Counter-ligand control of the electronic structure in dinuclear copper-tetrakisguanidine complexesElectronic supplementary information (ESI) available. CCDC 1413943 ([6{Cu(OAc)2}2]), 1413941 ([6(CuBr2)2]), 1413939 ([6(CuI)2](I3)2), 1413940 (8), 1413938 (9), 1413942 ([Cu(DAP)4I][CuI2(DAP)4](I3)) and 1414996 (6(PF6)2). For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/c5dt03270a

The redox-active GFA (Guanidino-Functionalized Aromatic compound) 1,4,5,8-tetrakis(tetramethylguanidino)-naphthalene ( 6 ) is used to synthesize new dinuclear copper complexes of the formula [ 6 (CuX 2 ) 2 ] with different electronic structures. With X = OAc, a dinuclear Cu II complex of the neutral GFA is obtained (electronic structure [Cu II -GFA-Cu II ], two unpaired electrons), and with X = Br a diamagnetic dinuclear Cu I complex of the dicationic GFA (electronic structure [Cu I -GFA 2+ -Cu I ], closed-shell singlet state). The different electronic structures lead to significant differences in the optical, structural and magnetic properties of the complexes. Furthermore, the complex [ 6 (CuI) 2 ] 2+ (electronic structure [Cu I -GFA 2+ -Cu I ], closed-shell singlet state) is synthesized by reaction of 6 2+ with two equivalents of CuI. Slow decomposition of this complex in solution leads to the fluorescent dye 2,7-bis(dimethylamino)-1,3,6,8-tetraazapyrene. In an improved synthesis of this tetraazapyrene, 6 is reacted with CuBr in the presence of dioxygen. Quantum chemical calculations show that the addition of counter-ligands to the trigonal planar Cu I atoms of [ 6 (CuI) 2 ] 2+ favors or disfavors one of the electronic structures, depending on the nature of the counter-ligand. Decision-making counter-ligands: a bridging redox-active ligand in a dinuclear copper complex could be either neutral (complex type [Cu II -GFA-Cu II ]) or dicationic (complex type [Cu I -GFA-Cu I ]), depending on the nature of the counter-ligands X.