Linkage isomerism in coordination polymers

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 Cu^II 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].

Solvent dielectric delimited nitro–nitrito photorearrangement in a perylenediimide derivative

The discovery of vibrant excited-state dynamics and distinctive photochemistry has established nitrated polycyclic aromatic hydrocarbons as an exhilarating class of organic compounds. Herein, we report the atypical photorearrangement of nitro-perylenediimide (NO₂-PDI) to nitrito-perylenediimide (ONO-PDI), triggered by visible-light excitation and giving rise to linkage isomers in the polar aprotic solvent acetonitrile. ONO-PDI has been isolated and unambiguously characterized using standard spectroscopic, spectrometric, and elemental composition techniques. Although nitritoaromatic compounds are conventionally considered to be crucial intermediates in the photodissociation of nitroaromatics, experimental evidence for this has not been observed heretofore. Ultrafast transient absorption spectroscopy combined with computational investigations revealed the prominence of a conformationally relaxed singlet excited-state (S^CR₁) of NO₂-PDI in the photoisomerization pathway. Theoretical transition state (TS) analysis indicated the presence of a six-membered cyclic TS, which is pivotal in connecting the S^CR₁ state to the photoproduct state. This article addresses prevailing knowledge gaps in the field of organic linkage isomers and provides a comprehensive understanding of the unprecedented photoisomerization mechanism operating in the case of NO₂-PDI.

The unprecedented photorearrangement of nitro-perylenediimide (NO₂-PDI) to nitrito-perylenediimide (ONO-PDI) is shown to occur through a cyclic six-membered transition state triggered by visible-light excitation.

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

The title structure consists of [Ni(CN)₄]^2– square-planar anions separated by layers of (C₁₀H₁₀N₃)⁺ cations. The crystal packing features N—H⋯N hydrogen bonds, which generate [101] chains.

In the title mol­ecular 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 intra­molecular 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 inter­actions 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.

Bis[tris(pyridin-2-yl)amine]iron(II) tris(dicyanomethylidene)methanediide

Both ions in the title compound lie across centres of inversion, with the anion being statistically disordered.

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 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 mol­ecules 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].

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

The Co^II atom in the title complex is octa­hedrally coordinated within an N₂O₄ donor set defined by two N-atom donors of the 1,10-phenanthroline ligand, sulfate-O and three aqua-O atoms, the latter occupying an octa­hedral face. In the crystal, supra­molecular layers parallel to (110) are sustained by aqua-O—H⋯O(sulfate) hydrogen bonding.

The Co^II atom in the title complex, [Co(SO₄)(C₁₂H₈N₂)(H₂O)₃] (or C₁₂H₁₄CoN₂O₇S), is octa­hedrally 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 octa­hedral face. In the crystal, supra­molecular 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 inter­action 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 mol­ecular 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-tri­aqua 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 = Ni^II and Co^II; 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 = 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.

Six tris-(bipyrid-yl)iron(II) complexes with 2-substituted 1,1,3,3-tetra-cyano-propenide, perchlorate and tetra-fluorido-borate anions; order versus disorder, hydrogen bonding and C-N⋯π inter-actions

Structures are reported for six closely related salts of tris-(bipyrid-yl)iron(II) cations, namely tris-(2,2'-bi-pyridine)-iron(II) bis-(1,1,3,3-tetra-cyano-2-meth-oxy-propenide) 0.776-hydrate, [Fe(C10H8N2)3](C8H3N4O)2.0.776H2O, (I), tris-(2,2'-bi-pyridine)-iron(II) 1,1,3,3-tetra-cyano-2-(propyl-sulfan-yl)propenide perchlor-ate, [Fe(C10H8N2)3](C10H7N4S)(ClO4), (II), tris-(5,5'-dimethyl-2,2'-bi-pyridine)-iron(II) 1,1,3,3-tetra-cyano-2-meth-oxy-propenide tetra-fluorido-borate ethanol 0.926-solvate, [Fe(C12H12N2)3](C8H3N4O)(BF4).0.926C2H2O, (III), tris-(5,5'-dimethyl-2,2'-bi-pyridine)-iron(II) 1,1,3,3-tetra-cyano-2-eth-oxy-propenide tetra-fluorido-borate, [Fe(C12H12N2)3](C9H5N4O)(BF4), (IV), tris-(5,5'-dimethyl-2,2'-bi-pyridine)-iron(II) 1,1,3,3-tetra-cyano-2-(ethyl-sufanyl)propenide tetra-fluorido-borate, [Fe(C12H12N2)3](C9H5N4S)(BF4), (V), and tris-(5,5'-dimethyl-2,2'-bi-pyri-dine)-iron(II) 1,1,3,3-tetra-cyano-2-prop-oxypropenide tetra-fluorido-borate, [Fe(C12H12N2)3](C10H7N4O)(BF4), (VI). In compound (I), one of the anions is disordered over two sets of atomic sites with equal occupancies while, in the second anion, just one of the C(CN)2 units is disordered, again over two sets of atomic sites with equal occupancies: the anionic components are linked by multiple C-H⋯N hydrogen bonds to form a three-dimensional framework. In compound (II), the polynitrile anion is disordered over two sets of atomic sites with occupancies in the approximate ratio 3:1, while the perchlorate anion is disordered over three sets of atomic sites: there are C-N⋯π inter-actions between the cations and the polynitrile anion. The polynitrile anion in compound (III) is fully ordered, but the tetra-fluorido-borate anion is disordered over two sets of atomic sites with occupancies 0.671 (4) and 0.329 (4): the cations and the tetra-fluorido-borate anions are linked by C-H⋯F inter-actions to form an inter-rupted chain. Compounds (IV) and (V) are isostructural and all of the ionic components are fully ordered in both of them: the cations and tetra-fluorido-borate anions are linked into C 2 2(12) chains. The polynitrile anion in compound (VI) is disordered over two sets of atomic sites with approximately equal occupancies, and here the chains formed by the cations and the tetra-fluorido-borate anions are of the C 2 2(13) type.

Three zinc(II) and cadmium(II) complexes containing 4-amino-3,5-bis(pyridin-2-yl)-1,2,4-triazole and polynitrile ligands: synthesis, molecular and supramolecular structures, and photoluminescence properties

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-κ²N¹,N⁵]bis(dicyanamido-κN¹)zinc(II), [Zn(C₁₂H₁₀N₆)₂(C₂N₃)₂], (I), bis[4-amino-3,5-bis(pyridin-2-yl)-1,2,4-triazole-κ²N¹,N⁵]bis(dicyanamido-κN¹)cadmium(II), [Cd(C₁₂H₁₀N₆)₂(C₂N₃)₂], (II), and bis[4-amino-3,5-bis(pyridin-2-yl)-1,2,4-triazole-κ²N¹,N⁵]bis(tricyanomethanido-κN¹)cadmium(II), [Cd(C₁₂H₁₀N₆)₂(C₄N₃)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.

Effect of the Metal Ion on the Enantioselectivity and Linkage Isomerization of Thiosemicarbazone Helicates

The effect of the metal ion and ligand design on the enantioselectivity and linkage isomerization of neutral cobalt and zinc bisthiosemicarbazone metallohelicates has been investigated in this work. The electrochemical synthesis has afforded the enantioselective formation of chirally pure cobalt helicates, and the ΛΛ isomer of a single enantiomer has been crystallized as only product for the cobalt methyl-substituted thiosemicarbazone helicate. Interestingly linkage isomers have been formed from zinc ethyl-substituted thiosemicarbazone helicate enantiomers for the first time. The co-existence of these isomers has been evaluated from the point of view of both experimental results and computational calculations.

Crystal structure of [tris-(4,4'-bi-pyridine)]-diium bis-(1,1,3,3-tetra-cyano-2-eth-oxy-propenide) trihydrate

The title hydrated salt, C30H26N62+·2C9H5N4O-·3H2O, 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 I2/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.

A Heterobimetallic Anionic 3,6-Connected 2D Coordination Polymer Based on Nitranilate as Ligand

In order to synthesize new coordination polymers with original architectures and interesting magnetic properties, we used the nitranilate ligand (C₆O₄(NO₂)₂^2- = C₆N₂O₈^2-), derived from the dianionic ligand dhbq^2- (2,5-dihydroxy-1,4-benzoquinone = H₂C₆O₄^2-). The use of this bis-bidentate bridging ligand led to [(DAMS)₂{FeNa(C₆N₂O₈)₃}·CH₃CN]_n (1) (DAMS⁺ = C₁₆H₁₇N₂⁺ = 4-[4-(dimethylamino)-α-styryl]-1-methylpyridinium), a 2D heterometallic coordination polymer presenting an unprecedented structure for any anilato-based compound. This structural type is a 3,6-connected 2D coordination polymer derived from the well-known honeycomb hexagonal structure, where Fe(III) ions alternate with Na⁺ dimers (as Na₂O₁₂ units) in the vertices of the hexagons and with an additional [Fe(C₆N₂O₈)₃]^3- anion located in the center of the hexagons connecting the three Na⁺ dimers. The magnetic properties of compound 1 show the presence of paramagnetic isolated high spin Fe(III) complexes with a zero field splitting, |D| = 8.5 cm^-1.

Multiple N-H···NC, C-H···NC and nitrile···π interactions in 4,4'-bipyridine-1,1'-diium bis(1,1,3,3-tetracyano-2-ethoxypropenide): structure determination and DFT calculations of anion···π cation interaction energies

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.

Crystal structure of μ-cyanido-1:2κ(2) N:C-dicyanido-1κC,2κC-bis-(quinolin-8-amine-1κ(2) N,N')-2-silver(I)-1-silver(II): rare occurrence of a mixed-valence Ag(I,II) compound

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.

Crystal structures of 2,2'-bipyridin-1-ium 1,1,3,3-tetracyano-2-ethoxyprop-2-en-1-ide and bis(2,2'-bipyridin-1-ium) 1,1,3,3-tetracyano-2-(dicyanomethylene)propane-1,3-diide

In 2,2'-bipyridin-1-ium 1,1,3,3-tetra-cyano-2-eth-oxy-prop-2-en-1-ide, C10H9N2 (+)·C9H5N4O(-), (I), the ethyl group in the anion is disordered over two sets of atomic sites with occupancies 0.634 (9) and 0.366 (9), and the dihedral angle between the ring planes in the cation is 2.11 (7)°. The two independent C(CN)2 groups in the anion make dihedral angles of 10.60 (6) and 12.44 (4)° with the central propenide unit, and the bond distances in the anion provide evidence for extensive electronic delocalization. In bis-(2,2'-bipyridin-1-ium) 1,1,3,3-tetra-cyano-2-(di-cyano-methyl-ene)propane-1,3-diide [alternative name bis-(2,2'-bipyridin-1-ium) tris-(di-cyano-methyl-ene)methane-diide], 2C10H9N2 (+)·C10N6 (2-) (II), the dihedral angles between the ring planes in the two independent cations are 7.7 (2) and 10.92 (17)°. The anion exhibits approximate C 3 symmetry, consistent with extensive electronic delocalization, and the three independent C(CN)2 groups make dihedral angles of 23.8 (2), 27.0 (3) and 27.4 (2)° with the central plane. The ions in (I) are linked by an N-H⋯N hydrogen bond and the resulting ion pairs are linked by two independent C-H⋯N hydrogen bonds, forming a ribbon containing alternating R 4 (4)(18) and R 4 (4)(26) rings, where both ring types are centrosymmetric. The ions in (II) are linked by two independent N-H⋯N hydrogen bonds and the resulting ion triplets are linked by a C-H⋯N hydrogen bond, forming a C 2 (1)(7) chain containing anions and only one type of cation, with the other cation linked to the chain by a further C-H⋯N hydrogen bond.

Crystal structure of tetra-aqua-[2-(pyridin-2-yl)-1H-imidazole-κ(2) N (2),N (3)]iron(II) sulfate

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.

catena-Poly[[[4-amino-3,5-bis(pyridin-2-yl)-4H-1,2,4-triazole-κ(2)N(1),N(5)](dicyanamido-κN)copper(II)]-μ2-dicyanamido-κ(2)N:N']: coordination polymer chains linked into a bilayer by hydrogen bonds and π-π stacking interactions

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.

Isolation of two different Ni2Zn complexes with an unprecedented cocrystal formed by one of them and a "coordination positional isomer" of the other

A new homometallic trinuclear Ni(II) complex [(NiL)2Ni(NCS)2] (1) and three heterometallic trinuclear Ni(II)-Zn(II)-Ni(II) complexes [(NiL)2Zn(NCS)2] (2), [(NiL)2Zn(NCS)2(CH3OH)2]·2CH3OH (3) and {[(NiL)2Zn(NCS)2(CH3OH)2]} {[(NiL)2Zn(NCS)2]} (4) have been synthesized by using the "complex as ligand" approach with the "metalloligand" [NiL] (H2L = N,N'-bis(salicylidene)-1,3-propanediamine) and thiocyanate in different ratios. All the complexes have been structurally and magnetically characterized. In the isomorphous complexes 1 and 2, the two terminal square planar Ni atoms and the central octahedral nickel atom (in 1) or zinc atom (in 2) are arranged in a bent structure where two cis κN-SCN(-) thiocyanate ions are coordinated to the central atom. The chemical composition of 3 is very similar to that of 2 but, in 3, the central Zn atom is tetrahedral and the κN-SCN(-) thiocyanate ions occupy an axial position of each terminal nickel atom (which now are octahedral with the sixth position occupied by a methanol molecule). Complex 4 consists of two closely related trinuclear units 4A and 4B. In 4A, the coordination environments of the metals are identical to those of 3 whereas 4B is a "coordination position isomer" of complex 2 with the central square pyramidal Zn and one of the terminal square pyramidal Ni atoms coordinated by two κN-SCN(-) thiocyanate ions. Complex 4 is a unique example of a cocrystal formed by two similar trinuclear units (4A and 4B) where 4A is identical to an existing complex (3) and 4B is a "coordination position isomer" of another existing complex (2).

Coordination chemistry of 6-thioguanine derivatives with cobalt: toward formation of electrical conductive one-dimensional coordination polymers

In this work we have synthetized and characterized by X-ray diffraction five cobalt complexes with 6-thioguanine (6-ThioGH), 6-thioguanosine (6-ThioGuoH), or 2'-deoxy-6-thioguanosine (2'-d-6-ThioGuoH) ligands. In all cases, these ligands coordinate to cobalt via N7 and S6 forming a chelate ring. However, independently of reagents ratio, 6-ThioGH provided monodimensional cobalt(II) coordination polymers, in which the 6-ThioG(-) acts as bridging ligand. However, for 2'-d-6-ThioGuoH and 6-ThioGuoH, the structure directing effect of the sugar residue gives rise to mononuclear cobalt complexes which form extensive H-bond interactions to generate 3D supramolecular networks. Furthermore, with 2'-d-6-ThioGuoH the cobalt ion remains in the divalent state, whereas with 6-ThioGuoH oxidation occurs and Co(III) is found. The electrical and magnetic properties of the coordination polymers isolated have been studied and the results discussed with the aid of DFT calculations, in the context of molecular wires.