Control of Intramolecular Ether‐Oxygen Coordination in the Crystal Structure of Copper(II) Complexes With Dipicolylamine‐Based Ligands

Abstract

Thirteen crystal structures of copper(II) complexes with a series of dipicolylamine (DPA)‐derived ligands, N‐(2‐methoxyethyl)‐N,N‐bis(2‐pyridylmethyl)amine (L1), N‐[2‐(2‐hydroxyethyloxy)ethyl]‐N,N‐bis(2‐pyridylmethyl)amine (L2) and N‐(3‐methoxypropyl)‐N,N‐bis(2‐pyridylmethyl)amine (L3), have been determined and the factors that control the coordination of the ether‐oxygen atom of these ligands to the copper centre are discussed. Complexes that have +1 or +2 charges exhibit coordination of the ether‐oxygen atom, whereas neutral complexes in which two anions are bound to the copper(II) centre tend to lose the oxygen coordination. Upon chelation of the oxygen atom, L3 forms a six‐membered chelate ring with respect to the 3‐aminopropyl ether moiety whereas L1 and L2 form a five‐membered chelate. This difference, especially in the nitrate and bromide complexes, determines whether the ether‐oxygen atom chelates to the metal centre to give a monocationic complex, or the second anion coordinates to the metal centre to form the ether‐free, neutral complex. The terminal anchor hydroxy group of L2 facilitates the ether‐oxygen coordination via a hydrogen bond interaction to the donor atom located trans to the aliphatic nitrogen atom in the basal plane. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)

Intramolecular ether oxygen coordination in the zinc complexes with dipicolylamine (DPA)-derived ligands

“…Previous works revealed that anchoring group such as hydroxyl group facilitates the ether oxygen coordination [10,43]. In this work, a hydrogen atom in the methyl group of L 0 was replaced with 2-pyridyl group to promote the coordination of ether oxygen atom, in which six-and five-membered chelate ring would be formed around 3-aminopropyl 2-pyridylmethyl ether moiety.…”

“…For the preparation of zinc complex with L 0 , replacement of chloride with perchlorate would yield the cationic complexes that tend to have ether oxygen-coordinated species because the coordination ability of perchlorate is weak [10]. The methanol solution of L 0 in the presence of Zn(ClO 4 ) 2 afforded [Zn(L 0 ) 2 ](ClO 4 ) 2 (3), in which six nitrogen atoms of cis-orientated two ligand molecules coordinated to the zinc center even in the presence of 1 eq of ligand (Fig.…”

“…As described above, linking an ether pendant chain to the DPA moiety would enhance the ether oxygen binding to the metal center [10]. Strong binding of the DPA unit to the copper(II) [5][6][7][8][9]11] assists the coordination of the anomeric oxygen atom of the sugar unit to the metal center, generating an asymmetric oxygen [12,13].…”

Homobinuclear sulfato-bridged and mononuclear nitrato complexes of Cu(II) with thiophen-2-yl-dipicolylamine; structure and anion-dependent absorption spectra

“…High sensitivity and selectivity toward Cu(II) and Cu(I) was observed by significant fluorescence quenching upon binding with copper ions, even in the presence of metal ions such as Ag + , Al 3+ , Ba 2+ , Ca 2+ , Co 2+ , Cr 3+ , Fe 2+ , Fe 3+ , Hg 2+ , K + , Mg 2+ , Mn 2+ , Na + , Ni 2+ , Pb 2+ , Sn 2+ , and Zn 2+ . Mikata et al [10] studied dpa-based complexes of Cu(II) and investigated the factors affecting intramolecular ether-oxygen coordination in their solid state structures. These authors noticed that the anion of the starting material plays a crucial role in this intramolecular coordination as well as the overall coordination environment of the metal ion.…”

“…Di-(2-picolyl)amine (dpa) has shown to coordinate to various transition metals as a tridentate ligand through the amine nitrogen and two pyridine nitrogen atoms with over 2500 hits in the CCDC [6]. Recently, the incorporation of Cu(II) into dpa based molecules has been reported [1][2][3][7][8][9][10][11]. Zhu and co-workers [1] synthesized a copper-sensitive fluoroionophore by modifying stilbene with dpa.…”