Synthesis, structure and spectroscopy of new thiopyrone and hydroxypyridinethione transition-metal complexes

The coordination chemistry of several O,S mixed donor ligands, namely thiopyrone and hydroxypyridinethione chelators, with a variety of middle and late first-row transition-metal ions is described. Complexes of 3-hydroxy-2-methyl-4-thiopyrone (thiomaltol) with cobalt(II), copper(II) and zinc(II); 3-hydroxy-1,2-dimethyl-4(1H)-pyridinethione (3,4-HOPTO) with iron(III), nickel(II), copper(II) and zinc(II); and 3-hydroxy-1-methyl-2(1H)-pyridinethione (3,2-HOPTO) with iron(III), nickel(II), copper(II) and zinc(II) have been synthesized and characterized. The structures, absorbance spectroscopy, cyclic voltammetry and superconducting quantum interferometer device (SQUID) measurements of selected metal complexes, as well as ligand protonation constants, are reported. Most of the metal complexes show coordination geometries indicative of a strong trans influence by the O,S chelators. The data presented herein provide the most detailed study of the transition-metal coordination chemistry of both thiopyrone and hydroxypyridinethione O,S donor ligands to date, and provide the basis for the investigation of these ligands in realm of biological inorganic chemistry.     

Vanadium complexes with mixed O,S anionic ligands derived from maltol: synthesis, characterization, and biological studies

Four mixed O,S binding bidentate ligand precursors derived from maltol (3-hydroxy-2-methyl-4-pyrone) have been chelated to vanadium to yield new bis(ligand)oxovanadium(IV) and tris(ligand)vanadium(III) complexes. The four ligand precursors include two pyranthiones, 3-hydroxy-2-methyl-4-pyranthione, commonly known as thiomaltol (Htma), and 2-ethyl-3-hydroxy-4-pyranthione, commonly known as ethylthiomaltol (Hetma), as well as two pyridinethiones, 3-hydroxy-2-methyl-4(H)-pyridinethione (Hmppt) and 3-hydroxy-1,2-dimethyl-4-pyridinethione (Hdppt). Vanadium complex formation was confirmed by elemental analysis, mass spectrometry, and IR and EPR (where possible) spectroscopies. The X-ray structure of oxobis(thiomaltolato)vanadium(IV),VO(tma)(2), was also determined; both cis and trans isomers were isolated in the same asymmetric unit. In both isomers, the two thiomaltolato ligands are arranged around the base of the square pyramid with the V=O linkage perpendicular; the vanadium atom is slightly displaced from the basal plane [V(1) = 0.656(3) A, V(2) = 0.664(2) A]. All of the new complexes were screened for insulin-enhancing effectiveness in streptozotocin-induced diabetes in rats, and VO(tma)(2) was profiled metabolically for urinary vanadium and ligand clearance by GFAAS and ESIMS, respectively. The new vanadium complexes did not lower blood glucose levels acutely, possibly because of rapid dissociation and excretion.     

Structural variation from 1D to 3D: effects of ligands and solvents on the construction of lead(II)-organic coordination polymers

A series of Pb(II) coordination polymers [Pb(ndc)(dpp)] (1), [Pb(ndc)(ptcp)].0.5 H2O (2), [Pb(ndc)(dppz)] (3), [Pb(ndc)(tcpn)(2)] (4), [Pb2(ndc)2(tcpp)] (5), [Pb(Hndc)2].H2O (6), [Pb(ndc)(dma)] (7), [Pb(bdc)(dma)] (8), [Pb(trans-chdc)(H2O)] (9), and [Pb2(cis-chdc)2].NH(CH3)2 (10), where ndc=1,4-naphthalenedicarboxylate, dpp=4,7-diphenyl-1,10-phenanthroline, ptcp=2-phenyl-1H-1,3,7,8-tetraazacyclopenta[l]phenanthrene, dppz=dipyrido[3,2-a:2',3'-c]phenazine, tcpn=2-(1H-1,3,7,8-tetraazacyclopenta[l]phenanthren-2-yl)naphthol, tcpp=4-(1H-1,3,7,8-tetraazacyclopenta[l]phenanthren-2-yl)phenol, dma=N,N-dimethylacetamide, bdc=1,4-benzenedicarboxylate, and chdc=1,4-cyclohexanedicarboxylate, have been synthesized from a hydrothermal or solvothermal reaction system by varying the ligands or the solvents. Compounds 1-5 crystallize with an N-donor chelating ligand and an aromatic dicarboxylate linker. Compounds 1-4 are 1D polymers with different pi-pi stacking interactions, whereas compound 5 consists of 2D layers. The structures of compounds 7, 8, and 10 are 3D frameworks formed by connection of the Pb(II) centers by organic acid ligands. Compound 7 is chiral although the ndc ligand is achiral, while the framework of 8 is a typical 3D (3,4)-connected net. Compound 10 is the first example of Pb(II) wheel cluster [Pb(8)O(8)] units bridged by carboxylate groups. Compound 6 contains 1D chains which are further extended to a 3D structure by pi-pi interactions. Compound 9 consists of a 2D network constructed by Pb(II) centers and trans-chdc ligands. The structural differences between 7 and 8 and between 9 and 10 indicate the importance of solvents for framework formation of the coordination polymers. By varying the solvent the cis and trans conformations of H(2)chdc in 9 and 10 were separated completely. The photoluminescence and nonlinear optical properties of the coordination polymers have also been investigated.     

Organic-acid effect on the structures of a series of lead(II) complexes

An investigation into the dependence of coordination polymer architectures on organic-acid ligands is reported on the basis of the reaction of Pb(NO3)2 and eight structurally related organic-acid ligands in the presence or absence of N-donor chelating ligands. Eight novel lead(II)-organic architectures, [Pb(adip)(dpdp)]2 1, [Pb(glu)(dpdp)] 2, [Pb(suc)(dpdp)] 3, [Pb(fum)(dpdp)] . H2O 4, [Pb2(oba)(dpdp)2] . 2(dpdp).2(NO3).2H2O 5, [Pb2(1,4-bdc)2(dpdp)2] . H2O 6, [Pb(dpdc)(dpdp)] 7, and [Pb(1,3-bdc)(dpdp)] . H2O 8, where dpdp = dipyrido[3,2-a:2',3'-c]-phenazine, H2adip = adipic acid, H2glu = glutaric acid, H2suc = succinic acid, H2fum = fumaric acid, H2oba = 4,4'-oxybis(benzoic acid), 1,4-H2bdc = benzene-1,4-dicarboxylic acid, H2dpdc = 2,2'-diphenyldicarboxylic acid, and 1,3-H2bdc = benzene-1,3-dicarboxylic acid, were successfully synthesized under hydrothermal conditions through varying the organic-acid linkers and structurally characterized by X-ray crystallography. Compounds 1-8 crystallize in the presence of organic-acid linkers as well as secondary N-donor chelating ligands. Diverse structures were observed for these complexes. 1 and 5 have dinuclear structures, which are further stacked via strong pi-pi interactions to form 2D layers. 2-3 and 6-8 feature chain structures, which are connected by strong pi-pi interactions to result in 2D and 3D supramolecular architectures. Compound 4 contains 2D layers, which are further extended to a 3D structure by pi-pi interactions. A systematic structural comparison of these 8 complexes indicates that the organic-acid structures have essential roles in the framework formation of the Pb(II) complexes.     

Holo- and hemidirected lead(II) in the polymeric [Pb(4)(mu-3,4-TDTA)2(H2O)2]*4H2O complex. N,N,N',N'-tetraacetate ligands derived from o-phenylenediamines as sequestering agents for lead(II)

The coordinating ability of the ligands 3,4-toluenediamine-N,N,N',N'-tetraacetate (3,4-TDTA), o-phenylenediamine-N,N,N',N'-tetraacetate (o-PhDTA), and 4-chloro-1,2-phenylenediamine-N,N,N',N'-tetraacetate (4-Cl-o-PhDTA) (H4L acids) toward lead(II) is studied by potentiometry (25 degrees C, I = 0.5 mol x dm(-3) in NaClO4), UV-vis spectrophotometry, and 207Pb NMR spectrometry. The stability constants of the complex species formed were determined. X-ray diffraction structural analysis of the complex [Pb4(mu-3,4-TDTA)4(H2O)2]*4H2O (1) revealed that 1 has a 2-D structure. The layers are built up by the polymerization of centrosymmetric [Pb4L2(H2O)2] tetranuclear units. The neutral layers have the aromatic rings of the ligands pointing to the periphery, whereas the metallic ions are located in the central part of the layers. In compound 1, two types of six-coordinate lead(II) environments are produced. The Pb(1) is coordinated to two nitrogen atoms and four carboxylate oxygens from the ligand, whereas Pb(2) has an O6 trigonally distorted octahedral surrounding. The lead(II) ion is surrounded by five carboxylate oxygens and a water molecule. The carboxylate oxygens belong to four different ligands that are also joined to four other Pb(1) ions. The selective uptake of lead(II) was analyzed by means of chemical speciation diagrams as well as the so-called conditional or effective formation constants K(Pb)eff. The results indicate that, in competition with other ligands that are strong complexing agents for lead(II), our ligands are better sequestering agents in acidic media.     

A novel nanosized {Co16} metallamacrocycle incorporating four linear {Co4} subunits bridged by polytriazolate ligands

The solvothermal reactions of Co(II) salts and three rigid polytriazolate ligands lead to a linear Co(4) cluster, [Co(4)(3,5-bptp)(2)(OMe)(2)(NO(3))(2)(MeOH)(2)]·1.5H(2)O·MeCN (1), and a square-shaped {Co(16)} metallamacrocycle, [Co(16)(1,3-bptb)(4)(3,5-bptpt)(4)(OMe)(12)(H(2)O)(2)]·25H(2)O (2), which comprises four linear {Co(4)} subunits similar to those of 1 bridged by the longer 3,5-bptpt(3-) ligands into a nanoscale molecular square.     

Formation of PbS materials from lead xanthate precursors

Six lead xanthate adducts Pb(S(2)COR)(2).L [R = Et, (n)Bu, L = bipy, TMEDA (tetramethylethylenediamine), PMDETA (pentamethyldiethylenetriamine)] have been synthesised and the structures of all, save Pb(S(2)COBu(n))(2).TMEDA (4) which is an oil, determined. Pb(S(2)COEt)(2).TMEDA (3) is seven-coordinate at lead through three chelating ligands and one weak intermolecular Pb‥S interaction. Both Pb(S(2)COR)(2).bipy [R = Et (1), (n)Bu (2)] are dimers in which one xanthate is terminal and the other μ(2) bridging at each sulphur, generating an eight-coordinate lead when the bipy donor is included. Both Pb(S(2)COR)(2).PMDETA [R = Et (5), (n)Bu (6)] are seven-coordinate at lead by virtue of two bidentate chelating xanthate ligands and a tridentate PMDETA; there are no intermolecular interactions. Trends in the (207)Pb NMR chemical shifts mirror the changes in the intramolecular coordination number across the series. Pb(S(2)COEt)(2).TMEDA (3) has been used to deposit PbS films on glass, Mo-coated glass and Si by AACVD. Pb(S(2)COEt)(2) also generated PbS nanocubes when decomposed under an autogenerated pressure.     

Tetradentate bis(o-iminobenzosemiquinonate(1-)) pi radical ligands and their o-aminophenolate(1-) derivatives in complexes of nickel(II), palladium(II), and copper(II)

The coordination chemistries of the potential tetradentate ligands N,N'-bis(3,5-di-tert-butyl-2-hydroxyphenyl)ethylenediamine, H4[L1], the unsaturated analogue glyoxal-bis(2-hydroxy-3,5-di-tert-butylanil), H2[L2], and N,N'-bis(2-hydroxy-3,5-di-tert-butylphenyl)-2,2-dimethylpropylenediamine, H4[L3], have been investigated with nickel(II), palladium(II), and copper(II). The complexes prepared and characterized are [Ni(II)(H3L1)2] (1), [Ni(II)(HL2)2].5/8CH2Cl2 (2), [Ni(II)(L3**)] (3), [Pd(II)(L3**)][Pd(II)(H2L3) (4), and [Cu(II)(H2O)(L4)] (5), where (L4)2- is the oxidized diimine form of (L3)4- and (L3**)2- is the bis(o-iminosemiquinonate) diradical form of (L3)4-. The structures of compounds 1-5 have been determined by single crystal X-ray crystallography. In complexes 1 and 2, the ligands (H3L1)- and (HL2)- are tridentate and the nickel ions are in an octahedral ligand environment. The oxidation level of the ligands is that of an aromatic o-aminophenol. 1 and 2 are paramagnetic (mu(eff) approximately 3.2 mu(B) at 300 K), indicating an S = 1 ground state. The diamagnetic, square planar, four-coordinate complexes 3 and [Pd(II)(L3**)] in 4 each contain two antiferromagnetically coupled o-iminobenzosemiquinonate(1-) pi radicals. Diamagnetic [Pd(II)(H2L3)] in 4 forms an eclipsed dimer via four N-H.O hydrogen bonding contacts which yields a nonbonding Pd.Pd contact of 3.0846(4) A. Complex 5 contains a five-coordinate Cu(II) ion and two o-aminophenolate(1-) halves in (L4)2-. The electrochemistries of complexes 3 and 4a ([Pd(II)(L3**)] of 4) have been investigated, and the EPR spectra of the monocations and -anions are reported.     

Influence of pH and counteranion on the structure of tropolonato-lead(II) complexes: structural and infrared characterization of formed lead compounds

Reactions of tropolone with lead(II) trifluoromethanesulfonate, perchlorate, and nitrate in water/methanol mixtures at pH below 1.0 lead to the formation of three different polymeric lead(II) complexes, [Pb(trop)(CF3SO3)(H2O)]n (1), [Pb3(trop)4(ClO4)2]n (2), and [Pb2(trop)2(NO3)2(CH3OH)]n (3), respectively. On the other hand, if the reactions are performed at pH above 2.0, the dimeric compound [Pb(trop)2]2 (4) is obtained independently of the lead(II) salt used, as long as lead(II) does not form any strong complexes with the counterion. The crystal structures of these compounds have been determined by single-crystal X-ray diffraction. The structure of solid tetrakis(tropolonato)lead(IV), Pb(trop)4 (5), has been studied by means of the EXAFS technique because it was not possible to obtain sufficiently large single crystals. In the polymeric structures, the counterions are coordinated to the lead(II) ions and act as bridges. The tropolonato ligand behaves as a chelating agent and a tri- or tetraconnective bridge. The total coordination number of the lead(II) ion is five in compound 4, seven in 1 and 3, and eight in 2, and the lead(IV) ion in 5 is eight-coordinated. The 6s2 lone electron pair on the lead(II) ion seems to be stereochemically active in all lead(II) complexes studied. All compounds have been characterized by IR spectroscopy as well.     

Pt]2Pb trinuclear systems: impact of the anionic platinum fragment on the lead environment and photoluminescence

A comparison of the solid structures of three novel trinuclear sandwich Pt 2Pb systems (NBu 4) 2[{Pt(C identical withCTol) 4} 2Pb(OH 2) 2] 1, [{Pt(bzq)(C identical withCPh) 2} 2Pb] 2, and (NBu 4)[{Pt(bzq)(C identical withCC 6H 4-CF 3-4) 2} 2Pb(O 2ClO 2)] 4 (NBu 4[ 3.(O 2ClO 2)]) with that of the previously reported (NBu 4) 2[{Pt(C 6F 5) 4} 2Pb] 5 showed that the local environment of Pb (II) is highly sensitive to the nature of the anionic platinate(II) precursors. The photoluminescence (PL) studies of all 1- 5 complexes revealed a dependence of PL on the structure type. Thus, complexes 1 and 5 exhibit metal centered emissions ( 1, 497 nm, 77 K; 5, 539 nm, varphi = 0.43, 298 K) related to the linear ( 5) or bent ( 1 Pt-Pb-Pt 149.9 degrees ) trinuclear entities. However, in complexes 2- 4, that have unprecedented Pb (II)...eta (1)(C identical withCR) bonding interactions and very short Pt...Pb and Pt...Pt distances, the emissive state in solid state (77 K) is attributed to a (3)MLM'CT [Pt(1)pi(C identical withCR)-->Pt(2)/Pb(sp)pi*(C identical withCR)] state mixed with some pipi* excimeric character in neutral complexes 2 (R = Ph) and 3 (R = C 6H 4-CF 3-4), and in the case of the adduct (NBu 4)[{Pt(bzq)(C identical withCC 6H 4-CF 3-4) 2} 2Pb(O 2ClO 2)] 4 modified also by Pb (II)...O (O 2ClO 2 (-)) contacts.     

Synthesis, crystal structure and antiradical effect of copper(II) Schiff base complexes containing five-, six- and unusual seven-membered rings

The synthesis and solid-state structure of mononuclear copper(II) complexes [Cu(SAIB)(H(2)O)(2)] (1), [Cu(SBAIB)(H(2)O)(2)]·H(2)O (2) and [Cu(SGABA)(H(2)O)(2)] (3) are described. Schiff base ligands H(2)SAIB, H(2)SBAIB and H(2)SGABA chelate the copper(II) ion in an O,N,O tridentate fashion. The square-pyramidal geometry of the final complexes is completed by two water ligands. The formation of an unusual seven-membered ring in the set of copper(II) N-salicylidene-aminoacidates is reported. Compounds 1-3 were evaluated by the antiradical activity assay.     

Influence of the reaction conditions on the self-assembly of lead(II) 5-sulfosalicylate coordination polymers with chelating amine ligands

The synthesis and crystal structures of [Pb(Hssal)(2,2'-bipy)(DMF)]n (1), [Pb(Hssal)(2,2'-bipy)(H2O)]n (2), [Pb(Hssal)(phen)(DMF)]n (3), and [Pb3(ssal)2(phen)3]n (4) were reported, where Hssal2- and ssal3- are doubly and fully deprotonated 5-sulfosalicylates, 2,2'-bipy is 2,2'-bipyridine, and phen is 1,10-phenanthroline. Compounds 1-4 were synthesized by the various reaction conditions, such as reaction temperature, molar ratio, and pH, and these structures are formed by infinite chains or layers where Pb(II) ions are linked by Hssal2- or ssal3- bridges. Compound 1, which has a ladderlike chain, was formed in DMF/H2O. Compound 2 with a H2O molecule coordinated to Pb(II) was prepared by a hydrothermal reaction. Compounds 3 and 4 were synthesized in a higher pH compared to compounds 1 and 2, containing the 2,2'-bipy ligand. In 1-3, 5-sulfosalicylates are doubly deprotonated, whereas in 4, 5-sulfosalicylate is fully deprotonated. Coordination modes of Hssal2- and ssal3- ligands in 1-4 are novel and are first reported in this presentation. Although compounds 1 and 3 have the same structural topology, their aromatic-aromatic interactions are significantly different. The coordination spheres of Pb(II) ions in 1 and 3 are holodirected, whereas in 2 and 4, they feature somewhat hemidirected properties with small holes or gaps. Compound 4 exhibits some interesting features that (1) there is not any solvent in the structure, (2) there are extensively aromatic-aromatic stacking interactions among aromatic rings, and (3) there is also a weak interaction between Pb(II) atoms in the trinuclear motif.     

207Pb-1H two-dimensional NMR spectroscopy: a useful new tool for probing lead(II) coordination chemistry

Despite the fact that lead poisoning is the most common disease of environmental origin in the United States, the spectroscopic properties of aqueous Pb(II) coordination compounds have not been extensively investigated. Spectroscopic techniques that can be used to probe the fundamental coordination chemistry of Pb(II) will aid in both the development of water-soluble ligands that bind lead both tightly and selectively and the characterization of potential biological targets. Here, we report the preparation and characterization of a series of Pb(II) complexes of amido- derivatives of EDTA. The 207Pb chemical shift observed in these complexes (2441, 2189, and 1764 ppm for [Pb(EDTA)]2-, Pb(EDTA-N2), and [Pb(EDTA-N4)]2+, respectively) provides an extremely sensitive measure of the local environment and the charge on each complex. These shifts help to map out the lead chemical shift range that can be expected for biologically relevant sites. In addition, we report the first two-dimensional 207Pb-1H heteronuclear multiple-quantum correlation (HMQC) nuclear magnetic resonance spectra and demonstrate that this experiment can provide useful information about the lead coordination environment in aqueous Pb(II) complexes. Because this technique allows 207Pb-1H couplings through three bonds to be identified readily, 207Pb-1H NMR spectroscopy should prove useful for the investigation of Pb(II) in more complex systems (e.g., biological and environmental samples).     

Amide Group Coordination to the Pb(2+) Ion

The binary and ternary (2,2'-bipyridine) complexes of dipositive lead formed by N-carbonyl and N-sulfonyl amino acids, which are ligands containing the peptide and the sulfonamide group, respectively, were investigated in aqueous solution by NMR and differential pulse polarography, and some were also characterized crystallographically. N-Tosylglycine, N-tosyl-beta-alanine, and N-benzoylglycine behave as simple carboxylate ligands at acid pH, while around neutrality they switch to dianionic N,O-bidentate chelating ligands due to the involvement of the deprotonated amide nitrogen as an additional donor site. The same coordination behavior is maintained in the presence of 2,2'-bipyridine. The binary and ternary species formed in solution, and their stability constants were determined and compared with those of the homologous complexes of Pd(2+), Cu(2+), Cd(2+), and Zn(2+). The Pb(2+) ion is the only dipositive metal which is effective in promoting peptide nitrogen deprotonation in benzoylglycine. The molecular structures of [Pb(N-tosylglycinato-N,O)(H(2)O)] (1), [Pb(N-benzoylglycinato-O)(2)(H(2)O)(2)].2H(2)O (2), and [Pb(N-tosylglycinato-O)(2)(bpy)] (3) were determined by X-ray crystallography (O and N,O refer to the ligands binding as carboxylates and as N,O-chelating dianions, respectively). These compounds are all polymeric with six- to eight-coordinate metals showing distorted coordination geometries indicative of a stereochemically active metal lone pair. Polymerization is invariably determined by a bidentate chelate carboxylate group with one oxygen bridging between two metals, and in 2 and 3 it occurs through the formation of chains of Pb(2)O(2) square-planar rings. The binding set in 1, involving a deprotonated amide nitrogen and a sulfonic oxygen, is unprecedented for the Pb(2+) ion. This work provides new information on the solution and solid state chemistry of dipositive lead with ligands of biological interest, a research area that has received little attention in the past, although it is of great relevance for understanding the mechanisms of metal toxicity.     

Intra and intermolecular magnetic interactions in a series of dinuclear Cu(II)/hxta complexes [H5hxta = N,N'-(2-hydroxy-1,3-xylylene)-bis-(N-carboxymethylglycine)]: correlation of magnetic properties with geometry

Nine dinuclear copper(II) complexes with hxta5- ligands [H5hxta = N,N'-(2-hydroxy-1,3-xylylene)-bis-(N-carboxymethylglycine)]: [Cu2(MeO-hxtaH)(H2O)2] x 4H2O (1), [Na(micro-H2O)2(H2O)6][Cu2(Cl-hxta)(H2O)3]2 x 6H2O (2), [Cu(H2O)6][Cu2(Me-hxta)(H2O)2](NO3) x 2H2O (3), [Cu2(R-hxtaH)(H2O)3] x 3H2O [R = Cl (4), CH3 (5), and MeO (6)], [Cu2(MeO-hxtaH2)(micro-X)(CH3OH)] x 3CH3OH [X = Cl (7), Br (8)] and K5Na(micro-H2O)10[Cu2(micro-CO3)(Me-hxta)]2 x 4H2O (9), have been synthesized and structurally characterized. In complexes 4-7, the dinuclear units are linked via novel pairwise supramolecular interactions involving the ligand carboxylate groups. The intra- and intermolecular magnetic interactions have been quantified, and the coupling constants have been related to the structural geometries.     

Unusual bridging modes for percholorate in a 2D polymeric lead(II) complex, {[Pb(bpy)(µ-OAc)]2(µ-O2ClO2)(µ-OClO2O)}n

A lead(II) complex containing 2,2′-bipyridine (bpy), acetate and perchlorate ligands, [Pb(bpy)(CH₃COO)(ClO₄)] has been synthesized and characterized by elemental analysis, IR-, ¹H NMR-, ¹³C NMR spectroscopy. Single crystal X-ray data show the complex is two dimensional polymeric as a result of an unusual perchlorate bi- and unidentate bridging with repeating dimeric {[Pb(bpy)(µ-OAc)]₂(µ-O₂ClO₂)(µ-OClO₂O)}_n units. The Pb atom has an unsymmetrical eight-coordinate geometry with a coordination gap around the Pb(II) ion, possibly occupied possibly by a stereo-active lone pair of electrons on lead(II).     

Topology analysis and nonlinear-optical-active properties of luminescent metal-organic framework materials based on zinc/lead isophthalates

Two 3D Zn(II) and Pb(II) isophthalates, [Zn(ip)]n (1) and [Pb4(mu4-O)(ip)3(H2O)]n (2) (H2ip = isophthalic acid), have been prepared under hydro(solvo)thermal conditions and characterized by single-crystal X-ray diffraction. The two complexes crystallize in different space groups (P4(3)2(1)2 for 1 and P2(1)/c for 2) and have different bridging modes of the ip ligand. The 3D framework of 1 is constructed by the interconnection of ZnO4 polyhedra via ip ligands, which represents a chiral net with PtS-type topology. In contrast, complex 2 is formed by the combination of Pb4O-cluster secondary building units and has a novel (3.4.5)(3(2).4(5).5(6).6(7).7(2)) topology, which is the first ever example of a (3,7)-connected net. Complex 1 displays a second harmonic generation efficiency of about 1.5 times that of KH2PO4. Optical properties and thermal stabilities of the two complexes have been studied. Additionally, the calculations of band structure and density of states of 1 have also been performed with the density functional theory method.     

Syntheses, structural characterization and properties of transition metal complexes of 5,5'-(1,4-phenylene)bis(1H-tetrazole) (H(2)bdt), 5',5'-(1,1'-biphenyl)-4,4'-diylbis(1H-tetrazole) (H(2)dbdt) and 5,5',5'-(1,3,5-phenylene)tris(1H-tetrazole) (H(3)btt)

The hydrothermal chemistry of a variety of M(II)SO(4) salts with the tetrazole (Ht) ligands 5,5'-(1,4-phenylene)bis(1H-tetrazole) (H(2)bdt), 5',5'-(1,1'-biphenyl)4,4'-diylbis(1H-tetrazole) (H(2)dbdt) and 5,5',5'-(1,3,5-phenylene)tris(1H-tetrazole) (H(3)btt) was investigated. In the case of Co(II), three phases were isolated, two of which incorporated sulfate: [Co(5)F(2)(dbdt)(4)(H(2)O)(6)]·2H(2)O (1·2H(2)O), [Co(4)(OH)(2)(SO(4))(bdt)(2)(H(2)O)(4)] (2) and [Co(3)(OH)(SO(4))(btt)(H(2)O)(4)]·3H(2)O (3·3H(2)O). The structures are three-dimensional and consist of cluster-based secondary building units: the pentanuclear {Co(5)F(2)(tetrazolate)(8)(H(2)O)(6)}, the tetranuclear {Co(4)(OH)(2)(SO(4))(2)(tetrazolate)(6)}(4-), and the trinuclear {Co(3)(μ(3)-OH)(SO(4))(2) (tetrazolate)(3)}(2-) for 1, 2, and 3, respectively. The Ni(II) analogue [Ni(2)(H(0.67)bdt)(3)]·10.5H(2)O (4·10.5H(2)O) is isomorphous with a fourth cobalt phase, the previously reported [Co(2)(H(0.67)bat)(3)]·20H(2)O and exhibits a {M(tetrazolate)(3/2)}(∞) chain as the fundamental building block. The dense three-dimensional structure of [Zn(bdt)] (5) consists of {ZnN(4)}tetrahedra linked through bdt ligands bonding through N1,N3 donors at either tetrazolate terminus. In contrast to the hydrothermal synthesis of 1-5, the Cd(II) material (Me(2)NH(2))(3)[Cd(12)Cl(3)(btt)(8)(DMF)(12)]·xDMF·yMeOH (DMF = dimethylformamide; x = ca. 12, y = ca. 5) was prepared in DMF/methanol. The structure is constructed from the linking of {Cd(4)Cl(tetrazolate)(8)(DMF)(4)}(1-) secondary building units to produce an open-framework material exhibiting 66.5% void volume. The magnetic properties of the Co(II) series are reflective of the structural building units.     

Stabilization of calcium- and terbium-carboxylate bonds by NH...O hydrogen bonds in a mononuclear complex: a functional model of the active site of calcium-binding proteins

Novel benzoic acid ligands with bulky amide groups at the ortho position, 2,6-(MeCONH)(2)C(6)H(3)CO(2)H (1) and 2,6-(t-BuCONH)(2)C(6)H(3)CO(2)H (2), and their tris- and tetrakis(carboxylate) complexes with Ca(II) and Tb(III) ions, (NEt(4))(2)[Ca(II)[O(2)C-2,6-(t-BuCONH)(2)C(6)H(3)](4)] (4), [Tb[O(2)C-2,6-(t-BuNHCO)(2)C(6)H(3)](3)(H(2)O)(3)]] (5), and (NMe)(4)[Tb[O(2)C-2,6-(t-BuNHCO)(2)C(6)H(3)](4)(thf)] (6), were synthesized. The formation of the NH...O hydrogen bonds between the amide NH and carboxylate for 2, (NEt(4))[2,6-(t-BuCONH)(2)C(6)H(3)CO(2)] (3), and 4 was determined by (1)H NMR spectroscopy in solution and in the solid state (CRAMPS, IR). The ligand exchange reactions were attempted between 4 and a large excess of 2,4,6- Me(3)C(6)H(3)CO(2)H in chloroform-d solution; however, exchange reaction did not take place, indicating that the Ca(II) ions bound strongly to the carboxylate in 4. The Ca(II) ion binding properties with the benzoate derivatives were also examined using Tb(III) ion as a fluorescence probe. These results indicate that the NH...O hydrogen bonding between the amide NH and the oxygen atom of the carboxylate contributes to strong Ca(II) binding and prevents the dissociation of the calcium-carboxylate bond. The X-ray structural analyses of these complexes revealed that the NH.O hydrogen-bonded carboxylate ligands prefer the chelate-type coordination and create a mononuclear [Ca(O(2)CR)(4)](2)(-) or [Tb(O(2)CR)(4)](-) core with anionic charge, which is known only in the active site of calcium-binding proteins.     

Synthesis, complexation and water exchange properties of Gd(III)-TTDA-mono and bis(amide) derivatives and their binding affinity to human serum albumin

With the objective of tuning the lipophilicity of ligands and maintaining the neutrality and stability of Gd(III) chelate, we designed and synthesized two bis(amide) derivatives of TTDA, TTDA-BMA and TTDA-BBA, and a mono(amide) derivative, TTDA-N-MOBA. The ligand protonation constants and complex stability constants for various metal ions were determined in this study. The identification of the microscopic sites of protonation of the amide ligand by 1H NMR titrations show that the first protonation site occurs on the central nitrogen atom. The values of the stability constant of TTDA-mono and bis(amide) complex are significantly lower than those of TTDA and DTPA, but the selectivity constants of these ligands for Gd(III) over Zn(II) and Cu(II) are slightly higher than those of TTDA and DTPA. On the basis of the water-exchange rate values available for [Gd(TTDA-BMA)(H2O)], [Gd(TTDA-BBA)(H2O)] and [Gd(TTDA-N-MOBA)(H2O)]-, we can state that, in general, the replacement of one carboxylate group by an amide group decreases the water-exchange rate of the gadolinium(III) complexes by a factor of about three to five. The decrease in the exchange rate is explained in terms of a decreased steric crowding and charge effect around the metal ion when carboxylates are replaced by an amide group. In addition, to support the HSA protein binding studies of lipophilic [Gd(TTDA-N-MOBA)(H2O)]- and [Gd(TTDA-BBA)(H2O)] complexes, further protein-complex binding was studied by ultrafiltration and relaxivity studies. The binding constants (KA) of [Gd(TTDA-N-MOBA)(H2O)]- and [Gd(TTDA-BBA)(H2O)] are 8.6 x 10(2) and 1.0 x 10(4) dm3 mol(-1), respectively. The bound relaxivities (r1(b)) are 51.8 and 52 dm3 mmol(-1) s(-1), respectively. The KA value of [Gd(TTDA-BBA)(H2O)] is similar to that of MS-325 and indicates a stronger interaction of [Gd(TTDA-BBA)(H2O)] with HSA.