Control of the Porosity in Manganese Trimer-Based Metal-Organic Frameworks by Linker Functionalization

Manganese complexes have attracted significant interest in chemical industries and academic research for their application as catalysts owing to their ability to attain a variety of oxidation states. Generally, sterically bulky ligands are required to isolate molecular homogeneous catalysts in order to prevent decomposition. Herein, we capitalize on the catalytic properties of Mn and circumvent the instability of these complexes through incorporation of Mn-atoms into porous crystalline frameworks, such as metal-organic frameworks (MOFs). MOFs are able to enhance the stability of these catalysts while also providing accessibility to the Mn sites for enhanced reactivity. We solvothermally synthesized two trinuclear Mn-based MOFs, namely [Mn₃O(BDC)₃(H₂O)₃]_n (Mn-MIL-88, where H₂BDC = benzene-1,4-dicarboxylic acid) and [Mn₃O(BDC-Me₄)₃(H₂O)₃]_n (Mn-MIL-88-Me₄, where H₂BDC-Me₄ = 2,3,5,6-tetramethylterephthalic acid). Through comprehensive single-crystal X-ray diffraction, spectroscopic, and magnetic studies, we revealed that both MOFs are in a Mn(II/III) mixed-valence state instead of the commonly observed Mn(III) oxidation state. Furthermore, the use of a methylated linker (BDC-Me₄) allowed access to permanent porosity in Mn-MIL-88-Me₄, which is an analogue of the flexible MIL-88 family, yielding a catalyst for alcohol oxidation.

Seven novel coordination polymers constructed by rigid 4-(4-carboxyphenyl)-terpyridine ligands: synthesis, structural diversity, luminescence and magnetic properties

Seven coordination polymers, namely [Mn(4-cptpy)2]n (1), [Co(4-cptpy)2]n (2), [Mn3(4-cptpy)6(H2O)]n·2nH2O (3), [Co(4-cptpy)(HCOO)(H2O)]n·nDMF (4), [Zn2(4-Hcptpy)2Cl4]n·2nC2H5OH·nH2O (5), [Co4(3-cptpy)4(HCOO)4(H2O)2]n (6), and [Mn(3-cptpy)2]n (7) (4-Hcptpy = 4-(4-carboxyphenyl)-4,2':6',4''-terpyridine; 3-Hcptpy = 4-(4-carboxyphenyl)-3,2':6',3''-terpyridine), have been synthesized under hydro(solvo)thermal conditions and structurally characterized. A general solvothermal method is proposed for preparing carboxylate complexes in DMF solution without any basic additive. 1 and 2 possess isostructural 3D metal-organic frameworks containing nanosized cavities. 3 is a beautiful 2D coordination polymer assembled by flower-like Mn3(4-cptpy)6(H2O) subunits. 4 and 6 both display 2D polymeric networks constructed from 4/3-cptpy(-) ligands, in which the formate ligands originate from the hydrolysis of DMF. 5 is a 1D 2(1) helical chain polymer. 7 shows a 2D network with a (3.6) two-nodal kgd topology. 4/3-Hcptpy ligands display seven types of coordination modes. The zinc complex 5 emits strong violet luminescence. 1 and 2 are both thermally stable below 440 °C and exhibit antiferromagnetic interactions.

Structure and magnetic exchange in heterometallic 3d-3d transition metal triethanolamine clusters

Synthetic methods are described that have resulted in the formation of seven heterometallic complexes, all of which contain partially deprotonated forms of the ligand triethanolamine (teaH(3)). These compounds are [Mn(III)(4)Co(III)(2)Co(II)(2)O(2)(teaH(2))(2)(teaH)(0.82)(dea)(3.18)(O(2)CMe)(2)(OMe)(2)](BF(4))(2)(O(2)CMe)(2)·3.18MeOH·H(2)O (1), [Mn(II)(2)Mn(III)(2)Co(III)(2)(teaH)(4)(OMe)(2)(acac)(4)](NO(3))(2)·2MeOH (2), [Mn(III)(2)Ni(II)(4)(teaH)(4)(O(2)CMe)(6)]·2MeCN (3), [Mn(III)(2)Co(II)(2)(teaH)(2)(sal)(2)(acac)(2)(MeOH)(2)]·2MeOH (4), [Mn(II)(2)Fe(III)(2)(teaH)(2)(paa)(4)](NO(3))(2)·2MeOH·CH(2)Cl(2) (5), [Mn(II)Mn(III)(2)Co(III)(2)O(teaH)(2)(dea)(Iso)(OMe)(F)(2)(Phen)(2)](BF(4))(NO(3))·3MeOH (6) and [Mn(II)(2)Mn(III)Co(III)(2)(OH)(teaH)(3)(teaH(2))(acac)(3)](NO(3))(2)·3CH(2)Cl(2) (7). All of the compounds contain manganese, combined with 3d transition metal ions such as Fe, Co and Ni. The crystal structures are described and examples of 'rods', tetranuclear 'butterfly' and 'triangular' Mn(3) cluster motifs, flanked in some cases by diamagnetic cobalt(III) centres, are presented. Detailed DC and AC magnetic susceptibility and magnetization studies, combined with spin Hamiltonian analysis, have yielded J values and identified the spin ground states. In most cases, the energies of the low-lying excited states have also been obtained. The features of note include the 'inverse butterfly' spin arrangement in 2, 4 and 5. A S = 5/2 ground state occurs, for the first time, in the Mn(III)(2)Mn(II) triangular moiety within 6, the many other reported [Mn(3)O](6+) examples having S = ½ or 3/2 ground states. Compound 7 provides the first example of a Mn(II)(2)Mn(III) triangle, here within a pentanuclear Mn(3)Co(2) cluster.