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

Abstract

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.

A Charge-Neutral Self-Assembled L2Zn2 Helicate as Bench-Stable Receptor for Anion Recognition at Nanomolar Concentration

“…The final assembly of the receptor is conducted by metal coordination which generally proceeds in a quantitative manner and does not require the use of suitable templates often seen, e.g., in organic macrocyclization reactions. An overwhelming number of helicates and lantern-shaped metallacages with the ability to encapsulate different anions have been reported in the last two decades − since the pioneering work of McMorran and Steel, who observed encapsulation of hexafluorophosphate in a [L 4 Pd 2 ] 4+ complex in 1998. All reported structures have a common ground besides their structural variety, which is their positively charged nature.…”

Computational studies of the magneto-structural correlations in a manganese dimer with Jahn–Teller distortions

“…17,18 As such, the effect of having both elongation and compression distortions on the magnetic exchange between two Mn III centres has not yet been determined. Among our group's work on derivatised salicylaldoximes, [28][29][30][31][32][33][34] the crystal structure of a complex featuring two manganese coordination centres in distorted octahedral environments: one elongated and the other compressed was obtained (Fig. 1, ESI †).…”

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

“…Our interest in the synthesis and characterization of polynuclear derivatized salicylaldoxime clusters − began in 2009 with the synthesis and structural characterization of a hexacopper trihelicate complex, [Cu 6 (μ 3 -OH 0.5 ) 2 (H 4 L -2H) 3 ]­(PF 6 ) 3 ( 1 , H 4 L = 3,3′-[ N , N ′-dimethyl-1,6-hexanediaminobis­(methylene)]­bis­[2-hydroxy-5- tert -butylbenzaldehyde oxime]) . There have been several analogous iron examples reported after the investigation of this copper complex.…”