**4. Conclusions**

In this study, we explored a still poorly studied tetracaboxylic acid, 3-(2,4-dicarboxyl phenoxy)phthalic acid (H4dpa), as a multifunctional linker for the hydrothermal synthesis of new CPs. Hence, a simple synthetic procedure led to the formation of a series of copper(II), manganese(II), and zinc(II) coordination polymers. These compounds feature distinct types of 2D metal-organic layers driven by the <sup>μ</sup>4-dpa<sup>4</sup><sup>−</sup> or <sup>μ</sup>6-dpa<sup>4</sup><sup>−</sup> linkers, as well as different topologies ranging from **sql** (**1**) and **3,6L66** (**2**) to **hcb** (**3**).

Catalytic activity of **1**−**3** was also explored in the mild cyanosilylation of benzaldehyde substrates with TMSCN, showing that the zinc(II) CP **3** functions as an effective and reusable heterogeneous catalyst to give cyanohydrin products in up to 93% yields. The effects of various reactions parameters as well as substrate scope were studied.

As main novelty features of this work, we can highlight (i) an application of H4dpa as an underexplored multifunctional linker for design of new CPs, (ii) a synthesis of three structurally and topologically distinct metal-organic architectures, and (iii) notable catalytic activity of a zinc(II) derivative in the cyanosilylation reactions. Besides, the obtained results widen the applications of coordination polymers in heterogeneous catalysis [43,44]. Further research on assembling related types of CPs and exploring their potential in other catalytic transformations are currently underway.

**Supplementary Materials:** The following data are available online at https://www.mdpi.com/ article/10.3390/catal11020204/s1. Figure S1: FT-IR spectra, Figure S2: TGA curves, Figures S3 and S9: PXRD patterns, Figure S4: emission spectra, Figures S5–S8: supplementary catalysis data, Tables S1 and S2: selected structural parameters for **1**–**3**. CCDC-2043757–2043759.

**Author Contributions:** Conceptualization, J.G., X.Z. and A.M.K.; data curation, C.L., Y.L.; funding acquisition, Y.L., J.G. and A.M.K.; investigation, C.L., X.Z., Y.L., J.G. and M.V.K.; methodology, J.G.; visualization, J.G. and M.V.K.; writing—original draft, Y.L., J.G., X.Z., M.V.K. and A.M.K.; writing—review and editing, A.M.K. All authors have read and agreed to the published version of the manuscript.

**Funding:** This work has been supported by Science and Technology Planning Project of Guangzhou (201904010381), the Foundation for Science and Technology (FCT) and Portugal 2020 (projects CEECIND/03708/2017, LISBOA-01-0145-FEDER-029697, PTDC/QUI-QIN/3898/2020, and UID/ QUI/00100/2013). This paper has been supported by the RUDN University Strategic Academic Leadership Program.

**Conflicts of Interest:** The authors declare no conflict of interest.
