Crystalline Non‐Equilibrium Phase of a Cobalt(II) Complex with Tridentate Ligands

Abstract

In six-coordinate complexes, flexible tridentate ligands enable mer, cis-fac, and trans-fac stereoisomers. With labile metal ions of the first transition metal series, typically only the final thermodynamic product is available because of the rapid isomerization processes. Here we report on the structural characterization of a so far elusive kinetic intermediate [a] 920 of [Co(ddpd) 2 ](BF 4 ) 2 (1; ddpd = N,NЈ-dimethyl-N,NЈ-dipyridine-2-yl-pyridine-2,6-diamine). Microcrystals of the cis-fac isomer of 1 were obtained by rapid precipitation. The solidstate structure of cis-fac-1 was determined from electron diffraction data. Scheme 1. Possible geometrical isomers in M(tridentate) 2 complexes and possible interconversion pathways. Eur. J. Inorg. Chem. 2015, 920-924

Ddpd as Expanded Terpyridine: Dramatic Effects of Symmetry and Electronic Properties in First Row Transition Metal Complexes

“…Paramagnetic NMR spectroscopy in acetonitrile solution indicates the presence of only a single metal complex isomer [63]. Re-crystallization from CH 3 (Figure 6b) [63]. In both stereoisomers, the cobalt(II) centres are in their high-spin state [63].…”

“…Reaction of Co(BF 4 ) 2 ×6H 2 O with ddpd in ethanol (Scheme 3) yields a precipitate, which contains two phases according to powder X-ray diffraction and SEM images [63]. Paramagnetic NMR spectroscopy in acetonitrile solution indicates the presence of only a single metal complex isomer [63]. Re-crystallization from CH 3 (Figure 6b) [63].…”

“…Re-crystallization from CH 3 (Figure 6b) [63]. In both stereoisomers, the cobalt(II) centres are in their high-spin state [63]. The cis-fac isomer is the kinetic product, while the mer isomer is the thermodynamically stable one.…”

“…[ Figure 6a). [63] and (c) mer-[Co(ddpd) 2 ][BF 4 ] 3 ×3CH 3 CN in the solid state; hydrogen atoms and solvent molecules omitted. Atom numbering unified for clarity.…”

Structure and Electronic Properties of an Expanded Terpyridine Complex of Nickel(II) [Ni(ddpd)2](BF4)2

“…The Jahn‐Teller splitting is larger than that of [Cu(tpy) 2 ] 2+ . Compared to five‐membered chelate rings, the larger flexibility of six‐membered chelates enables an energetically less favored cis ‐facial coordination in [Co(ddpd) 2 ] 2+ in addition to the thermodynamically preferred meridional isomer , . The equilibration of octahedral [Zn(ddpd) 2 ] 2+ complexes with trigonal‐bipyramidal ZnCl 2 (ddpd) and tetrahedral [ZnCl 4 ] 2– in the presence of chloride ions demonstrates the coordination diversity of d 10 ions in the absence of ligand field stabilization .…”