José Suárez-Varela

Anion influence on the structure and magnetic properties of a series of multidimensional pyrimidine-2-carboxylato-bridged copper(II) complexes.

Seven new polynuclear copper(II) complexes of formula [Cu(mu-pymca)2] (1) (pymca(-) = pyrimidine-2-carboxylato), [Cu(mu-pymca)Br] (2), [Cu(mu-pymca)Cl] (3), [Cu(mu-pymca)(SCN)(H2O)] x 4 H2O (4), [Cu(mu-pymca)N3] (5), [Cu2(mu1,5-dca)2(pymca)2] (6) (dca = dicyanamide), and K{[mu-Au(CN)2]2[(Cu(NH3)2)2(mu-pymca)]}[Au(CN)2]2 (7) have been synthesized by reactions of K-pymca with copper(II) ions in the presence of different counteranions. Compound 1 is a linear neutral chain with a carboxylato bridging ligand in a syn-anti coordination mode, whereas complexes 2 and 3 consist of cationic linear chains with cis and trans bis(chelating) pymca bridging ligands. Complex 4 adopts a helical pymca-bridged chain structure. In complex 5, zigzag pymca-bridged chains are connected by double end-on azide bridging ligands to afford a unique honeycomb layer structure. Complex 6 is a centrosymmetric dinuclear system with double mu 1,5-dicyanamide bridging ligands and pymca end-cap ligands. Complex 7 is made of pymca-bridged dinuclear [Cu(NH3)2(mu-pymca)Cu(NH3)2](3+) units connected by [Au(CN)2](-) anions to four other dinuclear units, giving rise to cationic (4,4) rectangular nets, which are linked by aurophilic interactions to afford a singular 3D network. Variable-temperature magnetic susceptibility measurements show that complex 1 exhibits a very weak antiferromagnetic coupling through the syn-anti (equatorial-axial) carboxylate bridge (J = -0.57 cm(-1)), whereas complexes 2-4 and 7 exhibit weak to strong antiferromagnetic couplings through the bis(chelating) pymca bridging ligand J = -17.5-276.1 cm(-1)). Quantum Monte Carlo methods have been used to analyze the experimental magnetic data for 5, leading to an antiferromagnetic coupling (J = -34 cm(-1)) through the pymca ligand and to a ferromagnetic coupling (J = 71 cm(-1)) through the azide bridging ligands. Complex 6 exhibits a very weak antiferromagnetic coupling through the dicyanamide bridging ligands (J = -5.1 cm(-1)). The magnitudes of the magnetic couplings in complexes 2-5 have been explained on the basis of the overlapping between magnetic orbitals and DFT theoretical calculations.

Rational design of azide-bridged bimetallic complexes. Crystal structure and magnetic properties of FeIIIMFeIII(M = NiII and CuII) trinuclear species

The first examples of azide-bridged bimetallic trinuclear complexes ([M(cyclam)][FeL(N3)(mu1,5-N3)]2) (H2L = 4,5-dichloro-1,2-bis(pyridine-2-carboxamido) benzene) have been structurally and magnetically characterized.

Crystal structure and magnetic properties of [Cu(ox)(py)2](py = pyridine): a ferromagnetic oxalate-bridged zigzag chain complex

The compound [Cu(ox)(py)2](ox = oxalate, py = pyridine) was obtained as a breakdown oxidized product of [Cu(epgly)2](Hepgly =N-2-ethylphenylglycine), and has been characterized by means of structural and magnetic measurements. The crystals are monoclinic, space group C2/c, with a= 14.088(3), b= 11.023(2), c= 8.689(2)A, β= 92.23(3)° and Z= 4. The structure was solved and refined to R= 0.039 and R′= 0.040. The structure consists of [Cu(py)2]2+ units bridged sequentially by centrosymmetric oxalate anions to form zigzag polymeric chains parallel to the c axis, with a copper–copper distance of 5.463(1)A. The copper ion is in distorted-octahedral environment and the equatorial co-ordination sites are occupied by N,N′ and O,O′ donors from two oxalate and two pyridine molecules at ca. 2.0 A. Two weaker axial bonds are formed with O″ and O″′ atoms from two oxalate anions, with a O(1″)–Cu–O(1″′) angle of 162.9(1)°. From the magnetic susceptibility measurements, the complex is found to exhibit weak ferromagnetic exchange interaction between nearest-neighbour copper(II) ions.

2D and 3D coordination polymers based on 2,2′-bipyrimidine and cyanide bridging ligands incorporating coordinated and guest ammonia molecules. Synthesis, crystal structures, magnetic properties and thermal analysis of {[Ni(CN)4]2[(Ni(NH3)2)2(bpym)]·2H2O}n and {[Cu2(CN)2(bpym)]·NH3}n

The coordination polymers {[Ni(CN)4]2[(Ni(NH3)2)2(bpym)]·2H2O}n1 and {[Cu2(CN)2(bpym)]·NH3}n2 have been prepared from the reactions of M(NO3)2·nH2O [Cu(II), n = 3 and M = Ni(II), n = 6] with NaCN and bpym (2,2′-bipyrimidine) in concentrated aqueous ammonia, respectively. The structure of 1 is made of bipyrimidine bridged centrosymmetric dinuclear [Ni(NH3)2(μ-bpym)Ni(NH3)2] fragments connected by four [Ni(CN)4]2− anions giving rise to a 2D framework. Layers, which adopt a stair-like conformation, are stacked with an ABAB… repeat pattern. Water molecules are located in the interlayer space and are involved in hydrogen bond interactions with the non-bridging cyanide groups of the [Ni(CN)4]2− anions and one of the ammonia molecules. Magnetic measurements clearly show the existence of antiferromagnetic exchange interactions between the local spin triplet states of the octahedral Ni(II) ions mainly mediated by the bpym exchange pathway with a J value of −16.82 cm−1. The structure of 2 consists of [Cu2(bpym)] centrosymmetric fragments connected by cyanide groups to four neighbouring Cu(I) ions giving rise to a 3D network with channels perpendicular to the bc plane. Guest ammonia molecules are located into channels. TG-XRD combined studies show that the structure of 1 is retained after dehydration whereas that of 2, however, collapses after ammonia elimination.

Interplay between covalent and aurophilic interactions in a series of isostructural 3D Hoffman-like frameworks containing bipyrimidine and dicyanoaurate bridges. X-Ray structure and magnetic properties of {(µ-Au(CN)2]2[(M(NH3)2)2(µ-bpym)]}[Au(CN)2]2 (M = Ni(II), Co(II) and Cu(II))

The isomorphous coordination polymers {micro-Au(CN)(2)](2)[(M(NH(3))(2))(2)(mu-bpym)]}[Au(CN)(2)](2) (M = Co(II) (1), Ni(II) (2), Cu(II) (3)) have been prepared from the reaction of 2 equiv. M(NO(3))(2) x nH(2)O (M = Cu(II), n = 3; M = Ni(II) and Co(II), n = 6) with 1 equiv. of bipyrimidine (bpym) in aqueous ammonia and then with an aqueous solution containing 1 equiv. of K[Au(CN)(2)]. The structures of these complexes are made of bpym bridged centrosymmetric dinuclear [M(NH(3))(2)(mu-bpym)M(NH(3))(2)] units connected by [Au(CN)(2)](-) anions to four other dinuclear units giving rise to a cationic 2D (4,4) rectangular grid network, its charge being balanced by two non-coordinated [Au(CN)(2)](-). The layers are stacked in such a way that the ammonia coordinated molecules are interdigitated and aligned above and below one sheet with cavities in neighbouring sheets, giving rise to an ABAB[dot dot dot] repeat pattern of layers. Gold atoms of bridging and non-bridging dicyanoaurate anions are involved in short aurophilic interactions (Au1-Au2 distances in the range 3.12-3.14 Angstrom), leading to a chain of gold atoms running along the a direction. Neighbouring gold chains are further connected by weaker aurophilic interactions (Au1-Au1 distances in the range 3.43-3.49 Angstrom), affording a honeycomb-like 2D network of gold atoms. The (4,4) rectangular sheets and (6,3) honeycomb sheets share the Au2 atoms, leading to a unique 3D network. Magnetic measurements clearly show the existence of antiferromagnetic exchange coupling between the metal ions with susceptibility maxima at 17 K (1), 22 K (2), and 17 K (3). The data of 1 were analyzed through a full Hamiltonian involving spin-orbit coupling, axial distortion, Zeeman interactions and magnetic exchange coupling between Co(II), and the best fit gives J = -9.23 cm(-1), kappa = 0.99, lambda = -142 cm(-1), Delta = -562 cm(-1). For 2 and 3, magnetic data were fitted to the theoretical equations derived from the isotropic Hamiltonian: H = -JS(1)S(2). The best fit parameters were g = 2.050(1), J = -17.51(1) and P = 0.01(2) for 2 and g = 2.068(5), J = -20.07(8) and P = 0.015(4) for 3, respectively (P takes into account the amount of paramagnetic impurity). In order to explain the weak magnetic interaction between copper(II) ions mediated by the bipyrimidine bridging ligand in 3, we have carried out electronic structure calculations based on the density functional theory (DFT).

Synthesis of polynuclear copper(II) complexes by controlling the conformation (cis or trans) of N,N′-bis(3-aminopropyl) oxamidate and the coordination mode of 2,2′-bipyrimidine

The synthesis, molecular structure and magnetic properties of three new polynuclear copper(II) complexes, [Cu( cis -oxpn)Cu(bpm)]- (ClO 4 ) 2 ·CH 3 OH ( 1 ), [Cu 2 ( trans -oxpn) (bpm) 2 ](ClO 4 ) 2 ·2H 2 O ( 2 ) and [Cu 2 ( trans -oxpn)( μ -bpm)](ClO 4 ) 2 ·2.5H 2 O ( 3 ) are reported. The compounds were prepared by controlling the conformation ( cis or trans ) of oxpn ( N , N ′-bis(3-aminopropyl)oxamidate and the coordination mode (bi- or bisbidentate) of bpm (2,2′-bipyrimidine). Complex 1 is a dinuclear complex in which the copper(II) ions are bridged by a cis -oxamidate group and where bpm acts as a bidentate terminal ligand. 2 is a trans -oxamidate-bridged dinuclear copper(II) complex with two bidentate terminal bpm molecules. In 3, a bisbidentate bpm molecule connects the dinuclear Cu 2 ( trans -oxpn) units to generate an alternating oxamidate-bpm polynuclear copper(II) chain complex. Magnetic susceptibility measurements reveal the occurrence of strong antiferromagnetic exchange couplings for the three compouns with J values of −386.0 and −328.9 cm −1 for 1 and 2 , respectively, and J = −340.0 cm −1 , with an alternation parameter α = 0.24, for 3 . Magnetic parameters are discussed on the basis of the structural results and compared with those of related complexes.

Ferromagnetic coupling and thermochromism in [Ni(rac-CTH)(µ1,1-N3)2Cu(N3)2], the first end-on azido-bridged bimetallic complex

Reaction of [Ni(rac-CTH)(ClO(4))(2)](rac-CTH = rac-5,7,7,12,14,14-hexamethyl-1,4,8,11-tetraazacyclotetradecane) with NaN(3) and Cu(NO(3))(2).3H(2)O produces the binuclear complex [Ni(rac-CTH)(mu(1,1)-N(3))(2)Cu(N(3))(2)] 1, which represents the first example of an end-on bridged bimetallic complex; 1 exhibits intramolecular ferromagnetic exchange coupling and thermochromism, this latter being a consequence of the intermolecular interaction at low temperature.

Palladium phosphine complexes from 8-(thio)-theophylline, 8-(methylthio)-theophylline and 8-(benzylthio)-theophylline

Abstract A series of palladium(II) complexes have been synthesized and characterized to examine the coordination chemistry of several 8-thio-purine derivatives: 8-(thio)-theophylline (8-TTH2), 8-(benzylthio)-theophylline (8-BzTTH) and 8-(methylthio)-theophylline (8-MTTH). All of the complexes have been studied by IR and multinuclear (1H, 31P, 13C NMR) spectroscopy. A representative example of a Pd complex, [cis-Pd(8-BzTT)2(PPh3)2], has been authenticated by X-ray crystallography. In this complex square-planar coordination about palladium occurs through two deprotonated N7 purine atoms cis to each other, and two triphenylphosphine phosphorus atoms. In this paper, we present and discuss details of the synthesis, characterization and structural properties of the novel complexes. The synthesis and the characterization of 8-(benzylthio)-theophylline (8-BzTTH), a new organic ligands based on the molecular skeleton of 8-thio-purine, and a new procedure to obtain 8-(methylthio)-theophylline (8-MTTH) are also presented.

Magnetic properties and crystal structure of {μ-pyrazine}bis[(aqua)(2,6-xylylaminodiacetato)copper(II)]. A pyrazine-bridged dinuclear copper(II) complex

The preparation, spectroscopic and magnetic study, and crystal structure of the complex {μ-pyrazine}bis[(aqua)(2,6- xylylaminodiacetato)copper(II)], [Cu2(L)2(H2O)2(pyz)], are reported. It crystallizes in the monoclinic space group P21/n with cell constants a=13.309(3), b=7.590(2), c=15.459(3) A, β=100.90(3)°, Z=2, R=0.038, Rw=0.045. The structure consists of neutral dinuclear [Cu2(L)2(H2O)2(pyz)] molecules, in which the copper(II) ions are bridged by a molecule of pyrazine, with a Cu···Cu distance of 5.786 A. Each of the CuN2O3 coordination polyhedra can be described as a square-based pyramid with a small distortion toward trigonal-bipyramid. The bridging pyrazine molecule is bonded in equatorial position and canted out of the basal coordination plane by 20.8°. The magnetic study indicates that a weak antiferromagnetic interaction operates between the copper(II) ions with an exchange coupling constant of −3.7 cm−1. The magnitude of the exchange interaction is discussed on the basis of structural data.

Aurophilicity as a cofactor in crystal engineering. Dicyanoaurate(I) anion as a building block in a novel Co(II)-Au(I) bimetallic assembly

A 2D grid-shaped cyanide-bridged Co(II)-Au(I) bimetallic coordination polymer, [Co(DMF)2(Au(CN)2)2], has been prepared from the [Au(CN)2]- building block; sheets associate pair-wise by aurophilic interactions and the compound exhibits zeolite-like properties.