From Vauquelin's and Magnus' salts to gels, uniaxially oriented films, and fibers: Synthesis, characterization, and properties of tetrakis(1-aminoalkane)metal(II) tetrachlorometalates(II)

Complexes of the type [Pt(NH₂R)₄][PtCl₄] with R = (CH₂)_nCH₃, where n is 3, 6, 7, 8, 9,11, or 13, were synthesized and characterized with various methods (e.g., IR spectroscopy, SAXS, XPS, NEXAFS, TEM, DSC, and TGA). For comparison, the classical Magnus' green and pink salt (where R = H) were also prepared. The designated alkyl-substituted platinum compounds are pink, but their structure seems to be related rather with Magnus' green than with the pink salt. However, the Pt-Pt distance in the pink alkyl-substituted compounds is most likely larger than in Magnus' green salt. This result is in agreement with the low electrical conductivity (<10^-10 S/cm) in the alkyl-substituted complexes. Because the Pt-Pt interactions in the [Pt(NH₂R)₄][PtCl₄] compounds are presumably weak, these substances may be regarded as self-assembled supramolecular structures. Nonetheless, the prepared complexes show some characteristics of rigid-rod polymers with flexible side chains; for example, they are insoluble when the alkyl chains are short but become soluble for longer alkyl chains, and they are able to form two-dimensional hexagonal or sheet structures. The complexes melt under decomposition above 100 °C. The soluble [Pt(NH₂R)₄][PtCl₄] complexes form gels with fibrillar structures at temperature ranges that depend on the length of R. Films and fibers with uniaxially oriented fibrils were prepared from gels by drawing and electrostatic spinning. The mixed-metal complexes [Pd(NH₂R)₄][PtCl₄] and [Pt(NH₂R)₄][PdCl₄] (R = octyl) were also synthesized. The chemical and physical properties of the compounds with palladium differed significantly from those of [Pt(NH₂R)₄][PtCl₄]. In particular, one of these complexes is insoluble, whereas the other one decomposes relatively quickly in solution.