Rational Synthesis and Investigation of Porous Metal–Organic Framework Materials from a Preorganized Heterometallic Carboxylate Building Block

Abstract

The tetranuclear heterometallic complex [LiZn(piv)(py)] (1, where piv = pivalate and py = pyridine) has been successfully employed as a presynthesized node for the construction of four porous metal-organic frameworks (MOFs) [LiZn(R-bdc)(bpy)]·solv (2-R, R-bdc; R = H, Br, NH, NO) by reaction with 4,4'-bipyridine (bpy) and terephthalate anionic linkers. The [LiZn] node is retained in the products, representing a rare example of the rational step-by-step design of isoreticular MOFs based on complex heterometallic building units. The permanent porosity of the activated frameworks was confirmed by gas adsorption isotherm measurements (N, CO, CH). Three compounds, 2-H, 2-Br, and 2-NH (but not 2-NO), feature extensive hysteresis between the adsorption and desorption curves in the N isotherms at low pressures. The substituents R decorate the inner surface and also control the aperture of the channels, the volume of the micropores, and the overall surface area, thus affecting both the gas uptake and adsorption selectivity. The highest CO absorption at ambient conditions (105 cm·g or 21 wt % at 273 K and 1 bar for 2-NO) is above the average values for microporous MOFs. The photoluminescent properties of the prototypic 2-H as well as the corresponding host-guest compounds with various aromatic molecules (benzene, toluene, anisole, and nitrobenzene) were systematically investigated. We discovered a rather complex pattern in the emission response of this material depending on the wavelength of excitation as well as the nature of the guest molecules. On the basis of the crystal structure of 2-H, a mechanism for these luminescent properties is proposed and discussed.

Rational synthesis and dimensionality tuning of MOFs from preorganized heterometallic molecular complexes

“…Tetranuclear coordination complex [Li 2 Co 2 (piv) 6 (py) 2 ] (1) was synthesized by a reaction of lithium pivalate salt Li(piv), polymeric amorphous [Co(piv) 2 ] n and pyridine in equimolar ratio in a mixture of CH 3 CN and THF. This synthetic methodic is similar to that for previously reported [Li 2 M 2 (piv) 6 ] (M = Ni, Co, Zn) complexes [30][31][32]. The compound 1 crystallizes in triclinic space group P−1 (Fig.…”

“…The six carboxylate anions are directed perpendicularly to the Co−Li axis of the node, while Co-N bonds are directed along this axis. In general complex is isostructural to previously reported [Li 2 Zn 2 (piv) 6 (py) 2 ] [32]. The only difference is that one µ 2bidentate oxygen atom in carboxylate group of pivalate anion connected to lithium cation.…”

“…It should be noted that all the reported compounds 2-6 were prepared from the complexes [Li 2 M 2 (piv) 6 ], which tetranuclear core is composed of two fused dinuclear units {LiM(piv) 3 } via lateral Li-O coordination interactions. In previous examples we showed the preservation of the tetranuclear core during the MOF assembly through linear ditopic ligands [32,40]. Apparently, the polycondensation in the presence of 3connected carboxylic ligands facilitates the dichotomy of the tetranuclear complex to dinuclear units and the formation of either 2D or 3D 3-conencted coordination networks, or only presence of N-donor ditopic ligands can stabilize the tetranuclear core [40].…”

Chemical Assembling of Heterometallic {Cd–M} (M=Li, Mg, Eu, Tb) Molecules with 3,5‐Di‐tert‐butylbenzoate Bridges and N‐Donor Ligands

“…[7][8][9][10][11] It is important that in many cases, the polynuclear structure of the metal moiety is preserved both upon replacement of N-donor ligands and carboxylate anions, which significantly expands the options for the chemical design of new heterometallic derivatives and allows one to manipulate the physical characteristics of molecules and even the crystals that are formed from them. [12] Cadmium(II) carboxylates, along with 3d-metal carboxylates, are attractive as a basis for the chemical design of practically important compounds. It was already shown that cadmium(II) trimethylacetate in the presence of alkaline earth metal ions is capable of forming CdÀ M II (M II = Mg, Ca, Sr) heterometallic tricyclic complexes [Cd 2 M(piv) 6 (lut) 2 ] (lut = 2,4lutidine).…”

Synthesis, Crystal Structures, and Properties of a New Supramolecular Polymer Based on Mixed Imidazole and Carboxylate Ligands

“…The MOFs possessing versatile structures and desired properties are mainly dependent on the appropriate organic linkers [9,10], and the external synthesis conditions such as pH values, molar ratio of reactants, reaction temperatures, solvent system, and counter anions play important roles in deciding the resulting architectures [11][12][13]. Up to now, the N-or O-donor organic ligands have been employed extensively to construct functional coordination polymers [14][15][16]. Particularly, the N-donor compounds such as imidazole, pyrazole, triazole, and tetrazole can exhibit flexible coordination modes and afford more predictable coordination modes, as a result, these types of ligands have been extensively employed to construct diverse complexes.…”