Tuning of the exchange interaction and the Curie temperature by mixed crystal formation of the bridging anionic ligands

Syntheses and crystal structures of the five- and sixfold coordinated complexes diiso-seleno-cyanato-tris-(2-methyl-pyridine N-oxide)cobalt(II) and diiso-seleno-cyanato-tetra-kis-(2-methyl-pyridine N-oxide)cobalt(II)

The reaction of CoBr2, KNCSe and 2-methyl-pyridine N-oxide (C6H7NO) in ethanol leads to the formation of crystals of [Co(NCSe)2(C6H7NO)3] (1) and [Co(NCSe)2(C6H7NO)4] (2) from the same reaction mixture. The asymmetric unit of 1 is built up of one CoII cation, two NCSe- iso-seleno-cyanate anions and three 2-methyl-pyridine N-oxide coligands, with all atoms located on general positions. The asymmetric unit of 2 consists of two cobalt cations, four iso-seleno-canate anions and eight 2-methyl-pyridine N-oxide coligands in general positions, because two crystallographically independent complexes are present. In compound 1, the CoII cations are fivefold coordinated to two terminally N-bonded anionic ligands and three 2-methyl-pyridine N-oxide coligands within a slightly distorted trigonal-bipyramidal coordination, forming discrete complexes with the O atoms occupying the equatorial sites. In compound 2, each of the two complexes is coordinated to two terminally N-bonded iso-seleno-cyanate anions and four 2-methyl-pyridine N-oxide coligands within a slightly distorted cis-CoN2O4 octa-hedral coordination geometry. In the crystal structures of 1 and 2, the complexes are linked by weak C-H⋯Se and C-H⋯O contacts. Powder X-ray diffraction reveals that neither of the two compounds were obtained as a pure crystalline phase.

Weakening the Interchain Interactions in One Dimensional Cobalt(II) Coordination Polymers by Preventing Intermolecular Hydrogen Bonding

The reaction of Co(NCS)₂ with N-methylaniline leads to the formation of [Co(NCS)₂(N-methylaniline)₂]_n (1), in which the cobalt(II) cations are octahedrally coordinated and linked into linear chains by pairs of thiocyanate anions. In contrast to [Co(NCS)₂(aniline)₂]_n (2) reported recently, in which the Co(NCS)₂ chains are linked by strong interchain N-H···S hydrogen bonding, such interactions are absent in 1. Computational studies reveal that the cobalt(II) ions in compound 1 show an easy-axis anisotropy that is lower than in 2, but with the direction of the easy axis being similar in both compounds. The high magnetic anisotropy is also confirmed by magnetic and FD-FT THz-EPR spectroscopy, which yield a consistent g_z value. These investigations prove that the intrachain interactions in 1 are slightly higher than in 2. Magnetic measurements reveal that the critical temperature for magnetic ordering in 1 is significantly lower than in 2, which indicates that the elimination of the hydrogen bonds leads to a weakening of the interchain interactions. This is finally proven by FD-FT THz-EPR experiments, which show that the interchain interaction energy in the N-methylaniline compound 1 is nine-fold smaller than in the aniline compound 2.

Synthesis, crystal structure and thermal decomposition pathway of bis-(iso-seleno-cyanato-κN)tetra-kis-(pyridine-κN)manganese(II)

The reaction of MnCl₂·2H₂O with KSeCN and pyridine in water leads to the formation of the title complex, [Mn(NCSe)₂(C₅H₅N)₄], which is isotypic to its Fe, Co, Ni, Zn and Cd analogues. In its crystal structure, discrete complexes are observed that are located on centres of inversion. The Mn cations are octa-hedrally coordinated by four pyridine coligands and two seleno-cyanate anions that coordinate via the N atom to the metal centres to generate trans-MnN(s)₂N(p)₄ octa-hedra (s = seleno-cyanate and p = pyridine). In the extended structure, weak C-H⋯Se contacts are observed. Powder X-ray diffraction (PXRD) investigations prove that a pure sample was obtained and in the IR and Raman spectra, the C-N stretching vibrations are observed at 2058 and 2060 cm^-1, respectively, in agreement with the terminal coordination of the seleno-cyanate anions. Thermogravimetric investigations reveal that the pyridine coligands are removed in two separate steps. In the first mass loss, a compound with the composition Mn(NCSe)₂(C₅H₅N)₂ is formed, whereas in the second mass loss, the remaining pyridine ligands are removed, which is superimposed with the decomposition of Mn(NCSe)₂ formed after ligand removal. In the inter-mediate compound Mn(NCSe)₂(C₅H₅N)₂, the CN stretching vibration is observed at 2090 cm^-1 in the Raman and at 2099 cm^-1 in the IR spectra, indicating that the Mn cations are linked by μ-1,3-bridging anionic ligands. PXRD measurements show that a compound has formed that is of poor crystallinity. A comparison of the powder pattern with that calculated for the previously reported Cd(NCSe)₂(C₅H₅N)₂ indicates that these compounds are isotypic, which was proven by a Pawley fit.

Synthesis, crystal structure and properties of bis-(iso-seleno-cyanato-κN)tetra-kis-(pyridine-κN)nickel(II)

The reaction of nickel chloride hexa-hydrate with potassium seleno-cyanate and pyridine in water leads to the formation of crystals of the title complex, [Ni(NCSe)₂(C₅H₅N)₄], which were characterized by single-crystal X-ray diffraction. Its crystal structure consists of discrete complexes, located on centers of inversion, in which the Ni cations are sixfold coordinated by two terminal N-bonded seleno-cyanate anions and four pyridine ligands within a slightly distorted octa-hedral coordination. In the crystal, the complexes are connected by weak C-H⋯Se inter-actions. PXRD investigations revealed that a pure crystalline phase has formed. In the IR and Raman spectra, the C-N stretching vibrations are observed at 2083 and 2079 cm^-1, respectively, in agreement with the presence of only terminally bonded anionic ligands. Upon heating, one well-resolved mass loss is observed, in which two of the four pyridine ligands are removed, leading to a compound with the composition Ni(NCSe)₂(C₅H₅N)₂. In this compound, the C-N stretching vibration is shifted to 2108 cm^-1 (Raman) and 2115 cm^-1 (IR), indicating the presence of μ-1,3-bridging anionic ligands. In its PXRD pattern, very broad reflections are observed, indicating for poor crystallinity and/or very small particle size. This crystalline phase is not isotypic to its Co and Fe analogs.

Synthesis, crystal structure and thermal properties of bis-(aceto-nitrile-κN)bis-(3-bromo-pyridine-κN)bis-(thio-cyanato-κN)cobalt(II)

Single crystals of the title compound, [Co(NCS)₂(C₅H₄BrN)₂(C₂H₃N)₂], were obtained by the reaction of Co(NCS)₂ with 3-bromo-pyridine in aceto-nitrile. The Co^II cations lie on crystallographic inversion centers and are coordinated by two N-bonded thio-cyanate anions, two 3-bromo-pyridine and two aceto-nitrile ligands thereby forming slightly distorted CoN₆ octa-hedra. In the crystal, these complexes are linked by C-H⋯S and C-H⋯N hydrogen bonds into a three-dimensional network. In the direction of the crystallographic b-axis, the complexes are arranged into columns with neighboring 3-bromo-pyridine ligands stacked onto each other, indicating π-π inter-actions. The CN stretching vibration of the thio-cyanate anions is observed at 2066 cm^-1, in agreement with the presence of only N-bonded anionic ligands. TG-DTA measurements reveal that in the first mass loss the aceto-nitrile ligands are removed and that in the second step, half of a 3-bromo-pyridine ligand is lost, leading to the formation of a polymeric compound with the composition [(Co(NCS)₂)₂(C₅H₄BrN)₃] _n already reported in the literature.

Magnetic order in a metal thiocyanate perovskite-analogue

Metal thiocyanate perovskite-analogues are a growing class of materials, but although they contain paramagnetic cations there have been no reports of their magnetic properties. Due to the large separations between...

Synthesis, crystal structure and thermal properties of poly[bis-[μ-3-(amino-meth-yl)pyridine-κ2 N:N']bis(thio-cyanato-κN)manganese(II)]

The reaction of Mn(NCS)2 with a stoichiometric amount of 3-(amino-meth-yl)pyridine in ethanol led to the formation of the title compound, [Mn(NCS)2(C6H8N2)2] n , which is isotypic to its Zn, Co and Cd analogues. The manganese cation is located on a centre of inversion and is octa-hedrally coordinated in an all-trans configuration by two terminal N-bonded thio-cyanate anions as well as four 3-(amino-meth-yl)pyridine co-ligands, of which two coordinate with the pyridine N atom and two with the amino N atom. The 3-(amino-meth-yl)pyridine co-ligands connect the MnII cations into layers extending parallel to (10). These layers are further connected into a three-dimensional network by relatively strong inter-molecular N-H⋯S hydrogen bonding. Comparison of the experimental X-ray powder diffraction pattern with the calculated pattern on the basis of single-crystal data proves the formation of a pure crystalline phase. IR measurements showed the CN stretching vibration of the thio-cyanate anions at 2067 cm-1, which is in agreement with the presence of terminally N-bonded anionic ligands. TG-DTA measurements revealed that the title compound decomposes at about 500 K.

Synthesis, crystal structure and thermal properties of poly[bis-[μ2-3-(amino-meth-yl)pyridine]-bis-(thio-cyanato)-cobalt(II)]

The reaction of Co(NCS)2 with 3-(amino-meth-yl)pyridine as coligand leads to the formation of crystals of the title compound, [Co(NCS)2(C6H8N2)2] n , that were characterized by single-crystal X-ray analysis. In the crystal structure, the CoII cations are octa-hedrally coordinated by two terminal N-bonded thio-cyanate anions as well as two pyridine and two amino N atoms of four symmetry-equivalent 3-(amino-meth-yl)pyridine coligands with all pairs of equivalent atoms in a trans position. The CoII cations are linked by the 3-(amino-meth-yl)pyridine coligands into layers parallel to the ac plane. These layers are further linked by inter-molecular N-H⋯S hydrogen bonding into a three-dimensional network. The purity of the title compound was determined by X-ray powder diffraction and its thermal behavior was investigated by differential scanning calorimetry and thermogravimetry.

Crystal structure of bis-(tetra-methyl-thio-urea-κS)bis-(thio-cyanato-κN)nickel(II)

In the course of our investigations regarding transition-metal thio-cyanates with thio-urea derivatives, the title compound, [Ni(NCS)2(C5H12N2S)2], was obtained. The asymmetric unit consists of one thio-cyanate anion and one tetra-methyl-thio-urea mol-ecule on general positions, as well as one NiII cation that is located on a twofold rotational axis. In this compound, discrete complexes are formed in which the NiII cations are surrounded by two trans-N-bonding thio-cyanate anions as well as two trans-S-bonding tetra-methyl-thio-urea mol-ecules within a distorted square-planar coordination geometry. The discrete complexes are linked by pairs of weak C-H⋯S hydrogen bonds between the thio-cyanate S and one of the tetra-methyl-thio-urea methyl hydrogen atoms into chains along the crystallographic a- and c-axis directions, which are combined into layers parallel to the ac plane. X-ray powder diffraction proves that a pure crystalline phase was obtained and measurements using thermogravimetry and differential thermoanalysis reveal that the compound decomposes at about 408 K, where all tetra-methyl-thio-urea mol-ecules are lost.

Crystal structure of bis-(tetra-methyl-thio-urea-κS)bis(thio-cyanato-κN)cobalt(II)

In the course of systematic investigations on the synthesis of Co(NCS)2 coordination compounds with different thio-urea ligands, the title compound, [Co(NCS)2(C5H12N2S)2], was obtained. In this compound the CoII cations are coordinated by two crystallographically independent N-bonded thio-cyanate anions and two tetra-methyl-thio-urea ligands into discrete complexes that are located in general positions and show a strongly distorted tetra-hedral geometry. Inter-molecular C-H⋯S hydrogen bonds of different strength can be observed between the discrete complexes, which are connected by pairs of hydrogen bonds into zigzag-like chains that elongate in the b-axis direction. These chains are additionally linked by strong C-H⋯S hydrogen bonds along the a-axis direction, resulting in the formation of layers that are parallel to the ab plane. There is also one weak intra-molecular C-H⋯S hydrogen bond between two neighbouring thio-urea ligands within the complexes. Comparison of the experimental PXRD pattern with that calculated from the single-crystal data prove that a pure phase has been obtained. Thermoanalytical investigations reveal that this compound melts at 364 K and decomposes upon further heating.

Influence of the Coligand onto the Magnetic Anisotropy and the Magnetic Behavior of One-Dimensional Coordination Polymers

Reaction of Co(NCS)₂ with different coligands leads to the formation of three compounds with the general composition [Co(NCS)₂(L)₂]_n (L = aniline (1), morpholine (2), and ethylenethiourea (3)). In all of these compounds the cobalt(II) cations are octahedrally coordinated by two trans thiocyanate N and S atoms and the apical donor atoms of the coligands and are linked into linear chains by pairs of anionic ligands. The magnetic behavior was investigated by a combination of static and dynamic susceptibility as well as specific-heat measurements, computational studies, and THz-EPR spectroscopy. All compounds show antiferromagnetic ordering as observed for similar compounds with pyridine derivatives as coligands. In contrast to the latter, for 1-3 significantly higher critical temperatures and no magnetic single-chain relaxations are observed, which can be traced back to stronger interchain interactions and a drastic change in the magnetic anisotropy of the metal centers. These results are discussed and compared with those of the pyridine-based compounds, which provides important insights into the parameters that govern the magnetic behavior of such one-dimensional coordination polymers.

Molybdenum(III) Thiocyanate- and Selenocyanate-Based One-Dimensional Heteronuclear Polymers: Coordination Affinity-Controlled Assemblage of Mixed Spin and Mixed Valence Derivatives with Ni(II) and Co(II/III)

One-dimensional coordination polymers constructed with the 4d metallo-ligand [Mo(NCS)₆]^3- associated with Ni^II and Co^II complexes are reported. The first series consists of anionic NCS-bridged [Mo-M^II]^- coordination polymers associated with a discrete paramagnetic complex or a diamagnetic Co^III complex acting as cations. The latter takes advantage of the coordination preference of the S-ligand for the soft 3d ions and has led to hetero-trimetallic [Mo^IIINi^IICo^III] and mixed valence [Mo^IIICo^IICo^III] compounds. A second series concerns neutral chains in which trinuclear [Mo M₂^II] units are bridged by an additional NCS anion. The soft character of the S atom was also the key to a rare example of a compound involving both high-spin and low-spin Co^II centers associated with [Mo(NCS)₆]. A [Mo-Ni] derivative obtained with [Mo(NCSe)₆]^3- has been considered in order to evaluate the effect of Se versus S on the exchange interaction. The spin distribution for selenocyanate metallo-ligand has been assessed by density functional theory calculations. The crystal structures for all compounds have been characterized, and their magnetic behaviors have been investigated. These ferrimagnetic systems are characterized by antiferromagnetic Mo-M^II interactions in the range of -40 to -90 cm^-1 (based on H = -JS_aS_b formalism) operative both with Co^II and with Ni^II, thus demonstrating the potential of the Mo^III-NCS combination for molecular systems in which exchange interactions play an important role.

Single-Chain Magnet Based on Cobalt(II) Thiocyanate as XXZ Spin Chain

The cobalt(II) in [Co(NCS)2 (4-methoxypyridine)2 ]n are linked by pairs of thiocyanate anions into linear chains. In contrast to a previous structure determination, two crystallographically independent cobalt(II) centers have been found to be present. In the antiferromagnetic state, below the critical temperature (Tc =3.94 K) and critical field (Hc =290 Oe), slow relaxations of the ferromagnetic chains are observed. They originate mainly from defects in the magnetic structure, which has been elucidated by micromagnetic Monte Carlo simulations and ac measurements using pristine and defect samples. The energy barriers of the relaxations are Δτ1 =44.9(5) K and Δτ2 =26.0(7) K for long and short spin chains, respectively. The spin excitation energy, measured by using frequency-domain EPR spectroscopy, is 19.1 cm-1 and shifts 0.1 cm-1 due to the magnetic ordering. Ab initio calculations revealed easy-axis anisotropy for both CoII centers, and also an exchange anisotropy Jxx /Jzz of 0.21. The XXZ anisotropic Heisenberg model (solved by using the density renormalization matrix group technique) was used to reconcile the specific heat, susceptibility, and EPR data.

Crystal structure, synthesis and thermal properties of bis-(4-benzoyl-pyridine-κN)bis-(iso-thio-cyanato-κN)bis-(methanol-κN)iron(II)

In the crystal structure of the title compound, [Fe(NCS)2(C12H9NO)2(CH4O)2], the FeII cations are octa-hedrally coordinated by two N atoms of 4-benzoyl-pyridine ligands, two N atoms of two terminal iso-thio-cyanate anions and two methanol mol-ecules into discrete complexes that are located on centres of inversion. These complexes are linked via inter-molecular O-H⋯O hydrogen bonds between the methanol O-H H atoms and the carbonyl O atoms of the 4-benzoyl-pyridine ligands, forming layers parallel to (101). Powder X-ray diffraction proved that a pure sample was obtained but that this compound is unstable and transforms into an unknown crystalline phase within several weeks. However, the solvent mol-ecules can be removed by heating in a thermobalance, which for the aged sample as well as the title compound leads to the formation of a compound with the composition Fe(NCS)2(4-benzoyl-pyridine)2, which exhibits a powder pattern that is similar to that of Mn(NCS)2(4-benzoyl-pyridine)2.

Impact of the synthetic approach on the magnetic properties and homogeneity of mixed crystals of tunable layered ferromagnetic coordination polymers

Different synthetic routes were applied to synthesize mixed crystals of [Co_xNi_1−x(NCS)₂(4-tert-butylpyridine)₂]_n that finally results in homogeneous samples for which the critical temperature can be tuned as function of the Co : Ni ratio.

Thermodynamically stable and metastable coordination polymers synthesized from solution and the solid state

Different Fe(ii) and Cd(ii) thiocyanate coordination compounds with unusual topology including isomeric modifications were synthesized with 4-picoline and investigated in regard to their thermodynamic relations.

In situ formation and solid-state oxidation of a triselenane NSeN-pincer MOF

Controlled partial decomposition of 2-selenonicotinic acid in the presence of Co²⁺ or Ni²⁺ resulted in the in situ formation of an unusual MOF based on triselenane ligands (RSeSeSeR) coordinated to M²⁺ centers as NSeN-pincers.

New isomeric Ni(NCS)2 coordination compounds: crystal structures, magnetic properties as well as ex situ and in situ investigations on their synthesis and transition behaviour

Some stable and metastable isomeric Ni(NCS)₂ chain compounds were synthesized and structurally characterized and investigated for their transformation behavior and their magnetic properties using a variety of methods.

Structural diversity in Cd(NCS)2-3-cyanopyridine coordination compounds: synthesis, crystal structures and thermal properties

Five new compounds with the compositions [Cd(NCS)2(3-cyanopyridine)2] n  · 3-cyanopyridine (1), [Cd(NCS)2(3-cyanopyridine)2] n  · 1/3 3-cyanopyridine (2), [Cd(NCS)2(3-cyanopyridine)2] n (3), {[Cd(NCS)2]2(3-cyanopyridine)3} n (4), and {[Cd(NCS)2]3(3-cyanopyridine)4} n (5) have been obtained by the reaction of Cd(NCS)2 with 3-cyanopyridine in different solvents. While large amounts of compounds 1–4 could be prepared as powders, only a few single crystals of 5 were accidently obtained. Thermoanalytical investigations have shown that 4 could also be obtained by annealing of 1 or 2 and that under slightly different conditions 5 could be obtained as part of a mixture with 4. The crystal structures of all compounds can be divided in two sets of compounds. Compounds 1, 2 and 3 consist of chains in which the Cd cations show three different coordination environments and in which the coligands are only terminally bonded. In the structures of 4 and 5 similar chains are observed, which are connected into layers via some of the 3-cyanopyridine coligands.

Crystal structure, synthesis and thermal properties of bis-(aceto-nitrile-κN)bis-(4-benzoyl-pyridine-κN)bis-(iso-thio-cyanato-κN)nickel(II)

In the crystal structure of the title com-pound, [Ni(NCS)2(CH3CN)2(C12H9NO)2] or Ni(NCS)2(4-benzoyl-pyridine)2(aceto-nitrile)2, the NiII ions are octa-hedrally coordinated by the N atoms of two thio-cyanate anions, two 4-benzoyl-pyridine ligands and two aceto-nitrile mol-ecules into discrete com-plexes that are located on centres of inversion. In the crystal, the discrete com-plexes are linked by centrosymmetric pairs of weak C-H⋯S hydrogen bonds into chains. Thermogravimetric measurements prove that, upon heating, the title com-plex loses the two aceto-nitrile ligands and transforms into a new crystalline modification of the chain com-pound [Ni(NCS)2(4-benzoyl-pyridine)2], which is different from that of the corresponding CoII, NiII and CdII coordination polymers reported in the literature. IR spectroscopic investigations indicate the presence of bridging thio-cyanate anions but the powder pattern cannot be indexed and, therefore, this structure is unknown.

Crystal structure, synthesis and thermal properties of tetra-kis-(4-benzoyl-pyridine-κN)bis-(iso-thio-cyanato-κN)iron(II)

The asymmetric unit of the title compound, [Fe(NCS)2(C12H9NO)4], consists of an FeII ion that is located on a centre of inversion, as well as two 4-benzoyl-pyridine ligands and one thio-cyanate anion in general positions. The FeII ions are coordinated by two N-terminal-bonded thio-cyanate anions and four 4-benzoyl-pyridine ligands into discrete complexes with a slightly distorted octa-hedral geometry. These complexes are further linked by weak C-H⋯O hydrogen bonds into chains running along the c-axis direction. Upon heating, this complex loses half of the 4-benzoyl-pyridine ligands and transforms into a compound with the composition Fe(NCS)2(4-benzoyl-pyridine)2, that might be isotypic to the corresponding MnII compound and for which the structure is unknown.