MOF with hydroxynaphthoquinone as organic linker: Molecular structure of [Zn(Chlorolawsone)2(H2O)2] and thermogravimetric studies

Zinc complexes as MOF with hydroxynaphthoquinone as organic linkers are synthesized and characterized. The complexes Zn-1; [Zn(lawsone)2(H2O)2]⋅3H2O and Zn-2; [Zn(chlorolawsone)2(H2O)2]⋅H2O, where lawsone is 2-hydroxy-1,4-naphthoquinone and chlorolawsone is 3-chloro-2-hydroxy-1,4-naphthoquinone, serve as hosts for adsorbed water molecules. νCO shows shift towards lower frequencies ∼25 cm−1 in Zn-1 and ∼35 cm−1 in Zn-2 in FTIR spectra. 1H NMR shows upfield shift in Zn-1 and downfield shift in Zn-2 to the benzenoid ring protons. Bathochromic shift has been observed to the charge transfer band in UV–visible spectra of both complexes. The mass loss of adsorbed water molecules have been observed <100 °C in thermogravimetric (TG) studies. Three adsorbed water molecules are present in Zn-1, while one in Zn-2. X-ray diffraction studies of Zn-2 show, distorted octahedral geometry around Zn(II). The two chlorolawsone ligands are in plane with the metal, while water molecules are trans to this plane. Formation of MOF has been observed in the synthesis of Zn-2 with chlorolawsone as organic linkers. The structure is stabilized by OH⋯O, CH⋯O hydrogen bonding H-bonding along with Cl⋯π interactions to form a beautiful MOF architecture. Zn(II) atoms along with organic ligand form a tetramer via OH⋅O interactions. The shortest Zn⋯Zn distance is 5.04 Å.

► Zinc complexes as MOF with hydroxynaphthoquinone as organic linkers are reported. ► The complexes Zn-1 and Zn-2 serve as hosts for adsorbed water molecules. ► OH⋯O and CH⋯O hydrogen bondings result in 3-D molecular assemblies in Zn-2. ► Each chain is stabilized by Cl⋯π interaction in the ligands (3.35 Å).