Redox-Triggered Switching of Conformational State in Triple-Decker Lanthanide Phthalocyaninates

Abstract

Double- and triple-decker lanthanide phthalocyaninates exhibit unique physical-chemical properties, particularly single-molecule magnetism. Among other factors, the magnetic properties of these sandwiches depend on their conformational state, which is determined via the skew angle of the phthalocyanine ligands. Thus, in the present work we report the comprehensive conformational study of substituted terbium(III) and yttrium(III) trisphthalocyaninates in solution depending on the substituents at the periphery of molecules, redox-states and nature of solvents. Conjunction of UV-vis-NIR spectroscopy and quantum-chemical calculations within simplified time-dependent DFT in Tamm–Dancoff approximation provided the spectroscopic signatures of staggered and gauche conformations of trisphthalocyaninates. Altogether, it allowed us to demonstrate that the butoxy-substituted complex behaves as a molecular switcher with controllable conformational state, while the crown-substituted triple-decker complex maintains a staggered conformation regardless of external factors. The analysis of noncovalent interactions within the reduced density gradient approach allowed to shed light on the nature of factors stabilizing certain conformers.

Solvation-Induced Conformational Switching of Trisphthalocyanates for Control of Their Magnetic Properties

“…Again, this is in line with spectroscopic data�trisphthalocyaninates exist in staggered conformations in aromatic solvents independently of the substitution pattern. 27,28 Thus, the dependence of conformational state of alkoxy-vs crown-substituted trisphthalocyaninates on the solvent nature confirms the role of specific solvation involving hydrogen bonds and CH•••π interactions in stabilizing the pairwise conformations either in staggered or gauche forms.…”

“…Assignment of the observed spectroscopic signatures to the indicated conformers has been made using simplified time-dependent DFT in Tamm−Dancoff approximation. 27 By contrast, crownsubstituted complexes M 2 [(15C5) 4 Pc] 3 are conformationally invariant�they exist in a staggered form in both types of solvents, which is also supported by comparative NMR studies. 28 To get deeper insights into the conformational behavior of triple-decker complexes, we have first synthesized novel heteroleptic homonuclear complexes [(BuO) 8 Pc]M-[(BuO) 8 Pc]M[(15C5) 4 Pc], M = Y or Tb containing both AlkO-and crown-substituted Pc ligands, which are fairly soluble in both types of solvents and, moreover, can be easily crystallized from them forming well-defined solvates as exemplified by CH 2 Cl 2 and toluene where different types of intermolecular solvent/solvate interactions can be readily identified, thus providing the first solid explanation of the role of substituents in the stabilization of staggered and gauche conformations in aromatic and aliphatic solvents.…”

“…This observation suggests that the presence of at least two neighboring [B 4 ] ligands is sufficient to provide the complex with solvation-induced conformational switching similar to the previously studied homoleptic complex M 2 [B 4 ] 3 . 27,28 Crystallographic Characterization. Crystallization of…”

“…22°, respectively (Figure ). , This switching is manifested in the difference of UV–vis spectra of complexes in different solvents: the staggered conformer with a narrow well-resolved Q-band is stabilized in benzene and toluene, while in chloroform and dichloromethane the broad Q-band of the gauche conformer is observed. Assignment of the observed spectroscopic signatures to the indicated conformers has been made using simplified time-dependent DFT in Tamm–Dancoff approximation .…”

“… , This switching is manifested in the difference of UV–vis spectra of complexes in different solvents: the staggered conformer with a narrow well-resolved Q-band is stabilized in benzene and toluene, while in chloroform and dichloromethane the broad Q-band of the gauche conformer is observed. Assignment of the observed spectroscopic signatures to the indicated conformers has been made using simplified time-dependent DFT in Tamm–Dancoff approximation . By contrast, crown-substituted complexes M 2 [(15C5) 4 Pc] 3 are conformationally invariantthey exist in a staggered form in both types of solvents, which is also supported by comparative NMR studies …”