Spin crossover iron(II) coordination polymer chains: syntheses, structures, and magnetic characterizations of [Fe(aqin)2(µ2-M(CN)4)] (M = Ni(II), Pt(II), aqin = quinolin-8-amine).

New Fe(II) coordination polymeric neutral chains of formula [Fe(aqin)2(µ2-M(CN)4)] (M = Ni(II) (1) and Pt(II) (2)) (aqin = Quinolin-8-amine) have been synthesized and characterized by infrared spectroscopy, X-ray diffraction, and magnetic measurements. The crystal structure determinations of 1-2 reveal in both cases a one-dimensional structure in which the planar [M(CN)4](2-) (M = Ni(II) (1) and Pt(II) (2)) anion acts as a µ2-bridging ligand, and the two aqin molecules as chelating coligands. Examination of the intermolecular contacts in the two compounds reveals that the main contacts are ascribed to hydrogen bonding interactions involving the amine groups of the aqin chelating ligands and the nitrogen atoms of the two non bridging CN groups of the [M(CN)4](2-) (M = Ni(II) (1) and Pt(II) (2)) anion. The average values of the six Fe-N distances observed respectively at room temperature (293 K) and low temperature (120 K), that is, 2.142(3) and 2.035(2) Å for 1, and 2.178(3) and 1.990(2) Å for 2, and the thermal variation of the cell parameters (performed on 2) are indicative of the presence of an abrupt HS-LS spin crossover (SCO) transition in both compounds. The thermal dependence of the product of the molar magnetic susceptibility times the temperature (χmT), in cooling and warming modes, confirms the SCO behavior at about 145 and 133 K in 1 and 2, respectively, and reveals the presence of a small thermal hysteresis of about 2 K for each compound.

Crystal structure of tetra-aqua-(5,5'-dimethyl-2,2'-bipyridyl-κ(2) N,N')iron(II) sulfate.

In the title compound, [Fe(C12H12N2)(H2O)4]SO4, the central Fe(II) ion is coordinated by two N atoms from the 5,5'-dimethyl-2,2'-bi-pyridine ligand and four water O atoms in a distorted octa-hedral geometry. The Fe-O coordination bond lengths vary from 2.080 (3) to 2.110 (3) Å, while the two Fe-N coordination bonds have practically identical lengths [2.175 (3) and 2.177 (3) Å]. The chelating N-Fe-N angle of 75.6 (1)° shows the largest deviation from an ideal octa-hedral geometry; the other coordination angles deviate from ideal values by 0.1 (1) to 9.1 (1)°. O-H⋯O hydrogen bonding between the four aqua ligands of the cationic complex and four O-atom acceptors of the anion leads to the formation of layers parallel to the ab plane. Neighbouring layers further inter-act by means of C-H⋯O and π-π inter-actions involving the laterally positioned bi-pyridine rings. The perpen-dicular distance between π-π inter-acting rings is 3.365 (2) Å, with a centroid-centroid distance of 3.702 (3) Å.

Multiple anion...π interactions in tris(1,10-phenanthroline-κ(2)N,N')iron(II) bis[1,1,3,3-tetracyano-2-(2-hydroxyethyl)propenide] monohydrate.

In the ionic structure of the title compound, [Fe(C12H8N2)3](C9H5N4O2)2·H2O, the octahedral tris-chelate [Fe(phen)3](2+) dications [Fe-N = 1.9647 (14)-1.9769 (14) Å; phen is 1,10-phenathroline] afford one-dimensional chains by a series of slipped π-π stacking interactions [centroid-to-centroid distances = 3.792 (3) and 3.939 (3) Å]. The 1,1,3,3-tetracyano-2-(2-hydroxyethyl)propenide anions, denoted tcnoetOH(-), reveal an appreciable delocalization of π-electron density, involving the central propenide [C-C = 1.383 (3)-1.401 (2) Å] fragment and four nitrile groups, and this is also supported by density functional theory (DFT) calculations at the B97D/6-311+G(2d,2p) level. Primary noncovalent inter-moiety interactions comprise conventional O-H...O(N) and weak C-H...O(N) hydrogen bonding [O...O(N) = 2.833 (2)-3.289 (5) Šand C...O(N) = 3.132 (2)-3.439 (2) Å]. The double anion...π interaction involving a nitrile group of tcnoetOH(-) and two cis-positioned pyridine rings (`π-pocket') of [Fe(phen)3](2+) [N...centroid = 3.212 (2) and 3.418 (2) Å] suggest the relevance of anion...π stackings for charge-diffuse polycyanoanions and common M-chelate species.

Tris(1,10-phenanthroline-κ(2) N,N')iron(II) bis-(1,1,3,3-tetra-cyano-2-eth-oxy-propenide) hemihydrate.

In the title hydrated mol-ecular salt, [Fe(C12H8N2)3](C9H5N4O)2·0.5H2O, the water mol-ecule site is half-occupied. The Fe-N bond lengths within the octa-hedral tris-chelate [Fe(phen)3](2+) ion (phen is 1,10-phenantroline) are indicative of a low-spin d(6) electronic configuration for the metal ion. The C-N, C-C and C-O bond lengths in the polynitrile anions indicate extensive electronic delocalization. In the crystal, the components are linked through O-H⋯N hydrogen bonds, forming [100] chains, as well as through Coulombic inter-actions.

(Adipato-κ(2) O,O')di-aqua-[bis-(pyridin-2-yl-κN)amine]-cobalt(II) trihydrate.

In the monomeric title complex, [Co(C6H8O4)(C10H9N3)(H2O)2]·3H2O, the distorted octa-hedral CoN2O4 coordination environment comprises two N-atom donors from the bidentate di-pyridyldi-amine ligand, two O-atom donors from one of the carboxyl-ate groups of the bidentate chelating adipate ligand and two water mol-ecules. In addition, there are three solvent water mol-ecules which are involved in both intra- and inter-unit O-H⋯O hydrogen-bonding inter-actions, which together with an amine-water N-H⋯O hydrogen bond produce a three-dimensional framework.

Racemic cis-bis-[bis-(pyrimidin-2-yl)amine-κN]bis(dicyanamido-κN1)iron(II) dihydrate: synthesis, crystal structure and Hirshfeld surface analysis.

The title compound, [Fe(C2N3)2(C8H7N5)2]·2H2O, has been synthesized solvothermally and characterized by single-crystal X-ray diffraction. The octa-hedral iron coordination polyhedron contains two di(pyrimidin-2-yl)amine ligands coordinated in a bidentate fashion, and two monodentate dicyanimido ligands, each coordinated via a terminal N atom, with the latter in a cis orientation. The ligand configuration about the iron atom is chiral, although the compound crystallizes as a racemic mixture: the Fe-N distances (> 2.07 Å) are characteristic of high-spin iron(II). In the crystal, an extensive series of N-H⋯N, O-H⋯N and O-H⋯O hydrogen bonds links the independent mol-ecular components into a three-dimensional framework. The H atoms of both water mol-ecules are disordered. The structure also features some π-π and anion-π inter-actions. The inter-molecular inter-actions were investigated by Hirshfeld surface analysis and two-dimensional fingerprint plots. Comparisons are made with some related compounds.

Linkage isomerism in coordination polymers.

The use of the recently prepared polynitrile ligand tcnopr3OH(-) ([(NC)(2)CC(OCH(2)CH(2)CH(2)OH)C(CN)(2)](-)) with different salts of Fe(II), Co(II), and Ni(II) has led to a very rare example of linkage isomerism in a coordination chain. These pairs of linkage isomers can be formulated as [M(tcnopr3OH-κN,κO)(2)(H(2)O)(2)]; M = Fe (1), Co (3), and Ni(5) and [M(tcnopr3OH-κN,κN')(2)(H(2)O)(2)]; M = Fe (2), Co (4), and Ni (6). Compounds 1-2, 3-4, and 5-6 are three pairs of linkage isomers since they present the same formula and chain structure and they only differ in the connectivity of the polynitrile ligand bridging the metal ions in the chain: through a N and an O atom (1κN:2κO-isomer) or through two N atoms (1κN:2κN'-isomer). The magnetic properties show, as expected, very similar behaviors for both isomers.

Concomitant dimorphism in poly[di-µ-azido-(5,5'-dimethyl-2,2'-bipyridine)iron(II)].

The title metal-organic polymer, catena-poly[[(5,5'-dimethyl-2,2'-bipyridine-κ2N,N')iron(II)]-di-µ-azido-κ2N1:N3-[(5,5'-dimethyl-2,2'-bipyridine-κ2N,N')iron(II)]-di-µ-azido-κ2N1:N1], [Fe(N3)2(C12H12N2)]n, features alternating µ-1,1 (end-on mode of coordination) and µ-1,3 (end-to-end mode of coordination) double azide bridges, forming chains running in the [100] direction. The octahedral coordination geometry around the FeII centre is completed by a bidentate 5,5'-dimethyl-2,2'-bipyridine ligand. Two polymorphs for this compound were obtained from the crude reaction product, the first in the space group P-1 and the other in P21/c. The molecular and crystal structures are very similar for both forms, the main difference being that the eight-membered Fe(µ-1,3-N3)2Fe metallacycle formed with end-to-end azide ligands has a nearly flat conformation in the triclinic form and a chair conformation in the monoclinic form. In spite of this geometric difference, both forms have the same density, the same packing index and similar arrangements of the one-dimensional chains in the crystal. As a consequence, they also share very similar Hirshfeld surfaces and fingerprint plots. However, a density functional theory (DFT) computational study showed that the monoclinic form is more stable than the triclinic form by ca 30.5 kJ mol-1.

trans-Bis(2,2'-di-pyridyl-amine-κ2 N,N')-bis-(1,1,3,3-tetra-cyano-2-eth-oxy-propenido-κN)copper(II).

The title compound, [Cu(C9H5N4O)2(C10H9N3)2], was synthesized solvothermally. The complex exhibits a distorted octa-hedral coordination geometry. The CuII atom is located on an inversion centre. The distorted octahedral CuN6 coordination sphere is composed of bidentate 2,2'-dipyrid-ylamine in the equatorial sites while the axial sites are occupied by 1,1,3,3-tetra-cyano-2-eth-oxy-propenide ligands. In the crystal, N-H⋯N hydrogen bonding results in chains parallel to [010].

A rare example of a double metamagnetic transition leading to 2D and 3D long-range order in the two-dimensional pyrazine- and azido-bridged cobalt(II) compound [Co(pyz)(N3)2].

The synthesis, characterization, crystal structure and detailed magnetic properties of a pyrazine (pyz) and azido (N3) bridged cobalt(II) compound of formula [Co(N3)2(pyz)] (1) are reported. Compound 1 shows a layered structure formed by Co(II) chains with double µ-N3(κN1,N1) bridges that are further connected by µ-(pyrazine-κN1,N4) bridges. The layers present weak van der Waals interactions between azido terminal groups. The magnetic properties show the presence of a metamagnetic behaviour in 1 with two critical fields of 200 and 400 mT at low temperatures. AC magnetic measurements show the presence of a long-range 2D ferromagnetic order at Tc ≈ 8.0-7.0 K for dc fields above 200 mT and a long-range 3D ferromagnetic order at Tc ≈ 4.5 K for dc fields above 400 mT.

catena-Poly[[bis-(quinolin-8-amine-κ2 N,N')cadmium(II)]-µ-cyanido-κ2 N:C-[dicyanidonickel(II)]-µ-cyanido-κ2 C:N].

In the title compound, [CdNi(C9H8N2)2(CN)4] n , the Cd and Ni atoms both lie on centres of inversion in space group P21/c. The Cd atom is coordinated by two bidentate quinolin-8-amine ligands and by the N atoms of two cyano ligands, while the square planar Ni atom is coordinated by the C atoms of four cyano ligands. These units form a one-dimensional coordination polymer containing an (-NC-Ni-CN-Cd-) n backbone, and the coordination polymer chains are linked into a three-dimensional array by a combination of N-H⋯N and C-H⋯N hydrogen bonds, augmented by a π-π stacking inter-action.

A new coordination complex based on a polynitrile ligand: bis(4-amino-3,5-di-2-pyridyl-4H-1,2,4-triazole)diaquairon(II) bis(1,1,3,3-tetracyano-2-methylsulfanylpropenide).

The new high-spin iron(II) complex, [Fe(C(12)H(10)N(6))(2)(H(2)O)(2)](C(8)H(3)N(4)S)(2) or [Fe(abpt)(2)(H(2)O)(2)](tcnsme)(2) [where abpt is 4-amino-3,5-di-2-pyridyl-4H-1,2,4-triazole and tcnsme is the 1,1,3,3-tetracyano-2-methylthiopropenide anion], consists of discrete [Fe(abpt)(2)(H(2)O)(2)](2+) dications, where the Fe(II) ion is coordinated by two N,N'-bidentate chelating abpt ligands in the equatorial plane and two water molecules in trans positions, generating a distorted octahedral [FeN(4)O(2)] environment. The cationic unit is neutralized by two polynitrile tcnsme anions, in which the C-N, C-C and C-S bond lengths indicate extensive electronic delocalization. In the crystal structure, the dications and anions are linked through O-H...N and N-H...N hydrogen bonds involving the water H atoms and those of the NH(2) groups and the N atoms of the CN groups, leading to the formation of a three-dimensional network.

Bis(2,2'-bi-1H-imidazole)-copper(II) bis-(1,1,3,3-tetra-cyano-2-eth-oxy-propenide).

In the title compound, [Cu(C(6)H(6)N(4))(2)](C(9)H(5)N(4)O)(2), the Cu(2+) ion (site symmetry ) is coordinated by two N,N'-bidentate 2,2'-biimidazole (H(2)biim) ligands, generating a square-planar CuN(4) geometry. The dihedral angle between the aromatic rings in the ligand is 0.70 (9)°. In the polynitrile 1,1,3,3-tetra-cyano-2-eth-oxy-propenide (tcnoet) anion, the C-N, C-C and C-O bond lengths indicate extensive electronic delocalization. An alternative description for the metal-ion geometry is an extremely distorted CuN(6) octa-hedron, with two N-bonded tcnoet anions completing the coordination. In the crystal, the components are linked by N-H⋯N and C-H⋯N inter-actions.

Bis[tris-(pyridin-2-yl)amine]-iron(II) tris-(di-cyano-methyl-idene)methane-diide.

In the title compound, [Fe{(C5H4N)3N}2][C{C(CN)2}3], both ions lie across centres of inversion, with the anion being statistically disordered over two sets of atomic sites having equal occupancy. The cation and anion have approximate and 32 symmetry, respectively, and the Fe-N bond lengths indicate low-spin FeII. A combination of two-centre C-H⋯N and three-centre C-H⋯(N)2 hydrogen bonds link the ions into complex sheets. Several low-occupancy water mol-ecules are present, whose H atoms could not be located: accordingly, the reflection data were subjected to the SQUEEZE procedure [Spek (2015 ▸). Acta Cryst. C71, 9-18].

Synthesis, crystal structure and Hirshfeld surface analysis of bis-{2-[(pyridin-2-yl)amino]-pyridinium} tetra-cyano-nickelate(II).

In the title mol-ecular salt, (C10H10N3)2[Ni(CN)4], the dihedral angle between the pyridine rings in the cation is 1.92 (13)° and the complete anion is generated by a crystallographic centre of symmetry. An intra-molecular N-H⋯N hydrogen bond occurs in the cation, which closes an S(6) ring. In the crystal, the components are linked by N-H⋯N and weak C-H⋯N hydrogen bonds, which generate chains propagating in the [101] direction. Weak aromatic π-π stacking inter-actions are also observed. A Hirshfeld surface analysis and two-dimensional fingerprint plots indicate that the most important contact types in the crystal packing are N⋯H/H⋯N, C⋯H/H⋯C and H⋯H with contributions of 37.2, 28.3 and 21.9%, respectively.

fac-Tri-aqua-(1,10-phenanthroline-κ2 N,N')(sulfato-κO)cobalt(II): crystal structure, Hirshfeld surface analysis and computational study.

The CoII atom in the title complex, [Co(SO4)(C12H8N2)(H2O)3] (or C12H14CoN2O7S), is octa-hedrally coordinated within a cis-N2O4 donor set defined by the chelating N-donors of the 1,10-phenanthroline ligand, sulfate-O and three aqua-O atoms, the latter occupying an octa-hedral face. In the crystal, supra-molecular layers lying parallel to (110) are sustained by aqua-O-H⋯O(sulfate) hydrogen bonding. The layers stack along the c-axis direction with the closest directional inter-action between them being a weak phenanthroline-C-H⋯O(sulfate) contact. There are four significant types of contact contributing to the calculated Hirshfeld surface: at 44.5%, the major contribution comes from O-H⋯O contacts followed by H⋯H (28.6%), H⋯C/C⋯H (19.5%) and C⋯C (5.7%) contacts. The dominance of the electrostatic potential force in the mol-ecular packing is also evident in the calculated energy frameworks. The title complex is isostructural with its manganese, zinc and cadmium containing analogues and isomeric with its mer-tri-aqua analogue.

Solid-state 1D → 3D transformation of polynitrile-based coordination polymers by dehydration reaction.

In crystal structures of two chain coordination polymers [M(tcnopr3OH)2(H2O)2] (M = NiII and CoII; tcnopr3OH- = [(NC)2CC(O(CH2)3OH)C(CN)2]-) based on a N,O or N,N'-bridge polynitrile ligand, the parallel chains are connected via, respectively, C[triple bond, length as m-dash]NH-O and O-HO hydrogen bonds between uncoordinated functional groups of the ligand and coordinated water molecules. Upon heating, both solids undergo dehydration accompanied by degradation of their single crystals. Powder X-ray diffraction showed that non-isostructural triclinic single crystals transformed to isostructural monoclinic compounds. The solid-state reaction yielded 3D coordination polymers [M(tcnopr3OH)2] (M = NiII and CoII) based on a N,N',O-connected tcnopr3OH-. Although previously tens of complexes based on tcnopr3OH and similar anions were synthesized and X-ray characterized, none of these contain a tridentate polynitrile ligand. Thus, this study provides evidence that solid-state reactions allow obtaining novel coordination modes of polynitrile ligands. The possible pathways for the transformation of H-bonded networks to 3D coordination polymers are discussed on the basis of the topological approach. Applicability of the topological approach to predict possible networks of solid-state reaction products based on the crystal structures of initial compounds is demonstrated.

Magnetic bistability and thermochromism in a molecular Cu(II) chain.

An original magnetic bistability and a thermochromic transition are observed in a new Cu(II) molecular chain. Thermal structural studies reveal changes in the Cu(II) coordination sphere, driven by a more pronounced Jahn-Teller effect at low temperature. These distortions provoke a gradual color change. The structural study at 10 K shows a dimerization of the molecular chain, in agreement with the abrupt magnetic transition observed at 30 K.

Hydrogen bonding and π-π interactions in the cocrystal salt [Fe(bpe)2(H2O)4](TCEP)2·2(bpe) [bpe is trans-1,2-bis(pyridin-4-yl)ethene and TCEP is 1,1,3,3-tetracyano-2-ethoxypropenide].

The cocrystal salt tetraaquabis[trans-1,2-bis(pyridin-4-yl)ethene-κN]iron(II) bis(1,1,3,3-tetracyano-2-ethoxypropenide)-trans-1,2-bis(pyridin-4-yl)ethene (1/2), [Fe(C12H10N2)2(H2O)4](C9H5N4O)2·2C12H10N2, is a rare example of a mononuclear FeII compound with trans-1,2-bis(pyridin-4-yl)ethane (bpe) ligands. The complex cation resides on a crystallographically imposed inversion center and exhibits a tetragonally distorted octahedral coordination geometry. Both the symmetry-independent bpe ligand and the cocrystallized bpe molecule are essentially planar. The 1,1,3,3-tetracyano-2-ethoxypropenide counter-ion is nonplanar and the bond lengths are consistant with significant electron delocalization. The extended structure exhibits an extensive O-H...N hydrogen-bonding network with layers of complex cations joined by the cocrystallized bpe. Both the coordinated and the cocrystallized bpe are involved in π-π interactions. Hirshfeld and fingerprint plots reveal the important intermolecular interactions. Density functional theory was used to estimate the strengths of the hydrogen-bonding and π-π interactions, and suggest that the O-H...N hydrogen bonds enhance the strength of the π-interactions by increasing the polarization of the pyridine rings.

Crystal structure of tris-(2,2'-bi-pyridine)-cobalt(II) bis-(1,1,3,3-tetra-cyano-2-eth-oxy-propenide).

In the title compound, [Co(C10H8N2)3](C9H5N4O)2, the tris-(2,2'-bi-pyridine)-cobalt(II) dication lies across a twofold rotation axes in the space group C2/c. The N atoms of the three bi-pyridine ligands form a distorted octa-hedron around the cobalt ion. All the N atoms of the polynitrile 1,1,3,3-tetra-cyano-2-eth-oxy-propenide anions participate in C-H⋯N hydrogen bonds ensuring crystal cohesion and forming a three-dimensional structure. The structure is further stabilized by C-H⋯π(cation) and anion⋯π(cation) inter-actions.