Roberto Cortés

Polynuclear NiII and MnII azido bridging complexes. Structural trends and magnetic behavior

Abstract The azide anion is a good bridging ligand for divalent metal ions, mainly Cu II , Ni II and Mn II . It may give end-to-end (1,3) or end-on (1,1) coordination modes. As a general trend, the 1,1 mode exhibits ferromagnetic coupling while the 1,3 mode creates antiferromagnetic coupling. This review focuses on polynuclear Ni II and Mn II azido bridging complexes. Polynuclear structures known to have these two cations are: discrete (normally dinuclear), one-, two- and three-dimensional nets. The main characteristics of these structures are reported together with their magnetic behavior. From a large number of known structures, magneto-structural correlations are made. Taking into account that M–N 3 distances are always similar, the angles within the M–(N 3 ) n –M unit are the main determinant of the type and magnitude of the exchange coupling. Moreover, some one-, two- and three-dimensional complexes exhibit cooperative effects (long-range magnetic order), behaving as molecular magnets. This behavior is also analyzed.

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.

Structure and magnetic properties of the ferromagnetically coupled nickel dimer [Ni(terpy)(NCO)(H2O)]2(PF6)2

SummaryThe crystal structure of the dimeric [{Ni(C15H11N3)(NCO)(H2O)}2](PF6)2 has been determined by x-ray diffraction methods. Crystal data are as follows: P 1,a=11.904(4) Å,b=10.392(4) Å,c=8.531(3) Å, α=111.87(2)o, β=90.61(3)o, γ=107.37(5)o, U=926.7(4) Å3, Z=2, Dm=1.77(2), Dx=1.78 g. cm−3, μ(Mo-Kα)=12.1 cm−1, F(000)=494. Least-squares refinement of 1230 reflections with I≥1.5σ(1) gave a final R =0.035 (Rω=0.038). The structure is formed by cationic [{Ni(C15H11N3)(NCO)(H2O)}2]2+ and anionic PF6− units, linked through hydrogen bonds between the water molecule and the hexafluorophosphate ion. The resulting coordination geometry around each nickel(II) ion is ferragonally elongated octahedral. The N-bridging cyanate groups occupy simultaneously an equatorial position in the coordination sphere of one of the nickel atoms and an axial position in the other. The remaining axial positions are occupied by the water molecules. Powder susceptibility data, between 2.0 and 300 K, show the existence of ferromagnetic exchange between nickel centres. The magnetic parameters are J/K=6.6K, D/K =−17.6 K, z′J′/K=0.57 and g-2.21.

Defective Dicubane-like Tetranuclear Nickel(II) Cyanate and Azide Nanoscale Magnets

Four tetrameric nickel(II) pseudohalide complexes have been synthesized and structurally, spectroscopically, and magnetically characterized. Compounds 1-3 are isostructural and exhibit the general formula [Ni(2)(dpk·OH)(dpk·CH(3)O)(L)(H(2)O)](2)A(2)·2H(2)O, where dpk = di-2-pyridylketone; L = N(3)(-), and A = ClO(4)(-) for 1, L = NCO(-) and A = ClO(4)(-) for 2, and L = NCO(-) and A = NO(3)(-) for 3. The formula for 4 is [Ni(4)(dpk·OH)(3) (dpk·CH(3)O)(2)(NCO)](BF(4))(2)·3H(2)O. The ligands dpk·OH(-) and dpk·CH(3)O(-) result from solvolysis and ulterior deprotonation of dpk in water and methanol, respectively. The four tetramers exhibit a dicubane-like core with two missing vertexes where the Ni(II) ions are connected through end-on pseudohalide and oxo bridges. Magnetic measurements showed that compounds 1-4 are ferromagnetic. The values of the exchange constants were determined by means of a theoretical model based on three different types of coupling. Thus, the calculated J values (J(1) = J(2), J(3), and D) were 5.6, 11.8, and 5.6 cm(-1) for 1, 5.5, 12.0, and 5.6 cm(-1) for 2, 6.3, 4.9, and 6.2 cm(-1) for 3, and (J(1), J(2), J(3), and D) 6.9, 7.0, 15.2, and 4.8 cm(-1) for 4.

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.