Structural and magnetic properties of metal complexes with pyridine-2,6-dicarboxylate and 5-(4-bromophenyl)-2,4′-bipyridine

A series of complexes has been synthesized based on pyridine-2,6-dicarboxylate (L1) as the bridging ligand and 5-(4-bromophenyl)-2,4′-bipyridine (L2) as the pendant with different metal ions such as Ni^II, Co^II, and Cu^II, under hydrothermal conditions. In nickel and cobalt complexes [M(L1)(L2)₂ · H₂O]_n (M = Ni²⁺ or Co²⁺), the metal ions are bridged by L1 to form 1D coordination zigzag polymeric chains with L2 pendants possessing hexa-coordinated distorted octahedral geometries. While the copper ions are penta-coordinated by L1 and L2 with distorted square pyramidal geometries forming the tetranuclear cluster with the formula [Cu₄(L1)₄(L2)₄] · 2H₂O. It has been found that both the structure and magnetic property of these complexes are metal ions dependent. Intramolecular antiferromagnetic interactions were observed in the nickel and cobalt 1D coordination polymers, while ferromagnetic coupling was found in the tetranuclear copper cluster. Density functional theory calculations suggested that the O–C–O bridges of L1 in a basal–apical mode are responsible for intracluster intermetallic ferromagnetic exchange for the tetranuclear copper cluster.     

Mixed ligand complexes of AEE hexafluoroacetylacetonates with diglyme: Synthesis,crystal structure and thermal behavior

The novel mixed ligand complexes [Ca(hfa)₂(diglyme)(H₂O)] (I), [Sr(hfa)₂(diglyme)(H₂O)] (II) and [Ba(hfa)₂(diglyme)₂] (III) (Hhfa = 1,1,1,5,5,5-hexafluoropentane-2,4-dione, diglyme = 2,5,8-trioxanonane) were synthesized by the reactions of the alkaline earth element (AEE) carbonates in n-hexane with a mixture of Hhfa and diglyme, and they were characterized by elemental analysis, ¹H and ¹³C NMR, and FTIR spectroscopy. The crystal structures of I–III, consisting of mononuclear isolated molecules, have been determined. The thermal behavior and composition of the vapor phase have been studied for I–III by thermal analysis at low pressure and mass spectrometry using a Knudsen cell. The stability of the mixed ligand complexes [M(hfa)₂(diglyme)_n] to the removal of diglyme molecules under heating decreases in the row I > II ≈ III, and only I evaporates as the mixed ligand complex after water removal.     

Construction of metal–organic frameworks with transitional metals based on the 3,5-bis(4-pyridyl)-1H-1,2,4-triazole ligand

Based on the versatile ligand 3,5-bis(4-pyridyl)-1H-1,2,4-triazole (Hbpt) derived from an in situ metal/ligand reaction, a series of coordination compounds CoCl₄(H₃bpt)(H₂O) (1), Cu(H₂bpt)₂(SO₄)₂(H₂O)₆ (2), [Ag(bpt)]_n (3), [Co(Hbpt)(pa)]_n (4), [Co(Hbpt)(pda)]_n (5) and [Cu(Hbpt)(pda)(H₂O)]_n (6) have been constructed (pa = phthalate, pda = 1,3-phenylenediacetate). The structures of these targeted complexes have been characterized by X-ray single-crystal diffraction techniques. Structural analysis reveals that Hbpt adopts versatile coordination modes to arrange the metal ions in 0-D point, simple (4,4) layers and dinuclear core chains in 1–3, which are further extended via the benzenedicarboxylate connectors to give rise to a variety of coordination networks such as (4,4), (4¹² · 6³), (6⁴ · 8²) topologies in 4–6. The supramolecular organization through hydrogen bonds is analyzed for these complexes and thermal stability of these crystalline materials has been explored by TG-DTG.     

Dependence of the product on the P–P ligand in reactions of [RuCl3(NO)(P–P)] complexes (P–P = aromatic diphosphines) with 2-mercaptopyridine

This study presents the syntheses and characterization of 2-mercaptopyridine (pyS⁻) complexes containing ruthenium(II) with the following general formula [Ru(pyS)₂(P–P)], P–P = (c-dppen) = cis-1,2-bis(diphenylphosphino)ethylene) (1); (dppe) = 1,2-bis(diphenylphosphino)ethane (2); (dppp) = 1,3-bis(diphenylphosphino)propane (3) and (dppb) = 1,4-bis(diphenylphosphino)butane (4). The complexes were synthesized from the mer- or fac-[RuCl₃(NO)(P–P)] precursors in the presence of triethylamine in methanol solution with dependence of the product on the P–P ligand. The reaction of pyS⁻ with a ruthenium complex containing a bulky aromatic diphosphine dppb disclosed a major product with a dangling coordinated dppbO-P, the [Ru(pyS)₂(NO)(η¹-dppbO-P)]PF₆(5). In addition, this work also presents and discusses the spectroscopic and electrochemical behavior of 1–5, and report the X-ray structures for 1 and 5.     

Fe Spin crossover materials based on dissymmetrical N4 Schiff bases including 2-pyridyl and 2R-imidazol-4-yl rings: Synthesis,crystal structure and magnetic and Mössbauer properties

The synthesis and characterization of new symmetrical Fe^II complexes, [FeL^A(NCS)₂] (1), and [FeL^Bx(NCS)₂] (2–4), are reported (L^A is the tetradentate Schiff base N,N′-bis(1-pyridin-2-ylethylidene)-2,2-dimethylpropane-1,3-diamine, and L^Bx stands for the family of tetradentate Schiff bases N,N′-bis[(2-R-1H-imidazol-4-yl)methylene]-2,2-dimethylpropane-1,3-diamine, with: R = H for L^B1 in 2, R = Me for L^B2 in 3, and R = Ph for L^B3 in 4). Single-crystal X-ray structures have been determined for 1 (low-spin state at 293 K), 2 (high-spin (HS) state at 200 K), and 3 (HS state at 180 K). These complexes remain in the same spin-state over the whole temperature range [80–400 K]. The dissymmetrical tetradentate Schiff base ligands L^Cx, N-[(2-R₂-1H-imidazol-4-yl)methylene]-N′-(1-pyridin-2-ylethylidene)-2,2-R₁-propane-1,3-diamine (R₁ = H, Me; R₂ = H, Me, Ph), containing both pyridine and imidazole rings were obtained as their [FeL^Cx(NCS)₂] complexes, 5–10, through reaction of the isolated aminal type ligands 2-methyl-2-pyridin-2-ylhexahydropyrimidine (R₁ = H, 5–7) or 2,5,5-trimethyl-2-pyridin-2-ylhexahydropyrimidine (R₁ = Me, 8–10) with imidazole-4-carboxaldehyde (R₂ = H: 5, 8), 2-methylimidazole-4-carboxaldehyde (R₂ = Me: 6, 9), and 2-phenyl-imidazole-4-carboxaldehyde (R₂ = Ph: 7, 10) in the presence of iron(II) thiocyanate. Together with the single-crystal X-ray structures of 7 and 9, variable-temperature magnetic susceptibility and Mössbauer studies of 5–10 showed that it is possible to tune the spin crossover properties in the [FeL^Cx(NCS)₂] series by changing the 2-imidazole and/or C2-propylene susbtituent of L^Cx.     

Novel rhenium(III) complexes with the picolinate ligand: Synthesis,spectroscopic investigations,X-ray structures and DFT calculations for [ReX2(pic)(PPh3)2] complexes

The paper presents a combined experimental and computational study of novel rhenium(III) complexes with the picolinate ligand – [ReCl₂(pic)(PPh₃)₂] (1) and [ReBr₂(pic)(PPh₃)₂] (2). Both complexes 1 and 2 have been characterised spectroscopically and structurally (by single-crystal X-ray diffraction). Complex 1 has been additionally studied by magnetic measurement. The magnetic behavior is characteristic of a mononuclear d⁴ low-spin octahedral Re(III) complex (³T_1g ground state) and arises because of the large spin–orbit coupling (ζ = 2500 cm⁻¹), which gives a diamagnetic ground state. DFT and time-dependent (TD)DFT calculations have been carried out for complex 1, and UV–vis spectra of the [ReX₂(pic)(PPh₃)₂] compounds have been discussed on this basis.     

Dimolybdenum complexes containing anions of N,N′-bis(pyrimidine-2-yl)formamidine and N-(2-pyrimidinyl)formamide

The reactions of Mo₂(O₂CCH₃)₄ with different equivalents of N,N′-bis(pyrimidine-2-yl)formamidine (HL1) and N-(2-pyrimidinyl)formamide (HL2) afforded dimolybdenum complexes of the types Mo₂(O₂CCH₃)(L1)₂(L2) (1) trans-Mo₂(L1)₂(L2)₂ (2) cis-Mo₂(L1)₂(L2)₂ (3) and Mo₂(L2)₄ (4). Their UV–Vis and NMR spectra have been recorded and their structures determined by X-ray crystallography. Complexes 2 and 3 establish the first pair of trans and cis forms of dimolybdenum complexes containing formamidinate ligands. The L1 ligands in 1–3 are bridged to the metal centers through two central amine nitrogen atoms, while the L2 ligands in 1–4 are bridged to the metal centers via one pyrimidyl nitrogen atom and the amine nitrogen atom. The Mo–Mo distances of complexes 1 [2.0951(17) Å], 2 [2.103(1) Å] and 3 [2.1017(3) Å], which contain both Mo?N and Mo?O axial interactions, are slightly longer than those of complex 4 [2.0826(12)–2.0866(10) Å] which has only Mo?O interactions.     

Synthesis and characterization of phosphorous-bridged bisphenoxy titanium complexes and their application to ethylene polymerization

Phosphorous-bridged bisphenoxy titanium complexes were synthesized and their ethylene polymerization behavior was investigated. Bis[3-tert-butyl-5-methyl-2-phenoxy](phenyl)phosphine tetrahydrofuran titanium dichloride (4a) was obtained by treatment of 3 equiv of n-BuLi with bis[3-tert-butyl-2-hydroxy-5-methylphenyl](phenyl)phosphine hydrochloride salt (3a) followed by TiCl₄(THF)₂ in THF. THF-free complexes 5a-5d were synthesized more conveniently by the direct reaction of MOM-protected ligands (2a-2d) with TiCl₄ in toluene. X-ray analysis of 4a revealed that the ligand is bonded to the octahedral titanium (IV) center in a facial fashion and two chlorine atoms possess cis-geometry. Complexes 4a and 5a-5d were utilized as catalyst precursors for ethylene polymerization. Complex 5c gave high molecular weight polyethylene (M_w = 1,170,000, M_w/M_n = 2.0) upon activation with Al(ⁱBu)₃/[Ph₃C][B(C₆F₅)₄] (TB). Ethylene polymerization activity of 5d activated with Al(ⁱBu)₃/TB reached 49.0 × 10⁶ g mol (cat) ⁻¹ h⁻¹.     

Synthesis and characterization of water-soluble palladium(II)-functionalized diphosphine complexes

Water-soluble functionalized bis(phosphine) ligands L (a–h) of the general formula CH₂(CH₂PR₂)₂, where for a: R = (CH₂)₆OH; b–g: R = (CH₂)_nP(O)(OEt)₂, n = 2–6 and n = 8; h: R = (CH₂)₃NH₂ ( Scheme 1), have been prepared photochemically by hydrophosphination of the corresponding 1-alkenes with H₂P(CH₂)₃PH₂. Water-soluble palladium complexes cis-[Pd(L)(OAc)₂] (1–8) were obtained by the reaction of Pd(OAc)₂ with the ligands a–h in a 1:1 mixture of dichloromethane:acetonitrile. The water-soluble phosphine ligands and their palladium complexes were characterized by IR, ¹H and ³¹P NMR. A crystallographic study of complex 1 shows that the Pd(II) ion has a square planar coordination sphere in which the acetate ligands and the diphosphine ligand deviate by less than 0.12 Å from ideal planar.     

Synthesis,structure and properties of supramolecular Mn,Co, Ni and Zn complexes containing Salen-type bisoxime ligands

Four supramolecular complexes [MnL¹(H₂O)₂] (1), {[CoL²(OAc)(H₂O)]₂Co}·5CH₃CH₂OH (2), {[NiL³(OAc)(CH₃OH)]₂Ni}·2CH₃COCH₃·2CH₃OH (3) and {[ZnL²(OAc)]₂Zn}·CHCl₃ (4), have been synthesized and characterized by elemental analyses, IR, UV–Vis spectra and X-ray diffraction techniques. All the complexes have the trinuclear configuration except for Mn^II complex being mononuclear configuration. Every trinuclear complex contains two acetate ions coordinate to the three metal ions via a familiar M–O–C–O–M (M = Co, Ni, Zn) coordinated mode. Although complexes 1 and 3 display 1D supramolecular chains, the different coordination environments (mononuclear in 1, trinuclear in 3) provoke divergence in the structures and aggregations of the chain subunits. Complex 2 forms a 3D hydrogen-bonding supramolecular networks possessing a channel composing of six O–H···O hydrogen bonds, while complex 4 exhibits a 2D hydrogen-bonding supramolecular networks with the formation of “grottos” occupied by chloroform molecules through intermolecular hydrogen-bond interactions. The spectral properties of the title complexes have been further discussed in detail.     

Synthesis,structure, and electrochemistry of pyridinecarboxamide cobalt(III) complexes; the effect of bridge substituents on the redox properties

Two series of complexes of the types trans-[Co^III(Mebpb)(amine)₂]ClO₄ {Mebpb²⁻ = N,N-bis(pyridine-2-carboxamido)-4-methylbenzene dianion, and amine = pyrrolidine (prldn) (1a), piperidine (pprdn) (2a), morpholine (mrpln) (3a), benzylamine (bzlan) (4a)}, and trans-[Co^III(cbpb)(amine)₂]X {cbpb²⁻ = N,N-bis(pyridine-2-carboxamido)-4-chlorobenzene dianion, and amine = pyrrolidine (prldn), X = PF₆ (1b), piperidine (pprdn), X = PF₆ (2b), morpholine (mrpln), X = ClO₄ (3b), benzylamine (bzlan), X = PF₆ (4b)} have been synthesized and characterized by elemental analyses, IR, UV–Vis, and ¹H NMR spectroscopy. The crystal structure of 1a has been determined by X-ray diffraction. The electrochemical behavior of these complexes, with the goal of evaluating the effect of axial ligation and equatorial substitution on the redox properties, is also reported. The reduction potential of Co^III, ranging from −0.53 V for (1a) to −0.31 V for (3a) and from −0.48 V for (1b) to −0.22 V for (3b) show a relatively good correlation with the σ-donor ability of the axial ligands. The methyl and chloro substituents of the equatorial ligand have a considerable effect on the redox potentials of the central cobalt ion and the ligand-centered redox processes.     

Syntheses,characterizations and crystal structures of monomeric or macrocyclic compounds of di- or triorganotin (IV) moieties with 4,4′-thiodibenzenethiol

Six organotin compounds with 4,4′-thiodibenzenethiol (LH₂) of the type R_nSnL_4−nSnR_n (n = 3: R = Me 1, Ph 2, PhCH₂3, n = 2: R = Me 4, Ph 5, PhCH₂6) have been synthesized. All compounds were characterized by elemental analysis, IR and NMR (¹H, ¹³C, and ¹¹⁹Sn) spectra. The structures of compounds 1, 2, 4, 5 and 6 were also determined by X-ray diffraction analysis, which revealed that compounds 1 and 2 were monomeric structures, compounds 4, 5 and 6 were centrosymmetric dinuclear macrocyclic structures, and all the tin(IV) atoms are four-coordinated. Furthermore, supramolecular structures were also found in compounds 1, 2, 4, 5 and 6, which exhibit one-dimensional chains, two-dimensional networks or three-dimensional structures through intermolecular C–H?S weak hydrogen bonds (WHBs), non-bonded Sn?S interactions or C–H?π interactions.     

Synthesis,crystal structure and reactivity of a new pentacoordinated chiral dioxomolybdenum(VI) complex

The novel tridentate chiral ligand 2,6-bis{[(1R,2S,4R)-2-hydroxy-1,3,3-trimethyl-bicyclo[2.2.1]hept-2-yl]}pyridine (1) was readily prepared by reaction of 2,6-dilithiopyridine with (R)-(−)-fenchone. Reaction of 1 with [MoO₂(acac)₂] resulted in the formation of the new metal-oxo five-coordinated complex [MoO₂(ONO)] (2) [ONO = (1 – 2H)]. The reactivity of 2 has been studied and the derivatives [MoS₂(ONO)] (3) and [MoO(O₂)(ONO)] (4) were prepared. The compounds 1–4 have been characterised by ¹H and ¹³C{¹H} NMR, microanalysis and IR spectroscopy. Furthermore, the molecular structures of 1 and 2 have been determined by single-crystal X-ray diffraction. The behaviour of 2 as catalyst in oxotransfer and in nucleophilic substitution of propargylic alcohols reactions has been tested.     

Syntheses,supramolecular structures and properties of six coordination complexes based on 5-sulfosalicylic acid and bipyridyl-like chelates

Six new complexes constructed by 5-sulfosalicylic acid and bipyridyl-like ligands (2,2′-bipy and 1,10-phen), namely [Cu₄(OH)₂(ssal)₂(phen)₄ · 7H₂O] (1), [Cu₄(OH)₂(ssal)₂(bipy)₄ · 2H₂O] (2), [Cd(Hssal)(bipy)] (3), [Cd(HL)₂(phen)₂] (4), [Cr(ssal)(bipy)(H₂O)₂ · 2H₂O] (5) and [Cr(ssal)(phen)₂] (6) (H₃ssal = 5-sulfosalicylic acid, H₂L = p-hydroxybenzenesulfonic acid, bipy = 2,2′-bipy, phen = 1,10-phen) were prepared under hydrothermal conditions and their structures were determined by single-crystal X-ray diffraction. Complexes 1 and 2 are both tetranuclear copper complexes with a stepped topology. In complex 3, a new coordination mode of the Hssal²⁻ group is reported in this work. During the synthetic process of complex 4, in situ decarboxylation of 5-sulfosalicylic acid into p-hydroxybenzenesulfonic acid is involved. Two chromium 5-sulfosalicylates (5 and 6) are reported for the first time. These new complexes display different supramolecular structures by O–H?O, C–H?O hydrogen bonds as well as π?π, C–H?π and O?π interactions. The results of magnetic determination show that ferromagnetic interactions exist in complex 1, however, antiferromagnetic interactions exist in 2.     

1D coordination polymers of Cu(II) and Cu(II) dimers with a dicyanomethanide ligand

Several new 1D coordination polymers have been synthesised using the anionic ligand carbamoyldicyanomethanide, C(CN)₂(CONH₂)⁻ (cdm). The polymeric complexes [Cu(cdm)₂(py)₂]·2MeOH (1), [Cu(cdm)₂(4-Etpy)₂]·2MeOH (2), [Cu(cdm)₂(3,5-Me₂pzH)₂]·2MeOH (3) and [Cu(cdm)₂(3-HOCH₂py)₂]·2MeOH (4) (py = pyridine; 3,5-Me₂pzH = 3,5-dimethylpyrazole) contain Cu(II) atoms bridged by μ₂-(N,N′) cdm ligands between equatorial and axial coordination sites. The use of monodentate co-ligands brings about polymeric products, in contrast to the use previously of chelating co-ligands which facilitate the formation of discrete products. These 1D polymeric complexes are connected by hydrogen bonding between the amide functionalities and the lattice solvent. In the structures of 3 and 4 the neutral ligands also contain hydrogen bond donor groups that supplement the amide ring motif. Two other complexes have been obtained that are polymeric chains of alkoxide-bridged Cu(II) dimers. The complexes [Cu(cdm)(MeO)(2-amp)] (5) and [Cu(cdm)(dmap)] (6) (2-amp = 2-(aminomethyl)pyridine and dmap = dimethylaminopropoxide) are remarkably similar despite the different ligands that they contain. Bridging between dimers is via μ₂-(N,O) cdm ligands, consequently altering the nature of the hydrogen bonding between adjacent chains compared to the simple polymeric species 1–3.     

Synthesis and electrochemical properties of bis(bipyridine)ruthenium(II) complexes bearing pyridinyl- and pyridinylidene ligands induced by cyclometalation of N′-methylated bipyridinium analogs

Ruthenium complexes with bipyridine-analogous quaternized (N,C) bidentate ligands [RuL(bpy)₂](PF₆)₂ (bpy = 2,2′-bipyridine, (1), L = L¹ = N′-methyl-2,4′-bipyridinium; (2), L = L² = N′-methyl-2,3′-bipyridinium) were synthesized and characterized. The structure of complex 2 was determined by the X-ray structure analysis. The ¹³C{¹H} NMR spectroscopic and cyclic voltammetric studies indicate that the coordination modes of these ligands are quite different, that is, the C-coordinated rings of (N,C)-ligands in 1 and 2 are linked to ruthenium(II) with a pyridinium manner and a pyridinylidene one, respectively. The ligand-localized redox potentials of 1 and 2 also revealed the substantial difference in the electron donating ability of both ligands.     

Copper(II) complexes of tridentate selenobisphenolate ligand in mixed ligand environments: Synthesis, crystal structure, EPR and electrochemical studies

A series of square-pyramidal copper(II) complexes, [Cu(L^Se)(N^∧N)] (H₂L^Se = seleno-bisphenolate; N^∧N = bipyridyl, phenanthroline or N,N-dimethylethylenediamine) have been synthesized and characterized by elemental analyses, magnetic measurements, IR, EPR, and electronic spectral studies. Single crystal X-ray structures of [Cu(L^Se)(bpy)]·H₂O (2), [Cu(L^Se)(phen)]·CH₂Cl₂ (3) and [Cu(L^Se)(N,N-Me₂en)] (4) showed that all the complexes have approximately square-pyramidal geometry. In complexes 2 and 3, the square plane is occupied by O(1), O(2), N(1) and N(2) and the apical position by Se atom of L^{Se 2−} ligand. The asymmetric unit of complex 4 contains two crystallographically independent discrete molecules A and B with CuN₂OSe chromophore comprising the square plane and the axial position being occupied by another phenolate oxygen atom. Complexes 2, 3 and 4 are found to be paramagnetic and EPR parameters extracted are: g_∥ = 2.232, g_⊥ = 2.069; 〈g_eff〉 = 1.95; and g_∥ = 2.232, g_⊥ = 2.083 for complexes 2, 3 and 4, respectively. Both the complexes 2 and 4 show three reduction processes: (a) a quasi-reversible reduction of Cu^II to Cu^I, (b) an irreversible reduction of Cu^I to Cu⁰ with the release of free ligand, and (c) a reduction process occurs at this coordinated ligand. They also show a well-defined quasi-reversible oxidation of Cu^II to Cu^III and an irreversible oxidation peak at ∼1.30 and 1.40 V vs. Ag/AgCl for 4 and 2, respectively, with no cathodic counterpart, and were attributed to the oxidation of the metal coordinated ligand.