Thiocyanato Anions Research Articles

Synthesis, structural characterization, and thermal properties of monomeric (Mn, Co, Ni, and Zn) and polymeric (Cd) complexes of thiocyanates with benzyl carbazate as an ancillary ligand

Five complexes [M(NCS)2(bc)2] M = Mn (1), Co (2), Ni (3), Zn (4), and [Cd(NCS)2(bc)]n (5), (bc) = benzyl carbazate (benzyl hydrazinecarboxylate), have been synthesized and characterized by physico-chemical and spectroscopic methods. The crystal structures of all five complexes have been confirmed by X-ray structural analysis. These results confirm that 1–4 are isotypes, and all four are centrosymmetric, with two mutually trans N,O chelating (bc) ligands in equatorial positions and a pair of trans-thiocyanate anions in the axial positions. The cadmium complex (5) is a coordination polymer. The asymmetric unit contains a square planar CdN2OS core, in which the (bc) ligand adopts an N, O bidentate coordination mode together with N and S bound thiocyanato anions. Polymer expansion increases the coordination number to six with the N and S bound thiocyanate ligands linking two adjacent complexes. This expansion results in double layers of cadmium octahedra propagating along the c axis direction. The thermal analyses of these compounds show endothermic decomposition processes to give respective metal thiocyanates as intermediates. For the Mn, Co, Ni, and Zn compounds these intermediates decompose exothermically to form metal oxides, whereas the Cd complex forms cadmium sulfide as the end product.

Spin State Crossover, Vibrational, Computational, and Structural Studies of FeII 1‐Isopropyl‐1H‐tetrazole Derivatives

Mononuclear complexes of formula [Fe(iptz)6]X2 {X = BF4– (1), ClO4– (2); iptz = 1‐isopropyl‐1H‐tetrazole} have been synthesized and characterized spectroscopically and structurally. These materials display a gradual and incomplete spin conversion around 95 K on cooling, as well as a reversible thermochromic effect. This magnetic behavior was satisfactorily simulated using the Sorai and Seki domain model (ΔH = 5.9 kJ mol–1, ΔS = 57 J mol–1 K–1 for 1, and ΔH = 5.4 kJ mol–1, ΔS = 63 J mol–1 K–1 for 2). Although spin crossover was observed earlier on a powdered sample of 1, we present the X‐ray crystal structure and magnetic properties of the crystalline compound for the first time. The crystal structures of four new iron complexes are also provided: two polymorphs of [Fe(iptz)4(NCS)2] (3), and compounds [Fe(iptz)4Cl2] (4) and [Fe(iptz)2(H2O)2(CH3SO3)2] (5). Compound 3, which is the first FeII mononuclear thiocyanato complex with coordinated 1‐R‐1H‐tetrazole ligands, is a high‐spin complex. DFT computations enabled the estimation of the spin state energies for the trans and cis isomers of [Fe(iptz)4(NCS)2] as well as the [Fe(iptz)6]2+ cation. The stereoisomerism in 3 related to the mutual orientation of the ligand rings was also studied, along with π‐acceptor properties of the iptz ligand, which are modified by the orientation of the coordinated ligand. The dependence between the Fe–N(CS) distance and the electronic energy of the tilt of the coordinated thiocyanato anion for trans‐[FeL2(NCS)2] and trans‐[FeL4(NCS)2] complexes is discussed, based on the comparison of X‐ray data and DFT modelling for selected complexes.

Template synthesis, structural variation, thermal behavior and antimicrobial screening of Mn(II), Co(II) and Ni(II) complexes of Schiff base ligands derived from benzyl carbazate and three isomers of acetylpyridine

Complexes of Mn(II), Co(II) and Ni(II) with ligands derived from the condensation of benzyl carbazate with three stereoisomers of acetylpyridine have been synthesized using a template method. The complexes have the compositions [Ni(bc-2ap)2] (1), [M(NCS)2(bc-3ap)2(bc)]·H2O; M=Co (2) or Ni (3), [Mn(NCS)2(bc-3ap)4]·2CH3OH (4), [M(NCS)2(bc-3ap)4]·2H2O; M=Co (5) or Ni (6) and [M(NCS)2(bc-4ap)2(CH3OH)2]; M=Mn (7) or Co (8) [where bc=benzyl carbazate, 2ap, 3ap and 4ap=2-, 3- and 4-acetylpyridine]. Characterization of the products involved elemental analysis, IR, UV–vis and 1H NMR, and in the case of 1, 2, 4, 5 and 8 single crystal X-ray structures have been determined. These are all six coordinate with octahedral coordination geometries. Compound 1 is unique with the 2-acetylpyridine ligand undergoing enolisation and deprotonation with two of the uninegative ligands coordinating to the Ni(II) cation in a tridentate chelate fashion. For 2 to 8 the charges of the M(II) cations are balanced in each case by two thiocyanato ligands, mutually cis for 2 and 3 but trans for 4–8. In these latter six-coordinate complexes, 2–8, the benzyl carbazate derived Schiff base ligands bind to the metal atoms in a trans monodentate fashion via the pyridine N atoms, two for 2, 3, 7 and 8 and four such ligands for 4, 5 and 6. In addition to the thiocyanato anions, the remaining coordination positions are filled by bidentate chelate carbazate molecules for 2 and 3, and two trans oriented methanol molecules for 7 and 8. Thermal reactivity of the complexes was studied by TG-DTA. In addition, antimicrobial screening confirmed that all of the complexes, except 1, have a moderate to good range of activity against both Gram-positive and Gram-negative bacterial strains and also against fungi.

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

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

Synthesis, Structures and Properties of Cobalt Thiocyanate Coordination Compounds with 4-(hydroxymethyl)pyridine as Co-ligand

Reaction of Co(NCS)2 with 4-(hydroxymethyl)pyridine (hmpy) leads to the formation of six new coordination compounds with the composition [Co(NCS)2(hmpy))4] (1), [Co(NCS)2(hmpy)4] × H2O (1-H2O), [Co(NCS)2(hmpy)2(EtOH)2] (2), [Co(NCS)2(hmpy)2(H2O)2] (3), [Co(NCS)2(hmpy)2]n∙4 H2O (4) and [Co(NCS)2(hmpy)2]n (5). They were characterized by single crystal and powder X-ray diffraction experiments, thermal and elemental analysis, IR and magnetic measurements. Compound 1 and 1-H2O form discrete complexes, in which the Co(II) cations are octahedrally coordinated by two terminal thiocyanato anions and four 4-(hydroxymethyl)pyridine ligands. Discrete complexes were also observed for compounds 2 and 3 where two of the hmpy ligands were substituted by solvent, either water (3) or ethanol (2). In contrast, in compounds 4 and 5, the Co(II) cations are linked into chains by bridging 4-(hydroxymethyl)pyridine ligands. The phase purity was checked with X-ray powder diffraction. Thermogravimetric measurements showed that compound 3 transforms into 5 upon heating, whereas the back transformation occurs upon resolvation. Magnetic measurements did not show any magnetic exchange via the hmpy ligand for compound 5.

Synthesis, structures, and properties of Mn(II) and Cd(II) thiocyanato coordination compounds with 2,5-dimethylpyrazine as co-ligand

AbstractReaction of manganese (II) thiocyanate with 2,5-dimethylpyrazine leads to the formation of three new coordination compounds of compositions Mn(NCS)2(2,5-dimethylpyrazine)2(H2O)2(1), Mn(NCS)2(H2O)2(MeOH)2-tris(2,5-dimethylpyrazine) solvate (2), and Mn(NCS)2(H2O)4-tetrakis(2,5-dimethylpyrazine) solvate (3) that were characterized by single crystal X-ray diffraction. In their crystal structures, the Mn(II) cations are sixfold coordinated by two terminally N-bonded thiocyanato anions and two water molecules as well as by two 2,5-dimethylpyrazine ligands (1), two ethanol (2), or two water molecules (3), within slightly distorted octahedra. In compounds2and3, additional 2,5-dimethylpyrazine ligands are located in the cavities of the structures as solvate molecules. X-ray powder diffraction has shown that compounds1and2cannot be prepared as pure phases and that batches of compound3contain only minor traces of a contamination. Differential thermoanalysis and thermogravimetry have revealed that upon heating of compound3, an intermediate of composition Mn(NCS)2(2,5-dimethylpyrazine) (4) is formed, which cannot be obtained from solution. To mimic the structure of4, single crystals of a Cd compound of the same composition (5) were prepared from the liquid phase, and single crystal X-ray analysis has shown that it is isotypic to4.

Synthesis, crystal structures and properties of Ni(NCS)2-4-(hydroxymethyl)pyridine coordination compounds

Reaction of Ni(NCS)2 with 4-(hydroxymethyl)pyridine leads to the formation of five new coordination compounds. The crystal structures of compounds 1-H2O, 1, 2 and 3 consist of discrete complexes, in which the Ni cations are coordinated by two terminal N-bonded thiocyanato anions and four neutral co-ligands, within slightly distorted octahedra. In the structure of 4, two Ni cations are linked into dimers by pairs of μ-1,3-bridging anions and are further connected into chains by the 4-(hydroxymethyl)pyridine ligand. Compound 4 shows an antiferromagnetic transition at TN=6.7K. The compounds were additionally characterized by IR spectroscopy, thermoanalytical methods and X-ray powder diffraction.

Thiocyanato Coordination Polymers with Isomeric Coordination Networks – Synthesis, Structures, and Magnetic Properties

AbstractThe reactions of M(NCS)2 (M = Mn, Fe, and Ni) with 4‐acetylpyridine (4‐Acpy) in water lead to the formation of discrete complexes of composition M(NCS)2(4‐Acpy)2(H2O)2, in which the metal cations are coordinated only N‐terminally to the thiocyanato anions. When heated, these precursors dehydrate, and some of them transform into compounds of composition [M(NCS)2(4‐Acpy)2]n, in which the metal cations are linked by pairs of μ‐1,3‐bridging anionic ligands into chains (1D isomer). In contrast, the thermal decomposition of Ni(NCS)2(4‐Acpy)4 or crystallization from solution leads to the formation of an isomeric 2D network of the same composition, which is thermodynamically more stable than the 1D isomer. Temperature‐dependent magnetic measurements of the 1D isomer [Fe(NCS)2(4‐Acpy)2]n at 200 Oe reveal antiferromagnetic ordering at TN = 4.5 K. Field‐dependent measurements show a metamagnetic transition into a saturated paramagnetic phase at a critical field of ca. 700 Oe. In contrast, magnetic measurements of the 2D isomer [Ni(NCS)2(4‐Acpy)2]n at 1000 Oe show a ferromagnetic transition at TC = 8.6 K, whereas only paramagnetic behavior is observed for the Ni 1D isomer.

Synthesis, Structure, and Properties of Coordination Polymers with Layered Transition‐Metal Thiocyanato Networks

AbstractReaction of 4‐tert‐butylpyridine (tBP) with transition‐metal thiocyanates leads to the formation of compounds of composition [M(NCS)2(tBP)4] [M = Mn (1‐Mn), Fe (1‐Fe), Co (1‐Co), Ni (1‐Ni)] that consist of discrete complexes, in which the metal centers are octahedrally coordinated by two terminal thiocyanato anions and four tBP ligands. If less tBP is used in the synthesis, two compounds of composition [M(NCS)2(tBP)2]n with M = Co (2‐Co) and Ni (2‐Ni) are obtained, in which the metal centers are linked into a 2D network by single thiocyanato anions. Thermal decomposition of 1‐Co leads to the formation of an additional modification of [Co(NCS)2(tBP)2] (3‐Co). Magnetic measurements of 2‐Ni and 2‐Co reveal that 2‐Ni shows a ferromagnetic phase transition at Tc = (14.8 ± 0.1) K and 2‐Co shows a transition to the magnetic state with uncompensated magnetic moment at (3.15 ± 0.03) K.

Investigations on the influence of the metal center coordination on the magnetic properties of Mn thiocyanato coordination polymers

Reaction of manganese(II) thiocyanate with the monodentate ligand 4-benzylpyridine (bp) leads to the formation of two compounds of composition Mn(NCS)2(4-benzylpyridine)4 (1-bp) and Mn(NCS)2(4-benzylpyridine)2 (2-bp). Compound 1-bp forms discrete complexes in which the Mn cations are coordinated by four 4-benzylpyridine ligands and two terminal N-bonding thiocyanato anions within slightly distorted octahedra. In compound 2-bp the metal cations are surrounded by two cis-coordinating 4-benzylpyridine ligands, two cis-coordinating S-bonded thiocyanato anions and two trans-coordinating N-bonded anionic ligands. The Mn cations are linked into zig–zag-like chains by pairs of μ-1,3-bridging anionic ligands. DTA–TG measurements on 1-bp prove that 2-bp is obtained as intermediate. Magnetic measurements on the chain compound 2-bp show dominating antiferromagnetic interactions between the Mn centers. On cooling a maximum is observed in the susceptibility curve indicative for an antiferromagnetic transition. The results of the magnetic measurements are compared with those obtained for other Mn thiocyanato chain compounds in which the thiocyanato anions are trans-coordinated.

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

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

Experimental and theoretical investigation of octahedral and square-planar isothiocyanato complexes of Ni(II) with acylhydrazones of 2-(diphenylphosphino)benzaldehyde

Octahedral and square-planar isothiocyanato complexes of Ni(II) with the condensation derivative of 2-(diphenylphosphino)benzaldehyde and Girard’s T reagent were synthesized and characterized by elemental analysis, IR spectroscopy and X-ray crystallography. Results of magnetic measurements for octahedral Ni(II) complex were also reported. In all the complexes the ligand is coordinated as tridentate via the phosphorus, the imine nitrogen and the carbonyl oxygen atoms while the remaining coordination positions are occupied with thiocyanato anions. Coordination of deprotonated phosphine ligand results in formation of square-planar complexes, while the octahedral complex was formed with protonated ligand. Reaction energetics with both forms of ligand were studied by the means of DFT and results were in complete agreement with experimental observations. Furthermore, ligand field splitting analysis gave the deeper insight in the relationship of the isolated complex coordination environment and protonation of the ligand.

Synthesis, Structures and Properties of a Fourth Modification of [Cd(NCS)2(pyridine)2]n

AbstractReaction of Cd(NCS)2 with pyridine in water accidently lead to the formation of crystals of a fourth modification of [Cd(NCS)2(pyridine)2]n, which most likely corresponds to form I reported by Taniguchi et al. but which was not structurally characterized by these authors. This modification crystallizes in the monoclinic space group C2/c with a = 10.6032(3) Å, b = 15.8676(5) Å, c = 26.2795(8), b = 96.001(2) °and V = 4397.2(2) Å3. The structure of this compound is very similar to that of form III reported recently, in which the Cd cations are octahedrally coordinated by two pyridine ligands and four thiocyanato anions. The cations are linked by pairs of anionic ligands into chains, in which the thiocyanato anions are always trans‐coordinated. Further investigations show that larger amounts of pure form I cannot be prepared because it is always contaminated with form II, in which the thiocyanato anions are cis‐coordinated. Solvent mediated conversion experiments using mixtures of the trans‐modifications I and III as well as the cis‐modification II prove that form III disappears first and therefore, is less stable than the second trans‐modification I. IR and Raman spectroscopic investigations show, that all forms cannot be distinguished from each other using these methods.

Synthesis, Crystal Structures, and Thermal and Spectroscopic Properties of Thiocyanato Coordination Compounds with 3-Acetylpyridine as a Ligand

Abstract The reaction of transition metal thiocyanates with 3-acetylpyridine (3-Acpy) leads to the formation of compounds of compositions M(NCS)2(3-Acpy)4 (M1; M = Mn, Fe, Ni) and M(NCS)2(3- Acpy)2(H2O)2 (M2; M = Mn, Fe, Ni). Thermogravimetric investigations show that in the first step some of these compounds transform into the new coordination polymers M(NCS)2(3-Acpy)2 (M3 with M = Mn, Fe and Ni), that decompose into the new compounds M(NCS)2(3-Acpy) (M4 with M = Mn and Ni) in the second step. Unfortunately, the powder patterns of compounds M3 and M4 cannot be indexed, and there are strong indications that these compounds are contaminated with a small amount of the precursor or unknown crystalline phases. IR spectroscopic investigations indicate that in compounds M3 the metal cations are linked by μ-1,3-bridging thiocyanato anions into 1D or 2D coordination polymers that are further linked by the 3-Acpy ligands in compounds M4.

Synthesis, Structures, and Properties of Transition Metal Thiocyanato Coordination Compounds with 4‐(4‐Chlorobenzyl)pyridine as Ligand

AbstractReactions of transition metal thiocyanates with 4‐(4‐chlorobenzyl)pyridine (Clbp) lead to the formation of compounds of composition M(NCS)2(4‐(4‐chlorobenzyl)pyridine)4 (Mn‐1, Fe‐1/I, Fe‐1/II, Ni‐1, and Cd‐1) and M(NCS)2(4‐(4‐chlorobenzyl)pyridine)2 (Mn‐2, Ni‐2, and Cd‐2). In the crystal structures of compounds M‐1 the metal cations are octahedrally coordinated by two terminal N‐bonded thiocyanato anions and four Clbp ligands, whereas in compounds M‐2 the metal cations are linked by μ‐1, 3‐bridging anionic ligands. IR spectroscopic investigations show that the value of the asymmetric C–N stretching vibration depends on the coordination mode of the thiocyanato ligand and the nature of the metal cations. The thermal properties were investigated by simultaneous differential thermoanalysis and thermogravimetry as well as temperature dependent X‐ray powder diffraction. On heating compound Ni‐1 looses half of the Clbp ligands and transforms into Ni‐2. Clbp deficient intermediates were also detected on thermal decomposition of Mn‐1 and Fe‐1/I but the samples are of low crystallinity and therefore, their structures cannot be determined. Magnetic investigations reveal that Ni‐2 shows only Curie‐Weiss paramagnetism without any magnetic anomaly.

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.

Syntheses and Characterization of Two New M(II)-5,5′-dimethyl-2,2′-bipyridine (M = Cd and Pb) Coordination Polymers and Study of Their Thermal and Electrochemical Properties

Two new cadmium(II) and lead(II)-thiocyanato coordination polymers with 5,5′-dimethyl-2,2′-bipyridine (5,5′-dm-2,2′-bpy) as chelating ligands were synthesized and characterized by elemental analysis, IR and 1H NMR spectroscopy and by X-ray crystallography. Thermal and electrochemical properties were also studied as well. These complexes have formed formula [Cd(5,5′-dm-2,2′-bpy)(NCS)2]n (1) and [Pb(5,5′-dm-2,2′-bpy)(CH3COO)(NCS)]n (2). The coordination numbers of CdII in 1 and PbII in 2 are six (CdN4S2) and seven (PbN3O3S2), respectively. In 2, “stereo-chemically active” electron lone pairs and the coordination spheres were hemidirected. Bridging properties of thiocyanato anions in 1 and 2 created one- and two-dimensional coordination polymers, respectively. The supramolecular features in these complexes were guided and controlled by weak directional intermolecular interactions.

Influence of the co-ligand on the magnetic and relaxation properties of layered cobalt(II) thiocyanato coordination polymers.

Reaction of Co(NCS)2 with 1,2-bis(4-pyridyl)-ethane (bpa) leads to the formation of [Co(NCS)2(bpa)2]n, which, on heating, transforms into the new layered coordination polymer [Co(NCS)2(bpa)]n. This compound can also be prepared in solution, but because no reasonable single crystals are available, its crystal structure was determined from X-ray powder data from scratch. In the crystal structure of [Co(NCS)2(bpa)]n, the cobalt(II) cations are coordinated by two S-bonded and two N-bonded thiocyanato anions and two N atoms of the bpa co-ligands in a distorted octahedral geometry. The cobalt(II) cations are linked into chains by pairs of μ-1,3 bridging thiocyanato anions. These chains are further connected into layers by the 1,2-bis(4-pyridyl)-ethane ligand. The compound was magnetically characterized, and, for comparative purposes, the complementary magnetic study of a known and very similar compound, [Co(NCS)2(bpe)]n (bpe = 1,2-bis(4-pyridyl)-ethylene), was also undertaken. The compounds differ in their interchain interactions, which are antiferromagnetic but significantly greater for [Co(NCS)2(bpe)]n. Magnetic measurements indicate that [Co(NCS)2(bpa)]n is a canted antiferromagnet with Néel temperature TN = 3.1 K and that Co(NCS)2(bpe) is an antiferromagnet with TN = 4.0 K. Both compounds show a metamagnetic transition with a critical field HC ∼ 40 Oe and ∼ 400 Oe, respectively. Magnetic relaxations were studied by means of dc and ac methods and analyzed using the Argand diagrams. Except for the thermally activated single chain and domain wall relaxations observed for both compounds, temperature-independent slow relaxations were observed for [Co(NCS)2(bpa)]n.

Synthesis, Structures, Polymorphism, and Magnetic Properties of Transition Metal Thiocyanato Coordination Compounds

Reaction of manganese, iron, and nickel thiocyanate with 4-ethylpyridine leads to the formation of single crystals of compounds with composition M(NCS)2(L)4 (1), M(NCS)2(L)2(H2O)2 (2-Mn), and M(NCS)2(L)2 (3) with M = Mn, Fe, and Ni and L = 4-ethylpyridine. For most compounds, different polymorphic modifications are observed, and their transition behavior and thermodynamic stability was investigated. Additionally, compounds of composition M(NCS)2(L)2 (M = Mn or Ni) were prepared from solution and by thermal decomposition of compounds 1 and 2, which lead to different stable and metastable modifications. The crystal structures of most compounds were determined by single crystal X-ray diffraction and some of them by Rietveld refinements. Compounds 1 and 2 consist of octahedrally coordinated discrete complexes with terminal N-bonded thiocyanato anions. In compounds 3, the metal cations are linked by pairs of μ-1,3-bridging thiocyanato anions into chains. Surprisingly, thermal decomposition of Ni(NCS)2(4-ethylpyridine)4 leads to the formation of a new compound of composition Ni(NCS)2(4-ethylpyridine) (4-Ni). Magnetic measurements reveal that 3-Mn/II and 3-Mn/III show antiferromagnetic ordering at TN = 21.5 and 23.9 K and that 4-Ni is a metamagnet with a critical field of 1.4 kOe at 2 K. All other compounds show Curie or Curie–Weiss behavior with no magnetic anomalies.

Synthesis, Thermal and Magnetic Properties of New Coordination Compounds based on Mn(NCS)2 with 2‐Chloropyrazine and 2‐Methylpyrazine as neutral Co‐Ligand

AbstractReaction of manganese(II) thiocyanate with 2‐chloropyrazine leads always to the formation of a compound of composition Mn(NCS)2(2‐chloropyrazine)4 (1‐Mn/Cl) that consists of discrete complexes, in which the manganese cation is coordinated by two terminal thiocyanato anions and four 2‐chloropyrazine ligands. In contrast, with 2‐methylpyrazine only an aqua complex of composition Mn(NCS)2(2‐methylpyrazine)2(H2O)2 (1‐Mn/CH3) is obtained that also consists of discrete octahedrally coordinated complexes. Moreover, a few single crystals of Mn(NCS)2(2‐chloropyrazine)4·Mn(NCS)2(2‐chloropyrazine)2(H2O)2·2‐chloropyrazine trisolvate (2‐Mn/Cl) and Mn(NCS)2(2‐methylpyrazine)2(H2O)2·Mn(NCS)2(H2O)4 (2‐Mn/CH3) were accidently obtained but no larger amounts are available. On heating, 1‐Mn/Cl and 1‐Mn/CH3 transforms into new compounds of composition Mn(NCS)2(L)2 (L = 2‐chloropyrazine) (4‐Mn/Cl) and 2‐methylpyrazine (3‐Mn/CH3). Surprisingly on further heating 1‐Mn/CH3 looses additional 2‐methylpyrazine ligands and transforms into a new compound of composition Mn(NCS)2(2‐methylpyrazine) (4‐Mn/CH3). Compound 4‐Mn/Cl is isotypic to its cobalt(II) analog and 4‐Mn/CH3 is isotypic to Cd(NCS)2(2‐methylpyrazine) reported recently and therefore, both structures were refined by the Rietveld method. The crystal structures of both compounds are strongly related. They consists of dimeric units, in which each two manganese cations are linked by pairs of μ‐1, 3‐bridging thiocyanato anions, which are further connected into layers by single μ‐1, 3‐bridging anionic ligands. In contrast to 4‐Mn/Cl, in 4‐Mn/CH3 these layers are further linked into a 3D coordination network by the 2‐methylpyrazine ligands. Magnetic measurements reveal that 1‐Mn/Cl, 1‐Mn/CH3, and 3‐Mn/CH3 shows only Curie‐ or Curie‐Weiss paramagnetism, whereas 4‐Mn/Cl and 4‐Mn/CH3 shows antiferromagnetic ordering at TN = 22.9 K and at 26.5 K. The results of these investigations are compared with those obtained for related compounds.