Terminal N-bonded Thiocyanato Anions Research Articles

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.

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.

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.

The influence of the metal cation and the N-donor ligand on the reactivity and structures of Cd and Zn coordination compounds with 3-bromopyridine and 3-chloropyridine

Reaction of cadmium thiocyanate and zinc thiocyanate with an excess of 3-bromopyridine and 3-chloropyridine leads to single crystals of four coordination compounds of composition M(NCS)2(3-bromopyridine)4 (M=Cd (Cd1-Br), Zn (Zn1-Br)) and M(NCS)2(3-chloropyridine)4 (M=Cd (Cd1-Cl), Zn (Zn1-Cl)). These compounds forms pairs of isotypic compounds (Cd1-Br and Zn1-Br in space group P-1 and Cd1-Cl and Zn1-Cl in space group C2/c) in which the metal cation are octahedral coordinated by two terminal thiocyanato anions and four neutral N-donor ligands into discrete complexes. If less N-donor ligands are used in the synthesis, compounds of composition M(NCS)2(3-bromopyridine)2 (M=Cd (Cd2-Br), Zn (Zn2-Br)) and M(NCS)2(3-chloropyridine)2 (M=Cd (Cd2-Cl), Zn (Zn2-Cl)) are obtained. In the crystal structure of the isotypic compounds Cd2-Br and Cd2-Cl (monoclinic space group P21/c) the metal cations are octahedral coordinated by two N-donor ligands and four thiocyanato anions and are linked into chains by the anionic ligands. In contrast, the Zn compounds Zn2-Br and Zn2-Cl are not isotypic but form similar discrete complexes in which the metal cations are tetrahedral coordinated by two terminal N-bonded thiocyanato anions and two neutral N-donor ligands. On heating compounds 1 half of the ligands are removed and a transformation into compounds 2 is observed. The structures and reactivity of these compounds are discussed and compared with those of related compounds.

Co(NCS)2(1,2-bis(2-pyridyl)ethylene)]n: A new 1D coordination polymer that shows a metamagnetic transition

Reaction of Co(NCS)2 with 1,2-bis(2-pyridyl)ethylene (2-bpe) leads to four new coordination compounds of composition [Co(NCS)2(CH3OH)4]·2(2-bpe) solvate (1), Co(NCS)2(2-bpe)2(CH3OH)2 (2), Co(NCS)2(2-bpe)2 (3) and Co(NCS)2(2-bpe) (4). The crystal structure of compounds 1 and 2 consists of discrete complexes in which the cobalt(II) cations are octahedral coordinated by two terminal thiocyanato anions and four methanol molecules in 1 and by two terminal N-bonded thiocyanato anions, two 2-bpe ligands and two methanol molecules in 2. In compound 3 also discrete complexes are found but in contrast to 1 and 2 each cobalt(II) cation is tetrahedral coordinated by two terminal N-bonded thiocyanato anions and two 1,2-bis(2-pyridyl)ethylene (2-bpe) ligands. In the most 2-bpe deficient compound 4 the Co cations are also tetrahedral coordinated but the metal cations are linked into chains by the 2-bpe ligands. Magnetic measurements on compound 3 shows only Curie–Weiss paramagnetism whereas for compound 4 a metamagnetic transition is observed at a critical field of HC=1.9kOe with antiferromagnetic ordering below and saturated paramagnetism above HC. These results are compared with those for the corresponding compound with 1,2-bis(4-pyridyl)ethylene as ligand.

Exploration and synthesis of condensed coordination networks with modified magnetic properties

Eight new coordination polymers based on Ni(NCS)2 and 2-methylpyrazine were discovered, structurally characterized and most of them investigated for their thermal and magnetic properties. In the crystal structures of Ni(NCS)2(2-methylpyrazine)4 (1), Ni(NCS)2(2-methylpyrazine)4·2-methylpyrazine solvate (2) and Ni(NCS)2(2-methylpyrazine)4·ethanol solvate (3), the nickel(II) cations are always octahedral coordinated by two terminal N-bonded thiocyanato anions and four N-bonded 2-methylpyrazine ligands into discrete complexes. The crystal structures of Ni(NCS)2(2-methylpyrazine)2(H2O)2 (4) and Ni(NCS)2(2-methylpyrazine)2(CH3OH)2 (5) also consist of discrete complexes, but in contrast to compounds 1–3 two terminal bonded 2-methylpyrazine ligands are exchanged by two water and methanol molecules, respectively. In [Ni(NCS)2(2-methylpyrazine)3(H2O)]·[Ni(NCS)2(2-methylpyrazine)4] (6) two different complexes are observed, in which one nickel(II) cation is coordinated by two terminal N-bonded thiocyanato anions, three 2-methylpyrazine ligands and one water molecule, whereas the second cation is coordinated by two terminal N-bonded thiocyanato anions and four 2-methylpyrazine ligands. Compounds 2, 3, 4 and 5 transformed into a 2-methylpyrazine deficient 1 : 2 (1 : 2 = ratio between metal and 2-methylpyrazine) compound with the composition Ni(NCS)2(2-methylpyrazine)2 (7) on heating. On further heating this compound subsequently transformed into a 1 : 1 compound with the composition [Ni(NCS)2(2-methylpyrazine)]n (8). Compound 7 can only be prepared by thermal decomposition and therefore, its structure was solved ab initio from X-ray powder data. It consists of [Ni(NCS)]2 dimers that are μ-1,3-bridged by single thiocyanato anions into layers. Single crystal structure analysis of compound 8 proves that nickel(II) cations are linked by the thiocyanato anions into Ni–(NCS)2–Ni double chains, which are further connected by the 2-methylpyrazine ligands into layers. Magnetic measurements on compounds 2, 3, 4 and 5 show only Curie or Curie–Weiss paramagnetism, whereas in the ligand-deficient compound 7 metamagnetic behavior is observed. The results of these investigations are discussed and compared with those obtained for related coordination compounds with e.g. pyrazine and pyridine as neutral co-ligands.

Synthesis, structures and magnetic properties of Fe(ii) and Co(ii) thiocyanato coordination compounds: on the importance of the diamagnetic counterparts for structure determination

Reaction of Fe(NCS)2 and Co(NCS)2 with 2-methylpyrazine in different molar ratios and solvents at room temperature leads to the formation of five new coordination compounds of composition M(NCS)2(2-methylpyrazine)2(H2O)2 (M = Fe (1-Fe) , Co (1-Co)), Co(NCS)2(2-methylpyrazine)2(CH3OH)2 (2-Co) and Co(NCS)2(2-methylpyrazine)4·2-methylpyrazine solvate (3-Co). In all of these compounds, discrete complexes are found in which the metal cations are octahedrally coordinated by two terminal N-bonded thiocyanato anions and four N- or O-donor co-ligands. On heating compounds 1-3 in a thermobalance new coordination polymers of composition M(NCS)2(2-methylpyrazine)2 (M = Co (4-Co) , Fe (4-Fe)) are obtained in the first step, which transform into M(NCS)2(2-methylpyrazine) (M = Co (5-Co) , Fe (5-Fe)) in the second. Because of the low chalcophilicity of these cations, compounds 4 and 5 are not accessible from solution. Further investigations prove that 4-Co and 4-Fe obtained by thermal decomposition are of low crystallinity, might be isotypic and might consist of metal cations, in which the anionic ligands are only terminal N-bonded. In contrast, 5-Co and 5-Fe are of good crystallinity but their structure cannot be solved from X-ray powder data. However, a compound of the same composition (5-Cd) based on the more chalcophilic cadmium can easily be crystallized from solution and characterized by single crystal X-ray diffraction. This compound is isotypic to 5-Co and 5-Fe and therefore their structures were determined by Rietveld refinements. In their crystal structures the metal atoms are linked by μ-1,3-bridging thiocyanato anions into a 2D network. Magnetic measurements reveal that compounds 1-4 show only Curie-Weiss paramagnetism and that for 5-Fe antiferromagnetic ordering is observed. In contrast, 5-Co shows metamagnetic behavior with a very large critical field. Finally, it was shown that 4-Co and 4-Fe are hygroscopic and transform within minutes into the hydrates 1-Co and 1-Fe.

Synthesis and crystal structures of Zn(ii) and Co(ii) coordination compounds with ortho substituted pyridine ligands: two structure types and polymorphism in the region of their coexistence

Reaction of cobalt(II) thiocyanate or zinc(II) thiocyanate with 2-methylpyridine, 2-bromopyridine and 2-chloropyridine at room-temperature lead to tetrahedral complexes of composition M(NCS)2L2 (M = Co, Zn; 1: L = 2-methylpyridine, 2: L = 2-bromopyridine, 3: L = 2-chloropyridine). For all compounds, X-ray diffraction showed that the M2+ cations are coordinated by two terminal N-bonded thiocyanato anions and two substituted pyridine ligands in a distorted tetrahedral geometry. In all cases, complexes derived from cobalt and zinc with the same ligands are isomorphous. Eight crystalline solids were studied, which belong to only two different structure types: two polymorphs were obtained for the compounds with 2-chloropyridine: 3-Mα is isotypic with the 2-methylpyridine complexes 1-M and crystallizes in the orthorhombic space group P212121, whereas 3-Mβ and the isotypic 2-bromopyridine complexes 2-M adopt space group Pbcn. The structure types differ with respect to molecular conformation and packing: the complexes crystallizing in the former type are less distorted with respect to metal coordination; in the latter structure type, the angle subtended by the two ligands is by far the largest in the coordination sphere. P212121 allows for a more efficient intermolecular arrangement, whereas the complex geometry in Pbcn features shorter non-bonding distances between the ortho substituents of the pyridine ligands and comes closer to the gas phase geometry. DSC measurements gave no hints of a transformation between these modifications but from a melt of 3-Coα, 3-Coβ was obtained. Solvent mediated conversion experiments revealed that 3-Mα represents the thermodynamically stable form at room-temperature whereas 3-Mβ is metastable, in agreement with its lower density. Therefore, the thermodynamically stable phases with 2-chloropyridine as ligand adopt the crystal structure of the compounds with 2-methylpyridine, whereas the metastable forms are isotypic to the compounds with 2-bromopyridine.

New cadmium thio- and selenocyanato coordination compounds: Structural snapshots on the reaction pathway to more condensed anionic networks

In this contribution several new coordination compounds on the basis of cadmium(II) thio- and selenocyanate with pyrimidine as co-ligand were prepared and investigated for their structural, thermal and spectroscopic properties. The reaction of cadmium(II) thiocyanate with pyrimidine leads to the formation of four compounds, which from a structural point of view are closely related. In the most pyrimidine-rich 1 : 2 compound [Cd(NCS)(2)(pyrimidine)(2)](n) (1A) (1 : 2 = ratio between metal salt and the co-ligand pyrimidine) the Cd cations are linked by the pyrimidine ligands into layers and are additionally coordinated by two terminal N-bonded anions. In the 2 : 3 compound {[Cd(NCS)(2)](2)(pyrimidine)(3)}(n) (1B) the Cd cations are linked into chains by μ-1,3 bridging thiocyanato anions, which are connected into layers by only half of the pyrimidine ligands, whereas the other co-ligands are only terminal coordinated. Further reduction of the pyrimidine content leads to the formation of the 1 : 1 2D compound [Cd(NCS)(2)(pyrimidine)](n) (1CI) in which the terminal N-bonded thiocyanato anions become bridging. Surprisingly, crystallization experiments lead to the formation of an additional pyrimidine-deficient intermediate of composition {[Cd(NCS)(2)](3)(pyrimidine)(2)}(n) (1D), in which some of the μ-1,3 coordinated anions transform into μ-1,1,3 bridging thiocyanato anions. Consequently the four structures can be used as snapshots of intermediates on the way to a more condensed thiocyanato coordination network. In contrast, with cadmium selenocyanate only two different compounds were obtained. The 1 : 2 compound [Cd(NCSe)(2)(pyrimidine)(2)](n) (2A) is not isotypic to 1A and shows a completely different coordination topology whereas the pyrimidine-deficient 1 : 1 compound (2B) shows a more condensed network with μ-1,3 coordinating selenocyanato anions. On heating, the 1 : 2 compound 1A decomposes into Cd(NCS)(2)via a new polymorphic modification (1CII) as intermediate which is metastable, whereas the 1 : 2 selenocyanato compound 2A transforms into the 1 : 1 compound 2B on heating which cannot be obtained phase pure under these conditions. If faster heating rates are used, there are indications for the formation of a 3 : 2 compound, which is amorphous to X-rays. The results are compared with those obtained for related thio- and selenocyanato coordination polymers with pyridine, pyridazine and pyrazine as co-ligand. Moreover, their impact on the structures and thermal reactivity of analogous paramagnetic compounds is discussed in detail. Based on the structural data of compound 1D the unknown structures of two intermediates were determined, which are formed in the thermal decomposition reaction of the Mn and Fe thiocyanato pyrimidine coordination polymers, reported recently.

Thermal Decomposition Reactions as Tool for the Synthesis of New Metal Thiocyanate Diazine Coordination Polymers with Cooperative Magnetic Phenomena

Reaction of nickel thiocyanate with pyrimidine at room temperature leads to the formation of the new ligand-rich 1:2 (1:2 = ratio between metal and ligand) compound [Ni(NCS)(2)(pyrimidine)(2)](n) (2) which is isotypic to [Co(NCS)(2)(pyrimidine)(2)](n) (1) reported recently. In the crystal structure, the Ni(2+) ions are coordinated by four N atoms of pyrimidine ligands, which connect the metal centers into layers, and two N atoms of terminal bonded thiocyanato anions within slightly distorted octahedra. If the synthesis is performed under solvothermal conditions and an excess of the metal thiocyanate is used, single crystals of the ligand-deficient 1:1 compound [Ni(NCS)(2)(pyrimidine)](n) (4) are obtained. Investigations on the synthesis of this compound show that it is always contaminated with large amounts of the corresponding ligand-rich 1:2 compound 2. In the crystal structure, the Ni(2+) ions are coordinated by two N atoms of pyrimidine ligands, which connect the metal centers into chains, and two N atoms as well as two S atoms of mu-1,3 bridged thiocyanato anions, which conntect these chains into layers, within a slightly distorted octahedral geometry. On heating compounds 1 and 2 transform quantitatively into the ligand-deficient 1:1 Ni compound 4 and its isotypic Co compound 3. If nickel and cobalt thiocyanate are reacted with an excess of pyrimidine in a solvent-free reaction, discrete ligand-rich 1:4 complexes of composition [M(NCS)(2)(pyrimidine)(4)] (M = Co 5 and Ni 6) are obtained, which could be determined by single crystal structure analysis. In their crystal structure the metal ions are coordinated by four terminal bonded pyrimidine ligands and two terminal N-bonded thiocyanato anions. For the ligand-rich 1:2 and ligand-deficient 1:1 compounds magnetic measurements were performed, which reveal different magnetic properties: The 1:2 compounds show a ferromagnetic and the 1:1 compounds an antiferromagnetic ordering at lower temperatures.

Coordination polymer changing its magnetic properties and colour by thermal decomposition: synthesis, structure and properties of new thiocyanato iron(ii) coordination polymers based on 4,4′-bipyridine as ligand

Thermal decomposition of the ligand-rich 1:2 precursor solvate (1:2 = ratio between metal and ligand) [{Fe(mu2-bipy-N,N')(NCS)2(H2O)2} x bipy]n (1I) (bipy = 4,4-bipyridine) reported recently leads to the stepwise formation of two new intermediates: a ligand-rich solvate-free 1:2 compound of composition [Fe(NCS)2(bipy)2]n (2) and a ligand-deficient 1:1 compound of composition [Fe(NCS)2(bipy)]n (3). The thermal decomposition is accompanied by a colour change from red (1I), via orange (2) into yellow (3). In the crystal structure of 2 the iron(II) cations are coordinated by four N atoms of bridging bipy ligands, which connect the metal centers into layers, and two terminal N-bonded thiocyanato anions within slightly distorted octahedra. In the crystal structure of 3 the iron(II) cations are coordinated by two N atoms of bridging bipy ligands, which are connected by the metal centers into chains, and two N atoms as well as two S atoms of mu-1,3 bridging thiocyanato anions within a slightly distorted octahedral geometry. The thiocyanato anions connect these chains into layers. Due to their connection mode of the metal centers, only for the latter compound can cooperative magnetic phenomena be expected. Magnetic measurements revealed two different magnetic properties: The 1:2 compounds 1I and 2 show Curie-Weiss paramagnetism and the 1:1 compound 3 shows an antiferromagnetic ordering at T(N) = 5.5 K. The reversibility of water reintercalation in the solvent-free compound 2 was investigated and followed by UV-Vis spectroscopy. Herein a new polymorphic metastable modification 1II of the pristine precursor compound 1I was obtained and characterized by single crystal X-ray determination.