Synthesis, structure and magnetic properties of two μ-oxo and thiocyanato-bridged manganese(II)-mercury(II) coordination polymers

Mixed-metal thiocyanate complexes [MnHg(SCN)₄(NOP)] (1) and [MnHg(SCN)₄(DMSO)] (2) (NOP = 3-methyl-4-nitropyridine-N-oxide, DMSO = dimethylsulfoxide) have been synthesized and structurally characterized by single crystal X-ray analysis. Complex 1 and 2 both contain a [Mn₂(μ₂-O)₂] lozenge, which is bridged to Hg(II) ions by end-to-end thiocyanate groups to form a 2-D and 3-D polymeric network, respectively. Magnetic studies indicate that both complexes are anti-ferromagnets, with 1 showing anti-ferrimagnetic ordering below 8.0 K.     

Crystal structure,magnetic and thermal properties of the one-dimensional complex [Nd(pzam)3(H2O)Mo(CN)8] · H2O

The new d–f cyanido-bridged 1D assembly [Nd(pzam)₃(H₂O)Mo(CN)₈] · H₂O was prepared by self-assembly of pyrazine-2-carboxamide (pzam), Nd(NO₃) · nH₂O and (Bu₃NH)₃[Mo(CN)₈] · 4H₂O in acetonitrile. X-ray crystallographic studies indicate that the complex comprises chains of alternating, cyanido-bridged [Nd(pzam)₃(H₂O)]³⁺ and Mo(CN)₈]^3? fragments. The magneto-structural properties have been studied by field-dependent magnetization and specific heat measurements at low temperatures (?0.3 K). Below ≈10 K the Nd(III) moment is well approximated by an effective spin S = 1/2, with anisotropic g-tensor. The exchange coupling between the Nd(III) and the Mo(V) spins S = 1/2 along the structural chains is found to be ferromagnetic, with J/k_B = 1.8 ± 0.2 K and approximately XY (planar) anisotropy. No evidence for 3D interchain magnetic ordering is found. A comparison with magneto-structural data of other cyanido-bridged complexes involving the Nd(III) ion is presented.     

Expanding the 4,4′-bipyridine ligand: Structural variation in {M(pytpy)2}2+ complexes (pytpy = 4′-(4-pyridyl)-2,2′:6′,2″-terpyridine,M = Fe,Ni, Ru) and assembly of the hydrogen-bonded,one-dimensional polymer {[Ru(pytpy)(Hpytpy)]}n3n+

The solid state structures of [Ni(1)₂][NO₃]₂ · 2MeOH · 2H₂O, [Fe(1)₂][ClO₄]₂ · 2MeOH · 0.5H₂O, [Ru(1)₂][PF₆]₂ and [Ru(1)₂][PF₆][NO₃] (1 = 4′-(4-pyridyl)-2,2′:6′,2″-terpyridine) are presented and the structural variation observed for the {M(1)₂}²⁺ unit is discussed. Protonation of the pendant pyridine group in [Ru(1)₂]²⁺ leads to the formation of a hydrogen-bonded, one-dimensional polymer [{Ru(1)(H1)}_n]³ⁿ⁺ exemplifed by the solid-state structure of [{Ru(1)(H1)}{Fe(NCS)₆} · 1.25H₂O]_n.     

Synthesis and structure of a novel molybdenum-iron-sulfur cluster with Mo2Fe2 core and all-disulfide chelate ligands, [Mo2Fe2(μ3-S)4(S2CNEt2)5] CH3CN

The cluster compound [Mo₂Fe₂(μ₃-S)₄- (S₂CNEt₂)₅]CH₃CN has been prepared from the reaction system containing (NH₄)₂MoS₄, FeCl₃, NaS₂CNEt₂, PhSH and NaOCH₃. The crystal and molecular structure have been determined by the low temperature X-ray diffraction technique. The compound crystallizes in space group P2₁/c of the monoclinic system with a = 19.397(7), b = 10.891(7), c = 24.302(8) Å, β = 108.95(2)° and Z = 4. With use of 2647 reflections (I)>2.5σ(I)) the structure was refined to R(R_w) = 0.045(0.036). The cluster Mo₂Fe₂S₄(S₂CNEt₂)₅ has a cubane-like skeleton [Mo₂Fe₂S₄]⁵⁺. Each metal atom is coordinated by three μ₃-S atoms and a disulfide chelate terminal ligand. The fifth S₂CNEt₂ group as a bridging ligand coordinates to two Mo atoms. In a molecule of the compound, the two Mo atoms are equivalent but the two Fe atoms are unequivalent.     

Influence of ligands on the fac⇌Δhνmer isomerization in [RuCl3(NO)(P–P)] complexes, [P–P = R2P(CH2)nPR2 (n = 1–3) and R2P(CH2)POR2, PR2–CHCH–PR2, R = Ph and (C6H11)2P-(CH2)2-P(C6H11)2]

[RuCl₃(NO)(P–P)], [P–P = R₂P(CH₂)_nPR₂ (n = 1–3) and R₂P(CH₂)POR₂, PR₂–CHCH–PR₂, R = Ph and (C₆H₁₁)₂P-(CH₂)₂-P(C₆H₁₁)₂] were obtained and characterized by ³¹P {¹H} NMR, IR spectroscopies and cyclic voltammetry. The structures of fac-[RuCl₃(NO)(P–P)], P–P = dppm (1), dppe (2), c-dppen (3) and dppp (4), mer-[RuCl₃(NO)(dcpe)] (6a) and mer-[RuCl₃(NO)(dppmO)] (7) have been determined by X-ray diffraction. Photochemical isomerization of fac- to mer-[RuCl₃(NO)(P–P)] was observed under white light in a CH₂Cl₂ solution and in solid state. The isomerization processes were followed by IR and ³¹P {¹H} spectra. The mer-[RuCl₃(¹⁵NO)(dppb)] isomer was used for the definition of the phosphorus atoms in the structure of the complex in solution. The electrochemical study shows that the oxidation/reduction processes observed in these complexes are dependent on both the isomer (fac or mer) and the solvent. In CH₂Cl₂, the NO⁺ reduction potentials are less negative for the mer-isomers than for the fac ones, while in CH₃CN solvent these potentials are, in general, very close for both isomers.     

Structure, spectroscopic and magnetic properties of a novel 1-D coordination copper(II) polymer containing BIMAM ligand [BIMAM = bis(imidazol-2-yl)methylaminomethane] and μ-1,3 squarato bridges

This paper reports the synthesis and complete characterization (structural, spectroscopic and magnetic) of [Cu(HBIMAM)Cl(C₄O₄)]_n · (H₂O)_n [BIMAM = bis(imidazol-2-yl)methylaminomethane]. This compound is made of infinite chains - running along c axis - built from [CuCl(HBIMAM)]⁺ units bridged together by μ-O¹,O³-bis(monodentate) squarate anions. Non-covalent interactions (H-bonds and π-π) drive the build-up of an infinite three-dimensional array. The coordination polyhedron about the copper(II) ion is distorted square pyramidal. The EPR spectrum is indicative of a d_z²-y² ground state for the Cu(II) ions with significant contribution of d_z². Magnetic susceptibility measurements in the range 1.8-200 K show weak antiferromagnetic exchange interactions (2J = −3.5(1) cm⁻¹). The observed magnetic behaviour is discussed in terms of the crystal structure and compared with that observed in related copper(II) complexes containing μ-O¹,O³-squarato bridges.     

Synthesis and structural characterization of a mixed-ligand diiron(II) complex formed by a linked bitopic tris(pyrazolyl)methane ligand: {HC(3,5-Me2pz)3Fe[μ-p-C6H4(CH2OCH2C(pz)3)2]Fe(3,5-Me2pz)3CH}(BF4)4 (pz = pyrazolyl ring)

The structure of {HC(3,5-Me₂pz)₃Fe[μ-p-C₆H₄(CH₂OCH₂C(pz)₃)₂]Fe(3,5-Me₂pz)₃CH}(BF₄)₄ (pz = pyrazolyl ring) contains two octahedral iron(II) centers linked by a semirigid, bitopic tris(pyrazolyl)methane ligand. The solid-state structure shows the two heteroleptic-bonded iron(II) centers are low-spin at 200 K and situated in a trans orientation with respect to the central linking arene ring.     

Influence of coordination modes of 4,4′-bipyridine and secondary bonds on the structural assembles: Syntheses,crystal structures and properties of two lead(II) 3-sulfobenzoate coordination polymers

Two novel structures, {[Pb(3-sb)(4,4′-bipy)_0.5](H₂O)}_n (1) together with the previously reported complex {[Pb(3-sb)(H₂O)₂](4,4′-bipy)}_n (2), where 3-sb is 3-sulfobenzoate dianion and 4,4′-bipy is 4,4′-bipyridine, were synthesized and characterized by IR, elemental analyses, TGA, powder X-ray, fluorescent and single-crystal X-ray analyses. The highly ordered 2-D structure of 2 exists as π–π stacking and hydrogen-bonding interactions, while complex 1 is a 3-D network with 2-D interpenetration layers without π–π and hydrogen-bonding interactions and with abundant secondary bonding interactions. Therefore, complex 1 has thermally more stable structure than that of complex 2, and water molecules can be removed and re-combined in complex 1.     

Interplay between halogen and chalcogen bonding in the XCl∙∙∙OCS∙∙∙NH3 (X = F,OH, NC,CN, and FCC) complex

The interplay between halogen and chalcogen bonding in the XCl???OCS and XCl???OCS???NH₃ (X = F, OH, NC, CN, and FCC) complex was studied at the MP2/6-311++G(d,p) computational level. Cooperative effect is observed when halogen and chalcogen bonding coexist in the same complex. The effect is studied by means of binding distance, interaction energy, and cooperative energy. Molecular electrostatic potential calculation reveals the electrostatic nature of the interactions. Cooperative effect is explained by the difference of the electron density. Second-order stabilization energy was calculated to study the orbital interaction in the complex. Atoms in molecules analysis was performed to analyze the enhancement of the electron density in the bond critical point.     

One- and two-dimensional copper benzenedicarboxylate coordination polymers incorporating the flexible tethering diimine N,N′-bis(3-pyridylmethyl)piperazine: Synthesis,structure, and thermal properties

A family of three copper benzenedicarboxylate coordination polymers has been constructed using the conformationally flexible and hydrogen-bonding capable tethering ligand N,N′-bis(3-pyridylmethyl)piperazine (3-bpmp). These three coordination polymers have been characterized via single crystal X-ray diffraction, infrared spectroscopy and elemental and thermogravimetric analysis. {[Cu(ph)(Hph)(H3-bpmp)(H₂O)] · 3H₂O} (1, ph = phthalate) manifests a 1-D chain motif held into a pseudo 3-D supramolecular structure through hydrogen bonding. While both {[Cu(ip)(3-bpmp)(H₂O)] · 2H₂O} (2, ip = isophthalate) and [Cu(tp)(3-bpmp)] (3, tp = terephthalate) exhibit 2-D (4,4) rhomboid grid-like layers, they possess different layer stacking patterns and supramolecular interactions due to coordination geometry variances.     

Synthesis,crystal structures and properties of three rare earth substituted germanotungstates: M/[α-GeW11O39] (M = Nd,Eu, and Tb)

Three new polyoxometalate compounds based on the lacunary Keggin anion [α-GeW₁₁O₃₉]^8? and the rare earth cations (Ln = Nd^III, Eu^III, Tb^III), [(CH₃)₄N]_2.5H_7.5[Eu(GeW₁₁O₃₉)(H₂O)₂]₂ · 4.5H₂O (1), [(CH₃)₄N]₂H₈[Tb(GeW₁₁O₃₉)(H₂O)₂]₂ · 2.5H₂O (2) and [Nd_0.5(H₂O)₂]H_0.5[Nd₂(GeW₁₁O₃₉)(DMSO)₂(H₂O)₈] · 5.5H₂O (3), have been synthesized and characterized by elemental analysis, inductively coupled plasmas (ICP) analysis, IR spectroscopy, single-crystal X-ray diffraction. The solid-state structures of compounds 1 and 2 consist of one-dimensional linear wires built of [α-GeW₁₁O₃₉]^8? anions connected by Eu³⁺/Tb³⁺ cations, while in compound 3, the introduction of the organic molecules DMSO (DMSO = dimethyl sulphoxide) leads to a double-parallel chainlike structure constructed by two linear wires {[Nd(1)(GeW₁₁O₃₉)(DMSO)(H₂O)₂]^5?}_n linked by Nd³⁺ coordination cation. Furthermore, the luminescent property of compound 1 and the thermal stability of compound 3 were also studied.     

Pt(II) complexes with (N,N′) or (C,N,E)− (E = N,S) ligands: Cytotoxic studies,effect on DNA tertiary structure and structure–activity relationships

The cytotoxic activity of two series of platinum(II) complexes containing the polyfunctional imines R¹–CHN–R² [R¹ = phenyl or ferrocenyl unit and R² = (CH₂)_n–CH₂–NMe₂ where n = 1 or 2) (1 and 2) or C₆H₄-2-SMe (3)] acting as a bidentate (N,N′) (4–7) or terdentate [C(phenyl or ferrocenyl),N,N′]^? (8–10) or [C(ferrocenyl),N,S]^? ligand (11) in front of A549 lung, MDA-MB231 breast and HCT116 colon human adenocarcinoma cell lines is reported. The results reveal that most of the platinum(II) complexes are active against the three assayed lines and compounds 6, 7 and the platinacycles 10 and 11 exhibit a remarkable antiproliferative activity, even greater than cisplatin itself, in the cisplatin resistant HCT116 human cancer cell line. Electrophoretic DNA migration studies showed that most of them modify the DNA tertiary structure in a similar way as the reference cisplatin. Solution studies of a selection of the most relevant complexes have also been performed in order to test: (a) their stability in the aqueous biological medium and/or the formation of biologically active species and (b) their proclivity to react with 9-methylguanine (9-MeG), as a model nucleobase. Computational studies at DFT level have also been performed in order to explain the different solution behaviour of the complexes and their proclivity to react with the nucleobase.     

Syntheses, structures and magnetic properties of μ1,5 dicyanamide bridged coordination polymers of copper(II) and nickel(II) containing a tetradentate N-donor Schiff base

One neutral [Cu₂(enbzpy)(dca)₄]_n (1) and one polycationic [Ni(enbzpy)(dca)]_n(ClO₄)_n (2) [enbzpy = N,N′-(bis-(pyridin-2-yl)benzylidene)ethane-1,2-diamine; dca = dicyanamide] 1D coordination polymers are synthesized and characterized. X-ray structural analyses reveal each copper(II) center in 1 to adopt a distorted square pyramidal geometry with a CuN₅ chromophore coordinated through two N atoms of the Schiff base behaving as a binucleting bis(bidentate) ligand and three nitrile N atoms of one terminal and two single μ_1,5 dca units leading to a 1D ladder structure. In 2, each nickel(II) center has a distorted octahedral coordination environment with an NiN₆ chromophore bound by four N atoms of enbzpy through tetradentate chelation and two nitrile N atoms of two different single bridged μ_1,5 dca units; the latter connects other neighboring metal centers in a non-ending fashion affording a 1D chain. Variable-temperature magnetic susceptibility measurements of 1 and 2 show weak antiferromagnetic interactions among the metal centers through μ_1,5 dca bridges.     

Octanuclear {Co6W2} aggregate versus mixed valence {Co}3 cluster in the assembling of Co(phen)2Cl2 (phen = 1,10-phenanthroline) with octacyano metallates: A case of non-isostructurality between {W(CN)8}4− and {Nb(CN)8}4−

An unprecedented octanuclear aggregate, [{Co(phen)₂}₆{W(CN)₈}₂Cl₂] · 2Cl, 2, resulted from the assembling of {Co(phen)₂Cl₂}, 1, and {W(CN)₈}^4?. Surprisingly, the reaction with the paramagnetic {Nb(CN)₈}^4? unit did not afford the homologous {Co–Nb} cluster. Instead the latter building unit undergoes dissociation which led to the formation of a mixed-valence [{Co^II(phen)₂}{Co^III(phen)(CN)₄}₂], 3. This observation is in contrast to the usual trend that {Nb^IV(CN)₈}^4? forms compounds isostructural to that observed for {Mo^IV(CN)₈}^4? and {W^IV(CN)₈}^4?. The structures of the compounds 2 and 3 have been established by single crystal X-ray diffraction. Magnetic behaviors for compounds 1–3 are reported.     

The reactivity of bromoform with [Au(CH2)2PPh2]2. The completion of the halomethane series CHyX4−y (y=3,2,1,0; X=Cl,Br, I) and reactivity with [Au(CH2)2PPh2]2

The reaction of [Au(CH₂)₂PPh₂]₂ with excess CHBr₃ in benzene initially gives [Au(CH₂)₂PPh₂]₂₋ (CHBr₂)Br. This observation establishes that halomethanes, CH_yX_4−y (y=3,2,1,0; X=Cl, Br, I), react with [Au(CH₂)₂PPh₂]₂ to initially give Au(II) adducts of the general form [Au(CH₂)₂PPh₂]₂₋(CH_yX_3−y)X (y=3,2,1,0) via oxidative addition across the carbon-halogen bond. The order of reactivity inversely follows the order of carbon-halogen bond dissociation energies of haloalkanes. Methyl chloride is the only halomethane of the series that does not give a Au(II) adduct under similar reaction conditions.     

Electrochemical studies of a series of antimetastatic mono- and di-ruthenium complexes [Na][trans-RuIIICl4(DMSO)(L)] and [Na]2[{trans-RuIIICl4(DMSO)}2(μ-L)] (L = N-donor heterocyclic bridging ligand)

A study of the electrochemical behavior of a series of antimetastatic mono- and di-ruthenium complexes, namely [Na][trans-Ru^IIICl₄(DMSO)(L)] and [Na]₂[{trans-Ru^IIICl₄(DMSO)}₂(μ-L)], L = pyrazine (pyz), pyrimidine (pym), 4,4′-bipyridine (bipy), and 1,2-bis-(4-pyridyl)ethylene (etbipy), is reported. The results obtained show that in all dimeric Ru(III) complexes linked by heterocyclic non-chelating N-donor bridges, the two redox centers behave independently (with no remarkable electrochemical interaction), thus conferring no advantage in the likely hypothesis they act as pro-drugs (activation by reduction). Moreover, electrochemical evaluation of interaction between albumin and the title complexes confirms that this protein can act as the vehicle for drugs of this type in blood.