Di- versus Trinuclear Copper(II) Cryptate for the Uptake of Dicarboxylate Anions

Abstract

Searching for receptors selective for the binding of dicarboxylate anions, the copper(II) complexes of the known ditopic octaazacryptand (t2pN8), derived from bistren [tren = tris(2-aminoethyl)amine] linked by p-xylyl spacers, were re-examined, with the expectation of observing a selective binding of oxalate or malonate by bridging the two copper centers of the [Cu2(t2pN8)(H2O)2](4+) receptor. Solution studies involving the supramolecular species formed by the receptor and oxalate (oxa(2-)), malonate (mal(2-)), and succinate (suc(2-)) anions are reported. The determined association constants revealed the unexpected formation of a 3:1:1 Cu/t2pN8/anion stoichiometry for the cascade species with oxa(2-) and mal(2-), and the single crystal X-ray structural characterization confirmed the presence of tricopper(II) complexes, with an unusual binding mode for the dicarboxylate anions. Each of the two copper atoms binds four nitrogen donor atoms of the t2pN8 cryptand and one additional hydroxide group, which bridges to the third copper. The square planar environment of this one is complete with two oxygen atoms from the oxalate (or the malonate). The two copper centers bound to the tren heads are ∼6.5 Å apart, each one at about 3.5 Å from the third Cu center. These studies were complemented by SQUID magnetization measurements and DFT calculations. The magnetic susceptibility measurements of the oxalate cascade complex showed a strong magnetic coupling (J = - 210 cm(-1)) between the Cu centers at a short distance (3.5 Å), while the coupling between the two equivalent Cu atoms (∼6.5 Å) was only -70 cm(-1). This result was well reproduced by DFT calculations.

A Chiral Halogen‐Bonding [3]Rotaxane for the Recognition and Sensing of Biologically Relevant Dicarboxylate Anions

“…Dicarboxylates (DC 2− ) constitute a large and structurally diverse class of anions that play crucial roles in biology and industry, with some implicated as environmental pollutants (e.g., oxalate) . Their biological importance has primarily driven the design and development of polytopic abiotic receptors that utilise hydrogen bonding (HB) interactions and Lewis acidic metal centres for binding and sensing . However, DC 2− are highly challenging targets for selective recognition because of their hydrophilicity and complex overall shapes, which arise from the diversity of spacer motifs between their anionic carboxylate termini.…”

Synthesis, Structure, and Magnetic Properties of Linear Trinuclear CuII and NiII Complexes of Porphyrin Analogues Embedded with Binaphthol Units

“…Inclusion of such trinuclear units inside a large macrocycle would improve their stability against decomposition, which is helpful to gain further insight into the properties and reaction behaviors of trinuclear complexes. Examples of linear trinuclear Cu II complexes of macrocyclic ligands are not abundant [31][32][33]. For example, the trinuclear Cu II complex A of an octaazacryptand ligand was recently reported [32] (Figure 1).…”

NEW MX2 AND M’Cl3 (M = Cu, Zn; M’= Y, Dy, Pr; X = Cl, Br) MALEATO COMPLEXES AND TETRAPHENYLANTIMONY FORMIATE ADDUCT: SYNTHESIS AND INFRARED STUDY

“…Maleic ammonium salts led to the formation of many complexes with metals such as, platine, copper, silver [1][2][3][4]. Organometallic compounds arouse a great interest because of the numerous applications found in various fields [5][6][7][8][9][10].…”