Syntheses, crystal structures, electronic spectra and magnetic properties of two ion-pair charge transfer complexes based on [Ni(mnt)₂]⁻

Two new bimetallic ion-pair complexes 1 and 2 with general formula [M(phen)₃][Ni(mnt)₂]₂ (phen = 1, 10-phenanthroline, mnt²⁻ = maleonitriledithiolate; M = Ni²⁺, Fe²⁺ for 1 and 2), have been prepared and characterized by IR, elemental analysis, single crystal X-ray diffraction, UV-vis-NIR spectra and magnetic measurements. The structural determination reveals that the crystals of two ion-pair complexes, with monoclinic space group C2/c, have similar cell parameters and the [M(phen)₃]²⁺ cations and the [Ni(mnt)₂]^- anions are packed by forming alternate layers. Thermogravimetric (TG) analyses revealed that 1 and 2 are thermally stable up to ∼170 °C. UV-vis-NIR spectra discloses that two complexes exhibit sizable absorption in near-IR region because of ion-pair charge transfer (IPCT) transitions in 1 and 2. Investigation of the magnetic properties 1 shows Curie-Weiss-type paramagnetic behavior in the temperature range 2–400 K. For 2, the paramagnetic behavior above ∼40 K indicated the [Fe(phen)₃]²⁺ ion has a low-spin state and the weak Curie-Weiss type tail below 40 K results from a trace amount of paramagnetic [Ni(mnt)₂]^- species.