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

Synthesis, crystal structure and thermal properties of catena-poly[[bis-(4-methyl-pyridine)-nickel(II)]-di-μ-thio-cyanato], which shows an alternating all-trans and cis-cis-trans-coordination of the NiS2Np 2Nt 2 octa-hedra (p = 4-methyl-pyridine, t = thio-cyanate)

The title compound, [Ni(NCS)2(C6H7N)2] n , was prepared by the reaction of Ni(NCS)2 with 4-methyl-pyridine in water. Its asymmetric unit consists of two crystallographically independent NiII cations, of which one is located on a twofold rotational axis whereas the second occupies a center of inversion, two independent thio-cyanate anions and two independent 4-methyl-pyridine co-ligands in general positions. Each NiII cation is octa-hedrally coordinated by two 4-methyl-pyridine coligands as well as two N- and two S-bonded thio-cyanate anions. One of the cations shows an all-trans, the other a cis-cis-trans configuration. The metal centers are linked by pairs of μ-1,3-bridging thio-cyanate anions into [101] chains. X-ray powder diffraction shows that a pure crystalline phase has been obtained and thermogravimetry coupled to differential thermoanalysis reveals that the title compound loses half of the 4-methyl-pyridine coligands and transforms into Ni(NCS)2(C6H7N). Nearly pure samples of this compound can be obtained by thermal annealing and a Rietveld refinement demonstrated that it is isotypic to its recently reported Cd analog [Neumann et al., (2020 ▸). CrystEngComm. 22, 184-194] In its crystal structure, the metal cations are linked by one μ-1,3(N,S)- and one μ-1,3,3(N,S,S)-bridging thio-cyanate anion into single chains that condense via the μ-1,3,3(N,S,S)-bridging anionic ligands into double chains.

Synthesis, crystal structure and thermal properties of a new polymorphic modification of diiso-thio-cyanato-tetra-kis-(4-methyl-pyridine)cobalt(II)

The title compound, [Co(NCS)2(C6H7N)4] or Co(NCS)2(4-methyl-pyridine)4, was prepared by the reaction of Co(NCS)2 with 4-methyl-pyridine in water and is isotypic to one of the polymorphs of Ni(NCS)2(4-methyl-pyridine)4 [Kerr & Williams (1977 ▸). Acta Cryst. B33, 3589-3592 and Soldatov et al. (2004 ▸). Cryst. Growth Des. 4, 1185-1194]. Comparison of the experimental X-ray powder pattern with that calculated from the single-crystal data proves that a pure phase has been obtained. The asymmetric unit consists of one CoII cation, two crystallographically independent thio-cyanate anions and four independent 4-meth-yl-pyridine ligands, all located in general positions. The CoII cations are sixfold coordinated to two terminally N-bonded thio-cyanate anions and four 4-methyl-pyridine coligands within slightly distorted octa-hedra. Between the complexes, a number of weak C-H⋯N and C-H⋯S contacts are found. This structure represent a polymorphic modification of Co(NCS)2(4-methyl-pyridine)4 already reported in the CCD [Harris et al. (2003 ▸). NASA Technical Reports, 211890]. In contrast to this form, the crystal structure of the new polymorph shows a denser packing, indicating that it is thermodynamically stable at least at low temperatures. Thermogravimetric and differential thermoanalysis reveal that the title compound starts to decomposes at about 100°C and that the coligands are removed in separate steps without any sign of a polymorphic transition before decomposition.

Synthesis, crystal structure and properties of poly[(μ-2-methyl-pyridine N-oxide-κ2O:O)bis-(μ-thio-cyanato-κ2N:S)cobalt(II)]

The title compound, [Co(NCS)2(C6H7NO)]n or Co(NCS)2(2-methyl-pyridine N-oxide), was prepared by the reaction of Co(NCS)2 and 2-methyl-pyridine N-oxide in methanol. All crystals obtained by this procedure show reticular pseudo-merohedric twinning, but after recrystallization, one crystal was found that had a minor component with only a very few overlapping reflections. The asymmetric unit consists of one CoII cation, two thio-cyanate anions and one 2-methyl-pyridine N-oxide coligand in general positions. The CoII cations are octa-hedrally coordinated by two O-bonding 2-methyl-pyridine N-oxide ligands, as well as two S- and two N-bonding thio-cyanate anions, and are connected via μ-1,3(N,S)-bridging thio-cyanate anions into chains that are linked by μ-1,1(O,O) bridging coligands into layers. No pronounced directional inter-molecular inter-actions are observed between the layers. The 2-methyl-pyridine coligand is disordered over two orientations and was refined using a split model with restraints. Powder X-ray diffraction (PXRD) indicates that a pure sample was obtained and IR spectroscopy confirms that bridging thio-cyanate anions are present. Thermogravimetry and differential thermoanalysis (TG-DTA) shows one poorly resolved mass loss in the TG curve that is accompanied by an exothermic and an endothermic signal in the DTA curve, which indicate the decomposition of the 2-methyl-pyridine N-oxide coligands.

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, thermal and spectroscopic properties of ZnX2-2-methylpyrazine (X = Cl, Br, I) coordination compounds

Reaction of zinc(II) chloride, bromide and iodide with 2-methylpyrazine (2-Mepyz) leads to the formation of coordination compounds with the composition ZnX2(2-Mepyz)2 (X = Cl; 1-Cl, Br; 1-Br and I; 1-I). In the compounds each Zn cation is tetrahedrally coordinated by two halide anions and two 2-methylpyrazine ligands forming discrete complexes. TG-DTA and temperature dependent PXRD measurements prove that upon heating compounds 1 transform into new compounds with the composition ZnX2(2-Mepyz) (2), that are subsequently converted into compounds with the composition (ZnX2)3(2-Mepyz) (3) upon further heating. It was also found that compounds 2 can be prepared directly in solution. For ZnI2(2-Mepyz) (2-I) crystals were obtained and characterized by single crystal X-ray diffraction, whereas the crystal structures of 2-Cl and 2-Br were determined ab initio from PXRD data. In these compounds the Zn cations are also tetrahedrally coordinated and linked into chains by bridging 2-methylpyrazine ligands. The (ZnX2)3(2-Mepyz) compounds can only be obtained by thermal decomposition, and the products are of poor crystallinity and extremely hygroscopic, which prevented structure determinations.

Magnetic Anisotropy and Relaxation of Pseudotetrahedral [N2 O2 ] Bis-Chelate Cobalt(II) Single-Ion Magnets Controlled by Dihedral Twist Through Solvomorphism

The methanol solvomorph 1 ⋅ 2MeOH of the cobalt(II) complex [Co(L^Sal,2-Ph )₂ ] (1) with the sterically demanding Schiff-base ligand 2-(([1,1'-biphenyl]-2-ylimino)methyl)phenol (HL^Sal,2-Ph ) shows the thus far largest dihedral twist distortion between the two chelate planes compared to an ideal pseudotetrahedral arrangement. The cobalt(II) ion in 1 ⋅ 2MeOH exhibits an easy-axis anisotropy leading to a spin-reversal barrier of 55.3 cm^-1 , which corresponds to an increase of about 17 % induced by the larger dihedral twist compared to the solvent-free complex 1. The magnetic relaxation for 1 ⋅ 2MeOH is significantly slower compared to 1. An in-depth frequency-domain Fourier-transform (FD-FT) THz-EPR study not only allowed the direct measurement of the magnetic transition between the two lowest Kramers doublets for the cobalt(II) complexes, but also revealed the presence of spin-phonon coupling. Interestingly, a similar dihedral twist correlation is also observed for a second pair of cobalt(II)-based solvomorphs, which could be benchmarked by FD-FT THz-EPR.

Synthesis, crystal structure and thermal properties of tetra-kis-(3-methyl-pyridine-κN)bis-(thio-cyanato-κN)nickel(II)

Reaction of Ni(NCS)₂ with 3-methyl-pyridine in water leads to the formation of crystals of the title compound, [Ni(NCS)₂(C₆H₇N)₄]. All of them are of poor quality and non-merohedrally twinned but a refinement using data in HKLF-5 format leads to a reasonable structure model and reliability factors. The crystal structure of the title compound consists of discrete complexes, in which the nickel cations are sixfold coordinated by two terminal N-bonded thio-cyanate anions and four 3-methyl-pyridine ligands within slightly distorted octa-hedra. One of the 3-methyl-pyridine ligands is disordered and was refined using a split model. The discrete complexes are arranged into layers. X-ray powder diffraction proves that pure samples have been obtained, and in the IR spectrum, the CN stretching vibration is observed at 2072 cm^-1, in agreement with the presence of only terminally coordinated thio-cyanate anions. Comparing the calculated powder pattern with those of the residues obtained by solvent removal from several solvates already reported in the literature proves that, in each case, this crystalline phase is formed. Assessing the crystal structures of the solvates in comparison with that of the ansolvate reveals some similarities.

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.

Co(NCS)2 Chain Compound with Alternating 5- and 6-Fold Coordination: Influence of Metal Coordination on the Magnetic Properties

The reaction of Co(NCS)₂ with 3-bromopyridine leads to the formation of discrete complexes [Co(NCS)₂(3-bromopyridine)₄] (1), [Co(NCS)₂(3-bromopyridine)₂(H₂O)₂] (2), and [Co(NCS)₂(3-bromopyridine)₂(MeOH)₂] (3) depending on the solvent. Thermogravimetric measurements on 2 and 3 show a transformation into [Co(NCS)₂(3-bromopyridine)₂]_n (4), which upon further heating is converted to [{Co(NCS)₂}₂(3-bromopyridine)₃]_n (5), whereas 1 transforms directly into 5 upon heating. Compound 5 can also be obtained from solution, which is not possible for 4. In 4 and 5, the cobalt(II) cations are linked by pairs of μ-1,3-bridging thiocyanate anions into chains. In compound 4, all cobalt(II) cations are octahedrally coordinated (OC-6), as is usually observed in such compounds, whereas in 5, a previously unkown alternating 5- and 6-fold coordination is observed, leading to vacant octahedral (vOC-5) and octahedral (OC-6) environments, respectively. In contrast to 4, the chains in 5 are very efficiently packed and linked by π···π stacking of the pyridine rings and interchain Co···Br interactions, which is the basis for the formation of this unusual chain. The spin chains in 4 demonstrate ferromagnetic intrachain exchange and much weaker interchain interactions, as is usually observed for such linear chain compounds. In contrast, compound 5 shows almost single-ion-like magnetic susceptibility, but the magnetic ordering temperature deduced from specific heat measurements is twice as high as that in 4, which might originate from π···π stacking and Co···Br interactions between neighboring chains. More importantly, unlike all linear Co(NCS)₂ chain compounds, a dominant antiferromagnetic exchange is observed for 5, which is explained by density functional theory calculations predicting an alternating ferro- and aniferromagnetic exchange within the chains. Theoretical calculations on the two different cobalt(II) ions present in 5 predict an easy-axis anisotropy that is much stronger for the octahedral cobalt(II) ion than for the one with the vacant octahedral coordination, with the magnetic axes of the two ions being canted by an angle of 84°. This almost orthogonal orientation of the easy axis of magnetization for the two cobalt(II) ions is the rationale for the observed non-Ising behavior of 5.

Relaxation processes in a single crystal of Co(NCS)2(4-methoxypyridine)2 spin chain

A single crystal of [Co(NCS)₂(4-methoxypyridine)₂]_n was obtained and investigated. The magnetic measurements performed along three perpendicular crystallographic directions are compared to the results obtained previously for a powder sample. The magnetic inter- and intrachain interactions do not differ, however, a change of the energy barrier of magnetic relaxations is obtained. For the single crystal sample the relaxation is much slower, which is attributed to the presence of longer chains, and show that below the ordering temperature the spin chains relax by the process that involves a single domain wall. Above the ordering temperature, a second relaxation process is observed, for which the relaxation time is temperature independent, indicating a negligible energy barrier. Such phenomenon was previously not observed for any of the powder samples of compounds from the [Co(NCS)₂(ligand)₂]_n family.

Syntheses, crystal structures and properties of tetrakis(3-methylpyridine-κN)bis(isothiocyanato-κN)manganese(II) and tetrakis(3-methylpyridine-κN)bis(isothiocyanato-κN)iron(II)

The crystal structures of the title compounds consist of discrete complexes, in which the metal cations are octa­hedrally coordinated.

The reaction of Mn(NCS)₂ or Fe(NCS)₂ with 3-methyl­pyridine (C₆H₇N) leads to the formation of two isostructural compounds with compositions [Mn(NCS)₂(C₆H₇N)₄] (1) and [Fe(NCS)₂(C₆H₇N)₄] (2). IR spectroscopic investigations indicate that only terminally coordinated thio­cyanate anions are present. This is confirmed by single-crystal structure analysis, which shows that their crystal structures consist of discrete centrosymmetric complexes, in which the metal cations are octa­hedrally coordinated by two N-bonded thio­cyanate anions and four 3-methyl­pyridine ligands. X-ray powder diffraction (XRPD) proves that pure samples have been obtained. Thermogravimetric measurements show that decomposition starts at about 90°C and that the two coligands are removed in one step for 1 whereas for 2 no clearly resolved steps are visible. XRPD measurements of the residue obtained after the first mass loss of 1 show that a new and unknown crystalline compound has been formed.

Synthesis, crystal structure and magnetic properties of coordination compounds of Mn(NCS)2 with the 3-bromopyridine ligand

Reactions of Mn(NCS)2 with 3-bromopyridine in acetonitrile lead to the formation of Mn(NCS)2(3-bromopyridine)4 (1) and Mn(NCS)2(3-bromopyridine)2(MeCN)2 (2) that were characterized by single crystal X-ray diffraction. Compounds 1 and 2 consist of discrete complexes, in which the Mn(II) cations are octahedrally coordinated by two trans-N-bonding thiocyanate anions and four pyridine (1) or two pyridine and two acetonitrile ligands (2). Thermoanalytical measurements on 1 and 2 have shown that upon heating half of the 3-bromopyridine co-ligands from 1 or both acetonitrile ligands from 2 are removed leading to a crystalline phase with the composition [Mn(NCS)2(3-bromopyridine)2] n (3-II). From dry n-butanol a phase with the same composition was obtained (3-I) that corresponds to a polymorphic or isomeric form of 3-II. Crystal structure analysis of 3-I shows that in this form the Mn cations are linked by pairs of anionic ligands into linear chains. The results of magnetic measurements on 3-I show antiferromagnetic interactions along the chains and the analysis of the magnetic susceptibility using the Fisher model for chains gave a J value of −5.76(5) K.

Crystal structures of two Co(NCS)2 urotropine coordination compounds with different Co coordinations

In the crystal structure of the title compounds, discrete complexes with different Co coordinations are observed, which are linked by inter­molecular hydrogen bonding into three-dimensional networks.

The reaction of Co(NCS)₂ with urotropine in ethanol leads to the formation of two different compounds, namely, bis­(ethanol-κO)bis­(hexa­methyl­ene­tetra­mine-κN)bis­(thio­cyanato-κN)cobalt(II)–di­aqua-κ²O-bis­(hexa­methyl­ene­tetra­mine-κN)bis­(thio­cyanato-κN)cobalt(II)–ethanol–hexa­methyl­ene­tetra­mine (1.2/0.8/1.6/4), [Co(NCS)₂(C₆H₁₂N₄)₂(C₂H₆O)₂]_1.2·[Co(NCS)₂(C₆H₁₂N₄)₂(H₂O)₂]_0.8·1.6C₂H₆O·4C₆H₁₂N₄, 1, and tris­(ethanol-κO)(hexa­methyl­ene­tetra­mine-κN)bis(thio­cyanato-κN)cobalt(II), [Co(NCS)₂(C₆H₁₂N₄)(C₂H₆O)₃], 2. In the crystal structure of compound 1, two crystallographically independent discrete complexes are observed that are located on centres of inversion. In one of them, the Co cation is octa­hedrally coordinated to two terminal N-bonded thio­cyanate anions, two urotropine ligands and two ethanol mol­ecules, whereas in the second complex 80% of the coordinating ethanol is exchanged by water. Formally, compound 1 is a mixture of two different complexes, i.e. di­aqua­dithio­cyanato­bis­(urotropine)cobalt(II) and di­ethano­ldi­thio­cyanato­bis­(uro­trop­ine)cobalt(II), that contain additional ethanol and urotropine solvate mol­ecules leading to an overall composition of [Co(NCS)₂(urotropine)₂(ethanol)_1.2(H₂O)_0.8·0.8ethanol·4urotropine. Both discrete complexes are linked by inter­molecular O—H⋯O and O—H⋯N hydrogen bonding and additional urotropine solvate mol­ecules into chains, which are further connected into layers. These layers combine into a three-dimensional network by pairs of centrosymmetric inter­molecular C—H⋯S hydrogen bonds. In the crystal structure of compound 2, di­thio­cyanato­(urotropine)tri­ethano­lcobalt(II), the cobalt cation is octa­hedrally coordinated to two terminal N-bonded thio­cyanate anions, one urotropine ligand and three ethanol mol­ecules into discrete complexes, which are located in general positions. These complexes are linked by inter­molecular O—H⋯N hydrogen bonding into layers, which are further connected into a three-dimensional network by inter­molecular C—H⋯S hydrogen bonding.

Crystal structure of di-ethano-lbis(thio-cyanato)-bis(urotropine)cobalt(II) and tetra-ethano-lbis(thio-cyanato)-cobalt(II)-urotropine (1/2)

The reaction of one equivalent Co(NCS)2 with four equivalents of urotropine (hexa-methyl-ene-tetra-mine) in ethanol leads to the formation of two compounds, namely, bis-(ethanol-κO)bis-(thio-cyanato-κN)bis-(urotropine-κN)cobalt(II), [Co(NCS)2(C6H12N4)2(C2H6O)2] (1), and tetra-kis-(ethanol-κO)bis-(thio-cyanato-κN)cobalt(II)-urotropine (1/2), [Co(NCS)2(C2H6O)4]·2C6H12N4 (2). In 1, the Co cations are located on centers of inversion and are sixfold coordinated by two terminal N-bonded thio-cyanate anions, two ethanol and two urotropine ligands whereas in 2 the cobalt cations occupy position Wyckoff position c and are sixfold coordinated by two anionic ligands and four ethanol ligands. Compound 2 contains two additional urotropine solvate mol-ecules per formula unit, which are hydrogen bonded to the complexes. In both compounds, the building blocks are connected via inter-molecular O-H⋯N (1 and 2) and C-H⋯S (1) hydrogen bonding to form three-dimensional networks.

Synthesis, crystal structure and thermal properties of bis-(1,3-di-cyclo-hexyl-thio-urea-κS)bis(iso-thiocyanato-κN)cobalt(II)

Crystals of the title compound, [Co(NCS)2(C13H24N2S)2], were obtained by the reaction of Co(NCS)2 with 1,3-di-cyclo-hexyl-thio-urea in ethanol. Its crystal structure consists of discrete complexes that are located on twofold rotation axes, in which the CoII cations are tetra-hedrally coordinated by two terminal N-bonded thio-cyanate anions and two 1,3-di-cyclo-hexyl-thio-urea ligands. These complexes are linked via inter-molecular N-H⋯S and C-H⋯S hydrogen bonding into chains, which elongate in the b-axis direction. These chains are closely packed in a pseudo-hexa-gonal manner. The CN stretching vibration of the thio-cyanate anions located at 2038 cm-1 is in agreement with only terminal bonded anionic ligands linked to metal cations in a tetra-hedral coordination. TG-DTA measurements prove the decomposition of the compound at about 227°C. DSC measurements reveal a small endothermic signal before decomposition at about 174°C, which might correspond to melting.

Comparison of the crystal structures of the low- and high-temperature forms of bis-[4-(di-methyl-amino)-pyridine]-dithio-cyanato-cobalt(II)

Single crystals of the high-temperature form I of [Co(NCS)2(DMAP)2] (DMAP = 4-di-methyl-amino-pyridine, C7H10N2) were obtained accidentally by the reaction of Co(NCS)2 with DMAP at slightly elevated temperatures under kinetic control. This modification crystallizes in the monoclinic space group P21/m and is isotypic with the corresponding Zn compound. The asymmetric unit consists of one crystallographically independent Co cation and two crystallographically independent thio-cyanate anions that are located on a crystallographic mirror plane and one DMAP ligand (general position). In its crystal structure the discrete complexes are linked by C-H⋯S hydrogen bonds into a three-dimensional network. For comparison, the crystal structure of the known low-temperature form II, which is already thermodynamically stable at room temperature, was redetermined at the same temperature. In this polymorph the complexes are connected by C-H⋯S and C-H⋯N hydrogen bonds into a three-dimensional network. At 100 K the density of the high-temperature form I (ρ = 1.462 g cm-3) is higher than that of the low-temperature form II (ρ = 1.457 g cm-3), which is in contrast to the values determined by XRPD at room temperature. Therefore, these two forms represent an exception to the Kitaigorodskii density rule, for which extensive inter-molecular hydrogen bonding in form II might be responsible.

Synthesis and crystal structure of di-aqua-bis-(hexa-methyl-enetramine-κN)bis-(thio-cyanato-κN)cobalt(II)-hexa-methyl-ene-tetra-mine-aceto-nitrile (1/2/2)

The crystal structure of the title solvated coordination compound, [Co(NCS)2(C6H12N4)2(H2O)2]·2C6H12N4·2C2H3N, consists of discrete complexes in which the Co2+ cations (site symmetry ) are sixfold coordinated by two N-bonded thio-cyanate anions, two water mol-ecules and two hexa-methyl-ene-tetra-mine (HMT) mol-ecules to generate distorted trans-CoN4O2 octa-hedra. The discrete complexes are each connected by two HMT solvate mol-ecules into chains via strong O-H⋯N hydrogen bonds. These chains are further linked by additional O-H⋯N and C-H⋯N and C-H⋯S hydrogen bonds into a three-dimensional network. Within this network, channels are formed that propagate along the c-axis direction and in which additional aceto-nitrile solvent mol-ecules are embedded, which are hydrogen bonded to the network. The CN stretching vibration of the thio-cyanate ion occurs at 2062 cm-1, which is in agreement with the presence of N-bonded anionic ligands. XRPD investigations prove the formation of the title compound as the major phase accompanied by a small amount of a second unknown phase.

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.

Thermodynamically metastable chain and stable layered Co(NCS)2 coordination polymers: thermodynamic relations and magnetic properties

Reaction of Co(NCS)2 with 4-bromopyridine leads to the formation of discrete complexes with the composition Co(NCS)2(4-bromopyridine)4·(CH3CN)0.67 (1), Co(NCS)2(4-bromopyridine)2(H2O)2 (2), Co(NCS)2(4-bromopyridine)2(CH3OH)2 (3) and Co(NCS)2(4-bromopyridine)2(CH3CN)2 (4). Upon heating compounds 2 and 4 transform into a crystalline product with the composition Co(NCS)2(4-bromopyridine)2 (5-I) that also can easily be obtained from solution. In this compound, the Co cations are linked by single μ-1,3-bridging thiocyanate anions into layers. Thermal decomposition of 3 leads to a second isomer (5-II), which is thermodynamically metastable and can also be synthesized from solution under kinetic control. In contrast to 5-I, the Co cations are linked by pairs of anionic ligands into linear chains. The magnetic exchange is very weak in 5-I, but much stronger and ferromagnetic along the linear chains in 5-II. AF ordering in 5-II is reached at 3.05 K, and magnetic relaxation is observed at the metamagnetic transition with an Arrhenius barrier of 17.1(3) cm-1. Ab initio computational studies reveal a different type of magnetic anisotropy to be present in the two crystallographically - independent Co centers in 5-II.

Crystal structure of bis-(N,N'-di-methyl-thio-urea-κS)bis-(thio-cyanato-κN)cobalt(II)

During systematic investigations on the synthesis of coordination polymers with Co(NCS)2 involving different thio-urea derivatives as coligands, crystals of the title compound Co(NCS)2(N,N'-di-methyl-thio-urea)2, or [Co(C3H8N2S)2(NCS)2], were obtained. These crystals were non-merohedric twins and therefore, a twin refinement using data in HKLF-5 format was performed. In the crystal structure of this compound, the CoII cations are coordinated by two N-terminally bonded thio-cyanate anions as well as two S-bonding N,N'-di-methyl-thio-urea mol-ecules, forming two crystallographically independent discrete complexes each with a strongly distorted tetra-hedral geometry. An intricate network of inter-molecular N-H⋯S and C-H⋯S hydrogen bonds can be found between the complexes. The thermogravimetric curve of the title compound shows two discrete steps in which all coligand mol-ecules have been emitted, which is also accompanied by partial decomposition of the cobalt thio-cyanate. If the measurement is stopped after the first mass loss, only broad reflections of CoS can be found in the XRPD pattern of the residue, which proves that this compound decomposes completely upon heating. However, at lower temperatures an endothermic signal can be found in the DTA and DSC curve, which corresponds to melting, as proven by thermomicroscopy.

Strengthening the Magnetic Interactions in Pseudobinary First-Row Transition Metal Thiocyanates, M(NCS)2

Understanding the effect of chemical composition on the strength of magnetic interactions is key to the design of magnets with high operating temperatures. The magnetic divalent first-row transition metal (TM) thiocyanates are a class of chemically simple layered molecular frameworks. Here, we report two new members of the family, manganese(II) thiocyanate, Mn(NCS)₂, and iron(II) thiocyanate, Fe(NCS)₂. Using magnetic susceptibility measurements on these materials and on cobalt(II) thiocyanate and nickel(II) thiocyanate, Co(NCS)₂ and Ni(NCS)₂, respectively, we identify significantly stronger net antiferromagnetic interactions between the earlier TM ions-a decrease in the Weiss constant, θ, from 29 K for Ni(NCS)₂ to -115 K for Mn(NCS)₂-a consequence of more diffuse 3d orbitals, increased orbital overlap, and increasing numbers of unpaired t_2g electrons. We elucidate the magnetic structures of these materials: Mn(NCS)₂, Fe(NCS)₂, and Co(NCS)₂ order into the same antiferromagnetic commensurate ground state, while Ni(NCS)₂ adopts a ground state structure consisting of ferromagnetically ordered layers stacked antiferromagnetically. We show that significantly stronger exchange interactions can be realized in these thiocyanate frameworks by using earlier TMs.

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.

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.