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Spin‐crossover complexes form one of the biggest families of switchable compounds. Here we show a new way to obtain spin‐crossover materials by direct synthesis from metallic iron. Four complexes of FeII with 4‐R‐1,2,4‐triazoles have been synthesized by a direct metal oxidation: [Fe(NH2trz)3]SO4, [Fe(NH2trz)3](BF4)2 and two polymorphs of [Fe(Htrz)2(trz)]BF4. Surprisingly high quality of PXRD pattern of [Fe(NH2trz)3]SO4 allowed to perform Rietveld refinement and obtain reliable crystal structure of the latter. All compounds have been studied by magnetic susceptibility measurements, optical reflectivity, differential scanning calorimetry and Raman spectroscopy. Importantly, spin‐crossover characteristics of the complexes obtained by this unusual method are preserved, thus revealing a new effective approach of "direct synthesis" towards switchable coordination compounds. [ABSTRACT FROM AUTHOR]

Spin transitions are a spectacular example of molecular switching that can provoke extreme electronic and structural reorganizations in coordination compounds. A new 3D cyanoheterometallic framework, [Fe(pz){Au(CN)2}2], has been synthesized in which a highly cooperative spin crossover has been observed at 367 and 349 K in heating and cooling modes, respectively. Mössbauer spectroscopy revealed a complete transition between the diamagnetic and paramagnetic states of the iron centres. The low-spin-to-high-spin transition induced a drastic structural distortion involving a large one-directional expansion (ca. 10.6 %) and contraction (ca. 9.6 %) of the lattice. Negative thermal expansion along the c axis was detected below and above the transition temperature. [ABSTRACT FROM AUTHOR]

The diversity of spin crossover (SCO) complexes that, on the one hand, display variable temperature, abruptness and hysteresis of the spin transition, and on the other hand, are spin-sensitive to the various guest molecules, makes these materials unique for the detection of different organic and inorganic compounds. We have developed a homochiral SCO coordination polymer with a spin transition sensitive to the inclusion of the guest 2-butanol, and these solvates with ( R)- and ( S)-alcohols demonstrate different SCO behaviours depending on the chirality of the organic analyte. A stereoselective response to the guest inclusion is detected as a shift in the temperature of the transition both from dia- to para- and from para- to diamagnetic states in heating and cooling modes respectively. Furthermore, the Mössbauer spectroscopy directly visualizes how the metallic centres in a chiral coordination framework differently sense the interaction with guests of different chiralities. [ABSTRACT FROM AUTHOR]

Three complexes [Ca(ClO4)(H2O)Cu5(o-picHA-2H)5(H2O)]ClO4 ( 1), [Pr(NO3)2(py)Cu5(o-picHA-2H)5(py)5]ClO4 ( 2), and [Nd(NO3)(H2O)(py)Cu5(o-picHA-2H)5(py)5](ClO4)2 ·5py ( 3) ( o-picHA = 2-picolinehydroxamic acid) were synthesized in order to retrace structural trends caused by the change of the ionic radius of the central metal ion as well as to assess the effect of the axial ligands on the arrangement of metallacrowns. The complexes were characterized by elemental analysis, ESI-mass spectrometry, IR spectroscopy, and single-crystal X-ray analysis. The heterometallic complexes have 15-MC-5 molecular topology with CaII or LnIII ion in the center of the metallamacrocyclic cavity. The Ca-O and Ln-O bond lengths follow the trend of changes of the corresponding metal ionic radii. While the CaII complex cation (without axial ligands) in 1 is almost flat, the LnIII containing cations in 2 and 3 have a 'partially opened umbrella' environment. [ABSTRACT FROM AUTHOR]

The synthesis and characterization of two new CuII complexes with pyrazole ligands formulated as [Cu3(μ-Pz)3(μ3-OH)(Pz)2Cl2][Cu3(μ-Pz)3(μ3-OH)(Pz)2Cl2(DMF)] ·2DMF ( 1) and [Cu3(μ-DMPz)3(DMF)4(OAc)(μ3-OH)(H2O)]+[Cu3(μ-DMPz)3(DMF)(NCS)3(μ3-OH)]- ( 2) (where Pz = 1 H-pyrazole and DMPz = 3, 5-dimethyl-1 H-pyrazole) are reported. The compounds were prepared by the reaction of zero valent copper metal and Pz or DMPz in the dimethylformamide solution in the presence of the different additional components (chloride or thiocyanate ligands). The crystal structures of both compounds were determined by single-crystal X-ray diffraction analysis. Both compounds 1 and 2 are hexanuclear clusters comprising from neutral ( 1) or charged ( 2) trinuclear triangular fragments Cu3(μ3-OH)(μ-Pz)3 of inverse azametallacrowns aza9-MCCuII-3 topology. Nevertheless, they exhibit relevant differences in their molecular structures. The magnetic measurement shows the isotropic antiferromagnetic interaction in 2 with J1 = -140 cm-1 for the cationic and J2 = -109 cm-1 (-2 JSi · Sj model) for the anionic part of the molecule above 100 K and significant influence of antisymmetric exchange at lower temperatures. [ABSTRACT FROM AUTHOR]

New methods are proposed for the synthesis of spin-crossover nano- and micro-objects. Several nano-objects that are based upon the spin-crossover complex [Fe(hptrz)3](OTs)2 (hptrz=4-heptyl-1,2,4-triazole, Ts= para-toluenesulfonyl) were prepared in homogeneous media. The use of various reagents (Triton X-100, PVP, TOPO, and PEGs of different molecular weights) as stabilizing agents yielded materials of different size (6 nm-2 μm) and morphology (nanorods, nanoplates, small spherical particles, and nano- and micro-crystals). In particular, when Triton X-100 was used, a variation in the morphology from nanorods to nanoplates was observed by changing the nature of the solvent. Interestingly, the preparation of the nanorods and nanoplates was always accompanied by the formation of small spherical particles. Alternatively, when PEG was used, 200-400 nm crystals of the complex were obtained. In addition, a very promising polymer-free synthetic method is discussed that was based on the preparation of relatively stable FeII-triazole oligomers in CHCl3. Their specific treatment led to micro-crystals, small nanoparticles, or gels. The size and morphology of all of these objects were characterized by TEM and by dynamic light scattering (DLS) where possible. Their spin-crossover behavior was studied by optical and magnetic measurements. The spin-transition features for large particles (>100 nm) were very similar to that of the bulk material, that is, close to room temperature with a hysteresis width of up to 8 K. The effects of the matrix and/or size-reduction led to modification of the transition temperature and an abruptness of the spin transition for oligomeric solutions and small nanoparticles of 6 nm in size. [ABSTRACT FROM AUTHOR]

The article discusses a study on a series of iso-structural lanthanide-copper metallacrown sulfates and structural trends with LnIII including Pr, Nd, SM, Eu, Gd, Dy and Ho as 15-metallacrown-5 family representatives. Researchers prepared the compounds then masses of dark-blue crystals formed after slow evaporation for elemental analyses. The study showed that values of unit-cell parameters and lengths of Ln-O bond are governed by lanthanide contraction.

The title compound, (C2H10N2)2[Ni(C2HN2O4)2]·2H2O, has an ionic structure containing a centrosymmetric complex 4–anion, charge-balancing ethylenediaminium dications and solvent water molecules. The oxalohydroxamate unit is triply deprotonated and forms five-membered chelate rings with the central Ni ion; the Ni ion lies on an inversion centre. The two hydroxamate O atoms in the complex anion are linked by short intramolecular hydrogen bonds. [ABSTRACT FROM AUTHOR]

The title compound, [Ni(C2H8N2)3][Ni(C3HN3O2)2]·H2O, appears to be a modular associate consisting of two complex counter-ions, containing bivalent nickel as the central atom in both cases, and a solvent water mol­ecule. The NiII ion in the complex cation lies on the C2 crystallographic axis. Its coordination environment is formed by six N atoms of three ethyl­ene­diamine (en) mol­ecules, representing a distorted octa­hedral geometry. The NiII ion in the complex anion occupies a position at the center of inversion. It exhibits a distorted square-planar coordination geometry formed by four N atoms belonging to the deprotonated oxidoimine and amide groups of the two doubly charged 2-cyano-2-(oxidoimino)acetamidate anions, situated in trans positions with respect to each other. In the crystal packing, the complex anions are linked by water mol­ecules via hydrogen bonds between the amide O atoms and water H atoms, forming chains translated along the a direction. The [Ni(en)3]2+ cations fill empty spaces between the translational chains, connecting them by hydrogen bonds between the oxime and amide O atoms of the anions and the amine H atoms of the cations, forming layers along the ac plane. The water mol­ecules provide connection between layers through N atoms of the cations, thus forming a three-dimensional modular structure. [ABSTRACT FROM AUTHOR]

The title compound, [Cu(ClO4)2(C6H6N2O2)2], contains neutral molecules of a centrosymmetric mononuclear copper(II) complex, in which the zwitterionic hydroxamic acid ligand is O, O′-chelated to the CuII atom. The CuII atom lies on an inversion centre and has a distorted tetragonal-bipyramidal environment, being coordinated by four O atoms of the two N-hydroxynicotinamide molecules forming the equatorial plane, and by two O atoms of the perchlorate anions occupying the axial positions. [ABSTRACT FROM AUTHOR]

The crystal structure of the title salt, C6H7N2O2+·Cl−, consists of N-hydroxy­isonicotinamidium cations and Cl− anions linked through N—H⋯Cl, O—H⋯Cl and N—H⋯O hydrogen bonds into layers arranged parallel to the (010) plane. [ABSTRACT FROM AUTHOR]

The centrosymmetric neutral mononuclear title complex, [Ni(C5H5N2O3)2(C2H8N2)2]·6H2O, has the Ni centre in a distorted octa­hedral environment, defined by six N atoms belonging to two chelating ethyl­enediamine mol­ecules and two cyano N atoms derived from cyanoxime ligands. The O atom of the deprotonated oxime group forms hydrogen bonds with two solvent water mol­ecules. [ABSTRACT FROM AUTHOR]

The title compound, [Cu2(C2O4)Cl2(C7H9N3)2], contains neutral mol­ecules of a centrosymmetric dinuclear oxalate-bridged copper(II) complex, in which the oxalate ligand is coordinated in a bis-bidentate bridging mode to the Cu atoms. Each Cu atom has a distorted square-pyramidal environment, being coordinated by two N atoms of the [1-(pyridin-2-yl)­ethyl­idene]hydrazine ligand, two O atoms of the doubly deprotonated oxalate anion and one Cl− anion. [ABSTRACT FROM AUTHOR]

In the cation of the title compound, C(7)H(12)ClN(2)Se(+)·Cl(-), the ethyl-ene groups and the Se-Cl fragment adopt a cis configuration with a C-Se-Cl angle of 96.09 (6)°. In the crystal, inter-molecular N-H⋯Cl hydrogen bonds link two cations and two chlorine anions into centrosymmetric clusters. π-π inter-actions between the pyrazole rings [centroid-centroid distance of 3.530 (2) Å] link these clusters into columns along [001] with short inter-molecular Se⋯Cl(-) contacts of 2.995 (1) Å.

The seven isostructural complexes, [Cu(5)Ln(C(2)H(4)N(2)O(2))(5)(SO(4))(H(2)O)(6.5)](2)(SO(4))·6H(2)O, where Ln(III) = Pr, Nd, Sm, Eu, Gd, Dy and Ho, are representatives of the 15-metallacrown-5 family. Each dianion of glycinehydroxamic acid (GlyHA) links two Cu(II) cations forming a cyclic [CuGlyHA](5) frame. The Ln(III) cations are located at the centre of the [CuGlyHA](5) rings and are bound by the five hydroxamate O atoms in the equatorial plane. Five water molecules are coordinated to Cu(II) cations, and one further water molecule, located close to an inversion centre between two adjacent [Cu(5)Ln(GlyHA)(5)](2+) cations, is disordered around this inversion centre and coordinated to a Cu(II) cation of either the first or second metallacrown ether. Another water molecule and one of the two crystallographically independent sulfate anions are coordinated, the latter in a bidentate fashion, to the Ln(III) cation in the axial positions. The second sulfate anion is not coordinated to the cation, but is located in an interstitial position on a crystallographic inversion centre, thus leading to disorder of the O atoms around the centre of inversion. The Ln-O bond distances follow the trend of the lanthanide contraction. The apical Ln-O bond distances are very close to the sums of the ionic radii. However, the Ln-O distances within the metallacrown units are slightly compressed and the Ln(III) cations protrude significantly from the plane of the otherwise flat metallacrown ligand, thus indicating that the cavity is somewhat too small to accommodate the Ln(III) ions comfortably. This effect decreases with the size of the lanthanide cation from complex (I) (Ln(III) = Pr; 0.459) to complex (VII) (Ln(III) = Ho; 0.422), which indicates that the smaller lanthanide cations fit the cavity of the pentacopper metallacrown ring better than the larger ones. The diminished contraction of Ln-O distances within the metallacrown planes leads to an aniostropic contraction of the unit-cell parameters, with a, c and V following the trend of the lanthanide contraction. The b axes, which are mostly aligned with the rigid planes of the metallacrown units, show only a little variation between the seven compounds., (© 2011 International Union of Crystallography)

The asymmetric unit of the title compound, [Cu(CHO(2))Cl(C(5)H(8)N(2))(3)](2)·[CuCl(2)(C(5)H(8)N(2))(2)] or 2[A]·[B], contains one A mol-ecule and one half-molecule of B, located on a centre of inversion. The Cu(II) environments in A and B are different. In A, the Cu(II) atom is coordinated by three N atoms from three 3,5-dimethyl-1H-pyrazole (L) ligands, one O atom from a formate ligand and a chloride anion in an axial position [Cu-Cl = 2.4275 (7) Å] in a distorted tetra-gonal-pyramidal geometry. The Cu(II) atom in B is coordinated by two N atoms from two L ligands and two chloride anions [Cu-Cl = 2.2524 (6) Å] in a distorted square-planar geometry. In the crystal, inter-molecular N-H⋯O hydrogen bonds link mol-ecules A into centrosymmetric dimers. Inter-molecular N-H⋯Cl hydrogen bonds further link these dimers with the B mol-ecules, forming chains propagating in [101].

In the title compound, [Ho(C(6)H(12)Cl(3)N(3)O(2)P)(3)(C(18)H(15)OP)], the Ho(III) ion is surrounded by six O atoms from the three bidentate N-[bis-(dimethyl-amino)phosphino-yl]-2,2,2-trichloro-acetamido ligands (L(-)) and by one O atom from the triphenyl-phosphine oxide ligand, with the formation of a distorted monocapped octa-hedron. In one ligand L(-), the trichloro-methyl group is rotationally disordered between two orientations in a 1:1 ratio, while two dimethyl-amino groups in another ligand L(-) are disordered between two conformations, each with the same 1:1 ratio.

The title compound, {[Cu(C(10)H(14)N(4)Se)(2)(H(2)O)](BF(4))(2)·2C(18)H(15)PO·H(2)O}(n), has a polymeric structure where each Cu(II) ion adopts a square-pyramidal coordination constituted by four N atoms of pyrazole moieties in the equatorial plane and an axial O atom of a water mol-ecule. A pair of bis-(3,5-dimethyl-1H-pyrazol-4-yl) selenide ligands bridges the Cu(II) centres into a chain extending along the c axis. The water mol-ecules, anions and triphenyl-phosphine oxide mol-ecules are involved in inter-molecular hydrogen bonding, which links the chains into a three-dimensional network.

In the title compound, {[Cu(C(10)H(14)N(4)Se)(2)(H(2)O)]Cl(2)·H(2)O}(n), the Cu(II) ion, lying on a twofold rotation axis, has a square-pyramidal geometry constituted by four N atoms of pyrazolyl groups in the basal plane and an apical O atom of a water mol-ecule. A pair of bis-(3,5-dimethyl-1H-pyrazol-4-yl) selenide ligands bridge the Cu centers into a polymeric double-chain extending along [001]. The chloride anions are involved in inter-molecular N-H⋯Cl and O-H⋯Cl hydrogen bonds, which link the chains into a three-dimensional network.

In the title compound, {[Cu(C(10)H(14)N(4)Se)(2)](ClO(4))(2)}(n), the Cu(II) ion is located on a twofold rotation axis and has a tetra-gonally distorted square-planar geometry constituted by four N atoms. A pair of bis(3,5-dimethyl-1H-pyrazol-4-yl) selenide (L) ligands bridges the copper centers into a polymeric chain extending along [001]. The perchlorate anions are involved in inter-molecular N-H⋯O hydrogen bonding, which links the chains into layers parallel to the bc plane.

The crystal structure of the title compound, K(+)·C(3)H(4)NO(4) (-)·H(2)O, consists of potassium cations, monoanions of 2-carboxy-acetohydroxamic acid [namely 2-(N-hydroxy-carbamo-yl)acetate] and solvent water mol-ecules. The elements of the structure are united in a three-dimensional network by numerous K⋯O coordinate bonds and O-H⋯O and N-H⋯O hydrogen bonds. The coordination sphere of the K(+) ions may be described as a distorted double capped octa-hedron. Bond lengths and angles are similar to those in related compounds.

The title compound, [Cu(2)(C(7)H(6)N(2)O(3))Cl(2)(C(5)H(5)N)(4)]·C(3)H(8)O, is a binuclear pyrazolate complex, in which the two Cu(II) atoms have different coordination numbers and are connected by a bridging Cl atom. One Cu(II) atom has a distorted square-pyramidal coordination environment formed by two pyridine N atoms, one bridging Cl atom and an N,O-chelating pyrazolate ligand. The other Cu(II) atom adopts an octa-hedral geometry defined by two pyridine N atoms at the axial positions, two Cl atoms and the coordinated pyrazolate ligand in the equatorial plane. An O-H⋯O hydrogen bond connects the complex mol-ecules and propan-2-ol solvent mol-ecules into pairs. These pairs form columns along the a axis.

The title structure, C(9)H(11)N(3)O(2), is a racemate. The chiral centre is situated at the N-C-N C atom of the imidazolidine ring. The inter-planar angle between the mean planes of the pyridine and imidazolidine rings is 89.41 (5)°. The methyl group is in a trans position with respect to the pyridine N atom. In the crystal, the mol-ecules are arranged in zigzag layers parallel to the b axis. The mol-ecules within the layers are inter-connected by strong O-H⋯N and weak N-H⋯O hydrogen bonds; the former take place between OH groups and amine N atoms and the latter between the amine N atom and the carbonyl O atom. In addition, C-H⋯O inter-actions are also present.

The mol-ecule of the title compound, C(14)H(12)N(2)O(4), lies across a crystallographic inversion centre situated at the mid-point of the C-C intra-annular bond. The mol-ecule is not planar, the dihedral angle between the aromatic rings being 50.1 (1)°. The oxime group is in an E position with respect to the -OH group and forms an intra-molecular O-H⋯N hydrogen bond. In the crystal structure, inter-molecular O-H⋯O hydrogen bonds link mol-ecules into chains propagating along [001]. The crystal structure is further stabilized by inter-molecular stacking inter-actions between the rings [centroid-to-centroid distance = 3.93 (1) Å], resulting in layers parallel to the bc plane.

In the title compound, [Cu(C(2)H(3)O(2))(2)(C(5)H(8)N(2))(2)], the Cu(II) atom has a distorted tetra-gonal-bipyramidal geometry, with the equatorial plane formed by two N atoms belonging to two 3,5-dimethyl-1H-pyrazole ligands and two O atoms from two acetate anions. The second O atoms of the acetate groups provide elongated Cu-O axial contacts, so that the acetates appear to be coordinated in a pseudo-chelate fashion. The pyrazole ligands are situated in cis positions with respect to each other. In the crystal structure, mol-ecules are linked through inter-molecular N-H⋯O hydrogen bonds, forming a one-dimensional chain.

In the title compound, [Cr(C(2)H(6)OS)(6)]Cl(3), each Cr(III) ion is located on a three-fold inversion axis and is coordinated by six dimethyl-sulfoxide ligands [Cr-O = 1.970 (2)-1.972 (2) Å; O-Cr-O = 88.19 (9) and 91.81 (9)°] in a slightly distorted octa-hedral geometry. The Cl(-) anions take part in the formation of weak C-H⋯Cl hydrogen bonds, which contribute to the crystal packing stabilization.

The title compound, (2,6-diacetylpyridine bis{[2-(hydroxyimino)propanoyl]hydrazone}(2-))nickel(II) dimethyl sulfoxide solvate monohydrate, [Ni(C(15)H(17)N(7)O(4))] x C(2)H(6)OS x H(2)O, represents the first example of square-planar N(4) coordination via N atoms with four different functions, namely amide, azomethine, hydroxyimino and pyridine. The coordination polyhedron of the central Ni atom has a slightly distorted square-planar geometry. The 2,6-diacetylpyridine bis{[2-(hydroxyimino)propanoyl]hydrazone} ligand forms one six- and two five-membered chelate rings, and a pseudo-chelate ring through an intramolecular hydrogen bond with an amide group as donor and a deprotonated hydroxyimino group as acceptor, resulting in a pseudomacrocyclic arrangement.

The title compound, {[Co(2)(C(15)H(14)N(4)O(3))(2)(C(5)H(5)N)(4)(H(2)O)(2)]ClO(4)·3.66H(2)O}(n), is a one-dimensional coordination polymer, with both Co(II) and Co(III) centres in its structure. The ligand environment surrounding Co(III) is formed by two N,N-chelating pyrazole-containing ligands and two pyridine mol-ecules in axial positions. The high-spin Co(II) ions, situated at crystallographic centres of inversion, exhibit a distorted octa-hedral coordination mode. The ClO(4) (-) anion is linked to the polymer chain via hydrogen bonds. The chains are connected by hydrogen bonds to produce a three-dimensional structure.

The title compound, [ZnCl(2)(C(10)H(12)N(4)O(2))]·0.5H(2)O, was readily prepared by the reaction between ZnCl(2) and 2-hydroxy-imino-N'-[1-(2-pyrid-yl)ethyl-idene]propanohydrazide. The Zn atom has a distorted trigonal-bipyramidal geometry with two Cl atoms and one azomethine N atom in the equatorial plane and one pyridine N atom and one amide O atom in the axial positions. In the crystal structure, complex mol-ecules are connected in pairs by N-H⋯Cl hydrogen bonds, formed between the amide NH of one mol-ecule and the Cl atom of a neighboring one. Mol-ecular pairs are connected by hydrogen bonds involving the uncoordinated water mol-ecule, which lies on a twofold axis.

In the title compound, [Cu(C(2)O(4))(C(5)H(8)N(2))(2)(H(2)O)], the Cu(II) atom is coordinated in a slightly distorted square-pyramidal geometry by two N atoms belonging to the two 3,5-dimethyl-1H-pyrazole ligands, two O atoms of the oxalate anion providing an O,O'-chelating coordination mode, and an O atom of the water mol-ecule occupying the apical position. The crystal packing shows a well defined layer structure. Intra-layer connections are realised through a system of hydrogen bonds while the nature of the inter-layer inter-actions is completely hydro-phobic, including no hydrogen-bonding inter-actions.

The title compound, (C2H10N2)2[Ni(C2HN2O4)2].2H2O, has an ionic structure containing a centrosymmetric complex 4- anion, charge-balancing ethylenediaminium dications and solvent water molecules. The oxalohydroxamate unit is triply deprotonated and forms five-membered chelate rings with the central Ni ion; the Ni ion lies on an inversion centre. The two hydroxamate O atoms in the complex anion are linked by short intramolecular hydrogen bonds.