M. Isabel Arriortua

Crystal structure and magnetic properties of [Ni(terpy)(N3)2]2.2H2O, a nickel(II) dinuclear complex with ferromagnetic interaction

Abstract The crystal structure of dimeric [Ni(C15H11N3)(N3)2]2·2H2O has been determined at room temperature. Crystal data are as follows: P21/a, Z=2, a=15.628(3), b=9.798(2), c=10.322(2) A, β=92.32(2)°, R=0.049 for 1137 reflections. The complex consists of isolated centrosymmetric [Ni(terpy)(N3)2]2·2H2O dimeric units, where the two metallic centers are linked through the N-end of two azide bridging groups. The Ni(II) atom displays a distorted octahedral coordination, being linked to three N atoms from the terpyridine ligand and three N atoms of three azide ligands. Magnetic susceptibility measurements have shown the existence of ferromagnetic exchange between nickel centers (J=+20.1 cm−1, D=−12.5 cm−1). The magnetic behavior of this and others related complexes is discussed and some magneto-structural trends are given.

Synthetic strategy, magnetic and spectroscopic properties of the terpyridine complexes [Cu(terpy)X(H2O)n]Y (X = NCO, NCS or N3; n= 0 or 1; Y = NO3 or PF6). Crystal structures of the azidenitrate and azidehexafluoro-phosphate

Eight copper(II) complexes with 2,2′:6′,2″-terpyridine (terpy) and pseudohalide ligands. [Cu(terpy)X-(H2O)n]Y [X = NCO, NCS or N3; n= 0 or 1; Y = NO3 or PF6] have been prepared by following a described synthetic strategy. The crystal structures [Cu(terpy)(N3)(H2O)]x[NO3]x and [Cu(terpy)(N3)-(H2O)]2[PF6]2 have been determined: monoclinic, space group P21/n, a= 8.849(2), b= 10.343(1), c= 18.168(3)A, β= 97.71(2)°, Z= 4; triclinic, space group P, a= 9.0609(6), b= 10.2798(8), c= 11.309(1)A, α= 105.22(7), β= 86.58(7), γ= 112.90(6)°, Z = 2. In both complexes [Cu(terpy)(N3)-(H2O)]+ entities are present. For the first compound these form a chain structure, via hydrogen bonding between the co-ordinated water molecule and the nitrate ion. However, the structure of the second compound is built from dimeric [Cu2(terpy)2(N3)2(H2O)2]2+ cations in which the copper ions are connected by one-end bridging azide groups and PF6– counter ions. The co-ordination geometry of the copper(II) ion is square pyramidal and octahedral for the two compounds respectively. The complexes studied can be grouped into three structural types, within each of which the compounds are isostructural. The anhydrous and hydrated hexafluorophosphates have dimeric structures; however, the nitrate compounds are associated in chains. Magnetic susceptibility measurements revealed weak magnetic interactions for all of them. The EPR spectra show ‘half-field’ forbidden transitions for all the complexes and even singlet-to-triplet forbidden transitions for the nitrates. From the positions of these last signals the exchange parameters for the nitrate compounds have been determined. The magnetic interactions have been analysed taking into account several exchange pathways.

Investigation of the CuII/NCS−/dpk Reaction System in CH3OH [dpk = Di(2-pyridyl) Ketone]: Isolation, Structural Analysis and Magnetic Properties of a Dimer and a 1D Polymer with the Same Empirical Formula [Cu(NCS)2(dpk·CH3OH)]

Two polymorphous compounds with the general formula [Cu(NCS)2(dpk·CH3OH)]n (dpk = di-2-pyridyl-ketone) have been synthesised and have been characterised both structurally and magnetically. The dpk·CH3OH ligand is the result of the metal-promoted solvolysis of dpk in methanol and acts as a neutral donor. X-ray analysis carried out on single crystals for both compounds revealed that compound 1 is dimeric exhibiting double (N,S)-thiocyanate bridges, while com

SYNTHESIS AND SPECTROSCOPIC PROPERTIES OF TWO PYRIDINE-2-CARBALDEHYDE THIOSEMICARBAZONECOPPER(II) COMPOUNDS : CUX2(C7H8N4S).H2O (X = BR, CL). CRYSTAL STRUCTURE OF THE BROMO COMPLEX

Abstract The [CuX2(C7H8N4S)] · H2O (C7H8N4S = pyridine-2-carbaldehyde thiosemicarbazone; X = Cl, Br) complexes have been synthesized and characterized. The crystal structure of the bromo compound has been solved. It crystallizes in the monoclinic system space group P21/c with a = 8.750(1), b = 9.834(1), c = 14.838(2) A , β = 99.37(1)°, V = 1259.7(3) A 3 , Z = 4, R = 0.050, R w = 0.047 . The framework consists of discrete monometric molecules with five-coordinate square-pyramidal copper(II) ions. One sulfur and two nitrogen atoms of the thiosemicarbazone ligand and one bromide ion are in the basal position, with another bromide ion in the apical one. Bond lengths are compared with those of other thiosemicarbazone complexes. The chloro complex is isostructural with the bromo one. Considering the electronic delocalization along the thiosemicarbazone ligand and the geometry of its chelating centers, an important influence in the copper orbitals sequence has been shown from the spectroscopic studies and molecular orbital calculations.

Synthesis, structural, spectroscopic and magnetic studies of two azido and thiocyanato nickel(II) dinuclear complexes with ferromagnetic interactions

From a newly synthesised tridentate ligand [pepci =N′-(2-pyridin-2-ylethyl)pyridine-2-carbaldimine] two new octahedrally co-ordinated nickel(II) dimers, [{Ni(pepci)(N3)2}2]1 and [{Ni(pepci)(NCS)2}2]2, have been prepared. The crystal structure 1 has been solved. It crystallizes in space group P21/c with four formula weights in a cell measuring a= 9.198(3), b= 17.382(6), c= 19.356(7)A, and β= 99.57(1)°. The structure consists of isolated dimeric units in which the nickel ions are linked by two azide bridging groups in an end-on fashion. Two pepci ligands and two terminal azide groups complete the co-ordination spheres. Inside the dimer, each Ni(pepci)(N3)2 entity is crystallographically non-equivalent. There are two different bridging angles Ni(A)–N(4A)–Ni(B) 102.2(2) and Ni(B)–N(4B)–Ni(A) 101.0(2)°. The co-ordination geometry at each nickel atom is approximately octahedral. The Ni(A)⋯ Ni(B) distance is 3.297(1)A. For complex 2 a dimeric structure involving end-to-end thiocyanate bridging groups is proposed. Magnetic susceptibility data, measured from 4 to 300 K, were fitted to the Ginsberg equation, giving the parameters (cm–1): J=+36.3, D=–18.8, z′J′= 0.0 (N3); and J=+4.9, D=–9.8, z′J′=+0.33 (NCS). The magnetic behaviour of these and related complexes is discussed and some magnetostructural trends are given.

Spectroscopic and magnetic properties of two ferromagnetically coupled nickel(II) dimers [{Ni(terpy)(NCX)2}2](terpy = 2,2′ :6′,2″-terpyridine, X = S or Se). Crystal structure of the thiocyanate

Two new binuclear nickel(II) complexes [{Ni(terpy)(NCX)2}2](X = S or Se) have been prepared from 2,2′ :6′,2″-terpyridine (terpy) ligand. The crystal structure of [{Ni(terpy)(NCS)2}2]1 was solved by direct methods and refined by least-squares analysis to a discrepancy factor of 0.050. The crystals are triclinic, space group P, with lattice constants a= 8.822(2), b= 9.569(1), c= 10.906(1)A, and α= 74.35(1), β= 85.19(2), γ= 78.75(2)°. The dimer, whose halves are related by a crystallographic inversion centre, consists of two nickel atoms co-ordinated to two terpy ligands, two terminal NCS ligands and two end-to-end NCS bridging ligands. Each NiII has a distorted-octahedral environment. The Ni ⋯ Ni distance is 5.633(3)A and the bridging angles are 100.0(8) and 159(2)°. The complex [{Ni(terpy)(NCSe)2}2]2 was found to be isomorphous [a= 8.867(3), b= 9.592(4), c= 11.047(3)A, α= 73.64(3), β= 83.44(3) and γ= 76.67(2)°]. Magnetic susceptibility data, measured from 2 to 300 K, were fitted to the Ginsberg equation, giving the parameters J=+4.9 cm–1, D=–4.3 cm–1 and z′ J′=+0.02 cm–1(NCS) and J=+10.1 cm–1, D=–10.0 cm–1 and z′ J′=+0.01 cm–1(NCSe). The magnetic behaviour of these and related complexes is discussed and some magnetostructural trends are given.

SYNTHESIS, STRUCTURE, SPECTROSCOPIC AND MAGNETIC PROPERTIES OF TWO COPPER(II) DIMERS CONTAINING PYRIDINE-2-CARBALDEHYDE THIOSEMICARBAZONATE (L), CUL(X )2 (X=CL OR BR)

The compounds [{CuL(X)}2](X = Cl 1 or Br 2, HL = pyridine-2-carbaldehyde thiosemicarbazone) have been synthesised and structurally characterized. Both crystallize in the triclinic space group P. For compound 1, a= 7.915(3), b= 8.262(5), c= 9.016(2)A, α= 67.97(3), β= 92.26(2), γ= 71.33(4)°, Z= 2, R= 0.046, R′= 0.054. For 2, a= 7.617(1), b= 8.451(3), c= 8.966(2)A, α= 68.50(2), β= 95.94(1), γ= 71.73(2)°, Z= 2, R=R′= 0.035. The copper(II) ions have square-pyramidal environments with the tridentate thiosemicarbazone ligands and the halide atoms in an equatorial position. The sulfur atom of the tridentate ligand acts as a bridging ligand occupying the apical position of the symmetric copper atom in the dimeric structure. Such a disposition of the sulfur bridges is very scarce. Q-Band ESR spectra of the two compounds show rhombic signals with g1= 2.183, g2= 2.053, g3= 2.033 for 1 and g1= 2.161, g2= 2.057, g3= 2.033 for 2. Magnetic measurements on 1 and 2 show antiferromagnetic couplings between the copper(II) cations through the sulfur bridges. The exchange parameter is J/k=–6.8K (–4.7 cm–1). Magnetostructural correlations have been analysed by using extended Huckel molecular orbital calculations.

The 2D and 3D Compounds [M2bpm(dca)4]·nH2O (M = Ni, Zn; bpm = bipyrimidine; dca = dicyanamide; n = 0, 1) − Structural Analysis and Magnetic Properties

The combined use of bpm (2,2′-bipyrimidine) and dca (dicyanamide) has led to the preparation of two compounds of general formula [M2bpm(dca)4]·nH2O. Compound 1 (M = Ni, n = 1) exhibits a 2D layered structure based on ladder-like moieties. These units, whose steps are bpm groups, extend through single dca bridges, the connection between distinct ladder-like units taking place through double dca bridges. Compound 2 (M = Zn, n = 0) consists of a 3D structure based on the same type of ladder-like moieties that are connected to another four on the plane perpendicular to the extension of the ladders.

Crystal structure and esr spectra of two M(II)-dpk-NCS coordination compounds (M=Mn, Cu and dpk=di-2-pyridylketone)

Abstract The di-2-pyridylketone ligand (dpk) has been observed to exhibit several coordination modes being a good candidate for the preparation of a variety of metal-containing extended structures. In order to contribute to the study of the factors which influence the different coordination modes of this ligand, two M-dpk-NCS (M=Cu, Mn) complexes were prepared under the same conditions (compound I: [Cu (dpk·H 2 O) 2 ] (NCS) 2 ·2H 2 O and compound II: [Mn (dpk) 2 (NCS) 2 ]). The characterisation of both of them (by X-ray diffraction and IR and ESR spectroscopies) revealed significant differences related to the hydration of the dpk ligand (taking place for M=Cu) as well as to the particular packing of the Mn-monomers.

Structural analysis, spectroscopic, and magnetic properties of the 1D triple-bridged compounds [M(dca)2(bpa)] (M = Mn, Fe, Co, Zn; dca = dicyanamide; bpa = 1,2-bis(4-pyridyl)ethane) and the 3D [Ni(dca)(bpa)2]dca·6H2O.

The family of compounds [Mn(dca)(2)(bpa)] (1), [Fe(dca)(2)(bpa)] (2), [Co(dca)(2)(bpa)] (3), [Zn(dca)(2)(bpa)] (4), and [Ni(dca)(bpa)(2)]dca·6H(2)O (5), with dca = dicyanamide and bpa = 1,2-bis(4-pyridyl)ethane, has been synthesized. These compounds have been characterized by single crystal (1, 2, 4, and 5) and powder X-ray diffraction (3), by Fourier transform infrared (FTIR), UV-vis, and electron paramagnetic resonance (EPR) spectroscopies, and by magnetic measurements. Compound 1 crystallizes in the monoclinic C2/c space group, Z = 4, with a = 16.757(6), b = 9.692(3), and c = 13.073(4) Å, and β = 123.02(2)°; Compound 2 crystallizes in the monoclinic C2/c space group, Z = 4, with a = 16.588(5), b = 9.661(3), c = 12.970(5) Å, and β = 123.16(3)°; Compound 4 crystallizes in the monoclinic C2/c space group, Z = 4, with a = 16.519(2), b = 9.643(2), c = 12.943(2) Å, and β = 123.15(1)°; Compound 5 crystallizes in the monoclinic C2/c space group, Z = 4, with a = 18.504(4), b = 19.802(3), and c = 8.6570(18) Å, and β = 99.74(2)°. The compounds 1-4 are isostructural and show a one dimensional (1D) disposition, with the metal(II) ions bridged by double μ(1,5) dca ligands and unusually by a third bridge consisting of the bpa ligand, which adopts a very low torsion angle to accommodate in the structure. This kind of structure is unusual, even considering the voluminous bpa bridge. The compound 5 shows a 3D structure with layers of Ni-bpa joined by single dca bridges. Magnetic susceptibility measurements show antiferromagnetic couplings, increasing for 1-3. Compound 5 shows very slight antiferromagnetic interactions.