DOSY NMR, X-ray Structural and Ion-Mobility Mass Spectrometric Studies on Electron-Deficient and Electron-Rich M6L4 Coordination Cages

Pia Bonakdarzadeh †, Filip Topić †, Elina Kalenius †, Sandip Bhowmik †, Sota Sato ‡, Michael Groessl§, Richard Knochenmuss §, and Kari Rissanen *†

† University of Jyväskylä, Department of Chemistry, Nanoscience Center, P.O. Box 35, FI-40014, University of Jyväskylä, Finland

‡ AIMR, Department of Chemistry, and JST ERATO, Tohoku University, Aoba-ku, Sendai 980-8578, Japan

§ Tofwerk AG, Uttigenstr. 22, 3600 Thun, Switzerland

Inorg. Chem., Article ASAP

DOI: 10.1021/acs.inorgchem.5b01082

Publication Date (Web): June 3, 2015

Copyright © 2015 American Chemical Society

*E-mail: kari.t.rissanen@jyu.fi.

Synopsis

A facile approach is presented for modification of M6L4 cages. Two new C3-symmetric ligands were synthesized which upon complexation with cis-protected Pd2+ or Pt2+ afforded four new electron-deficient or electron-rich M6L4 cages. Crystallographic study reveals the expected octahedral shape of the cages with the sizes of the cages obtained in solution (DOSY) and gas-phase (IM-MS) in good agreement with the solid-state structures.

Abstract

A novel modular approach to electron-deficient and electron-rich M6L4 cages is presented. From the same starting compound, via a minor modulation of the synthesis route, two C3-symmetric ligands L1 and L2 with different electronic properties are obtained in good yield. The trifluoro-triethynylbenzene-based ligand L1 is more electron-deficient than the well-known 2,4,6-tri(4-pyridyl)-1,3,5-triazine, while the trimethoxy-triethynylbenzene-based ligand L2 is more electron-rich than the corresponding benzene analogue. Complexation of the ligands with cis-protected square-planar [(dppp)Pt(OTf)2] or [(dppp)Pd(OTf)2] corner-complexes yields two electron-deficient (1a and 1b) and two electron-rich (2a and 2b) M6L4 cages. The single crystal X-ray diffraction study of 1a and 2a confirms the expected octahedral shape with a ca. 2000 Å3cavity and ca. 11 Å wide apertures. The crystallographically determined diameters of 1a and 2aare 3.7 and 3.6 nm, respectively. The hydrodynamic diameters obtained from the DOSY NMR in CDCl3:CD3OD (4:1), and diameters calculated from collision cross sections (CCS) acquired by ion-mobility mass spectrometry (IM-MS) were for all four cages similar. In solution, the cage structures have diameters between 3.3 to 3.6 nm, while in the gas phase the corresponding diameters varied between 3.4 to 3.6 nm. In addition to the structural information the relative stabilities of the Pt6L4 and Pd6L4 cages were studied in the gas phase by collision-induced dissociation (CID) experiments, and the photophysical properties of the ligands L1 and L2 and cages 1a, 1b, 2a, and 2b were studied by UV–vis and fluorescence spectroscopy.http://pubs.acs.org/doi/abs/10.1021/acs.inorgchem.5b01082