Synthesis, molecular orbital, optical and device characterization of mononuclear mixed ligand nickel(II) complex of phthalate with N,N,N′,N′-tetramethylethylenediamine for photodiode applications

•Mononuclear mixed ligand complex, [Ni(Phth)(Me4en)(H2O)2]·4H2O were synthesized.•Crystalline structure with hexagonal system were confirmed by TEM and SAED.•Multiple peaks were resolved and two direct allowed transitions were obtained.•Crystalline characteristics of [Ni(Phth)(Me4en)(H2O)2]·4H2O were studied by TEM and SAED.•Photoresponsivity supports the device for optoelectronic applications.

In this work, a new synthesized mononuclear mixed ligand nickel(II) complex was characterized by various techniques. Crystalline characteristics of [Ni(Phth)(Me4en)(H2O)2]·4H2O were studied by using transmission electron microscope(TEM). Well crystalline structure corresponds to the hexagonal crystal system and identified by selected area electron diffraction (SAED) were achieved. Coordination of the nickel(II) ion with the functional groups of the ligands was established from the IR spectrum. Molar conductance of the current complex in DMF (10−3 mol/L) indicated a non-electrolytic nature of the complex. Electronic spectra showed a strong band in the region 661–684 nm; MeCN (661 nm), CHCl3 (663 nm), MeOH (667 nm), Me2CO (675 nm), DMSO (682 nm) and DMF (684 nm) which can be assigned to 3A2g(F) → 3T1g(F) transition of an octahedral structure around nickel(II). Multiple peaks were easily resolved from the spectral dependence of the absorption coefficient (α) measurements and the analysis near the fundamental absorption edge showed two direct allowed transition with energy gaps of 1.18 and 2.53 eV. Dark current–voltage and capacitance–voltage characteristics of [Ni(Phth)(Me4en)(H2O)2]·4H2O/n-Si heterojunctions were studied to extract the main important parameters of the heterojunction device. The electrical characteristics of the heterojunction device under illumination hold the suitability of the device for optoelectronic applications.

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