Temperature-dependent dimerization of TCNQ anion-radical in [Ni(bpy)3]2(TCNQ–TCNQ)(TCNQ)2·6H2O: Single-crystal structure, magnetic and quantum chemical study

The crystal structure of [Ni(bpy)3]2(TCNQ–TCNQ)(TCNQ)2·6H2O (1) was studied by X-ray single-crystal analysis at 145 K and 100 K. structures 1 these two temperatures are essentially the same as previously 200 K: is built up [Ni(bpy)3]2+ complex cations, centrosymmetric crystallographically independent TCNQ·- anion-radicals, disordered σ- π-dimerized (TCNQ)2 units, water molecules crystallization. Lowering temperature from K, via K–100 has shown that lower proportions π-dimerization in unit shifted favor σ-dimerization; moreover, variation weaker C–C σ-bond formed upon dimerization observed. In addition, lowering led to a shortening distance between anion-radicals which stacked along b-axis with overlapped exo groups. quantum chemical calculations showed smallest energy difference for σ π-dimer respect line lowest proportion observed experimentally. Temperature-dependent (1.8–270 K) magnetic study contribution Ni(II) ions (S = 1) four S 1/2 species carried TCNQ radicals higher temperatures, strongly coupled antiferromagnetic (AFM) exchange interaction 270 while low negligible TNCQ radical spins