Diferrocenes containing thiadiazole connectivities

2,5-Diferrocenyl-1,3,4-thiadiazole, 2,5-Fc₂-^cC₂N₂S, (3) has been synthesized by a two-fold Negishi ferrocenylation of dibromothiadiazole (1) with FcZnCl (2) (Fc = Fe(η⁵-C₅H₄)(η⁵-C₅H₅)) in presence of [Pd(Ph₃P)₄] as catalyst. Additional spacer units between the ferrocenyls and the ^cC₂N₂S core could be introduced by using the Sonogashira C,C cross-coupling protocol. Reaction of 2,5-Br₂-^cC₂N₂S (1) or 2,5-(C₆H₄-4′-I)₂-^cC₂N₂S (6) with FcCCH (4) using [PdCl₂(Ph₃P)₂] and [CuI] as catalyst produced the appropriate organometallics 2,5-(FcCC)₂-^cC₂N₂S (5) or 2,5-(C₆H₄-4′-CCFc)₂-^cC₂N₂S (7). The electronic and structural properties of 3, 5, and 7 were investigated with UV-Vis spectroscopy and single crystal X-ray diffraction (3). Complex 3 adopts a solid state structure with none of the ferrocenyl substituents being coplanar with the thiadiazole ring. Cyclic, square wave, linear sweep voltammetry and in-situ NIR spectro-electrochemistry highlight the electrochemical properties of 3. In dichloromethane (0.1 mol L⁻¹ [N(ⁿBu)₄][B(C₆F₅)₄]), compound 3 displays two well resolved electrochemical reversible one-electron events with formal reduction potentials of 0.192 and 0.338 V versus FcH/FcH⁺. In contrast, in presence of [N(ⁿBu)₄][PF₆], the thiadiazoles 3 (E⁰ = 0.22 V), 5 (E⁰ = 0.18 V) and 7 (E⁰ = 0.09 V) show simultaneously oxidation of the two ferrocenyl termini versus FcH/FcH⁺. Spectro-electrochemical studies, performed in a dichloromethane solution of 0.2 mol L⁻¹ [N(ⁿBu)₄][B(C₆F₅)₄], also show that 3 can successively be oxidized via 3⁺ to 3²⁺. A weak IVCT absorption (ε ca. 300 L mol⁻¹ cm⁻¹) at 1560 nm was found and is consistent with appreciable interactions between neutral ferrocenyl and positively charged ferrocenium mixed valent intermediates. Mixed-valent compound 3⁺ corresponds to a class II molecule according to Robin and Day.     

Synthesis, characterization, and magnetic properties of new binuclear CuCu bis(oxamato) complexes

Two new neutral, binuclear Cu^IICu^II bis(oxamato) complexes with the formula [Cu₂(opba)(pmdta)(MeOH)] · 1/2MeOH · dmf (3) and [Cu₂(nabo)(pmdta)(MeOH)] (4), with opba = o-phenylene-bis(oxamato), nabo = 2,3-naphthalene-bis(oxamato), pmdta = N,N,N′,N″,N″-pentamethyldiethylenetriamine and dmf = dimethylformamide have been synthesized and their crystal structures have been determined. The structure of 3 consists of dimeric [Cu₂(opba)(pmdta)(MeOH)] entities, joined together by mutual intermolecular Cu?O contacts of the Cu²⁺ ion of one [Cu(opba)]²⁻ complex fragment and one carboxylate atom of the oxamato group of a second [Cu(opba)]²⁻ complex fragment. The structure of 4 consists of neutral binuclear complexes joined together by hydrogen bonds and π-π interactions, giving rise to an unique supramolecular 1D-chain. The magnetic properties of 3 and 4 were studied by susceptibility measurements versus temperature. For the intramolecular J parameter, identical values of (−114 ± 2) cm⁻¹ (3) and (−112 ± 2) cm⁻¹ (4) were obtained.     

The synthesis and characterisation of phenolate complexes of Cu(II) and Ni(II) that are capable of supporting a phenoxyl radical ligand

New Cu^II and Ni^II complexes of potentially tridentate N₂O Schiff base ligands 1 and 2 have been synthesised and characterised. [Cu(2)(OH₂)]⁺ possesses a square planar geometry in the solid state whereas [Ni(1)₂] possesses a distorted octahedral geometry in which the amine donors of 1 coordinate weakly to the Ni^II centre. EPR spectroscopy demonstrates that the N₂O₂ coordination sphere of [Cu(2)(OH₂)]⁺ is retained in CH₂Cl₂ solution. [Cu(2)(OH₂)]⁺ exhibits a reversible one electron oxidation at E_1/2 = 0.54 V versus [Fc]⁺/[Fc], the product of which has been characterised by UV-Vis absorption and EPR spectroscopies. The spectroscopic signature of the oxidised product is consistent with the formation of a stable phenoxyl radical ligand bound to a Cu^II centre. [Ni(1)₂] possesses a reversible metal-based oxidation process at E_1/2 = 0.03 V versus [Fc]⁺/[Fc] and a further oxidation, attributed to the generation of a phenoxyl radical centre, at  = 0.44 V versus [Fc]⁺/[Fc]. UV-Vis absorption and EPR spectroscopic studies indicate that the lower potential process is a formal Ni^III/II couple. In contrast, the pro-ligands 1H and 2H exhibit chemically irreversible oxidation processes at  = 0.42 and 0.40 V versus Fc⁺/Fc, respectively, and do not support the formation of stable phenoxyl radical species.     

Synthesis, characterization, crystal structures and magnetic properties of dissymmetrical double schiff base heterotrinuclear complexes: [CuL(H2O)CoCuL] · H2O · CH3OH and [(CuL)2Ni] · 2H2O

A dissymmetrical double Schiff base Cu(II) mononuclear complex: CuHL (1) (where H₃L is N-3-carboxylsalicylidene-N^′-salicylaldehyde-1,2-diaminoethane) and two trinuclear complexes: [CuL(H₂O)CoCuL] · H₂O · CH₃OH (2) and [(CuL)₂Ni] · 2H₂O (3) have been synthesized and characterized by means of elemental analyses, IR and electronic spectra. The crystal structures of two heterotrinucler complexes were determined by X-ray analysis. Each dissymmetrical cell unit of the complex 2 contains two heterotrinucler neutral molecules. In each neutral molecule, the central Co²⁺ ion is located at the site of O₆ with a distorted octahedral geometry and one terminal Cu²⁺ ion at the four-coordination site of N₂O₂, but the other one at the square-pyramidal environment of N₂O₃. Each dissymmetrical unit of the complex 3 contains a heterotrinucler neutral molecule, whose structure is similar to that of 2 except two terminal Cu²⁺ ions both at the inner site of N₂O₂. The magnetic properties of two heterotrinucler complexes have been determined in the temperature range of 5-300 K, which indicate that the interaction between the central Co²⁺ ion or Ni²⁺ ion and the outer Cu²⁺ ions is antiferromagnetic. The exchange integrals are equal to −26.2 cm⁻¹ for 2 and −50.6 cm⁻¹ for 3.     

A water-soluble ribosyl-based fluorescent sensor for Hg and Cu ions

A water-soluble ribosyl-based fluorescent sensor 5 was prepared. The sensor contains an anthracene as the fluorophore and a set of complex groups as recognition sites, which bears two triazole ring spacers linked to two ribosyl carboxylic acids groups. The association constants of 5 in water are 2.15 × 10⁵ M⁻¹ and 9.57 × 10⁴ M⁻¹ for Cu²⁺ and Hg²⁺ ions, respectively, and both metals formed complexes with 5 at a 1:1 metal to ligand ratio. The binding of 5 to Cu²⁺ shows a broad pH range (5-10) and a low detection limit (57 ppb) in water, thus indicating it an efficient and promising cation probe.     

UV-Vis and fluorimetric Al, Zn, Cd and Pb complexation studies of two 3-hydroxyflavones and a 3-hydroxythioflavone

The complexation of Al³⁺, Zn²⁺, Cd²⁺ and Pb²⁺ by the 3-hydroxyflavones: 3-hydroxy-2-(2-methoxyphenyl)-4H-1-benzopyran-4-one (H1) and 3-hydroxy-2-(4-methoxyphenyl)-4H-1-benzopyran-4-one (H2), and by the 3-methoxythioflavone: 3-hydroxy-2-(2-methoxyphenyl)-4H-1-benzopyran-4-thione (H3) have been studied spectrophotometrically and fluorimetrically to determine the corresponding complexation constants, K_sp and K_fl, in 5:95 water:ethanol (v/v) solution for which [HClO₄] was either 10⁻² or 10⁻⁵ mol dm⁻³ and I = 0.10 mol dm⁻³ (NaClO₄) at 298.2 K. Complexation occurs dominantly through the deprotonated ligand for [Al(1)]²⁺ and [Al(2)]²⁺ for which log K_sp = 4.51 and 4.73, respectively, in 10⁻² mol dm⁻³ HClO₄ and 4.21 and 4.61 in 10⁻⁵ mol dm⁻³ HClO₄. For Pb²⁺ complexation by H1, H2 and H3 is characterized by log K_sp = 2.20, 2.57 and 3.22, respectively, in 10⁻² mol dm⁻³ HClO₄ and 4.70, 5.38 and 5.74 in 10⁻⁵ mol dm⁻³ HClO₄. Equilibrium mixtures of [Pb(H1)]²⁺ and [Pb1]⁺, [Pb(H2)]²⁺ and [Pb2]⁺, and [Pb(H3)]²⁺ and [Pb3]⁺ appear to be formed. Complexation of Zn²⁺ and Cd²⁺ by all three ligands was only detected in 10⁻⁵ mol dm⁻³ HClO₄. For Zn²⁺ complexation by H1, H2 and H3 log K_sp = 3.22, 3.74 and 4.46 and for Cd²⁺ the corresponding values are 2.39, 2.40 and 3.72 for Cd²⁺. Only [Al1]²⁺ and [Al2]²⁺ show significant fluorescence and are characterized by log K_fl = 6.30 and 7.49 in 10⁻² mol dm⁻³ HClO₄.     

Syntheses, crystal structures and magnetic properties of trinuclear and [3 × 1 + 1 × 2] pentanuclear complexes derived from a compartmental ligand: Role of solvent on nuclearity and number of components

Reaction of [Cu^IIL⊂(H₂O)] (H₂L = N,N′-ethylenebis(3-ethoxysalicylaldimine)) with nickel(II) perchlorate in 1:1 ratio in acetone produces the trinuclear compound [(Cu^IIL)₂Ni^II(H₂O)₂](ClO₄)₂ (1). On the other hand, on changing the solvent from acetone to methanol, reaction of the same reactants in same ratio produces the pentametallic compound [(Cu^IIL)₂Ni^II(H₂O)₂](ClO₄)₂·2[Cu^IIL⊂(H₂O)]·2MeOH (2A), which loses solvated methanol molecules immediately after its isolation to form [(Cu^IIL)₂Ni^II(H₂O)₂](ClO₄)₂·2[Cu^IIL⊂(H₂O)] (2B). Clearly, formation of 1 versus 2A and 2B is solvent dependent. Crystal structures of 1 and 2A have been determined. Interestingly, compound 2A is a [3 × 1 + 1 × 2] cocrystal. The cryomagnetic profiles of 1 and 2B indicate that the two pairs of copper(II)···nickel(II) ions in the trinuclear cores in both the complexes are coupled by almost identical moderate antiferromagnetic interaction (J = −22.8 cm⁻¹ for 1 and −26.0 cm⁻¹ for 2B).     

Dicopper(II) and dinickel(II) complexes of Schiff-base macrocycles derived from 5,5-dimethyl-1,9-diformyldipyrromethane

The synthesis and characterisation of two dicopper(II) and two dinickel(II) macrocyclic complexes, [Cu^II₂L^Pr] (10), [Cu^II₂L^Bu] (11), [Ni^II₂L^Pr] (12) and [Ni^II₂L^Bu] (13), are reported. The two new Schiff-base macrocycles (L^Pr)⁴⁻ and (L^Bu)⁴⁻ are isolated as dimetallic complexes 10-13 by the [2+2] condensation of 5,5-dimethyl-1,9-diformyldipyrromethane (9) and 1,3-diaminopropane or 1,4-diaminobutane, respectively, using Cu²⁺ or Ni²⁺ template ions. Single crystal X-ray structure determinations carried out on 10-13 show that each metal atom is in a square planar N₄ geometry, being bound to two deprotonated pyrrole nitrogen atoms of one dipyrromethane unit and to the two adjacent imine nitrogen atoms. NMR spectra obtained for the two dinickel(II) complexes 12 and 13 show that in CDCl₃ solution they are highly symmetrical and diamagnetic.     

The effects of point of substitution on the electrochemical behavior of new manganese phthalocyanines, tetra-substituted with diethylaminoethanethiol

The syntheses and comparative studies of the spectral, voltammetry and spectroelectrochemical properties of new manganese phthalocyanine complexes, tetra-substituted with diethylaminoethanethio at the peripheral (complex 3a) and non-peripheral positions (complex 3b) are reported. Solution electrochemistry of complex 3a showed quasi-reversible metal-based (Mn^IIIPc⁻²/Mn^IIPc⁻², E_1/2 = −0.07 V vs. Ag|AgCl) and ring-based (Mn^IIPc⁻²/Mn^IIPc⁻³, E_1/2 = −0.78 V vs. Ag|AgCl) reductions, but no ring-based oxidation. However, complex 3b showed weak irreversible ring-oxidation signal (E_p = +0.86 vs. Ag|AgCl). Reversible metal-based (Mn^IIIPc⁻²/Mn^IIPc⁻², E_1/2 = −0.04 V vs. Ag|AgCl) and ring-based (Mn^IIPc⁻²/Mn^IIPc⁻³, E_1/2 = −0.68 V vs. Ag|AgCl) reductions were also observed for complex 3b. Spectroelectrochemistry was used to confirm these processes. Reduction process involving the metal (Mn^IIIPc⁻²/Mn^IIPc⁻²) was associated with the formation of manganese μ-oxo complex in complex 3a.     

Copper complexes of tripodal κN-donor ligands: A structural, EPR spectroscopic and electrochemical study

A new tris(pyridylhydrazonyl)methane ligand, HC[N(Me)NC(H)Py]₃ (L2) (Py = pyridyl), has been synthesized. The latter is accessible from triethyl orthoformate and 2-(2-methylhydrazono)methylpyridine in 63% isolated yield. We have investigated its coordination chemistry towards copper ions and compared the results with those obtained for the recently developed multifunctional ligand, (S)P[N(Me)NC(H)Py]₃ (L1). The copper(II) complexes [Cu(L1)](OTf)₂ (3) and [Cu(L2)](OTf)₂ (4) (OTf = triflate, (O₃SCF₃)⁻) are mononuclear with the cations coordinated by three imino and three pyridine nitrogen atoms. Almost axial symmetric EPR spectra have been obtained in frozen solutions at X-band. The spectra show resolved hyperfine couplings to the copper nuclei on one of the three g values. X-ray structural analyses revealed in each case a cis bond distortion and a trigonal twist due to Jahn-Teller effects. The Cu^II/Cu^I reduction potentials of 3 and 4 were shown to be remarkably low ( = −0.11 V for 3;  = −0.34 V for 4), especially for 3 consisting of the phosphorus supported ligand L1. The corresponding copper(I) complexes [Cu(L1)](OTf) (5) and [Cu(L2)](OTf) (6) are accessible by reduction using decamethyl ferrocene. Both copper(I) complexes have been characterized in detail including X-ray structure analyses.     

Synthesis, characterization and crystal structure of a novel 2D network structure based on hexacopper(II) substituted tungstoantimonate

The dimeric, hexacopper(II) substituted tungstoantimonate NaK₆[Cu₆Cl(SbW₉O₃₃)₂] · 14H₂O (1a) has been synthesized in good yield using a one-pot procedure by reaction of Cu²⁺ ions with the trilacunary precursor salt Na₉[α-B-SbW₉O₃₃] and characterized by IR spectroscopy, UV electronic spectroscopy, cyclic voltammetry and single-crystal X-ray diffraction. The title polyanion represents the first tungstoantimonate substituted by six copper centers and the polyanion as basic building unit is assembled into a two-dimensional network-like complex by Cu-OW bonds. The electrochemical behavior of 1a was investigated in buffer solution (pH 3.0) by cyclic voltammetry. In the potential range between −0.7 and 0.6 V, the compound exhibits the successive redox processes of the addenda atoms (W) followed by the redox reaction originating from the substituted Cu^II, which revealed the stepwise reduction of Cu²⁺ centers within the polyanion 1 before deposition of Cu⁰ on the glassy carbon electrode surface. The compound 1a is shown to have electrocatalytic properties towards the reductions of nitrate and nitrite.     

Bidentate guanidine ligands with ethylene spacer in copper-dioxygen chemistry: Structural characterization of bis(μ-hydroxo) dicopper complexes

The syntheses of the aliphatic bidentate guanidine-amine-hybrid ligands DMEGdmae (L1), TMGdmae (L2), TMGdeae (L3) and DPipGdmae (L4) as well as the reaction of their Cu(I) complexes with molecular oxygen (monitored by UV-Vis spectroscopy) are reported. The molecular structures of 10 bis(μ-hydroxo) dicopper complexes based on these ligands are described. The solid state structures of [Cu₂(μ-OH)₂(DMEGdmae)₂]X₂ (X⁻ = I⁻ (1), CF₃SO₃⁻ (2), SbF₆⁻ (3), PF₆⁻ (4)), [Cu₂(μ-OH)₂(TMGdmae)₂]X₂ (X⁻ = I⁻ (5), CF₃SO₃⁻ (6)), [Cu₂(μ-OH)₂(TMGdeae)₂]Cu₂I₄ (7) and [Cu₂(μ-OH)₂(DPipGdmae)₂]X₂ (X⁻ = CF₃SO₃⁻ (8), SbF₆⁻ (9), PF₆⁻ (10)) show a square-planar distorted coordination of the copper(II) ion. The bis(μ-hydroxo) dicopper complex 1 exhibits a Cu···Cu distance of 2.860(1) Å, which is one of the smallest observed for hydroxo-bridged copper compounds so far. The influence of the anion on the structure of the bis(μ-hydroxo) dicopper(II) unit is analyzed for the reported complexes and a literature overview with emphasis on the structural characteristics of the Cu₂O₂ moiety of bis(μ-hydroxo) dicopper(II) and bis(μ-oxo) dicopper(III) is given.     

Co and Cu complexes of reduced Schiff bases: Generation of phenoxyl radical species

The three complexes [Co^IIIL¹Cl] (1), [Co^IIIL²]⁺·ClO₄⁻ (2⁺·ClO₄⁻), and [Cu^IIH₂L²]²⁺·2ClO₄⁻ (H₂3²⁺·2ClO₄⁻) [where H₂L¹ = N,N′-dimethyl-N,N′-bis(2-hydroxy-3,5-di-tert-butylbenzyl)ethylenediamine, H₂L² = N,N′-bis(2-pyridylmethyl)-N,N′-bis(2-hydroxy-3,5-di-tert-butylbenzyl)ethylenediamine] have been prepared. The bis-phenolate and bis-phenol complexes, 2⁺ and H₂3²⁺ respectively, have been characterized by X-ray diffraction, showing a metal ion within an elongated octahedral geometry. 1-2 exhibit in their cyclic voltammetry curves two anodic reversible waves attributed to the successive oxidation of the phenolates into phenoxyl radicals. The cobalt radical species (1)⁺, (2)²⁺, and (2)³⁺ have been characterized by combined UV-Vis and EPR spectroscopies. In the presence of one equivalent of base, one phenolic arm of H₂3²⁺ is deprotonated and coordinates the metal. The resulting complex (H3⁺) exhibits a single reversible redox wave at ca. 0.3 V. The electrochemically generated oxidized species is EPR silent and exhibits the typical features of a radical compound, with absorption bands at 411 and 650 nm. The fully deprotonated complex 3 is obtained by addition of two equivalents of nBu₄N⁺OH⁻ to H₂3²⁺. It exhibits a new redox wave at a lower potential (−0.16 V), in addition to the wave at ca. 0.3 V. We assigned the former to the one-electron oxidation of the uncoordinated phenolate into an unstable phenoxyl radical.     

Copper(II) complexes derived from tripodal tris[(2-ethyl-(1-pyrazolyl)]amine

Three mono-nuclear copper(II) complexes [Cu(tepza)X]ClO₄ (X = Cl, 1; X = NCS, 2; X = dca, 3) and two dinuclear bridging complexes [Cu₂(tepza)₂(μ-C₄O₄)](ClO₄)₂·H₂O(4) and [Cu₂(tepza)₂(μ-C₅O₅)](ClO₄)₂(5) where tepza = tris[2-ethyl(1-pyrazolyl)]amine, dca = dicyanamide, C₄O₄²⁻ = 3,4-dihydroxycyclobut-3-ene-1,2-dionate (squarate dianion) and C₅O₅²⁻ = 4,5-dihydroxycyclopent-4-ene-1,2,3-trionate (croconate dianion) were synthesized and structurally characterized by IR and UV-Vis spectroscopy as well as by single X-ray crystallography. In the solid state, the geometry of copper(II) centers in these complexes are as follows: close to SP in 2, distorted TBP in 3, predominant SP in 4, and distorted octahedral in 5, whereas in solution distorted SP geometry was generally found. The squarato and the croconato dianions in complexes 4 and 5 are bridging the two copper(II) centers in cis-bis-monodentate and bis-bidentate bonding modes, respectively. Magnetic susceptibility measurements at variable temperatures (2-300 K) reveal the weak antiferromagnetic coupling in the two bridging dinuclear complexes 4 (J = −24.9 cm⁻¹) and 5 (J = −3.1 cm⁻¹).     

Carboxy-derived (tpy)2Ru complexes as sub-units in supramolecular architectures: The solubilized ligand 4′-(4-carboxyphenyl)-4,4″-di-(tert-butyl)tpy and its homoleptic Ru(II) complex

We herein describe the synthesis and characterization of a series of homoleptic, Ru(II) complexes bearing peripheral carboxylic acid functionality based upon the novel ligand 4′-(4-carboxyphenyl)-4,4″-di-(tert-butyl)tpy (L₁), as well as 4′-(4-carboxyphenyl)tpy (L₂) and 4′-(carboxy)tpy (L₃) (where tpy = 2,2′: 6′,2″-terpyridine). Inspection of the metal-based oxidations (E_1/2 = 1.22-1.42 V) indicates an anodic shift (∼0.2 V) for (L₃)₂Ru²⁺ (3b) (E_1/2 = 1.40 V) relative to (L₂)₂Ru²⁺ (2b) (E_1/2 = 1.22 V). The metal-based oxidation (E_1/2 = 1.22 V) and ligand-based reductions (E_1/2 = −1.25 to −1.52 V) of (L₁)₂Ru²⁺ (1) are essentially invariant relative to those of the structural analogue 2b (PF₆)₂, which suggests no significant electronic effect caused by the tert-butyl groups. This is supported by invariance in the metal-to-ligand charge transfer bands in both the electronic absorption (494-489 nm) and emission spectra (654-652 nm). However, contrary to 2b, complex 1 is both very soluble and exhibits a highly porous solid-state structure with internal cavity dimensions of 15 Å × 14 Å due to the preclusion of inter-annular interactions by the bulky tert-butyl substituents.     

Diverse dimensionalities and structures in copper coordination polymers incorporating substituted aliphatic dicarboxylate ligands and 4,4′-bipyridine

Hydrothermal synthesis has afforded a series of divalent copper coordination polymers with substituted glutarate ligands and the rigid rod tether 4,4′-bipyridine (bpy): {[Cu(Hdmg)₂(bpy)]·H₂O}_n (1, dmg = 3,3-dimethylglutarate), {[Cu₂(dmg)(bpy)₂](ClO₄)]_n (2), [Cu₂(emg)₂(bpy)]_n (3, emg = 3-ethyl, 3-methylglutarate) and [Cu₂(cda)₂(bpy)]_n (4, cda = 1,1-cyclopentanediacetate). All materials were characterized by single-crystal X-ray diffraction. Compound 1 manifests μ₂-oxygen bridged [Cu₂(Hdmg)₄] “X”-patterns connected into a ribbon motif by bpy linkers. On the other hand, 2 possesses mixed-valence [Cu^ICu^IICu^IICu^I] tetrameric clusters bridged by dmg ligands and pillared into an 8-connected body-centered cubic (bcu) cationic lattice by bpy linkers. Compounds 3 and 4 are structurally very similar, displaying chain motifs with {Cu₂(CO₂)₄} paddlewheels connected by dicarboxylates, in turn conjoined into (4,4)-grid coordination polymer layers by bpy tethers. Variable temperature magnetic data indicate the presence of very strong antiferromagnetic coupling within the {Cu₂(CO₂)₄} paddlewheels in the latter two complexes, with g = 2.30(2) and J = −352(3) cm⁻¹ for 3 and g = 2.35(2) and J = −352(5) cm⁻¹ for 4. Significant structural contrasts are evident when compared to previously reported divalent copper/4,4′-bipyridine coordination polymers with unsubstituted or 2-methyl substituted glutarate ligands.     

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

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

Dinuclear terephthalato-bridged nickel(II) complexes. Structural characterization and magnetic properties

The dinuclear terephthalato-bridged nickel(II) complexes [Ni₂(cyclen)₂(μ-tp)](ClO₄)₂ (1) [Ni₂(trpn)₂(μ-tp)(H₂O)₂](ClO₄)₂ (2) and [Ni₂(3,3,3-tet)₂(μ-tp)(H₂O)₂](ClO₄)₂ · 2H₂O (3), where tp = terephthalate dianion, cyclen = 1,4,7,10-tetraazacyclododecane, trpn = tris(3-aminopropyl)amine and 3,3,3-tet = 1,5,9,13-tetraazatridecane, were synthesized and structurally characterized by X-ray crystallography. Their magnetic susceptibilities were also determined at variable temperatures over the range 2-300 K. The structures of these complexes consist of μ-tp bridging two Ni(II) centers in a bis(bidentate) bonding fashion in 1 and in bis(monodentate) bonding fashion in 2 and 3. The coordination geometry around the Ni(II) ions in these compounds has a distorted octahedral geometry with four nitrogen atoms from the amine ligand (cyclen, trpn or 3,3,3-tet) and two coordinated oxygen atoms supplied by the chelated carboxylate group of the bridged terephthalate ligand in 1, and by one tp-carboxylate-oxygen in 2 and 3. The sixth coordination site in the last two complexes 2 and 3 is achieved via an oxygen atom from a coordinated water molecule. The intradimer Ni…Ni distances in these complexes are 10.740, 11.428 and 11.537 Å for 1, 2 and 3, respectively. The electronic spectra of the complexes in aqueous solutions are in complete agreement with the assigned X-ray geometry around the Ni(II) centers. Also, the analysis of the infrared spectral data for the ν(COO⁻) stretching frequencies of the tp-carboxalato groups reveals the existence of the bis(bidentate) and bis(monodentate) coordination modes for the bridged terephthalate ligand in 1, 2 and 3, respectively. Despite the different coordination modes of the tp bridging ligand in these complexes, they all exhibit very weak antiferromagnetic coupling. The coupling constants J were found to be −2.2, −0.6 and −1.5 cm³ K mol⁻¹ for the complexes 1, 2 and 3, respectively. The structural and magnetic results of 1-3 are discussed in relation to the other related published μ-terephthalato dinuclear Ni(II) compounds.     

Synthesis, crystal structures and density functional theory study of dimeric copper(II) complexes of a tridentate Schiff-base ligand

Oxalate- or 4,4′-bipyridine-bridged dimeric copper(II) complexes, [Cu₂L₂(μ-ox)] (1) and [Cu₂L₂(μ-bipy)](BF₄)₂ (2) [where ox = oxalate, bipy = 4,4′-bipyridine, HL = N-(1H-pyrrol-2-ylmethylene)-2-pyridineethanamine, L⁻ = HL−H⁺], have been synthesised and characterised by elemental analysis, IR, UV-Vis and single crystal X-ray diffraction. Crystal structure determinations carried out on 1 and 2 reveal that 1 is an oxalate-bridged centrosymmetrical square pyramidal dimeric copper(II) complex while 2 is a 4,4′-bipyridine-bridged non-centrosymmetric square planar dinuclear copper(II) complex. Comparison of the optimised geometries with the corresponding crystal structures suggests that the B3LYP/LANL2DZ level can reproduce the structures of 1 and 2 on the whole. The electronic spectra of 1 and 2 predicted by B3LYP/LANL2DZ method show some blue shifts compared with their experimental data. Thermal analysis carried out on 1 shows that there is only one exothermal peak at about 260 °C and the residue is presumably Cu₂O₄N₆.     

Molecular structures and redox properties of oxorhenium(V) ‘3+1’ mixed ligand complexes with heterocyclic thiolates containing nitrogen

Reactions of chloro(3-thiapentane-1,5-dithiolato)oxorhenium(V) [ReO(SSS)Cl] with N-methyl-1H-imidazole-2-thiol (HL¹) and 2-pyrimidinethiol (HL²) have been studied to form ‘3+1’ oxorhenium(V) complexes. In the absence of triethylamine, [Re(SSS)(HL¹)]Cl (1a) was formed, while in the presence of triethylamine [Re(SSS)L¹] (1b) and [Re(SSS)L²] (2) were produced. Molecular structures of complexes 1a and 2 were determined to be distorted square pyramidal by single crystal X-ray analytical method. From cyclic voltammetric studies, furthermore, it was proposed that complexes 1b and 2 are irreversibly oxidized to Re(VI) at around 0.84 and 1.01 V versus Ag/AgNO₃, respectively, and are reduced to Re(IV) at −1.55 and −1.51 V with the dissociation of L¹ or L², followed by the quasi-reversible reductions to Re(III) at around −1.69 V, respectively.