Metal Nuclearity Modulated Four‐, Six‐, and Eight‐Connected Entangled Frameworks Based on Mono‐, Bi‐, and Trimetallic Cores as Nodes

TLDR

The study investigates how metal nuclearity influences network connectivity by synthesizing 3D entangled coordination frameworks with mono‑, bi‑, and trimetallic cores. The authors synthesized the frameworks by self‑assembly of Zn and Cd salts with the flexible ligand L and aromatic dicarboxylate ligands bdc and oba, then examined their thermal and luminescent properties. The results show that increasing metal nuclearity progressively raises network connectivity, yielding a tetrahedral Zn‑SBU diamondoid array, a bimetallic six‑connected alpha‑Po network, a novel (3,4)-connected net, and an unprecedented eight‑connected 4(20)6(8) topology with trinuclear Cd clusters, establishing the highest‑connected self‑penetrating framework known.

Abstract

To investigate the relationship between network connectivity and metal nuclearity, we designed and synthesized a series of three-dimensional (3D) entangled coordination frameworks based on different metal cores, namely [Zn(2)(bdc)(2)(L)(2)]2H(2)O (1), [Zn(bdc)(L)(0.5)] (2), [Zn(oba)(L)(0.5)] (3) and [Cd(3)(bdc)(3)(L)(2)(H(2)O)(2)] (4) by self-assembly of d(10) metal salts with the flexible long-chain ligand 1,4-bis(1,2,4-triazol-1-yl)butane (L), and with the rigid and nonrigid aromatic dicarboxylate ligands 1,4-benzenedicarboxylate (bdc) and 4,4'-oxybis(benzoate) (oba). Compound 1 exhibits a threefold interpenetrated diamondoid array typically based on a tetrahedral second building unit (SBU) at a single Zn center. Compound 2 adopts a threefold interpenetrated alpha-polonium-type network that is built from bimetallic cores as six-connected vertices. The structure of 3 also consists of dinuclear units; it comprises a novel (3,4)-connected threefold interpenetrated net with complex (4610)(46(2)10(3)) topology when single zinc centers act as four-connected nodes (or the alpha-Po topology if dinuclear units are considered as six-connected nodes). Compound 4, derived from a crosslinked fivefold interpenetrated diamond-like substructure, is an unusual example of a self-penetrating coordination framework displaying an unprecedented eight-connected 4(20)6(8) topology with trinuclear cadmium clusters as eight-connected nodes which, to our knowledge, not only defines a new topology for eight-connected coordination networks, but also represents the highest connected topology presently known for self-penetrating systems. Detailed structural comparison of these complexes indicates that the increase in metal nuclearity induces the progressive increase in the connectivities of the ultimate nets: that is, the metal nuclearity plays a significant role in tuning the connectivity of a specific network. The thermal and luminescent properties of these compounds are discussed.