Crystal Structures and Polymorphism of Nickel and Copper Coordination Polymers with Pyridine Ligands

Structure determination from unindexed powder data from scratch by a global optimization approach using pattern comparison based on cross-correlation functions

A method of ab initio crystal structure determination from powder diffraction data for organic and metal-organic compounds, which does not require prior indexing of the powder pattern, has been developed. Only a reasonable molecular geometry is required, needing knowledge of neither unit-cell parameters nor space group. The structures are solved from scratch by a global fit to the powder data using the new program FIDEL-GO (`FIt with DEviating Lattice parameters - Global Optimization'). FIDEL-GO uses a similarity measure based on cross-correlation functions, which allows the comparison of simulated and experimental powder data even if the unit-cell parameters deviate strongly. The optimization starts from large sets of random structures in various space groups. The unit-cell parameters, molecular position and orientation, and selected internal degrees of freedom are fitted simultaneously to the powder pattern. The optimization proceeds in an elaborate multi-step procedure with built-in clustering of duplicate structures and iterative adaptation of parameter ranges. The best structures are selected for an automatic Rietveld refinement. Finally, a user-controlled Rietveld refinement is performed. The procedure aims for the analysis of a wide range of `problematic' powder patterns, in particular powders of low crystallinity. The method can also be used for the clustering and screening of a large number of possible structure candidates and other application scenarios. Examples are presented for structure determination from unindexed powder data of the previously unknown structures of the nanocrystalline phases of 4,11-difluoro-, 2,9-dichloro- and 2,9-dichloro-6,13-dihydro-quinacridone, which were solved from powder patterns with 14-20 peaks only, and of the coordination polymer dichloro-bis(pyridine-N)copper(II).

4-Cyanopyridine complexes [MX2(4-CNpy)x]n (with X = Cl, Br and x = 1, 2): crystal structures, thermal properties and a comparison with [MX2(3-CNpy)x]n complexes

Crystal structures of [MX₂(4-CNpy)_x] with X = Cl and Br, M = Mn, Fe, Co, Ni, Cu, and Zn, and x = 1 and 2 were determined by X-ray powder diffraction. 4-Cyanopyridine can build chain and net structures.

Coordination compounds built up from MIICl2 and 3-cyanopyridine: double chains, single chains and isolated complexes

Crystal structures of [M^IICl₂(3-CNpy)_x], with M = Mn, Fe, Co, Ni, Cu, Zn and x = 1, 2, were determined by X-ray powder diffraction. Surprisingly, 3-cyanopyridine coordinates monodentately only.

3-Cyanopyridine as a bridging and terminal ligand in coordination polymers

Crystal structures of [M^IIBr₂(3-CNpy)_x]_(n) with M = Mn, Fe, Co, Ni and x = 1, 2, 4 were determined by powder diffraction. For x = 1, the 3-cyanopyridine ligand is bridging two metal atoms.

4-Cyanopyridine, a versatile mono- and bidentate ligand. Crystal structures of related coordination polymers determined by X-ray powder diffraction

4-Cyanopyridine (4-CNpy) as a monodentate ligand in single or double chains or as a bidentate ligand in two-dimensional networks.

Crystal structure of [bis-(2-amino-ethyl-κN)(2-{[4-(tri-fluoro-meth-yl)benzyl-idene]amino}-eth-yl)amine-κN]di-chlorido-copper(II)

The Cu(II) atom in the title compound, [CuCl2(C14H21F3N4)], adopts a coordination geometry that is between distorted square-based pyramidal and very Jahn-Teller-elongated octa-hedral. It is coordinated by three N atoms from the bis-(2-amino-eth-yl)(2-{[4-(tri-fluoro-meth-yl)benzyl-idene]amino}-eth-yl)amine and two chloride ligands. The two crystallographically unique copper complexes present in the asymmetric unit exhibit noticeable differences in the coordination bond lengths. Considering the Cu(II) atoms as having square-pyramidal geometry, the basal Cu-Cl bond lengths are typical [2.2701 (12) and 2.2777 (12) Å], while the apical distances are considerably elongated [2.8505 (12) and 2.9415 (12) Å]. For each mol-ecule, a Cu(II) atom from inversion-related mol-ecules are in nearby proximity to the remaining axial Cu(II) sites, but the Cu⋯Cl distances are very long [3.4056 (12) and 3.1645 (12) Å], attributable to van der Waals contacts. Nonetheless, these contacts appear to have some structure-directing properties, leading to association into dimers. These dimers associate via stacking of the aromatic rings to form extended zigzag chains.