Homobinuclear sulfato-bridged and mononuclear nitrato complexes of Cu(II) with thiophen-2-yl-dipicolylamine; structure and anion-dependent absorption spectra

A new ligand, bispyridin-2-ylmethyl-thiophen-2-ylmethylamine, 2ThDPA (1), was synthesized and its complexes of Cu(II) were isolated. When Cu(NO3)2 was used as the metal source, a mononuclear complex with the formula [Cu(1)(NO3)2], 2, was isolated featuring both nitro groups coordinated bidentate to the Cu. 2 crystallizes in the monoclinic P21/c space group with a = 14.848, b = 8.212, c = 32.752 Å, β = 102.52° and V = 3898.3 Å3. When CuSO4 was used as the metal source, a homobinuclear sulfato-bridged complex was isolated with the formula [Cu(1)SO4]2·CH3CN, 3. 3 crystallizes in the monoclinic P21/n space group with a = 10.457, b = 17.035, c = 12.425 Å, β = 108.72° and V = 2096.17 Å3. The structures of 2 and 3 are shown to be stabilized by an extended system of π–π stacking and hydrogen-bonding interactions. Comparison of the electronic absorption spectra of the ligand and complexes shows that complexation is maintained in solution and that the ligand absorption is attenuated in the complexes, depending on the counter-anion utilized.