Chiral and SHG-Active Metal–Organic Frameworks Formed in Solution and on Surfaces: Uniformity, Morphology Control, Oriented Growth, and Postassembly Functionalization

Abstract

We demonstrate the formation of uniform and oriented metal–organic frameworks using a combination of anion effects and surface chemistry. Subtle but significant morphological changes result from the nature of the coordinative counteranion of the following metal salts: NiX 2 with X = Br – , Cl – , NO 3 – , and OAc – . Crystals could be obtained in solution or by template surface growth. The latter results in truncated crystals that resemble a half structure of the solution-grown ones. The oriented surface-bound metal–organic frameworks (sMOFs) are obtained via a one-step solvothermal approach rather than in a layer-by-layer approach. The MOFs are grown on Si/SiOx substrates modified with an organic monolayer or on glass substrates covered with a transparent conductive oxide (TCO). Regardless of the different morphologies, the crystallographic packing is nearly identical and is not affected by the type of anion or by solution versus the surface chemistry. A propeller-type arrangement of the nonchiral ligands around the metal center affords a chiral structure with two geometrically different helical channels in a 2:1 ratio with the same handedness. To demonstrate the accessibility and porosity of the macroscopically oriented channels, a chromophore (resorufin sodium salt) was successfully embedded into the channels of the crystals by diffusion from solution, resulting in fluorescent crystals. These “ colored ” crystals displayed polarized emission (red) with a high polarization ratio because of the alignment of these dyes imposed by the crystallographic structure. A second-harmonic generation (SHG) study revealed Kleinman symmetry-forbidden nonlinear optical properties. These surface-bound and oriented SHG-active MOFs have the potential for use as single nonlinear optical (NLO) devices.

Molecular cannibalism: Sacrificial materials as precursors for hollow and multidomain single crystals

“…The positive charges of the metal centers are balanced by chloride (Cl − ), as indicated by an average ratio of Cl/Ni = 2.2. These anions (from chloroform) 29 , 30 , 34 , 37 – 39 are not resolved as part of the crystallographic structures. The reaction with NiCl 2 and TPVA under solvothermal conditions resulted in uniform, sub-micron-sized crystals having a different morphology than observed in this study with NiBr 2 39 .…”

Crystalline Porous Materials for Nonlinear Optics

“…Wen et al used the tetrahedral pyridyl ligand 1,3,5,7-tetrakis(4-((E)-2-(pyridin-4-yl)vinyl) phenyl)adamantane (Ad-DB), which has a tendency to form a variety of highly uniform structures, [85,86] to react with NiX 2 (X = Br − , NO 3 − , and OAc − ) to prepare chiral MOFs. [87] In crystalline MOF-NiBr 2 , the propeller arrangement of achiral Ad-DB ligands around the metal center provides a chiral structure. Moreover, the unit cell of MOF contains only propellers with the same handedness, and hence the molecules crystallize in the NCS P622 space group, exhibiting a polarization dependent SHG response.…”

Design, Synthesis and Applications of Chiral Metal-Organic Frameworks

“…(B) [Pr(TDA)-(H 2 O)]•2.5H 2 O 的一维螺旋链 [38] Figure 4 (A) The coordinate structure of [Co(en) 3 ] 2 ＋ (en ＝ ethylenediamine) [37] . (B) The 1D helical chain of [Pr(TDA)(H 2 O)]• 2.5H 2 O [38] Lahav 等 [39]…”