Synthesis and Characterization of Cu-Ni Mixed Metal Paddlewheels Occurring in the Metal-Organic Framework DUT-8(Ni0.98Cu0.02) for Monitoring Open-Closed-Pore Phase Transitions by X-Band Continuous Wave Electron Paramagnetic Resonance Spectroscopy

Matthias Mendt; Sebastian Ehrling; Irena Senkovska; Stefan Kaskel; Andreas Pöppl

doi:10.1021/acs.inorgchem.9b00123

Synthesis and Characterization of Cu-Ni Mixed Metal Paddlewheels Occurring in the Metal-Organic Framework DUT-8(Ni_0.98Cu_0.02) for Monitoring Open-Closed-Pore Phase Transitions by X-Band Continuous Wave Electron Paramagnetic Resonance Spectroscopy

Inorg Chem. 2019 Apr 1;58(7):4561-4573. doi: 10.1021/acs.inorgchem.9b00123. Epub 2019 Mar 14.

Authors

Matthias Mendt¹, Sebastian Ehrling², Irena Senkovska², Stefan Kaskel², Andreas Pöppl¹

Affiliations

¹ Felix Bloch Institute for Solid State Physics , Leipzig University , Linnéstrasse 5 , 04103 Leipzig , Germany.
² Department of Inorganic Chemistry , Dresden University of Technology , Bergstrasse 66 , 01062 Dresden , Germany.

PMID: 30869884
DOI: 10.1021/acs.inorgchem.9b00123

Abstract

A Cu²⁺-doped metal-organic framework (DUT-8(Ni_0.98Cu_0.02), M₂(NDC)₂DABCO, M = Ni, Cu, NDC = 2,6-napththalene dicarboxylate, DABCO = 1,4-diazabicyclo[2.2.2]octane, DUT = Dresden University of Technology) was synthesized in the form of large (>1 μm) and small crystals (<1 μm) to analyze their switchability by X-band continuous wave (cw) electron paramagnetic resonance (EPR) spectroscopy. The large crystals are flexible and in a porous open pore (op) phase after solvation in N, N-dimethylformamide (DMF), but in the activated solvent-free form, a nonporous closed pore (cp) phase forms. EPR measurements of the rigid Ni-free DUT-8(Cu) show a characteristic electron spin S = 1 room temperature signal of the antiferromagnetically coupled Cu²⁺-Cu²⁺ paddlewheel building unit of this metal-organic framework. None of the mixed metal DUT-8(Ni_0.98Cu_0.02) materials showed comparable signals, indicating the absence of dimeric Cu²⁺-Cu²⁺ paddlewheel units in the materials. Instead, characteristic electron spin S = 3/2 signals are detected for all DUT-8(Ni_0.98Cu_0.02) samples at temperatures T < 77 K, which can be assigned to ferromagnetically coupled mixed metal Ni²⁺-Cu²⁺ paddlewheel units. Those signals differ characteristically for the op and cp phase and enable monitoring the reversible op-cp transition during the de-/adsorption of DMF.