Montserrat Monfort

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.

Crystal structure and magnetic properties of the first 1D nickel(II) complex with bridging thiocyanato ligands in cis position: {catena-(μN,S-NCS)[Ni(en)2]}(PF6)

Abstract The μN,S-thiocyanato nickel(II) monodimensional complex, {catena-(μN,S-NCS)[Ni(en)2]}(PF6) where en=ethylenediamine, has been synthesized and characterized. The crystal structure of this 1D complex has been solved by Patterson synthesis and refined by full-matrix least-squares method to a discrepancy factor of 0.046. {catena-(μN,S-NCS)[Ni(en)2]}(PF6) is the first structurally reported nickel(II) chain in which the neighboring nickel(II) ions are linked by thiocyanato bridging ligands in a cis geometry. The Ni(II) atoms present a distorted octahedral geometry. Magnetic susceptibility data, measured from 300 to 4 K show weak ferromagnetic behavior. These data were fitted to the de Neef equation, giving the parameters J=0.2 cm−1, g=2.19 and D=−1.8 cm−1.

High nuclearity in azido/oximate chemistry: Ni14 and Ni13 clusters with S = 6 and 9 ground states.

In the present work, we report a family of Ni(14) and unprecedented Ni(13) clusters linked by end-on azido and oximato bridges. Ferrimagnetic response gives S = 6 and 9 ground states, resulting in the largest nuclearities and spins in nickel oximato chemistry.

Ferromagnetic coupling in a unique Cu(II) metallacyclophane with functionalized diazamesocyclic ligands formed by Cu(II)-directed self-assembly: magneto-structural correlations for dichloro-bridged Cu(II) dinuclear complexes

Two new di-μ-Cl dinuclear CuII complexes [Cu(HL1)Cl2]2(ClO4)2 (1) and [Cu2(L2)2Cl2](ClO4)2 (2) with the pyridyl-functionalized diazamesocyclic ligands 1,5-bis(pyridin-4-ylmethyl)-1,5-diazacyclooctane (L1) and 1-(pyridin-2-ylmethyl)-1,4-diazacycloheptane (L2) have been synthesized and structurally characterized by single crystal X-ray diffraction. Complex 1 is a unique paramagnetic CuII metallamacrocycle (ca. 14.1 × 3.5 A2) directly self-assembled by metal ions and the organic spacer under strongly acidic conditions. The magnetic properties of both complexes have been investigated by variable-temperature magnetic susceptibility measurements. Although complexes 1 and 2 have almost the same geometrical parameters for CuII, their magnetic parameters vary from ferromagnetic for 1 to antiferromagnetic for 2. The magneto-structural correlation of such complexes has been further developed.

Structural and first magnetic characterization of unique mono-μ-chloro bridged dinuclear CuII complexes with heterocycle-functionalized diazamesocyclic ligands

Two new diazamesocyclic ligands based on 1,4-diazacycloheptane (DACH), functionalized by additional heterocyclic donor groups, 1,4-bis(pyridin-2-ylmethyl)-1,4-diazacycloheptane (L1) and 1,4-bis(imidazol-4-ylmethyl)-1,4-diazacycloheptane (L2), together with their CuII complexes [Cu2(μ-Cl)(L1)2](ClO4)3 (1) and [Cu2(μ-Cl)(L2)2](ClO4)3 (2), have been synthesized and characterized. Single crystal X-ray diffraction analyses revealed that both complexes have the unique mono-μ-Cl dimeric [Cu2(μ-Cl)(L)2]3+ structural motif. For both complexes, each CuII center is penta-coordinate in a distorted square-pyramidal environment with the bridging chloride atom at the apical position. The magnetic properties of mono-μ-chloro CuII dinuclear complexes have been investigated for the first time through the study of complexes 1 and 2 by variable temperature magnetic susceptibility and magnetization measurements. Weak ferromagnetic (for 1) or anti-ferromagnetic (for 2) interactions between the two CuII centers have been found and possible magneto-structural correlations have been analyzed.

Versatility of the azido bridging ligand in the first two examples of ferro–antiferromagnetic alternating nickel(II) chains

A one-pot reaction of Ni(ClO4)2·6H2O, N,N-dimethylethylenediamine (dmen) or 2-aminoethylpyridine (aep) and NaN3 affords the two [Ni(dmen)(µ-Na3)2]n1 and [Ni(aep)(µ-N3)2]n2 chains with unprecedented alternating end-on and end-to-end bridging loops perpendicular to one another; magnetic susceptibility measurements indicate that they are the first two ferro–antiferromagnetic alternating chains of NiII.

Four new NiII antiferromagnetic complexes with azido bridges

Four new nickel(II) compound with formulas trans-catena-[Ni(N-Pren)2(μ1,3-N3)](ClO4) (1), trans-catena-[Ni(N,N-Me2en)2(μ1,3-N3)](PF6) (2), trans-catena-[Ni(N,N′-Pren)2(μ1,3-N3)](PF6) (3) and [Ni(N-Metn)2(μ1,3-N3)]2(ClO4)2 (4) (N-Pren = N-propylethylenediamine, N,N-Me2en = N,N-dimethylethylenediamine, N,N′-Pren = N,N′-dipropylethylenediamine and N-Metn = N-methylpropanediamine) were synthesized and characterised. A single-crystal structure analysis revealed that compounds (1), (2) and (3) consist of a single end-to-end azido bridged nickel(II) chains in trans position, whereas compound (4) is a dinuclear NiII complex with double end-to-end azido bridges between the two nickel(II) centres. From the magnetic point of view, compounds (1) and (2) are uniform antiferromagnetic one-dimensional chains with only one value of J and g. Compound (3) shows two kinds of NiII in the structure, but all the azido bridges are equivalent, which generates only one value for the superexchange J but two values for g. Compound (4) shows moderate antiferromagnetic coupling. The best fit parameters obtained for all the compounds are in agreement with the structural parameters and compares well with other similar compounds reported in the literature.

Synthesis of N3−/SCN− bridged polynuclear complexes of nickel(II) using N,N,N′-trimethylethane-1,2-diamine as a blocking ligand: low temperature magnetic study and single crystal structure of [Ni(μ1,1-N3)(μ1,3-N3)(N,N,N′-Me3en)]n

Seven new complexes of nickel(II), derived from azido, thiocyanato and nitrito bridging ligands and N,N,N′-trimethylethylenediamine (N,N,N′-Me3en) as blocking ligand, were synthesised and characterised; four of them are one-dimensional compounds: [Ni(μ1, 3-N3)(N,N,N′-Me3en)2]n(ClO4)n1, [Ni(μ1, 3-N3)(N,N,N′-Me3en)2]n(PF6)n2, [Niμ1, 1-N3)(μ1, 3-N3)(N,N,N′-Me3en)]n3, [Ni(μ-SCN)2(N,N,N′-Me3en)]n4, and three mononuclear: [Ni(NCS)2(N,N,N′-Me3en)2] 5, [Ni(NO2)(N,N,N′-Me3en)2]PF66, [Ni(NO2)2(N,N,N′-Me3en)] 7. Crystal structures for 3 and 6 were determined by X-ray diffraction methods. Compound 3 may be described as a one-dimensional system with double azido bridging ligands alternately in end-on and end-to-end co-ordination modes. Compound 6 is a mononuclear complex in which a nitrito ligand acts as a chelate. The magnetic properties of all the compounds were studied by susceptibility measurements vs. temperature. The χMvs.T plots for 1 and 2 show the typical shape for moderate antiferromagnetic one-dimensional nickel(II) complexes, while global strong antiferromagnetic behaviour with a maximum at about 200 K is observed for 3 and 4 exhibits a very weak ferromagnetic interaction. Compounds 5, 6, and 7 follow the Curie law, typical behaviour of mononuclear NiII compounds. The superexchange parameter J for 1, 2 and 4 was deduced from the spin Hamiltonian −JΣSiSi+1 and from −Σ(JAFS2iS2i+1 + JFS2iS2i−1) for 3. J values for 1 and 2 are −15.5 and −16.6 cm−1, respectively, JAF = −132 cm−1 and JFM = 99 cm−1 for 3, and 1.34 cm−1 for 4.

Kinetic parameters and solid state mechanism of the thermal dehydration of trans[CrF(H2O)(aa′)2]K[Cr(CN)6]H2O And trans[CrF(H2O)(aa′)2]K[CrNO(CN)5]H2O (aa′=ethylenediamine or 1,3-diaminopropane)

Abstract The solid phase thermal deaquation of trans [CrF(H 2 O)(aa′) 2 ]K[Cr(CN) 6 ]H 2 O and trans [CrF(H 2 O)(aa′) 2 ]K[CrNO(CN) 5 ]H 2 O (aa′=ethylenediamine or 1,3-diaminopropane) has been investigated by means of TG measurements. The kinetic parameters (activation energy, E a , activation entropy, Δ S # , and frequency factor, k 0 ) have been determined by comparison of the isothermal and non-isothermal studies for all the principal g(α) expressions. The values found for the activation energy are low (between 80 and 110 kJ mole −1 , approximately) and permit the assignment of the deaquation-anation mechanism of the S N 1 type, involving square-pyramid activated complex and elimination of water as Frenkel defects.

Kinetic parameters and solid state mechanism of the thermal dehydration of [M(H2O)(NH3)5][Co(CN)6] [M=Co(III), Rh(III) and Ir(III)]

Abstract The solid phase thermal deaquation—anation of isostructural [M(H 2 O)(NH 3 ) 5 ][Co(CN) 6 ] salts [M = Co(III), Rh(III) and Ir(III)] has been investigated by means of isothermal and non-isothermal TG measurements. The physical model of these reactions (nucleation—growth according to the Avrami—Erofeev law) has been found by comparison of the isothermal and non-isothermal TG data for all the principal g(α) expressions (0.2 ⩽ α ⩽ 0.8) and by the shape of the isothermal curves. The values found for the activation energy are low (about 130 kJ mol −1 for the Co compound; approximately 110 kJ mol −1 for the Rh compound and about 95 kJ mol −1 for the Ir compound). These data permit the assignment of the deaquation—anation mechanism of the S N 1 dissociative type, involving square based pyramid activated complex and elimination of water as Frenkel defects. The lower values of Rh and Ir compounds are consistent with the greater volume of these cations and, consequently, the existence of more free space in the lattice to escape the water molecule.