Synthesis, characterization, and aqueous chemistry of cytotoxic Au(III) polypyridyl complexes

This work reports the synthesis, characterization, and aqueous chemistry of a series of cytotoxic [Au(polypyridyl)Cl₂]PF₆ complexes {(where polypyridyl = dipyrido[3,2-f:2′,3′-h] quinoxaline (DPQ), dipyrido[3,2-a:2′,3′-c] phenazine (DPPZ) and dipyrido[3,2-a:2′,3′-c](6,7,8,9-tetrahydro) phenazine (DPQC))}. The crystal structure of [Au(DPQ)Cl₂]PF₆ was determined as example of the series and exhibits the anticipated square planar geometry common for d⁸ coordination complexes. The crystals of the complex belong to the space group P2₁/n with a = 7.624(2) Å, b = 18.274(5) Å, c = 14.411(14) Å, β = 98.03(3)°, and Z = 4. In ¹H NMR studies of these compounds in the presence of aqueous buffer, all four complexes rapidly converted to the dihydroxy species [Au(polypyridyl)(OH)₂] in a stepwise fashion. However, the [Au(polypyridyl)]³⁺ fragment believed to impart cytotoxicity in human ovarian cancer cell lines (A2780) remained intact and appeared stable for days. It was also noted that these Au(III) complexes were readily reduced in the presence of the common biological reducing agents, reduced glutathione and sodium ascorbate. How solution and redox stability may affect the biological activity of these novel Au(III) complexes is discussed.     

The auration of 2-hydroxy-pyridine (2-pyridone): preparative and structural studies and a comparison with reactions of related aliphatic O,N-donors

In a study of the isolobal analogy between the proton H⁺ and the ligand-backed gold(I) cations [(R₃P)Au]⁺, the reaction of the mixture of 2-pyridone/2-hydroxy-pyridine tautomers with [(Ph₃P)Au]BF₄ has been investigated. It affords the 1:1 complex with the gold atom N-bonded to the 2-hydroxy-pyridine tautomer: {(Ph₃P)Au[NC₅H₄-(OH-2)]}⁺BF₄ ⁻, which is related to known salts with the 2-hydroxy-pyridinium cation such as [HNC₅H₄(OH-2)]⁺Cl⁻. The structure was derived from analytical and spectroscopic data and from a comparison with the salt [(Ph₃P)Au(pyr)]BF₄, prepared and investigated structurally as a reference compound. An analogue was also prepared with 2-dimethylamino-ethanol as a substrate, which also affords the N-bonded complex [(Ph₃P)Au([Me₂NCH₂CH₂OH)]⁺BF₄ ⁻, the structure of which has been determined. The OH group is not attached to the gold atom but engaged in hydrogen bonding with the counterion. By contrast, in the complex [(Ph₃P)Au(Me₂NCH₂CH₂NMe₂)]⁺BF₄ ⁻ synthesized similarly with tmeda and crystallized as the dichloromethane solvate, one nitrogen atom is bonded firmly to the metal atom, but the second nitrogen atom is also weakly engaged in coordinative bonding. The compound is fluxional in solution, where a site exchange is observed which is rapid on the NMR time scale. The reaction of two equivalents of [(Ph₃P)Au]BF₄ with an alkali 2-pyridinolate, prepared from the above tautomeric mixture and sodium metal or a potassium alkoxide, yields the diaurated product {N,O-[(Ph₃P)Au]₂(NC₅H₄-O-2)}BF₄. In the crystal structure determination of a sesqui-solvate with dichloromethane it has been shown that one gold atom is attached solely to the nitrogen atom and the other solely to the oxygen atom. The dinuclear cations are associated into cyclic dimers through head-to-tail aurophilic bonding. From the geometrical characteristics of the core unit of the cations the ligand can be assigned a 2-pyridinolate form featuring pyridine and phenolate donor sites.     

Novel Pt(II) and Pt(IV) complexes with 3-amino-5-methyl-5-(4-pyridyl)-2,4-imidazolidenedione. Synthesis, physicochemical, chemometric and pharmacological investigation

Platinum(II) and platinum(IV) complexes with 3-amino-5-methyl-5-(4-pyridyl)-2,4-imidazolidenedione (L) with general formulaе cis-[PtL₂X₂]·nH₂O and [PtL₂Cl₄], where X = Cl⁻, Br⁻, I⁻ and n = 2-4) were synthesized. The novel compounds were fully characterized by elemental analysis, IR, ¹H, ¹³C, ¹⁹⁵Pt NMR spectra, thermal analysis and molar conductivity. The geometry of Pt(II) complexes and of the organic ligand in the gas phase were optimized using the hybrid DFT method B3LYP with LANL2DZ and 6-31G** basis sets. Some physicochemical parameters as dipole moment, HOMO, LUMO energies and ESP charges were calculated. The comparison of the bond length and angles, obtained from the X-ray analysis and DFT calculations is realized. The cytotoxic effects of these complexes in human T-cell leukemia KE-37 (SKW-3) are reported.     

Multinuclear magnetic resonance study of Pt(II) compounds with sulfoxide ligands and crystal structures of complexes of the types [Pt(R2SO)X3] and Pt(R2SO)2Cl2

Pt(II) complexes of the types K[Pt(R₂SO)X₃], NR₄[Pt(R₂SO)X₃] and Pt(R₂SO)₂Cl₂ (where X = Cl or Br) were characterized by multinuclear magnetic resonance spectroscopy (¹⁹⁵Pt, ¹H and ¹³C). In ¹⁹⁵Pt NMR, the chloro ionic compounds have shown signals between −2979 and −3106 ppm, while the cis disubstituted complexes were observed at higher fields, between −3450 and −3546 ppm. The signal of the compound trans-Pt(DPrSO)₂Cl₂ was found at higher field (−3666 ppm) than its cis analogue (−3517 ppm), since π-back-donation is considerably less effective in the trans geometry. In ¹H NMR, a single signal was observed for the sulfoxide in [Pt(DMSO)Cl₃]⁻, but for the other more sterically hindered ligands, two series of resonances were observed for the protons in α and β positions. The coupling constant ³J(¹⁹⁵Pt-¹H) are between 15 and 33 Hz. The ¹³C NMR results were interpreted in relation to the concept of inversed polarization of the π sulfoxide bond. The ²J(¹⁹⁵Pt-¹³C) values vary between 35 and 66 Hz, while a few ³J(¹⁹⁵Pt-¹³C) couplings were observed (13-26 Hz). The crystal structures of five monosubstituted ionic compounds N(n-Bu)₄[Pt(TMSO)Cl₃], N(Me)₄[Pt(DPrSO)Cl₃], K[Pt(EMSO)Cl₃], K[Pt(TMSO)Br₃] · H₂O and N(Et)₄[Pt(DPrSO)Br₃] and one disubstituted complex cis-Pt(DBuSO)₂Cl₂ were determined. The trans influence of the different ligands is discussed.     

Overcoming cisplatin resistance using gold(III) mimics: anticancer activity of novel gold(III) polypyridyl complexes

Gold(III) compounds have been recognized as anticancer agents due to their structural and electronic similarities with currently employed platinum(II) species. An added benefit to gold(III) agents is the ability to overcome cisplatin resistance. This work identified four gold(III) compounds, [Au(Phen)Cl₂]PF₆, [Au(DPQ)Cl₂]PF₆, [Au(DPPZ)Cl₂]PF₆, and [Au(DPQC)Cl₂]PF₆, (Phen = 1,10-phenanthroline, DPQ = dipyrido[3,2-d:2′,3′-f]quinoxaline, DPPZ = dipyrido[3,2-a:2′,3′-c] phenazine, DPQC = dipyrido[3,2-d:2′,3′-f] cyclohexyl quinoxaline) that exhibited anticancer activity in both cisplatin sensitive and cisplatin resistant ovarian cancer cells. Two of these compounds, [Au(DPQ)Cl₂]PF₆ (AQ) and [Au(DPPZ)Cl₂]PF₆ (AZ), displayed exceptional anticancer activity and were the focus of more intensive mechanistic study. At the molecular level, AQ and AZ formed DNA adducts, generated free radicals, and upregulated pro-apoptotic signaling molecules (p53, caspases, PARP, death effectors). Taken together, these two novel gold(III) polypyridyl complexes exhibit potent antitumor activity in cisplatin resistant cancer cells. These activities may be mediated, in part, by the activation of apoptotic signaling.     

Synthesis, characterisation of a complex of Cu(II) with a multidentate macrocyclic ligand and its interactions with anions

A macrocyclic ligand possessing a donor set of {N₃S₂} synthesised via Cs⁺-templation, 4-(pyridin-2-ylmethyl)-1,7-dithia-4,10-diazacyclododecane (L) and its Cu(II) complex, [CuL(NCMe)]²⁺ (6), are described. This Cu(II) complex interacts with a range of anions, F⁻, Cl⁻, Br⁻, I⁻, HCOO⁻, AcO⁻, CO₃²⁻, NO₃⁻, C₂O₄²⁻, H₂PO₄⁻, SCN⁻, CN⁻, BF₄⁻. Of the investigated anions, I⁻, SCN⁻, and CN⁻, show strong interaction with the Cu(II) centre as indicated by their spectral variations. The iodide particularly demonstrates distinct change in colour. This change originates from a newly appeared band at 471 nm upon iodide binding, which arises from the ligand (I⁻) to Cu(II) charge transfer (LMCT) in the iodide-substituted Cu(II) complex, [CuLI]⁺ (7). All organic compounds are characterised by NMR spectroscopy and/or microanalysis. The identities of the two Cu(II) complexes are confirmed by using microanalysis and the complex 6 is crystallographically analysed.     

The synthesis and toxicity of tripodal tricarbonyl rhenium complexes as radiopharmaceutical models

We report the synthesis and toxicity of a series of rhenium(I) tricarbonyl complexes incorporating the trisaminomethylethane (TAME) ligand. Compounds with the (TAME)Re(CO)₃⁺ cation were synthesized via several routes, including by use of Re(CO)₅X precursors as well as the aqueous cation Re(CO)₃(H₂O)₃⁺. Salts of the formula [(TAME)Re(CO)₃]X where X = Br⁻, Cl⁻, NO₃⁻, PF₆⁻ and ClO₄⁻ were evaluated using two cell lines: the monoclonal S3 HeLa line and a vascular smooth muscle cell line harvested from mice. All compounds have isostructural cations and differ only in the identity of the non-coordinating anion. None of the complexes exhibited any appreciable toxicity in the HeLa line up to the solubility limit. In the vascular smooth muscle cell line, the bromide salt exhibited some cytotoxicity, but this observation most likely results from the presence of bromide anion, which has been shown to have limited toxicity.     

Nickel(II) complexes of di- and tri-substituted thiourea mono- and di-anions

Reaction of nickel(II) acetate, 1,2-bis(diphenylphosphino)ethane (dppe), and a di- or tri-substituted thiourea R¹NHC(S)R²R³ (R³ = H or alkyl) with trimethylamine in hot methanol gave cationic nickel(II) complexes containing N,S-chelated thiourea monoanion ligands [Ni{SC(NR²R³)NR¹}(dppe)]⁺, which can be readily isolated as their BPh₄⁻ salts. The X-ray crystal structure of [Ni{SC(NMe₂)NPh}(dppe)]⁺BPh₄⁻ is reported.     

Copper(I) complexes with Schiff base and 1,2-bis(diphenylphosphino)ethane as ligands: Synthesis, structure and catalytic properties for the amination of aryl halide

Some copper(I) complexes of the type [Cu(L)(dppe)]X (1-4) [where L = (3-trifluoromethylphenyl)pyridine-2-ylmethylene-amine; dppe = 1,2-bis(diphenylphosphino)ethane; X = Cl⁻, CN⁻, ClO₄⁻ and BF₄⁻] have been synthesized by the condensation of 3-aminobenzotrifluoride with 2-pyridinecarboxaldehyde followed by the reaction with CuCl, CuCN, [Cu(MeCN)₄]ClO₄ and [Cu(MeCN)₄]BF₄ in presence of dppe. The complexes 1-4 were then characterized on the basis of elemental analysis, IR, UV-Vis and ¹H NMR spectral studies. The representative complex of the series 4 has been characterized by single crystal X-ray diffraction which reveal that in complex the central copper(I) ion assumes the irregular pseudo-tetrahedral geometry. The catalytic activity of the complexes was tested and it was found that all the complexes worked as effective catalyst in the amination of aryl halide.     

[Ni(L)(MeCN)]complex cation as a template for the assembly of extended I3 · I5 and I5 · I7 polyiodide networks {L=2,5,8-trithia[9](2,9)-1,10-phenanthrolinophane}. Synthesis and structures of [Ni(L)(MeCN)]I8 and [Ni(L)(MeCN)]I12

The compounds [Ni(L)(MeCN)]I₈ (1) and [Ni(L)(MeCN)]I₁₂ (2) have been obtained from the reactions of the complexes [Ni(L)(L^′)][BF₄]_(2 + n) {L=2,5,8-trithia[9](2,9)-1,10-phenanthrolinophane; L^′=MeCN, Cl⁻, Br⁻, I⁻; n=charge of L^′} with an excess of I₂ (molar ratios of 6, 10 and 20 have been used), in the presence of the stoichiometric amount of I⁻ (as Bu₄ⁿNI) necessary to balance the charge of the complex cation [Ni(L)(L^′)]^(2 + n)+. An X-ray diffraction analysis shows that, independently of the nature of L^′, both 1 and 2 contain the complex cation [Ni(L)(MeCN)]²⁺, which is therefore capable of templating two different polyiodide networks based on interacting I₃⁻/I₅⁻ and I₅⁻/I₇ units, respectively. The solid state FT-Raman spectra of 1 and 2 are discussed based on their structural features.     

Syntheses and electrochemical properties of ruthenium(II) complexes with 4,4-bipyrimidine and 4,4-bipyrimidinium ligands

The syntheses and electrochemical properties of novel ruthenium(II) polypyridyl complexes with 4,4^′-bipyrimidine, [Ru(trpy)(bpm)Cl](X) ([1](X; X=PF₆⁻, BF₄⁻)) and with a quaternized 4,4^′-bipyrimidinium ligand, [Ru(trpy)(Me₂bpm)Cl](BF₄)₃ ([2](BF₄)₃) (trpy=2,2^′:6^′,2″-terpyridine, bpm=4,4^′-bipyrimidine, Me₂bpm=1,1^′-dimethyl-4,4^′-bipyrimidinium) are presented. The bpm complex [1]⁺ was prepared by the reaction of Ru(trpy)Cl₃ with 4,4^′-bipyrimidine in EtOH/H₂O. The structural characterization of [1]⁺ revealed, that the bpm ligand coordinated to the ruthenium atom with the bidentate fashion. Diquaternization of the non-coordinating nitrogen atoms on bpm of [1]⁺ by (CH₃)₃OBF₄ in CH₃CN gave [2](BF₄)₃. The electrochemical and spectroelectrochemical properties of the complexes are described.     

Reactivity of [PdCl(bdtp)](BF4) with monodentate neutral and anionic ligands. Structure of [Pd(bdtp)(PPh3)](BF4)2 (bdtp = 1,5-bis(3,5-dimethyl-1-pyrazolyl)-3-thiapentane)

Complex [PdCl(bdtp)](BF₄), in presence of AgBF₄ or NaBF₄, reacts with pyridine (py), triphenylphosphine (PPh₃), cyanide (CN⁻), thiocyanate (SCN⁻) or azide (N₃⁻) ligands, leading to the formation of the following complexes: [Pd(bdtp)(py)](BF₄)₂ [1](BF₄)₂, [Pd(bdtp)(PPh₃)](BF₄)₂ [2](BF₄)₂, [Pd(CN)(bdtp)](BF₄) [3](BF₄), [Pd(SCN)(bdtp)](BF₄) [4](BF₄) and [Pd(N₃)(bdtp)](BF₄) [5](BF₄). These complexes were characterised by elemental analyses, mass spectrometry, conductivity measurements, infrared and NMR spectroscopies. The crystal structure of [2](BF₄)₂ was determined by single-crystal X-ray diffraction methods. The metal atom is coordinated by two azine nitrogen atoms, and one sulfur atom of the thioether-pyrazole ligand and one triphenylphosphine in a distorted square-planar geometry.     

Vanadocene complexes of amino acids containing secondary amino group: The first evidence of O,O-bonded carboxylic group to vanadocene(IV) moiety

Reaction of vanadocene dichlorides (Cp₂VCl₂ and (η⁵-C₅H₄Me)₂VCl₂) with amino acids containing secondary amino groups gives three types of complexes: a) compounds with N,O-bonded amino acid, b) O-bonded amino acids and c) O,O-bonded amino acid. The complexes with N,O-bonded amino acid and O-bonded amino acids were observed in the case of l-proline and N-methylglycine (NMG). Reactions with N-phenylglycine (NPG) give O,O-chelates as the sole products. All three types of the complexes were characterized by spectroscopic methods. Structures of [(η⁵-C₅H₄Me)₂V(O-Pro)][BPh₄], [Cp₂V(O-Pro)₂][PF₆]₂, [Cp₂V(N,O-NMG)][BPh₄]·MeOH, [(η⁵-C₅H₄Me)₂V(N,O-NMG)][BPh₄]·MeOH, [Cp₂V(O-NMG)₂][Cl]₂·2H₂O, [(η⁵-C₅H₄Me)₂V(O-NMG)₂][Cl]₂·H₂O and [(η⁵-C₅H₄Me)₂V(O,O-NPG)][BPh₄] were determined by X-ray crystallography.     

Enhanced DNA photocleavage properties of Ru(II) terpyridine complexes upon incorporation of methylphenyl substituted terpyridine and/or the polyazine bridging ligand dpp (2,3-bis(2-pyridyl)pyrazine)

The heteroleptic complexes, [(MePhtpy)RuCl(dpp)](PF₆) and [(tpy)RuCl(dpp)](PF₆), have been synthesized, characterized, and investigated with respect to their photophysical, redox, and DNA photocleavage properties (where MePhtpy = 4′-(4-methylphenyl)-2,2′:6′,2′′-terpyridine and dpp = 2,3-bis(2-pyridyl)pyrazine, tpy = 2,2′:6′,2′′-terpyridine). The X-ray crystal structure confirms the identity of the new [(MePhtpy)RuCl(dpp)](PF₆) complex. These heteroleptic complexes were found to photocleave DNA in the presence of oxygen, unlike the previously studied complex, [Ru(tpy)₂](PF₆)₂. The photophysical, redox, and DNA photocleavage properties of the heteroleptic complexes were compared with those of the homoleptic complexes, [Ru(MePhtpy)₂](PF₆)₂ and [Ru(tpy)₂](PF₆)₂. The heteroleptic complexes showed intense metal to ligand charge transfer (MLCT) transition at lower energy ([(MePhtpy)RuCl(dpp)](PF₆), 522 nm; [(tpy)RuCl(dpp)](PF₆), 516 nm) and longer excited state lifetimes as compared to the homoleptic complexes. The [Ru(MePhtpy)₂]²⁺ complex was found to photocleave DNA in contrast to [Ru(tpy)₂]²⁺. The introduction of a methylphenyl group on the tepyridine ligand not only enhances the ³MLCT excited state lifetime but also increases the lipophilicity and thereby the DNA binding ability of the molecule. An increase in lipophilicity upon addition of a methylphenyl group on the 2,2′:6′,2′′-terpyridine ligand was confirmed by determination of the partition coefficient ([(MePhtpy)RuCl(dpp)](PF₆), log P = +1.16; [(tpy)RuCl(dpp)](PF₆), log P = −1.27). The heteroleptic complexes photocleave DNA more efficiently than the homoleptic complexes, with the greatest activity being observed for the newly prepared [(MePhtpy)RuCl(dpp)](PF₆) complex.     

Cyanide and chloride exchange on homoleptic gold(III) square-planar complexes: variable pressure kinetic investigation by heteronuclear NMR

Kinetic studies of X⁻ exchange on [AuX₄]⁻ square-planar complexes (where X=Cl⁻ and CN⁻) were performed at acidic pH in the case of chloride system and as a function of pH for the cyanide one. Chloride NMR study (330-365 K) gives a second-order rate law on [AuCl₄]⁻ with the kinetic parameters: (k₂^Au,Cl)²⁹⁸=0.56±0.03 s⁻¹ mol⁻¹ kg; ΔH₂^‡ Au,Cl=65.1±1 kJ mol⁻¹; ΔS₂^‡ Au,Cl=−31.3±3 J mol⁻¹ K⁻¹ and ΔV₂^‡ Au,Cl=−14±2 cm³ mol⁻¹. The variable pressure data clearly indicate the operation of an I_a or A mechanism for this exchange pathway. The proton exchange on HCN was determined by ¹³C NMR as a function of pH and the rate constant of the three reaction pathways involving H₂O, OH⁻ and CN⁻ were determined: k₀^HCN,H=113±17 s⁻¹, k₁^HCN,H=(2.9±0.7)×10⁹ s⁻¹ mol⁻¹ kg and k₂^HCN,H=(0.6±0.2)×10⁶ s⁻¹ mol⁻¹ kg at 298.1 K. The rate law of the cyanide exchange on [Au(CN)₄]⁻ was found to be second order with the following kinetic parameters: (k₂^Au,CN)²⁹⁸=6240±85 s⁻¹ mol⁻¹ kg, ΔH₂^‡ Au,CN=40.0±0.8 kJ mol⁻¹, ΔS₂^‡ Au,CN=−37.8±3 J mol⁻¹ K⁻¹ and ΔV₂^‡ Au,CN=+2±1 cm³ mol⁻¹. The rate constant observed varies about nine orders of magnitude depending on the pH and HCN does not act as a nucleophile. The observed rate constant of X⁻ exchange on [AuX₄]⁻ are two or three orders of magnitude faster than the Pt(II) analogue.     

Metal-metal stacking patterns between and with [Pt(tpy)X] cations

A comparative study of metallophilic interactions of [Pt(tpy)X]⁺ cations (tpy = 2,2′:6′,2″-terpyridine) in the presence of two different types of anions, (i) []⁻ anions that form double salts and (ii) simple p-block anions, is reported. Single-crystal X-ray diffraction data, solution-state ¹⁹⁵Pt NMR spectra, and variable temperature solid-state luminescence spectra are reported. Three [Pt(tpy)Cl]Y derivatives (Y = SbF₆, 1, SbF₆·CH₃CN, 4, PF₆, 2) and the [Pt(tpy)Br]PF₆ analog, 3, as well as two new double salts [Pt(tpy)CN][Au(CN)₂], 5, and [Pt(tpy)CN]₂[Au(C₆F₅)₂](PF₆), 6, have been synthesized and characterized. Structural analysis shows consistent patterns in Pt···Pt interactions that vary slightly depending on the coordinating halogen or pseudo-halogen X, counter anion Y, and lattice solvent. Metallophilic interactions are seen between [Pt(tpy)X]⁺ cations with all types of X ligands, but only with π-accepting X′ ligands from []⁻ anions are Pt?Au metallophilic interactions seen to be favored over Pt?Pt interactions. The [Au(CN)₂]⁻ anion consistently forms Pt···Au metallophilic contacts, unlike [Au(C₆F₅)₂]⁻. The ¹⁹⁵Pt NMR chemical shifts are ∼−2750 ppm for π-donor ligands and near −3120 ppm for π-acceptor ligands in [Pt(tpy)X]PF₆ compounds. Luminescence data show an unusual blue shift in [Pt(tpy)CCPh][Au(C₆F₅)₂] versus [Pt(tpy)CCPh]PF₆ ascribed to an intermolecular charge transfer.     

Enantioselective acylation of (RS)-phenylethylamine catalysed by lipases

The enzymatic acylation of (RS)-phenylethylamine with different acyl donors catalysed by lipases, was studied in organic solvents with different hydrophobicities and in mixtures with ionic liquids ((ILs); [BMIm][BF₄], [BMIm][SCN], [BMIm][Cl] and [BMIm][PF₆]). Using lipases from Candida antarctica B (CAL-B) and from Aspergillus niger higher conversion degrees and E-values were obtained with ethyl acetate as the acyl donor. When CAL-B was used as the biocatalyst, in a two-phase system formed by [BMIm][X]/dichloromethane or [BMIm][X]/chloroform, the selectivity was better than that obtained in pure organic solvents. The selectivity was found to be related to individual anions in ILs. In this reaction, the ion effectiveness in enhancing the enzyme selectivity followed the series: Cl⁻ > SCN⁻ > BF₄⁻ > PF₆⁻ in mixtures with dichloromethane, and PF₆⁻ > BF₄⁻ > SCN⁻ > Cl⁻ in mixtures with chloroform.     

Hydrothermal synthesis and structure of a Cu(I) bromide coordination polymer, [(tpyprz)3Cu10Br10] (tpyprz = tetra-2-pyridylpyrazine)

The hydrothermal reaction of CuBr₂ and tpyprz in the presence of NH₄VO₃ and HF for 72 h at 170 °C provided [(tpyprz)₃Cu₁₀Br₁₀] (1) in 20% yield. The two-dimensional structure of 1 may be described as Cu(I)-tpyprz chains, linked through {Cu₄Br₅}⁻ clusters in the ac-plane and decorated with {Cu₃Br₅}²⁻ clusters projecting from one face of the layer in the b-direction. The Cu(I) sites exhibit distorted trigonal coordination {CuBr₃} and distorted tetrahedral geometries, {CuBr₂N₂} and {CuN₄}. Crystal data for 1: monoclinic space group C2, a = 12.7561(8) Å, b = 19.359(1) Å, c = 15.860(1) Å, β = 97.178(1)°, V = 3885.8(4) Å³, Z = 2, D_calc = 2.222 g cm⁻³, μ(Mo Kα) = 78.75 cm⁻¹.     

Synthesis, structure, and magnetic properties of dinuclear nickel(II) complexes with a phenol-based dinucleating ligand with four methoxyethyl chelating arms

Dinuclear nickel(II) complexes [Ni₂(bomp)(MeCO₂)₂]BPh₄ (1) and [Ni₂(bomp)(PhCO₂)₂]BPh₄ (2) were synthesized with the dinucleating ligand 2,6-bis[bis(2-methoxyethyl)aminomethyl]-4-methylphenol [H(bomp)]. X-Ray analysis revealed that the complex 1 · 0.5CHCl₃ contains two nickel(II) ions bridged by phenolic oxygen and two acetate groups, forming a μ-phenoxo-bis(μ-acetato)dinickel(II) core. Electronic spectra were investigated for 1 and 2 in the range of 400-1800 nm, and the data were typical for the octahedral high-spin nickel(II) complexes. Obtained spectral components were well simulated based on the angular overlap model assuming the trigonally distorted octahedral geometry. Magnetic susceptibility was measured for 1 and 2 over a temperature range of 4.5-300 K. The optimized magnetic data were J = 1.75 cm⁻¹, zJ′ = −0.234 cm⁻¹, g = 2.21, D = 15.1 cm⁻¹, and TIP = 370 × 10⁻⁶ cm⁻¹ for complex 1 and J = 3.55 cm⁻¹, zJ′ = −0.238 cm⁻¹, g = 2.23, D = 21.8 cm⁻¹, and TIP = 470 × 10⁻⁶ cm⁻¹ for complex 2. The data revealed ferromagnetic interactions between the two nickel(II) ions.     

Ligand-to-ligand electron transfer and temperature induced valence tautomerism in o-dioxolene chelated manganese complexes

Three polymeric o-dioxolene chelated manganese(III) complexes, {[Mn^III(H₂L¹)(Cl₄Cat)₂][Mn^III(Cl₄Cat)₂(H₂O)₂]}_∞ (1) (L¹ = N,N′-bis(2-pyridylmethyl)-1,4-butanediamine, Cl₄Cat = tetrachlorocatecholate dianion], {[Mn^III(H₂L¹)(Br₄Cat)₂][Mn^III(Br₄Cat)₂(H₂O)₂]·4DMF}_∞, (2) and {[Mn^III(H₂L²)(Br₄Cat)₂][Mn^III(Br₄Cat)₂(DMF)₂]}_∞ (3) (L² = N,N′-bis(2-pyridylmethyl)-1,6-hexanediamine, Br₄Cat = tetrabromocatecholate dianion) have been synthesized and structures were determined by X-ray crystallography. All the complexes were fully characterized by various spectroscopic techniques and their electronic properties are described. It was found that the simple protonation or deprotonation of the bridging ligand (L¹ or L²) coordinated to metal-dioxolene chromophore induce a change in the oxidation state of the coordinated dioxolene ligand without affecting the metal oxidation state. As a result, drastic change in the optical absorption properties of the complexes is observed in the visible and near-IR region as the transformation involves semiquinone-catecholate ligands. Moreover, all three complexes undergo thermally induced valence tautomerism in solution. For all the complexes, on increasing the temperature, the intensity of the lower energy Inter Valence Charge Transfer (IVCT) band at about 1930 nm increases with corresponding decrease of 600 nm band with an isosbestic point at 1820 nm due to the formation of mixed valence species Mn^II(X₄SQ)(X₄Cat)⁻ from (X = Cl or Br) by the transfer of one electron from Cat²⁻ to Mn^III center.