Formamidinate Ligands Research Articles

Binuclear Lantern Complexes of All First-Row 3d Metals Scandium to Zinc: Metal-Metal Bond Lengths and Bond Orders, with Measures of Intrinsic Metal-Metal Bond Strength.

The B3LYP and M06-L functionals with the cc-pVTZ basis set are used to study lantern-type binuclear complexes of all the first-row (3d block) metals scandium to zinc in various low-energy spin states, out of which the ground states are predicted. These complexes are studied as models using mostly the unsubstituted formamidinate ligand. For each metal, metal-metal (MM) bond lengths are related to the formal MM bond orders (zero to five), derived by MO analysis and by electron counting. The predicted ground-state spin multiplicities and MM bond lengths of the model complexes generally agree fairly well with available experimental results on substituted analogues. Finally, values of the formal shortness ratio and Wiberg index for the MM bonds in all of these complexes in all spin states studied are categorized into ranges according to the MM bond orders 0 to 5 in steps of 0.5. The trends shown validate their use in estimating intrinsic metal-metal bond strength regardless of the metal.

A Diruthenium Metallodrug as a Potent Inhibitor of Amyloid-β Aggregation: Synergism of Mechanisms of Action.

The physical and chemical properties of paddlewheel diruthenium compounds are highly dependent on the nature of the ligands surrounding the bimetallic core. Herein, we compare the ability of two diruthenium compounds, [Ru2Cl(D-p-FPhF)(O2CCH3)3]·H2O (1) (D-p-FPhF- = N,N'-bis(4-fluorophenyl)formamidinate) and K3[Ru2(O2CO)4]·3H2O (2), to act as inhibitors of amyloid aggregation of the Aβ1-42 peptide and its peculiar fragments, Aβ1-16 and Aβ21-40. A wide range of biophysical techniques has been used to determine the inhibition capacity against aggregation and the possible mechanism of action of these compounds (Thioflavin T fluorescence and autofluorescence assays, UV-vis absorption spectroscopy, circular dichroism, nuclear magnetic resonance, mass spectrometry, and electron scanning microscopy). Data show that the most effective inhibitory effect is shown for compound 1. This compound inhibits fiber formation and completely abolishes the cytotoxicity of Aβ1-42. The antiaggregatory capacity of this complex can be explained by a binding mechanism of the dimetallic units to the peptide chain along with π-π interactions between the formamidinate ligand and the aromatic side chains. The results suggest the potential use of paddlewheel diruthenium complexes as neurodrugs and confirm the importance of the steric and charge effects on the properties of diruthenium compounds.

Steric hindrance and charge influence on the cytotoxic activity and protein binding properties of diruthenium complexes

Paddlewheel diruthenium complexes are being used as metal-based drugs. It has been proposed that their charge and steric properties determine their selectivity towards proteins. Here, we explore these parameters using the first water-soluble diruthenium complex bearing two formamidinate ligands, [Ru2Cl(DPhF)2(O2CCH3)2], and two derivatives, [Ru2Cl(DPhF)(O2CCH3)3] and K2[Ru2(DPhF)(CO3)3] (DPhF− = N,N′-diphenylformamidinate), with one formamidinate. Their protein binding properties have been assessed employing hen egg white lysozyme (HEWL). The results confirm the relationship between the type of interaction (coordinate/non-coordinate bonds) and the charge of diruthenium complexes. The crystallization medium is also a key factor. In all cases, diruthenium species maintain the M–M bond and produce stable adducts. The antiproliferative properties of these diruthenium complexes have been evaluated on an eukaryotic cell-based model. Our data show a correlation between the number of the formamidinate ligands and the anticancer activity of the diruthenium derivatives against human epithelial carcinoma cells. Increased cytotoxicity may be related to increased steric hindrance and Ru25+ core electronic density. However, the effect of increasing the lipophilicity of diruthenium species by introducing a second N,N′-diphenylformamidinate must be also considered. This work illustrates a systematic approach to shed light on the relevant properties of diruthenium compounds to design metal-based metallodrugs and diruthenium metalloenzymes.

Cytotoxicity Evaluation of Unmodified Paddlewheel Dirhodium(II,II)-Acetate/-Formamidinate Complexes and Their Axially Modified Low-Valent Metallodendrimers.

Two diphenyl formamidine ligands, four dirhodium(II,II) complexes, and three axially modified low-valent dirhodium(II,II) metallodendrimers were synthesized and evaluated as anticancer agents against the A2780, A2780cis, and OVCAR-3 human ovarian cancer cell lines. The dirhodium(II,II) complexes show moderate cytotoxic activity in the tested tumor cell lines, with acetate and methyl-substituted formamidinate compounds displaying increased cytotoxicity that is relative to cisplatin in the A2780cis cisplatin resistant cell line. Additionally, methyl- and fluoro-substituted formamidinate complexes showed comparable and increased cytotoxic activity in the OVCAR-3 cell line when compared to cisplatin. The low-valent metallodendrimers show some activity, but a general decrease in cytotoxicity was observed when compared to the precursor complexes in all but one case, which is where the more active acetate-derived metallodendrimer showed a lower IC50 value in the OVCAR-3 cell line in comparison with the dirhodium(II,II) tetraacetate.

Enhancing the Air Stability of Dimolybdenum Paddlewheel Complexes: Redox Tuning through Fluorine Substituents.

The optical and electrochemical properties of quadruply bonded dimolybdenum paddlewheel complexes (Mo2PWCs) make them ideal candidates for incorporation into functional materials or devices, but one of the greatest bottlenecks for this is their poor stability toward atmospheric oxygen. By tuning the potential at which the Mo2 core is oxidized, it was possible to increase the tolerance of Mo2PWCs to air. A series of homoleptic Mo2PWCs bearing fluorinated formamidinate ligands have been synthesized and their electrochemical properties studied. The oxidation potential of the complexes was tuned in a predictable fashion by controlling the positions of the fluorine substituents on the ligands, as guided by a Hammett relationship. Studies into the air stability of the resulting complexes by multinuclear NMR spectroscopy show an increased tolerance to atmospheric oxygen with increasingly electron-withdrawing ligands. The heteroleptic complex Mo2(DFArF)3(OAc) [where DFArF = 3,5-(difluorophenyl)formamidinate] shows remarkable tolerance to oxygen in the solid state and in chloroform solutions. Through the employment of easily accessible ligands, the stability of the Mo2 core toward oxygen has been enhanced, thereby making Mo2PWCs with electron-withdrawing ligands more attractive candidates for the development of functional materials.

Face-Centered Cubic Silver Nanoclusters Consolidated with Tetradentate Formamidinate Ligands.

Growing attention has been paid to nanoclusters with face-centered cubic (fcc) metal kernels, due to its structural similarity to bulk metals. We demonstrate that the use of tetradentate formamidinate ligands facilitate the construction of two fcc silver nanoclusters: [Ag52(5-F-dpf)16Cl4](SbF6)2 (Ag52, 5-F-Hdpf = N,N'-di(5-fluoro-2-pyridinyl)formamidine) and [Ag53(5-Me-dpf)18](NO3)5 (Ag53, 5-Me-Hdpf = N,N'-di(5-methyl-2-pyridinyl)formamidine). Single-crystal X-ray structural analysis revealed that the silver atoms in both clusters are in a layer-by-layer arrangement, which can be viewed as a portion of the fcc packing of silver. The nitrogen donors of amidinate ligands selectively passivate the {111} facets. All silver atoms are involved in the fcc packing, that is, no staple motifs are observed due to the linear arrangement of the four N donors of the dpf ligands. The characteristic optical absorption bands of Ag52 and Ag53 have been studied with a time-dependent density functional theory. This work provides a facile access to assembling atomically precise fcc-type nanoclusters and shows the prospect of amidinates as protecting ligands in synthesizing metal nanoclusters.

A New Look at Molecular and Electronic Structure of Homoleptic Diiron(II,II) Complexes with N,N-Bidentate Ligands: Combined Experimental and Theoretical Study.

Paddlewheel-type binuclear complexes featuring metal-metal bonding have been the subject of widespread interest due to fundamental concern in their electronic structures and potential applications. Here, we explore the molecular and electronic structures of diiron(II,II) complexes with N,N'-diarylformamidinate ligands. While a paddlewheel-type diiron(II,II) complex with N,N'-diphenylformamidinate ligands (DPhF) exhibits the centrosymmetric [Fe2 (μ-DPhF)4 ] structure, a minor alteration in the ligand system, i. e., switching from phenyl to p-tolyl N-substituted formamidinate ligand (DTolF), resulted in the isolation of an unprecedented non-centrosymmetric [Fe(μ-DTolF)3 Fe(κ2 -DTolF)] complex. Both complexes were characterized using single-crystal X-ray diffraction, magnetic measurements, 57 Fe Mössbauer spectroscopy, and cyclic voltammetry along with high-level ab-initio calculations. The results provide a new view on a range of factors controlling the ground-state electronic configuration and structural diversity of homoleptic diiron(II,II) complexes. Model calculations determined that the Mayer bond orders for Fe-Fe interactions are significantly lower than 1 and equal to 0.15 and 0.28 for [Fe2 (μ-DPhF)4 ] and [Fe(μ-DTolF)3 Fe(κ2 -DTolF)], respectively.

Silver(I) complexes ofN,N′‐diarylformamidine ligands: Synthesis, crystal structures, and in vitro antibacterial studies

AbstractNine silver(I)N,N′‐diarylformamidine complexes of type [Ag (Ln)2X] (where X = NO3−, CF3COO−, and CF3SO3−,n = 1–5) were synthesised and characterised by physiochemical and spectroscopic techniques. Further confirmation for the formation of the complexes was provided by single‐crystal X‐ray crystallography. All complexes (but one) adopted linear geometry in which coordination was via twoNatoms of two formamidine ligands with the anion (X) displaced from coordination sphere. In the structure of the exception, the anion is part of the coordination sphere and a T‐shaped geometry was adopted. The antimicrobial activity of the Ag(I) complexes were investigated against two Gram‐positive bacteria, that is,S. aureusATCC 25923 andMethicillin‐resistant S. aureusATCC 700699 (MRSA) and four Gram‐negative bacteria, that is,K. pneumoniaeATCC 31488,S. typhimuriumATCC 14026,P. aeruginosaATCC 27853 andE. coliATCC 25922 and they were evaluated based on ciprofloxacin and silver nitrate standards. The newly synthesised target complexes demonstrated promising antibacterial activity against Gram‐positive bacteria although less than the reference drug ciprofloxacin. The best active silver(I) complex contains a nitrate counter‐ion.

Non-redox reactivity of V(II) and Fe(II) formamidinates towards CO2 resulting in the formation of novel M(II) carbamates.

Chemical fixation of CO2 is a powerful tool for the preparation of novel multinuclear metal complexes and functional materials. Particularly, the insertion of CO2 into a metal-X bond (X = H, C, N, O) often is a key elementary step in the various processes transforming this greenhouse gas into valuable products. Herein, we report on the reactivity between CO2 and V(II) and Fe(II) complexes supported by N,N'-bis(2,6-diisopropylphenyl)formamidinate ligands (DippF). The reactions proceeded with multiple insertions of CO2 into the M-N bonds leading to the isolation of three novel complexes: [(κ2-DippFCO2)(THF)V(μ-DippFCO2)3V(THF)], [(κ2-DippFCO2)Fe(μ-DippFCO2)2(μ-DippF)Fe(THF)] and [(κ2-DippFCO2)Fe(μ-DippFCO2)3Fe(κ1-DippFH)], which were characterised using single-crystal X-ray diffraction, FTIR and 57Fe Mössbauer spectroscopy (for the diiron compounds). We provide the first well-documented studies of the CO2 reactivity towards the V-N bond and broaden the state-of-the-art of the undeveloped area of the reactivity of low-valent V(II) complexes. Moreover, we showed that the effectivity of the examined CO2 insertion processes strongly depends on the used solvent's characteristics (for the Fe(II) system) and the metal centre's coordination sphere geometry (for the V(II) system).

Ultrasound-assisted synthesis of water-soluble monosubstituted diruthenium compounds

The elusive monosubstituted diruthenium complexes [Ru2Cl(DAniF)(O2CMe)3] (1), [Ru2Cl(DPhF)(O2CMe)3] (2), [Ru2Cl(D-p-CNPhF)(O2CMe)3] (3), [Ru2Cl(D-o-TolF)(O2CMe)3] (4), [Ru2Cl(D-m-TolF)(O2CMe)3] (5), [Ru2Cl(D-p-TolF)(O2CMe)3] (6) and [Ru2Cl(p-TolA)(O2CMe)3] (7) have been synthesized using for the first time ultrasound-assisted synthesis to carry out a substitution reaction in metal–metal bonded dinuclear compounds (DAniF− = N,N′-bis(4-anisyl)formamidinate; DPhF− = N,N′-diphenylformamidinate; D-p-CNPhF− = N,N′-bis(4-cyanophenyl)formamidinate; D-o/m/p-TolF− = N,N′-bis(2/3/4-tolyl)formamidinate; p-TolA− = N-4-tolylamidate). This is a simpler and greener method than the tedious procedures described in the literature, and it has permitted to obtain water-soluble complexes with good yields in a short period of time. A synthetic study has been implemented to find the best experimental conditions to prepare compounds 1–7. Two different types of ligands, formamidinate and amidate, have been used to check the generality of the method for the preparation of monosubstituted complexes. Five new compounds (2–6) have been obtained using a formamidinate ligand, the synthesis of the previously described compound 1 has been improved, and an unprecedented monoamidate complex has been achieved (7). The crystal structures of compounds 3 and 7 have been solved by single crystal X-ray diffraction. These compounds show the typical paddlewheel structure with three acetate ligands and one formamidinate (3) or amidate (7) bridging ligand at the equatorial positions. The axial positions are occupied by the chloride ligand giving rise to one-dimensional polymer structures that were previously unknown for monosubstituted compounds.

Robust Gold Nanocluster Protected with Amidinates for Electrocatalytic CO2 Reduction.

The first all-amidinate-protected gold nanocluster [Au28 (Ph-form)12 ](OTf)2 (Ph-form=N,N'-diphenylformamidinate) (Au28 ) has been synthesized and structurally resolved. Single crystal X-ray diffraction reveals that Au28 has a compact Au4 @Au24 tetrahedral core-shell structure of T symmetry, which is fully protected by 12 bridging formamidinate ligands. This cluster is quite robust as indicated by the fact that it can stay intact in solution at 80 °C for 6 d. It exhibits excellent catalytic performance for the electroreduction of CO2 with 96.5 % Faradaic efficiency (FE) at -0.57 V and a maximum TOF of 1731 h-1 at -0.87 V. Its superior stability is also manifested in the fact that the supported catalyst Au28 /CNTs maintains stable potentials at ca. -0.69 V for 40 h with FE(CO)s>91 %. A superatomic electron configuration of 1S2 1P6 2S2 1D4 has been clarified by DFT computations, and the strong gold-ligand binding and geometric shell closure account for the superior stability of Au28 .

Robust Gold Nanocluster Protected with Amidinates for Electrocatalytic CO2 Reduction

AbstractThe first all‐amidinate‐protected gold nanocluster [Au28(Ph−form)12](OTf)2 (Ph‐form=N,N′‐diphenylformamidinate) (Au28) has been synthesized and structurally resolved. Single crystal X‐ray diffraction reveals that Au28 has a compact Au4@Au24 tetrahedral core–shell structure of T symmetry, which is fully protected by 12 bridging formamidinate ligands. This cluster is quite robust as indicated by the fact that it can stay intact in solution at 80 °C for 6 d. It exhibits excellent catalytic performance for the electroreduction of CO2 with 96.5 % Faradaic efficiency (FE) at −0.57 V and a maximum TOF of 1731 h−1 at −0.87 V. Its superior stability is also manifested in the fact that the supported catalyst Au28/CNTs maintains stable potentials at ca. −0.69 V for 40 h with FE(CO)s>91 %. A superatomic electron configuration of 1S21P62S21D4 has been clarified by DFT computations, and the strong gold–ligand binding and geometric shell closure account for the superior stability of Au28.

Bimodal substitution behavior in the reaction of N,N’-diisopropylformamidine with [Os3(CO)10(NCMe)2]: Kinetics and molecular structures of the formamidinate-substituted clusters HOs3(CO)9[μ-C(O)NPriC(H)NPri], HOs3(CO)10[μ-NPriC(H)NPri], and HOs3(CO)9[μ3-NPriC(H)NPri

The dinitrogen donor N,N’-diisopropylformamidine [PriN=C(H)NHPri] reacts with the triosmium cluster Os3(CO)10(NCMe)2 at room temperature to yield the isomeric clusters HOs3(CO)9[μ-C(O)NPriC(H)NPri] (1) and HOs3(CO)10[μ-NPriC(H)NPri] (2) in a 1:2.8 ratio. 1 contains an edge-bridging iminocarbamoyl ligand, while 2 contains a bridging formamidinate ligand. Thermolysis of 1 yields 2 plus the face-capped cluster HOs3(CO)9[μ3-NPriC(H)NPri] (3). The decarbonylation of 2 to 3 + CO confirms the molecularity of the observed reaction steps. The three products have been fully characterized in solution by IR and NMR spectroscopies, and the solid-state structures for 1-3 have been determined by X-ray crystallography. The kinetics for the thermolysis reaction were investigated over the temperature range 342–383 K, and the concentration versus time profiles for the conversion of 1 → 2 → 3 + CO have been successfully modeled using two consecutive, irreversible first-order reactions. The bonding in clusters 1-3 have been examined by DFT, and these data support cluster 1 as the kinetic substitution product and cluster 2 as the thermodynamically favored isomer.

Synthesis and characterization of sodium, potassium, zinc and aluminium formamidinate complexes

The metalation reactions of N,N’-bis-(2,4-dimethylphenyl)formamidine (DMFormH) and N,N’-bis-(phenyl)formamidine (PhFormH) with KN(SiMe3)2 or NaN(SiMe3)2 in toluene/1,2-dimethoxyethane (dme) resulted in the formation of [K(DMForm)(dme)]n (K1), [K2(PhForm)(N(SiMe3)2)]n (K2), [Na(DMForm)(dme)2] (Na1), and [Na(PhForm)(dme)]2 (Na2). Treatment of PhFormH with ZnEt2 or AlMe3 in toluene/tetrahydrofuran (thf) yielded [Zn4(PhForm)6O]·2.5thf (Zn1) and [Al(PhForm)3] (Al1), respectively. The potassium-formamidinate compounds (K1 and K2) are polymeric. K1 has six-coordinate potassium with additional C…K interactions. Reducing the steric effect of the formamidinate changes the formamidinate bonding mode. Thus, for potassium complexes, it led to both inter- and intra-molecular η6-arene-K binding in K2. With the sodium complexes, the structure changed from a six-coordinate monomer in [Na(DMForm)(dme)2] to a five-coordinate dimer in [Na(PhForm)(dme)]2 in which there is a μ 2-1κ(N,N’): 2κ (N) formamidinate binding mode. Zn1 has a pseudo-cubane oxide centered cage like structure, whereas Al1 is monomeric with six-coordinate aluminium and chelating formamidinate ligands.

Ultrasound-Assisted Synthesis of Water-Soluble Monosubstituted Diruthenium Compounds

The elusive monosubstituted diruthenium complexes [Ru2Cl(DAniF)(O2CMe)3] (1), [Ru2Cl(DPhF)(O2CMe)3] (2), [Ru2Cl(D-p-CNPhF)(O2CMe)3] (3), [Ru2Cl(D-o-TolF)(O2CMe)3] (4), [Ru2Cl(D-m-TolF)(O2CMe)3] (5), [Ru2Cl(D-p-TolF)(O2CMe)3] (6) and [Ru2Cl(p-TolA)(O2CMe)3] (7) have been synthesized using for the first time ultrasound-assisted synthesis to carry out a substitution reaction in metal-metal bonded dinuclear compounds (DAniF- = N,N’-bis(4-anisyl)formamidinate; DPhF- = N,N’-diphenylformamidinate; D-p-CNPhF- = N,N’-bis(4-cyanophenyl)formamidinate; D-o/m/p-TolF- = N,N’-bis(2/3/4-tolyl)formamidinate; p-TolA- = N-4-tolylamidate). This is a simpler and greener method than the tedious procedures described in the literature, and it has permitted to obtain water-soluble complexes with good yields in a short period of time. A synthetic study has been implemented to find the best experimental conditions to prepare compounds 1-7. Two different types of ligands, formamidinate and amidate, have been used to check the generality of the method for the preparation of monosubstituted complexes. Five new compounds (2-6) have been obtained using a formamidinate ligand, the synthesis of the previously described compound 1 has been improved, and an unprecedented monoamidate complex has been achieved (7). The crystal structures of compounds 3 and 7 have been solved by single crystal X-ray diffraction. These compounds show the typical paddlewheel structure with three acetate ligands and one formamidinate (3) or amidate (7) bridging ligand at the equatorial positions. The axial positions are occupied by the chloride ligand giving rise to one-dimensional polymer structures that were previously unknown for monosubstituted compounds.

Impact of Electronic and Steric Changes of Ligands on the Assembly, Stability, and Redox Activity of Cu4(μ4-S) Model Compounds of the CuZ Active Site of Nitrous Oxide Reductase (N2OR).

Model compounds have been widely utilized in understanding the structure and function of the unusual Cu4(μ4-S) active site (CuZ) of nitrous oxide reductase (N2OR). However, only a limited number of model compounds that mimic both structural and functional features of CuZ are available, limiting insights about CuZ that can be gained from model studies. Our aim has been to construct Cu4(μ4-S) clusters with tailored redox activity and chemical reactivity via modulating the ligand environment. Our synthetic approach uses dicopper(I) precursor complexes (Cu2L2) that assemble into a Cu4(μ4-S)L4 cluster with the addition of an appropriate sulfur source. Here, we summarize the features of the ligands L that stabilize precursor and Cu4(μ4-S) clusters, along with the alternative products that form with inappropriate ligands. The precursors are more likely to rearrange to Cu4(μ4-S) clusters when the Cu(I) ions are supported by bidentate ligands with 3-atom bridges, but steric and electronic features of the ligand also play crucial roles. Neutral phosphine donors have been found to stabilize Cu4(μ4-S) clusters in the 4Cu(I) oxidation state, while neutral nitrogen donors could not stabilize Cu4(μ4-S) clusters. Anionic formamidinate ligands have been found to stabilize Cu4(μ4-S) clusters in the 2Cu(I):2Cu(II) and 3Cu(I):1Cu(II) states, with both the formation of the dicopper(I) precursors and subsequent assembly of clusters being governed by the steric factor at the ortho positions of the N-aryl substituents. Phosphaamidinates, which combine a neutral phosphine donor and an anionic nitrogen donor in the same ligand, form multinuclear Cu(I) clusters unless the negative charge is valence-trapped on nitrogen, in which case the resulting dicopper precursor is unable to rearrange to a multinuclear cluster. Taken together, the results presented in this study provide design criteria for successful assembly of synthetic model clusters for the CuZ active site of N2OR, which should enable future insights into the chemical behavior of CuZ.

Reduction of CO2 by Hydrosilanes in the Presence of Formamidinates of Group 13 and 12 Elements

Homoleptic complexes 1-M of group 13 and 12 elements (M = B–In and M = Zn, respectively) incorporating electron-withdrawing formamidinate ligands {(C6F5)N═CHN(C6F5)}− ({NCN}−) were synthesized and ...

Redox Potential Tuning of Dimolybdenum Systems through Systematic Substitution by Guanidinate Ligands.

We report the synthesis and characterization of a series of dimolybdenum paddlewheel complexes of the type Mo2(DAniF)4-n(hpp)n (n = 1-3), where DAniF is the anion of N,N'-di-p-anisyl-formamidine and hpp is the anion of 1,3,4,6,7,8-hexahydro-2H-pyrimido[1,2-a]pyrimidine. The effect on the electronic structure of these tetragonal paddlewheel dimolybdenum compounds was studied upon systematic substitution of formamidinate ligands by the more basic guanidinates. Mo-Mo distances in the paddlewheel structures decreased upon guanidinate ligand substitution, and were found to be 2.0844(6) and 2.0784(6), for Mo2(DAniF)3(hpp) (1) and trans-Mo2(DAniF)2(hpp)2 (2), respectively. Electrochemical studies show that the half-wave potential of the Mo25+/Mo24+ couple shifts cathodically upon ancillary ligand substitution ranging from -0.286 V for the tetraformamidinate complex to -1.795 V for the tetraguanidinate analogue and with redox potentials of -0.75, -1.07, and -1.14 V for 1, 2, and 3 (Mo2(DAniF)(hpp)3), respectively. The presence of a second redox event assigned to the Mo26+/Mo25+ couple was not observed until two guanidinate ligands were introduced. Raman spectroscopy shows that the v(M-M) stretch gets systematically strengthened upon formamidinate ligand substitution by the guanidinate ligand hpp. The induced delta bond destabilization by the basic hpp ligand was measured using DFT calculations by tracking the energy of the frontier orbitals. The decrease in the HOMO-LUMO energy gap was supported by the red shift in the UV-vis spectra of the compounds: 412, 442, and 450 nm for 1, 2, and 3, respectively.

Synthesis, structure, and photoluminescent properties of lanthanide (Ln = Dy, Tb) chlorides and thiophenolates supported by formamidinate ligands

The [Dy(DippForm)2Cl(THF)] (1a) and [Tb(DippForm)2Cl(THF)2] (1b) complexes are syn­thesized using salt metathesis reactions between lanthanide chlorides and K(DippForm) (DippForm = N,N'-bis(2,6-diisopropylphenyl)formamidinate). In contrast to K(DippForm), a reaction of its less sterically demanding analogue K(MesForm) (MesForm = N,N'-bis(me­sityl)formamidinate) with LnCl3 at any ratio of the reagents leads to the formation of the ho­moligand [Ln(MesForm)3] (Ln = Dy (2a), Tb (2b)) complexes. The [Ln(MesForm)2Cl(THF)] compounds are not isolated. Compounds 1a and 1b are successfully used as starting reagents for the preparation of new thiophenolate complexes [Ln(DippForm)2(SPh)(THF)] (Ln = Dy (3a), Tb (3b)). Crystal structures of compounds 1—3 are determined by single crystal X-ray diffraction. Photoluminescent properties of the complexes obtained are studied. The analysis of the spectra of both DippForm– and SPh– ligands shows an antenna effect for both Dy(III) and Tb(III). However, MesForm– acts as an efficient antenna for Tb(III) rather than Dy(III).

Synthesis and structural studies of nickel(II)- and copper(II)-N,N′-diarylformamidine dithiocarbamate complexes as antimicrobial and antioxidant agents

A series of six N′N-diarylformamidine dithiocarbamate ligands and their metal complexes of Cu(II) and Ni(II) chloride salts have been synthesized. Three symmetrical, N,N′-bis(2,6-dimethylphenyl)formamidine dithiocarbamate (DL1), N,N′-bis(2,6-disopropylphenyl)formamidine dithiocarbamate (DL2), N,N′-mesityl formamidine dithiocarbamate (DL3) and three unsymmetrical N′-(2,6-dichlorophenyl-N-(2,6-dimethylphenyl)formamidine dithiocarbamate (DL4), N′-(2,6-dichlorophenyl)-N-(2,6-diisopropylphenyl)formamidine dithiocarbamate (DL5) and N′-(2,6-dichlorophenyl)-N-mesityl formamidine dithiocarbamate (DL6) dithiocarbamate ligands were reacted with CuCl2 and NiCl2 to give [Ni-(DL1)2] (1), [Ni-(DL2)2]·H2O (2), [Ni-(DL3)2] (3), [Ni-(DL4)2]·3H2O (4), [Ni-(DL5)2]·H2O (5), [Ni-(DL6)2] (6), [Cu-(DL1)2]·3H2O (7), [Cu-(DL2)2] (8), [Cu-(DL3)2]·2H2O (9), [Cu-(DL4)2]·3H2O (10), [Cu-(DL5)2]·3H2O (11) and [Cu-(DL6)2] (12). All ligands and the complexes were characterized using FT-IR, UV–Vis, 1H and 13C NMR, mass spectrometry and by elemental analysis. In addition, the structures of complexes 1, 5, 8 and 11 were confirmed by single crystal X-ray diffraction analysis as mononuclear neutral species in which the geometry around the metal centers is distorted square planar. In this coordination manner, the metal centers bound to four sulfur atoms from two dithiocarbamate ligand in a bidentate fashion. All complexes showed moderate to good antibacterial activities against Gram-negative, Salmonella typhimurium, Pseudomonas aeruginosa, Escherichia coli and Klebsiella pneumoniae and gram-positive, Staphylococcus aureus (methicillin resistant) and Staphylococcus aureus bacteria. Complexes 4 and 5 were found to be more active than ciprofloxacin against E. coli and K. pneumoniae. In addition, complexes with chloro substituted ligands displayed higher activities. Antioxidant activities of complexes with symmetrical formamidine ligands were generally high compared to the ones with the unsymmetrical formamidine moieties, with 2 having an IC50 value of 1.10 × 10−3 mM and 12 had 2.91 mM.