Syntheses, Crystal Structures, and Properties of Ferrocene–Carboxylate Coordination Complexes Through Modulating the Auxiliary Ligands

Self-assemblies of the flexible ferrocenyl block (3-carboxy-1-oxopropyl)-ferrocene with Zn(II)/Cd(II) cations in the presence of different N-containing auxiliary ligands have led to four coordination complexes, namely, [{Zn(FcCOC2H4COO)2(Pbbbm)}2] · 1/2CH3OH (I), [{Zn-(FcCOC2H4COO)2(Btx)}2] · 2H2O (II), [Zn(FcCOC2H4COO)2(Bbbmd)] (III), and [Cd(η2-FcCOC2H4COO)2(Bbbmd)] (IV) (Fc = (η5-C5H4)Fe(η5-C5H4), Pbbbm = 1,4-bis(benzimidazol-1-ylmethyl)-benzene, Btx = 1,4-bis(1,2,4-triazol-1-ylmethyl)-benzene, Bbbmd = bis-(1-benzimidazolymethylene)-(2,5-thiadiazoly)-disulfide). Their structures have been determined by single-crystal X-ray diffraction analyses (CIF files CCDC nos. 948969 (I), 948970 (II), 948971 (III), 948972 (IV)), and further characterized by elemental analyses, IR spectra, and thermogravimetric analyses. Crystallographic characterization shows the two neutral complexes I and II to have dinuclear structures which are bridged through Pbbbm and btx, while complexes III and IV give mononuclear structures. The four complexes exhibit some differences in their conformations, which can be attributed to the influence of auxiliary ligands. Notably, various weak interactions are discovered in I–IV, and they have significant contributions to self-assembly, which extend the two dimers or mononuclear complexes to infinite 3D supramolecular networks. The electrochemical studies of I–IV in DMF solution display irreversible redox waves and they all show single peaks in correspondence with redox processes of Fe(II)/Fe(III) couple electron-transfer process of ferrocenyl moieties.

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