Dicarboxylato Ligands Research Articles

Diosmium carbonyl sawhorse complexes containing a ferrocenedicarboxylato ligand

In an attempt to prepare a supramolecular assembly consisting of two, three, or four diosmium carbonyl sawhorse units linked together by dicarboxylato ligands, the reaction of [Os3(CO)12] with ferrocene-1,1′-dicarboxylic acid, Fe(C5H4COOH)2, was carried out with microwave heating. Instead of an assembly, the lone diosmium product was the single sawhorse complex [Os2(μ-ferrocene-1,1′-dicarboxylato)(CO)6] (1) with a tetradentate doubly bridging Fe(C5H4CO2 –)2 ligand, a metal–metal single bond, four equatorial carbonyl ligands, and two axial carbonyl ligands. Two additional sawhorse complexes, [Os2(μ-ferrocene-1,1′-dicarboxylato)(CO)4(tri-p-tolylphosphine)2] (2) and [Os2(μ-ferrocene-1,1′-dicarboxylato)(CO)4(N,N-dimethylaminomethylferrocene)2] (3), were prepared by substituting the axial CO ligands in 1 with P- or N-donor ligands, respectively. Clusters 1, 2, and 3 represent the first examples of carbonyl sawhorse complexes with ferrocenedicarboxylato ligands, and all three were characterized with single-crystal X-ray diffraction studies.

Beclin1 affected by DN604 upregulates chemo-sensitivity of cervix SiHa cancer cells via inhibiting CK2-MRN-DSBs repair.

DN604, containing a functional dicarboxylato ligand as carboplatin analogue, was significantly studied to explore its potency of antitumour activity. In vitro and in vivo experimental evidence indicated that DN604 exhibited superior antitumor activity than present platinum(II)-based agents in cervix squamous carcinoma SiHa cancer cells. Moreover, DN604 showed negligible toxic effects in vivo as confirmed as Pt accumulation and body weights of mice. Mechanistic studies have shown that DN604 suppressed CK2-mediated MRN complex to improve its antitumor efficacy by promoting DNA double-strand breaks repair. Furthermore, DN604 could inhibit Beclin1 and attenuate CK2-mediated several DSBs repair-related pathways, thus leading to cell apoptosis. Taken together, our research demonstrated that DN604 with the functional dicarboxylato ligand as the leaving group could effectively enhance chemo-sensitivity of SiHa cells to platinum-based agents via suppressing Beclin1 and CK2-mediated MRN-DSBs repair.

Enhancement of Electrical Conductivity due to Structural Distortion from Linear to Nonlinear Dicarboxylato-Bridged Zn(II) 1D-Coordination Polymers

Coordination polymers are useful materials in different fields of applications, including the development of supramolecular electrical devices for the use of renewable energy sources. In this work, we have designed two new classes of mixed-ligand one-dimensional coordination polymers (1D CPs) [Zn(ADC)(PBT)2(H2O)2]n (1) and [Zn(Succ)(PBT)2(H2O)2]n (2) (ADC2–, acetylenedicarboxylato; Succ2–, succinato; PBT, 2-pyridin-4-ylbenzothiazole) and characterized them by elemental analysis, infrared spectra (IR), single-crystal X-ray diffraction data, powder X-ray diffraction (PXRD), and thermogravimetric analysis (TGA) data. In the structural motif Zn(II) is bridged by an aliphatic dicarboxylato ligand (ADC/Succ) and two axial positions are occupied by pyridyl-N of PBT along with water coordination. ADC acts as a monodentate carboxylato-O ligand in compound 1, whereas in 2 Succ serves as a carboxylato-O,O chelator. Compounds 1 and 2 are both isostructural and construct 3D supramolecular networks by hydrogen bonds (b...

DN604: A platinum(II) drug candidate with classic SAR can induce apoptosis via suppressing CK2-mediated p-cdc25C subcellular localization in cancer cells

DN604, a carboplatin analogue with a functional dicarboxylato ligand, was deeply investigated to explore its ability to induce apoptosis as well as its antitumor mechanism of action. Both in vitro and in vivo assays indicated that DN604 could effectively inhibit cell viability of SGC-7901 gastric cancer cells and exhibited stronger antitumor activity than carboplatin and comparable activity to cisplatin. Significantly in contrast to cisplatin, DN604 resulted in negligible toxic effects in vivo with the same tumor growth inhibition effect as cisplatin. The mechanism study indicated that DN604 inhibited CK2-phosphorylated cdc25C activation to decrease p-cdc25C subcellular localization, leading to the inactivation of cdc2/Cyclin B and G2/M cell cycle arrest and apoptosis in SGC-7901 cancer cells. Our research revealed for the first time that the dicarboxylato ligand containing a suitable functional moiety as the leaving group in the platinum(II) complex can effectively induce cell cycle arrest and apoptosis via inhibiting key checkpoint proteins.

Rational design of dicarboxylato platinum(II) complexes with purine-mimetic ligands as novel anticancer agents

Six novel platinum(II) complexes containing purine-mimetic ligands (5,7-dimethyl-1,2,4-triazolo[1,5-a]pyrimidine (dmtp), 7-isobutyl-5-methyl-1,2,4-triazolo[1,5-a]pyrimidine (ibmtp), 5,7-ditertbutyl-1,2,4-triazolo[1,5-a]pyrimidine (dbtp)) and dicarboxylato ligands (glutarato (glut) or cyclobutane-1,1-dicarboxylato (CBDC)) have been prepared and characterized with multinuclear magnetic resonance (1H, 13C, 15N, 195Pt) NMR, infrared (IR) and X-ray crystallography. Spectroscopic data in solid state and in solution unambiguously confirm the square-planar geometry of Pt(II) with two monodentate N3-bonded 5,7-disubstituted-1,2,4-triazolo[1,5-a]pyrimidine ligands and one O-chelating dicarboxylato ligand. Next, the effect of all the platinum(II) compounds on the viability of normal or cancer cells and their putative mechanisms of action have been investigated. Of the studied platinum(II) complexes, two ([Pt(glut)(dbtp)2] and [Pt(CBDC)(dbtp)2]) overcame the cisplatin resistance in human ovarian tumor cells (A2780cis or OVCAR-3) and arrested the cell cycle at S phase in mice mammary gland cancer cells (4T1), which indicates a mechanism of action different from that of cisplatin. Interestingly, preliminary in vivo toxicity assays revealed that both compounds tested in mice ([Pt(glut)(dbtp)2] 3 and [Pt(CBDC)(dbtp)2] 6) were less toxic in vivo than cisplatin or oxaliplatin. Additionally, compound 6 did not cause myelosuppression and showed over fivefold less accumulation in the liver than its glutarato analog 3.

Dicarboxylato ligands in osmium carbonyl sawhorse clusters: Chelating vs. bridging

Seven new complexes comprising of diosmium(I) tetracarbonyl sawhorse units bound to dicarboxylate anions (DCAs) have been synthesized using microwave heating. Succinic, adipic, pimelic, suberic, tetradecanedioic, and terephthalic acids react with Os3(CO)12 at temperatures ranging from 180 to 205 °C for 12–20 min to produce the osmium sawhorse complexes, which are subsequently reacted with phosphine ligands to replace the labile axial CO ligands. X-ray crystallographic analysis was used to determine the molecular structures of these complexes. Two complexes, those with suberato and tetradecanedioato ligands, are dinuclear species containing Os2 sawhorse molecules with chelating DCAs that form intramolecular loops. The succinato, adipato and pimelato complexes are tetranuclear species consisting of two Os2 sawhorse moieties linked together by two bridging DCAs. Thus the straight-chain hydrocarbon backbone of the DCAs must contain at least six carbon atoms in order for these ligands to prefer to chelate a single Os2 unit instead of forming bridges between multiple Os2 units. The terephthalato complex is a triangular hexanuclear species consisting of a trimer of dimers with three bridging dicarboxylato anions.

Tuning Interchain Interactions in Two-Dimensional Networks of Mn(III) Schiff-Base Complexes and Dicarboxylic Acids by Varying the Linker.

Two-dimensional (2D) coordination polymers consisting of Mn(III) Schiff-base complexes and dicarboxylic acids, [{Mn(salen)}4(L1)](PF6)2·(CH3OH)2 (C4; H2L1 = adipid acid) and [{Mn(salen)}4(L2)](PF6)2·(CH3OH)4 (C4'; H2L2 = E,E-1,3-butadiene-1,4-dicarboxylic acid) (salen(2-) = N,N'-(ethylene)bis(salicylideneiminato), were synthesized by using a one-pot reaction and characterized by using single-crystal X-ray crystallographic analysis. One-dimensional (1D) chains composed of Mn(salen) dimers, [Mn2], bridged by carboxylato ligands (-[Mn2]-OCO--[Mn2]-), were linked by dicarboxylato ligands with n-butyl (-C4H8-) (C4) and butadienyl aliphatic groups (-C4H4-) (C4'). From static magnetic measurements on both C4 and C4', there were ferromagnetic interactions between the Mn(III) ions through the phenoxo oxygen atoms of the salen(2-), and antiferromagnetic interactions between the Mn(III) ions through carboxylato ligands (-OCO-). As a result, weak ferromagnetism occurred because of the zigzag-shaped chain structure of C4 and C4', and magnetic anisotropy for Mn(salen). In the magnetization curves for C4', weak interchain interactions (Jlinker) occurred through the π-conjugated butadienyl linkers in C4', which C4 did not have. In other words, changing from saturated to unsaturated aliphatic groups in the dicarboxylic acid linkers resulted in weak interactions between 1D-magnetic chain moieties. Therefore, in the case of only C4', antiferromagnetic phase transition appeared at 2.3 K. Both coordination polymers exhibited slow relaxation of the magnetizations, which originated from SCM moieties, because C4 and C4' showed magnetic correlations. It is noteworthy that alternating current (ac) susceptibilities for C4' are frequency-dependent around the Néel temperature. From analysis of the ac susceptibilities for C4, α (dispersion coefficient of the relaxation of magnetization) varied linearly with 1/T. This signifies that C4 behaved as an SCM with a single relaxation process. On the other hand, in α versus 1/T plots for C4', an inflection point was observed at the Néel temperature, indicating that Jlinkers had an effect on the distribution of the relaxation times. Moreover, the inflection point for C4' disappeared when a dc magnetic field was applied. This is the first report showing a direct correlation between an antiferromagnetic phase transition and slow magnetic relaxation.

Effect of Dicarboxylato Ligands on the Self‐Assembly of Two Cadmium(II) Coordination Polymers Containing Multidentate N‐donor Ligands

AbstractTwo CdII‐containing coordination polymers based on a multidentate N‐donor ligand and two structure‐related dicarboxylate ions, namely, [Cd2(3,4′‐tmbpt)(o‐bdc)2]·2H2O (1) and [Cd2(3,4′‐tmbpt)2(p‐bdc)2]·6.5H2O (2) [3,4′‐tmbpt = 1‐((1H‐1,2,4‐triazol‐1‐yl)methyl)‐3‐(4‐pyridyl)‐5‐(3‐pyridyl)‐1,2,4‐triazole, o‐H2bdc = 1,2‐benzenedicarboxylic acid, and p‐H2bdc = 1,4‐benzenedicarboxylic acid], were prepared under hydrothermal conditions. The structures of the two compounds were determined by single‐crystal X‐ray diffraction analysis and further characterized by infrared spectra (IR) and elemental analysis. Compound 1 is a 3D framework containing infinite Cd–O chains. Compound 2 displays a 2D → 2D interdigitated architecture. The effect of the dicarboxylate ions on the structures of the compounds was discussed. Moreover, the optical bandgaps and photoluminescent properties of the compounds were investigated.

Di- and tetraosmium carbonyl complexes with dicarboxylato ligands serving as intramolecular rings and intermolecular bridges

The osmium(I) carbonyl complexes Os2(μ-sebacate)(CO)4(dmso)2 (1) and [Os2(CO)6]2(μ4-1,3-adamantanediacetate)2 (2) have been prepared by microwave heating and structurally characterized by X-ray crystallographic analysis. The reaction of Os3(CO)12 with sebacic acid in 1,2-dichlorobenzene at 205 °C produces Os2(μ-sebacate)(CO)6 in 45% yield. Subsequent treatment with dimethylsulfoxide at 70 °C results in conversion to the dmso adduct 1. The reaction of Os3(CO)12 with 1,3-adamantanediacetic acid in 1,2-dichlorobenzene at 208 °C produces 2. Clusters 1 and 2 contain Os2(CO)4 units with sawhorse geometries and Os–Os single bonds. In the diosmium complex 1, a sebacato (decanedioato) ligand forms an intramolecular chelate ring within a single Os2 sawhorse unit. In the tetraosmium complex 2, two 1,3-adamantanediacetato ligands form intermolecular bridges that join two Os2 sawhorse units into a molecular loop.

Coordination polymers of lanthanide complexes with benzene dicarboxylato ligands

Three kinds of coordination polymers of lanthanide complexes with benzene dicarboxylato ligands, [Ln(L1)1.5(H2O)2]·H2O (H2L1 = 2,5-dibenzoylterephthalic acid; Ln = Pr (1), Nd (2), Sm (3), Eu (4), Gd (5), Tb (6), Dy (7)), [Ln(L2)(phen)(OH)] (H2L2 = 4,6-dibenzoylisophthalic acid; phen = 1,10-phenanthroline; Ln = Sm (8), Eu (9), Tb (10), Dy (11), Er (12), Yb (13)) and [Ln(L1)0.5(L2)(H2O)2] (Ln = Er (14), Ho (15)), were synthesized under hydrothermal conditions. They were characterized by elemental analysis, IR spectroscopy and thermogravimetric analysis. Their solid-state structures were determined by single-crystal X-ray diffraction. Complexes 1–7 are isostructural, each featuring the L1 connected dinuclear unit of Ln2O2(CO2)6 to produce a 6-connected 3D network with (412·63) topology. Isostructural complexes 8–13 possess 2D layer structures consisting of left- and right-handed helical chains that are further assembled into 3D supramolecular architectures through C–H⋯O, C–H⋯π and π⋯π interactions. Complexes 14 and 15 display 2D layer structures, and are further linked into 3D supramolecular architectures through C–H⋯O and π⋯π interactions. The luminescence properties of 3, 4 and 6–11 were investigated.

Monomeric, Dimeric Helical, and 1D Nickel Polyoxotungstates Structured by Carboxylate Derivatives

AbstractThree new nickel‐substituted Keggin‐type polyoxometalates functionalized by carboxylate derivatives were characterized. In the monomeric tetranuclear complex Na1.5K2.5[Ni(H2O)6]0.5[(SiW9O34)(OH)3Ni4(C6H13NO2)3]·17H2O (1), three dimethylaminobutyrate amino acids are connected to a {SiW9Ni4} subunit through the carboxylato groups, and the pendant amino functions are protonated. In the dimeric, octanuclear species Na2K12[Ni(H2O)6][(SiW9O34)2(OH)6Ni8(C6H8O4)3]·40H2O (2), three saturated adipato (C6, dicarboxylate) ligands connect two {SiW9Ni4} fragments. This unique molecular‐helical polyoxometalate is obtained as a racemic mixture of the M and P enantiomers. When the aromatic dicarboxylate p‐phenylenediacetate is used as a bridging ligand, the compound Na6K8[(SiW9O34)2(OH)6Ni8(C10H8O4)3]·45H2O (3) is obtained. In this species, two equivalent p‐phenylenediacetato linkers connect two {SiW9Ni4} subunits to form a {Si2W18Ni8} assembly, and a third dicarboxylato ligand connects these fragments, which affords a 1D polyoxometalate with a zigzag‐chain topology. Solution 1H NMR studies and IR experiments show that redissolving all these species in water affords carboxylato‐free compounds after few hours. The magnetic properties of complexes 1 and 2 were also studied. For these two compounds, a quantification of the magnetic exchange interactions revealed the presence of competitive antiferromagnetic and ferromagnetic interactions.

Synthetic Control to Achieve Lanthanide(III)/Pyrimidine-4,6-dicarboxylate Compounds by Preventing Oxalate Formation: Structural, Magnetic, and Luminescent Properties

Control over the synthetic conditions in many metal/diazinedicarboxylato systems is crucial to prevent oxalate formation, since dicarboxylato ligands easily undergo degradation in the presence of metal salts. We report here an efficient route to obtain oxalato-free compounds for the lanthanide/pyrimidine-4,6-dicarboxylato (pmdc) system on the basis of the reaction temperature and nonacidic pH or oxygen free atmosphere. Two different crystal architectures have been obtained: {[Ln(μ-pmdc)(1.5)(H(2)O)(3)]·xH(2)O}(n) (1-Ln) and {[Ln(2)(μ(4)-pmdc)(2)(μ-pmdc)(H(2)O)(2)]·H(2)O}(n) (2-Ln) with Ln(III) = La-Yb, except Pm. Both crystal structures are built from distorted two-dimensional honeycomb networks based on the recurrent double chelating mode established by the pmdc. In compounds 1-Ln, the tricapped trigonal prismatic coordination environment of the lanthanides is completed by three water molecules, precluding a further increase in the dimensionality. Crystallization water molecules are arranged in the interlamellar space, giving rise to highly flexible supramolecular clusters that are responsible for the modulation found in compound 1-Gd. Two of the coordinated water molecules are replaced by nonchelating carboxylate oxygen atoms of pmdc ligands in compounds 2-Ln, joining the metal-organic layers together and thus providing a compact three-dimensional network. The crystal structure of the compounds is governed by the competition between two opposing factors: the ionic size and the reaction temperature. The lanthanide contraction rejects the sterically hindered coordination geometries whereas high-temperature entropy driven desolvation pathway favors the release of solvent molecules leading to more compact frameworks. The characteristic luminescence of the Nd, Eu, and Tb centers is improved when moving from 1-Ln to 2-Ln compounds as a consequence of the decrease of the O-H oscillators. The magnetic properties of the compounds are dominated by the spin-orbit coupling and the ligand field perturbation, the exchange coupling being almost negligible.

Metal(II) Complexes Based on Imidazo[4, 5‐f]‐1, 10‐phenanthroline and Bridging Dicarboxylato Ligands: Synthesis, Characterization and Photoluminescence

AbstractEight metal(II) complexes based on imidazo[4, 5‐f]‐1, 10‐phenanthroline (HIMP) and bridging dicarboxylato ligands such as 4, 4′‐biphenyldicarboxylic acid (H2BPDC), 1, 4‐benzenedicarboxylic acid (H2BDC), thiophene‐2, 5‐dicarboxylic acid (H2TDC), and 2, 6‐naphthalenedicarboxylic acid (H2NDC) were hydrothermally synthesized and structurally characterized by single‐crystal X‐ray diffraction. Complexes 1, 3, 6, and 7 are molecular dinuclear metal complexes. Complexes 2, 4, and 5 exhibit chain‐like structures. Compound 8 shows a novel 3D architecture, in which ZnII dimers are connected by four NDC2– anions. In the metal(II) complexes, HIMP exhibits a similar chelating coordination mode. Different π···π stacking interactions are observed in the complexes. The emission of HIMP is completely quenched in complexes 1–4 due to the strong π···π stacking interactions in the structures. Complexes 5–8 exhibit different photoluminescence properties. Firstly, we quantitatively investigated the effect of the strong HIMP–HIMP stacking interactions on the emission quenching of HIMP in the metal complexes. It was found that a higher extent of π···π stacking interactions in the complexes resulted in a higher extent of the emission quenching of HIMP. The introduction of aromatic conjugated carboxylate groups into metal(II)‐HIMP complexes changed the extent of the strong π···π stacking interactions in the structures and thus the photoluminescence properties of the complexes.

A unique unit cell containing simultaneous doubly and triply copper(II) complexes bridging by 2,4-pyridine dicarboxylate

Abstract The reaction of an aqueous solution containing Cu(ClO4)2, N,N,N′,N″,N″-pentamethylethylene-triamine (pmedien) and 2,4-pyridine dicarboxylic acid disodium salt (Na2.2,4-pydc) afforded {[Cu3(pmedien)3(μ-2,4-pydc)(H2O)2](ClO4)4,[Cu2(pmedien)2(μ-2,4-pydc)(H2O)](ClO4)2}∙4H2O (1). The complex was structurally and magnetically characterized. Single X-ray crystallography for 1 reveals the existence of two independent molecules in the unit cell in which the dinuclear and trinuclear Cu(II) centers are bridging by the 2,4-pyridine dicarboxylato ligands. Magnetic susceptibility measurements of the complex showed that the Cu(II) ions are antiferromagnetically weakly coupled (J = − 0.27 cm−1).

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 [Ni 2(ntb) 2(μ-tp)(H 2O) 1.61(CH 3OH) 0.39](NO 3) 2·5.13CH 3OH·2.25H 2O (1) and [Ni 2(ntb) 2(μ-fum)(H 2O)(CH 3OH)](NO 3) 2·6CH 3OH·H 2O (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.

Dimers and chains of {3d–4f} single molecule magnets constructed from heterobimetallic tectons

A tetranuclear complex and a 1-D coordination polymer with a ladder-like topology have been obtained by connecting [Ni(II)Dy(III)] nodes with dicarboxylato ligands: [Ni₂(valpn)₂Dy₂(III)(pdca)₂(NO₃)(H₂O)₆](NO₃)·4H₂O 1, and (∞)¹[Ni₂(H₂O)₂(valpn)₂Dy₂(tfa)₃]·4CH₃CN 2 (valpn²⁻ = the dianion of the Schiff base resulting from reacting o-vanillin with 1,3-propanediamine; pdca²⁻ = the dianion of 2,6-pyridinedicarboxylic acid; tfa²⁻ = the dianion of the terephthalic acid). The magnetic measurements show a ferromagnetic interaction between Ni(II) and Dy(III), and that both compounds behave like SMM with strong tunnelling. The barrier of 2 (17.4 K) is higher than that of 1 (13.6 K).

One dimensional assembly of Mn6 single molecule magnets linked by oligothiophene bridges

A new 1D coordination polymer comprised of [Mn(III)(6)O(2)(Et-sao)(6)(EtOH)(4)(H(2)O)(2)](2+) units and bithiophene dicarboxylato was synthesized by mixing EtsaoH(2) (salicylaldoxime), H(2)btda (2,2'-bithiophene-5,5'-dicarboxylic acid) and Mn(ClO(4))(2)·6H(2)O in the presence of NEt(4)OH. The crystal structure was determined and consists of Mn(6) clusters bridged by the bithiophene dicarboxylato ligands coordinated to two of the Mn(III) ions of the Mn(6) polynuclear complex. Direct current magnetic measurements show an overall ferromagnetic interaction between the Mn(III) ions within the Mn(6) cluster leading to an S = 12 ground state for the Mn(6) unit. Furthermore, this compound presents single-molecule magnet behaviour. Slow relaxation of the magnetization is observed at low temperature following a thermal activated regime with U(eff) approximately 50 K and tau(0) approximately 2.2 10(-10) s. The magnetic measurements do not show any noticeable interaction between the Mn(6) clusters through the bithiophene dicarboxylato bridges.

Structural and magnetic characterization of a novel series of dinuclear Cu(II) complexes bridging by 2,5-pyrazine dicarboxylate

A new series of dinuclear 2,5-pyrazine dicarboxylato-bridged copper(II) complexes were synthesized and characterized by spectroscopic techniques. The complexes have the general structural formula [Cu 2(L) 2(μ-pyzdc)](ClO 4) 2· nH 2O where L = TPA, n = 2 ( 1); L = pmedien, n = 2 (2); L = aepn, n = 3 ( 3); L = dpt, n = 2 ( 4); L = Medpt, n = 0 ( 5); L = dien, n = 0 ( 6) and L = MeDPA, n = 2 ( 7) with TPA = tris(2-pyridylmethyl)amine, pmdien = N,N,N′,N′′,N′′-pentamethyldiethylenetriamine, aepn = N-(2-aminoethyl)-1,3-diaminopropane, dpt = dipropylene-triamine, Medpt = 3,3′-diamino-N-methyldipropylamine, dien = diethylenetriamine, MeDPA = N,N-di(2-pyridylmethyl)methylamine. In these complexes, the bridging nature of the 2,5-pyrazine dicarboxylato ligand (pyzdc) was confirmed by single-crystal X-ray crystallography. The structure of the TPA complex 1 consists of μ-pyzdc bridging two Cu(II) centers in a bis(monodentate) bonding fashion through a single oxygen atom supplied by each carboxylate group of the bridged pyzdc in a distorted trigonal bipyramidal geometry achieved by the four nitrogen atoms from the TPA ligand. In the complexes 2– 5 derived from tridentate amines, the bridged pyzdc acts as a bis(bidentate) ligand in a distorted square pyramidal geometry achieved by one nitrogen and one carboxylate-oxygen of pyzdc, and by the three N-atoms of the amine coligands. The intradimer Cu ⋯ Cu distances in the complexes 2– 5 are in the range 6.97–7.45 Ǻ and in it is 10.96 Ǻ in 1. The corresponding intermolecular distances are even shorter (5.34–7.99 Ǻ). The susceptibility measurements at variable temperatures over the 5–300 K range reveal weak antiferromagnetic coupling with J values ranging from −0.61 to −4.78 cm −1.

Synthesis and study of Pt(II)-aromatic amines complexes of the types cis- and trans-Pt(amine) 2(NO 3) 2 and cis-Pt(amine) 2(R(COO) 2)

Complexes of the types cis- and trans-Pt(amine) 2(NO 3) 2 with amines containing a phenyl group were synthesized and studied mainly by IR and multinuclear magnetic resonance spectroscopies. The cis complexes could be synthesized pure only with the amines of the type Ph–R–NH 2 (R = alkyl), while pure trans compounds were synthesized with all the studied amines. In 195Pt NMR spectroscopy, the dinitrato complexes of the amines Ph–R–NH 2 were observed around −1700 ppm for the cis isomers and at about −1580 for the trans complexes. For the other amines, where a phenyl ring is directly attached to the amino group, the signals were observed at lower fields, −1528 ppm for cis-Pt(PhNH 2)(NO 3) 2 and around −1450 ppm for all the trans isomers. There is a linear relationship between the δ(Pt) of the Pt(amine) 2(NO 3) 2 complexes and the p K a of the protonated amines. The coupling constants 2 J( 195Pt– 1HN) are larger in the cis compounds (ave. 76 Hz) than in the trans isomers (ave. 63 Hz). The complexes cis-Pt(amine) 2(R(COO) 2) with bidentate dicarboxylato ligands were also synthesized and characterized mainly by IR spectroscopy. The compounds apparently decompose in DMF and are too insoluble in other solvents for solution studies.

Dinuclear fumarato- and terephthalato-bridged copper(II) complexes: Structural characterization and magnetic properties

The dinuclear dicarboxylato-bridged copper(II) complexes [Cu 2(TPA) 2(μ-tp)](ClO 4) 2 · H 2O ( 1), [Cu 2(TPA) 2(μ-fum)](ClO 4) 2 · 2H 2O ( 2) and [Cu 2(pmedien) 2(μ-fum)(H 2O) 2](ClO 4) 2 ( 3) (tp = terephthalate dianion, fum = fumarate dianion, TPA = tris(2-pyridylmethyl)amine and pmedien = N, N, N′, N″, N″-pentamethyldiethylenetriamine) were synthesized and structurally characterized by X-ray crystallography. The structures of the TPA complexes 1 and 2 consist of μ-tp or μ-fum bridging two Cu(II) centers in a bis(monodentate) bonding fashion. The coordination geometry around the Cu(II) ions in these compounds has a distorted trigonal bipyamidal geometry, TBP with four nitrogen atoms from the TPA ligand and a coordinated oxygen atom supplied by the carboxylate group of the bridged dicarboxylato ligand. Complex 3 has a distorted square pyramidal geometry achieved by the three N-atoms of the pmedien, one fum-carboxylate-oxygen and by an oxygen atom from a coordinated water molecule. The intradimer Cu…Cu distances in these complexes are 11.078(3), 8.663(4) and 9.520(3) 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 Cu(II) centers. Also, analysis of the infrared spectral data for the ν(COO −) stretching frequencies of the tp-carboxalato groups reveals the existence of the bis(mondentate) coordination mode for the bridged dicarboxylato ligands in compounds 1 and 2. The susceptibility measurements at variable temperature over the 2–300 K range are reported. For 1– 3, it has been observed slight antiferromagnetic coupling with J values of −0.8, −3.0 and −2.9 cm −1, respectively.