Synthesis, Crystal Structure, and Magnetic Properties of the Coordination Polymer [Fe(NCS)2(1,2-bis(4-pyridyl)-ethylene)]n Showing a Two Step Metamagnetic Transition

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.

Low-Frequency Sub-Terahertz Absorption in HgII -XCN-FeII (X=S, Se) Coordination Polymers

Self-assembly Fe^II complexes of phenazine (Phen), quinoxaline (Qxn), and 4,4'-trimethylenedipyridine (Tmp) with tetrahedral building blocks of [Hg^II (XCN)₄ ]^2- (X=S or Se) formed six new high-dimensional frameworks with the general formula of [Fe(L)_m ][Hg(XCN)₄ ]⋅solvents (L=Phen, m/X=2/S, 1; L=Qxn, m/X=2/S, 2; L=Qxn, m/X=1/S, 3; L=Qxn, m/X=1/Se, 3-Se; L=Tmp, m/X=1/S, 4; and L=Tmp, m/X=1/Se, 4-Se). 1, 3, and 3-Se show an intense sub-terahertz (sub-THz) absorbance of around 0.60 THz due to vibrations of the solvent molecules coordinated to the Fe^II ions and crystallization organic molecules. In addition, crystals of 1, 4, and 4-Se display low-frequency Raman scattering with exceptionally low values of 0.44, 0.51, and 0.53 THz, respectively. These results indicate that heavy metal Fe^II -Hg^II systems are promising platforms to construct sub-THz absorbers.

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.

Photosynthesis of a Dihydroimidazopyridine Chelate Shines Light on the Reactions of a Photoactivated Iron(III) Complex with O2

The high-spin (S = ⁵/₂) meridional diastereoisomer of [Fe^III(tpena)]²⁺ (tpena = N,N,N'-tris(2-pyridylmethyl)ethylendiamine-N'-acetate), mer-[Fe(tpena)]²⁺, undergoes photolytic CO₂ release to produce an iron(II) intermediate of a radical dihydroimidazopyridine ligand (L^•). The structure of this unprecedented transient iron(II)(L^•) complex is supported by UV-vis and Mössbauer spectroscopies, DFT calculations, as well as the X-ray structural characterization of an μ-oxo iron(III) complex of the oxidized derivative of L^•, namely, [Fe^III₂O(Cl)₂(L⁺)₂](ClO₄)₄(MeCN)₂ (L⁺ = 2-(2-(bis(pyridin-2-ylmethyl)amino)ethyl)-2,3-dihydro-1H-imidazo[1,5-a]pyridin-4-ium). [Fe^III₂O(Cl)₂(L⁺)₂]⁴⁺ is obtained only in the absence of O₂. Under aerobic conditions, O₂ will intercept the iron(II)(L^•) complex to form a putative Fe(III)-alkylperoxide complex which cascades to an iron(II) complex of SBPy3 (SBPy3 = N,N-bis(2-pyridylmethyl)amine-N-ethyl-2-pyridine-2-aldimine). Thus, through different oxidative pathways, the unknown ligand L⁺ or SBPy3 forms by loss of a one-carbon-atom or a two-carbon-atom unit, respectively, from the glycyl arm of tpena. Acceleration of the photodecarboxylation step is achieved by addition of thiocyanate because of transient formation of a more photoreactive NCS^- adduct of [Fe(tpena)]²⁺. This has allowed for kinetic observation of the reaction of [Fe^II(L^•)]²⁺ with O₂ which is, unexpectedly, promoted also by light. We propose that this corresponds to the energy needed for the conversion of the ring-closed radical ligand L^• to a ring-opened tautomer to allow for O₂ insertion between the C and Fe atoms of the iron(II) complex.

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

The asymmetric unit of the title compound, [Ni(NCS)2(C12H9NO)2(CH3OH)2]·CH3OH, comprises one NiII cation, two thio-cyanate anions, two 4-benzoyl-pyridine coligands, two coordinating, as well as one non-coordinating methanol mol-ecule. The NiII cation is coordinated by two terminally N-bonded thio-cyanate anions, the N atoms of two 4-benzoyl-pyridine coligands and the O atoms of two methanol ligands within a slightly distorted octa-hedron. Individual complexes are linked by inter-molecular O-H⋯S hydrogen bonding into chains parallel to [010] that are further connected into layers parallel to (10) by C-H⋯S hydrogen bonds. Additional C-H⋯O hydrogen-bonding inter-actions lead to the formation of a three-dimensional network that limits channels extending parallel to [010] in which the non-coordinating methanol mol-ecules are located. They are hydrogen-bonded to the coordinating methanol mol-ecules. X-ray powder diffraction revealed that the compound could not be prepared as a pure phase.

Tetra-kis(4-benzoyl-pyridine-κN)bis-(iso-thio-cyanato-κN)manganese(II)

The asymmetric unit of the title compound, [Mn(NCS)2(C12H9NO)4], consists of one MnII cation located on a centre of inversion, one thio-cyanate anion and two 4-benzoyl-pyridine co-ligands. The MnII cation is octa-hedrally coordinated by two terminally N-bonded anionic ligands and four N-bonded 4-benzoyl-pyridine co-ligands within a slightly distorted octa-hedron. Individual complexes are linked by inter-molecular C-H⋯O hydrogen-bonding inter-actions into chains running along the c-axis direction. Simultaneous thermogravimetry and differential scanning calorimetry measurements reveal a decomposition in two separate steps, in each of which two co-ligands are removed. The compound obtained after the first step has the composition [Mn(NCS)2(C12H9NO)2] and is of unknown structure, before in the second step decomposition into [Mn(NCS)2] is observed. Magnetic susceptibility measurements show the MnII cations to be in the high-spin state, and that weak anti-ferromagnetic inter-actions between the complexes are present.

Crystal structures of (aceto-nitrile-κN)tris-(pyridine-4-thio-amide-κN)bis-(thio-cyanate-κN)cobalt(II) aceto-nitrile disolvate and tetra-kis-(pyridine-4-thio-amide-κN)bis-(thio-cyanate-κN)nickel(II) methanol penta-solvate

Reaction of Co(NCS)2 or Ni(NCS)2 with pyridine-4-thio-amide in different solvents led to the formation of two compounds with composition [Co(NCS)2(C2H3N)(C6H6N2S)3]·2CH3CN (1) and [Ni(NCS)2(C6H6N2S)4]·5CH3OH (2), respectively. The asymmetric unit of compound 1 consists of one cobalt(II) cation, two thio-cyanate anions, three pyridine-4-thio-amide ligands, one coordinating and two solvate aceto-nitrile mol-ecules. One of the two aceto-nitrile solvate mol-ecules is disordered over two sets of sites in a 0.62:0.38 ratio. The asymmetric unit of compound 2 comprises of one nickel(II) cation, two thio-cyanate anions, four N-bonding pyridine-4-thio-amide ligands and five methanol solvate mol-ecules. In compound 1, the cobalt(II) cations are octa-hedrally coordinated into discrete complexes by two terminal N-bonding thio-cyanate anions, the N atoms of three pyridine-4-thio-amide ligands and one aceto-nitrile mol-ecule. Additional aceto-nitrile solvate mol-ecules are located between the complexes,. The complexes and solvate mol-ecules are linked via inter-molecular hydrogen bonding into a three-dimensional framework. In compound 2, the nickel(II) cations are likewise octa-hedrally coordinated by two terminal N-bonded thio-cyanate anions and four N-bonding pyridine-4-thio-amide ligands into discrete complexes. From their arrangement cavities are formed, in which the methanol solvate mol-ecules are located. Again, the complexes and solvate mol-ecules are linked into a three-dimensional framework by inter-molecular hydrogen bonding.

Crystal structure of octa-kis-(4-meth-oxy-pyridinium) bis-(4-meth-oxy-pyridine-κN)tetra-kis-(thio-cyanato-κN)ferrate(III) bis-[(4-meth-oxypyri-dine-κN)pentakis-(thio-cyanato-κN)ferrate(III)] hexa-kis-(thio-cyanato-κN)ferrate(III) with iron in three different octa-hedral coordination environments

The crystal structure of the title salt, (C6H8NO)8[Fe(NCS)4(C6H7NO)2][Fe(NCS)5(C6H7NO)]2[Fe(NCS)6], comprises three negatively charged octa-hedral FeIII complexes with different coordination environments in which the FeIII atoms are coordinated by a different number of thio-cyanate anions and 4-meth-oxy-pyridine ligands. Charge balance is achieved by 4-meth-oxy-pyridinium cations. The asymmetric unit consists of three FeIII cations, one of which is located on a centre of inversion, one on a twofold rotation axis and one in a general position, and ten thio-cyanate anions, two 4-meth-oxy-pyridine ligands and 4-meth-oxy-pyridinium cations (one of which is disordered over two sets of sites). Beside to Coulombic inter-actions between organic cations and the ferrate(III) anions, weak N-H⋯S hydrogen-bonding inter-actions involving the pyridinium N-H groups of the cations and the thio-cyanate S atoms of the complex anions are mainly responsible for the cohesion of the crystal structure.

Crystal structures of tetra-kis-(pyridine-4-thio-amide-κN)bis-(thio-cyanato-κN)cobalt(II) monohydrate and bis-(pyridine-4-thio-amide-κN)bis-(thio-cyanato-κN)zinc(II)

Reaction of Co(NCS)2 and Zn(NCS)2 with 4-pyridine-thio-amide led to the formation of compounds with composition [Co(NCS)2(C6H6N2S)4]·H2O (1) and [Zn(NCS)2(C6H6N2S)2] (2), respectively. The asymmetric unit of compound 1, consists of one cobalt(II) cation, two thio-cyanate anions, four 4-pyridine-thio-amide ligands and one water mol-ecule whereas that of compound 2 comprises one zinc(II) cation that is located on a twofold rotation axis as well as one thio-cyanate anion and one 4-pyridine-thio-amide ligand in general positions. In the structure of compound 1, the cobalt(II) cations are octa-hedrally coordinated by two terminal N-bonding thio-cyanate anions and by the N atoms of four 4-pyridine-thio-amide ligands, resulting in discrete and slightly distorted octa-hedral complexes. These complexes are linked into a three-dimensional network via inter-molecular N-H⋯S hydrogen bonding between the amino H atoms and the thio-cyanate S atoms. From this arrangement, channels are formed in which the water mol-ecules are embedded and linked to the host structure by inter-molecular O-H⋯S and N-H⋯O hydrogen bonding. In the structure of compound 2, the zinc(II) cations are tetra-hedrally coordinated by two N-bonding thio-cyanate anions and the N atoms of two 4-pyridine-thio-amide ligands into discrete complexes. These complexes are likewise connected into a three-dimensional network by inter-molecular N-H⋯S hydrogen bonding between the amino H atoms and the thio-amide S atoms.

Crystal structures of bis-[4-(di-methyl-amino)-pyridinium] tetra-kis-(thio-cyanato-κN)manganate(II) and tris-[4-(di-methyl-amino)-pyridinium] penta-kis(thio-cyanato-κN)manganate(II)

The crystal structures of the title salts, (C7H11N2)2[Mn(NCS)4] (1) and (C7H11N2)3[Mn(NCS)5] (2), consist of manganese(II) cations that are tetra-hedrally (1) or trigonal-bipyramidally (2) coordinated to four or five terminal N-bonded thio-cyanate ligands, respectively, into discrete anionic complexes. The negative charge is compensated by two (1) or three (2) 4-(di-methyl-amino)-pyridinium cations, which are protonated at the pyridine N atom. The asymmetric unit of compound 1 consists of one anionic complex and two 4-(di-methyl-amino)-pyridinium cations, whereas that of compound 2 consists of two anionic complexes and six 4-(di-methyl-amino)-pyridinium cations, all of them located in general positions. These complexes are linked by N-H⋯S, C-H⋯S and C-H⋯N hydrogen-bonding inter-actions between the 4-(di-methyl-amino)-pyridinium cations and the thio-cyanate ligands into three-dimensional network structures.

Crystal structure of bis-(pyridine-4-carbo-thio-amide-κN1)bis-(thio-cyanato-κN)cobalt(II) methanol monosolvate

The asymmetric unit of the title compound, [Co(NCS)2(C6H6NS)4]·CH3OH, consists of one cobalt(II) cation, two thio-cyanate anions, four pyridine-4-carbo-thio-amide ligands and one methanol mol-ecule that are located in general positions. The CoII cations are coordinated by two terminal N-bonding thio-cyanate anions and four N-bonding pyridine-4-carbo-thio-amide ligands, resulting in discrete and slightly distorted octa-hedral complexes. These complexes are linked into a three-dimensional network via inter-molecular N-H⋯S hydrogen bonding between the amino H atoms and the thio-cyanate and pyridine-4-carbo-thio-amide S atoms. From this arrangement, channels are formed in which the methanol solvate mol-ecules are embedded and linked to the host structure by inter-molecular O-H⋯S and N-H⋯O hydrogen bonding.

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

Two 1D Co(NCS)₂ coordination polymers were synthesized and their magnetic properties were investigated by susceptibility and specific heat measurements as well as DFT and ab initio calculations.

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

Two new ferromagnetic layered Co(ii) and Ni(ii) thiocyanate coordination polymers were synthesized, structurally characterized and investigated for their magnetic behavior using susceptibility measurements and theoretical methods.

A single molecule magnet to single molecule magnet transformation via a solvothermal process: Fe4Dy2 → Fe6Dy3

Under ambient and solvothermal conditions four new compounds [FeIII4LnIII2(μ₃-OH)₂(mdea)₄(m-NO₂C₆H₄COO)₈]·3MeCN and [FeIII6LnIII3(μ₄-O)₃(μ₃-O)(mdea)₅(m-NO₂C₆H₄COO)₉]·3MeCN (Ln = Y and Dy) have been synthesised and their magnetic properties investigated.

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.

Metal-organic frameworks based on the [1,1':3',1''-terphenyl]-3,3'',5,5''-tetracarboxylic acid ligand: syntheses, structures and magnetic properties

The solvothermal reactions of [1,1':3',1''-terphenyl]-3,3'',5,5''-tetracarboxylic acid (H4TPTA) with transition metal cations afforded five novel coordination polymers in the presence of three pyridine ligands (4,4'-bipy = 4,4'-bipyridine, 2,2'-bipy = 2,2'-bipyridine and phen = 1,10-phenanthroline), namely [M(TPTA)0.5(4,4'-bpy)0.5(H2O)2]n (M = Co for (1), Ni for (2)), {[Mn2(TPTA)(2,2'-bpy)H2O]·1.5H2O}n (3), and [M(H2TPTA)(phen)]n (M = Mn for (4), Co for (5)). Their structures were determined by single-crystal X-ray diffraction analyses and further characterized by elemental analyses, IR spectroscopy, powder X-ray diffraction (PXRD), and thermogravimetric (TG) analyses. Polymers 1 and 2 are isomorphous and exhibit 3D 4-fold interpenetrated networks with the point Schläfli symbol of (4(2)·10(4)) (4·10(2)). Polymer 3 shows a 2D layer framework. Polymers 4 and 5 are also isomorphous and each displays a one-dimensional (1D) chain, which further forms a 2D supramolecular architecture via inter-chain π···π interactions. Moreover, variable-temperature magnetic susceptibilities of polymers 3-5 exhibit overall weak antiferromagnetic coupling between the adjacent M(II) ions.

Mn(ii) coordination polymers assembled from 8 or 9-connected trinuclear secondary building units: topology analysis and research of magnetic properties

Two highly-connected trinuclear Mn(ii)-cluster polymers were successfully fabricated. The FC and ZFC data of 1 show a divergence over a temperature range of 40–3.5 K. 2 features a ferrimagnetic chain with a (5/2, 10/2) spin topology.

Layered transition metal carboxylates: synthesis, structural aspects and observation of multi-step magnetic transition through phase diagram

Two new layered transition metal carboxylate frameworks, [Co3(L)2(H2O)6]·2H2O () and [Ni3(L)2(H2O)6]·2H2O () (L = tartronate anion or hydroxymalonic acid), have been synthesized and characterized by X-ray single crystal analysis. Both compounds have similar 2D structures. In both compounds there are two types of metal centers where one center is doubly bridged by the alkoxy oxygen atoms through μ2-O bridging to form a 1D infinite chain parallel to the crystallographic b-axis with the corners shared between the metal polyhedra. Magnetic susceptibility measurements revealed the existence of antiferromagnetic short range correlations between Co(Ni) intra-chain metal centers (with exchange constants JCo = -22.6 and JNi = -35.4 K). At low temperatures, long range order is observed in both compounds at Néel temperatures of 11 (for ) and 16 (for ) K, revealing that other exchange interactions, rather than the intra-chain ones, play a role in these systems. Whereas compound has an antiferromagnetic ground state, compound exhibits a ferromagnetic component, probably due to spin canting. Isothermal magnetization data unveiled a rich phase diagram with three metamagnetic phase transitions below 8 K in compound .