title: Structural variation in transition-metal bispidine compounds.
abstract: The experimentally determined molecular structures of 40 transition metal complexes with the tetradentate bispyridine-substituted bispidone ligand, 2,4-bis(2-pyridine)-3,7-diazabicyclo[3.3.1]nonane-9-one [M(bisp)XYZ]n+; M = CrIII, MnII, FeII, CoII, CuII, CuI, ZnII; X, Y, Z = mono- or bidentate co-ligands; penta-, hexa- or heptacoordinate complexes) are characterized in detail, supported by force-field and DFT calculations. While the bispidine ligand is very rigid (N3...N7 distance = 2.933 +/- 0.025 A), it tolerates a large range of metal-donor bond lengths (2.07 A < sigma(M-N)/4 < 2.35 A). Of particular interest is the ratio of the bond lengths between the metal center and the two tertiary amine donors (0.84 A < M-N3/M-N7 < 1.05 A) and the fact that, in terms of this ratio there seem to be two clusters with M-N3 < M-N7 and M-N3 > or = M-N7. Calculations indicate that the two structural types are close to degenerate, and the structural form therefore depends on the metal ion, the number and type of co-ligands, as well as structural variations of the bispidine ligand backbone. Tuning of the structures is of importance since the structurally differing complexes have very different stabilities and reactivities.
authors.affiliation: Anorganisch-Chemisches Institut, Universität Heidelberg Im Neuenheimer Feld 270, 69120 Heidelberg, Germany. comba@akcomba.oci.uni-heidelberg.de
authors.forename: Peter
authors.initials: P
authors.lastname: Comba
authors.forename: Marion
authors.initials: M
authors.lastname: Kerscher
authors.forename: Michael
authors.initials: M
authors.lastname: Merz
authors.forename: Vera
authors.initials: V
authors.lastname: Müller
authors.forename: Hans
authors.initials: H
authors.lastname: Pritzkow
authors.forename: Rainer
authors.initials: R
authors.lastname: Remenyi
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Schiek
authors.forename: Yun
authors.initials: Y
authors.lastname: Xiong