Origin of the data: Experimental spectroscopic measurements; Computer modelling. Data type: experimental measurements, models. The obtained data are in txt, DCS, DTA, SPC and PAR format. Data generated by a machine. Information on the machine: firm which produced the machine: BRUKER; version of the machine: ESP 300E for measurements at X-band frequency and Elexys E580 for measurements at Q-band frequency. Methodology used to collect the data and to process the data: EPR Spectroscopy Analytical and procedural information: EPR Spectroscopy Definitions of variables: Magnetic field and temperature. Units of measurement: milli Tesla (mT), Kelvin (K), Megahertz (MHz). Abbreviation mg70 for the data related to the binary system MgCl2/TiCl4, Abbreviation mg21 for the data related to the ternary system MgCl2/TiCl4/monoether Abbreviation mg36 for the data related to the ternary system MgCl2/TiCl4/diester. Specialized abbreviations: EPR – Electron Paramagnetic Resonance, CW– Continuous Wave, ESE – Electron Spin Echo, ESEEM – Electron Spin Echo Envelope Modulation, HYSCORE – Hyperfine Sublevel Correlation, ZN catalyst – Ziegler-Natta catalyst, ID – internal donor. To read the data, OriginPro 9.0 and Matlab R2019a have been used on Windows platform. For simulation Easyspin 5.2.28 simulation package has been used. To read the data, also Python can be used based on the convenience of the users. To process the data, OriginPro 9.0 and Matlab R2019a have been used in Windows platform. Python can also be used based on the convenient of users. Where to get OriginPro 9.0, Matlab R2019a and Easyspin 5.2.28: MATLAB R2019a: https://nl.mathworks.com/downloads/web_downloads/select_release?mode=gwylf OriginPro 9.0: https://www.originlab.com/index.aspx?go=PRODUCTS/Origin Easyspin 5.2.28: https://easyspin.org/easyspin/documentation/index.html Where to get the licenses: For MATLAB R2019a the website to download the licence is: https://nl.mathworks.com/downloads/web_downloads/select_release?mode=gwylf For OriginPro 9.0: https://www.originlab.com/index.aspx?go=PURCHASE/LicensingOptions