From infinite one-dimensional helix to discrete Cu(II)15 cluster along with in situ S(N)2 ring-cleavage of cis-epoxysuccinic acid: pH-controlled assemblies, crystal structures, and properties

Two Cu(II) coordination complexes {[Cu(ces)(H(2)O)(2)](H(2)O)(0.5)}(n) (1) and [Cu(15)(dhs)(6)(OH)(6)(H(2)O)(10)](H(2)O)(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 ring-cleavage 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.