Encapsulation of a Ni salen complex in zeolite Y: an experimental and DFT study

Abstract

It is observed that for a square planar Ni(II)-Schiff base complex of the general formula {Ni(II)L}, where L is {L: N,N'-bis(5-hydroxy-salicylidene)ethylenediamine}, when encapsulated in a supercage of zeolite Y the bulky guest complex adopts a non-planar geometry without disturbing the integrity of the zeolite framework. Detailed comparative characterization is carried out to understand the structural change of the guest complex as a result of steric and electronic interactions with the host framework. UV-Vis spectroscopic studies of the encapsulated and 'neat' complex show a significant blue shift in the d-d transition after encapsulation and the diamagnetic 'neat' complex exhibits paramagnetism after encapsulation. DFT studies of the Ni(II)-Schiff base complex have been carried out for different spin states in neat and encapsulated form and the UV-Vis spectra are simulated using TD-DFT to understand the observed spectra in detail.

The functionality of the hybrid systems driven by molecular dimension of the guest copper Schiff‐base complexes entrapped in Zeolite‐Y

“…It is quite interesting to perceive a regular blue shift and intensification of the d‐d transitions in the encapsulated copper ‐ Schiff‐base complexes. Such behavior already has been observed in the zeolite Y encapsulated complexes . Observed modified electronic behavior in the d‐d region is certainly an effect of different geometry of the co‐ordination sphere, which the guest complex has adopted under the space restrictions of host supercage.…”

“…Scanning electron microscopy also supports the fact that the complex formation is primarily taking place inside the host cavities. From the SEM images (SEM micrographs given in Figure a‐c before Soxhlet extraction for CuS4‐Y with different resolution; Figure d‐f for CuS4‐Y and Figure g‐i for CuSp4‐Y after Soxhlet extraction and Figure S4 in supporting information for CuS1‐Y and CuSp1‐Y), it is observed that before Soxhlet extraction, there are some detectable surface species probably due to the formation of the complex at the surface or un‐reacted ligands, however, are disappeared after Soxhlet extraction . making zeolite particle boundaries more clearly visible.…”

“…Observed modified electronic behavior in the d‐d region is certainly an effect of different geometry of the co‐ordination sphere, which the guest complex has adopted under the space restrictions of host supercage. Theoretical studies have also revealed the fact that changes in the bond angles, bond lengths, and HOMO‐LUMO gaps can be introduced in the guest complex by the process of encapsulation in zeolites . In the present study, the copper complexes have chosen on the basis of their molecular dimensions (i.e., end to end distances) of the complexes, which follow the order as CuS1 < CuS2 < CuS3 < CuS4 and CuSp1 < CuSp2 < CuSp3 < CuSp4 for the salen and salophen copper complexes respectively.…”

“…The Si/Al ratio of host framework remains unaffected even after the complete synthesis of the metal complex inside it which essentially signifies the lack of dealumination during the whole process of ion exchange and encapsulation (EDX data are given in supporting information Figure S1). [28] The concentration of metals in different samples are determined by atomic absorption spectroscopy and it is found that the metal content in the encapsulated Cu complexes is always less than that present in the Cu-exchanged zeolite Y (AAS data given in Table 1). The observation essentially indicates the complex formation inside the host cavity with slight leaching of some of the metal ions during the process of encapsulation.…”

“…From the SEM images (SEM micrographs given in Figure 3a-3c before Soxhlet extraction for CuS4-Y with different resolution; Figure 3d-3f for CuS4-Y and Figure 3g-3i for CuSp4-Y after Soxhlet extraction and Figure S4 in supporting information for CuS1-Y and CuSp1-Y), it is observed that before Soxhlet extraction, there are some detectable surface species probably due to the formation of the complex at the surface or un-reacted ligands, however, are disappeared after Soxhlet extraction. [28,31] making zeolite particle boundaries more clearly visible. The clarity in the observation of boundaries of host lattice in SEM micrographs and the persistent color of Soxhlet extracted final product are certainly logical indications of successful encapsulation of the complex inside the cavities of zeolite Y.…”