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.

Graphical AbstractCopper(II) complexes with a new thiophen-2-yl derivatized dpa ligand and nitrato and sulfato anions were prepared and characterized displaying unique bridging-bidentate coordination by the sulfato anions and anion dependent electronic spectra.Figure optionsDownload as PowerPoint slideResearch highlights
► New tripodal N3S-type dipicolylamine-based ligand with a thiophene ring pendant.
► Cu(II) complexes display structure dependent on the counter-anion.
► Mononuclear nitrato complex, rare bridging bidentate sulfato homobinuclear complex.
► Quenching of the ligand's π–π* absorption band is dependent on the counter-anion.