Mono- and trichloride clathrochelate iron (II) chloroglyoximates and their functionalization: The effect of the substituents in the clathrochelate framework on the reactivity of the chlorine-containing fragments in nucleophilic substitution reactions

The direct template macrocyclization of the three chloroglyoxime molecules with boron-containing Lewis acids on the iron (II) ion matrix led to the formation of a mixture of fac- and mer-isomers of clathrochelate complexes in the 1:3 ratio, which is equal to a statistical one. The yields of tris-chloroglyoximate precursors (25-40%) were practically the same as those for their earlier-studied chloromethylglyoximate analogs, whereas the reactivity of the former complex has proved to be markedly higher than that of the latter clathrochelates: the triamine clathrochelates were the major products in the reaction of (mer + fac)-Fe(ClHGm)₃(BC₆H₅)₂ and (mer + fac)-Fe(ClHGm)₃(BF)₂ complexes with n-butylamine, whereas for (mer + fac)-Fe(ClCH₃Gm)₃(BC₆H₅)₂ clathrochelate an analogs reaction produced the diamine complex only. The mixture of the diamine clathrochelate isomers was obtained in both cases with less reactive cyclohexylamine. The reaction of the trichloride precursors with alkyl- and arylthiols in the presence of triethylamine has proceeded more readily and led to the formation of trisulfide clathrochelates.The monochloride FeBd₂(ClHGm)(BF)₂ complex, obtained by the condensation of the macrocyclic bis-dioximate [FeBd₂(BF₂)₂ (CH₃CN)₂] with chloroglyoxime, readily underwent the nucleophilic substitution of the reactive chlorine atom with amines and thiol-containing functionalizing agents. The clathrochelate complexes with pendant substituents, containing reactive terminal HO-, H₂N- and HS-groups, were obtained. Thiolate FeBd₂(H(HSCH₂CH₂S)Gm)(BF)₂ clathrochelate underwent the intramolecular elimination of ethylene sulfide in basic media to yield the clathrochelate with attached HS-group. Clathrochelates obtained have been characterized using elemental analysis, PD and MALDI-TOF mass, IR, UV-Vis, ⁵⁷Fe Mössbauer and ¹H, ¹³C and ¹¹B NMR spectroscopies, and X-ray crystallography (for the fac-Fe(ClHGm)₃(BC₆H₅)₂ and FeBd₂{H(CH₃S)Gm}(BF)₂ · 2C₆H₆ complexes). X-ray structure of a fac-isomer of clathrochelate complex was solved for the first time in this study. Configurations intermediate between trigonal prismatic and trigonal antiprismatic have been deduced for the low-spin iron (II) ion coordination polyhedra of all clathrochelates obtained using ⁵⁷Fe Mössbauer parameters.     

Template synthesis and structure of mono- and trisubstituted ribbed-functionalized iron(II) clathrochelates

The template condensation of three methylchloroglyoximate molecules with phenylboronic acid and with BF₃ · O(C₂H₅)₂ on an iron(II) ion afforded reactive trichloride phenylboron- and fluoroboron-capped precursors, respectively. The monochloride FeBd₂(CH₃ClGm)(BF)₂ precursor (where Bd²⁻ and CH₃ClGm²⁻ are α-benzyldioxime and methylchloroglyoxime dianions) was synthesized by condensation of macrocyclic iron(II) α-benzyldioximate FeBd₂(BF₂)₂(CH₃CN)₂ with CH₃ClGmH₂. Mono- and trifunctionalized amine, alkylsulfide, and arylsulfide clathrochelate iron(II) tris-dioximates were prepared starting from these precursors by nucleophilic substitution reactions. The complexes obtained were characterized using elemental analysis, PD mass, IR, UV-Vis, ¹H, ¹³C NMR, and ⁵⁷Fe Mössbauer spectra, and X-ray crystallography. An encapsulated low-spin iron(II) ion was found to have distorted trigonal-prismatic coordination N₆-environment in all clathrochelates synthesized.     

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

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

Synthesis, crystal structures and magnetic studies of terephthalato- and fumarato-bridged dinickel(II) complexes with tripodal poly-benzimidazole ligand

Two novel dinuclear nickel(II) complexes [Ni₂(ntb)₂(μ-tp)(H₂O)_1.61(CH₃OH)_0.39](NO₃)₂·5.13CH₃OH·2.25H₂O (1) and [Ni₂(ntb)₂(μ-fum)(H₂O)(CH₃OH)](NO₃)₂·6CH₃OH·H₂O (2) (tp = terephthalate dianion, fum = fumarate dianion, ntb = tris(2-benzimidazolylmethyl)amine) containing tetradentate poly-benzimidazole ligand were synthesized and structurally characterized by IR spectra, UV-Vis, elemental analysis and X-ray crystallography. The Ni(II) ions in 1 and 2 have distorted octahedral geometry with four nitrogen atoms of ntb, one oxygen atom of water and one oxygen atom supplied by the carboxylate group of the bridged dicarboxylato ligand. Complexes 1 and 2 consist of terephthalato- and fumarato-bridged dinickel(II) centers in bis(monodentate) bonding fashion. The Ni?Ni distances are 11.333 Å for 1 and 8.966 Å for 2. The magnetic susceptibility measurements at variable temperature show that two complexes exhibit weak antiferromagnetic interactions between nickel(II) ions with J values of −0.25 cm⁻¹ and −0.36 cm⁻¹, respectively.     

Synthesis, X-ray structure and redox properties of the macrobicyclic iron(II) N2- and S2-containing vic-dioximates

Nucleophilic substitution of the reactive chlorine atoms of the boron-capped macrobicyclic vic-di- and hexahalogen-containing iron(II) precursors with 1,2-ethanedithiol and 1,2-benzenedithiol in dichloromethane as a solvent in the presence of triethylamine as a strong organic base afforded the corresponding di- and hexasulfide mono- and triribbed-functionalized clathrochelates, respectively, in relatively high yields. In the case of the low-reactive tin-capped clathrochelate [Fe(Cl₂Gm)₃(SnCl₃)₂]²⁻ dianion this reaction was performed in DMF with the potassium salt of 1,2-benzenedithiol. The reaction of the dichlorine-containing FeBd₂(Cl₂Gm)(BF)₂ precursor with an excess of ethylenediamine in DMF led to the clathrochelate with N₂-containing vic-dioximate ribbed fragment. The complexes obtained were characterized using elemental analysis, MALDI-TOF mass spectrometry, IR, UV-vis, ¹H and ¹³C{¹H} NMR, ⁵⁷Fe Mössbauer spectroscopies, and X-ray crystallography.The nature and number of the ribbed substituents affect the geometry of a clathrochelate framework, first of all, the distortion of the trigonal prismatic-trigonal antiprismatic iron(II) coordination polyhedra, whereas the apical substituents at the capping boron atoms influe on the B-O distances in the apical RBO₃ fragments. The geometry of the tin-capped hexasulfide clathrochelate complex was deduced from EXAFS data using the scattering both on the encapsulated iron(II) and capping tin(IV) ions.The electrochemical properties of the iron(II) complexes obtained were studied by cyclic voltammetry. The electrochemically generated unstable reduced anionic forms are destabilized by the electron-donating ribbed substituents, whereas the oxidation led to the formation of the cationic macrobicycles, the stability of which depends on the nature of the apical capping groups and ribbed substituents as well. The pseudo-aromatic disulfide ribbed fragments stabilize the oxidized forms of the clathrochelate complexes.     

Synthesis, structures and magnetic properties of oxamido-bridged trinuclear Cu(II)-Mn(II)-Cu(II) complexes

Based on self-assembly of the dissymmetrical mononuclear entity CuL(CH₃OH) [H₂L = (E)-N¹-(2-((2-aminocyclohexydiimino)(phenyl)methyl)-4-chlorophenyl)-N²-(2-benzyl-4-chlorophenyl)oxalamide] with Mn(II), two trinuclear complexes were prepared. They are of the formula [(LCuN₃)₂Mn(CH₃OH)₂] · 2CH₃OH · 2H₂O (1) and [(LCuSCN)₂Mn(H₂O)₂] · 4CH₃OH (2). Their magnetic properties were studied by susceptibility versus temperature measurement, the best fitting of the experimental data led to J = −14.40 cm⁻¹ for 1 and J = −15.48 cm⁻¹ for 2. Hydrogen bonds help complex 1 to produce a novel S type one-dimensional chain-like supramolecular structure. In complex 2, Cl?Cl interaction also results in the formation of a one-dimensional structure.     

The preparation and structural elucidation of uranium (VI) complexes and salts of the phosphorus ylides Ph3PCHCOPh, Ph3PC(COMe)(COPh) and Ph3PCHCOOCH2CH3

The reaction in methanol of the phosphorus ylides Ph₃PCHCOPh, benzoylmethylenetriphenylphosphorane (BPPY), and Ph₃PC(COMe)(COPh), α-acetyl-α-benzoylmethylenetriphenylphosphorane (ABPPY) with UO₂(NO₃)₂ · 6H₂O at 273 K leads to the formation of O-coordinated bis(ylide)-uranium (VI) complexes of the type [UO₂(ylide)₂(NO₃)₂], whereas the reaction of BPPY and UO₂(NO₃)₂ · 6H₂O under reflux in benzene yields the salt . The reaction of Ph₃PCHCOOCH₂CH₃, carbethoxymethylenetriphenylphosphorane (EPPY) with UO₂(CH₃COO)₂ · 2H₂O produces the salt [H-EPPY]⁺[UO₂(CH₃COO)₃]⁻. The structures of the free ylides ABPPY and EPPY are also discussed.     

Metal complexes with the ligand derived from 6-acetyl-1,3,7-trimethyllumazine and benzohydrazide. Molecular structures of two new Co(II) and Rh(III) complexes and analysis of in vitro antitumor activity

The structures and spectroscopic properties of new Mn(II), Co(II), Cd(II), Hg(II), Ag(I), Rh(III), and Ir(I) complexes with the ligand BZLMH derived from 6-acetyl-1,3,7-trimethyllumazine (lumazine = pteridine-2,4(1H,3H)-dione) and benzohydrazide are reported. Complexes have been characterized by elemental analyses, spectroscopic studies (IR, UV-vis, ¹H, ¹³C and ¹⁵N NMR) and magnetic measurements. In all the complexes, the lumazine-derived ligand appears to be coordinated in either tridentate (N5, N61 and O63) or tetradentate forms (O4, N5, N61 and O63). The molecular structures of the [Co(BZLMH)(H₂O)(CH₃CN)₂](ClO₄)₂ · CH₃CN and [RhCl₂(BZLM)(CH₃CN)] · CH₃CN complexes, determined by single crystal X-ray diffraction, have allowed to corroborate both coordination behaviours.The cytotoxic activity of the free ligand and complexes against human neuroblastoma NB69 cell line is also described. The differential analysis of the initial cytotoxic screening data has shown good activity only for the [RhCl₂(BZLM)(CH₃CN)] · CH₃CN compound at concentrations at around 2 μM; for the other complexes, a modulation of the cell growth was not found upon complexation, this non-specific effect strongly suggesting an apoptotic behaviour.     

Formation and structural chemistry of the unusual cyanide-bridged dinuclear species [Ru2(NN)2(CN)7] (NN = 2,2′-bipyridine or 1,10-phenanthroline)

Crystallisation of simple cyanoruthenate complex anions [Ru(NN)(CN)₄]²⁻ (NN = 2,2′-bipyridine or 1,10-phenanthroline) in the presence of Lewis-acidic cations such as Ln(III) or guanidinium cations results, in addition to the expected [Ru(NN)(CN)₄]²⁻ salts, in the formation of small amounts of salts of the dinuclear species [Ru₂(NN)₂(CN)₇]³⁻. These cyanide-bridged anions have arisen from the combination of two monomer units [Ru(NN)(CN)₄]²⁻ following the loss of one cyanide, presumably as HCN. The crystal structures of [Nd(H₂O)_5.5][Ru₂(bipy)₂(CN)₇] · 11H₂O and [Pr(H₂O)₆][Ru₂(phen)₂(CN)₇] · 9H₂O show that the cyanoruthenate anions form Ru-CN-Ln bridges to the Ln(III) cations, resulting in infinite coordination polymers consisting of fused Ru₂Ln₂(μ-CN)₄ squares and Ru₄Ln₂(μ-CN)₆ hexagons, which alternate to form a one-dimensional chain. In [CH₆N₃]₃[Ru₂(bipy)₂(CN)₇] · 2H₂O in contrast the discrete complex anions are involved in an extensive network of hydrogen-bonding involving terminal cyanide ligands, water molecules, and guanidinium cations. In the [Ru₂(NN)₂(CN)₇]³⁻ anions themselves the two NN ligands are approximately eclipsed, lying on the same side of the central Ru-CN-Ru axis, such that their peripheries are in close contact. Consequently, when NN = 4,4′-^tBu₂-2,2′-bipyridine the steric bulk of the t-butyl groups prevents the formation of the dinuclear anions, and the only product is the simple salt of the monomer, [CH₆N₃]₂[Ru(^tBu₂bipy)(CN)₄] · 2H₂O. We demonstrated by electrospray mass spectrometry that the dinuclear by-product [Ru₂(phen)₂(CN)₇]³⁻ could be formed in significant amounts during the synthesis of monomeric [Ru(phen)(CN)₄]²⁻ if the reaction time was too long or the medium too acidic. In the solid state the luminescence properties of [Ru₂(bipy)₂(CN)₇]³⁻ (as its guanidinium salt) are comparable to those of monomeric [Ru(bipy)(CN)₄]²⁻, with a ³MLCT emission at 581 nm.     

Dinuclear iron, ruthenium and cobalt complexes containing 1,4-dimethyl-1,4,7-triazacyclononane ligands as well as carboxylato and oxo or hydroxo bridges

The reaction of 1,4-dimethyl-1,4,7-triazacyclononane (L-Me₂) with FeSO₄ · 7H₂O in aqueous ethanol gives, in the presence of sodium carboxylates, hydrogen peroxide, sodium hydroxide and KPF₆, the dinuclear Fe(III)-Fe(III) complex cations [(L-Me₂)₂Fe₂(O)(OOCR)₂]²⁺ (R = H: 1, R = CH₃: 2, R = C₆H₅: 3), which crystallise as the hexafluorophosphate salts. The corresponding reaction with RuCl₃ · nH₂O does not work, however, the analogous Ru(III)-Ru(III) complex [(L-Me₂)₂Ru₂(O)(OOCCH₃)₂]²⁺ (5) can be synthesised by reacting Ru(dmso)₄Cl₂ with L-Me₂, HCl and air in refluxing ethanol, followed by addition of sodium acetate, the mononuclear intermediate (L-Me₂)RuCl₃ · H₂O (4) being also isolated and characterised. The reaction of L-Me₂, sodium acetate, hydrogen peroxide and triethylamine with CoCl₂ · 6H₂O in acetonitrile yields, however, the hydroxo-bridged Co(III)-Co(III) complex [(L-Me₂)₂Co₂(OH)(OOCCH₃)₂]³⁺ (6). The molecular structures of 2, 5 and 6, solved by single-crystal X-ray structure analyses of the hexafluorophosphate salts, reveal for the orange crystals of [2][PF₆]₂ a Fe-Fe distance of 3.104(1) Å, for the purple crystals of [5][PF₆]₂ a Ru-Ru distance of 3.230(1) Å, and for the violet crystals of [6][PF₆]₃ · (CH₃)₂CO a Co-Co distance of 3.358(1) Å. All six complexes show catalytic activity for the oxidation of isopropanol with hydrogen peroxide in water to give acetone in the presence of ascorbic acid as co-catalyst.     

Synthesis, characterization, and magnetic properties of new homotrinuclear bis(oxamato) copper(II) complexes with an asymmetric central N,N′-bridge

The new mononuclear bis(oxamato) complex [n-Bu₄N]₂[Cu(obbo)] (1) (obbo=o-benzyl-bis(oxamato)) has been synthesized as a precursor for trinuclear oxamato-bridged transition metal complexes. Starting from 1 the homotrinuclear complexes [Cu₃(obbo)(pmdta)₂(NO₃)](NO₃)·CH₂Cl₂·H₂O (2) and [Cu₃(obbo)(tmeda)₂(NO₃)₂(dmf)] (3) have been prepared, where pmdta = N,N,N′,N″,N″-pentamethyldiethylenetriamine, tmeda = N,N,N′,N′-tetramethylethylenediamine and dmf = dimethylformamide. The crystal structures of 1-3 were solved. The magnetic properties of 2 and 3 were studied by susceptibility measurements versus temperature. For the intramolecular J parameter values of −111 cm⁻¹ (2) and −363 cm⁻¹ (3) were obtained.     

Two cobalt(II) one-dimensional ribbon of rings polymers: Syntheses, structures and non-linear optical properties

Two cobalt(II) coordination polymers {[Co(SCN)₂(3-bpit)₂] · 2CH₃OH}_n (1) (3-bpit = N,N′-bis(3-pyridylformyl)imidazolidine-2-thione) and {[Co(SCN)₂(4-bpit)₂] · CH₃OH · CH₃CN}_n (2) (4-bpit = N,N′-bis(4-pyridylformyl)imidazolidine-2-thione) have been synthesized for study of the third-order non-linear properties. X-ray crystal structural analyses reveal that the two polymers show the same topological motif: a ribbon of rings. Their third-order non-linear optical (NLO) properties in DMF solution have been studied by Z-scan techniques with a linearly polarized laser light (λ = 532 nm; pulse widths = 7 ns). Both of them exhibit strong self-focusing effect. The third-order NLO susceptibility χ⁽³⁾ values are calculated to be 2.61 × 10⁻¹¹ esu (1) and 2.76 × 10⁻¹¹ esu (2), respectively. The values are comparable to those of the reported good NLO materials.     

Influence of coanions on construction of copper(II)/4,4′-dipyridyl sulfide(dps) coordination polymers

The influence of coanion on self-assembly of CuSO₄ and 4,4′-dipyridyl sulfide (dps) was studied in this paper. During the formation of Cu(II)/dps coordination polymers, coanions Cl⁻, SCN⁻ and were added in the solution respectively. Three novel coordination polymers were obtained, {[Cu(dps)₂ · (SO₄)₂][Cu(dps) · Cl · (H₂O)₂]₂ · 12H₂O}_n (1 · 12H₂O, a 3D network), {[Cu(SCN)₂(dps)(CH₃OH)₂][Cu(dps)₂ · SO₄][Cu(dps)(CH₃CH₂OH)₂ · SO₄] · 5H₂O}_n (2 · 5H₂O, a 3D network), and {[Cu(dps)₂(H₂O)₂] · (PF₆)₂ · 3H₂O}_n (3 · 3H₂O, a 2D lattice network). Different coanion shows different influence on framework construction. In 1 and 2, Cl⁻ and SCN⁻ act as terminal ligands and similar 3D frameworks were composed of [Cu(dps)] layer with larger cavity (ca. 400 Å) and sulfate bridge; in 3, replaces entirely and the 3D framework was broken due to the removal of bridging anions. However, a 2D [Cu(dps)]₄ undulating grid was preserved in 3.     

Synthesis, crystal structures and magnetic properties of the copper(II) complexes containing isophthalate anion as coligand

Two new dinuclear isophthalato-bridged copper(II) complexes [Cu₂(ntb)₂(μ-ipt)](ClO₄)₂·4CH₃OH·0.33H₂O (1), [Cu₂(bbma)₂(μ-ipt)(NO₃)(CH₃OH)]NO₃·CH₃OH (2) and one mononuclear complex [Cu(bbma)(ipt)(CH₃OH)_0.67(H₂O)_0.33]·2CH₃OH (3) containing tetradentate and tridentate poly-benzimidazole ligands were synthesized, where ntb is tris(2-benzimidazolylmethyl)amine, bbma is bis(benzimidazol-2-yl-methyl)amine and ipt is isophthalate dianion. All of the complexes were characterized by elemental analysis, IR spectra and X-ray crystallography. The structures of complexes 1 and 2 consist of μ-ipt bridging two Cu(II) centers in a bis(monodentate) bonding fashion. The coordination geometry around the Cu(II) ions of both compounds has a distorted square pyramidal geometry. The Cu···Cu distances are 9.142 and 10.435 Å for 1 and 2, respectively. Complex 3 has a distorted square pyramidal geometry achieved by the three N-atoms of the bbma ligand, one isophthalate-oxygen atom and one oxygen atom from a coordinated methanol molecule. The magnetic susceptibility measurements at variable temperature over the 2-300 K range for complexes 1 and 2 are reported, with J values to be −0.013 and −0.32 cm⁻¹, respectively. The results show that the two complexes exhibit very weak antiferromagnetic interactions between the dinuclear copper(II) centers.     

Bioinspired FeIIICdII and FeIIIHgII complexes: synthesis, characterization and promiscuous catalytic activity evaluation

In this work we report on the synthesis, crystal structure, and physicochemical characterization of the novel dinuclear [Fe^IIICd^II(L)(μ-OAc)₂]ClO₄·0.5H₂O (1) complex containing the unsymmetrical ligand H₂L = 2-bis[{(2-pyridyl-methyl)-aminomethyl}-6-{(2-hydroxy-benzyl)-(2-pyridyl-methyl)}-aminomethyl]-4-methylphenol. Also, with this ligand, the tetranuclear [Fe₂^IIIHg₂^II(L)₂(OH)₂](ClO₄)₂·2CH₃OH (2) and [Fe^IIIHg^II(L)(μ-CO₃)Fe^IIIHg^II(L)](ClO₄)₂·H₂O (3) complexes were synthesized and fully characterized. It is demonstrated that the precursor [Fe^III₂Hg^II₂(L)₂(OH)₂](ClO₄)₂·2CH₃OH (2) can be converted to (3) by the fixation of atmospheric CO₂ since the crystal structure of the tetranuclear organometallic complex [Fe^IIIHg^II(L)(μ-CO₃)Fe^IIIHg^II(L)](ClO₄)₂·H₂O (3) with an unprecedented {Fe^III(μ-O_phenoxo)₂(μ-CO₃)Fe^III} core was obtained through X-ray crystallography. In the reaction 2 → 3 a nucleophilic attack of a Fe^III-bound hydroxo group on the CO₂ molecule is proposed. In addition, it is also demonstrated that complex (3) can regenerate complex (2) in aqueous/MeOH/NaOH solution. Magnetochemical studies reveal that the Fe^III centers in 3 are antiferromagnetically coupled (J = − 7.2 cm^− 1) and that the Fe^III-OR-Fe^III angle has no noticeable influence in the exchange coupling. Phosphatase-like activity studies in the hydrolysis of the model substrate bis(2,4-dinitrophenyl) phosphate (2,4-bdnpp) by 1 and 2 show Michaelis-Menten behavior with 1 being ~ 2.5 times more active than 2. In combination with k_H/k_D isotope effects, the kinetic studies suggest a mechanism in which a terminal Fe^III-bound hydroxide is the hydrolysis-initiating nucleophilic catalyst for 1 and 2. Based on the crystal structures of 1 and 3, it is assumed that the relatively long Fe^III…Hg^II distance could be responsible for the lower catalytic effectiveness of 2.     

Discrete and 1D coordination polymeric chloro-bridged copper(II) dimers exhibiting ferro- and antiferromagnetic exchange coupling: Magneto-structural correlations and non-covalent interactions

The synthesis and characterization of two 1D coordination polymers [Cu₂(MHL)Cl₂][ClO₄]₂ · CH₃CN · THF (2 · CH₃CN · THF) and [Cu₂(MPyPz)Cl₂][ClO₄]₂ · CH₃CN (3 · CH₃CN), having repetitive units, of m-xylyl-based ligands with terminal tridentate (2-pyridyl)alkylamine (MHL = α,α′-bis[N-(2-pyridylethyl)-N-(2-pyridylmethyl)amino]-m-xylene) and (2-pyridyl)alkylamine/pyrazole (MPyPz = α,α′-bis[N-(2-pyridylethyl)-N-(pyrazol-1-ylmethyl)amino]-m-xylene) coordination have been accomplished. X-ray crystallographic studies reveal that the copper(II) centers in the recently reported dichloro-bridged discrete complex [{Cu(MeL)Cl}₂][ClO₄]₂ (1) of a tridentate (2-pyridyl)alkylamine ligand [MeL = methyl[2-(2-pyridyl)ethyl](2-pyridylmethyl)amine], 2 · CH₃CN · THF, and 3 · CH₃CN have distorted square-pyramidal geometry, sharing a base-to-apex edge with parallel basal planes. Variable-temperature susceptibility measurements in the range of 2-300 K reveal antiferromagnetic for 1 [J (singlet-triplet energy gap) = −3.89 cm⁻¹] and 2 · CH₃CN · THF (J = −1.84 cm⁻¹), and ferromagnetic for 3 · CH₃CN (J = +6.27 cm⁻¹) coupling. The complexes provide useful information for the magneto-structural correlations.     

Cyclic and acyclic compartmental Schiff bases, their reduced analogues and related mononuclear and heterodinuclear complexes

[1+1] macrocyclic and [1+2] macroacyclic compartmental ligands (H₂L), containing one N₂O₂, N₃O₂, N₂O₃, N₄O₂ or O₂N₂O₂ Schiff base site and one O₂O_n (n=3, 4) crown-ether like site, have been prepared by self-condensation of the appropriate formyl- and amine precursors. The template procedure in the presence of sodium ion afforded Na₂(L) or Na(HL) · nH₂O. When reacted with the appropriate transition metal acetate hydrate, H₂L form M(L) · nH₂O, M(HL)(CH₃COO) · nH₂O, M(H₂L)(X)₂ · nH₂O (M=Cu²⁺, Co²⁺, Ni²⁺; X=CH₃COO⁻, Cl⁻) or Mn(L)(CH₃COO) · nH₂O according to the experimental conditions used. The same complexes have been prepared by condensation of the appropriate precursors in the presence of the desired metal ion. The Schiff bases H₂L have been reduced by NaBH₄ to the related polyamine derivatives H₂R, which form, when reacted with the appropriate metal ions, M(H₂R)(X)₂ (M= Co²⁺, Ni²⁺; X=CH₃COO⁻, Cl⁻), Cu(R) · nH₂O and Mn(R)(CH₃COO) · nH₂O. The prepared ligands and related complexes have been characterized by IR, NMR and mass spectrometry. The [1+1] cyclic nature of the macrocyclic polyamine systems and the site occupancy of sodium ion have been ascertained, at least for the sodium (I) complex with the macrocyclic ligand containing one N₃O₂ Schiff base and one O₂O₃ crown-ether like coordination chamber, by an X-ray structural determination. In this complex the asymmetric unit consists of one cyclic molecule of the ligand coordinated to a sodium ion by the five oxygen atoms of the ligand. The coordination geometry of the sodium ion can be described as a pentagonal pyramid with the metal ion occupying the vertex. In the mononuclear complexes with H₂L or H₂R the transition metal ion invariantly occupies the Schiff base site; the sodium ion, on the contrary, prefers the crown-ether like site. Accordingly, the heterodinuclear complexes [MNa(L)(CH₃COO)_x] (M=Cu²⁺, Co²⁺, Ni², x=1; M=Mn³⁺, x=2) have been synthesised by reacting the appropriate formyl and amine precursors in the presence of M(CH₃COO)_n · nH₂O and NaOH in a 1:1:1:2 molar ratio. The reaction of the mononuclear transition metal complexes with Na(CH₃COO) · nH₂O gives rise to the same heterodinuclear complexes. Similarly [MNa(R)(CH₃COO)_x] have been prepared by reaction of the appropriate polyamine ligand H₂R with the desired metal acetate hydrate and NaOH in 1:1:2 molar ratio.     

Synthesis, structures, and magnetic properties of dicopper(II) and dinickel(II) complexes with a new bis(macrocycle), 7,7-(2-hydoxypropane-1,3-diyl)bis{3,7,11,17-tetraazabicyclo[11.3.1]- heptadeca-1(17),13,15-triene}

A new bis(macrocycle) ligand, 7,7^′-(2-hydoxypropane-1,3-diyl)-bis{3,7,11,17-tetraazabicyclo[11.3.1]heptadeca-1(17),13,15-triene} (HL), and its dicopper(II) ([Cu₂(HL)Cl₂](NO₃)₂ · 4H₂O (4a), [Cu₂(HL)I₂]I₂ · H₂O (4b)) and dinickel(II) ([Ni₂(L)(OH₂)](ClO₄)₃ (5a), [Ni₂(L)(OH₂)]I₃ · 2H₂O (5b), [Ni₂(L)N₃](N₃)₂ · 7H₂O (5c)) complexes have been synthesized. The alkoxide bridged face-to-face structure of the dinickel(II) complex 5c has been revealed by X-ray crystallography, as well as the “half-opened clamshell” form of the bis(macrocyclic) dicopper(II) complex 4b. Variable temperature magnetic susceptibility studies have indicated that there exists intramolecular antiferromagnetic coupling (J=−33.8 cm⁻¹ (5a), −32.5 cm⁻¹ (5b), and −29.7 cm⁻¹ (5c)) between the two nickel(II) ions in the nickel(II) complexes.     

Preparation, structures and properties of dinuclear and trinuclear copper(II) complexes bridged by one oximato and one hydroxo ligands

The dinuclear and trinuclear copper(II) complexes [Cu₂(L)(OH)(ClO₄)(phen)(H₂O)]ClO₄ · [Cu₂(L)(OH)(ClO₄)₂(phen)(CH₃OH)] (1) and [Cu₃(L)₂(OH)₂(H₂O)₂](NO₃)₂ (2) (HL=2-[2-(α-pyridyl)ethyl]imino-3-butanone oxime and phen=1,10-phenanthroline) were prepared and their crystal structures have been determined by X-ray crystallography. Complex 1 is composed of [Cu₂(L)(OH)(ClO₄)(phen)(H₂O)]ClO₄ (1a) and [Cu₂(L)(OH)(ClO₄)₂(phen)(CH₃OH)] (1b). In 1a and 1b, one oximato of L and one hydroxo group bridge two copper(II) ions. The linear trinuclear cation [Cu₃(L)₂(OH)₂(H₂O)₂]²⁺ in 2 is centrosymmetric, and one oximato and one hydroxo group bridge the central and terminal copper(II) ions. The strong antiferromagnetic interactions within the dinuclear and trinuclear complexes 1 and 2 have been observed (2J=∼−900 cm⁻¹ for 1 and 2, respectively, H=−2JS₁·S₂).     

Structural and equilibrium studies on mixed ligand complexes of Co(II), Ni(II), Cu(II) and Zn(II) with N-(2-benzimidazolyl)methyliminodiacetic acid and typical N, N donor ligands

Mixed ligand complexes: [Co(L)(bipy)] · 3H₂O (1), [Ni(L)(phen)] · H₂O (2), [Cu(L)(phen)] · 3H₂O (3) and [Zn(L)(bipy)] · 3H₂O (4), where L²⁻ = two -COOH deprotonated dianion of N-(2-benzimidazolyl)methyliminodiacetic acid (H₂bzimida, hereafter, H₂L), bipy = 2,2′ bipyridine and phen = 1,10-phenanthroline have been isolated and characterized by elemental analysis, spectral and magnetic measurements and thermal studies. Single crystal X-ray diffraction studies show octahedral geometry for 1, 2 and 4 and square pyramidal geometry for 3. Equilibrium studies in aqueous solution (ionic strength I = 10⁻¹ mol dm⁻³ (NaNO₃), at 25 ± 1 °C) using different molar proportions of M(II):H₂L:B, where M = Co, Ni, Cu and Zn and B = phen, bipy and en (ethylene diamine), however, provides evidence of formation of mononuclear and binuclear binary and mixed ligand complexes: M(L), M(H₋₁L)⁻, M(B)²⁺, M(L)(B), M(H₋₁L)(B)⁻, M₂(H₋₁L)(OH), (B)M(H₋₁L)M(B)⁺, where H₋₁L³⁻ represents two -COOH and the benzimidazole N₁-H deprotonated quadridentate (O⁻, N, O⁻, N), or, quinquedentate (O⁻, N, O⁻, N, N⁻) function of the coordinated ligand H₂L. Binuclear mixed ligand complex formation equilibria: M(L)(B) + M(B)²⁺ ? (B)M(H₋₁L)M(B)⁺ + H⁺ is favoured with higher π-acidity of the B ligands. For Co(II), Ni(II) and Cu(II), these equilibria are accompanied by blue shift of the electronic absorption maxima of M(II) ions, as a negatively charged bridging benzimidazolate moiety provides stronger ligand field than a neutral one. Solution stability of the mixed ligand complexes are in the expected order: Co(II) < Ni(II) < Cu(II) > Zn(II). The Δ log K_M values are less negetive than their statistical values, indicating favoured formation of the mixed ligand complexes over the binary ones.