J.M. Moreno

Structure and magnetic properties of a syn-anti carboxylate bridged linear trinuclear copper(II) complex with ferromagnetic exchange interaction

Abstract The synthesis, crystal structure and magnetic properties are reported for the trinuclear compound [Cu(H2O)4{Cu(HL)(H2O)(ClO4)}2][ClO4]2·2H2O, where HL is the monodeprotonated form of 6-methylamino-1,3-dimethyl-5-[(2′-carboxyphenyl)azo]uracil. The compound crystallizes in the triclinic system, space0 group P 1 , with cell constants a=7.824(3), b=12.278(3), c=13.705(9) A, α=104.34(3), β=91.80(3), γ=103.37(5)° and Z=1. The structure was solved and refined to R=0.071 (Rw=0.064). The structure consists of trinuclear [Cu(H2O)4{Cu(HL)(H2O)(ClO4)}2]2+ cations, non-coordinated perchlorate anions and crystal water molecules, held together by a network of hydrogen bonds. The central copper is in an elongated octahedral CuO6 chromophore and the terminal copper atoms in distorted square-pyramidal CuNO4 chromophores. Adjacent copper atoms are linked by carboxylate groups in a syn-anti conformation. From the magnetic susceptibility measurements, the complex is found to exhibit weak ferromagnetic interaction between nearest-neighbour copper(II) ions. The magnitude and nature of the exchange coupling are discussed on the basis of the structural data.

Solution–solid-state study of the system Cu(II)/N-2-(4-amino-1,6-dihydro-1-methyl-5-nitroso-6-oxopyrimidinyl)glycine.: Mononuclear and polynuclear ladder-like chain complex crystalline structures

An aqueous solution-solid-state study of the Cu(II) / HL system (HL5N-2-(4-amino-1,6-dihydro-1-methyl-5-nitroso-6-ox- opyrimidinyl)glycine) is reported. The solution studies have been carried out on the protonation equilibria of HL and the Cu(II) / HL system, at molar ratios of 1:1 and 1:5. Two complexes were obtained in the solid state, Cu(II) / HL molar ratio51:1, and were characterized by spectroscopic and X-ray single-crystal diffraction techniques. Mononuclear complex 1 ((CuCl (HL) ) crystallizes with 22 n a hexacoordinated coordination mode around the Cu(II) ion, while complex 2 (CuCl(L)(H O) ) is an infinite polynuclear ladder-like 22 chain, with a distorted asymmetric square-based bipyramid. None of those crystalline complexes were detected in the solution study.

The preparation, spectroscopic study and crystal structures of two copper(II) complexes of closely related carboxyphenylazopyrimidine ligands, involving distorted square-pyramidal CuN4O and CuN3O2 chromophores

Abstract The preparation, spectroscopic properties and crystal structures of two isostructural complexes [Cu(L1)(dpa)] (1) [H2L1-6-amino-1,3-dimethyl-5(2′-carboxyphenyl)azouracil, dpa-2,2′-dipyridylamine] and [Cu(L2)(dpa)] (2) [H2L2 is 1,3-dimethyl-5(2′-carboxyphenyl)azobarbituric acid] are reported. The H2L ligands act in a double-deprotonated tridentate mode giving rise to CuN4O and CuN3O2 chromophores with distorted square-pyramidal geometry. The EPR spectra of 1 and 2 show that the replacement of the 6-amino group in the former by a hydroxyl group in the latter increases g‖ and decreases A‖ values, clearly indicating that the in-plane ligand field strength of L1 is greater than that of L2 in 2.

Solution study and 2-D layered structures of zinc(II) and cadmium(II) complexes with N-2-(6-amino-3,4-dihydro-3-methyl-5-nitroso-4-oxopyrimidinyl)-l-methionine as ligand

Abstract The solution study of the N-2-(6-amino-3,4-dihydro-3-methyl-5-nitroso-4-oxopyrimidinyl)- l -methionine has revealed that it acts as a monoprotic acid in the pH range 2.5–9.5. In solution the complexes detected with Zn(II) and Cd(II) at 1:1 and 1:4 metal-to-ligand molar ratios were the mononuclear species [ZnL2], [CdL2] and [Cd(HL)]2+, with the ligand coordinating through the carboxylate group in the two former and through the pyrimidine ring in the later. From these, two layered complexes of Zn(II) and Cd(II) with HL were obtained. {[Zn(μ-L)2]·2H2O}n, monoclinic, space group P21, a=10.882(3), b=7.473(2), c=18.534(4) A, β=90.92(2)°, Z=2; {[Cd(μ-L)2]·3H2O}n, triclinic, space group P1, a=7.615(2), b=10.427(2), c=11.129(2) A, α=86.29(3), β=78.87(3), γ=71.13(3)°, Z=1. The structures of both complexes are very similar except for the coordination numbers of five and seven for Zn(II) and Cd(II), respectively. These facts point out the versatility of this family of N-pyrimidine amino acids as ligands, as well as the importance of the crystallization processes in obtaining supramolecular compounds.

Solution and solid study of Zn(II) and Cd(II) complexes with N-(6-amino-3,4-dihydro-3-methyl-5-nitroso-4-oxo-pyrimidin-2-yl)glycine as ligand. Crystal structures of [ZnL2(H2O)4]·6H2O and {[Cd(μ-L)Cl(H2O)2]·H2O}n

Abstract Reactions of N -(4-amino-1,6-dihydro-1-methyl-5-nitroso-6-oxo-pyrimidin-2-yl)glycine with Zn(II) and Cd(II) (1:1 and 1:4 metal/ligand ratios, in aqueous media at 35°C and 0.1 M KCl ionic strength) were studied by potentiometric methods. This study has revealed a similar qualitative behaviour to that found by us for this family of N -pyrimidine aminoacids, the primary coordination site being either the pyrimidine or the carboxylate group depending on whether the ligand acts in neutral form or deprotonated, respectively. In solid state two complexes were obtained by working in 1:1 metal-to-ligand ratio: [Zn(L) 2 (H 2 O) 4 ]·6H 2 O and {[Cd(μ-L)Cl(H 2 O) 2 ]·H 2 O} n , which were characterised by IR and NMR spectroscopies, TG and DSC techniques and single crystal X-ray diffraction. The former complex is mononuclear with the Zn(II) ion hexacoordinated in a distorted octahedral geometry. The coordination sphere is formed by four water molecules and two ligands coordinating in a monodentate fashion through the carboxylate group. The Cd(II) complex consists of a 1D infinite chain, with the metal ion heptacoordinated in a distorted pentagonal bipyramid. The ligand bridges the metal ions coordinating in a bis-didentate fashion through the pyrimidine and the carboxylate group. The nature of these complexes is very different to that shown by the Zn(II) and Cd(II) complexes with the related methionine derivative, which is attributed to he effect of the R substituent on the aminoacid moiety.

ORTHOMETALATION OF 6-AMINO-1,3-DIMETHYL-5-PHENYLAZOURACIL : CRYSTAL STRUCTURE AND SPECTROSCOPIC PROPERTIES OF TRANS-RHIIICL2(L)(H2O).3H2O

Abstract The preparation and spectroscopic characterization of two iso-structural complexes trans-[RhIIIX2(L)(H2O)]·3H2O (HL is 6-amino-1,3-dimethyl-5-phenylazouracil and X stands for Cl and Br) are reported. In addition, the crystal structure of the complex trans-[RhIIIX2(L)(H2O)]·3H2O has been solved and refined to R = 0.039 (Rw = 0.045). The compound crystallizes in the triclinic space group P 1 (No. 2) with cell constants a = 57.395(4), b = 11.412(3), c = 11.776(4) A , α = 77.42(2) , β = 75.14(3), γ =78.67(2)°, V = 927(2) A 3 , Z = 2, D c = 1.74 g cm −3 , D exp = 1.75(2) g cm −3 , F(000) = 5 , μ(Mo Kα) = 1.305 mm−1. In this complex the ligand undergoes orthometalation, coordinating in a monodeprotonated fashion tridentate through an exocyclic oxo group, the azo group and the carbon atom of the phenyl ring ortho to the azo group. The three remaining positions are occupied by two chlorine atoms in trans position and a water molecule.

Study of the reactivity of Cd(II) with 4,6-dimethyl-2-thiopyrimidine. Crystal structure of 4,6-dimethyl-2-thiopyrimidinium trichlorocadmiatum(II)

Abstract The distribution species and stability constants of the 4,6-dimethyl-2-thiopyrimidine (HL)/CdCl2 system have been determined by potentiometric measurements at 25 °C and 0.1 M KCl ionic strength. The solid complexes CdL(OH) and {[H2L]CdCl3}n were obtained and characterized by IR, 1H and 13C NMR spectroscopic amd thermal techniques. In addition, the structure of the complex {[H2L][CdCl3]}n has been established by single-crystal X-ray diffraction. Crystals of the compound are orthorhombic space group Pbca (No. 61) with cell constants a = 6.723(1), b = 17.624(4), c = 19.401(4) A , Z = 8, D c = 2.080 g cm −3 . The structure was solved and refined to R = 0.055 (Rw = 0.079) and consists of Cd(II) centres hexacoordinated by chloride ions in an octahedral arrangement. These octahedra are linked by opposite faces giving rise to infinite [CdCl3]n chains which are bridged by H2L units through hydrogen bonds.

Reactions of the polynuclear chain complex [Cu(L)(H2O)]n (H2L is 5-[(2′-carboxyphenyl)azo]-1,3-dimethylbarbituric acid) with imidazole. Crystal structures of the dinuclear and mononuclear derivatives and EPR study of the dimer-monomer equilibrium in solution

On treating the polynuclear chain complex [Cu(L)(H2O)]n (H2L is 5-[(2′-carboxyphenyl)azo]-1, 3-dimethylbarbituric acid) with imidazole the complexes [Cu(L)(Him)]2 (1) and [Cu(L)(Him)2] (2) are obtained. The structures of 1 and 2 have been determined by X-ray crystallographic methods. The structure of 1 consists of dinuclear units in which the copper ions are bridged by the barbituric ring. It crystallizes in the monoclinic space group P21/c with cell constants a = 8.654(2), b = 22.64(2), c = 8.8048(8) A, β = 103.76(1)°, Z = 2, R = 0.051 and Rw = 0.041. The structure of 2 consists of discrete [Cu(L)(Him)2] molecules held together by intermolecular hydrogen bonds to form infinite chains. It crystallizes in the triclinic space group P1 with cell constants a 8.268(2), b = 9.412(3), c = 13.798(5) A, α = 99.07(3), β = 91.20(3), γ = 108.64(2)°, Z = 2, R = 0.041 and Rw = 0.035. Comparison of the crystal structure of 1 with analogous complexes containing nitrogen heterocyclic ligands reveals that the replacement of imidazole by pyrazole or pyridine leads to very different crystal structures, which has been attributed to the different nature of the nitrogen heterocyclic ligand used in their syntheses. In dmso solution, EPR spectra of both complexes clearly indicate the existence of a monomer-dimer equilibrium.

Bifunctional pyrimidine-amino-acid ligands: solution study and crystal structure of a Mn(II) chain alternating six- and sevenfold coordination environments

The acid � /base characterization in aqueous solution of the N -2-[4-amino-1,6-dihydro-1-methyl-5-nitroso-6-oxopyrimidinyl)methionine, a member of a family of bifunctional N -pyrimidine a-amino acids ligands, has been carried out by potentiometric and UV � /Vis techniques in the 2.5 � /9.0 pH range, indicating a quasi -zwitterionic structure. The solution study of the HL/Mn(II) system at 1:2, 2:1 and 4:1 molar ratios (25 8C and pHB/6), reveals that both moieties are active in coordinating to the metal ion, through the carboxylate group when the ligand is deprotonated or through the pyrimidinic fragment when acting in its molecular form. A solid complex with MnL2/6 / 1 /H2O stoichiometry was isolated from an aqueous 1:3 [HL]/[Mn(II)] mixture at pH 6. The X-ray single-crystal characterization has revealed that this complex can be formulated as {[Mn(H2O)4(m-L)2Mn(L)2(H2O)]/8H2O}n ,a n infinite chain in which two different Mn(II) ions having six- and sevenfold coordination environments alternate along the chain. The asymmetric unit contains two ligands coordinating in different fashion. One of these coordinates monodentately through the oxygen atom belonging to the exocyclic nitroso group while the other exhibits a 3 h-bridging pattern between the six- and sevenfold Mn(II) arrangements. The versatile coordination modes of this ligand is discussed and compared to other complexes of this bifunctional family of ligands. # 2003 Elsevier B.V. All rights reserved.

Coordination modes of N-2-(4-amino-1-methyl-5-nitroso-6-oxo-1,6-dihydropyrimidinyl) potassium L-alaninate toward Ag(I), Cd(II) and Pd(II). Crystal structure of {Ag((η4-μ3-L)]·3H2O}n, first example of a silver 3D-polymer with a pyrimidine-derivative ligand

The acid-base behaviour of the N-2-(4-amino-1-methyl-5-nitroso-6-oxo-1,6-dihydropyrimidinyl) potassium L-alaninate (KL) and its reactivity with Ag(I), Cd(II) and Pd(II) metal ions have been studied. Three solid species with formulae AgL·3H 2 O, CdL 2 ·6H 2 O and PdClL·H 2 O have been obtained and characterized by IR, 1 H and 13 C NMR spectroscopic methods and thermal, conductivity and magnetic measurements. The structure of {Ag((η 4 -μ 3 -L)]·3H 2 O} n has been established by single-crystal X-ray diffraction and consists in a 3D-polymer. Within the polymer each Ag(I) ion is tetrahedrally coordinated to three differents L anions, while each ligand is coordinated in a rather unusual η 4 -μ 3 coordination mode. Spectroscopic data show a similar coordination mode for the Cd(II) complex, while for the Pd(II) one a different coordination mode is proposed.