From Infinite One-Dimensional Helix to Discrete Cu15II Cluster along with in Situ SN2 Ring-Cleavage of cis-Epoxysuccinic Acid: pH-Controlled Assemblies, Crystal Structures, and Properties

Two Cu-II coordination complexes {[Cu(ces)(H2O)(2)](H2O)(0.5)}(n) (1) and [Cu-15(dhs)(6)(OH)(6)(H2O)(10)](H2O)(20) (2) have been synthesized from cis-epoxysuccinic acid (cis-H(2)ces) and Cu-II perchlorate under different pH conditions (ces = cis-epoxysuccinate and dhs = 2,3-dihydroxysuccinate), and fully characterized by IR spectra, elemental analyses, as well as single crystal and powder X-ray diffraction techniques. Notably, when the reaction was performed at pH above about 7.4, a one-dimensional (1-D) helical chain complex 1 is formed, whereas a neutral isolated Cu-15 nanocluster 2 is generated when the pH value is decreased to the range of about 6.6-7.3, being concomitant with in situ S(N)2 ringcleavage reaction of cis-H(2)ces to form (2S,3S)- and (2R,3R)-H(4)dhs. Further, extended supramolecular architectures are constructed via secondary interactions in both structures. The magnetic properties of 1 and 2 have also been studied in detail, showing that 1 is an antiferromagnetic helical chain of S= 1/2 spins and 2 possesses an S=3/2 spin ground state.