New Series of Indium Formates: Hydrothermal Synthesis, Structure and Coordination Modes

Three new indium(III) compounds, In(HCOO)3 (1), In2(HCOO)5(OH) (2), and In(HCOO)2(OH) (3), were synthesized
under hydrothermal conditions and characterized by single crystal and powder X-ray diffraction experiments, as
well as by IR spectroscopy, elemental analysis, and coupled TG-DSC−MS measurement. All of these compounds
adopt 3D framework structures consisting of InO6 octahedra and the 2.11 binding modes of formate with the (syn,
syn-; syn, anti-; anti, anti-) configurations. The structural investigation of these indium formates reveals that the
gradual introduction of the hydroxyl groups into the structures induces the polymerization of the InO6 octahedra,
that is, InO6 is isolated in 1, becomes dimeric in 2, and finally forms 1D chains in 3. In addition, a simple formula
that may be used for estimating the overall coordination number of the formate in Ma(HCOO)bLc is proposed.