Metal atom-induced electronic and magnetic properties in racemic metal-organic crystals

Organic molecules, particularly bio-organic systems, were suggested as electronic and spintronic elements. However, their relatively low conductivity limits their practical utility. In this study, we investigated the crystal of DL-phenylalanine amino acid coordinated with copper ions (DL-Phe-Cu(II)). Single-crystal X-ray diffraction (SCXRD) and powder X-ray diffraction (PXRD) analyses confirmed that the crystals form in a monoclinic system with a non-centrosymmetric space group (P12₁1), containing a ((DL-Phe)₂Cu)²⁺ complex where two DL-Phe ligands coordinate to a Cu(II) ion via amino and carboxylate groups. Optical absorption spectroscopy indicated changes in electronic structure upon complex formation, while circular dichroism (CD) spectroscopy showed no significant Cotton effects, confirming the racemic and optically inactive nature of the complex. Electrospray ionization mass spectrometry (ESI-MS) further validated the formation of the ((DL-Phe)₂Cu)²⁺ complex in solution, supporting a 2 : 1 ligand-to-metal ratio. Electrical conductivity studies indicated semiconducting behaviour with a temperature-dependent transition. Below ∼50 K, the DL-Phe-Cu(II) crystals displayed high resistivity, indicative of localized charge carriers. Above ∼100 K, the system exhibited thermally activated conduction with Arrhenius-type behaviour, suggesting a wide-bandgap semiconductor. Current-voltage (I-V) measurements confirmed increasing conductivity with rising temperature, consistent with enhanced charge carrier mobility.