Synthesis, Structure and Magnetic Properties of a Tetranuclear Copper(II) Complex on the Basis of a 2‐Substituted Glucopyranoside Schiff Base Ligand

Condensation of a derivatized 2‐aminoglucose fragment with salicylaldehyde affords the new sugar‐based Schiff base ligand benzyl 4,6‐ O ‐benzylidene‐2‐deoxy‐2‐salicylideneamino‐α‐ D ‐glucopyranoside (H 2 L). The reaction of the dibasic ligand H 2 L with [Cu(CH 3 COO) 2 ] · H 2 O leads to the formation of the tetranuclear copper(II) complex [{Cu(L)} 4 ] ( 3 ) by a self‐assembly process. The X‐ray structural analysis of complex 3 which crystallizes together with two molecules of chloroform and one molecule of ethanol in the space group P 2 1 2 1 2 1 revealed for all copper atoms a NO 3 coordination environment with a square‐planar geometry. The tetranuclear molecule 3 consists of four chiral building blocks {Cu(L)} with the rare 2,3‐coordination of the trans ‐configured donor atoms of the sugar backbone. The observed coordination mode of the building blocks exemplifies how chitosan‐derived polysaccharide ligands can act as a chiral support for transition‐metal complexes. The C‐3 alcoholate oxygen atoms of the carbohydrate unit is bridging adjacent {Cu(L)} moieties resulting in an eight‐membered Cu 4 O 4 ring with a boat‐like conformation. Temperature‐dependent magnetic measurements of 3 indicate moderate antiferromagnetic interactions between the four copper(II) ions with a coupling constant of J = –130 cm –1 .(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)