New terpyridine-containing macrocycle for the assembly of dimeric Zn(II) and Cu(II) complexes coupled by bridging hydroxide anions and pi-stacking interactions

The synthesis of the new terpyridine-containing macrocycle 2,5,8,11,14-pentaaza[15](6,6' ')cyclo(2,2':6',2' ')terpyridinophane (L) is reported. The ligand contains a pentaamine chain linking the 6,6' ' positions of a terpyridine unit. A potentiometric, (1)H NMR, UV-vis spectrophotometric and fluorescence emission study on the acid-base properties of L in aqueous solutions shows that the first four protonation steps occur on the polyamine chain, whereas the terpyridine nitrogens are involved in proton binding only at strongly acidic pH values. L can form both mono- and dinuclear Cu(II), Zn(II), Cd(II), and Pb(II) complexes in aqueous solution. The crystal structures of the Zn(II) and Cd(II) complexes ([ZnLH](2)(micro-OH))(ClO(4))(5) (6) and ([CdLH](2)(micro-Br))(ClO(4))(5).4H(2)O (7) show that two mononuclear [MLH](3+) units are coupled by a bridging anion (OH(-) in 6 and Br(-) in 7) and pi-stacking interactions between the terpyridine moieties. A potentiometric and spectrophotometric study shows that in the case of Cu(II) and Zn(II) the dimeric assemblies are also formed in aqueous solution containing the ligand and the metals in a 1:1 molar ratio. Protonation of the complexes or the addition of a second metal ion leads to the disruption of the dimers due to the increased electrostatic repulsions between the two monomeric units.     

Structure-activity studies on the cleavage of an RNA analogue by a potent dinuclear metal ion catalyst: effect of changing the metal ion

Dinuclear Cd(II), Cu(II), and Zn(II) complexes of L2OH (L2OH = 1,3-bis(1,4,7-triazacyclonon-1-yl)-2-hydroxypropane) are compared as catalysts for cleavage of the RNA analogue HpPNP (HpPNP = 2-hydroxypropyl 4-nitrophenyl phosphate) at 25 degrees C, I = 0.10 M (NaNO(3)). Zn(II) and Cu(II) readily form dinuclear complexes at millimolar concentrations and a 2:1 ratio of metal ion to L2OH at neutral pH. The dinuclear Zn(2)(L2O) and Cu(2)(L2O) complexes have a bridging alkoxide group that brings together the two cations in close proximity to facilitate cooperative catalysis. Under similar conditions, the dinuclear complex of Cd(II) is a minor species in solution; only at high pH values (pH 10.4) does the Cd(2)(L2O) complex become the predominant species in solution. Analysis of the second-order rate constants for cleavage of HpPNP by Zn(2)(L2O) is straightforward because a linear dependence of pseudo-first-order rate constant on dinuclear complex is observed over a wide pH range. In contrast, plots of pseudo-first-order rate constants for cleavage of HpPNP by solutions containing a 2:1 ratio of Cd(II) to L2OH as a function of increasing L2OH are curved, and second-order rate constants are obtained by fitting the kinetic data to an equation for the formation of the dinuclear Cd(II) complex as a function of pH and [L2OH]. Second-order rate constants for cleavage of HpPNP by these dinuclear complexes at pH 9.3 and 25 degrees C vary by 3 orders of magnitude in the order Cd(2)(L2O) (2.8 M(-)(1) s(-)(1)) > Zn(2)(L2O) (0.68 M(-)(1) s(-)(1)) > Cu(2)(L2O) (0.0041 M(-1) s(-1)). The relative reactivity of these complexes is discussed in terms of the different geometric preferences and Lewis acidity of the dinuclear Zn(II), Cu(II), and Cd(II) complexes, giving insight into the importance of these catalyst properties in the cleavage of phosphate diesters resembling RNA.     

Solvent extraction of metals with potassium-dihydro-bispyrazolyl-borate

The extraction of Cu(II), Ni(II), Co(II), Cd(II), Zn(II), Pb(II) and Mn(II) with potassium-dihydro-bispyrazolyl-borate (H(2)BPz(2)(-)) in dichloromethane has been studied. Extraction constants (logK(ex)) have been calculated for all metal systems and were compared with those obtained with dibenzoylmethane (DBM), thenoyltrifluoroacetone (HTTA) and 1-phenyl-3-methyl-4-benzoyl-5-pyrazolone (HPMBP). The method has been used for the determination of Cu(II), Co(II), Cd(II), Zn(II), Pb(II) and Mn(II) in standard alloys and for preconcentration of metal ions in synthetic samples.     

Coordination polymers of macrocyclic oxamide with 1,3,5-benzenetricarboxylate: syntheses, crystal structures and magnetic properties

Solvothermal reactions of mixed ligands H(3)BTC and macrocyclic oxamide complexes (ML, M = Cu, Ni) with M(ClO(4))(2)·6H(2)O (M = Co, Zn, Ni and Cd) afford six new complexes, including [M'(4)(BTC)(2)(ML)(2)(OH)(2)(H(2)O)(2)]·2H(2)O (M' = Co, M = Ni, for (1); M' = Zn, M = Ni, for (2); M' = Zn, M = Cu, for (3)), [Ni(3)(BTC)(2)(NiL)(2)(H(2)O)(6)]·2CH(3)OH·2H(2)O (4), [Cd(4)(BTC)(2)(HBTC)(NiL)(4)(H(2)O)]·3H(2)O (5) and [Cd(HBTC)(CuL)]·H(2)O (6) (ML, H(2)L = 2, 3-dioxo-5, 6, 14, 15-dibenzo-1,4,8,12-tetraazacyclo-pentadeca-7,13-dien; H(3)BTC = 1,3,5-benzenetricarboxylic acid). Complexes 1-3 consist of a 2D layer framework formed by the linkage of M(II)(M = Ni, Cu) and M'(4) (M' = Co, Zn) cluster via the oxamide and BTC(3-) bridges and display a (3,6)-connected network with a (4(3))(2)(4(6).6(6).8(3)) topology. The structure of 4 consists of pentanuclear [Ni(II)(5)] units and arranges in a 1D cluster chain. Complex 5 exhibits a 2D layered structure characterized by 3,4,3-connected (4.6(2))(3)(4.6(3).8(2))(4(2).6(3).8)(4(2).6) topology. Complex 6 possesses a 3D network with sra topology. The magnetic properties of complexes 1 and 4 were investigated.     

Structures and magnetic properties of an antiferromagnetically coupled polymeric copper(II) complex and ferromagnetically coupled hexanuclear nickel(II) clusters

Reactions between 2,6-diformyl-4-methylphenol (DFMF) and tris(hydroxymethyl) aminomethane (THMAM = H(3)L2) in the presence of copper(II) salts, CuX(2) (X = CH(3)CO(2)(-), BF(4)(-), ClO(4)(-), Cl(-), NO(3)(-)) and Ni(CH(3)CO(2))(2) or Ni(ClO(4))(2)/NaC(6)H(5)CO(2), sodium azide (NaN(3)), and triethylamine (TEA), in one pot self-assemble giving a coordination polymer consisting of repeating pentanuclear copper(II) clusters {[Cu(2)(H(5)L(2-))(μ-N(3))](2)[Cu(N(3))(4)]·2CH(3)OH}(n) (1) and hexanuclear Ni(II) complexes [Ni(6)(H(3)L1(-))(2)(HL2(2-))(2)(μ-N(3))(4)(CH(3)CO(2))(2)]·6C(3)H(7)NO·C(2)H(5)OH (2) and [Ni(6)(H(3)L1(-))(2)(HL2(2-))(2)(μ-N(3))(4)(C(6)H(5)CO(2))(2)]·3C(3)H(7)NO·3H(2)O·CH(3)OH (3). In 1, H(5)L(2-) and in 2 and 3 H(3)L1(-) and HL2(2-) represent doubly deprotonated, singly deprotonated, and doubly deprotonated Schiff-base ligands H(7)L and H(4)L1 and a tripodal ligand H(3)L2, respectively. 1 has a novel double-stranded ladder-like structure in which [Cu(N(3))(4)](2-) anions link single chains comprised of dinuclear cationic subunits [Cu(2)(H(5)L(2-))(μ-N(3))](+), forming a 3D structure of interconnected ladders through H bonding. Nickel(II) clusters 2 and 3 have very similar neutral hexanuclear cores in which six nickel(II) ions are bonded to two H(4)L1, two H(3)L2, four μ-azido, and two μ-CH(3)CO(2)(-)/μ-C(6)H(5)CO(2)(-) ligands. In each structure two terminal dinickel (Ni(2)) units are connected to the central dinickel unit through four doubly bridging end-on (EO) μ-azido and four triply bridging μ(3)-methoxy bridges organizing into hexanuclear units. In each terminal dinuclear unit two nickel centers are bridged through one μ-phenolate oxygen from H(3)L1(-), one μ(3)-methoxy oxygen from HL2(2-), and one μ-CH(3)CO(2)(-) (2)/μ-C(6)H(5)CO(2)(-) (3) ion. Bulk magnetization measurements on 1 show moderately strong antiferromagnetic coupling within the [Cu(2)] building block (J(1) = -113.5 cm(-1)). Bulk magnetization measurements on 2 and 3 demonstrate that the magnetic interactions are completely dominated by ferromagnetic coupling occurring between Ni(II) ions for all bridges with coupling constants (J(1), J(2), and J(3)) ranging from 2.10 to 14.56 cm(-1) (in the ? = -J(1)(?(1)?(2)) - J(1)(?(2)?(3)) - J(2)(?(3)?(4)) - J(1)(?(4)?(5)) - J(1)(?(5)?(6)) - J(2)(?(1)?(6)) - J(3)(?(2)?(6)) - J(3)(?(2)?(5)) - J(3)(?(3)?(5)) convention).     

Reaction behaviour of dinuclear copper(I) complexes with m-xylyl-based ligands towards dioxygen

Intramolecular ligand hydroxylation was observed during the reactions of dioxygen with the dicopper(I) complexes of the ligands L(1)(L(1)=alpha,alpha'-bis[(2-pyridylethyl)amino]-m-xylene) and L(3)(L(3)=alpha, alpha'-bis[N-(2-pyridylethyl)-N-(2-pyridylmethyl)amino]-m-xylene). The dinuclear copper(I) complex [Cu(2)L(3)](ClO(4))(2) and the dicopper(II) complex [Cu(2)(L(1)-O)(OH)(ClO(4))]ClO(4) were characterized by single-crystal X-ray structure analysis. Furthermore, phenolate-bridged complexes were synthesized with the ligand L(2)-OH (structurally characterized [Cu(2)(L(2)-O)Cl(3)] with L(2)=alpha, alpha'-bis[N-methyl-N-(2-pyridylethyl)amino]-m-xylene; synthesized from the reaction between [Cu(2)(L(2)-O)(OH)](ClO(4))(2) and Cl(-)) and Me-L(3)-OH: [Cu(2)(Me-L(3)-O)(mu-X)](ClO(4))(2)xnH(2)O (Me-L(3)-OH = 2,6-bis[N-(2-pyridylethyl)-N-(2-pyridylmethyl)amino]-4-methylphenol and X = C(3)H(3)N(2)(-)(prz), MeCO(2)(-) and N(3)(-)). The magnetochemical characteristics of compounds were determined by temperature-dependent magnetic studies, revealing their antiferromagnetic behaviour [-2J(in cm(-1)) values: -92, -86 and -88; -374].     

Solvent control: dinuclear versus tetranuclear complexes of a bis-tetradentate pyrimidine-based ligand

A new bis-tetradentate acyclic amine ligand L(Et) has been synthesized from 4,6-bis(aminomethyl)-2-phenylpyrimidine and 2-vinylpyridine. Dinuclear complexes, Mn(II)(2)L(Et)(MeCN)(H(2)O)(3)(ClO(4))(4) (1), Fe(II)(2)L(Et)(H(2)O)(4)(BF(4))(4) (2), Co(II)(2)L(Et)(H(2)O)(3)(MeCN)(2)(BF(4))(4) (3), Ni(II)(2)L(Et)(H(2)O)(4)(BF(4))(4) (4), Ni(II)(2)L(Et)(H(2)O)(4)(ClO(4))(4)·8H(2)O (4'), Cu(II)(2)L(Et)(BF(4))(4)·MeCN (5), Zn(II)(2)L(Et)(BF(4))(2)(BF(4))(2)·?MeCN (6), were obtained from 1 : 2 reactions of L(Et) and the appropriate metal salts in MeCN, whereas in MeOH tetranuclear complexes, Mn(II)(4)(L(Et))(2)(OH)(4)(ClO(4))(4) (7), Fe(II)(4)(L(Et))(2)(F)(4)(BF(4))(4)·5/2H(2)O (8), Co(II)(4)(L(Et))(2)(F)(4)(BF(4))(4)·3H(2)O (9), Ni(II)(4)(L(Et))(2)(F)(4)(BF(4))(4)·4H(2)O (10), Cu(II)(4)(L(Et))(2)(F)(4)(BF(4))(4)·3H(2)O (11) and Zn(II)(4)(L(Et))(2)(F)(4)(BF(4))(4) (12), result. Six complexes have been structurally characterized: in all cases each L(Et) is bis-tetradentate and provides a pyrimidine bridge between two metal centres. As originally anticipated, complexes 1, 4' and 6 are dinuclear, while 9, 10 and 12 are revealed to be tetranuclear, with two M(2)(L(Et))(4+) moieties bridged by two pairs of fluoride anions. Weak to moderate antiferromagnetic coupling between the metal centres is a feature of complexes 2, 3, 4, 8, 9 and 10. The dinuclear complexes 1-6 undergo multiple, mostly irreversible, redox processes. However, the pyrimidine-based dicopper(II) complex 5 undergoes a two electron quasi-reversible reduction, Cu(II)(2)→ Cu(I)(2), and this occurs at a more positive potential [E(m) = +0.11 V (E(pc) = -0.03 and E(pa) = +0.26 V) vs. 0.01 M AgNO(3)/Ag] than for either of the dicopper(II) complexes of the analogous pyrazine-based ligands.     

Structures and dynamic behavior of large polyhedral coordination cages: an unusual cage-to-cage interconversion

The bis-bidentate bridging ligand L {α,α'-bis[3-(2-pyridyl)pyrazol-1-yl]-1,4-dimethylbenzene}, which contains two chelating pyrazolyl-pyridine units connected to a 1,4-phenylene spacer via flexible methylene units, reacts with transition metal dications to form a range of polyhedral coordination cages based on a 2M:3 L ratio in which a metal ion occupies each vertex of a polyhedron, a bridging ligand lies along every edge, and all metal ions are octahedrally coordinated. Whereas the Ni(II) complex [Ni(8)L(12)](BF(4))(12)(SiF(6))(2) is an octanuclear cubic cage of a type we have seen before, the Cu(II), Zn(II), and Cd(II) complexes form new structural types. [Cu(6)L(9)](BF(4))(12) is an unusual example of a trigonal prismatic cage, and both Zn(II) and Cd(II) form unprecedented hexadecanuclear cages [M(16)L(24)]X(32)(X = ClO(4) or BF(4)) whose core is a skewed tetracapped truncated tetrahedron. Both Cu(6)L(9) and M(16)L(24) cages are based on a cyclic helical M(3)L(3) subunit that can be considered as a triangular "panel", with the cages being constructed by interconnection of these (homochiral) panels with additional bridging ligands in different ways. Whereas [Cu(6)L(9)](BF(4))(12) is stable in solution (by electrospray mass spectrometry, ES-MS) and is rapidly formed by combination of Cu(BF(4))(2) and L in the correct proportions in solution, the hexadecanuclear cage [Cd(16)L(24)](BF(4))(32) formed on crystallization slowly rearranges in solution over a period of several weeks to the trigonal prism [Cd(6)L(9)](BF(4))(12), which was unequivocally identified on the basis of its (1)H NMR spectrum. Similarly, combination of Cd(BF(4))(2) and L in a 2:3 ratio generates a mixture whose main component is the trigonal prism [Cd(6)L(9)](BF(4))(12). Thus the hexanuclear trigonal prism is the thermodynamic product arising from combination of Cd(II) and L in a 2:3 ratio in solution, and arises from both assembly of metal and ligand (minutes) and rearrangement of the Cd(16) cage (weeks); the large cage [Cd(16)L(24)](BF(4))(32) is present as a minor component of a mixture of species in solution but crystallizes preferentially.     

Di- and tetra-nuclear copper(II), nickel(II), and cobalt(II) complexes of four bis-tetradentate triazole-based ligands: synthesis, structure, and magnetic properties

Four bis-tetradentate N(4)-substituted-3,5-{bis[bis-N-(2-pyridinemethyl)]aminomethyl}-4H-1,2,4-triazole ligands, L(Tz1)-L(Tz4), differing only in the triazole N(4) substituent R (where R is amino, pyrrolyl, phenyl, or 4-tertbutylphenyl, respectively) have been synthesized, characterized, and reacted with M(II)(BF(4))(2)·6H(2)O (M(II) = Cu, Ni or Co) and Co(SCN)(2). Experiments using all 16 possible combinations of metal salt and L(TzR) were carried out: 14 pure complexes were obtained, 11 of which are dinuclear, while the other three are tetranuclear. The dinuclear complexes include two copper(II) complexes, [Cu(II)(2)(L(Tz2))(H(2)O)(4)](BF(4))(4) (2), [Cu(II)(2)(L(Tz4))(BF(4))(2)](BF(4))(2) (4); two nickel(II) complexes, [Ni(II)(2)(L(Tz1))(H(2)O)(3)(CH(3)CN)](BF(4))(4)·0.5(CH(3)CN) (5) and [Ni(II)(2)(L(Tz4))(H(2)O)(4)](BF(4))(4)·H(2)O (8); and seven cobalt(II) complexes, [Co(II)(2)(L(Tz1))(μ-BF(4))](BF(4))(3)·H(2)O (9), [Co(II)(2)(L(Tz2))(μ-BF(4))](BF(4))(3)·2H(2)O (10), [Co(II)(2)(L(Tz3))(H(2)O)(2)](BF(4))(4) (11), [Co(II)(2)(L(Tz4))(μ-BF(4))](BF(4))(3)·3H(2)O (12), [Co(II)(2)(L(Tz1))(SCN)(4)]·3H(2)O (13), [Co(II)(2)(L(Tz2))(SCN)(4)]·2H(2)O (14), and [Co(II)(2)(L(Tz3))(SCN)(4)]·H(2)O (15). The tetranuclear complexes are [Cu(II)(4)(L(Tz1))(2)(H(2)O)(2)(BF(4))(2)](BF(4))(6) (1), [Cu(II)(4)(L(Tz3))(2)(H(2)O)(2)(μ-F)(2)](BF(4))(6)·0.5H(2)O (3), and [Ni(II)(4)(L(Tz3))(2)(H(2)O)(4)(μ-F(2))](BF(4))(6)·6.5H(2)O (7). Single crystal X-ray structure determinations revealed different solvent content from that found by microanalysis of the bulk sample after drying under a vacuum and confirmed that 5', 8', 9', 11', 12', and 15' are dinuclear while 1' and 7' are tetranuclear. As expected, magnetic measurements showed that weak antiferromagnetic intracomplex interactions are present in 1, 2, 4, 7, and 8, stabilizing a singlet spin ground state. All seven of the dinuclear cobalt(II) complexes, 9-15, have similar magnetic behavior and remain in the [HS-HS] state between 300 and 1.8 K.     

Determination of Metal Ions in Natural Waters by Flame-AAS after Preconcentration on a 5-Amino-1,3,4-Thiadiazole-2-Thiol Modified Silica Gel.

ABSTRACT

5-amino-1,3,4-thiadiazole-2-thiol groups attached on a silica gel surface have been used for adsorption of Cd(II), Co(II), Cu(II), Fe(III), Ni(II), Pb(II) and Zn(II) from aqueous solutions. The adsorption capacities for each metal ion were (in mmol.g^?1): Cd(II)= 0.35, Co(II)= 0.10, Cu(II)= 0.15, Fe(III)= 0.20, Hg(II)= 0.46, Ni(II)= 0.16, Pb(II)= 0.13 and Zn(II)= 0.15. The modified silica gel was applied in the preconcentration and quantification of trace level metal ions present in water samples (river, and bog water).     

Synthesis, characterization, crystal structure and preliminary reactivity behaviour of new heteropolytopic ligands based on the 1,3,5-triazine spacer and pyrazolyl, tris-pyrazolylmethyl and tris-pyrazolylethoxy bonding fragments

Four new potentially polytopic nitrogen donor ligands based on the 1,3,5-triazine fragment, L(1)-L(4) (L(1) = 2-chloro-4,6-di(1H-pyrazol-1-yl)-1,3,5-triazine, L(2) = N,N'-bis(4,6-di(1H-pyrazol-1-yl)-1,3,5-triazin-2-yl)ethane-1,2-diamine, L(3) = 2,4,6-tris(tri(1H-pyrazol-1-yl)methyl)-1,3,5-triazine, and L(4) = 2,4,6-tris(2,2,2-tri(1H-pyrazol-1-yl)ethoxy)-1,3,5-triazine) have been synthesized and characterized. The X-ray crystal structure of L(3) confirms that its molecular nature consists of a 1,3,5-triazine ring bearing three tripodal tris(pyrazolyl) arms. L(1), L(2), and L(4) react with Cu(I), Cu(II), Pd(II) and Ag(I) salts yielding mono-, di-, and oligonuclear derivatives: [Cu(L(1))(Cy(3)P)]ClO(4), [{Ag(2)(L(2))}(CF(3)SO(3))(2)]·H(2)O, [Cu(2)(L(2))(NO(3))(2)](NO(3))(2)·H(2)O, [Cu(2)(L(2))(CH(3)COO)(2)](CH(3)COO)(2)·3H(2)O, [Pd(2)(L(2))(Cl)(4)]·2H(2)O, [Ru(L(2))(Cl)(OH)]·CH(3)OH, [Ag(3)(L(4))(2)](CF(3)SO(3))(3) and [Ag(3)(L(4))(2)](BF(4))(3). The interaction of L(3) with Ag(I), Cu(II), Zn(II) and Ru(II) complexes unexpectedly produced the hydrolysis of the ligand with formation, in all cases, of tris(pyrazolyl)methane (TPM) derivatives. In detail, the already known [Ag(TPM)(2)](CF(3)SO(3)) and [Cu(TPM)(2)](NO(3))(2), as well as the new [Zn(TPM)(2)](CF(3)SO(3))(2) and [Ru(TMP)(p-cymene)]Cl(OH)·2H(2)O complexes have been isolated. Single-crystal XRD determinations on the latter derivatives confirm their formulation, evidencing, for the Ru(II) complex, an interesting supramolecular arrangement of the anions and crystallization water molecules.     

Molecular squares, cubes and chains from self-assembly of bis-bidentate bridging ligands with transition metal dications

The two new ligands L(fur) and L(th) consist of two chelating pyrazolyl-pyridine termini connected to furan-2,5-diyl or thiophene-2,5-diyl spacers via methylene groups. Reaction of these with a range of transition metal dications that prefer octahedral coordination affords a series of unusual structures which are all based on a 2M : 3L ratio. [M(8)(L(fur))(12)]X(16) (M = Co, Cu, X = BF(4); and M = Zn, X = ClO(4)) are octanuclear cubes with approximate D(4) symmetry in which two cyclic tetranuclear helicate M(4)L(4) units are connected by four additional 'pillar' ligands. In contrast [Ni(4)(L(fur))(6)](BF(4))(8) is a centrosymmetric molecular square consisting of two dinuclear Ni(2)L(2) units of opposite chirality that are connected by a pair of additional L(fur) ligands such that the four edges of the Ni(4) square are spanned by alternately two and one bridging ligands. [M(4)(L(th))(6)](BF(4))(8) (M = Co, Ni, Cu) are likewise molecular squares with similar structures to [Ni(4)(L(fur))(6)](BF(4))(8) with the significant difference that the two crosslinked double helicate M(2)L(2) units are now homochiral. The Cd(II) complexes both behave quite differently to the first-row metal complexes, with [Cd(L(fur))(BF(4))](BF(4)) being a simple mononuclear complex with a single ligand in which the furan oxygen atom is weakly interacting with the Cd(II) centre. In contrast, in {[Cd(2)(L(th))(3)](BF(4))(4)}(∞), where this quasi-pentadentate coordination mode of the ligand is not possible because thiophene is too poor an electron donor, the ligand reverts to bis-bidentate bridging coordination to afford a one-dimensional chain consisting of an infinite sequence of crosslinked, homochiral, Cd(2)(L(th))(2) double helicate units.     

Crystal structure and magnetic interactions in nickel(II) dibridged complexes formed by two azide groups or by both phenolate oxygen-azide, -thiocyanate, -carboxylate, or -cyanate groups

Tridentate/tetradentate Schiff base ligands L(1) and L(2), derived from the condensation of o-vanillin or pyridine-2-aldehyde with N,N-dimethylethylenediammine, react with nickel acetate or perchlorate salt and azide, cyanate, or thiocyanate to give rise to a series of dinuclear complexes of formulas [Ni(L(1))(micro(1,1)-N(3))Ni(L(1))(N(3))(OH(2))].H(2)O (1), [[Ni(L(1))(micro(1,1)-NCS)Ni(L(1))(NCS)(OH(2))][Ni(L(1))(micro-CH(3)COO)Ni(L(1))( NCS) (OH(2))]] (2) [[2A][2B]], [Ni(L(1))(micro(1,1)-NCO)Ni(L(1))(NCO)(OH(2))].H(2)O (3), and [Ni(L(2)-OMe)(micro(1,1)-N(3))(N(3))](2) (4), where L(1) = Me(2)N(CH(2))(2)NCHC(6)H(3)(O(-))(OCH(3)) and L(2) = Me(2)N(CH(2))(2)NCHC(6)H(3)N. We have characterized these complexes by analytical, spectroscopic, and variable-temperature magnetic susceptibility measurements. The coordination geometry around all of the Ni(II) centers is a distorted octahedron with bridging azide, thiocyanate/acetate, or cyanate in a micro(1,1) mode and micro(2)-phenolate oxygen ion for 1-3, respectively, or with a double-bridging azide for 4. The magnetic properties of the complexes were studied by magnetic susceptibility (chi(M)) versus temperature measurements. The chi(M) nus T plot reveals that compounds 1 and 4 are strongly ferromagnetically coupled, 3 shows a weak ferromagnetic behavior, and 2 is very weakly antiferromagnetically coupled.     

Coordination properties of new bis(1,4,7-triazacyclononane) ligands: a highly active dizinc complex in phosphate diester hydrolysis

The synthesis and characterization of three new bis([9]aneN(3)) ligands, containing respectively 2,2'-bipyridine (L(1)), 1,10-phenanthroline (L(2)), and quinoxaline (L(3)) moieties linking the two macrocyclic units, are reported. Proton binding and Cu(II), Zn(II), Cd(II), and Pb(II) coordination with L(1)-L(3) have been studied by potentiometric titrations and, for L(1) and L(2), by spectrophotometric UV-vis measurements in aqueous solutions. All ligands can give stable mono- and dinuclear complexes. In the case of L(1), trinuclear Cu(II) complexes are also formed. The stability constants and structural features of the formed complexes are strongly affected by the different architecture and binding properties of the spacers bridging the two [9]aneN(3) units. In the case of the L(1) and L(2) mononuclear complexes, the metal is coordinated by the three donors of one [9]aneN(3) moiety; in the [ML(2)](2+) complexes, however, the phenanthroline nitrogens are also involved in metal binding. Finally, in the [ML(3)](2+) complexes both macrocyclic units, at a short distance from each other, can be involved in metal coordination, giving rise to sandwich complexes. In the binuclear complexes each metal ion is generally coordinated by one [9]aneN(3) unit. In L(1), however, the dipyridine nitrogens can also act as a potential binding site for metals. The dinuclear complexes show a marked tendency to form mono-, di-, and, in some cases, trihydroxo species in aqueous solutions. The resulting M-OH functions may behave as nucleophiles in hydrolytic reactions. The hydrolysis rate of bis(p-nitrophenyl)phosphate (BNPP) was measured in aqueous solution at 308.1 K in the presence of the L(2) and L(3) dinuclear Zn(II) complexes. Both the L(2) complexes [Zn(2)L(2)(OH)(2)](2+) and [Zn(2)L(2)(OH)(3)](+) and the L(3) complex [Zn(2)L(3)(OH)(3)](+) promote BNPP hydrolysis. The [Zn(2)L(3)(OH)(3)](+) complex is ca. 2 orders of magnitude more active than the L(2) complexes, due both to the short distance between the metal centers in [Zn(2)L(3)(OH)(3)](+), which could allow a bridging interaction of the phosphate ester, and to the simultaneous presence of single-metal bound nucleophilic Zn-OH functions. These structural features are substantially corroborated by semiempirical PM3 calculations carried out on the mono-, di-, and trihydroxo species of the L(3) dizinc complex.     

Coordination chemistry of a new cofacial binucleating macropolycycle derived from 1,4,7-triazacyclononane

We have prepared and characterized a new phenol-based compartmental ligand (H(2)L) incorporating 1,4,7-triazacyclononane ([9]aneN(3)), and we have investigated its coordination behavior with Cu(II), Zn(II), Cd(II), and Pb(II). The protonation constants of the ligand and the thermodynamic stabilities of the 1:1 and 2:1 (metal/ligand) complexes with these metal ions have been investigated by means of potentiometric measurements in aqueous solutions. The mononuclear [M(L)] complexes show remarkably high stability suggesting that, along with the large number of nitrogen donors available for metal binding, deprotonated phenolic functions are also involved in binding the metal ion. The mononuclear complexes [M(L)] show a marked tendency to add a second metal ion to afford binuclear species. The formation of complexes [M(2)(H(2)L)](4+) occurs at neutral or slightly acidic pH and is generally followed by metal-assisted deprotonation of the phenolic groups to give [M(2)(HL)](3+) and [M(2)(L)](2+) in weakly basic solutions. The complexation properties of H(2)L have also been investigated in the solid state. Crystals suitable for X-ray structural analysis were obtained for the binuclear complexes [Cu(2)(L)](BF(4))(2).(1)/(2)MeCN (1), [Zn(2)(HL)](ClO(4))(3).(1)/(2)MeCN (2), and [Pb(2)(L)](ClO(4))(2).2MeCN (4). In 1 and 2, the phenolate O-donors do not bridge the two metal centers, which are, therefore, segregated each within an N(5)O-donor compartment. However, in the case of the binuclear complex [Pb(2)(L)](ClO(4))(2).2MeCN (4), the two Pb(II) centers are bridged by the phenolate oxygen atoms with each metal ion sited within an N(5)O(2)-donor compartment of L(2)(-), with a Pb.Pb distance of 3.9427(5) A.     

Single‐armed salamo‐like dioxime and its multinuclear Cu (II), Zn (II) and Cd (II) complexes: Syntheses,structural characterizations,Hirshfeld analyses and fluorescence properties

Three multinuclear Cu (II), Zn (II) and Cd (II) complexes, [Cu₂(L)(μ‐OAc)]·CHCl₂ ( 1 ), [Zn₂(L)(μ‐OAc)(H₂O)]·3CHCl₃ ( 2 ) and [{Cd₂(L)(OAc)(CH₃CH₂OH)}₂]·2CH₃CH₂OH ( 3 ) with a single‐armed salamo‐like dioxime ligand H₃L have been synthesized, and characterized by FT‐IR, UV–vis, X‐ray crystallography and Hirshfeld surfaces analyses. The ligand H₃L has a linear structure and C‐H···π interactions between the two molecules. The complex 1 is a dinuclear Cu (II) complex, Cu1 and Cu2 are all five‐coordinate possessing distorted square pyramidal geometries. The complex 2 also forms a dinuclear Zn (II) structure, and Zn1 and Zn2 are all five‐coordinate bearing distorted trigonal bipyramidal geometries. The complex 3 is a symmetrical tetranuclear Cd (II) complex, and Cd1 is a hexa‐coordinate having octahedral configuration and Cd2 is hepta‐coordinate with a pentagonal bipyramidal geometry, and it has π···π interactions inside the molecule. In addition, fluorescence properties of the ligand and its complexes 1 – 3 have also been discussed.     

Cooperativity between metal ions in the cleavage of phosphate diesters and RNA by dinuclear Zn(II) catalysts

A series of ligands containing linked 1,4,7-triazacyclononane macrocycles are studied for the preparation of dinuclear Zn(II) complexes including 1,3-bis(1,4,7-triazacyclonon-1-yl)-2-hydroxypropane (L2OH), 1,5-bis(1,4,7-triazacyclonon-1-yl)pentane (L3), 2,9-bis(1-methyl-1,4,7-triazacyclonon-1-yl)-1,10-phenanthroline (L4), and alpha,alpha'-bis(1,4,7-triazacyclonon-1-yl)-m-xylene (L5). The titration of these ligands with Zn(NO(3))(2) was monitored by (1)H NMR. Each ligand was found to bind two Zn(II) ions with a very high affinity at near neutral pH under conditions of millimolar ligand and 2 equiv of Zn(NO(3))(2). In contrast, a stable mononuclear complex was formed in solutions containing 5.0 mM L2OH and 1 equiv of Zn(NO(3))(2). (1)H and (13)C NMR spectral data are consistent with formation of a highly symmetric mononuclear complex Zn(L2OH) in which a Zn(II) ion is sandwiched between two triazacyclononane units. The second-order rate constant k(Zn) for the cleavage of 2-hydroxypropyl-4-nitrophenyl phosphate (HPNP) at pH 7.6 and 25 degrees C catalyzed by Zn(2)(L2O) is 120-fold larger than that for the reaction catalyzed by the closely related mononuclear complex Zn(L1) (L1 = 1,4,7-triazacyclononane). By comparison, the observation that the values of k(Zn) determined under similar reaction conditions for cleavage of HPNP catalyzed by the other Zn(II) dinuclear complexes are only 3-5-fold larger than values of k(Zn) for catalysis by Zn(L1) provides strong evidence that the two Zn(II) cations in Zn(2)(L2O) act cooperatively in the stabilization of the transition state for cleavage of HPNP. The extent of cleavage of an oligoribonucleotide by Zn(L1), Zn(2)(L5), and Zn(2)(L2O) at pH 7.5 and 37 degrees C after 24 h incubation is 4,10, and 90%. The rationale for the observed differences in catalytic activity of these dinuclear Zn(II) complexes is discussed in terms of the mechanism of RNA cleavage and the structure and speciation of these complexes in solution.     

Metal complexes with a new N(4)O(3) amine pendant-armed macrocyclic ligand: synthesis, characterization, crystal structures, and fluorescence studies

The synthesis of a new oxaaza macrocyclic ligand, L, derived from O(1),O(7)-bis(2-formylphenyl)-1,4,7-trioxaheptane and tren containing an amine terminal pendant arm, and its metal complexation with alkaline earth (M = Ca(2+), Sr(2+), Ba(2+)), transition (M = Co(2+), Ni(2+), Cu(2+), Zn(2+), Cd(2+)), post-transition (M = Pb(2+)), and Y(3+) and lanthanide (M = La(3+), Er(3+)) metal ions are reported. Crystal structures of [H(2)L](ClO(4))(2).3H(2)O, [PbL](ClO(4))(2), and [ZnLCl](ClO(4)).H(2)O are also reported. In the [PbL] complex, the metal ion is located inside the macrocyclic cavity coordinated by all N(4)O(3) donor atoms while, in the [ZnLCl] complex, the metal ion is encapsulated only by the nitrogen atoms present in the ligand. pi-pi interactions in the [H(2)L](ClO(4))(2).3H(2)O and [PbL](ClO(4))(2) structures are observed. Protonation and Zn(2+), Cd(2+), and Cu(2+) complexation were studied by means of potentiometric, UV-vis, and fluorescent emission measurements. The 10-fold fluorescence emission increase observed in the pH range 7-9 in the presence of Zn(2+) leads to L as a good sensor for this biological metal in water solution.     

Hexacyanometalate molecular chemistry: heptanuclear heterobimetallic complexes; control of the ground spin state

Following a bottom-up approach to nanomaterials, we present a rational synthetic route from hexacyanometalates [M(CN)(6)](3-) (M=Cr(III), Co(III)) cores to well-defined heptanuclear complexes. By changing the nature of the metallic cations and using a localised orbital model it is possible to control and to tune the ground state spin value. Thus, with M=Cr(III), d(3), S=3/2, three heptanuclear species were built and characterised by mass spectrometry in solution, by single-crystal X-ray diffraction and by powder magnetic susceptibility measurements, [Cr(III)(CNbondM'L(n))(6)](9+) (M'=Cu(II), Ni(II), Mn(II), L(n)=polydentate ligand), showing spin ground states S(G)=9/2 [Cu(II)], with ferromagnetic interactions J(Cr,Cu)=+45 cm(-1), S(G)=15/2 [Ni(II)] and J(Cr,Ni)=+17.3 cm(-1), S(G)=27/2 [Mn(II)], with an antiferromagnetic interaction J(Cr,Mn)=-9 cm(-1), (interaction Hamiltonian H=-J(Cr,M) [S(Cr)Sigma(i)S(M)(i)], i=1-6). With M=Co(III), d(6), S=0, the heptanuclear analogues [Co(III)(CN-M'L(n))(6)](9+) (M'=Cu(II), Ni(II), Mn(II)) were similarly synthesised and studied. They present a singlet ground state and allow us to evaluate the weak antiferromagnetic coupling constant between two next-nearest neighbours M'-Co-M'.     

Metal-catalysed oxidation processes in thiosemicarbazones: new complexes with the ligand N-{2-([4-N-ethylthiosemicarbazone]methyl)phenyl}-p-toluenesulfonamide

The coordination behaviour of a new thiosemicarbazone Schiff-base building block, N-{2-([4-N-ethylthiosemicarbazone]methyl)phenyl}-p-toluenesulfonamide, H2L1 (1), incorporating a bulky tosyl group, towards Mn II, Fe II, Co II, Ni II, Cu II, Zn II, Cd II, Ag I, Sn II, and Pb II has been investigated by means of an electrochemical preparative procedure. Most metal complexes of L1 have the general formula [M(L1)]2.nX (M=Mn, Fe, Co, Ni, Cu, Cd, Pb; n=0-4, X=H2O or CH3CN), as confirmed by the structure of [Pb(L1)]2 (15), in which the lone pair on lead is stereochemically active. This lead(II) complex shows an intense fluorescence emission with a quantum yield of 0.13. In the case of silver, the complex formed was found to possess a stoichiometry of [Ag2(L1)]2.3H2O. During reactions with manganese and copper metals, interesting catalysed processes have been found to take place, with remarkable consequences regarding the ligand skeleton structure. In synthesising the manganese complex, we obtained an unexpected dithiolate thiosemicarbazone tosyl ligand, H2L2, as a side-product, which has been fully characterised, including by X-ray diffraction analysis. In the case of copper, the solid complex has the formula [CuL1]2, but the crystallised product shows the copper atoms coordinated to a new cyclised thiosemicarbazone ligand, H2L3, as in the structures of the complexes [Cu(L3)]2.CH3CN (8) and [Cu(L3)(H2O)]2.CH3CN.H2O (9). The zinc complex [Zn(L1)]4 (12) displays a particular tetranuclear zeolite-type structure capable of hosting small molecules or ions, presumably through hydrogen bonding.