Can self-assembly of copper(ii) picolinamide building blocks be controlled??

CrystEngComm Pub Date: 2013-07-08 DOI: 10.1039/C3CE41011K

Abstract

Four copper(II) derivatives with picolinamide (piaH), [Cu(N3)2(piaH)2] (1), [Cu(NCO)2(piaH)2] (2), [Cu(pia)2]·2H2O (3) and [Cu(pia)(piaH)(ClO4)]2 (4) are reported. 1 and 2 were isolated as powders shortly after precipitation, becoming crystalline (3) after prolonged standing in mother liquor. The single crystal X-ray analysis revealed the deprotonation of the amide nitrogen (pia) in both 3 (mononuclear square planar [Cu(pia-N,N)2] building blocks) and 4 (pia acting as a bridge between copper(II) ions within the dimer). MAGSUS χMT versus T curves suggest only weak magnetic interactions between the copper(II) species in 3 and 4, though 4 is dinuclear. The magnetic coupling was reproduced by DFT calculations on the experimentally determined structures. The mechanism of formation of compounds 3 and 4 was analyzed by DFT calculations. Models of 1 and 2 underwent transfer of two hydrogen atoms from the piaH ligands to the two axial ligands N3? or NCO? that were released yielding 3. In the reaction leading to 4, the perchlorate is a very weak base that cannot deprotonate the piaH ligand and after the first hydrogen transfer to acetate the dimer 4 is formed. This reactivity, favoring alternative pathways, may switch off an expected self-assembly process.

Graphical abstract: Can self-assembly of copper(ii) picolinamide building blocks be controlled?
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