Inke Jess

Synthesis of new stable and metastable thiocyanato coordination polymers by thermal decomposition and by solution reactions

Investigations on the thermal behavior of the 1 : 4 (ratio between metal and neutral co-ligand) compound [Cd(NCS)2(pyridine)4] (1-Cd) show that the pyridine ligands can be removed in three separate steps. In the first TG step a pyridine-deficient 1 : 2 compound of composition [Cd(NCS)2(pyridine)2]n (2-Cd/III) is obtained, which transforms into an 1 : 1 compound of composition [Cd(NCS)2(pyridine)]n (3-Cd) on further heating. Rietveld refinement of 2-Cd/III proves that this compound represents a new form, which is different from that of the 1 : 2 compounds 2-Cd/I and 2-Cd/II reported recently. In further experiments a fourth 1 : 2 compound of composition [Cd(NCS)2(pyridine)2]n (2-Cd/IV) was crystallized and characterized by single crystal X-ray diffraction. In the crystal structures of 2-Cd/II, 2-Cd/III and 2-Cd/IV the metal cations are linked by the anionic ligands into chains, in which the Cd cations are coordinated by two trans-oriented pyridine ligands and four thiocyanato anions within slightly distorted octahedra. For the literature known compound 2-Cd/I no atomic coordinates are given, but for 2-Cd/II an all-cis, for 2-Cd/III an all-trans and for 2-Cd/IV an alternating cis-cis-trans arrangement of the thiocyanato anions is observed. Solvent mediated conversion experiments prove that 2-Cd/III transforms into 2-Cd/IVvia2-Cd/II as intermediate and therefore, the cis-cis-trans coordinated compound 2-Cd/IV represents the thermodynamic stable form at room-temperature. The 1 : 1 compound 3-Cd can also be prepared from solution. In its crystal structure the Cd cations are coordinated by one pyridine ligand as well as two N-bonded and three S-bonded thiocyanato anions. Two neighboring octahedra are connected by two μ-1,1,3(S,S,N)-coordinating anions into double octahedra, which are further linked into chains by μ-1,1,3(S,S,N)- and μ-1,3-coordinating thiocyanato anions. IR investigations of the 1 : 4, 1 : 2 and 1 : 1 compounds reveal that the different coordination modes of the anionic ligands can be rationalized by analyzing the changes in the values of their asymmetric νas(CN) stretching vibration. Additional investigations on 2-Cd/II, 2-Cd/III and 2-Cd/IV using differential scanning calorimetry and X-ray powder diffraction reveal that on heating additional crystalline 1 : 2 compounds are formed in reversible and irreversible phase transitions.

Luminescence properties of “double-stranded staircase” copper(I) halide coordination polymers with N-containing ligands

A set of CuIXL coordination polymers (X = Cl, Br, I; L = derivatives of pyrazine and bipyridine) with double-stranded staircase structures was analyzed by X-ray crystallography and luminescence spectroscopy to find a relationship between the structure and luminescence properties of the polymers. Our measurements have proved that luminescence emission wavelengths varied between 500–750 nm, after the polymers were irradiated by light with a wavelength of 370 nm. Although each coordination polymer has shown different emission maximum, we observed several interesting trends related to the structure of the compounds. There is a clear correlation between the emission maxima and the halide size and/or Cu–X distance, respectively. On the other hand, the substitution of the ligand L (pyrazine derivatives, 4,4′-bipyridine) has no significant contribution to the emission spectra. This observation supports the theory that the halide to metal charge transfer (XMCT) plays a key role in the photoluminescence of staircase polymers.

Thermodynamic and structural relationships between the two polymorphs of 1,3-dimethylurea

The title compound exists as polymorph (I), Fdd2 with Z = 8 [Perez-Folch et al. (1997). J. Chem. Cryst. 27, 367-369; Marsh (2004). Acta Cryst. B60, 252-253], and as polymorph (II), P2(1)2(1)2 with Z = 2 [Martins et al. (2009). J. Phys. Chem. A, 113, 5998-6003]. We have redetermined both structures at somewhat lower temperatures [(I) at 180 K rather than room temperature; (II) at 100 K rather than 150 K]. For polymorph (I) the space group Fdd2 is confirmed rather than the original choice of Cc. The molecular structures of both polymorphs are essentially identical, with exact crystallographic twofold symmetry, approximate C(2v) symmetry, and a trans orientation of the H-N-C=O moiety. In both polymorphs the molecules associate into chains of rings with graph set C(4)[R(2)(1)(6)] via bifurcated hydrogen-bond systems C(N-H)(2)···O=C. In the polar structure (I) the chains are necessarily all parallel, whereas in (II) equal numbers of parallel and antiparallel chains are present. Further physical investigations [differential scanning calorimetry (DSC), powder investigations, solvent-induced phase conversions] were undertaken: these showed: (i) that the commercially available compound consists predominantly of polymorph (II), which on heating transforms into polymorph (I) by an endothermic reaction, so that both polymorphs are related by enantiotropism; (ii) that polymorph (I) represents the more stable modification at room temperature, where polymorph (II) is metastable, with the thermodynamic transition temperature lying somewhere between 253 K and room temperature. An apparent third polymorph, consisting of fibrous needles, was shown by powder diffraction to consist of a mixture of polymorphs (I) and (II).

Synthesis and crystal structures of Zn(II) and Co(II) coordination compounds with ortho substituted pyridine ligands: two structure types and polymorphism in the region of their coexistence

Reaction of cobalt(II) thiocyanate or zinc(II) thiocyanate with 2-methylpyridine, 2-bromopyridine and 2-chloropyridine at room-temperature lead to tetrahedral complexes of composition M(NCS)2L2 (M = Co, Zn; 1: L = 2-methylpyridine, 2: L = 2-bromopyridine, 3: L = 2-chloropyridine). For all compounds, X-ray diffraction showed that the M2+ cations are coordinated by two terminal N-bonded thiocyanato anions and two substituted pyridine ligands in a distorted tetrahedral geometry. In all cases, complexes derived from cobalt and zinc with the same ligands are isomorphous. Eight crystalline solids were studied, which belong to only two different structure types: two polymorphs were obtained for the compounds with 2-chloropyridine: 3-Mα is isotypic with the 2-methylpyridine complexes 1-M and crystallizes in the orthorhombic space group P212121, whereas 3-Mβ and the isotypic 2-bromopyridine complexes 2-M adopt space group Pbcn. The structure types differ with respect to molecular conformation and packing: the complexes crystallizing in the former type are less distorted with respect to metal coordination; in the latter structure type, the angle subtended by the two ligands is by far the largest in the coordination sphere. P212121 allows for a more efficient intermolecular arrangement, whereas the complex geometry in Pbcn features shorter non-bonding distances between the ortho substituents of the pyridine ligands and comes closer to the gas phase geometry. DSC measurements gave no hints of a transformation between these modifications but from a melt of 3-Coα, 3-Coβ was obtained. Solvent mediated conversion experiments revealed that 3-Mα represents the thermodynamically stable form at room-temperature whereas 3-Mβ is metastable, in agreement with its lower density. Therefore, the thermodynamically stable phases with 2-chloropyridine as ligand adopt the crystal structure of the compounds with 2-methylpyridine, whereas the metastable forms are isotypic to the compounds with 2-bromopyridine.

2-(1,2,3,4-Tetra-hydro-naphthalen-1-yl-idene)hydrazinecarbothio-amide.

The molecular structure of the title compound, C11H13N3S, is not planar: the maximum deviation from the mean plane of the non-H atoms is 0.521 (2) Å for an aliphatic C atom, which corresponds to an envelope conformation for the non-aromatic ring. The hydrazinecarbothioamide substituent and the benzene ring have maximum deviations from the mean planes through the non-H atoms of 0.0288 (16) and 0.0124 (27) Å, respectively, and the dihedral angle between the two planes is 8.84 (13)°. In the crystal, molecules are linked into chains along [10] by pairs of N—H⋯S hydrogen bonds between molecules related by centres of symmetry.

Poly[bis­(cyanato-κN)bis­(μ-pyrazine-κ2N:N′)cobalt(II)]

In the crystal structure of the title compound, [Co(NCO)2(C4H4N2)2]n, the Co(II) cation is coordinated by four N-bonded pyrazine ligands and two N-bonded cyanate anions in a slightly distorted octahedral geometry. The crystal structure consists of μ-N:N′ pyrazine-bridged cobalt cyanate chains; these are further linked by additional μ-N:N′-bridging pyrazine ligands into layers, which are stacked perpendicular to the crystallographic a axis. The C and O atoms in both crystallographic independent cyanate anions are disordered in two orientations and were refined using a split model with site occupation factor ratios of 0.75/0.25 and 0.7/0.3.

Two polymorphs of 4-hydroxypiperidine with different NH configurations

4-Hydroxypiperidine 1 exists in two crystal forms, tetragonal 1t, space group P21c and orthorhombic 1o, space group Fdd2, both with one molecule in the asymmetric unit. The latter form was obtained only rarely and in small quantities. In form 1t, the NH hydrogen is axial, whereas in 1o it is equatorial; the OH group is equatorial in both structures. The packing of both forms involves one hydrogen bond N–H⋯O and one O–H⋯N. In solution, NMR spectra indicate the presence of separate axial and equatorial forms (with respect to the OH group) below ca. −53 °C; however, not even at −104 °C, the lowest temperature reached, could any freezing out of the inversion at nitrogen be observed, implying that the energy barrier for this process is (as expected) small. We were unable to convert 1t, which appears to be the more stable form over the whole temperature range up to the melting point, to 1o by heating or via melting and re-cooling (or by any other method), perhaps because the hydrogen-bonding pattern is resistant to change. The crystalline forms 1t and 1o, despite being polymorphs of 1 with different NH configurations, should not be described as “configurational polymorphs” because of the facile interconversion in solution.

N-Phenyl-2-(1,2,3,4-tetra­hydro­naph­thalen-1-yl­idene)hydrazinecarbo­thio­amide

The conformation of the title molecule, C17H17N3S, is stabilized by an intramolecular N—H⋯N hydrogen bond involving the azometinic group. The dihedral angle between the two aromatic rings is 36.49 (06)°. The non-aromatic ring of the tetralone substituent adopts a sofa conformation. In the crystal, molecules are linked by pairs of N—H⋯S hydrogen bonds related via centres of symmetry, forming dimers.

Synthesis, Crystal Structures and Polymorphism of New Cadmium and Zinc Thio- and Selenocyanato Coordination Compounds with 4-Acetylpyridine as N-Donor Ligand

Reactions of cadmium(II) thio- and selenocyanate with 4-acetylpyridine in different molar ratios and in different solvents always lead to the formation of compounds of composition Cd(NCS)2(4- acetylpyridine)2 (Cd1-I) and Cd(NCSe)2(4-acetylpyridine)2 (Cd2). Both compounds are isotypic and crystallize in the monoclinic space group C2/c. In their crystal structures the Cd cations are coordinated by two N-bonded 4-acetylpyridine ligands as well as two N- and two S/Se-bonded thio- or selenocyanato anions within a slightly distorted octahedral geometry. The Cd cations are linked into chains by pairwise μ-1,3-coordinating thio- or selenocyanato anions. In one reaction single crystals of a second polymorphic modification of composition Cd(NCS)2(4-acetylpyridine)2 (Cd1-II) were obtained by accident. This modification crystallizes monoclinically in space group P21/c, exhibits the same topology of the coordination network as in Cd1-I and Cd2 but a different arrangement of the chains in the crystal. Similar investigations with Zn(II) have revealed that only one compound of composition Zn(NCS)2(4-acetylpyridine)2 can be prepared that crystallizes in the triclinic space group P1. Its structure consists of discrete complexes in which the Zn(II) cations are tetrahedrally coordinated. A corresponding selenocyanato coordination compound could not be prepared Graphical Abstract Synthesis, Crystal Structures and Polymorphism of New Cadmium and Zinc Thio- and Selenocyanato Coordination Compounds with 4-Acetylpyridine as N-Donor Ligand

1-(5-Bromo-2-oxoindolin-3-yl­idene)thio­semicarbazone

The title molecule, C9H7BrN4OS, is essentially planar [r.m.s. deviation = 0.066 (2) Å], the maximum deviation from the mean plane through the non-H atoms being 0.190 (3) Å for the terminal amine N atom. In the crystal, molecules are linked through N—H⋯O and N—H⋯S interactions, generating infinite chains along the b-axis direction. In turn, the chains are stacked along the a axis via π–π interactions [centroid–centroid distance = 3.470 (2) Å] and further connected by N—H⋯Br interactions into a three-dimensional network. An intramolecular N—H⋯O hydrogen bond is also observed.