Variation of the Chain Geometry in Isomeric 1D Co(NCS)2 Coordination Polymers and Their Influence on the Magnetic Properties.

Two different isomers of [Co(NCS)2(4-chloropyridine)2]n (3C and 3L) were synthesized from solution and by thermal decomposition of Co(NCS)2(4-chloropyridine)2(H2O)2 (2), which show a different metal coordination leading to corrugated chains in 3C and to linear chains in 3L. Solvent mediated conversion experiments prove that 3C is thermodynamically stable at room temperature where 3L is metastable. Magnetic measurements reveal that the magnetic exchange in 3L is comparable to that observed for previously reported related chain compounds, whereas in 3C with corrugated chains, the ferromagnetic interaction within the chains is strongly suppressed. The magnetic ordering takes place at 2.85 and 0.89 K, for 3L and 3C, respectively, based on specific heat measurements. For 3L the field dependence of magnetic relaxations in antiferromagnetically ordered ferromagnetic chains is presented. In addition, 3L is investigated by FD-FT THz-EPR spectroscopy, revealing a ground to first excited state energy gap of 14.0 cm-1. Broken-symmetry DFT calculations for 3C and 3L indicate a ferromagnetic intrachain interaction. Ab initio CASSCF/CASPT2/RASSI-SO computational studies reveal significantly different single-ion anisotropies for the crystallographically independent cobalt(II) centers in 3C and 3L. Together with the geometry of the chains this explains the magnetic properties of 3C and 3L. The ab initio results also explain the weaker exchange interaction in 3C and 3L as compared to previously reported [Co(NCS)2(L)2]n compounds with linear chains.

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.

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.

Crystal structure of bis-(4-benzoyl-pyridine-κN)bis-(methanol-κO)bis-(thio-cyanato-κN)cobalt(II).

The crystal structure of the title compound, [Co(NCS)2(C12H9NO)2(CH3OH)2], consists of cobalt(II) cations that are octa-hedrally coordinated by two N-terminal bonding thio-cyanato anions, two methanol mol-ecules and two 4-benzoyl-pyridine ligands into discrete complexes that are located on centres of inversion. These complexes are further linked by O-H⋯O hydrogen bonding between the hy-droxy H atom of the methanol ligand and the carbonyl O atom of the 4-benzoyl-pyridine ligand of a neighboring complex into layers parallel to (101). No pronounced inter-molecular inter-actions are observed between these layers.

Crystal structure of bis-(aceto-nitrile-κN)bis-(4-benzoyl-pyridine-κN)bis-(thio-cyanato-κN)cobalt(II).

The crystal structure of the title compound, [Co(NCS)2(C2H3N)2(C12H9NO)2], consists of cobalt(II) cations that are octa-hedrally coordinated by the N atoms of two terminal thio-cyanate anions, two aceto-nitrile mol-ecules and two 4-benzoyl-pyridine ligands. The discrete complexes are located on centres of inversion. They are connected by weak inter-molecular C-H⋯O and C-H⋯S hydrogen-bonding inter-actions between one of the pyridine H atoms and the carbonyl O atom, and between one of the methyl H atoms of the aceto-nitrile mol-ecule and the thio-cyanate S atoms into layers parallel to (101). No pronounced inter-molecular inter-actions are observed between these layers.

Influence of metal coordination and co-ligands on the magnetic properties of 1D Co(NCS)2 coordination polymers.

Two new transition metal thiocyanate coordination polymers with the composition [Co(NCS)2(4-vinylpyridine)2]n (1) and [Co(NCS)2(4-benzoylpyridine)2]n (2) were synthesized and their crystal structures were determined. In both compounds the Co cations are octahedrally coordinated by two trans-coordinating 4-vinyl- or 4-benzoylpyridine co-ligands and four µ-1,3-bridging thiocyanato anions and linked into chains by the anionic ligands. While in 1 the N and the S atoms of the thiocyanate anions are also in trans-configuration, in 2 they are in cis-configuration. A detailed magnetic study showed that the intra-chain ferromagnetic coupling is slightly stronger for 2 than for 1, and that the chains in both compounds are weekly antiferromagnetically coupled. Both compounds show a long range magnetic ordering transition at Tc = 3.9 K for 1 and Tc = 3.7 K for 2, which is confirmed by specific heat measurements. They also show a metamagnetic transition at a critical field of 450 Oe (1) and 350 Oe (2), respectively. Below Tc1 and 2 exhibit magnetic relaxations resembling relaxations of single chains. The exchange constants obtained from magnetic and specific heat data are in good accordance with those obtained from constrained DFT calculations carried out on isolated model systems. The ab initio calculations allowed us to find the principal directions of anisotropy.

Crystal structure of bis-(3,5-di-methyl-pyridine-κN)bis-(methanol-κO)bis-(thio-cyanato-κN)cobalt(II).

The asymmetric unit of the title complex, [Co(NCS)2(C7H9N)2(CH3OH)2], comprises of one CoII cation located on a centre of inversion, one thio-cyanate ligand, one methanol ligand and one 3,5-di-methyl-pyridine ligand. The CoII cation is octa-hedrally coordinated by two terminal N-bonding thio-cyanate anions, two methanol mol-ecules and two 3,5-di-methyl-pyridine ligands into a discrete complex. The complex mol-ecules are linked by inter-molecular O-H⋯S hydrogen bonding into chains that elongate in the direction parallel to the b axis.

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.

Crystal structure of di-aqua-bis-(2-chloro-pyridine-κN)bis-(thio-cyanato-κN)nickel(II).

The asymmetric unit of the title compound, [Ni(NCS)2(C5H4ClN)2(H2O)2], consists of one nickel(II) cation that is located on a center of inversion and one thio-cyanate anion, one water mol-ecule and one 2-chloro-pyridine ligand all occupying general positions. The NiII cation is octa-hedrally coordinated by two terminal N-bound thio-cyanato ligands, two aqua ligands and two N-bound 2-chloro-pyridine ligands into discrete complexes. Individual complexes are linked by inter-molecular O-H⋯S and O-H⋯Cl hydrogen-bonding inter-actions into a layered network extending parallel to the bc plane. Weak inter-actions of types C-H⋯S and C-H⋯Cl consolidate the crystal packing.

Crystal structure of bis-[4-(di-methyl-amino)-pyridine-κN (1)]bis-(methanol-κO)bis-(thio-cyanato-κN)manganese(II).

The whole mol-ecule of the title compound, [Mn(NCS)2(CH3OH)2(C5H6N2)2], is generated by inversion symmetry. The Mn(II) ion, which is located on an inversion center, is coordinated by two 4-(di-methyl-amino)-pyridine ligands, two methanol ligands and two terminally N-bonded thio-cyanate anions, forming a slightly distorted octa-hedron. In the crystal, mol-ecules are linked by O-H⋯S hydrogen bonds, forming chains extending along the a-axis direction.

Crystal structure of tetra-aqua-bis-(thio-cyanato-κN)nickel(II)-2,5-di-methyl-pyrazine (1/4).

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

Thermodynamically metastable thiocyanato coordination polymer that shows slow relaxations of the magnetization.

Reaction of cobalt thiocyanate with 4-acetylpyridine leads to the formation of [Co(NCS)2(4-acetylpyridine)2]n (3/I). In its crystal structure the Co cations are connected by pairs of µ-1,3-bridging thiocyanato ligands into dimers that are further connected into layers by single anionic ligands. DTA-TG measurements of Co(NCS)2(4-acetyl-pyridine)4 (1) led to the formation of 3/I. In contrast, when the hydrate Co(NCS)2(4-acetyl-pyridine)2(H2O)2 (2) is decomposed, a mixture of 3/I and a thermodynamically metastable form 3/II is obtained. Further investigations reveal that thermal annealing of 2 leads to the formation of 3/II, that contains only traces of the stable form 3/I. DSC and temperature dependent X-ray powder diffraction (XRPD) measurements prove that 3/II transforms into 3/I on heating. The crystal structure of 3/II was determined ab initio from XRPD data. In its crystal structure the Co cations are linked by pairs of bridging thiocyanato anions into a 1D coordination polymer, and thus, 3/II is an isomer of 3/I. Magnetic measurements disclose that the stable form 3/I only shows paramagnetism without any magnetic anomaly down to 2 K. In contrast, the metastable form 3/II shows ferromagnetic behavior. The phase transition into ordered state at Tc = 3.8 K was confirmed by specific heat measurements. Alternating current susceptibility measurements show frequency dependent maxima in χ' and χ″, which is indicative for a slow relaxation of the magnetization.

Crystal structure of bis-(2,2'-bi-pyridine-κ(2) N,N')bis-(thio-cyanato-κN)mang-anese(II) 2,2'-bi-pyridine monosolvate.

In the crystal structure of the mononuclear title compound, [Mn(NCS)2(C10H8N2)2]·C10H8N2, the Mn(II) cation is coordin-ated in an all-cis configuration by two N-bound thio-cyanate anions and two 2,2'-bi-pyridine ligands within a slightly distorted octa-hedral environment. The asymmetric unit consists of one Mn(II) cation, two thio-cyanate anions and two 2,2'-bi-pyridine ligands, as well as two non-coordinating 2,2'-bi-pyridine ligands that are each located on centres of inversion. In the crystal structure, the discrete [Mn(NCS)2(C10H8N2)2] complex mol-ecules are arranged in such a way that cavities are formed, in which the solvent 2,2'-bi-pyridine mol-ecules are located. Apart from van der Waals forces, there are no remarkable inter-molecular inter-actions present in the crystal structure.

Crystal structure of tri-aqua-(2,6-di-methyl-pyrazine-κN (4))bis-(thio-cyanato-κN)manganese(II) 2,5-di-methyl-pyrazine disolvate.

In the crystal structure of the title complex, [Mn(NCS)2(C6H8N2)(H2O)3]·2C6H8N2, the Mn(II) cation is coordinated by two terminally N-bonded thio-cyanate anions, three water mol-ecules and one 2,6-di-methyl-pyrazine ligand within a slightly distorted N3O3 octa-hedral geometry; the entire complex mol-ecule is generated by the application of a twofold rotation axis. The asymmetric unit also contains an uncoordinating 2,5-di-methyl-pyrazine ligand in a general position. Obviously, the coordination to the 2,6-di-methyl-pyrazine ligand is preferred because coordination to the 2,5-di-methyl-pyrazine 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-di-methyl-pyzazine/2,5-di-methyl-pyza-zine) hydrogen bonding, forming a three-dimensional network. In the crystal, mol-ecules 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 di-aqua-bis-(2,6-di-methyl-pyrazine-κN (4))bis-(thio-cyanato-κN)cobalt(II) 2,5-di-methyl-pyrazine monosolvate.

In the crystal structure of the title compound, [Co(NCS)2(C6H8N2)2(H2O)2]·C6H8N2, the Co(II) cation is coordinated by the N atoms of two terminal thio-cyanate anions, the O atoms of two water mol-ecules and two N atoms of two 2,6-di-methyl-pyrazine ligands. The coordination sphere of the resulting discrete complex is that of a slightly distorted octa-hedron. The asymmetric unit comprises a Co(II) cation and half of a 2,5-di-methyl-pyrazine ligand, both of which are located on centres of inversion, and a water ligand, a 2,6-di--methyl-pyrazine ligand and one thio-cyanate 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-di-methyl-pyrazine solvent mol-ecules are located. The coordination of the 2,5-di-methyl-pyrazine mol-ecules 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-di-methyl-pyrazine 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-di-methyl-pyrazine ligands. The remaining water H atom is hydrogen bonded to one N atom of the 2,5-di-methyl-pyrazine solvent mol-ecule. This arrangement leads to the formation of a two-dimensional network extending parallel to (010).

Crystal structure of di-aqua-bis-(2,6-di-methyl-pyrazine-κN)bis-(thio-cyanato-κN)cobalt(II) 2,5-di-methyl-pyrazine tris-olvate.

In the crystal structure of the title compound, [Co(NCS)2(C6H8N2)2(H2O)2]·3C6H8N2, the Co(II) cation is coordinated by two terminally N-bound thio-cyanate anions, two water mol-ecules and two 2,6-di-methyl-pyrazine ligands, forming a discrete complex with a slightly distorted octa-hedral N4O2 coordination environment. The asymmetric unit contains one Co(II) cation and three halves of 2,5-di-methyl-pyrazine solvate mol-ecules, all entities being completed by inversion symmetry, as well as one thio-cyanate anion, an aqua ligand and a 2,6-di-methyl-pyrazine ligand, all in general positions. In the crystal, discrete complexes are arranged in a way that cavities are formed where the noncoordinating 2,5-di-methyl-pyrazine mol-ecules are located. The coordination of the latter to the metal is prevented due to the bulky methyl groups in vicinal positions to the N atoms, leading to a preferential coordination through the 2,6-di-methyl-pyrazine ligands. The complex mol-ecules are linked by O-H⋯N hydrogen bonds between the water H atoms and the N atoms of 2,5-di-methyl-pyrazine solvent mol-ecules, leading to a layered structure extending parallel to (100).

Crystal structure of poly[[(2,2'-bi-pyridine)manganese(II)]-di-µ-thio-cyanato].

In the crystal structure of the polymeric title compound, [Mn(NCS)2(C10H8N2)] n , the Mn(II) cations are coordinated by one chelating 2,2'-bi-pyridine ligand and four thio-cyanate anions (two N- and two S-coordinating), forming a distorted [MnN4S2] octa-hedron. The asymmetric unit consists of one manganese cation located on a twofold rotation axis and half of a 2,2'-bi-pyridine ligand, the other half being generated by the same twofold rotation axis, as well as one thio-cyanate anion in a general position. The Mn(II) cations are linked by two pairs of µ1,3-bridging thio-cyanate ligands into chains along the c axis; because the N atoms of the 2,2'-bi-pyridine ligands, as well as the N and the S atoms of the thio-cyanate anions, are each cis-coordinating, these chains show a zigzag arrangement.

Redetermination of bis-(acetyl-acetonato-κ(2) O,O')(1,10-phenanthroline-κ(2) N,N')manganese(II).

In the crystal structure of the title compound, [Mn(C5H7O2)2(C12H8N2)], the Mn(2+) cation is coordinated by one bidentate 1,10-phenanthroline ligand and two acetyl-acetonate anions within a slightly distorted N2O4 octa-hedron. The asymmetric unit consists of one Mn(2+) cation situated on a twofold rotation axis, one half of a 1,10-phenanthroline ligand and one acetyl-acetonate anion. In comparison with the previous determination based on visually estimated intensities recorded on precession photographs, the current redetermination with image-plate data reveals bond lengths and angles with much higher precision.

Bis(acetyl-acetonato-κ(2) O,O')(pyridine-κN)(thio-cyanato-κN)manganese(III): a redetermination using data from a single crystal.

In the crystal structure of the title compound, [Mn(C5H7O2)2(NCS)(C5H5N)], the Mn(3+) cation is coordin-ated by two acetyl-acetonate anions, one terminal thio-cyanate anion and one pyridine ligand within a slightly distorted octa-hedron. The asymmetric unit consists of half a complex mol-ecule with the Mn(3+) cation, the thio-cyanate anion and the pyridine ligand located on a mirror plane. The acetyl-acetonate anion is in a general position. The title compound was previously described [Stults et al. (1975 ▶). Inorg. Chem. 14, 722-730] but could only be obtained as a powder. Suitable crystals have now been obtained for a high-precision single-crystal structure determination.