title: Construction of copper chains with new fluorescent guanidino-functionalized naphthyridine ligands.
abstract: The three new blue-fluorescent ligands 2,7-bis(tetramethylguanidino)-1,8-naphthyridine (1), 2,7-bis(N,N'-dimethylethylene-guanidino)-1,8-naphthyridine (2) and 2,7-bis(N,N'-diisopropylguanidino)-1,8-naphthyridine (3) are synthesized, and their optical properties (electronic absorption and emission spectroscopy) studied. Reactions of 1 or 2 with [Cu(CH3CN)4]BF4yield the Cu4chain compounds [Cu4(1)2](BF4)4(that crystallizes as [Cu4(1)2(CH3CN)2](BF4)4·2CH2Cl2) and [Cu4(2)2](BF4)4. The variations of the optical properties upon coordination are evaluated, and the electronic transitions identified by time-dependent DFT (TD-DFT) calculations. Then the redox properties of the new Cu4chain complexes are studied. In the course of these experiments, the new Cu6complex [Cu4(1)2(CuCl2)2]2+, in which two CuCl2-units coordinate to the Cu4chain in [Cu4(1)2]4+, was fully characterized. In addition, the Cu3chain complexes [Cu3(1)3]3+and [Cu3(1)2]3+were isolated as products of redox-induced degradation processes. Finally, we show by quantum chemical calculations that in [M4(1)2]4+complexes (M = coinage metal), the HOMO changes from a ligand-centered to a metal-centered orbital for replacement of M = Cu by Au.
authors.affiliation: Anorganisch-Chemisches Institut, Ruprecht-Karls-Universität Heidelberg, Im Neuenheimer Feld 270, 69120 Heidelberg, Germany. hans-jorg.himmel@aci.uni-heidelberg.de.
authors.forename: Christoph
authors.initials: C
authors.lastname: Krämer
authors.forename: Simone
authors.initials: S
authors.lastname: Leingang
authors.forename: Olaf
authors.initials: O
authors.lastname: Hübner
authors.forename: Elisabeth
authors.initials: E
authors.lastname: Kaifer
authors.forename: Hubert
authors.initials: H
authors.lastname: Wadepohl
authors.forename: Hans-Jörg
authors.initials: HJ
authors.lastname: Himmel