Copper() complexes with the Schiff base methylbis[3-(5-methylimidazol-4-ylmethyleneimino)propyl]amine (BDPA), [Cu(BDPA)][ClO 4 ] 2 ؒH 2 O 1 and [Cu(BDPA)][PF 6 ] 2 2, and with a deprotonated Schiff base ligand [H 2 BIPO = 1,3-bis[(5-methylimidazol-4-ylmethyleneimino)propan-2-ol], {[Cu(HBIPO)]ClO 4 ؒH 2 O} n 3 and 4, have been prepared. Single-crystal structures show that 1 adopts a distorted square-pyramidal geometry with the basal plane occupied by an imidazole nitrogen, two imines and one

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... ino nitrogen atom and the apical position by another nitrogen atom from BDPA. 2 adopts a distorted trigonal-bipyramidal geometry with two imidazole nitrogen atoms at axial positions. Both 3 and 4 adopt distorted square-pyramidal geometry with four nitrogen atoms from HBIPO in the basal plane and the apical position occupied by a deprotonated imidazole nitrogen atom from an adjacent [Cu(HBIPO)] unit, resulting in polynuclear complexes. The differences in geometry and crystallization pathway between 1 and 2, and 3 and 4, are discussed based on the crystal structures, indicating that hydrogen bonding to the basal plane imidazole group plays an important role both in the change of geometry and crystallization form of the copper() complexes. 3 and 4 (BDPA = methylbis[3-(5-methylimidazol-4-ylmethyleneimino)propyl]amine, H 2 BIPO = 1,3-bis(5-methylimidazol-4-ylmethyleneimino)propan-2-ol, Scheme 1). The difference in geometry and crystallization forms between 1 and 2, and between 3 and 4, is discussed, focusing on hydrogen bond interaction with the metal-bound ligands.