Synthesis and Characterization of Symmetrically versus Unsymmetrically Proton-Bridged Hexa-Iron Clusters.

Syntheses and magnetic and structural characterization of hexa-iron complexes of derivatized salicylaldoximes are discussed. Complexation of Fe(BF4)2·6H2O with each ligand (H2 L1 and H4 L2) in a methanolic-pyridine solution resulted in hexa-iron compounds (C1 and C2, respectively), which each contain two near-parallel metal triangles of [Fe3-µ3-O], linked by six fluoride bridges and stabilized by a hydrogen-bonded proton between the µ3-O groups. Within each metal triangle of C2, Fe(III) ions are connected via the amine "straps" of (H4 L2-2H). Variable-temperature magnetic susceptibility and Mössbauer data of C1 and C2 indicate the presence of dominant antiferromagnetic interactions between the high-spin (S = 5/2) Fe(III) centers. For C1, two quadrupole doublets are observed at room temperature and 5 K, consistent with structural data from which discrete but disordered [Fe3-µ3-O] and [Fe3-µ3-OH] species were inferred. For C2, a single sharp quadrupole doublet with splitting intermediate between those determined for C1 was observed, consistent with the symmetric [Fe3-µ3-O···H···µ3-O-Fe3] species inferred crystallographically from the very short µ3-O···µ3-O separation. The differences in the physical properties of the complexes, as seen in the Mössbauer, X-ray, and magnetic data, are attributed to the conformational flexibility imparted by the nature of the linkages between the closely related ligands.

New salicylaldoximato-borate ligands resulting from anion hydrolysis and their respective copper and iron complexes.

Anion hydrolysis reactions between salicylaldoximato ligands (L'-L''') and copper and iron BF4- metal salts, have resulted in the formation of new salicylaldoximato borate containing transition metal complexes: [Fe2(L' + 2H)2](BF4)2(MeOH)4 (C1), [Fe3(L'' + 4H)(OH)2(Py)2](BF4)2(H2O)2(Py)2 (C2), and [Cu2(L''' + H)2Cl2] (C3). Each of the complexes have been structurally characterised, revealing the indirect role boron plays in the formation of these complexes. For complexes C1 and C2, Mössbauer spectroscopy confirmed the existence of Fe(iii) oxidation states. SQUID magnetometry measurements were performed on complexes C2 and C3, revealing the presence of two competing exchange pathways between the three Fe(iii) centres in C2, with antiferromagnetic exchange dominating. For C3 weak antiferromagnetic exchange dominated between the two Cu(ii) centres.

Piperazine linked salicylaldoxime and salicylaldimine-based dicopper(ii) receptors for anions.

The syntheses and single crystal X-ray analyses of five strapped salicylaldoxime/salicylaldimine based dicopper(ii) receptors utilising a new piperazine linker are described. The complexes form 2 + 2 metallocycles and the molecular structures of all four complexes possess a small internal cavity with the utilisation of a short piperazine linker. The molecular structures of complexes [Cu2(L(4) - H)(L(4) - 2H) ⊂ DMF]BF4·DMF, and [Cu2(L(4) - H)2Br]Br·1.25DMSO·H2O·MeOH, show that intramolecular H-bonding interactions due to the presence of -OH (oxime moiety) groups lead to a Pacman-like cleft arrangement of the two metal coordinating subunits in the metallo-macrocycle. The geometrical constraints brought about by this constrained cleft make the receptor coordinate strongly to a bromide anion involving both metal centres as evidenced by whereas in the larger tetrafluroborate anion is excluded. Absence of the oxime moiety around the metal coordination site of the ligand as demonstrated in the complexes [Cu2(L(5))2BF4](BF4)3, and [Cu2(L(5))2Br]Br3·2MeOH, resulted in less constrained dicopper(ii) helicate forms. For these complexes no anion size discrimination was observed. The addition of pyridine solvent to a slightly modified piperazine-linked ligand produces an expanded 3 + 3 tube-like tricopper complex [Cu3(L(4a) - H)3Py3](BF4)2·(MeOH)3·PF6·(H2O)3, , with two coordinated pyridine molecules occupying the newly formed cavity.