Abstract A mono-nuclear copper (II) complex 1, formulated {[Cu(phen)2(CO3)]·7H2O} has been synthesized and characterized by X-ray diffraction studies, FTIR, and thermogravimetric (TG) analysis. However, there is a self-assembly structure of (H2O)38 cluster in this complex 1, and it is worth reporting. The adjacent (H2O)38 clusters connect together resulting in an infinite 2D water layer structure. The water morphology is stable at room temperature, but upon thermal decomposition, the water loss is irreversible. Graphical Abstract A mono-nuclear copper (II) complex 1, formulated {[Cu(phen)2(CO3)].7H2O} has been synthesized and characterized by X-ray diffraction studies, FTIR, and thermogravimetric (TG) analysis. However, there is a self-assembly structure of (H2O)38 water cluster in this complex 1, and it is worth reporting. The discrete (H2O)38 cluster connects together resulting in an infinite 2D water layer structure. The alternate arrangement of the complex 1 and the 2D water layer produce infinite through-channels along a axis direction, and the part moieties of complex 1 are located inside these channels. The water rings are stable at room temperature, and when thermally decomposes the water loss is irreversible. [ABSTRACT FROM AUTHOR]