Molecular Packing Dependent Solid State Fluorescence Response of Supramolecular Metal–Organic Frameworks: Phenoxo-Bridged Trinuclear Zn(II) Centered Schiff Base Complexes with Halides and Pseudohalides

Abstract

Molecular packing plays a key role in determining the photophysical properties in the aggregated state, but fine controlling of molecular packing is a great challenge. Here we report a series of new phenoxo-bridged homometallic trinuclear Zn (II) metal complexes (BN3, BNCS, BN­(CN)­2, BCl, BBr, and BI [complexes 1–6] having different anions with an aim to vary the photophysical properties of the complexes, where B stands for the ligand, N,N′-bis­(3-ethoxysalicylidenimino)-1,4-diaminobutane. All the complexes are structurally characterized by single crystal X-ray diffraction technique. The crystallographic investigation indicates that the complexes contain two types of Zn (II) centers: distorted square pyramidal and octahedral. The crystal structures are stabilized by intermolecular hydrogen bonding and C–H---π interactions leading to distinct supramolecular frameworks. The ground state and excited state electronic properties of these metal complexes have been investigated. In solution state, all the metal complexes are found to be moderately fluorescent and emit at similar wavelengths with no significant effect of anions on fluorescence emission. However, interestingly, solid state emission properties have been found to be significantly dependent on molecular assembly. In this series, dicyanamide [2] and thiocyanate [3] complexes exhibit significantly red-shifted high fluorescence response in the solid state which is attributed to their distinct packing in comparison to others. To the best of our knowledge, these complexes are the first example of Schiff base complexes demonstrating intriguing molecular packing dependent fluorescence emission.

Mono- and Rare Trinuclear Zn(II) Complexes with Near-Infrared Emissive Ligands: Anion-Responsive Nuclearity Control, Interconversion, Solid-State NIR Emission, and Latent Fingerprint Imaging

“…The ability to control the nuclearity of complexes derived from a series of similar ligands is important in developing metal–organic systems with predesigned properties. However, such nuclearity control is often difficult due to the involvement of multiple variables. − The common approaches employed for nuclearity control in metal complexes include changing the anions, reaction temperatures, reaction conditions, and additives. − Similarly, the development of strategies for the interconversion of metal complexes of different nuclearities is also vital as a synthetic approach. − Still, the predictable nuclearity control and the interconversion of metal complexes of different nuclearities remain challenging tasks to achieve. Further, the situation becomes more complicated if the metal ions do not show any crystal field stabilization energy for a particular geometry .…”

Unusual Effect of Minor Change in Ligand Substitution in Modulation of NIR Emission: A Case Study with [L–ZnII–LnIII] Complexes

“…Such interesting blue shifting of absorption bands on Ln–ligand complexation is also reported in the literature. − In contrast, we have also encountered several reports where redshift is mentioned on complexation . This discrepancy is presumably because the dilute solution of the lanthanide metal complex does not show the lowest energy band with appreciable optical density to be detected and is thereby often missed. ,, All complexes here have displayed three characteristic bands at 229 nm and 274 nm (intraligand charge transfer) and 353 nm (ligand to metal charge transfer).…”

“…The L1 and L2 ligands were synthesized according to the scheme presented in Scheme . − In short, 1,4-diaminobutane (1 mol) was condensed with 3-methoxysalicylaldehyde (2 mol) by refluxing in ethanol for 3 h to provide L1 (vide Scheme ). 3-Ethoxysalicylaldehyde was used to obtain L2 following the same Scheme .…”

1D Copper(II)-Aroylhydrazone Coordination Polymers: Magnetic Properties and Microwave Assisted Oxidation of a Secondary Alcohol

“…Transition metal complexes derived from multidentate Schiff base ligands received high significance due to their wide dimension of applications in the areas of molecular magnetism (Benelli and Gatteschi, 2002;Sutradhar et al, 2012Sutradhar et al, , 2013Sutradhar et al, , 2014bSutradhar et al, , 2015aSutradhar et al, , 2018Cho et al, 2016;Andruh, 2018), crystal engineering (Dong et al, 2000;Kitaura et al, 2004;Andruh et al, 2009), supramolecular chemistry (Pradeep and Das, 2013;El-Bindary et al, 2016;Dwivedi et al, 2018), catalysis (Sutradhar et al, 2013(Sutradhar et al, , 2014b(Sutradhar et al, , 2015a(Sutradhar et al, ,b,c, 2016a(Sutradhar et al, ,b,c, 2017(Sutradhar et al, , 2018(Sutradhar et al, , 2019, etc. Molecular magnetism is one of the significant domains determining magneto-structural correlations to design magnetic materials (Benelli and Gatteschi, 2002;Sutradhar et al, 2012Sutradhar et al, , 2013Sutradhar et al, , 2014bSutradhar et al, , 2015aSutradhar et al, , 2018Cho et al, 2016;Andruh, 2018).…”