Stefan Suckert

Synthesis, structures, magnetic, and theoretical investigations of layered Co and Ni thiocyanate coordination polymers

Reaction of cobalt(ii) and nickel(ii) thiocyanate with ethylisonicotinate leads to the formation of [M(NCS)2(ethylisonicotinate)2]n with M = Co (2-Co) and M = Ni (2-Ni), which can also be obtained by thermal decomposition of M(NCS)2(ethylisonicotinate)4 (M = Co (1-Co), Ni (1-Ni)). The crystal structure of 2-Ni was determined by single crystal X-ray diffraction. The Ni(ii) cations are octahedrally coordinated by two N and two S bonding thiocyanate anions and two ethylisonicotinate ligands and are linked by pairs of anionic ligands into dimers, that are connected into layers by single thiocyanate bridges. The crystal structure of 2-Co was refined by Rietveld analysis and is isostructural to 2-Ni. For both compounds ferromagnetic ordering is observed at 8.7 K (2-Ni) and at 1.72 K (2-Co), which was also confirmed by specific heat measurements. Similar measurements on [Co(NCS)2(4-acetylpyridine)2]n that exhibits the same layer topology also prove magnetic ordering at 1.33 K. Constrained DFT calculations (CDFT) support the ferromagnetic interactions within the layers. The calculated exchange constants in 2-Ni were used to simulate the susceptibility by quantum Monte Carlo method. The single-ion magnetic anisotropy of the metal ions has been investigated by CASSCF/CASPT2 calculations indicating significant differences between 2-Ni and 2-Co.

Reversible and Topotactic Solvent Removal in a Magnetic Ni(NCS)2 Coordination Polymer

Reaction of Ni(NCS)2 with 4-(Boc-amino)pyridine in acetonitrile leads to the formation of a new coordination polymer with the composition Ni(NCS)2(4-(Boc-amino)pyridine)2·MeCN (1-MeCN). In the crystal structure the Ni(II) cations are linked by the anionic ligands into chains that are further connected into layers by intermolecular N-H···O hydrogen bonding. These layers are stacked and channels are formed, in which acetonitrile molecules are located. Solvent removal leads to the ansolvate 1, which shows microporosity as proven by sorption measurements. Single crystal X-ray investigations reveal that the solvent removal leads to a change in symmetry from primitive to C-centered, which is reversible and which proceeds via a topotactic reaction leaving the network intact. The magnetic properties of 1-MeCN and 1 are governed by the ferromagnetic exchange between spins of Ni(II) forming chains. The susceptibility and specific heat for such a quantum Heisenberg chain of S = 1 spins with zero-field splitting are calculated using the DMRG method and compared with the experimental results.

Structures, Thermodynamic Relations, and Magnetism of Stable and Metastable Ni(NCS)2 Coordination Polymers

Reaction of Ni(NCS)2 with 4-aminopyridine in different solvents leads to the formation of compounds with the compositions Ni(NCS)2(4-aminopyridine)4 (1), Ni(NCS)2(4-aminopyridine)2(H2O)2 (2), [Ni(NCS)2(4-aminopyridine)3(MeCN)]·MeCN (3), and [Ni(NCS)2(4-aminopyridine)2] n (5-LT). Compounds 1, 2, and 3 form discrete complexes, with octahedral metal coordination. In 5-LT the Ni cations are linked by single thiocyanate anions into chains, which are further connected into layers by half of the 4-aminopyridine coligands. Upon heating, 1 transforms into an isomer of 5-LT with a 1D structure (5-HT), that on further heating forms a more condensed chain compound [Ni(NCS)2(4-aminopyridine)] n (6) that shows a very unusual chain topology. If 3 is heated, a further compound with the composition Ni(NCS)2(4-aminopyridine)3 (4) is formed, which presumably is a dimer and which on further heating transforms into 6 via 5-HT as intermediate. Further investigations reveal that 5-LT and 5-HT are related by enantiotropism, with 5-LT being the thermodynamic stable form at room-temperature. Magnetic and specific heat measurements reveal ferromagnetic exchange through thiocyanate bridges and magnetic ordering due to antiferromagnetic interchain interactions at 5.30(5) K and 8.2(2) K for 5-LT and 6, respectively. Consecutive metamagnetic transitions in the spin ladder compound 6 are due to dipolar interchain interactions. A convenient formula for susceptibility of the ferromagnetic Heisenberg chain of isotropic spins S = 1 is proposed, based on numerical DMRG calculations, and used to determine exchange constants.

Crystal structure of tri­aqua­(2,6-di­methyl­pyrazine-κN4)bis­(thio­cyanato-κN)manganese(II) 2,5-di­methyl­pyrazine disolvate

In the crystal structure of the title complex, [Mn(NCS)2(C6H8N2)(H2O)3]·2C6H8N2, the MnII cation is coordinated by two terminally N-bonded thiocyanate anions, three water molecules and one 2,6-dimethylpyrazine ligand within a slightly distorted N3O3 octahedral geometry; the entire complex molecule is generated by the application of a twofold rotation axis. The asymmetric unit also contains an uncoordinating 2,5-dimethylpyrazine ligand in a general position. Obviously, the coordination to the 2,6-dimethylpyrazine ligand is preferred because coordination to the 2,5-dimethylpyrazine is hindered due to the bulky methyl group proximate to the N atom. The discrete complexes are linked by water-O—H⋯N(2,6-dimethylpyzazine/2,5-dimethylpyzazine) hydrogen bonding, forming a three-dimensional network. In the crystal, molecules are arranged in a way that cavities are formed in which unspecified, disordered solvent molecules reside. These were modelled employing the SQUEEZE routine in PLATON [Spek (2015 ▸). Acta Cryst. C71, 9–18]. The composition of the unit cell does not take into account the presence of the unspecified solvent.

Crystal structure of bis­(aceto­nitrile-κN)bis­(4-benzoyl­pyridine-κN)bis­(thio­cyanato-κN)cobalt(II)

The crystal structure of the title compound consists of discrete octahedral complexes, that are linked by intermolecular C—H⋯O and C—H⋯S hydrogen bonding into layers.

Crystal structure of tetra­aqua­bis­(thio­cyanato-κN)nickel(II)–2,5-di­methyl­pyrazine (1/4)

In the crystal structure of the title compound, [Ni(NCS)2(H2O)4]·4C6H8N2, the NiII cations are coordinated by four water ligands and two trans-coordinated terminally N-bonded thiocyanate anions in a slightly distorted octahedral geometry. The asymmetric unit consists of a Ni2+ cation located on a centre of inversion, two water molecules and one thiocyanate ligand, as well as two uncoordinated 2,5-dimethylpyrazine ligands in general positions. In the crystal, discrete complex molecules are linked into a three-dimensional network by O—H⋯N hydrogen bonding between the water H atoms and the 2,5-dimethylpyrazine N atoms.

Crystal structure of di­aqua­bis­(2,6-di­methyl­pyrazine-κN4)bis­(thio­cyanato-κN)cobalt(II) 2,5-di­methyl­pyrazine monosolvate

In the crystal structure of the title compound, [Co(NCS)2(C6H8N2)2(H2O)2]·C6H8N2, the CoII cation is coordinated by the N atoms of two terminal thiocyanate anions, the O atoms of two water molecules and two N atoms of two 2,6-dimethylpyrazine ligands. The coordination sphere of the resulting discrete complex is that of a slightly distorted octahedron. The asymmetric unit comprises a CoII cation and half of a 2,5-dimethylpyrazine ligand, both of which are located on centres of inversion, and a water ligand, a 2,6-dimethylpyrazine ligand and one thiocyanate anion in general positions. In the crystal, the discrete complexes are arranged in such a way that cavities are formed in which the 2,5-dimethylpyrazine solvent molecules are located. The coordination of the 2,5-dimethylpyrazine molecules to the metal is apparently hindered due to the bulky methyl groups in vicinal positions to the N atoms, leading to a preferential coordination of the 2,6-dimethylpyrazine ligands. The discrete complexes are linked by O—H⋯N hydrogen bonds between one water H atom and the non-coordinating N atom of the 2,6-dimethylpyrazine ligands. The remaining water H atom is hydrogen bonded to one N atom of the 2,5-dimethylpyrazine solvent molecule. This arrangement leads to the formation of a two-dimensional network extending parallel to (010).

Synthesis, structures, and properties of Mn(II) and Cd(II) thiocyanato coordination compounds with 2,5-dimethylpyrazine as co-ligand

Abstract Reaction of manganese (II) thiocyanate with 2,5-dimethylpyrazine leads to the formation of three new coordination compounds of compositions Mn(NCS)2(2,5-dimethylpyrazine)2(H2O)2 (1), Mn(NCS)2(H2O)2(MeOH)2-tris(2,5-dimethylpyrazine) solvate (2), and Mn(NCS)2 (H2O)4-tetrakis(2,5-dimethylpyrazine) solvate (3) that were characterized by single crystal X-ray diffraction. In their crystal structures, the Mn(II) cations are sixfold coordinated by two terminally N-bonded thiocyanato anions and two water molecules as well as by two 2,5-dimethylpyrazine ligands (1), two ethanol (2), or two water molecules (3), within slightly distorted octahedra. In compounds 2 and 3, additional 2,5-dimethylpyrazine ligands are located in the cavities of the structures as solvate molecules. X-ray powder diffraction has shown that compounds 1 and 2 cannot be prepared as pure phases and that batches of compound 3 contain only minor traces of a contamination. Differential thermoanalysis and thermogravimetry have revealed that upon heating of compound 3, an intermediate of composition Mn(NCS)2(2,5-dimethylpyrazine) (4) is formed, which cannot be obtained from solution. To mimic the structure of 4, single crystals of a Cd compound of the same composition (5) were prepared from the liquid phase, and single crystal X-ray analysis has shown that it is isotypic to 4.

Crystal structure of di­aqua­bis­(2-chloro­pyridine-κN)bis­(thio­cyanato-κN)nickel(II)

The crystal structure of the title compound consists of discrete octahedral complexes that are linked by intermolecular O—H⋯S, C—H⋯Cl, C—H⋯S and C—H⋯Cl hydrogen bonding.

Crystal structure of bis­(3,5-di­methyl­pyridine-κN)bis­(methanol-κO)bis­(thio­cyanato-κN)cobalt(II)

The crystal structure of the title cobalt(II) compound consists of discrete octahedral complexes that are linked by intermolecular O—H⋯S hydrogen bonding into chains.