On, off and intermediate coordination of a bridgehead triarylamine donor in tripodal complexes: Towards the tuning of coordinative bond distance

Abstract

A series of first row transition metal complexes of the tripodal ligand 2,2',2"-nitrilotribenzoic acid H3L has been prepared and characterised by X-ray crystallography: Mononuclear [M(L)]- species [Cu(H2O)4]3[Cu(L)(H2O)]6.25H2O (2), [Co(H2O)6][Co(L)(H2O)].8H2O (4), [Zn(H2O)6][Zn(L)(H2O)].8H2O (5) and a neutral [M(L)] complex [Fe(III)2(L)(H2O)3].5H2O (8) are formed as well as dimeric [M(L)]2 2- species (HNEt3)2[Cu(L)]2.2CH3CN (1), (HNEt3)3[Ni(L)]2(ClO4).H2O (3), (HNEt3)2[Fe(II)(L)]2.2CH3CN (6) and (HNEt3)2[Fe(III)2(L)2(mu-O)](7). The complexes display a unique variation in the M-N distance (2.09 A for Cu(II) to 3.29 A for Fe(III)) to the bridgehead triphenylamine donor and are classified into compounds with "On","Off" and "Intermediate" N-coordination. The trigonal-bipyramidal coordination polyhedron changes towards tetrahedral in the intermediate and octahedral in the Off-state. The M-N distance of individual complexes is reversibly tuned by external chemical input such as changes of metal ion oxidation state (Fe(II)/Fe(III)) or variation of the axial coligand as a consequence of solvent or pH variation. Possible reasons for the exceptional tolerance of the M-N bond to distance variations are discussed under consideration of gas phase DFT calculations of [Zn(L)]-.

Tracking the Structure‐Reactivity Relationship of Zinc Guanidine‐Pyridine Hybrid Complexes Initiating Lactide Polymerisation

“…This tendency has been observed quite frequently for such systems. [18,23,24] In contrast, the Zn-O distances in 1 and 3 are predicted around 0.5 Å too short, thus overestimating the donor strength of the mesylate. For this reason, the donor strength of the N donor might be underestimated.…”

Lactide Polymerisation with Air‐Stable and Highly Active Zinc Complexes with Guanidine–Pyridine Hybrid Ligands

“…[32] For most complexes, the predicted Zn À N distances are about 0.03 too long, which is a known tendency for such systems. [32,33] Hence, ligands L1-L4 and the model ligand HGqu were examined with B3LYP density functional theory and only the 6-31G(d) basis set (Table S6 in the Supporting Information and Figure 7). …”

Synthesis, crystal structures, and properties of three metal complexes with N-phenylanthranilic acid

“…As shown in Fig. 5b, the Zn II are six coordinate by four oxygen atoms from two different N-phenylanthranilic ligands and two nitrogen atoms from 2,2 0 -bipyridine through chelating mode, the coordination geometry around Zn II [22]. Notably, two pyridine rings of the 2,2 0 -bipyridine are nearly planar with a dihedral angle being 5.078°and the dihedral angle between the planes of the phenyl rings of the two NPA ligands in Zn II (1) unit is 40.86°and 59.35°, which are slightly different from that of complex 1 (41.316°and 47.810°).…”