Constantina Papatriantafyllopoulou

Using pyridine amidoximes in 3d-metal cluster chemistry: a novel ferromagnetic Ni12 complex from the use of pyridine-2-amidoxime

The use of pyridine-2-amidoxime in reaction with NiCl2.6H2O in the presence of NaOMe has led to a cationic NiII 12 cluster with novel structural features; each cluster molecule is a ferromagnet with a spin ground state of S = 6 arising from ferromagnetic exchange between the six octahedral NiII ions, but with intercationic interactions also affecting the magnetic properties.

In search of molecules displaying ferromagnetic exchange: multiple-decker Ni12 and Ni16 complexes from the use of pyridine-2-amidoxime

The use of pyridine-2-amidoxime (pyaoxH2) in Ni chemistry has provided access to a dodecanuclear complex and a hexadecanuclear Ni cluster, namely [Ni12(pyaox)6(pyaoxH)6(MeOH)2Cl2]Cl4·5MeOH (1·5MeOH) and [Ni16(pyaox)8(pyaoxH)8(MeOH)4](SO4)4·10H2O·26MeOH (2·10H2O·26MeOH). Complex 1·5MeOH was isolated by the reaction of NiCl2·6H2O, pyaoxH2 and NaOMe in a 1 : 1 : 2 molar ratio in MeOH in 60% yield. Treatment of NiSO4·6H2O with pyaoxH2 and NEt3 in a 1 : 1 : 2 molar ratio in MeOH afforded 2·10H2O·26MeOH in good yield (65%). The two compounds display a multi-decker configuration based on stacked Ni4 layers, {Ni4(pyaox)2(pyaoxH)2}2+x (x = 3, 1·5MeOH; x = 4, 2·10H2O·26MeOH); each deck consists of two square planar and two octahedral NiII centres. The number of decks observed in 1·5MeOH and 2·10H2O·26MeOH depends on the nature of the inorganic anion that is present in the reaction system, which provides elements of synthetic control towards new high nuclearity NiII species. 2·10H2O·26MeOH is the first structurally characterized complex of any metal displaying a quadruple-decker configuration, being also the highest nuclearity metal cluster bearing pyaoxH2 and the highest nuclearity NiII cluster with any type of 2-pyridyl oxime. Each cluster cation displays ferromagnetic exchange between the octahedral NiII ions resulting in a spin ground state of S = 6 for 1 and S = 8 for 2. Magnetothermal studies have been performed and discussed for both clusters.

Supramolecular patterns of cationic and neutral Ni(II) complexes from the interplay of hydrogen-bonding, stacking interactions and metal-coordination motifs

In an effort to explore the way in which the chemical subunits of crystal structures of transition metal complexes are put together in periodic ordered arrays in the solid state via noncovalent interactions, an investigation on a series of 13 nickel(II) complexes has been carried out. The complexes were isolated from the general NiII/X−/L or HL′ [X− = Cl−, Br−, I−, NO3−, NO2−, ClO4−; L = 1-methyl-4,5-diphenylimidazole, and HL′ = 4,5-diphenylimidazole] reaction system. A single-crystal diffraction analysis shows that, independently of the ligand used, most of the complexes contain the rigid square planar [NiL4]2+ (1–5) or [Ni(HL′)4]2+ (6–10) cation, which seems to have an impact on the self-assembly process by adopting a structure-directing role: the supramolecular assembly is organized around the rigid bulky cations via interactions with the surrounding counterion/solvent clusters in each individual structure. The components of the clusters, i.e. OH−/H2O (1), [NiCl4]2–/EtOH (2), Br−/H2O (3), NO3−/MeOH (4), ClO4−/Me2CO (5), Cl−/H2O (6), Br−/MeCN (7), I−/Me2CO/H2O (8), NO3−/EtOH/H2O (9), and ClO4−/Me2CO (10), are held tightly together by strong or weak hydrogen bonding. The structure-directing action of the cations is accomplished via weak C–H⋯O/Cl/Br−, π⋯π and C–H⋯π interactions (for L-containing complexes) or strong recurring N–H⋯/Cl−/Br−/I−/O motifs dominating the molecular self-assembly together with weak interactions (for HL′-containing complexes). The variety of the stereochemistries observed among the studied compounds (square planar, 1–10; tetrahedral, 11 and 12; octahedral, 13) seems to advocate the choice of nickel as an interesting candidate in metallosupramolecular research.