Magnetism and crystal structures of CuIIMnII and CuIINiII ordered bimetallic chains

Structural Diversity, XAS and Magnetism of Copper(II)-Nickel(II) Heterometallic Complexes Based on the [Ni(NCS)6]4- Unit

The new heterometallic compounds, [{Cu(pn)₂}₂Ni(NCS)₆]_n·2nH₂O (1), [{Cu^II(trien)}₂Ni(NCS)₆Cu^I(NCS)]_n (2) and [Cu(tren)(NCS)]₄[Ni(NCS)₆] (3) (pn = 1,2-diaminopropane, trien = triethylenetetramine and tren = tris(2-aminoethylo)amine), were obtained and characterized by X-ray analysis, IR spectra, XAS and magnetic measurements. Compounds 1, 2 and 3 show the structural diversity of 2D, 1D and 0D compounds, respectively. Depending on the polyamine used, different coordination polyhedron for Cu(II) was found, i.e., distorted octahedral (1), square pyramidal (2) and trigonal bipyramidal (3), whereas coordination polyhedron for nickel(II) was always octahedral. It provides an approach for tailoring magnetic properties by proper selection of auxiliary ligands determining the topology. In 1, thiocyanate ligands form bridges between the copper and nickel ions, creating 2D layers of sql topology with weak ferromagnetic interactions. Compound 2 is a mixed-valence copper coordination polymer and shows the rare ladder topology of 1D chains decorated with [Cu^II(tren)]²⁺ antennas as the side chains attached to nickel(II). The ladder rails are formed by alternately arranged Ni(II) and Cu(I) ions connected by N2 thiocyanate anions and rungs made by N3 thiocyanate. For the Cu(I) ions, the tetrahedral thiocyanate environment mixed N/S donor atoms was found, confirming significant coordination spheres rearrangement occurring at the copper precursor together with the reduction in some Cu(II) to Cu(I). Such topology enables significant simplification of the magnetic properties modeling by assuming magnetic coupling inside {Ni^IICu^II₂} trinuclear units separated by diamagnetic [Cu(NCS)(SCN)₃]^3- linkers. Compound 3 shows three discrete mononuclear units connected by N-H…N and N-H…S hydrogen bonds. Analysis of XAS proves that the average ligand character and the covalency of the unoccupied metal d-based orbitals for copper(II) and nickel(II) increase in the following order: 1 → 2 → 3. In 1 and 2, a weak ferromagnetic coupling between copper(II) and nickel(II) was found, but in 2, additional and stronger antiferromagnetic interaction between copper(II) ions prevailed. Compound 3, as an ionic pair, shows, as expected, a spin-only magnetic moment.

Synthesis, crystal structure and magnetism of [Cu(cyclam)Ni(NCS)4(H2O)2]n

[Cu(cyclam)Ni(NCS)4(H2O)2]n(1) (cyclam = 1,4,8,11-tetraazacyclodecane) exhibits bent 1D crystal structure in which paramagnetic Cu(II) and Ni(II) atoms are linked by bridging μ2-NCS- ligands. The Cu(II) atom exhibit tetragonally elongated hexacoordination in the 4+2 form with one tetradentate macrocyclic cyclam ligands placed in the equatorial plane while the axial positions are occupied by S atoms from bridging NCS- ligands. The Ni(II) atom in NiN4O2donor set is deformed octahedrally coordinated by four isothiocyanato ligands among which two in trans positions are bridging in nature; additional aqua ligands occupy the remaining two positions in trans arrangement. Weak hydrogen bonding interactions of the O-H···S type links the formed chains into 3D supramolecular structure. The magnetism of 1 is dominated by a sizable single-ion anisotropy DNi/hc = +7.49 cm-1along with a weak exchange interaction of the ferromagnetic nature.

Synthesis, structure and light scattering properties of tetraalkylammonium metal isothiocyanate salts

A series of ammonium and tetraalkylammonium metal isothiocyanate salts of the type Q(y)[M(NCS)x] (M = Cr(III), x = 6, y = 3, Q = NH4(+), Me4N(+), Et4N(+), n-Bu4N(+); M = Mn(II), x = 6, y = 4, Q = Me4N(+); M = Mn(II), x = 5, y = 3, Q = Et4N(+); M = Fe(III), x = 6, y = 3, Q = Me4N(+), Et4N(+), n-Bu4N(+); M = Co(II), x = 4, y = 2, Q = n-Bu4N(+); M = Eu(III), Gd(III), Dy(III), x = 6, y = 3, Q = Bu4N(+)) has been synthesized and structurally characterized. The octahedral Cr(III) salts are isostructural to previously and newly reported Fe(III) salts. The Ln(III)-containing anions are also octahedral. For Mn(II), although the Me4N(+) salt is octahedral, the Et4N(+) salt [Mn(NCS)5](3-) possesses a distorted trigonal bipyramidal geometry. For (Et4N)3[Fe(NCS)6] and (n-Bu4N)3[Fe(NCS)6], a solid-state size-dependent change in colour from red to green was observed and was attributed to a light scattering phenomenon in the crystalline samples.