Can self-assembly of copper(ii) picolinamide building blocks be controlled?Electronic supplementary information (ESI) available: Fig. S1-S3, TG-DTA curves for the complexes 1, 2 and 3. Fig. S4-S7, X-ray powder diffraction patterns for the complexes 1, 2, 3 and 4. Fig. S8, reaction pathway from 1-NNN. CCDC 906738 and 906739. For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/c3ce41011k

Four copper( ii ) derivatives with picolinamide (piaH), [Cu(N 3 ) 2 (piaH) 2 ] ( 1 ), [Cu(NCO) 2 (piaH) 2 ] ( 2 ), [Cu(pia) 2 ]·2H 2 O ( 3 ) and [Cu(pia)(piaH)(ClO 4 )] 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 χ M T 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 N 3 − 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. The reaction pathways of [Cu(pia) 2 ]·2H 2 O and [Cu(pia)(piaH)(ClO 4 )] 2 are determined by the base strength of monodentate ligands in starting octahedral [Cu(piaH) 2 L 2 ] species, azide, cyanate, or acetate, as perchlorate is too weak.