One-dimensional (1D) [Ni(mnt)2]−-based spin-Peierls-like complexes: Structural, magnetic and transition properties

Bis(1-ethyl-4,4′-bipyridin-1-ium) bis(1,2-dicyanoethene-1,2-dithiolato-κ2S,S′)nickelate(II)

In the anion of the title compound, (C₁₂H₁₃N₂)[Ni(C₄N₂S₂)₂], the Ni^II atom is coordinated by four S atoms from two 1,2-di­cyano­ethene-1,2-di­thiol­ate (mnt) ligands in a suqare-planar geometry. Weak C—H⋯N and C—H⋯S hydrogen bonds between the 1-ethyl-4,4′-bipyridin-1-ium cations and mnt anions and weak π–π inter­actions between the pyridine rings of the cations [centroid–centroid distances = 3.808 (3) and 3.972 (3) Å] lead to a two-dimensional network parallel to (010).

1,1'-(Ethane-1,2-di-yl)dipyridinium bis-(1,2-di-cyano-ethene-1,2-di-thiol-ato-κ(2) S,S')cuprate(II)

In the title ion-pair complex, (C12H14N2)[Cu(C4N2S2)2], the complex anion exhibits a highly twisted coordination environment around the tetra-coordinated Cu(II) atom. The dihedral angles between the 1,2-di-cyano-ethene-1,2-di-thiol-ato ligands and between the two pyridine rings in the cation are 37.49 (3) and 29.18 (10)°, respectively. Weak C-H⋯N and C-H⋯S hydrogen bonds link the cations and anions into a three-dimensional network.

Observation of intramolecular vibrations cooperating with the magnetic phase transition in a nickel-bis-dithiolene compound

A new one-dimensional (1-D) ion-pair compound, [1,7-bis(1-methylimidazolium)heptane][Ni(mnt)(2)](2) (mnt(2-) = maleonitriledithiolate), was synthesized and characterized structurally and magnetically. This compound shows a spin-Peierls-type transition at around 235 K. Its crystal structure belongs to the monoclinic system with space group C2/c and the magnetic [Ni(mnt)(2)](-) anions form uniform stacks in the high-temperature (HT) phase. The crystal undergoes a transformation into the triclinic space group P1 accompanied by the magnetic transition and the anion stacks become dimerized in the low-temperature (LT) phase. The entropy changes (ΔS) are estimated to be 0.772 J K(-1) mol(-1) for the spin-Peierls-type transition, from DSC data, which is much less than the spin entropy change (ΔS = R ln 2 ≈ 5.76 J K(-1) mol(-1)), indicating that a substantial short-range order persists above the transition temperature. The variable temperature IR spectra showed that the peak positions and intensities for the bands near 1160 and 725 cm(-1), which correspond respectively to the ν(C-C) + ν(C-S) mode of the mnt(2-) ligands and the rocking vibration mode of the methylene group γ(r)(CH(2)) in the cation moiety, undergo an abrupt change at around 240 K, close to the transition temperature. This observation demonstrates that the intramolecular vibrations of both the anion and the counter-cation probably couple with the spins to cooperate with the spin-Peierls-type phase transition in this 1-D spin system.

Influence of isotope substitution on lattice and spin-Peierls-type transition features in one-dimensional nickel bis-dithiolene spin systems

Four new 1D spin-Peierls-type compounds, [D(5)]1-(4'-R-benzyl)pyridinium bis(maleonitriledithiolato)nickelate ([D(5)]R-Py; R=F, I, CH(3), and NO(2)), were synthesized and characterized structurally and magnetically. These 1D compounds are isostructural with the corresponding non-deuterated compounds, 1-(4'-R-benzyl)pyridinium bis(maleonitriledithiolato)nickelate (R-Py; R=F, I, CH(3), and NO(2)). Compounds [D(5)]R-Py and R-Py (R=F, I, CH(3), and NO(2)) crystallize in the monoclinic space group P2(1)/c with uniform stacks of anions and cations in the high-temperature phase and triclinic space group P1 with dimerized stacks of anions and cations in the low-temperature phase. Similar to the non-deuterated R-Py compounds, a spin-Peierls-type transition occurs at a critical temperature for each [D(5)]R-Py compound; the magnetic character of the 1D S=1/2 ferromagnetic chain for [D(5)]F-Py and the 1D S=1/2 Heisenberg antiferromagnetic chain for others appear above the transition temperature. Spin-gap magnetic behavior was observed for all of these compounds below the transition temperature. In comparison to the corresponding R-Py compound, the cell volume is almost unchanged for [D(5)]F-Py and shows slight expansion for [D(5)]R-Py (R=I, CH(3), and NO(2)) as well as an increase in the spin-Peierls-type transition temperature for all of these 1D compounds in the order of F>I≈CH(3)≈NO(2). The large isotopic effect of nonmagnetic countercations on the spin-Peierls-type transition critical temperature, T(C), can be attributed to the change in ω(0) with isotope substitution.

Bis[1-(eth-oxy-carbonyl-meth-yl)pyridinium] bis-(1,2-dicyano-ethene-1,2-dithiol-ato-κ(2)S,S')nickelate(II)

The asymmetric unit of the title ion-pair complex, (C(9)H(12)NO(2))(2)[Ni(C(4)N(2)S(2))(2)], contains two 1-(eth-oxy-carbonyl-meth-yl)pyridinium cations and one bis-(1,2-dicyano-ethene-1,2-dithiol-ato)nickelate(II) dianion, which exhibits a slightly distorted square-planar coordination geometry. In the crystal, the cations are linked by strong C-H⋯O hydrogen bonds into C(6) chains along [100]. The cations and anions are linked into a three-dimensional architecture by weak C-H⋯N and C-H⋯S inter-actions.

Bis(4-dimethyl-amino-1-ethyl-pyridinium) bis-(1,2-dicyano-ethene-1,2-dithiol-ato-κ(2)S,S')nickelate(II)

The asymmetric unit of the title complex, (C₉H₁₅N₂)₂[Ni(C₄N₂S₂)₂], comprises one 4-dimethyl­amino-1-ethyl­pyri­din­ium cation and one half of a [Ni(mnt)₂]²⁻ (mnt²⁻ = maleo­nitrile­dithiol­ate) anion; the complete anion is generated by the application of a centre of inversion. The Ni^II ion is coordinated by four S atoms of two mnt²⁻ ligands and exhibits a square-planar coordination geometry.

Observation of metal ion dependent packing structures and magnetic behaviors of metal-bis-1, 2-dithiolene complexes

The crystal structures and magnetic properties were investigated experimentally and theoretically for two S = ½ spin chain complexes, which consist of [M(mnt)(2)](-) (M = Pt for 1 or Pd for 2) with 1-(4'-bromo-2'-flurobenzyl)-4-aminopyridinium (1-BrFBz-4-NH(2)Py(+)). The 1-BrFBz-4-NH(2)Py(+) cations exhibit different molecular conformations and arrangements in 1 and 2; the [M(mnt)(2)](-) anions form regular stacks in 1, whereas they form irregular stacks in 2. In addition, the intermolecular interactions between the [M(mnt)(2)](-) anions and cations are also different from each other in the crystals of 1 and 2. Complex 1 shows the magnetic characteristics of a low-dimensional antiferromagnetic coupling spin system with a spin-Peierls-type transition around 7 K, and complex 2 exhibits diamagnetism over the temperature range of 5-300 K. Theoretical analyses, based on the calculations for the charge density distributions of [Pt(mnt)(2)](-) and [Pd(mnt)(2)](-) anions and the magnetic exchange constants within the anion spin chains, addressed the diverse molecular alignments in the crystals of 1 and 2 and distinct magnetic behaviors between 1 and 2.

Bis(4-cyano-1-methyl-pyridinium) bis-(1,2-dicyano-ethene-1,2-dithiol-ato-κS,S')cuprate(II)

The title ion-pair compound, (C₇H₇N₂)₂[Cu(C₄N₂S₂)₂], was obtained by the direct reaction of CuCl₂·2H₂O, disodium maleonitrile­dithiol­ate (Na₂mnt) and 4-cyano-1-methyl­pyridinium iodide. The anion and one pyridinium cation lie entirely on a mirror plane, whereas for the other cation, a crystallographic mirror plane runs through the N and para-C atoms of the pyridine ring, the methyl C atom, and the cyano group. In the crystal, ions are linked into a three-dimensional network by C—H⋯N hydrogen bonds.

1-Butyl-pyridinium bis-(1,2-dicyano-ethene-1,2-dithiol-ato)nickelate(III)

The Ni^III atom in the anion of the title complex, (C₉H₁₄N)[Ni(C₄N₂S₂)₂], is coordinated by four S atoms of two maleonitrile­dithiol­ate ligands, and exhibits a square-planar coordination geometry.

Bis(8-hy-droxy-1-methyl-quinolin-1-ium) bis-(1,2-dicyano-ethene-1,2-dithiol-ato)nickelate(II) dihydrate

In the title ion-pair complex, (C(10)H(10)NO)(2)[Ni(C(4)N(2)S(2))(2)]·2H(2)O, the anion has crystallographically imposed centre of symmetry. The Ni(II) atom exhibits a slightly distorted square-planar coordination geometry. In the crystal, the water mol-ecule links anions and cations into a three-dimensional network via O-H⋯N, O-H⋯S and O-H⋯O hydrogen bonds. The structure is further stabilized by weak S⋯π contacts [S⋯centroid = 3.8047 (9) Å] and π-π stacking inter-actions [centriod-centroid distance = 3.8653 (7) Å].

3-Butyl-1-methyl-1H-imidazol-3-ium bis-(1,2-dicyano-ethene-1,2-dithiol-ato-κS,S')nickel(III)

In the title compound, (C₈H₁₅N₂)[Ni(C₄N₂S₂)₂], the Ni^III atom is coordinated by four S atoms of two maleonitrile­dithiol­ate ligands and exhibits a distorted square-planar geometry. In the crystal, the cations and anions are connected alternately by weak inter­molecular C—H⋯N hydrogen bonds, forming a zigzag chain along [201].

Unexpected isotopic effect of a deuteriumed countercation on the spin-Peierls-type transitions in quasi-one-dimensional bis(maleonitriledithiolato)nickelate monoanion spin systems

Two deuteriumed quasi-one-dimensional (quasi-1D) spin-Peierls-type compounds, 4-X-benzylpyridinium-d(5) bis(maleo-nitriledithiolato)nickelate (the substituent X = Br or Cl), were structurally characterized. Compared with the corresponding non-deuteration compounds, the transition temperature T(C) shifts to higher temperature. The isotopic effect of countercations on T(C) is probably related to the change of phonon frequency ω(0) and 'chemical pressure' resulted from the substitution of pyridine by pyridine-d(5).

Bis[1-(4-cyano-benz-yl)pyrazinium] bis-(1,2-dicyano-ethene-1,2-dithiol-ato)nickelate(II)

The asymmetric unit of the title complex, (C₁₂H₁₀N₃)₂[Ni(C₄N₂S₂)₂], consists of one 1-(4-cyano­benz­yl)pyrazinium cation and one half of an [Ni(mnt)₂]²⁻ dianion (mnt²⁻ is 1,2-dicyano­ethene-1,2-dithiol­ate). The Ni²⁺ ion is located on an inversion center and is coordinated by four S atoms from two mnt²⁻ ligands, exhibiting a square-planar coordination geometry. The cation adopts a conformation where both the pyrazine ring and the benzene ring are twisted with respect to the C—C—N reference plane by 16.5 (2) and 69.8 (1)°, respectively.

Bis(3,5,7-triaza-1-azoniatricyclo-[3.3.1.1]deca-ne) bis-(1,2-dicyano-ethene-1,2-dithiol-ato)nickelate(II)

The asymmetric unit of the title complex, (C₆H₁₃N₄)₂[Ni(C₄N₂S₂)₂], comprises one 1-azonia-3,5,7-triaza­tricyclo­[3.3.1.1^3,7]decane cation and one half of an [Ni(mnt)₂]²⁻ (mnt²⁻ is maleonitrile­dithiol­ate or 1,2-dicyano­ethene-1,2-dithiol­ate) dianion. The Ni²⁺ ion is located on a center of inversion and is coordinated by four S atoms from two mnt²⁻ ligands in a square-planar coordination mode. Inter­molecular N—H⋯N hydrogen-bond inter­actions link one anion and two cations in the crystal structure.