Solid-state transformation of [Co(NCS)2(pyridine)4] into [Co(NCS)2(pyridine)2]n: from Curie–Weiss paramagnetism to single chain magnetic behaviour

Long-Chain Bio-Based Nylon 514 Salt: Crystal Structure, Phase Transformation, and Polymerization

Nylon 514 is one of the new long-chain bio-based nylon materials; its raw material, 1,5-pentanediamine (PDA), is prepared by biological techniques, using biomass as the raw material. The high-performance monomer of nylon 514, 1,5-pentanediamine-tetradecanedioate (PDA-TDA) salt, was obtained through efficient crystallization methods. Here, two crystal forms of PDA-TDA, anhydrous and dihydrate, were identified and studied in this paper. From the characterization data, their crystal structures and thermal behaviors were investigated. Lattice energy was calculated to gain further insight into the relationship between thermal stability and crystal structures. The contribution of hydrogen bonds and other intermolecular interactions to the crystal structure stability have been quantified according to detailed Hirshfeld and IRI analyses. Additionally, the transformation mechanism of the anhydrate and dihydrate was established through a series of well-designed stability experiments, in which the temperature and water activity play a significant role in the structural stability of crystalline forms. Eventually, we obtained nylon 514 products with good thermal stability and low absorption using stable dihydrate powders as monomers. The properties of nylon 514 products prepared by different polymerization methods were also compared.

The effect of polymorphism on polymer properties: crystal structure, stability and polymerization of the short-chain bio-based nylon 52 monomer 1,5-pentanediamine oxalate

The compound 1,5-pentanediamine (PDA) is prepared by biological methods using biomass as raw material. The salt of 1,5-pentanediamine oxalate (PDA-OXA) was used directly as the monomer for the preparation of a new bio-based nylon 52 material. High-performance polymer materials require initial high-quality monomers, and crystallization is an essential approach to preparing such a monomer. In this work, three crystal forms of PDA-OXA, the anhydrate, dihydrate and trihydrate, were found and the single crystals of two hydrates were obtained. Their crystal structures were determined using single-crystal and powder X-ray diffraction. The thermal behaviors were characterized by thermodynamic analysis, and the lattice energy was calculated to further explore the relationship between the thermal stability and crystal structure. Detailed computational calculations, Hirshfeld analyses and lattice energy calculations were performed to quantify both the contribution of intra- and intermolecular interactions to the supramolecular assembly, as well as the influence on the stability of the structure. The structure-property relationship between the PDA-OXA crystal forms was established. Moreover, the phase transformation mechanism between the crystalline forms of PDA-OXA has been established, and the control strategy of specific crystal forms was developed from the water activity-temperature phase diagram and relevant thermodynamic data. Finally, the influence of the polymorphism of the monomer and the polymerization methods on the properties of the polymer was investigated. The nylon 52 product obtained showed good appearance, high hardness and thermal stability, the polymer made using the anhydrate as the monomer has better thermodynamic properties than that prepared from the dihydrate, indicating practical industrial application prospects.

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.

Monohydrate and anhydrate of nylon 5I monomer 1,5-pentanediamine-isophthalate

Nylon 5I is one of the new bio-based nylon materials. Its raw material 1,5-pentanediamine (PDA) is prepared by biological methods using biomass as the raw material. The high-performance polymer materials require the original high-quality monomers. 1,5-Pentanediamine–isophthalate (PDA–IPA) was taken as the direct monomer for the preparation of nylon 5I, and the crystallization was a valuable and essential approach to preparing the good-performance monomer salt. In this report, we found and obtained two crystal forms of PDA–IPA, monohydrate and an anhydrous form. Their crystal structures were determined and analyzed by single crystal X-ray diffraction (SCXRD), powder X-ray diffraction (PXRD), and Fourier transform infrared spectroscopy (FTIR). Hirshfeld surface maps were employed to capture the differences in the interactions present in the two forms. The thermal behaviors were characterized by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). Moreover, the monohydrate and anhydrous phase can transform to each other through solid–solid transformation or solution-mediated phase transformation, and the critical values of the phase transformation were determined. Finally, the relative stability of the two forms under different thermodynamic conditions was discussed, especially the influence of temperature and water activity on the stability.

Monohydrate and anhydrous phases of PDA–IPA single crystals have been identified by single crystal X-ray diffraction. The monohydrate and anhydrate phases can achieve mutual transformation under certain conditions, and depend strongly on the temperature and water activity.

Crystal forms and phase transformation of 1,5-pentanediamine-terephthalate: a bio-based nylon 5T monomer

Nylon 5T is one of the bio-based nylons, its raw material 1,5-pentanediamine is derived from biomass resources and produced by biological methods. 1,5-pentanediamine-terephthalate (PDA-TPA) is the monomeric salt for nylon 5T polymerization, and its own product quality has a significant impact on the performance of nylon 5T. PDA-TPA was prepared by anti-solvent crystallization in this study. It exists in two solid forms, a monohydrate [form (I)] and an anhydrous phase [form (II)]. The transition temperature of the two phases was around 65°C in the given ethanol-water binary (7:1) mixture. The characterization of monohydrate and anhydrate phases regarding structures and stabilities was carefully carried out using powder X-ray diffraction, single crystal X-ray diffraction, differential scanning calorimetry, thermogravimetric analysis, hot-stage microscopy and Fourier transform infrared spectroscopy. The relationship between the molecular interactions of monohydrate and anhydrate phases under different packing architectures and their thermal behaviours was analysed and established. In addition, the relationships between the structures and thermal behaviours for the two solid forms were analysed and established. In addition, the effect of solvent on phase conversion, the relationships between the temperature and water activity, as well as the relative stability of monohydrate and anhydrate phases under different thermodynamic conditions, were investigated by solid-solid transformation and solvent-mediated transformation experiments. It was obvious that the transition temperature of monohydrate and anhydrate phases of PDA-TPA was significantly influenced by water activity, and the larger the value of water activity is, the higher is the transition temperature. These studies give insight into the transformation of nylon 5T monomer salt and contribute to the control of target crystal preparation.

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.

Tuning of Spin Crossover Properties in a Series of Mononuclear Cobalt(II) Complexes Based on Macrocyclic Tetradentate Ligand and Pseudohalide Coligands

The three mononuclear cobalt(II) complexes, [Co(L)(NCX)2] (L = N,N'-di-tert-butyl-2,11-diaza[3,3](2,6)pyridinophane, and X = S (1), Se (2), and [C(CN)2] (3)), have been synthesized and characterized using variable temperature single-crystal X-ray crystallography,...

How to link theory and experiment for single-chain magnets beyond the Ising model: magnetic properties modeled from ab initio calculations of molecular fragments

Magnetic properties of coordination polymers like single-chain magnets (SCMs) are based on magnetic domains, which are formed due to magnetic exchange between neighboring anisotropic spin centers. However, the computational restrictions imposed by the high level of theory needed for an adequate ab initio quantum mechanical treatment on the basis of multi-reference methods for these systems limit the feasibility of such calculations to mononuclear fragments as appropriate structural cutouts for the metal centers along the chains. Hence, results from such calculations describe single-ion properties and cannot be directly correlated with experimental data representing magnetic domains. We present a theoretical approach based on n-membered Ising-spin rings with n = 3-12, which allows us to simulate magnetic domains and to derive important magnetic properties for SCM compounds. Magnetic exchange, which is not provided by calculations of mononuclear fragments, is obtained by fitting the theoretical magnetic susceptibility against experimental data. The presented approach is tested for cobalt(ii)-based SCMs with three types of repeating sequences, which differ in nuclearity and symmetry. The magnetic parameters derived using the presented approach were found to be in good agreement with the experimental data. Moreover, the energy spectra obtained for the three test cases using the presented approach are characteristic of a deviation of the individual systems from the ideal Ising behavior. An extrapolation technique towards larger systems (n > 12) is presented which can provide information on the statistical mean length of the magnetic domains in the three investigated SCM compounds.

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

Mixed crystals with the composition [Co(NCS)x(NCSe)2-x(pyridine)2]n were prepared from solution and by annealing of Co(NCS)x(NCSe)2-x(pyridine)4. With increasing selenocyanate content, an increase of the magnetic exchange constant and of the critical temperature (Curie temperature) is observed, which offers a rational route to control these parameters in detail, without changing the metal cations.

Static and dynamic magnetic properties of the ferromagnetic coordination polymer [Co(NCS)2(py)2]n

The static and dynamic properties of the Ising like chain ferromagnet are studied by magnetic measurements and high field-high frequency ESR spectroscopy.

Slow relaxation of the magnetization observed in an antiferromagnetically ordered phase for SCM-based two-dimensional layered compounds

We showed 2D-layered compounds exhibiting SCM-like behavior in an AF ordered phase. By introducing counteranions with a different size, Néel temperature and spin-flip inversion field could be tuned.

Synthesis, structure and properties of [Co(NCS)2(4-(4-chlorobenzyl)pyridine)2]n, that shows slow magnetic relaxations and a metamagnetic transition

[Co(NCS)₂(4-(4-chlorobenzyl)pyridine)₂]_n shows a metamagnetic behavior and slow relaxations of magnetization indicative of a single chain magnet behavior.

A Co(II) thiocyanato coordination polymer with 4-(3-phenylpropyl)pyridine: the influence of the co-ligand on the magnetic properties

Three new coordination compounds with the composition Co(NCS)2(4-(3-phenylpropyl)pyridine)4 (1), Co(NCS)2(4-(3-phenylpropyl)pyridine)4(H2O)2 (2) and [Co(NCS)2(4-(3-phenylpropyl)pyridine)2]n (3) were prepared and investigated. The crystal structures of compounds 1 and 2 consist of discrete complexes, in which the Co(II) cations are coordinated by only terminal N-bonded thiocyanato anions. In the crystal structure 3 of the Co(II) cations are linked into chains by pairs of μ-1,3-bridging thiocyanato anions. DTA-TG measurements on compound 1 show decomposition without the formation of 3 as an intermediate. In contrast, on heating compound 2 two water molecules are removed in the first step leading to the formation of compound 3 in the second step. Magnetic measurements on reveal ferromagnetic interactions between Co(II) ions along chains with J = 29.5(1) K, and also ferromagnetic interactions between chains with zJ' = 0.38(1) K. The ferromagnetic transition is observed at 3.3 K, which is confirmed by specific heat measurements. The temperature dependent ac susceptibility shows slow relaxations above and below 3.3 K. The results for this quasi-one dimensional Ising ferromagnet, having also some features of a cluster spin-glass, are compared with those of related compounds.

catena-Poly[[bis-(pyridine-κN)nickel(II)]-di-μ-thio-cyanato-κ(2) N:S;κ(2) S:N]

In the title compound, [Ni(NCS)₂(C₅H₅N)₂]_n, the Ni²⁺ cation is coordinated by four thio­cyanate anions (μ-1,3) and two pyridine ligands within a slightly distorted octa­hedral configuration. The Ni—N bond lengths to the pyridine rings are 2.1189 (17) and 2.1241 (17) Å, whereas those to the thiocyanate anions are 2.0299 (18) and 2.0359 Å. The Ni—S bond lengths are 2.5357 (6) and 2.5568 (6) Å. The Ni²⁺ cations are linked by N:S-bridging thio­cyanate ligands into chains extending along [010]. The Ni⋯Ni distance within the chains is 5.5820 (5) Å. The asymmetric unit contains two Ni²⁺ cations of which one is located on a centre of inversion, whereas the second is located on a general position.

Poly[(aceto-nitrile-κN)-μ3-thio-cyanato-κ(3) N:S:S-μ2-thio-cyanato-κ(2) N:S-cadmium]

The asymmetric unit of the title compound, [Cd(NCS)₂(CH₃CN)]_n, consists of one Cd^II cation, two thio­cyanate anions and one aceto­nitrile ligand, all in general positions. The Cd^II cation is coordinated by three N atoms of two thio­cyanate anions and one aceto­nitrile ligand, as well as three S atoms of symmetry-related thio­cyanate anions within a slightly distorted octa­hedral coordination environment. The Cd^II cations are linked by μ-1,3(N,S) and μ-1,1,3(S,S,N) thio­cyanate anions into layers that are located in the ab plane.

First row transition metal(II) thiocyanate complexes, and formation of 1-, 2-, and 3-dimensional extended network structures of M(NCS)2(solvent)2 (M = Cr, Mn, Co) composition

The reaction of first row transition M(II) ions with KSCN in various solvents form tetrahedral (NMe4)2[M(II)(NCS)4] (M = Fe, Co), octahedral trans-M(II)(NCS)2(Sol)4 (M = Fe, V, Ni; Sol = MeCN, THF), and K4[M(II)(NCS)6] (M = V, Ni). The reaction of M(NCS)2(OCMe2)2 (M = Cr, Mn) in MeCN and [Co(NCMe)6](BF4)2 and KSCN in acetone and after diffusion of diethyl ether form M(NCS)2(Sol)2 that structurally differ as they form one-dimensional (1-D) (M = Co; Sol = THF), two-dimensional (2-D) (M = Mn; Sol = MeCN), and three-dimensional (3-D) (M = Cr; Sol = MeCN) extended structures. 1-D Co(NCS)2(THF)2 has trans-THFs, while the acetonitriles have a cis geometry for 2- and 3-D M(NCS)2(NCMe)2 (M = Cr, Mn). 2-D Mn(NCS)2(NCMe)2 is best described as Mn(II)(μ(N,N)-NCS)(μ(N,S)-NCS)(NCMe)2 [= Mn2(μ(N,N)-NCS)2(μ(N,S)-NCS)2(NCMe)4] with the latter μ(N,S)-NCS providing the 2-D connectivity. In addition, the reaction of Fe(NCS)2(OCMe2)2 and 7,7,8,8-tetracyanoquino-p-dimethane (TCNQ) forms 2-D structured Fe(II)(NCS)2TCNQ. The magnetic behavior of 1-D Co(NCS)2(THF)2 can be modeled by a 1-D Fisher expression (H = -2JS(i)·S(j)) with g = 2.4 and J/kB = 0.68 K (0.47 cm(-1)) and exhibit weak ferromagnetic coupling. Cr(NCS)2(NCMe)2 and Fe(II)(NCS)2TCNQ magnetically order as antiferromagnets with Tc's of 37 and 29 K, respectively, while Mn(NCS)2(NCMe)2 exhibits strong antiferromagnetic coupling. M(NCS)2(THF)4 and K4[M(NCS)6] (M = V, Ni) are paramagnets with weak coupling between the octahedral metal centers.

catena-Poly[[[bis-(methanol-κO)bis-(seleno-cyanato-κN)manganese(II)]-μ-1,2-bis-(pyridin-4-yl)eth-ene-κ(2) N:N'] 1,2-bis-(pyridin-4-yl)eth-ene mono-solvate]

In the crystal structure of the title compound, {[Mn(NCSe)2(C12H10N2)(CH3OH)2]·C12H10N2} n , the Mn(II) cation is coordin-ated by two terminal N-bonded seleno-cyanate anions, two methanol mol-ecules and two 1,2-bis-(pyridin-4-yl)eth-ene (bpe) ligands within a slightly distorted octahedral geometry. The Mn(II) cations are linked into chains along the c-axis direction by the bpe ligands, which are further connected by inter-molecular O-H⋯N hydrogen bonding between the methanol H atoms and additional bpe mol-ecules that are not coordinated to the metal atoms. The Mn(II) cation and both crystallographically independent bpe ligands are located on centers of inversion, whereas the seleno-cyanate and methanol ligands occupy general positions.

catena-Poly[[[bis(methanol-κO)bis(selenocyanato-κN)manganese(II)]-μ-1,2-bis(pyridin-4-yl)ethane-κ2N:N′] 1,2-bis(pyridin-4-yl)ethane monosolvate]

The reaction of manganese seleno­cyanate with 1,2-bis­(pyridin-4-yl)ethane (bpa) leads to the title compound, {[Mn(NCSe)₂(C₁₂H₁₂N₂)(CH₃OH)₂]·C₁₂H₁₂N₂}_n. The Mn^II cation is coordinated by two N-bonded seleno­cyanate anions, two bpa ligands and two O-bonded methanol mol­ecules, within a slightly distorted octa­hedral geometry. The Mn^II cations and the non-coordinating N-donor ligands are located on centers of inversion while the coordinating N-donor co-ligands are located on a twofold rotation axis. In the crystal, the Mn^II cations are linked into chains along the c-axis direction by the bpa ligands. The chains are further connected via a non-coordinating bpa ligand into layers parallel to (3-10) via O—H⋯N hydrogen-bonding inter­actions.

Assembly of alternating spin-chains with magnetically anisotropic cobalt(II) dimers

A dimeric carboxylato complex of cobalt(II), [Co(2)(II)(1,2-chedc)(2)(Im)(2)] (1) (1,2-chedc = cyclohex-1-ene-1,2-dicarboxylate and Im = imidazole), has been isolated. This complex can be further linked by chloro- or carboxylato-ligands, affording respectively one-dimensional chain structures of (1)(∞)[Co(2)(II)(μ-Cl)(2)(1,2-chedc)(Im)(2)] (2) and (1)(∞)[Co(II)(1,2-chedc)(Im)] (3). Compound 1 shows weak antiferromagnetic interactions passing through the body of the dicarboxylate as well as substantial single-ion magnetic anisotropy (zero-field splitting energy Δ = 8.5 cm(-1)). Both 2 and 3 exhibit typical alternating spin-chain behaviour in the higher-temperature region, but they display disparate behaviours at lower temperatures. For 2, alternating F-AF interactions compete (J(1) = 6.7 K and J(2) = -8.2 K), resulting in paramagnet-like behaviour with no clear evidence of three-dimensional contact. Compound 3 exhibits stronger intrachain AF-AF exchange-coupling interactions (J(1) = -9.3 K and J(2) = -4.3 K), leading to non-diamagnetic ground state due to the tiling of adjacent spins. Long-range magnetic ordering was observed below 10 K. Its narrow hysteresis loop suggests the use of 3 as a soft magnet.

Bis(4,4'-sulfanediyldipyridinium) tetra-chloridonickelate(II) dichloride

In the title compound, (C10H10N2S)2[NiCl4]Cl2, the Ni(2+) cation is tetra-hedrally coordinated by four chloride anions. Two 4,4'-sulfanediyldipyridinium cations and two non-coordinating chloride anions are connected via N-H⋯Cl hydrogen-bonding inter-actions into 20-membered rings, in the middle of which are situated the [NiCl4](2-) complex anions. These rings are stacked in the b-axis direction. The Ni(2+) cation is located on a twofold rotation axis, whereas the chloride anions and the 4,4'-sulfanediyldipyridinium cations occupy general positions.