Metal−organic frameworks (MOFs) with cuproushalide-aggregates have shown superiority as organic LED (OLED) and semiconductor materials, while engineering MOF flexibility by involving the expansion of cuprous aggregates remains a great challenge. In this particular work, a dissolution−recrystallization structural transformation (DRST) with the dramatic growth of Cu I −I aggregates, from 2D NJNU-100 to 3D NJNU-101 has been successfully realized. The unsaturated coordination nodes (2positional nitrogen atoms) in NJNU-100 have been demonstrated to be the driven force for DRST to NJNU-101 via the formation of coordination bonds. The structural transformation process was irreversible and observed with optical microscopy and powder XRD. The expansion of Cu I −I aggregates was also computational simulated accompanying with the rotation of the neutral tripodal TTTMB ligand (1,3,5-tris(1,2,4-triazol-1-ylmethyl)-2,4,6trimethylbenzene) and the reduction of Cu II to Cu I . Moreover, the intermediate product NJNU-102 was captured by adding the planar molecular anthrancene to shut down the reaction, where only partial 2-positional nitrogen atoms coordinated to the aggregates and the anthrancene was oxidized to anthraquinone. NJNU-102 has further confirmed that DRST involved the breakage and recombination of coordination bonds and the electron transfer. NJNU-100 and NJNU-101 could be applied as semiconductor and OLED materials. This work has provided insights for crystal engineering, especially for the construction of the Cu Ix X y aggregates, and illustrated that DRST could be controlled with a rational design (as the unsaturated coordination modes).

Efficient non-noble metal catalysts for oxygen reduction reaction (ORR) have been highly attractive for the fabrication of cost-effective fuel cells. Metal–organic frameworks (MOFs) derived heteroatom-doped carbon-based (NC) electrocatalysts have exhibited comparable electrocatalytic activity for ORR as commercial Pt/C catalyst, which were highly dependent on their MOF precursor/template structures. In this particular work, two NC composites, NC-1100 and MnO@NC-1100 (NC, nitrogen-doped carbon), have been successfully synthesized, which were derived from novel nitrogen-rich tetrazolate-based metal–organic frameworks, [Cd2(L)­(OH)­(H2O)] (1) and [Cd3Mn­(L)2(OH)2(H2O)2] (2) (L, 5′-(4-(1H-tetrazol-5-yl)­(benzamido)­benzene-1,3-dioic acid), respectively. The structural differences between complexes 1 and 2 arose from the introduction of Mn­(II) to complex 2, where the Cd­(II) in 1 was partially replaced by Mn­(II). Both complexes 1 and 2 possessed three-dimensional (3D) structures with one-dimensional (1D) open channels. The resultant MnO@NC-1100 from the pyrolysis of complex 2 at 1100 °C under Ar atmosphere has indicated much better electrocatalystic behavior for ORR over the NC-1100 from complex 1, due to the existence of additional active sites of cubic phase MnO particles. The presence of initial Cd­(II) benefits the spatial isolation of Mn­(II) and prevents the sintering of MnO during the pyrolysis for MnO@NC-1100. The evaporation of Cd­(II) and the explosion of nitrogen-rich tetrazolate groups would also promote the surface area of the resulting catalysts. Our study further demonstrated that the multiple metal centers of MOF could be the rational strategy to enhance the electrocatalytical performance. Compared with NC-1100, MnO@NC-1100 exhibited the enhanced electrocatalytic activity with an onset potential (E onset ) of 0.90 V and a half-wave potential (E half‑wave ) of 0.74 V, which provided an insight view of the structure–property relationship.

Methyl orange (MO) is a main organic water pollutants that has been attracted a lot of attention; it can be degraded under photoirradiation in the presence of H 2 O 2 . Herein, we developed two Cu(I)-based coordination complexes (named H 2 (Cu 4 Br 6 )[(Cu 4 Br 3 )(TTTMB) 2 (H 2 O)] 2 (ZZY-2) and (Cu 5 Br 6 )-(Cu 6 Br 9 )[Cu 3 Br(TTTMB) 2 ] (ZZY-3)), which could degrade the MO dye in the presence of H 2 O 2 with or without photoirradiation (TTTMB = 1,3,5tris(1,2,4-triazol-1-ylmethyl)-2,4,6-trimethylbenzene). Three-dimensional (3D) frameworks ZZY-2 and ZZY-3 were based on the molecule cage [Cu 3 (TTTMB) 2 ] with the homochiral (−Cu−Br−Cu−) n triple-stranded helical chain and multinuclear Cu 5 Br 6 and Cu 6 Br 9 units, respectively, which could be obtained via the dissolution−recrystallization structural transformation (DRST) from two-dimensional (2D) network ZZY-1 ([Cu 3 (TTTMB) 2 (H 2 O) 6 Cl 6 ]•2H 2 O). The addition of CuBr 2 and the amount of HCOOH were decisive for the DRST, where the formation of a Cu−N coordination bond between the free 2-positional nitrogen atom and Cu(II) was the initiator for DRST. ZZY-2 and ZZY-3 had superior chemical stability, which could maintain the structures after three cycles of degradation reactions. MO degradation catalyzed by ZZY-2 and ZZY-3 could undergo a Fenton-like reaction to produce the active species •OH in the presence of H 2 O 2 . No requirement of photoirradiation for ZZY-2 and ZZY-3 to degrade MO provided more practical meaning to sewage treatment. Cu(II)-based ZZY-4 was also obtained as ZZY-1 in the presence of HNO 3 , which demonstrated the influence of acid on the structure of nitrogen-based ligands. ZZY-4 has shown no capacity to degrade MO, which indicated that the oxidation of Cu(I) by H 2 O 2 could be the key step to initiate the MO degradation.

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