Naslov
Approaching the structure of tetranuclear Ni-complex: a journey through the maze of non-crystallographic information
(Approaching the structure of tetranuclear Ni- complex: a journey through the maze of non- crystallographic information)

Autori
Šišak Jung, Dubravka ; Pinar Prieto, Ana Belan ; Lazić, Predrag ; Pavlović, Gordana ; Cindrić, Marina

Vrsta, podvrsta i kategorija rada
Sažeci sa skupova, sažetak, znanstveni

Izvornik
29th European Crystallographic Meeting, Book of Abstracts / - , 2015, 490-490

Skup
29th European Crystallographic Meeting

Mjesto i datum
Rovinj, Hrvatska, 23.08.2015. - 28.08.2015

Vrsta sudjelovanja
Poster

Vrsta recenzije
Nije recenziran

Ključne riječi
X-ray Powder Diffraction; structure determination; TG; quantum mechanics; Nickel complex; combining methods

Sažetak
As a result of various synthetic paths, a cubane-type Ni-complex was obtained. Its single-crystal structural analysis revealed four nickel atoms coordinated with five donors from organic ligand and one methanol molecule.Heating this sample to 180 °C lead to a change of magnetic properties from ferro- to antiferromagnetic, and of color from green to red. For clarity, the former sample will be referred to as cubane-Ni, and the latter as cubane-Ni-180. In order to solve the structure of cubane Ni-180, X- Ray Powder Diffraction (XRPD) data were measured using the MYTHEN detector installed at Swiss Light Source. Any radiation damage was avoided by collecting 120 °C of data within ten second. However, the data resolution was only 3 Å. This, combined with lack of molecular model hindered classical structure determination, so additional information had to be considered. Thermogravimetric analysis showed a single weight loss, indicating that all methanol molecules were removed from the cubane-Ni structure upon heating. In fact, when the cubane-Ni-180 was exposed to a methanol atmosphere, it transformed back to cubane-Ni. These observations, supported by IR spectroscopy results, suggested that the Ni-ligand moiety was preserved. The XRPD patterns of both samples were found to be similar, so the unit cell parameters of the cubane-Ni could be used to facilitate the indexing of the cubane-Ni-180 pattern, which exhibited very few peaks. Quantum mechanical methods were subsequently used to assist in the structure solution. First, a starting structural model was built by removing the methanol ligands from the cubane-Ni structure. This model was subjected to series of energy optimizations, all resulting in clusters of four square-planar coordinated Ni-centers. This geometry was found to comply with the antiferromagnetic properties of the sample. Notwithstanding that the molecular structure was reasonable, the fit between the calculated and measured XRPD patterns was not satisfactory. In order to exclude the possibility of a strong model-bias, direct-space optimization of the modified molecular structure of cubane-Ni was tried. The last obstacle, preferred orientation of the crystallites, was addressed by adding geometrical restraints to the optimization. This way, solutions with chemically reasonable intermolecular distances could be favored. Finally, examination of the structures obtained by both approaches allowed the most likely structure of cubane-Ni-180 to be proposed.

Izvorni jezik
Engleski

Znanstvena područja
Kemija

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