis studies of a family of ruthenium phosphonium alkylidene complexes

The synthesis of four ruthenium phosphonium alkylidene complexes [(H₂IMes)Cl₂RuCH(PCy₃)]⁺[A]⁻ (1, A = B(C₆F₅)₄; 2, A = BF₄; 3, A = OTf; 4, A = BPh₄), differing only in the anion is described. The X-ray structures of 1, 3 and 4 show them to be isostructural in the cation, with no interaction between the Ru centers and the anion. Ring closing metathesis of a substrate to a six-membered methylcyclohexene at 0 °C in CD₂Cl₂ using 1 mol% catalyst, shows that catalysts 1-4 behave very similarly, and exhibit superior activity in comparison to Grubbs second generation and fast-initiating catalysts.     

Organotin(IV) 4-methoxyphenylethanoates: Synthesis, spectroscopic characterization, X-ray structures and in vitro anticancer activity against human prostate cell lines (PC-3)

A series of organotin(IV) carboxylates, [Bu₂SnL₂] (1), [Et₂SnL₂] (2), [Me₂SnL₂] (3), [Bu₃SnL]_n(4), [Me₆Sn₂L₂]_n(5), [Ph₃SnL]_n(6) and [Oct₂SnL₂] (7), where L = O₂CCH₂C₆H₄OCH₃-4, have been synthesized. These complexes have been characterized by elemental analysis, FT-IR and multinuclear NMR (¹H, ¹³C and ¹¹⁹Sn). Based on spectroscopic results, the ligand appeared to coordinate to the Sn atom through COO moiety. Single crystal analysis has shown a bridging behavior of ligand in tributyl- and trimethyltin(IV) derivatives, and a chelating bidentate mode in diethyltin(IV) complex. Bioassay results have shown that these compounds have good antibacterial, antifungal and antitumor activity. The activity against prostate cancer cell lines (PC-3) decreased in the order 1 > 5 > 2 > 3 > 7.     

The influence of substituents (R) at N atom of thiophene-2-carbaldehyde thiosemicarbazones {(C4H3S)HCN-N(H)-C(S)NHR} on bonding, nuclearity and H-bonded networks of copper(I) complexes

The nuclearity, bonding and H-bonded networks of copper(I) halide complexes with thiophene-2-carbaldehyde thiosemicarbazones {(C₄H₃S)HC²N³-N(H)-C¹(S)N¹HR} are influenced by R substituents at N¹ atom. Thiophene-2-carbaldehyde-N¹-methyl thiosemicarbazone (HttscMe) or thiophene-2-carbaldehyde-N¹-ethyl thiosemicarbazone (HttscEt) have yielded halogen-bridged dinuclear complexes, [Cu₂(μ-X)₂(η¹-S-Htsc)₂(Ph₃P)₂] (Htsc, X: HttscMe, I, 1; Br, 2; Cl, 3; HttscEt, I, 4; Br, 5; Cl, 6), while thiophene-2-carbaldehyde-N¹-phenyl thiosemicarbazone (HttscPh) has yielded mononuclear complexes, [CuX(η¹-S-HttscPh)₂] (X, I, 7a; Br 8; Cl, 9) and a sulfur bridged dinuclear complex, [Cu₂(μ-S-HttscPh)₂(η¹-S-HttscPh)₂I₂] 7b co-existing with 7a in the same unit cell. These results are in contrast to S-bridged dimers [Cu₂(μ-S-Httsc)₂(η¹-Br)₂(Ph₃P)₂] · 2H₂O and [Cu₂(μ-S-Httsc)₂(η¹-Cl)₂(Ph₃P)₂] · 2CH₃CN obtained for R = H and X = Cl, Br (Httsc = thiophene-2-carbaldehyde thiosemicarbazone) as reported earlier. The intermolecular CH_Ph?π interaction in 1-3 (2.797 Å, 1; 3.264 Å, 2; 3.257 Å, 3) have formed linear polymers, whereas the CH_Ph?X and N³?HCH interactions in 4-6 (2.791, 2.69 Å, 5; 2.776, 2.745 Å, 6, respectively) have led to the formation of H-bonded 2D polymer. The PhN¹H?π, interactions (2.547 Å, 8, 2.599 Å, 9) have formed H-bonded dimers only. The Cu?Cu separations are 3.221-3.404 Å (1-6).     

Coordination chemistry of heterocycle-functionalized diazamesocycles: tuning the productive Ni complexes through altering the pendants of ligands

In order to further understand the coordination chemistry of diazamesocyclic systems, a series of mononuclear Ni^II complexes with 1,4-diazacycloheptane (DACH) functionalized by additional imidazole or pyridine donor pendants, including [NiL¹](ClO₄)₂ · H₂O (1), [NiL¹Cl](ClO₄) (2), [NiL²Cl](ClO₄) · CH₃OH (3), [NiL²Cl][NiL²](ClO₄)₃ (4) and [NiL³](ClO₄)₂ (5), where L¹ = 1,4-bis(N-1-methylimidazol-2-yl-methyl)-1,4-diazacycloheptane, L² = 1,4-bis(pyridyl-2-yl-methyl)-1,4-diazacycloheptane, and L³ = 1,4-bis-(imidazol-4-yl-methyl)-1,4-diazacycloheptane, have been prepared and characterized. A detailed study on the solid structures and solution spectra of these complexes indicates that tetradentate ligands L¹, L² and L³ would lead to new Ni^II complexes with different coordination environments in the solid states and solution. The N-methyl substituted imidazole functionalized ligand L¹ forms green compound 2 and yellow product 1; while the pyridine functionalized ligand L² affords red product 4 and green complex 3; the ligand L³ results in only one stable mononuclear Ni^II product 5. The solution behaviors of these interesting compounds were also investigated by UV-Vis technique.     

Synthesis and single crystal structures of first examples of tridentate ligands of (Te, N, S) type and their complexes with palladium(II), platinum(II) and ruthenium(II)

The First examples of (Te, N, S) type ligands, 2-CH₃SC₆H₄CHNCH₂CH₂TeC₆H₄-4-OCH₃ (L¹) and 2- CH₃SC₆H₄CHNHCH₂CH₂TeC₆H₄-4-OCH₃ (L²), and their metal complexes, [PdCl(L¹)]PF₆ · CHCl₃ · 0.5H₂O (4), [PtCl(L¹)]PF₆ (5), [PdCl(L²)]ClO₄.CHCl₃ (6), [PtCl(L²)]ClO₄ (7), and [Ru(p-cymene)(L²)](PF₆)₂ · CHCl₃ (8), have been synthesized and characterized. The single crystal structures of 4, 6 and 8 have revealed that both the ligands coordinate in them in a tridentate (Te, N, S) mode. The geometry around Pd in both the complexes has been found to be square planar, whereas for Ru in a half sandwich complex 8, it is found to be octahedral. Between two molecules of 4 there are intra and inter molecular weak Te?Cl [3.334(3) and 3.500(3) Å, respectively] interactions along with weak intermolecular Pd?Te [3.621(2) Å] interactions. The Pd-Te bond lengths are between 2.517(6) and 2.541(25) Å and the Ru-Te bond length is 2.630(6) Å. The crystal structure of [PdCl₂(4-MeO-C₆H₄- TeCH₂CH₂NH₂)] (9) is also determined. It is formed when KPF₆ is not added in the synthesis of 4 and Pd-complex of L¹ is recrystallized. Apart from Te?Cl secondary interactions, C-H?π interactions also exist in the crystal of 9.     

Rhenium(III) and technetium(III) complexes with 2-mercapto-1,3-azole ligands and X-ray crystal structures

Reactions of labile [MCl₃(PPh₃)₂(NCMe)] (M = Tc, Re) precursors with 1H-benzoimidazole-2-thiol (H₂L¹), 5-methyl-1H-benzoimidazole-2-thiol (H₂L²) and 1H-imidazole-2-thiol (H₂L³), in the presence of PPh₃ and [AsPh₄]Cl gave a new series of trigonal bipyramidal M(III) complexes [AsPh₄]{[M(PPh₃)Cl(H₂L^1-3)₃]Cl₃} (M = Re, 1-3; M = Tc, 4-6). The molecular structures of 1 and 3 were determined by X-ray diffraction. When the reactions were carried out with benzothiazole-2-thiol (HL⁴) and benzoxazole-2-thiol (HL⁵), neutral paramagnetic monosubstituted M(III) complexes [M(PPh₃)₂Cl₂(L^4,5)] (M = Re, 8, 9; M = Tc, 10, 11) were obtained. In these compounds, the central metal ions adopt an octahedral coordination geometry as authenticated by single crystal X-ray diffraction analysis of 8 and 11. Rhenium and technetium complexes 1, 4 and rhenium chelate compounds 8, 9 have been also synthesized by reduction of [MO₄]⁻ with PPh₃ and HCl in the presence of the appropriate ligand. All the complexes were characterized by elemental analyses, FTIR and NMR spectroscopy.