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In the hydrated title complex, [Fe(dpa) 2 (N 3 ) 2 ]·H 2 O (dpa is 2,2'-di-pyridyl-amine, C 10 H 9 N 3 ), the Fe II ion is coordinated in a distorted octa-hedral manner by two neutral, chelating dpa ligands and two anionic, monodentate azide (N 3 - ) ions in a cis -configuration. Distortion results from different Fe-N bond lengths [2.1397 (13)-2.2254 (12) Å] and (N-Fe-N) cis [80.12 (4)-96.72 (5)°] and (N-Fe-N) trans [166.73 (4)-176.62 (5)°] bond angles. Hydrogen bonds exist between two symmetry-related water mol-ecules as hydrogen donors to the γ-N atoms of azido ligands of two adjacent iron complexes and as acceptors from the amide group of the dpa ligands of two additional iron complexes. The hydrogen-bonding pattern results in eight-membered ⋯H-O-H⋯N⋯ rings and a band-like arrangement of the mol-ecules involved. Additional, weaker hydrogen bonds between the α-N atom of the second azido ligand as acceptors and the amide groups of the second dpa ligands as donors cross-link neighboring bands to layers extending parallel to (001)., (© Setifi et al. 2024.)

The title compound, [Zn 2 (C 6 H 8 O 4 ) 2 (C 10 H 9 N 3 ) 2 ]·3H 2 O or {Zn 2 [(C 5 H 4 N) 2 NH] 2 [μ-(CH 2 ) 4 (COO) 2 ] 2 }·3H 2 O, was separ-ated from the solvothermal reaction of zinc(II) sulfate hepta-hydrate, 2,2'-di-pyridyl-amine and sodium adipate. The dinuclear metal complex has a centrosymmetric structure, with the Zn II atom adopting a highly distorted octa-hedral coordination sphere composed of four oxygen atoms from bridging adipato ligands and two pyridine nitro-gen atoms. In the crystal, the title compound aggregates into a tri-periodic supra-molecular structure through inter-molecular hydrogen-bonding networks of the form O-H⋯O and N-H⋯O., (© Setifi et al. 2024.)

The title coordination polymer, [Co(N 3 ) 2 (C 9 H 8 N 2 )] n , was synthesized solvothermally. The Co II atom exhibits a distorted octa-hedral [CoN 6 ] coordination geometry with a bidentate 8-amino-quinoline ligand and four azide ligands. Bridging azide ligands result in chains extending along [100]. N-H⋯N hydrogen bonds join the chains to give an extended structure with sheets parallel to (002)., (© Setifi et al. 2024.)

The title compound, [Fe(C 2 N 3 ) 2 (C 8 H 7 N 5 ) 2 ]·2H 2 O, 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., (© Saadallah et al. 2023.)

The title compound, [Cu(C 9 H 5 N 4 O) 2 (C 10 H 9 N 3 ) 2 ], was synthesized solvothermally. The complex exhibits a distorted octa-hedral coordination geometry. The Cu II atom is located on an inversion centre. The distorted octahedral CuN 6 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]., (© Saadallah et al. 2022.)

The title metal-organic polymer, catena-poly[[(5,5'-dimethyl-2,2'-bipyridine-κ 2 N,N')iron(II)]-di-μ-azido-κ 2 N 1 :N 3 -[(5,5'-dimethyl-2,2'-bipyridine-κ 2 N,N')iron(II)]-di-μ-azido-κ 2 N 1 :N 1 ], [Fe(N 3 ) 2 (C 12 H 12 N 2 )] 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 Fe II 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 P2 1 /c. The molecular and crystal structures are very similar for both forms, the main difference being that the eight-membered Fe(μ-1,3-N 3 ) 2 Fe 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 .

The synthesis, characterization, crystal structure and detailed magnetic properties of a pyrazine (pyz) and azido (N 3 ) bridged cobalt(II) compound of formula [Co(N 3 ) 2 (pyz)] (1) are reported. Compound 1 shows a layered structure formed by Co(II) chains with double μ-N 3 (κN 1 ,N 1 ) bridges that are further connected by μ-(pyrazine-κN 1 ,N 4 ) 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 T c ≈ 8.0-7.0 K for dc fields above 200 mT and a long-range 3D ferromagnetic order at T c ≈ 4.5 K for dc fields above 400 mT.

In the title compound, [CdNi(C 9 H 8 N 2 ) 2 (CN) 4 ] n , the Cd and Ni atoms both lie on centres of inversion in space group P 2 1 / 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., (© Khelfa et al. 2021.)

In the title mol-ecular salt, (C 10 H 10 N 3 ) 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., (© Setifi et al. 2020.)

In the title compound, [Fe{(C 5 H 4 N) 3 N} 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 Fe II . 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. C 71 , 9-18]., (© Setifi et al. 2020.)

In crystal structures of two chain coordination polymers [M(tcnopr3OH) 2 (H 2 O) 2 ] (M = Ni II and Co II ; tcnopr3OH - = [(NC) 2 CC(O(CH 2 ) 3 OH)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 = Ni II and Co II ) 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.

The Co II atom in the title complex, [Co(SO 4 )(C 12 H 8 N 2 )(H 2 O) 3 ] (or C 12 H 14 CoN 2 O 7 S), is octa-hedrally coordinated within a cis-N 2 O 4 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., (© Setifi et al. 2020.)

The title compound, [Ni(C 10 H 8 N 2 ) 3 ](C 9 H 5 N 4 O) 2 ·2H 2 O, crystallizes as a racemic mixture in the monoclinic space group C 2/ c . In the crystal, the 1,1,3,3-tetracyano-2-ethoxypropenide anions and the water molecules are linked by O-H⋯N hydrogen bonds, forming chains running along the [010] direction. The bpy ligands of the cation are linked to the chain via C-H⋯π(cation) inter-actions involving the CH 3 group. The inter-molecular inter-actions were investigated by Hirshfeld surface analysis and two-dimensional fingerprint plots.

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(C 12 H 10 N 2 ) 2 (H 2 O) 4 ](C 9 H 5 N 4 O) 2 ·2C 12 H 10 N 2 , is a rare example of a mononuclear Fe II 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.

In the title compound, [Co(C 10 H 8 N 2 ) 3 ](C 9 H 5 N 4 O) 2 , the tris-(2,2'-bi-pyridine)-cobalt(II) dication lies across a twofold rotation axes in the space group C 2/ 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.

In the title compound, [Fe(C 11 H 11 N 3 ) 2 ](C 10 N 6 ), the Fe II cation is coordinated by two bis(pyridin-2-yl)methanamine (dipa) ligands and has crystallographic twofold symmetry. There are deviations from ideal octa-hedral geometry due to the steric requirements of the ligands. The polynitrile 1,1,3,3-tetra-cyano-2-(di-cyano-methylid-ene)propane-1,3-diide (tcpd 2- ) dianion is disordered about an inversion center and is not coordinated to the Fe atom. The anion is not planar but has a propeller shape. In the crystal, weak N-H⋯N inter-actions between the amine H atoms of the dipa ligands and two nitrile groups of the anion form an alternating chain of cations and anions related by the C -centering of the unit cell.

The redetermination of the structure of the title compound, [Fe(C 15 H 12 N 4 ) 2 ](ClO 4 ) 2 , (I), confirms the structure previously reported [Kucharski et al. (1978 a ▸). Aust. J. Chem . 31 , 53-56], but models the perchlorate over four sets of atomic sites, rather than using just one set of sites as in the original report. The supra-molecular assembly, not reported previously, takes the form of a complex three-dimensional framework built from C-H⋯O hydrogen bonds. The isotypic nickel(II) analogue, [Ni(C 15 H 12 N 4 ) 2 ](ClO 4 ) 2 , (III), has been refined using the original data set [Wang et al. (2011 ▸). Acta Cryst. E 67 , m 78], again using a four-component disorder model for the anion, rather than a two-component model as in the original report, leading to more satisfactory Cl-O distances and O-Cl-O angles.

Three photoluminescent complexes containing either Zn II or Cd II have been synthesized and their structures determined. Bis[4-amino-3,5-bis(pyridin-2-yl)-1,2,4-triazole-κ 2 N 1 ,N 5 ]bis(dicyanamido-κN 1 )zinc(II), [Zn(C 12 H 10 N 6 ) 2 (C 2 N 3 ) 2 ], (I), bis[4-amino-3,5-bis(pyridin-2-yl)-1,2,4-triazole-κ 2 N 1 ,N 5 ]bis(dicyanamido-κN 1 )cadmium(II), [Cd(C 12 H 10 N 6 ) 2 (C 2 N 3 ) 2 ], (II), and bis[4-amino-3,5-bis(pyridin-2-yl)-1,2,4-triazole-κ 2 N 1 ,N 5 ]bis(tricyanomethanido-κN 1 )cadmium(II), [Cd(C 12 H 10 N 6 ) 2 (C 4 N 3 ) 2 ], (III), all crystallize in the space group P-1, with the metal centres lying on centres of inversion, but neither analogues (I) and (II) nor Cd II complexes (II) and (III) are isomorphous. A combination of N-H...N and C-H...N hydrogen bonds and π-π stacking interactions generates three-dimensional framework structures in (I) and (II), and a sheet structure in (III). The photoluminescence spectra of (I)-(III) indicate that the energies of the π-π* transitions in the coordinated triazole ligand are modified by minor changes of the ligand geometry associated with coordination to the metal centres.

The hydrated title salt, [Cd 2 Cl 2 (C 10 H 8 N 2 ) 4 ](C 9 H 5 N 4 O) 2 ·0.81H 2 O, was obtained from the hydro-thermal reaction between 2,2'-bi-pyridine, cadmium(II) chloride and potassium 1,1,3,3-tetra-cyano-2-eth-oxy-propenide. The binuclear cation lies across a centre of inversion in the space group P 2 1 / c , with the other components in general positions. The cation has approximate, but non-crystallographic 2/ m symmetry and each of the Cd II atoms is a stereogenic centre, one having the Δ configuration and the other the Λ configuration. In the anion, one of the C(CN) 2 units is disordered over two sets of atomic sites having occupancies 0.75 (2) and 0.25 (2). The cations are linked by two independent C-H⋯Cl hydrogen bonds to form a sheet of R 2 2 (14) and R 4 2 (24) rings.

The search for new mol-ecular materials with inter-esting magnetic properties using the pseudohalide azide ion and quinolin-8-amine (aqin, C 9 H 8 N 2 ) as a chelating ligand, led to the synthesis and structure determination of the title complex, [Fe(N 3 ) 2 (C 9 H 8 N 2 ) 2 ]. The complex shows an octa-hedral geometry, with the Fe II atom surrounded by six N atoms; the two N 3 - anions coordinate in a cis configuration, while the remaining N atoms originate from the two quinolin-8-amine ligands with the quinoline N atoms lying on opposite sides of the Fe atom. The crystal packing is dominated by layers of hydro-philic and aromatic regions parallel to the ac plane, stabilized by a two-dimensional hydrogen-bonded network and π-π stacking.

The title hydrated salt, C 30 H 26 N 6 2+ ·2C 9 H 5 N 4 O - ·3H 2 O, was obtained as an unexpected product from the hydro-thermal reaction between potassium 1,1,3,3-tetra-cyano-2-eth-oxy-propenide, 4,4'-bi-pyridine and iron(II) sulfate hepta-hydrate. The cation lies across a twofold rotation axis in the space group I 2/ a with the other components all in general positions. In the cation, the H atom linking the pyridine units is disordered over two adjacent sites having occupancies of 0.66 (4) and 0.36 (4), i.e. as N-H⋯N and N⋯H-N. The water mol-ecules of crystallization are each disordered over two sets of atomic sites, having occupancies of 0.522 (6) and 0.478 (6) for one, and 0.34 (3) and 0.16 (3) for the other, and it was not possible to reliably locate the H atoms associated with these partial-occupancy sites. In the crystal, four independent C-H⋯N hydrogen bonds link the ionic components into a three-dimensional network.

The search for new mol-ecular materials with inter-esting magnetic properties, using the pseudohalide azide ion and di-2-pyridyl-amine (dpa, C10H9N3) as a chelating ligand, led to the synthesis and structure determination of the title compound, [Co(N3)2(dpa)2]2SO4·2H2O. The crystal structure comprises discrete [Co(dpa)2(N3)2](+) cations, sulfate anions, as well as H2O solvent mol-ecules. The Co(III) cations display a slightly distorted octa-hedral coordination sphere defined by two N atoms from azide anions and four N atoms from the pyridyl rings of two dpa ligands. In the crystal, extensive C-H⋯O, N-H⋯O, and O-H⋯O inter-actions result in supra-molecular sheets that lie parallel to the ab plane. The sheets are further linked through O-H⋯N inter-actions between the water mol-ecules of one sheet and azide anions of another sheet, forming a supra-molecular framework.

Polynitrile anions are important in both coordination chemistry and molecular materials chemistry, and are interesting for their extensive electronic delocalization. The title compound crystallizes with two symmetry-independent half 4,4'-bipyridine-1,1'-diium (bpyH2(2+)) cations and two symmetry-independent 1,1,3,3-tetracyano-2-ethoxypropenide (tcnoet(-)) anions in the asymmetric unit. One of the bpyH2(2+) ions is located on a crystallographic twofold rotation axis (canted pyridine rings) and the other is located on a crystallographic inversion center (coplanar pyridine rings). The ethyl group of one of the tcnoet(-) anions is disordered over two sites with equal populations. The extended structure exhibits two separate N-H···NC hydrogen-bonding motifs, which result in a sheet structure parallel to (010), and weak C-H···NC hydrogen bonds form joined rings. Two types of multicenter CN···π interactions are observed between the bpyH2(2+) rings and tcnoet(-) anions. An additonal CN···π interaction between adjacent tcnoet(-) anions is observed. Using density functional theory, the calculated attractive energy between cation and anion pairs in the tcnoet(-)···π(bipyridinediium) interactions were found to be 557 and 612 kJ mol(-1) for coplanar and canted bpyH2(2+) cations, respectively.

The title dinuclear complex, [Ag2(CN)3(C9H8N2)2], may be considered as an Ag(II) compound with the corresponding metal site coordinated by two bidentate quinolin-8-amine mol-ecules, one cyanide group and one dicyanidoargentate(I) anion, [Ag(CN)2](-). Since this latter ligand contains an Ag(I) atom, the complex should be a class 1 or class 2 mixed-valence compound, according to the Robin-Day classification. The Ag(II) atom is six-coordinated in a highly distorted octa-hedral geometry, while the Ag(I) atom displays the expected linear geometry. In the crystal, the amino groups of the quinolin-8-amine ligands form N-H⋯N hydrogen bonds with the N atoms of the non-bridging cyanide ligands, forming a two-dimensional network parallel to (102). The terminal cyanide ligands are not engaged in polymeric bonds and the title compound is an authentic mol-ecular complex. The title mol-ecule is thus a rare example of a stable Ag(I,II) complex, and the first mixed-valence Ag(I,II) mol-ecular complex characterized by X-ray diffraction.

In the title compound, [Fe(C8H7N3)(H2O)4]SO4, the central Fe(II) ion is octa-hedrally coordinated by two N atoms from the bidentate 2-(pyridin-2-yl)-1H-imidazole ligand and by four O atoms of the aqua ligands. The largest deviation from the ideal octa-hedral geometry is reflected by the small N-Fe-N bite angle of 76.0 (1)°. The Fe-N coordination bonds have markedly different lengths [2.1361 (17) and 2.243 (2) Å], with the shorter one to the pyrimidine N atom. The four Fe-O coordination bond lengths vary from 2.1191 (18) to 2.1340 (17) Å. In the crystal, the cations and anions are arranged by means of medium-strength O-H⋯O hydrogen bonds into layers parallel to the ab plane. Neighbouring layers further inter-connect by N-H⋯O hydrogen bonds involving the imidazole fragment as donor group to one sulfate O atom as an acceptor. The resulting three-dimensional network is consolidated by C-H⋯O, C-H⋯π and π-π inter-actions.

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.

In the title compound, catena-poly[bis[(2,2'-bipyridine-κ(2)N,N')(1,1,3,3-tetracyano-2-ethoxypropenido-κN)copper(II)]-μ4-hexanedioato-κ(6)O(1),O(1'):O(1):O(6),O(6'):O(6)], [Cu2(C9H5N4O)2(C6H8O4)(C10H8N2)2]n, the adipate (hexanedioate) dianion lies across a centre of inversion in the space group P1. The Cu(II) centre adopts a distorted form of axially elongated (4+2) coordination, and the Cu(II) and adipate components form a one-dimensional coordination polymer from which the 2,2'-bipyridine and 1,1,3,3-tetracyano-2-ethoxypropenide components are pendent, and where each adipate dianion is bonded to four different Cu(II) centres. The coordination polymer chains are linked into a three-dimensional framework structure by a combination of C-H···N and C-H···O hydrogen bonds, augmented by a π-π stacking interaction.

In the title compound, [Fe(C10H8N2)3](C9H5N4O)2·2H2O, the chiral cations lie across twofold rotation axes in the space group C2/c. The anions and the water molecules are linked by two independent O-H···N hydrogen bonds to form C2(2)(8) chains, and these chains are linked by the cations via C-H···N and C-H···O hydrogen bonds to form two interpenetrating three-dimensional frameworks, each of which contains only one enantiomeric form of the chiral cation.

In the title compound, [Cu(C2N3)2(C12H10N6)]n or [Cu(dca)2(abpt)]n, where abpt is 4-amino-3,5-bis(pyridin-2-yl)-4H-1,2,4-triazole and dca is the dicyanamide anion, the Cu(II) centre is five-coordinate with an approximately square-pyramidal geometry. One of the two dicyanamide ligands is a terminal ligand, but the other one acts as a μ1,5-bridging ligand between pairs of Cu(II) centres, so generating a one-dimensional coordination polymer. A combination of N-H···N and C-H···N hydrogen bonds, augmented by π-π stacking interactions, links the coordination polymer chains into a bilayer structure. Comparisons are made with some related Cu(II) complexes containing dca ligands and heteroaromatic co-ligands.

In the title salt, C14H18N2(2+) · 2C9H5N4O(-), the 1,1'-diethyl-4,4'-bipyridine-1,1'-diium dication lies across a centre of inversion in the space group P21/c. In the 1,1,3,3-tetracyano-2-ethoxypropenide anion, the two independent -C(CN)2 units are rotated, in conrotatory fashion, out of the plane of the central propenide unit, making dihedral angles with the central unit of 16.0(2) and 23.0(2)°. The ionic components are linked by C-H...N hydrogen bonds to form a complex sheet structure, within which each cation acts as a sixfold donor of hydrogen bonds and each anion acts as a threefold acceptor of hydrogen bonds.

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.

In the title compound, [Cu(C9H5N4O)Cl(C12H8N2)]n or [Cu(tcnoet)Cl(phen)]n, where phen is 1,10-phenanthroline and tcnoet is 1,1,3,3-tetracyano-2-ethoxypropenide, the axially elongated (4 + 2) coordination polyhedron around the Cu(II) centre contains N atoms from three different tcnoet ligands. The resulting coordination polymer takes the form of sheets which are linked in pairs by a single C-H...N hydrogen bond to form bilayers. The bond lengths provide evidence for significant bond fixation in the phen ligand and extensive electronic delocalization in the tcnoet ligand, where the two -C(CN)2 units are rotated, in conrotatory fashion, out of the plane of the central C3O fragment.

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) Å and 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.

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.

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.

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.

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.

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.

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.

The preparation, X-ray crystal structure, EPR data, and magnetic measurement of [Cu(II)(hfac)(2)(TTF-py)(2)](PF(6)).2CH(2)Cl(2), a novel material where the conducting and the localized spin systems are covalently linked through conjugated bridges, are reported. The partial oxidation of the TTF-type organic donor ligand yielded the first radical cation salt of a paramagnetic transition metal complex. Moreover, this compound shows a mixed valence state at the unimolecular level, and additionally, the arrangement of the molecules in the crystal structure revealed the presence of isolated mixed valence TTF dimers.