Piperazine linked salicylaldoxime and salicylaldimine-based dicopper(ii) receptors for anionsElectronic supplementary information (ESI) available. CCDC 1042536-1042540. For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/c5dt02551f

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 1-4 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 [Cu 2 (L 4 − H)(L 4 − 2H) ⊂ DMF]BF 4 ·DMF, 1 and [Cu 2 (L 4 − H) 2 Br]Br·1.25DMSO·H 2 O·MeOH, 2 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 2 whereas in 1 the larger tetrafluroborate anion is excluded. Absence of the oxime moiety around the metal coordination site of the ligand as demonstrated in the complexes [Cu 2 (L 5 ) 2 BF 4 ](BF 4 ) 3 , 3 and [Cu 2 (L 5 ) 2 Br]Br 3 ·2MeOH, 4 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 [Cu 3 (L 4a − H) 3 Py 3 ](BF 4 ) 2 ·(MeOH) 3 ·PF 6 ·(H 2 O) 3 , 5 , with two coordinated pyridine molecules occupying the newly formed cavity. A series of piperazine dicopper metallo-macrocyles have been synthesised and the crystal structures reveal the extent that intramolecular hydrogen binding influences the resulting structure and ability to encapsulated anions.