Polynuclear 3d complexes based on potentially tetra-anionic heptadentate ligands including amido,amino and phenoxo donors: Synthesis,crystal structure and magnetic properties

The synthesis and characterization of new dinuclear Mn^III and tetranuclear Cu^II complexes, [HL¹Mn(DMSO)]₂ (1) and [H₂L²Cu₂(MeO)₂]₂ (2), are reported (H₄L¹ = 2-hydroxy-N-[2-({2-[(2-hydroxybenzoyl)amino]ethyl}amino)ethyl]benzamide and H₄L² = 2-hydroxy-N-[3-({3-[(2-hydroxybenzoyl)amino]propyl}(methyl)amino)propyl]benzamide). Single crystal X-ray structures have been determined for 1 and 2. In 1 only one of the two amide functions of H₄L¹ is deprotonated in addition to the phenol ones, while in 2 all the amide functions of H₄L² are protonated and none of the potential nitrogen donors (amide and amine) is involved in the coordination to copper. HL¹ and H₂L² do not play the role of compartmental ligands and do not wrap around one Mn and one Cu ion, respectively, but embrace two metal centers yielding, with the respective assistance of auxiliary DMSO and methoxo ligands, dinuclear manganese and tetranuclear copper complexes, respectively. 1 includes two well isolated Mn^III ions (Mn?Mn′ = 7.33 Å) that do not interact magnetically. The intermolecular Mn?Mn″ distance along the 1D chains (10.17 Å) is also too large to allow extended magnetic interactions. The pairwise magnetic interactions between the copper(II) ions in the tetranuclear complex 2 are so large that the χ_MT product is already equal to zero at room temperature, implying that the antiferromagnetic interaction is around −1000 cm⁻¹, as observed previously for di-μ-hydroxo–dicopper complexes.     

Synthesis and redox properties of bis-ferrocenylethynyl derivatives of bis(dimethylphosphinoethane)manganese

Paramagnetic Mn^II and Mn^III complexes containing two ferrocenylethynyl ligands were synthesized. Their redox reactions were studied by cyclic voltammetry and chemical methods. The structures of the resulting compounds were determined by IR, ¹H NMR, and ESR spectroscopy. The structure of the complex [(FcCC)₂Mn(dmpe)₂]⁺PF₆ ^– was established by X-ray diffraction analysis.     

Auxiliary aromatic-acid effect on the structures of a series of Zn coordination polymers: Syntheses, crystal structures, and photoluminescence properties

Five novel Zn^II-(pyridyl)imidazole derivative coordination polymers, [Zn(L)₂] (1), [Zn₂(μ₃-OH)L(m-BDC)] (2), [Zn₂(μ₃-OH)L(p-BDC)]·H₂O (3), [Zn₂L(BTC)(H₂O)]·2.5H₂O (4) and [Zn_3.5(μ₃-OH)L₂(BTEC)(H₂O)]·H₂O (5) (L=4-((2-(pyridine-2-yl)-1H-imidazol-1-yl)methyl)benzoic acid, p-H₂BDC=1,4-benzenedicarboxylic acid, m-H₂BDC=1,3-benzenedicarboxylic acid, H₃BTC=1,3,5-benzenetricarboxylic acid, H₄BTEC=1,2,4,5-benzenetetracarboxylic acid), were successfully synthesized under hydrothermal conditions through varying auxiliary aromatic-acid ligands and structurally characterized by X-ray crystallography. Compound 1 exhibits a 1D chain linked via double L bridges. Compound 2 features a well-known pcu topology with bent dicarboxylate ligand (m-H₂BDC) as an auxiliary ligand, while 3 displays a bcu network with linear dicarboxylate ligand (p-H₂BDC) as an auxiliary ligand. The structure of compound 4 is a novel 3D (3,5)-connected network with (4·6²)(4·6⁴·8²·10·12²) topology. It is interesting that compound 5 shows an intricate (3,4,8)-connected framework with (4·6²)(4²·6³·8)(4²·6⁴)(4²·6¹⁸·7·8⁶·10) topology. In addition, their infrared spectra (IR), X-ray powder diffraction (XPRD) and photoluminescent properties were also investigated in detail.     

Coordination of a mesogenic Schiff-base with Mn, Co, Ni, Cu and Zn: Synthesis, spectral studies and crystal structures

A novel mesogenic (nematic) Schiff-base, N,N′-di-4-(4′-pentyloxybenzoate)salicylidene diaminoethane, H₂dpbsde (abbreviated as H₂L⁵) was synthesized and its structure studied. The Schiff-base crystallizes in the non-centrosymmetric space group Pna2₁ with Z = 4, and the mesogenic isomorphous nickel and copper complexes, [NiL⁵]₂ and [CuL⁵], in the centrosymmetric space group P2₁/c with Z = 4. The (L⁵)²⁻ species coordinates to the metal ions through two phenolate oxygens and two azomethine nitrogens. Both the [NiL⁵]₂ and [CuL⁵] complexes involve cis-MN₂O₂ planes; the former complex has a low-spin distorted square-pyramidal geometry with a Ni–Ni bonding of 3.337 Å and the latter, a square-planar geometry.     

Syntheses,structures, and properties of CdII and CoII complexes with 5-(pyridin-4-yl)isophthalate

A N-donor containing carboxylic ligand, 5-(pyridin-4-yl)isophthalic acid (H₂L), was applied to construct two new coordination polymers [Cd(L)(DMF)] _n (1, DMF?=?N,N-dimethylformamide) and {[Co(L)(H₂O)₂]?·?0.5CH₃OH?·?1.5H₂O} _n (2) under different conditions. The complexes were characterized by IR, elemental, and thermogravimetric analyses, powder and single crystal X-ray diffraction. In 1 each L^2? links four Cd^II to form a 3-D framework, while in 2 each L^2? connects three metals to form a 2-D layer structure, which is further connected together by hydrogen bonds to form a 3-D architecture. The thermal stability of the complexes and the photoluminescence of 1 were investigated.     

A new oxamato-bridged heterotrinuclear NiIICuIINiII complex: synthesis,structure and properties

A new oxamato-bridged Ni^IICu^IINi^II species, [Ni(iprtacn)]₂[Cu(pba)(H₂O)_0.5](BPh₄)₂ (1), (iprtacn?=?1,4,7-triisopropyl-1,4,7-triazacyclononane; pba?=?1,3-propylenebis(oxamato)) has been synthesized and structurally as well as magnetically characterized. Complex 1 has a discrete trinuclear Ni^IICu^IINi^II structure: Two nickel(II) ions are bridged by [Cu(pba)]^2? with the macrocyclic ligand iprtacn a terminal ligand of nickel(II). Fitting the magnetic data of 1 led to g _Cu?=?2.16, g _Ni?=?2.18, J?=??112.5?cm^?1, D?=?±7.78?cm^?1. The irregular spin state structure and interaction of complex 1with DNA are described here.     

Hydrothermal synthesis, crystal structures, and properties of Co and Ni supramolecular complexes with 2,4,6-trimethyl benzoate and 4,4′-bipyridyl

Two new coordination complexes, viz. [Co(tmb)₂(4,4′-bpy)₂(H₂O)₂](Htmb)₂ (1) and {[Ni(tmb)₂(μ-4,4′-bpy)₂(H₂O)₂](4,4′-bpy)}_n (2), have been hydrothermally synthesized by reaction of the corresponding metal acetate with 2,4,6-trimethylbenzoic acid (Htmb) and 4,4′-bipyridyl (4,4′-bpy). X-ray single-crystal diffraction suggests that complex 1 represents a discrete mononuclear species in which the central metal ion is coordinated by the terminal carboxylate moiety and the 4,4′-bipyridyl ligand. The crystal structure of complex 2 reveals a 1D chain coordination polymer in which the Ni(II) ions are connected by the bridging 4,4′-bipyridyl ligands. In both cases, the coordination arrays are further extended via hydrogen bonding interactions to generate 3D supramolecular networks. Complexes 1 and 2 have also been characterized by spectroscopic (IR and UV/Vis), thermal (TGA) and magnetic susceptibility measurements. In addition, both complexes exhibit antimicrobial activity.     

Synthesis and structural characterization of nitrite-coordinating CoII and CoIII complexes as models for the reaction center of Co-substituted nitrite reductase

Co^II and Co^III complexes containing nitrite and tridentate aromatic amine compounds [bis(6-methyl-2-pyridylmethyl)amine (Me₂bpa) and bis(2-pyridylmethyl)amine (bpa)] have been prepared as models of the catalytic center in Co-substituted nitrite reductase: [Co^II(Me₂bpa)(NO₂)Cl]₂ · acetone (2), Co^II(Me₂bpa)(NO₂)₂ (3), Co^II(bpa)(NO₂)Cl (4), Co^II(bpa)(NO₂)₂ (5), Co^III(Me₂bpa)(NO₂)(CO₃) (6), and Co^III(bpa)(NO₂)₃ (7). The X-ray crystal structure analyses of these Co^II and Co^III complexes indicated that the geometries of the cobalt centers are distorted octahedral and the Me₂bpa and bpa with three nitrogen donors exhibit mer- (2, 3, and 7) and fac-form (4 and 6). The coordination mode of nitrite depends on the cobalt oxidation state, to Co^II through the oxygen (nitrito coordination, O- and O,O-coordination) and to Co^III through nitrogen (nitro coordination, N-coordination mode). These findings are consistent with the results of their IR spectra, except that another oxygen of the O-coordinated nitrito group in 3 might interact weakly with Co^II according to its IR spectrum. Reductions of the nitrite in 2, 3, 4, and 5 to nitrogen monoxide were not accelerated in the presence of proton, perhaps due to the nitrito coordination in these Co^II complexes.     

Synthesis,crystal structure and magnetic properties of a new macrocyclic trinuclear CuII-CuII-CuII complex

A new oxamido-bridged trinuclear copper(II) complex [(CuL)₂Cu](ClO₄)₂·0.5H₂O (L?=?the dianion of 2,3-dioxo-5,6,14,15-dibenzo-7,13-bis(ethoxycarbonyl)-1,4,8,12-tetraazacyclotetradeca-7,12-diene) has been synthesized by self-assembly and characterized. X-ray diffraction analysis reveals that the title complex is monoclinic, space group P2₁, with a?=?16.213(5), b?=?9.811(3), c?=?18.802(6)?Å, β?=?96.790(5)°. The central copper(II) ion lies in a distorted octahedral environment. Terminal coppers have square pyramidal coordination geometry. Magnetic measurements show there is strong antiferromagnetic interaction between the central and the terminal Cu(II) ions.     

A kinetic study of the oxidation of hydroxamic acids by compounds I and II of horseradish peroxidase: Effect of transition metal ions

Abstract

Oxidation of hydroxamic acids (HXs) generates HNO, and it is not clear whether it is formed also in the presence of metal ions. The kinetics of the oxidation of HXs, such as acetohydroxamic acid, suberohydroxamic acid, and suberoylanilide hydroxamic acid (SAHA), by compounds I and II of horseradish peroxidase (HRP) at pH 7.0 and 25?°C have been studied using rapid-mixing stopped-flow. The kinetics of these reactions were compared to those observed in the presence of Cu(ClO₄)₂, NiSO₄, or ZnSO₄. The rates decrease upon increasing [Cu^II] at constant [HXs], and no oxidation of HX occurs when [HX]/[Cu^II] ≈ 2, implying that HX oxidation in the presence of Cu^II proceeds through the free ligand since the predominant complex is CuX₂. In the case of Ni^II, the oxidation rate decreases upon increasing the ratio [Ni^II]/[HX] beyond 1, where the predominant complex is Ni^IIX⁺, implying that its oxidation is feasible. The effect of Zn^II could be studied only on the rate of HXs oxidation by compound II demonstrating similar behavior to that of Ni^II. HXs were also oxidized catalytically by HRP/H₂O₂ at pH 7.0, demonstrating that metal ions facilitate the formation of HNO while hardly affecting its yield and the extent of HX oxidation.     

Syntheses and structures of two NiIICoIINiII complexes of macrocyclic ligands

Two new linear trinuclear complexes, [Co(NiL¹)₂(SCN)₂] (1) and [Co(NiL²)₂(H₂O)₂](ClO₄)₂?·?2C₂H₅OH (2), have been prepared by using Co(ClO₄)₂?·?6H₂O and two macrocyclic complex ligands NiL¹ and NiL². L¹ and L² are the doubly deprotonated forms of dimethyl 5,6,7,8,15,16-hexahydro-6,7-dioxodibenzo[1,4,8,11]tetraazabicyclo[12.4.0^15,16]13,18-dicarboxylate and dimethyl 5,6,7,8,15,16-hexahydro-15-methyl-6,7-dioxodibenzo[1,4,8,11]tetraazacyclotetradecine-13,18-dicarboxylate, respectively. X-ray single crystal analyses reveal the coordination geometries around Ni(II) in both 1 and 2 are identical and slightly distorted square planar with N₄ donors; all Ni–N bonds in the two complexes are very short. The Co(II) ions are at the centers of the trinuclear complexes and have distorted octahedral coordination geometries of O₄N₂ donors in 1 and an O₆ in 2. π?···?π interactions involving aromatic and non-aromatic π-systems join the trinuclear entities to form 2-D layers in the crystals of 1 and 2.     

Cyano-complexes and salts with tetracyanonickellateII and N,N-bis(2-hydroxyethyl)-ethylenediamine: synthesis,IR spectra,magnetic properties,thermal analyses,and crystal structures

Four cyano complexes, [Ni(N-bishydeten)Ni(CN)₄] _n (c1), [Cu(N-bishydeten)₂][Ni(CN)₄] (c2), [Zn₂(N-bishydeten)₂Ni(CN)₄] _n (c3), and [Cd(N-bishydeten)₂][Ni(CN)₄] (c4), have been synthesized and characterized by FT-IR, elemental, and thermal analyses. The structures of c2 and c4 were determined by single-crystal X-ray diffraction studies; both structures contain isolated cations and anions. The c2 consists of [Cu(N-bishydeten)₂]²⁺ with octahedrally coordinated Cu^II and diamagnetic [Ni(CN)₄]^2–, but c4 consists of [Cd(N-bishydeten)₂]²⁺, in which Cd^II is eight coordinate with two tetradentate N-bishydeten and diamagnetic [Ni(CN)₄]^2–. The value of the shape measure S (^o) indicates that the coordination geometry around Cd^II lies along D _2d [dodecahedron; (dd)], C _2v [bicapped trigonal prism; (btp)], and D _4d [square antiprism; (sap)] but close to D _2d and D _4d. Variable temperature magnetic susceptibility measurements of c1 and c2 show the presence of little antiferromagnetic interaction below 20?K. Thermal analyses reveal that first neutral N-bishydeten and then cyano ligands were liberated from the complexes.     

X-Ray Structural Analysis of NiII, PdII, and PtII Complexes with the Potentially Tridentate Ligand 1,3-Bis(diphenylphosphinomethyl)benzene, 1,3-C6H4(CH2PPh2)2

The ligand 1,3-bis(diphenylphosphinomethyl)benzene, 1,3-C₆H₄(CH₂PPh₂)₂ undergoes cyclometalation reactions, thus forming derivatives containing the tridentate moiety 2,6-bis(diphenylphosphinomethyl)phenyl,2,6-C₆H₃(CH₂PPh₂)₂. Complexes of the type trans-[MBr(C₆H₃CH₂PPh_{2 2})] with M = Ni^II, Pd^II, and Pt^II could be obtained and their crystal structures were here determined by X-ray diffraction (XRD) methods. The Ni complex belongs to the space group P2 ₁/c with a = 10.257(2), b = 16.234(5), c = 17.475(4) Å, = 109.34(2), and Z = 4. The Pd complex belongs to the space group P2 ₁/n with a = 10.325(3), b = 16.279(4), c = 17.303(4) Å = 105.34(3), and Z = 4. The Pt complex belongs to the space group P2 ₁/n with a = 10.127(2), b = 14.776(2), c = 19.023(3) Å, = 91.01(1), and Z = 4. Different distortions are induced by the rigid tridentate ligand on the square planar coordinations of the three metals. A significant difference between the two M-P bond distances is present in the Pt complex and can also be found in an analogous Pd complex.     

Synthesis, structure, and properties of chromium(III) sulfates

Reactions between CrO₃ and 50- are studied at temperatures up to the boiling point of the acid. Depending on the H₂SO₄ concentration and synthesis temperature, Cr₂(SO₄)₃, CrH(SO₄)₂, (H₃O)[Cr(SO₄)₂], Cr₂(SO₄)₃·H₂SO₄·4H₂O (gross formula), and (H₅O₂)[Cr(H₂O)₂(SO₄)₂], are obtained as identified reaction products in addition to the incompletely characterized chromic-sulfuric acid. The Cr^III-based sulfates are characterized by X-ray powder diffraction, thermogravimetric, and magnetic susceptibility measurements. The nuclear and magnetic structures of Cr₂(SO₄)₃ at are determined, the structure type of (H₃O)[Cr(SO₄)₂] is established, and the crystal structure of (H₅O₂)[Cr(H₂O)₂(SO₄)₂] is firmly stipulated. Magnetic susceptibility data suggest that the samples of CrH(SO₄)₂ are in a micro-crystalline rather than in an amorphous state. All Cr^III-based sulfates synthesized in this study appear to undergo paramagnetic-to-antiferromagnetic transitions at around .     

Synthesis,structures, and magnetic properties of two pyrazolato-bridged trinuclear copper(II) complexes

One nonlinear and one linear trinuclear copper(II) complex [Cu₃(dien)₂(pdc)₂CH₃OH]₂?·?6CH₃OH (1) and [Cu₃(pdc)₂(CH₃OH)₆(H₂O)₄] (2) were prepared and characterized structurally, where dien is diethylenetriamine and pdc^3? the trianion of 3,5-pyrazoledicarboxylic acid. Both complexes consist of 3,5-pyrazoledicarboxylato-bridged trinuclear copper(II) centers. In 1, copper(II) ions are five-coordinate in distorted square pyramids with bond angles 164.78° for Cu(1)–Cu(2)–Cu(3) and 164.51° for Cu(4)–Cu(5)–Cu(6). In 2, the three copper(II) ions are six-coordinate with elongated octahedral geometry. The trinuclear units of 1 and 2 interact through hydrogen bonds to form 3-D and 2-D supramolecular networks, respectively. Variable temperature magnetic susceptibility measurements show that 1 and 2 are antiferromagnetically coupled with J values of ?11.2 and ?13.3?cm^?1.     

Four Zn(II)/Cd(II) coordination polymers derived from isomeric benzenedicarboxylates and 1,6-bis(triazol)hexane ligand: synthesis,crystal structure,and luminescent properties

Four coordination polymers, [Zn(o-bdc)(bth)_0.5(H₂O)] _n (1), [Cd(o-bdc)(bth)_0.5(H₂O)] _n (2), [Zn(m-bdc)(bth)] _n (3), and [Cd(p-bdc)(bth)?·?(H₂O)₂] _n (4) (where o-bdc?=?1,2-benzenedicarboxylate, m-bdc?=?1,3-benzenedicarboxylate, p-bdc?=?1,4-benzenedicarboxylate, and bth?=?1,6-bis(triazol)hexane), have been hydrothermally synthesized and structurally characterized. Both 1 and 2 are isostructural, featuring two binodal architectures: (6³)(6⁵·8) topology in terms of o-bdc and Zn^II/Cd^II as three- and four-connected nodes. Complex 3 shows a 2-D (4,4) network with the Zn?···?Zn?···?Zn angle of 57.84°, whereas 4 exhibits planar 2-D (4,4) network. These 2-D networks of 3 and 4 are extended by supramolecular interactions, such as CH?···?π/π–π stacking and hydrogen-bonding into 3-D architecture. A structural comparison of these complexes demonstrates that the dicarboxylate building blocks with different dispositions of the carboxyl site play a key role in governing the coordination motifs as well as 3-D supramolecular lattices. Solid-state properties such as photoluminescence and thermal stabilities of 1–4 have also been studied.     

Synthesis,structures and magnetic properties of cyano- and amide-bridged FeIII-LnIII tetranuclear heterometallic clusters

Three Fe^III₂Ln^III₂ tetranuclear heterometallic clusters, [H₄LGd(H₂O)Tp*Fe(CN)₃]₂·8H₂O·2MeOH (1) and [H₄LLn(MeOH)Tp*Fe(CN)₃]₂·6MeOH·2MeCN (Ln?=?Tb and Dy for 2 and 3, respectively, H₆L = N,N′-(2,6-pyridine-dicarboxyl)-disalicylhydrazide, Tp* = hydridotris(3,5dimethylpyrazol-1-yl)-borate), were synthesized by use of the [(Tp*)Fe(CN)₃]^? unit as a metalloligand toward LnCl₃ and H₆L species. Structural analyses reveal that Fe^III and Ln^III ions in all complexes are connected to each other by one cyanide to form a heterobinuclear unit of [Ln(H₄L)][(Tp*)Fe(CN)₃], which is dimerized through Ln–N–C?=?O–Ln interaction. Magnetic susceptibility measurements show weak antiferromagnetic interactions between cyano-bridged Fe^III and Gd^III ions and amide-bridged Gd^III ions are operative. Complex 1 displays the magnetocaloric effect with ?ΔS_m^max = 12.70 J·kg^?1·K^?1 at 4.0 K for ΔH?=?7 T. No single-molecule magnetic properties are observed for 2 or 3 down to 1.8 K.     

5-(Pyridylmethylidene)-substituted 2-thiohydantoins and their complexes with CuII, NiII, and CoII: Synthesis, electrochemical study, and adsorption on the cystamine-modified gold surface

A series of Cu^II, Ni^II, and Co^II complexes with 5-(pyridylmethylidene)-substituted 2-thiohydantoins (L) were synthesized by the reactions of the corresponding organic ligands with MCl₂·nH₂O. The resulting complexes have the composition LMCl₂ (M = Cu or Ni) or L₂MCl₂ (M = Co). The reactions with N(3)-unsubstituted thiohydantoins afford complexes containing four-membered metallacycles, in which the metal ion is coordinated by the S and N(3) atoms of the thiohydantoin ligand. The reactions of N(3)-substituted thiohydantoins give complexes in which the S and N(1) atoms are involved in coordination. Study by IR spectroscopy demonstrated that the pyridine nitrogen atom is not involved in coordination. Based on the results of electrochemical study of the ligands and complexes by cyclic voltammetry and calculation of their frontier orbitals by the PM3(tm) method, the mechanism of oxidation and reduction of these compounds was proposed. In the first reduction and oxidation steps, the metal atom in the copper and nickel complexes remains, apparently, intact, and these processes occur with the involvement of the ligand fragments, viz., the coordinated thiohydantoin ligand and chloride anion, respectively. In the cobalt complexes, the first reduction step occurs at the ligand; the first oxidation state, at the metal atom. Measurements of the contact angle of aqueous wetting and electrochemical study demonstrated that carboxy-containing 2-thiohydantoins and their complexes can be adsorbed on the cystamine-modified gold surface. The structures of the complexes on the surface differ from the structures of these complexes in solution. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 978–990, June, 2006.     

Synthesis and VT-NMR studies of cationic hydride platinum clusters

The synthesis of three trinuclear platinum hydrides [Pt₃(L-L)₃(H)₃]⁺ (L-L = 1,2-bis(diphenylphosphino)ethane, dppe, l; 1-diphenylphosphino-2-diphenylarsinoethane, dppae. 2; 1,2-bis(diphenylarsino)ethane, dpae, 3) is reported. The complexes were characterized by IR, FAB-MS, and NMR (¹H,³¹P and¹⁹⁵Pt) spectroscopic techniques. The fast exchange of the hydride ligands, observed at ambient temperature, is frozen out at low temperature. The low-temperature¹H and³¹P NMR spectra are consistent with an open array of Pt atoms in the clusters, in keeping with a 16-electron configuration on each platinum atom. Two of the hydride ligands are terminally bonded to two metal centers, whereas the third one is µ₃-coordinated, interacting more tightly with the unique platinum atom.