A phosphorus supported multisite coordinating tris hydrazone P(S)[N(Me)N=CH-C6H4-o-OH]3 as an efficient ligand for the assembly of trinuclear metal complexes: synthesis, structure, and magnetism

A phosphorus supported multisite coordinating ligand P(S)[N(Me)N=CH-C(6)H(4)-o-OH](3) (2) was prepared by the condensation of the phosphorus tris hydrazide P(S)[N(Me)NH(2)](3) (1) with o-hydroxybenzaldehyde. The reaction of 2 with M(OAc)(2).xH(2)O (M = Mn, Co, Ni, x = 4; M = Zn, x = 2) afforded neutral trinuclear complexes [P(S)[N(Me)N=CH-C(6)H(4)-o-O](3)](2)M(3) [M = Mn (3), Co (4), Ni (5), and Zn (6)]. The X-ray crystal structures of compounds 2-6 have been determined. The structures of 3-6 reveal that the trinculear metal assemblies are nearly linear. The two terminal metal ions in a given assembly have an N(3)O(3) ligand environment in a distorted octahedral geometry while the central metal ion has an O(6) ligand environment also in a slightly distorted octahedral geometry. In all the complexes, ligand 2 coordinates to the metal ions through three imino nitrogens and three phenolate oxygens; the latter act as bridging ligands to connect the terminal and central metal ions. The compounds 2-6 also show intermolecular C-H...S=P contacts in the solid-state which lead to the formation of polymeric supramolecular architectures. The observed magnetic data for the (s = 5/2)3 L(2)(Mn(II))(3) derivative, 3, show an antiferromagnetic nearest- and next-nearest-neighbor exchange (J = -4.0 K and J' = -0.15 K; using the spin Hamiltonian H(HDvV) = -2J(S(1)S(2) + S(2)S(3)) - 2J'S(1)S(3)). In contrast, the (s = 1)(3) L(2)(Ni(II))(3) derivative, 5, displays ferromagnetic nearest-neighbor and antiferromagnetic next-nearest-neighbor exchange interactions (J = 4.43 K and J' = -0.28 K; H = H(HDvV)+ S(1)DS(1) + S(2)DS(2)+ S(3)DS(3)). The magnetic behavior of the L(2)(Co(II))(3) derivative, 4, reveals only antiferromagnetic exchange analogous to 3 (J = -4.5, J' = -1.4; same Hamiltonian as for 3).     

Ligating properties of a potentially tetradentate Schiff base [(CH3)2NCH2CH2N=CHC6H3(OH)(OMe)] with zinc(II), cadmium(II), cobalt(II), cobalt(III) and manganese(III) ions: synthesis and structural studies

A series of Zn(II), Cd(II), Co(II), Co(III) and Mn(III) complexes with the Schiff base [(CH3)2NCH2CH2N=CHC6H3(OH)(OMe)], LH, derived from 2-dimethylaminoethylamine and o-vanillin, has been synthesised and structures of all the products have been established by X-ray crystallography. In the cases of zinc and cadmium, dimeric complexes [Zn(LH)2(NCS)] [Zn2(L)(mu(1,1)-CH3COO)(NCS)3] (1), [Cd2(L)2(Cl)2] (2) and [Cd2(L)2(NCS)2] (3), and for cobalt and manganese, monomeric complexes [Co(LH)2(NCS)]2 [Co(NCS)4] (4), [Co(LH)2(NCS)]ClO4 (5), [Co(L)(N3)(o-vanillinate)] x 0.5 MeOH (6) and [Mn(LH)2(MeOH)2](ClO4)3 (7), are formed with various terminal ligands. All the complexes have been characterised by elemental analysis and IR spectra. UV-Vis and NMR spectroscopy, magnetic, and electrochemical studies, were also carried out where feasible. The Schiff base functions as a bi-, tri- or tetra-dentate chelating agent and coordinates via the protonated or deprotonated phenolic oxygen, amine and imine nitrogens, and only in case of 1 with the methoxy oxygen atoms, to the metal ion leading to the formation of mono- or bi-metallic complexes.     

Di- and trinuclear complexes derived from hexakis(2-pyridyloxy)cyclotriphosphazene. Unusual P-O bond cleavage in the formation of [{(L'CuCl)2(Co(NO3)}Cl] (L' = N3P3(OC5H4N)5(O))

Hexakis(2-pyridyloxy)cyclotriphosphazene (L) is an efficient multisite coordination ligand which binds with transition metal ions to produce dinuclear (homo- and heterometallic) complexes [L(CuCl)(CoCl3)], [L(CuCl)(ZnCl3)], [L(CoCl)(ZnCl3)], and [L(ZnCl2)2]. In these dinuclear derivatives the cyclophosphazene ligand utilizes from five to six nitrogen coordination sites out of the maximum of nine available sites. Further, the spacer oxygen that separates the pyridyl moiety from the cyclophosphazene ring ensures minimum steric strain to the cyclophosphazene ring upon coordination. This is reflected in the near planarity of the cyclophosphazene ring in all the dinuclear derivatives. In the dinuclear heterobimetallic derivatives one of the metal ions [Cu(II) or Co(II)] is hexacoordinate and is bound by the cyclophosphazene in a eta5-gem-N5 mode. The other metal ion in these heterobimetallic derivatives [Co(II) or Zn(II)] is tetracoordinate and is bound in an eta(1)-N(1) fashion. In the homobimetallic derivative, [L(ZnCl2)2], one of the zinc ions is five-coordinate (eta3-nongem-N3), while the other zinc ion is tetracoordinate(eta2-gem-N2). The reaction of L with CuCl2 followed by Co(NO3)2.6H2O yields a trinuclear heterobimetallic complex [{(L'CuCl)2Co(NO3)}Cl] [L' = N3P3(OC5H4N)5(O)]. In the formation of this compound an unusual P-O bond cleavage involving one of the phosphorus-pyridyloxy bonds is observed. The molecular structure of [{(L'CuCl)2Co(NO3)}Cl] [L' = N3P3(OC5H4N)5(O)] reveals that each of the two the P-O-cleaved L' ligands is involved in binding to Cu(II) to generate the motif L'CuCl. Two such units are bridged by a Co(II) ion. The coordination environment around the bridging Co(II) ion contains four oxygen (two P-O units, one chelating nitrate) and two nitrogen atoms (pyridyloxy nitrogens).     

Lanthanide complexes of tritopic bis(hydrazone) ligands: single-molecule magnet behavior in a linear Dy(III)3 complex

Tritopic pyridinebis(hydrazone)-based ligands typically produce square M(9) [3 × 3] grid complexes with first-row transition-metal ions (e.g., M = Mn, Fe, Co, Cu, Zn), but with larger lanthanide ions, such coordination motifs are not produced, and instead linear trinuclear complexes appear to be a preferred option. The reaction of 2pomp [derived from pyridine-2,6-bis(hydrazone) and 2-acetylpyridine] with La(III), Gd(III), and Dy(III) salts produces helical linear trinuclear [Ln(3)(2pomp)(2)]-based complexes, where each metal ion occupies one of the three tridentate ligand pockets. Two ligands encompass the three metal ions, and internal connections between metal ions occur through μ-O(hydrazone) bridges. Coligands include benzoate, nitrate, and N,N-dimethylformamide. The linear Dy(III)(3) complex exhibits single-molecule magnet behavior, demonstrated through alternating-current susceptibility measurements. Slow thermal magnetic relaxation was detected in an external field of 1800 Oe, where quantum-tunneling effects were suppressed (U(eff) = 14 K).     

Correlation among crystal shape, absolute configuration, and circular dichroism spectrum of enantiomorphs of Tris[2-(((2-phenylimidazol-4-yl)methylidene)amino)ethyl]-aminemetal(II) nitrate-methanol (1/1)

A series of metal(II) complexes of a tripod-type ligand with the chemical formulas [M(H(3)L)](NO(3))(2).MeOH (M = Mn (1), Fe (2), Co (3), Ni (4), Zn (6)) and [Cu(H(3)L)](NO(3))(2).CH(3)CN.H(2)O (5) were synthesized and characterized (H(3)L = tris[2-(((2-phenylimidazol-4-yl)methylidene)amino)ethyl]amine). The crystal structures were determined, in which those of 1-4 and 6 are isomorphous and conglomerates, because they crystallize into the acentric space group P2(1)2(1)2(1). Each metal(II) ion of 1-4 and 6 assumes an octahedral coordination environment with the N(6) donor atoms of the tripod ligand and becomes either a C (clockwise) or an A (anticlockwise) enantiomorph because of the screw arrangement of the tripod-type ligand around the metal(II) ion. The crystals were divided into two groups, where their crystal shapes are mirror images and their CD spectra show enantiomeric patterns. The circular dichroism (CD) spectrum of the crystal used for the X-ray analysis was measured. The absolute configuration of the enantiomorph of the crystal used for the X-ray analysis was determined by the Flack parameter. The correlation among the crystal shape, the absolute configuration, and the CD spectral pattern was thus confirmed for 1-4 and 6. On the other hand, 5 assumes a square pyramidal coordination geometry with the N(5) donor atoms, and hence, there are no optical isomers.     

Acyclic bis(N2O2 chelate) ligand for trinuclear d-block homo- and heterometal complexes

We have synthesized a new type of acyclic bis(N2O2 chelate) ligand that affords a C-shaped O6 site by the metalation of the N2O2 salamo sites. UV-vis titration clearly showed that complexation of H4L with MII (MnII, CoII, and NiII) affords the 1:3 complex [LM3]2+ in a cooperative fashion, whereas complexation with copper(II) gave two or more complexes in a stepwise fashion. The manganese(II) complex [LMn3(OAc)2(MeOH)2] crystallizes in the triclinic system, space group P_1, with unit cell parameters a = 9.584(6) A, b = 13.666(9) A, c = 15.566(10) A, alpha = 108.702(8) degrees, beta = 95.255(4) degrees, gamma = 101.023(8) degrees, and Z = 2, and the cobalt(II) complex [LCo3(OAc)2(EtOH)2].2CHCl3 crystallizes in the triclinic system, space group P_1, with unit cell parameters a = 13.291(6) A, b = 13.913(7) A, c = 14.599(8) A, alpha = 88.27(2) degrees, beta = 67.391(15)degrees, gamma = 73.90(2) degrees, and Z = 2. In the crystal structures, three metal ions occupied both the N2O2 and O6 sites of the ligand L4-. The resultant trinuclear complexes have a C- or S-shaped structure depending on the metal employed. The different nature of the N2O2 and O6 sites of the ligand H4L leads to the site-selective introduction of two different d-block transition metals. An X-ray crystallographic analysis revealed the structures of the two heterotrinuclear complexes, [LZn2Mn(OAc)2(MeOH)2] and [LCu2Zn(OAc)2(H2O)].     

Trinuclear heterobimetallic Ni2Ln complexes [L2Ni2Ln][ClO4] (Ln=La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, and Er; LH3=(S)P[N(Me)NCH-C6H3-2-OH-3-OMe]3): from simple paramagnetic complexes to single-molecule magnet behavior

The reaction of LH3 with Ni(ClO4)(2).6H 2O and lanthanide salts in a 2:2:1 ratio in the presence of triethylamine leads to the formation of the trinuclear complexes [L2Ni2Ln][ClO4] (Ln=La (2), Ce (3), Pr (4), Nd (5), Sm (6), Eu (7), Gd (8), Tb (9), Dy (10), Ho (11) and Er (12) and L: (S)P[N(Me)NCH-C6H3-2-O-3-OMe]3). The cationic portion of these complexes consists of three metal ions that are arranged in a linear manner. The two terminal nickel(II) ions are coordinated by imino and phenolate oxygen atoms (3N, 3O), whereas the central lanthanide ion is bound to the phenolate and methoxy oxygen atoms (12O). The Ni-Ni separations in these complexes range from 6.84 to 6.48 A. The Ni-Ni, Ni-Ln and Ln-O phenolate bond distances in 2-12 show a gradual reduction proceeding from 2 to 12 in accordance with lanthanide contraction. Whereas all of the compounds (2-12) are paramagnetic systems, 8 displays a remarkable ST=(11)/2 ground state induced by an intramolecular Ni. . .Gd ferromagnetic interaction, and 10 is a new mixed metal 3d/4f single-molecule magnet generated by the high-spin ground state of the complex and the magnetic anisotropy brought by the dysprosium(III) metal ion.     

三核过渡金属配合物〔M_3~ⅢO(OOCR)_6L_3〕 (M=Cr,Fe,Mn;R=CH_3,C_2H_5,CH_2NH_2;L=C_5H_5N,H_2O)的~1H NMR性质

采用１ＨＮＭＲ谱研究了通式为〔Ｍ３ⅢＯ（ＯＯＣＲ）６Ｌ３〕＋（Ｍ＝Ｃｒ,Ｆｅ,Ｍｎ;Ｒ＝ＣＨ３,Ｃ２Ｈ５,ＣＨ２ＮＨ２;Ｌ＝Ｃ５Ｈ５Ｎ,Ｈ２Ｏ）的一系列氧心三核过渡金属配合物,主要考察其１Ｈ化学位移随金属、配体、温度、溶剂等因素变化而变化的规律。结果表明,骨架金属对化学位移的影响最大,Ｍ３Ｏ中的３个金属离子间存在反铁磁交换相互作用。对Ｍｎ配合物中顺磁中心对化学位移和线宽的影响机制的研究表明,其１Ｈ各向同性位移主要由接触作用贡献     

Syntheses,Crystal Structures,and Antibacterial Activities of Four Schiff Base Copper(II), Zinc(II), and Cadmium(II) Complexes Derived from 2‐[(2‐Dimethylaminoethylimino)methyl]phenol

Four Schiff base complexes, [Zn₂L₂(NCS)₂] ( 1 ), [Cd₂L₂(NCS)₂]_n ( 2 ), [Zn₄L₂(N₃)₂Cl₄(OH₂)(CH₃OH)] ( 3 ), and [Cu₄L₂(N₃)₂Cl₄(OH₂)(CH₃OH)] ( 4 ) (where L = 2‐[(2‐dimethylaminoethylimino)methyl]phenol), were synthesized and characterized by elemental analyses, infrared spectroscopy, and single crystal X‐ray determinations. Both 1 and 2 are structurally similar polynuclear complexes. In 1 , each Zn atom has a slightly distorted square‐pyramidal coordination configuration. In the basal plane, the Zn atom is coordinated by one O and two N atoms of one L, and by one O atom of another L. The apical position is occupied by one terminal N atom of a coordinated thiocyanate anion. The Zn···Zn separation is 3.179(3) Å. While in 2 , the Cd1 atom is six‐coordinated in an octahedral coordination. In the equatorial plane, the Cd1 atom is coordinated by one O and two N atoms of one L, and by one O atom of another L. The axial positions are occupied by the terminal N and S atoms from two bridging thiocyanate anions. The coordination of Cd2 atom in 2 is similar to those of the zinc atoms in 1 . The Cd···Cd separation is 3.425(2) Å. Both 3 and 4 are novel tetra‐nuclear complexes. Each metal atom in the complexes has a slightly distorted square‐pyramidal coordination. The arrangements of the terminal metal atoms are similar, involving one O and two N atoms of one L ligand and one bridging Cl atom defining the basal plane, and one O atom of a coordinated water molecule or MeOH molecule occupying the apical position. The coordinations of the central metal atoms are also similar. The basal plane of each metal atom involves one O atom of one L ligand, one terminal Cl atom, and two terminal N atoms from two bridging azide groups. The apical position is occupied by a bridging Cl atom which also acts as a basal donor atom of the terminal metal atom. The Schiff base ligand and the four complexes showed high selectivity and antibacterial activities against most of the bacteria.     

2-[(8-Hydroxyquinolinyl)methylene]hydrazinecarboxamide: expanding the coordination sphere of 8-hydroxyquinoline for coordination of rare-earth metal(III) ions

The semicarbazone of 8-hydroxyquinoline-2-carbaldehyde can be easily synthesized and is an effective tetradentate ligand for the coordination of rare-earth(III) ions. Investigations with yttrium(III) and lanthanum(III) in solution and in the solid state show, that the small yttrium ion can form 2 : 2 (1 : 1 stoichiometry) and 2 : 1 ligand to metal complexes (X-ray structures: [LY(NO3)(DMF)2]2Cl2 x 2DMF and [LL'Y] x 3MeOH x Et2O). With the larger lanthanum(III) ion only a well defined 1 : 1 complex (X-ray structure: [LLa(NO3)(MeOH)2]2(NO3)2) can be observed but probably 2 : 1 complexes are also formed. The X-ray structure analyses of [(L-H)MCl3] x MeOH (M = Er, Ho) and Na[(micro-NO3){LEu(NO3)2}2] x 2DMF show different coordination modes of the ligand. It can coordinate in its deprotonated but also in the protonated form.     

Syntheses, structures, and properties of trinuclear complexes [M(bpca)(2)(M'(hfac)(2))(2)], constructed with the complexed bridging ligand [M(bpca)(2)] [M, M' = Ni(II), Mn(II); Cu(II), Mn(II); Fe(II), Mn(II); Ni(II), Fe(II); and Fe(II), Fe(II); Hbpca = Bis(2-pyridylcarbonyl)amine, Hhfac = Hexafluoroacetylacetone

Five trinuclear complexes [M(bpca)(2)(M'(hfac)(2))(2)] (where MM'(2) = NiMn(2), CuMn(2), FeMn(2), NiFe(2), and FeFe(2); Hbpca = bis(2-pyridylcarbonyl)amine; and Hhfac = hexafluoroacetylacetone) were synthesized almost quantitatively by the reaction of [M(bpca)(2)] and [M'(hfac)(2)] in 1:2 molar ratio, and their structures and magnetic properties were investigated. Three complexes, with M' = Mn, crystallize in the same space group, Pna2(1), whereas two complexes, with M' = Fe, crystallize in P4(1), and complexes within each set are isostructural to one another. In all complexes, [M(bpca)(2)] acts as a bis-bidentate bridging ligand to form a linear trinuclear complex in which three metal ions are arranged in the manner M'-M-M'. The central metal ion is in a strong ligand field created by the N(6) donor set, and hence the Fe(II) in the [Fe(bpca)(2)] moiety is in a low-spin state. The terminal metal ions (M') are surrounded by O(6) donor sets with a moderate ligand field, which leads to the high-spin configuration of Fe(II). Three metal ions in all complexes are almost collinear, and metal-metal distances are ca. 5.5 A. The magnetic behavior of NiMn(2) and NiFe(2) shows a weak ferromagnetic interaction between the central Ni(II) ion and the terminal Mn(II) or Fe(II) ions. In these complexes, sigma-spin orbitals of the central Ni(II) ion and those of terminal metal ions have different symmetry about a 2-fold rotation axis through the Ni-N(amide)-M'(terminal) atoms, and this results in orthogonality between the neighboring sigma-spin orbitals and thus ferromagnetic interactions.     

An allosteric synthetic catalyst: metal ions tune the activity of an artificial phosphodiesterase

A trinuclear metal complex of general formula (L-H)M3(Mf)2 represents the first allosteric low molecular weight catalyst. L is a polyaza ligand having a tetradentate and two bidentate metal binding sites, Ms is a "structural" (allosteric) metal, and Mf are functional (catalytic) metals which interact with a substrate. In mononuclear [(L-H)Ms]+ complexes [(L-H)Cu(MeOH)]ClO4 (1a). [(L-H)Cu]NO3 x 2H2O (1b), [(L-H)Ni]ClO4 x 4H2O (2), and [(L-H)Pd]ClO4 x 2H2O (3), prepared from L and M2+ salts, the metal is strongly bound by an in-plane N4-coordination (confirmed by X-ray crystal structure determination of la). Formation of trinuclear complexes [(L-H)MsCu2]5+, with two functional Cu2+ ions coordinated to the bidentate sites of L, was evidenced in solution by photometric titration and by isolation of [(L-H)Cu3][PO4][ClO4]2 x 9H2O (4). The trinuclear complexes catalyze the cleavage of RNA-analogue 2-(hydroxypropyl)-p-nitrophenyl phosphate (HPNP), an activated phosphodiester. From a kinetic analysis of the cleavage rate at various HPNP concentrations, parameters KHPNP (the equilibrium constant for binding of HPNP to [(L-H)MsCu2]5+ and kcat (first-order rate constant for cleavage of HPNP when bound to the catalyst) were derived: KM= 170 (Ms= Cu2+), 340 (Ms = Ni2+), 2,600 (Ms = Pd2+) M(-1), kcat = 17 x 10(-3) (Ms= Cu2+) 3.1 x 10(-3) (Ms=Ni2+), 0.22 x 10(-3) (Ms = Pd2+) s(-1). Obviously, the nature of the allosteric metal ion Ms strongly influences both substrate affinity and reactivity of the catalyst [(L-H)MsCu2]5+. Our interpretation of this observation is that subtle differences in the ionic radius of Ms and in its tendency to distort the N4-Ms coordination plane have a significant influence on the conformation of the catalyst (i.e., preorganization of functional Cu2+ ions) and thus on catalytic activity.     

Phenolate- and acetate (both mu(2)-1,1 and mu(2)-1,3 mode)-bridged face-shared trioctahedral linear Ni(II)(3), Ni(II)(2)M(II) (M = Mn, Co) complexes: ferro- and antiferromagnetic coupling

The complexes [(L)(2)Ni(II)(2)M(II)(mu(2)-1,3-OAc)(2)(mu(2)-1,1-OAc)(2)(S)(2)] x xMeOH [HL = N-methyl-N-(2-hydroxybenzyl)-2-aminoethyl-2-pyridine; M = Ni, S = MeOH, x = 6 (1); M = Mn, S = H(2)O, x = 0 (2); M = Co, S = MeOH, x = 6 (3)] have been synthesized. Crystal structures reveal that three octahedral MII ions form a linear array with two terminal moieties {(L)Ni(II)(mu(2)-1,3-OAc)(mu(2)-1,1-OAc)(MeOH/H(2)O)}(-) in a facial donor set and a central MII ion which is connected to the terminal ions via bridging phenolate and two types of bridging acetates. Magnetic measurements reveal that the Ni(II)(3) and Ni(II)(2)Co(II) centers are ferromagnetically and Ni(II)(2)Mn(II) center is antiferromagnetically coupled. An attempt has been made to rationalize the observed magneto-structural behavior.     

Synthesis, structure, and magnetic behavior of a series of trinuclear Schiff base complexes of 5f (UIV, ThIV) and 3d (CuII, ZnII) ions

The reaction of [M(H(2)L(i))] (M = Cu, Zn) and U(acac)(4) in refluxing pyridine produced the trinuclear complexes [[ML(i)(py)(x)](2)U] [L(i) = N,N'-bis(3-hydroxysalicylidene)-R, R = 1,2-ethanediamine (i = 1), 2-methyl-1,2-propanediamine (i = 2), 1,2-cyclohexanediamine (i = 3), 1,2-phenylenediamine (i = 4), 4,5-dimethyl-1,2-phenylenediamine (i = 5), 1,3-propanediamine (i = 6), 2,2-dimethyl-1,3-propanediamine (i = 7), 2-amino-benzylamine (i = 8), or 1,4-butanediamine (i = 9); x = 0 or 1]. The crystal structures show that the central U(IV) ion adopts the same dodecahedral configuration in all of these compounds, while the Cu(II) ion coordination geometry and the Cu...U distance vary with the length of the diimino chain of the Schiff base ligand L(i). These geometrical parameters have a major influence on the magnetic properties of the complexes. For the smallest Cu...U distances (i = 1-5), the Cu-U coupling is antiferromagnetic and weak antiferromagnetic interactions are present between the Cu(II) ions, while for the largest Cu...U distances (i = 6-9), the Cu-U coupling is ferromagnetic and no interaction is observed between the Cu(II) ions. The magnetic behavior of the [[CuL(i)](2)Th] compounds (i = 1, 2), in which the Th(IV) ion is diamagnetic, confirms the presence of weak intramolecular antiferromagnetic coupling between the Cu(II) ions.     

An unsymmetrical tripodal ligand with NOS2-donor set: coordination chemistry with nickel(II) and zinc(II)

The synthesis of the novel tripodal ligand [N(CH2CH2CH2OH)(CH2CH2SH)2] H3-4 is reported. The aliphatic tetradentate ligand is equipped with an unsymmetrical NOS2 donor set. It reacts with Ni(OAc)2 x 4H2O or Zn(BF4)2 x xH2O to give the complexes [Ni(H-4)]2 5 and [Zn(H-4)]4 6, respectively. The molecular structures of 5 and 6 have been determined by X-ray diffraction. In both cases multinuclear, mu-thiolato-bridged complexes, wherein the ligand coordinates with only three (NS2) of the four donor groups, had formed. The dinuclear complex 5 adopts a butterfly geometry and contains nickel(II) ions in a square-planar NS3 coordination environment. Cyclic voltammetry experiments indicate that the nickel centers in 5 are electron-rich but not overly sensitive toward oxidation. Complex 6 is tetranuclear and the four thiolato-bridged metal centers form a ring. It shows a distorted tetrahedral coordination geometry for the zinc(II) ions in an NS3 coordination sphere. In both complexes the hydroxyl functionalized ligand arm of the tripodal ligand remains uncoordinated.     

Metal-ion-coordinating properties of the dinucleotide 2'-deoxyguanylyl(5'-->3')-2'-deoxy-5'-guanylate (d(pGpG)3-): isomeric equilibria including macrochelated complexes relevant for nucleic acids

The interaction between divalent metal ions and nucleic acids is well known, yet knowledge about the strength of binding of labile metal ions at the various sites is very scarce. We have therefore studied the stabilities of complexes formed between the nucleic acid model d(pGpG) and the essential metal ions Mg2+ and Zn2+ as well as with the generally toxic ions Cd2+ and Pb2+ by potentiometric pH titrations; all four ions are of relevance in ribozyme chemistry. A comparison of the present results with earlier data obtained for M(pUpU)- complexes allows the conclusion that phosphate-bound Mg2+ and Cd2+ form macrochelates by interaction with N7, whereas the also phosphate-coordinated Pb2+ forms a 10-membered chelate with the neighboring phosphate diester bridge. Zn2+ forms both types of chelates with formation degrees of about 91% and 2.4% for Zn[d(pGpG)]cl/N7 and Zn[d(pGpG)]-cl/PO, respectively; the open form with Zn2+ bound only to the terminal phosphate group, Zn[d(pGpG)]-op, amounts to about 6.8 %. The various intramolecular equilibria have also been quantified for the other metal ions. Zn2+, Cu2+, and Cd2+ also form macrochelates in the monoprotonated M[H;d(pGpG)] species (the proton being at the terminal phosphate group), that is, the metal ion at N7 interacts to some extent with the P(O)2(OH)- group. Thus, this study demonstrates that the coordinating properties of the various metal ions toward a pGpG unit in a nucleic acid differ: Mg2+, Zn2+, and Cd2+ have a significant tendency to bridge the distance between N7 and the phosphate group of a (d)GMP unit, although to various extents, whereas Pb2+ (and possibly Ca2+) prefer a pure phosphate coordination.     

Reactivity of the heterometallic clusters [HMCo3(CO)12] and [Et4N][MCo3(CO)12] (M = Fe, Ru) toward phosphine selenides, including selenium transfer. Crystal structures of [HRuCo3(CO)7(mu-CO)3(mu-dppy)], [MCo2(mu3-Se)(CO)7(mu-dppy)], and [RuCo2(mu3-Se)(CO)7(mu-dppm)] [dppy = Ph2(2-C5H4N)P, dppm = Ph2PCH2PPh2

The reactivity of [HMCo3(CO)12] and [Et4N][MCo3(CO)12] (M = Fe, Ru) toward phosphine selenides such as Ph3PSe, Ph2P(Se)CH2PPh2, Ph2(2-C5H4N)PSe, Ph2(2-C4H3S)PSe, and Ph2[(2-C5H4N)(2-C4H2S)]PSe has been studied with the aim to obtain new selenido-carbonyl bimetallic clusters. The reactions of the hydrido clusters give two main classes of products: (i) triangular clusters with a mu3-Se capping ligand of the type [MCo2(mu3-Se)(CO)(9-x)L(y)] resulting from the selenium transfer (x = y = 1, 2, with L = monodentate ligand; x = 2, 4, and y = 1, 2, with L = bidentate ligand) (M = Fe, Ru) and (ii) tetranuclear clusters of the type [HMCo3(CO)12xL(y)] obtained by simple substitution of axial, Co-bound carbonyl groups by the deselenized phosphine ligand. The crystal structures of [HRuCo3(CO)7(mu-CO)3(mu-dppy)] (1), [MCo2(mu3-Se)(CO)7(mu-dppy)] (M = Fe (16) or Ru (2)), and [RuCo2(mu3-Se)(CO)7(mu-dppm)] (12) are reported [dppy = Ph2(2-C5H4N)P, dppm = Ph2PCH2PPh2]. Clusters 2, 12, and 16 are the first examples of trinuclear bimetallic selenido clusters substituted by phosphines. Their core consists of metal triangles capped by a mu3-selenium atom with the bidentate ligand bridging two metals in equatorial positions. The core of cluster 1 consists of a RuCo3 tetrahedron, each Co-Co bond being bridged by a carbonyl group and one further bridged by a dppy ligand. The coordination of dppy in a pseudoaxial position causes the migration of the hydride ligand to the Ru(mu-H)Co edge. In contrast to the reactions of the hydrido clusters, those with the anionic clusters [MCo3(CO)12]- do not lead to Se transfer from phosphorus to the cluster but only to CO substitution by the deselenized phosphine.     

Versatile chelating behavior of benzil bis(thiosemicarbazone) in zinc, cadmium, and nickel complexes

Reactions of benzil bis(thiosemicarbazone), LH(6), with M(NO(3))(2).nH(2)O (M = Zn, Cd, and Ni), in the presence of LiOH.H(2)O, show the versatile behavior of this molecule. The structure of the ligand, with the thiosemicarbazone moieties on opposite sides of the carbon backbone, changes to form complexes by acting as a chelating molecule. Complexes of these metal ions with empirical formula [MLH(4)] were obtained, although they show different molecular structures depending on their coordinating preferences. The zinc complex is the first example of a crystalline coordination polymer in which a bis(thiosemicarbazone) acts as bridging ligand, through a nitrogen atom, giving a 1D polymeric structure. The coordination sphere is formed by the imine nitrogen and sulfur atoms, and the remaining position, in a square-based pyramid, is occupied by an amine group of another ligand. The cadmium derivative shows the same geometry around the metal ion but consists of a dinuclear structure with sulfur atoms acting as a bridge between the metal ions. However, in the nickel complex LH(6) acts as a N(2)S(2) ligand yielding a planar structure for the nickel atom. The ligand and its complexes have been characterized by X-ray crystallography, microanalysis, mass spectrometry, IR, (1)H, and (13)C NMR spectroscopies and for the cadmium complex by (113)Cd NMR in solution and in the solid state.     

Ferromagnetic coupling promoted by kappa3N:kappa2N bridging system

Syntheses, structures, and magnetic properties of novel trinuclear complexes of the same motif [M{Cu(pz2bg)2}M]4+ (M = CuII, NiII, CoII, MnII), catena-[Cu2{Cu(pz2bg)2}(Hpz)2(PhSO3)2](PhSO3)2.4H2O (2.4H2O), [Ni2{Cu(pz2bg)2}(MeOH)2(H2O)4](NO3)4 (3), [Co2{Cu(pz2bg)2}(NO3)2(EtOH)2](NO3)2 (4), and [Mn2{Cu(pz2bg)2}(NO3)4(MeCN)2] (5), which include the complex ligand [Cu(pz2bg)2] (1), are reported (Hpz = pyrazole, pz2bg- = di(pyrazolecarbimido)aminate; bispyrazolyl derivative of biguanidate). The reaction of Cu(ClO4)2.6H2O, sodium dicyanamide, Hpz, and PhSO3H.H2O (1:2:4:4) in MeOH yielded blue crystals of [Cu2(1)(Hpz)2(PhSO3)2](PhSO3)2.4H2O (2.4H2O). In 2, the tricopper(II) units, which consist of two Cu(II) ions bridged by 1, are linked by benzenesulfonate anions to form a ladder structure. Complex 1 was isolated by removing the terminal Cu(II) ions from 2 with use of Na(4)edta. Complexes 3-5 were obtained by the reaction of 1 with an excess of each M(II) ion. In 2-5, the adjoining metal ions are ferromagnetically coupled via the pz2bg- ligand with J values of +7.2(1), +7.5(1), +2.7(1), and +0.3(1) cm(-1), respectively, using a spin Hamiltonian H = -2J(S(M1)S(Cu) + S(Cu)S(M2)). The ferromagnetic interaction was attributed to the strict orthogonality of magnetic dsigma orbitals, which are controlled by the kappa3N:kappa2N bridging geometry of the pz2bg- ligands.     

Amino acid and peptide bioconjugates of copper(II) and zinc(II) complexes with a modified N,N-bis(2-picolyl)amine ligand

Four chelating nitrogen ligands 2-5 derived from N,N-bis(2-picolyl)amine (bpa, 1) were synthesized, namely, (PyCH(2))(2)N-CH(2)-p-C(6)H(4)-CO(2)R (R = Me, 2, and R = H, 3) and (PyCH(2))(2)N-(CH(2))(n)-CO(2)H (n = 2, 4, and n = 5, 5). Amino acid conjugates 6 and 7 were formed by condensation of 3 with H-Phe-OMe and H-betaAla-OMe, respectively. Cu(II) and Zn(II) complexes of 1-7 were prepared and fully characterized. The X-ray structures of 1(Zn), 2(Zn), 4(Cu), and 7(Cu) were determined. The Zn complexes 1(Zn) and 2(Zn) as well as 7(Cu) show a distorted trigonal bipyramidal coordination environment in the solid state. An octahedral complex is observed for 4(Cu) which forms chains along the crystallographic b axis by intermolecular coordination of the carboxylic acid to the metal ion of a neighboring complex. Ligand 3 was used to prepare the peptide bioconjugate 8 (3-Ahx-Pro-Lys-Lys-Lys-Arg-Lys-Phe-NH(2)) with a nuclear localization signal (nls) heptapeptide by solid phase synthesis. Cu(II) and Zn(II) complexes of 8 were synthesized in situ and studied by FAB-MS, ESI-MS, UV/vis, and EPR (for 8(Cu)), and FAB-MS, ESI-MS, and NMR (for 8(Zn)). All spectroscopic results clearly support metal coordination to the bpa ligand in the bioconjugates 8(M), even in the presence of other potential ligands from amino acid side chains of the peptide. We suggest metal-peptide conjugates like 8(M) as artificial metallochaperones because they have the potential to deliver metal ions to specific compartments in the cell as determined by the peptide moieties.