NCS Anions Research Articles

Synthesis, structural characterization and antitumor activities of manganese and cobalt isothiocyanate complexes with 2,2’-bipyridine

[Mn(SCN)2(2,2′-bipy)2] (1) and [Co(SCN)2(2,2′-bipy)2] (2) were synthesized at ambient temperature by adding aqueous solutions of manganese(II) or cobalt(II) chloride hydrate to aqueous acetonitrile solutions of 2,2′-bipyridine (2,2′-bipy) and potassium thiocyanate. Elemental analyses, FT-IR and UV–vis spectra were used to characterize 1 and 2. Single crystal X-ray diffraction was used to analyze the crystal structures of 1 and 2, revealing that the two are structurally similar. The molecular structures of 1 and 2 consist of Mn or Co ion chelated by two molecules of 2,2′-bipy through four nitrogen atoms and two NCS anions, giving distorted octahedral geometries. The isothiocyanate group is not bridging, instead, two ligands coordinate in a cis arrangement to the manganese or cobalt center by their nitrogen atoms while the sulfur atoms are free. Through hydrogen bonding and π–π stacking interactions, the discrete units of 1 and 2 extend to 3D supramolecular networks with flower and fishbone-like structures. The luminescence behavior of 2,2′-bipy, 1 and 2 were investigated. On HepG2 (liver) and MCF-7 (breast) cancer cells, the anticancer effects of 1 and 2 were evaluated. The activity of 1 and 2 on MCF-7 is more significant than that of HepG2. The IC50 of 1 was lower in HepG2 and MCF-7 cells than for 2.

Field-Assisted Slow Magnetic Relaxation in a Six-Coordinate Co(II)-Co(III) Complex with Large Negative Anisotropy.

The reaction of Co(CH3COO)2·4H2O with the Schiff base ligand LH4 derived from o-vanillin and tris(hydroxymethyl)aminomethane produces the dinuclear mixed-valence complex [CoIICoIII(LH2)2(CH3COO)(H2O)](H2O)3 (1), which has been investigated using IR spectroscopy, X-ray crystallography, temperature-dependent magnetic susceptibility, magnetization, HFEPR spectroscopy, and ac susceptibility measurements at various frequencies, temperatures, and external magnetic fields. The structure of 1 consists of neutral molecules in which two cobalt ions with distorted octahedral geometries, CoIIO6 and CoIIIN2O4, are bridged by two deprotonated -CH2O- groups of the two LH22- ligands. 1 completes a series with Cl, Br, NO3, and NCS anions published before by different authors. Low-temperature HFEPR measurements reveal that the ground electronic state of the Co(II) center in 1 is a highly anisotropic Kramers doublet; the effective g values of 7.18, 2.97, and 1.96 are frequency-independent over the frequency ranges 200-630, 200-406, and 200-300 GHz for the highest, intermediate, and lowest geff values, respectively. The two lower values were not seen at higher frequencies because the magnetic field was not high enough. Temperature-dependent magnetic susceptibility and field-dependent magnetization data confirm high magnetic anisotropy of the easy axis type. Complex 1 behaves as a single-ion magnet under a small applied external field and demonstrates two relaxation modes that strongly depend on the applied static dc field. The observation of multiple relaxation pathways clearly distinguishes 1 from the Cl and Br analogues.

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

[Co(NCS)2(py)2]n (py = pyridine) is composed of ferromagnetic chains of Co(ii) cations connected by double NCS bridges. The chains are irregular because of two crystallographically inequivalent Co(ii) cations. The coordination polyhedron of the Co(ii) cations is a distorted octahedron built from two N and two S atoms of four equatorial NCS anions and two apical N atoms of the pyridine ligands. Magnetic and specific heat studies show that the compound undergoes a phase transition at 3.7 K to a ferromagnetic state. The determined magnetic interactions, intrachain (J/kB = 28 K) and interchain (zJ'/kB = 0.5 K), confirm the quasi 1D Ising magnetic character of [Co(NCS)2(py)2]n. Using AC magnetic susceptibility measurements the energy barriers for magnetization reversal of different relaxation processes were determined including those of the individual chains. By means of high field-high frequency ESR study the magnetic excitations were observed and explained in the frame of the Ising model in agreement with the results of the magnetic study. Ab initio calculations confirm the high magnetic anisotropy of the system and allow determination of the direction of the easy-axis. The broken symmetry DFT calculations support the ferromagnetic intrachain interactions. The energetic relations relevant for relaxations are discussed. It is concluded that the magnetic model of [Co(NCS)2(py)2]n is not a pure Ising but the transversal exchange plays a role.

Synthesis, crystal structure and DFT studies of a Zinc(II) complex of 1,3-diaminopropane (Dap), [Zn(Dap)(NCS)2][Zn(Dap)(NCS)2]n. The additional stabilizing role of S⋯π chalcogen bond

A zinc(II) complex of 1,3-diaminopropane (Dap), [Zn(Dap)(NCS)2][Zn(Dap)(NCS)2]n (1) has been prepared and characterized by elemental analysis, IR, 1H &13C NMR spectroscopy, and its crystal structure was determined by X-ray crystallography. The crystal structure of 1 consists of two types of molecules, a discrete monomer and a polymeric one. In the monomeric unit, the zinc atom is bound to one terminal Dap molecule and to two N-bound thiocyanate ions, while in the polymeric unit, Dap acts as a bridging ligand forming a linear chain. The Zn(II) ions in both assume a slightly distorted tetrahedral geometry. The structures of two systems: the [Zn(Dap)(NCS)2][Zn(Dap)(NCS)2]3 complex as a model of 1 and [Zn(Dap)(NCS)2]4 as a simple polymeric structure were optimized with the B3LYP-D3 method. The DFT results support that the experimentally determined structure (1) is more stable in comparison to a simple polymeric structure, [Zn(Dap)(NCS)2]n (2). The interaction energies (ΔE) for NCS anions obtained by B3LYP-D3 method are about −145 kcal mol−1, while the calculated ΔE values for neutral organic ligands are about twice smaller. The X-ray structure of 1 shows that the complex is stabilized mainly by hydrogen bonds. We also found that weak chalcogen bonds play an additional role in stabilization of compound 1. Some of the intermolecular S⋯N distances are smaller than the sum of the van der Waals radii of the corresponding atoms. To the best of our knowledge, this is the first study that shows the structure where the trivalent sulfur is involved in formation of a S⋯π chalcogen bond. The NBO and NCI analyses confirm the existence of this kind of interactions.

Spectroscopic and DFT studies of zinc(II) complexes of diamines and thiocyanate; crystal structure of (cis-1,2-diaminocyclohexane)bis(thiocyanato-κN)zinc(II)

Zinc(II) complexes of diamines, cis-1,2-diaminocyclohexane (Dach) and N,N,N,N-tetramethylethylenediamine (Tmen), [Zn(Dach)(NCS)2] (1) and [Zn(Tmen)(NCS)2] (2) have been prepared and characterized by elemental analysis, IR, 1H &13C NMR spectroscopy. The crystal structure of [Zn(Dach)(NCS)2] (1) was determined by X-ray crystallography. In 1, the Zn(II) atom is bound to one 1,2-diaminocyclohexane molecule and to two terminal thiocyanate ions via the nitrogen atoms adopting a slightly distorted tetrahedral geometry. In the crystal structure, molecules are linked through intermolecular NH⋯S hydrogen bonds, forming chains running along the a axis. The structures of 1 and 2 as well as of [Zn(En)(NCS)2] (3) (En = 1,2-diaminoethane) were predicted using theoretical (DFT) method. The interaction energies (ΔE) for NCS anions obtained by B3LYP-D3 method are about −140 kcal mol−1, while the calculated ΔE values for neutral organic ligands are about twice smaller. The atomic charges and second-order interaction energies between orbitals were calculated with natural bond orbital (NBO) analysis.

Synthesis, X-ray characterization, DFT calculations and Hirshfeld surface analysis of Zn(ii) and Cd(ii) complexes based on isonicotinoylhydrazone ligand

In this manuscript we report the synthesis and X-ray characterization of four Zn(II) complexes and three Cd(II) complexes with an asymmetrical hydrazone–pyridine based ligand {HL = 2-acetyl-pyridyl-isonicotinoylhydrazone (HAPIH)}; i.e. {[Zn(HL)2](NO3)2·H2O} (1), [Zn(HL)Br2] (2), [Zn(HL)I2] (3), [Zn(HL)(NCS)2] (4), [Cd(L)2] (5), {[Cd(HL)Br2]·CH3OH} (6) and {[Cd(HL)I2]·2CH3OH} (7). The Schiff base acts as a tridentate N2O-donor ligand through the oxygen, the imine and pyridine nitrogen atoms in all the complexes. In most complexes, the ligand is observed to coordinate as a zwitterion since the proton in the hydrazine group (N–NH–CO) shifted to the uncoordinated pyridine ring, except in 7. On the other hand, in 5 the ligand acts as a negatively charged species and is bound to the cadmium center in the enolic form (N–NC–O−). In complexes 2–4, 6 and 7, the coordination geometry around each metal center is distorted trigonal bipyramidal, with the coordination sphere of the metal completed by two halide or NCS anions. On the other hand, in homoleptic complexes 1 and 5, the metal, chelated by two tridentate Schiff base ligands, exhibits an octahedral geometry. In the crystal packing of all compounds, the pyridine rings favour π–π interactions among the symmetry related complexes. The noncovalent interactions among the complexes have been analyzed using Hirshfeld surface analysis and DFT calculations using Grimme's D3 dispersion correction to properly describe the π–π interactions.

Crystal structure of bis-[trans-(1,4,8,11-tetra-aza-cyclo-tetra-decane-κ(4) N)bis-(thio-cyanato-κN)chromium(III)] tetra-chlorido-zincate from synchrotron data.

The structure of the title compound, [Cr(NCS)2(cyclam)]2[ZnCl4] (cyclam = 1,4,8,11-tetra-aza-cyclo-tetra-decane, C10H24N4), has been determined from synchrotron data. The asymmetric unit contains two independent halves of the Cr(III) complex cations and half of a tetra-chlorido-zincate anion. In each complex cation, the Cr(III) atom is coordinated by the four N atoms of the cyclam ligand in the equatorial plane and by two N-bound NCS(-) anions in a trans axial arrangement, displaying a distorted octa-hedral geometry with crystallographic inversion symmetry. The mean Cr-N(cyclam) and Cr-N(NCS) bond lengths are 2.065 (4) and 1.995 (6) Å, respectively. The macrocyclic cyclam moieties adopt centrosymmetric trans-III configurations with six- and five-membered chelate rings in chair and gauche configurations, respectively. The [ZnCl4](2-) anion, which lies about a twofold rotation axis, has a slightly distorted tetra-hedral geometry. The crystal packing is stabilized by hydrogen-bonding inter-actions between the N-H groups of the cyclam ligands, the S atoms of the NCS(-) groups and the Cl(-) ligands of the anion.

Cis-(1,4,8,11-Tetraazacyclotetradecane-κN4)bis(thiocyanato-κN)chromium(III) thiocyanate

The crystal structure of [Cr(NCS)2(cyclam)]NCS (cyclam = 1,4,8,11-tetra­aza­cyclo­tetra­deca­ne, C10H24N4) has been determined by using synchrotron radiation at 98 K. The CrIII atom is in a slightly distorted octa­hedral environment with four N atoms of the macrocyclic ligand and two N-coordinated NCS− anions in cis positions. The average Cr—N(cyclam) and Cr—NCS bond lengths are 2.085 (5) and 1.996 (15) Å, respectively. In the crystal, the uncoordinating SCN− anion is hydrogen bonded through N—H⋯S and N—H⋯N inter­actions to neighbouring complex cations.

Spin-crossover in a trans-[FeL2(NCS)2] family (L = triaryltriazole): remote substituent effects on spin transition modes and temperature

We report the syntheses, characterisations, and spin-crossover behaviours of four mononuclear trans-[Fe(L1-L4)2(NCS)2] complexes (L = 4-(p-R1-phenyl)-3,5-bis(2-pyridyl)-4H-1,2,4-triazole and 4-(p-methylphenyl)-3-(p-R2-phenyl)-5-(2-pyridyl)-4H-1,2,4-triazole, (1) R1 = Cl (L1); (2) R1 = Me (L2); (3) R2 = MeO (L3); (4) R2 = F (L4)). The X-ray single crystal structural analysis reveals that 1 and 2 crystallize in the triclinic space group P1, whereas 3·0.5H2O and 4 crystallize in the monoclinic space group P2(1)/c, and all complexes possess a similar distorted [FeN6] octahedron with two trans-positions NCS(-) anions. Changing of the distal substituent on the phenyl ring of the triaryltriazoles causes differences in the crystal packing of the complexes that are key to their magnetic properties. Magnetic measurements indicate that 1 shows an abrupt transition with T(1/2) = 235 K, 2 displays a 3 K hysteresis loop with T(1/2)(↓) = 217 K and T(1/2)(↑) = 220 K, 3 exhibits a gradual spin transition with T(1/2) = 156 K and 4 undergoes an incomplete (70%) spin transition with T(1/2) = 97 K. The substituted group effects and intermolecular interactions appear to be critical to spin transition modes and temperature in this family.

Complexes of a porphyrin-like N4-donor Schiff-base macrocycle

A metal-free 16-membered N4-donor [1 + 1] Schiff-base macrocycle was isolated as HL(Pr)·2acid, by 1 : 1 condensation of diphenylamine-2,2'-dicarboxaldehyde (1), dipropylene triamine and an excess of either acetic or formic acid, or as HL(Pr)·(tosylic acid) when just one equivalent of tosylic acid was employed. Interestingly, the acid-free synthesis employed for the 14-membered analogue HL(Et) failed to generate pure HL(Pr) macrocycle, but nevertheless the crude product obtained was able to be used in subsequent complexation reactions to form five mononuclear complexes: Zn(II)L(Pr)(BF4)·H2O·0.5IPA (where IPA is isopropylalcohol), [Cu(II)L(Pr)](BF4), [Ni(II)L(Pr)](BF4), [Co(II)L(Pr)](BF4)·0.5H2O, [Fe(III)L(Pr)(NCS)2]·1.5H2O. Crystal structure determinations show that, like the HL(Et) analogues, [Ni(II)L(Pr)](BF4) features a square planar N4 coordinated Ni(II) centre and [Fe(III)L(Pr)(NCS)2]·0.15MeOH·0.2H2O features an octahedral N6 coordinated Fe(III) centre (two NCS anions bound axially). In both cases the N4-donor macrocycle is bound equatorially to the metal ion. Cyclic voltammograms of the BF4 complexes were carried out in MeCN vs. 0.01 mol L(-1) AgNO3/Ag and revealed multiple redox processes. The Zn(II) complex exhibits multiple ligand-centered redox processes. Interestingly, [Ni(II)L(Pr)](BF4) has two reversible redox processes, at E(m) = +0.38 (ΔE = 0.06 V) and -1.7 V (ΔE = 0.06 V), whereas the previously reported analogue [Ni(II)L(Et)](BF4) had a process at E(pc) = +0.59 V with only a weak return wave. Likewise, [Cu(II)L(Pr)](BF4) has a reversible process, at E(m) = -1.17 V (ΔE = 0.06 V) plus a process at E(pc) = +0.45 V, whereas previously reported [Cu(II)L(Et)](BF4) only featured irreversible processes, with the oxidation occurring at E(pc) = +0.50 V.

Tetrakis(1-phenyl-1H-imidazole-κN3)bis(thiocyanato-κN)nickel(II)

The title compound, [Ni(NCS)2(C9H8N2)4], crystallizes with two independent half-mol­ecules in the asymmetric unit and the NiII ions situated on centres of symmetry. In both independent mol­ecules, the NiII ion displays a compressed octa­hedral environment formed by four N atoms from the 1-phenyl-1H-imidazole ligands, which define the equatorial plane, with a mean Ni—N distance of 2.119 (11) Å, and two axial N atoms from two NCS− anions, with a mean Ni—N distance of 2.079 (7) Å. The crystal packing exhibits weak inter­molecular S⋯S contacts of 3.411 (2) Å.

Tetrakis(1-allyl-1H-imidazole-κN3)bis(thiocyanato-κN)manganese(II)

The structure of the title compound, [Mn(NCS)2(C6H8N2)4], consists of isolated mol­ecules of [Mn(NCS)2(Aim)4] (Aim = 1-allyl­imidazole), which contain a compressed octa­hedral MnN6 chromophore (site symmetry ). The NCS− anions are trans and four N atoms from the Aim ligands define the equatorial plane. The mean Mn—N(Aim) and Mn—N(NCS) distances are 2.270 and 2.229 Å, respectively. Weak C—H⋯N inter­actions contribute to the crystal packing stability.

Interdependence of Conformational and Chemical Reaction Dynamics during Ion Assembly in Polar Solvents

We have utilized time-resolved vibrational spectroscopy to study the interdependence of the conformational and chemical reaction dynamics of ion assembly in solution. We investigated the chemical interconversion dynamics of the LiNCS ion pair and the (LiNCS)(2) ion-pair dimer, as well as the spectral diffusion dynamics of these ionic assemblies. For the strongly coordinating Lewis base solvents benzonitrile, dimethyl carbonate, and ethyl acetate, we observe Li(+) coordination by both solvent molecules and NCS(-) anions, while the weak Lewis base solvent nitromethane shows no evidence for solvent coordination of Li(+) ions. The strong interaction between the ion-pair dimer structure and the Lewis base solvents leads to ion-pair dimer solvation dynamics that proceed more slowly than the ion-pair dimer dissociation. We have attributed the slow spectral diffusion dynamics to electrostatic reorganization of the solvent molecules coordinated to the Li(+) cations present in the ion-pair dimer structure and concluded that the dissociation of ion-pair dimers depends more critically on longer length scale electrostatic reorganization. This unusual inversion of the conformational and chemical reaction rates does not occur for ion-pair dimer dissociation in nitromethane or for ion pair association in any of the solvents.

Synthesis and complexes of an N4 Schiff-base macrocycle derived from 2,2′-iminobisbenzaldehyde

An N(4) tetradentate [1 + 1] Schiff base metal free macrocycle HL was prepared, by 1 : 1 condensation of 2,2'-iminobisbenzaldehyde (1) and diethylenetriamine, and characterised. Seven mononuclear complexes, [Zn(II)L(py)](BF(4)) (2), [Cu(II)L](BF(4))]·H(2)O (3), [Ni(II)L](BF(4))·H(2)O (4), [Co(II)L](BF(4))]·H(2)O (5), Fe(III)L(BF(4))(2)·2H(2)O·MeCN (6), [Co(III)L(NCS)(2)]·0.3py (7) and [Fe(III)L(NCS)(2)] (8), of L(-) are reported. The Cu(II) and Ni(II) complexes were prepared by a template approach whereas the others were accessed by metallation of pre-formed HL. The X-ray crystal structure determinations show that [Cu(II)L](BF(4)) and [Ni(II)L](BF(4)) feature square planar N(4) coordinated Cu(II) and Ni(II) centres, respectively, whereas [Fe(III)L(NCS)(2)]·NO(2)Me features an octahedral N(6) coordinated Fe(III) centre (two NCS anions bound axially) and the Zn(II) complex, which crystallised as 2{[Zn(II)L(py)](BF(4))}·py, features square pyramidal Zn(II) ions (a pyridine molecule bound axially). In all cases the N(4) macrocycle is bound equatorially to the metal ion. Cyclic voltammograms of the soluble BF(4) complexes, 2-5, were carried out in MeCN vs. 0.01 mol L(-1) AgNO(3)/Ag and revealed multiple, mostly irreversible or quasi-reversible, redox processes. The Zn(II) complex 2 exhibited two irreversible oxidation processes and one irreversible reduction process, all of which are ligand-centered. The Ni(II) complex 4 showed a process with a weak return wave at E(m) = +0.57 V (ΔE = 0.05 V). Interestingly, after controlled potential coulometry experiments on 2, 3 and 4 (at +0.48, +0.61 and +0.71 V which transferred 1.2, 1.0 and 1.6 e(-) equiv. per complex, respectively), a new reversible or quasi-reversible process was obtained, with a lower potential than beforehand (E(m) (ΔE)/V = +0.16 (0.08), +0.31 (0.13) and +0.45 (0.11) respectively).

Bis(2,3,5-triphenyltetrazolium) tetrathiocyanatocobaltate(II)

The title compound, (C19H15N4)2[Co(NCS)4], has two crystallographycally different molecules of bis­(2,3,5-triphenyl­tetra­zolium) tetra­thio­cyanatecobaltate in the asymmetric unit. There are only minor geometric differences between them. Each cobalt(II) ion is coordinated by the N atoms of four NCS anions, showing the magnitude of the magnetic moment expected from the NCS− crystal field strength.

Pseudohalogeno Complexes of Sterically Hindered Tripyrrinatopalladium (TrpyPd) Fragments

AbstractEight new pseudohalogeno complexes of sterically hindered TrpyPd fragments 4–11 have been prepared by salt metathesis in one step from known trifluoroacetates TrpyPdOAcF 1–3, using sodium salts of N3, NCO, NCS, NCSe, dicyanamide (dca) and tricyanomethanide (tcm) anions. Despite the propensity of the co‐ligands to bind to two or more metal centres in a bridging coordination mode all new complexes have been shown by NMR spectroscopy to be essentially monomeric in solution. X‐ray diffraction studies performed on TrpyPdNCS(6), TrpyPddca(8), TrpyPddca(9), and TrpyPdtcm(10) revealed the presence of two different conformers in the solid state, one with a helically distorted Trpy backbone for 6 and 10, and one with an almost planar tripyrrole but a tetrahedral distortion of the PdII coordination, a so‐called pseudoplanar form, for 8 and 9. Interestingly the helical forms are also detected by unusual wavenumbers for the νCN stretching bands in their IR spectra. The reason for the occurrence of two different conformers in the solid state appears to be the crystal packing which depends mainly on the shape of the anionic co‐ligand and on the presense of alkyl groups on the TrpyPd fragment.

Cr(III)-Tetraaza Macrocyclic Complexes Containing Auxiliary Ligands (Part III); Synthesis and Characterization of Cr(III)-Isothiocyanato, -Azido and -Chloroacetato Macrocyclic Complexes

The reaction of cis-[Cr([14]-decane)(OH 2 ) 2 ] + ([14]-decane = rac-5,5,7,12,12,14-hexamethyl-1,4,8,11-teraazacyclotetradecane) with auxiliary ligands {L a = isothiocyanate (NCS - ), azide (N 3 - ) or chloroacetate(caa)} leads to a new cis-[Cr([14]-decane)(NCS) 2 ]ClO 4 .H 2 O (1), cis-[Cr([14]-decane)(N 3 ) 2 ]ClO 4 (2) or cis-[Cr([14]-decane)(caa) 2 ]ClO 4 (3). These complexes have been characterized by a combination of elemental analysis, conductivity, IR and Vis spectroscopy, mass spectrometry, and X-ray crystallography. Analysis of the crystal structure of cis-[Cr([14]-decane)(NCS) 2 ]ClO 4 .H 2 O reveals that central chromium(III) has a distorted octahedral coordination environment and two NCS anions are bonded to the chromium(III) ion via the N-donor atom in the cis positions. The angle N a x a l -Cr-N a x i a l deviates by 13° from the ideal value of 180 for a perfect octahedron. The bond angle N-Cr-N between the Cr(III) ion and the two nitrogen atoms of the isothiocyanate ligands is close to 90°. The bond lengths of Cr-N between the chromium and NCS - groups are 1.964(5) and 2.000(5) A. They are shorter than those between chromium and nitrogen atoms of the macrocycle. The IR spectra of 1, 2 and 3 display bands at 2073, 1344 and 1684 cm - 1 attributed to the NCS - , N 3 - and caa groups stretching vibrations, respectively.

Synthesis, crystal structures and magnetic properties of [Co 3(NCS) 6(admtrz) 6]·CH 3OH·H 2O and [Ni 3(NCS) 6(admtrz) 6]·1.5H 2O (admtrz=4-amino-3,5-dimethyl-1,2,4-triazole)

Two linear trinuclear complexes [Co 3(NCS) 6(admtrz) 6]·CH 3OH·H 2O ( 1) and [Ni 3(NCS) 6(admtrz) 6]·1.5H 2O ( 2) containing 1,2,4-triazole and NCS anion as bridging ligands have been isolated, and characterized by X-ray diffraction methods. The two complexes are the isostructural neutral linear trimers, in which the central and terminal metal(II) ions are linked by two N1,N2-1,2,4-triazole ligands and one N-bridging NCS anion, while the terminal metal ions complete their octahedral coordination with one monodentate triazole and two N-bonded NCS anions. The magnetic behavior was investigated in the temperature range 5–300 K. The magnetic susceptibility measurements show that the Co(II) ions are weakly antiferromagnetically coupled with J=−2.8 cm −1, while Ni(II) ions are ferromagnetically coupled with J=10.45 cm −1. The nature and the magnitude of the magnetic-exchange of the two complexes have been discussed on the basis of the structural features.

Synthesis, Structure and Properties of a Mixed Mononuclear/Dinuclear Iron(II) Spin-Crossover Compound with the Ligand 4-(p-Tolyl)-1,2,4-triazole

A new iron(II) compound with the formula [Fe2(L)5(NCS)4]2[Fe(L)2(NCS)2(H2O)2] (I) [where L = 4-(p-tolyl)-1,2,4-triazole] has been synthesized and subjected to X-ray structure determination. Compound I crystallizes in the triclinic space group P–1 (no. 2) with a = 14.5785(11), b = 16.1253(11), c = 16.1963(8) Å, α = 80.930(5), β = 85.796(5), γ = 78.132(6)°, V = 3676.2(4) Å3. The structure refinement converged to wR2 = 0.172, RF = 0.084. The structure was found to consist of two types of iron-containing structural units, a mononuclear unit and a dinuclear one. The mononuclear unit has a crystallographic inversion centre, and is coordinated by two NCS anions, two triazole N1 nitrogen atoms, and two water molecules, each hydrogen-bonded to one of the two dinuclear units. The dinuclear units consist of two iron(II) ions bridged by three triazole ligands in a 1,2-fashion. The coordination spheres of both iron ions are completed by two NCS anions and one monodentate triazole ligand. The monodentate triazole ligands are connected through the non-coordinating N atom to the mononuclear iron unit by hydrogen bonds from its coordinated water molecule. Magnetic susceptibility measurements indicate a spin transition (ST) only for the iron ions in the dinuclear units, centred at around T1/2 = 111 K. The transition takes place within a relatively narrow T range. The mononuclear iron ion remains in the high-spin (HS) state even at very low temperature, yielding a ratio of 4:1 for the ST and HS iron ions. Temperature-dependent Mössbauer spectroscopy confirms these results.

Synthesis, Structure and Properties of a Mixed Mononuclear/Dinuclear Iron(II) Spin-Crossover Compound with the Ligand 4-(p-Tolyl)-1,2,4-triazole

A new iron(II) compound with the formula [Fe2(L)5(NCS)4]2[Fe(L)2(NCS)2(H2O)2] (I) [where L = 4-(p-tolyl)-1,2,4-triazole] has been synthesized and subjected to X-ray structure determination. Compound I crystallizes in the triclinic space group P–1 (no. 2) with a = 14.5785(11), b = 16.1253(11), c = 16.1963(8) Å, α = 80.930(5), β = 85.796(5), γ = 78.132(6)°, V = 3676.2(4) Å3. The structure refinement converged to wR2 = 0.172, RF = 0.084. The structure was found to consist of two types of iron-containing structural units, a mononuclear unit and a dinuclear one. The mononuclear unit has a crystallographic inversion centre, and is coordinated by two NCS anions, two triazole N1 nitrogen atoms, and two water molecules, each hydrogen-bonded to one of the two dinuclear units. The dinuclear units consist of two iron(II) ions bridged by three triazole ligands in a 1,2-fashion. The coordination spheres of both iron ions are completed by two NCS anions and one monodentate triazole ligand. The monodentate triazole ligands are connected through the non-coordinating N atom to the mononuclear iron unit by hydrogen bonds from its coordinated water molecule. Magnetic susceptibility measurements indicate a spin transition (ST) only for the iron ions in the dinuclear units, centred at around T1/2 = 111 K. The transition takes place within a relatively narrow T range. The mononuclear iron ion remains in the high-spin (HS) state even at very low temperature, yielding a ratio of 4:1 for the ST and HS iron ions. Temperature-dependent Mössbauer spectroscopy confirms these results.