Structural and electronic trends for five coordinate 1st row transition metal complexes: Mn(ii) to Zn(ii) captured in a bis(iminopyridine) framework

Abstract

The preparation and characterization of a series of divalent 3d transition metal complexes supported by a tridentate planar bis(iminopyridine) ligand are reported. The complexes {2,6-[PhCN(tBu₂C₆H₃)]₂C₅H₃N}MBr₂ (M = Mn, Fe, Co, Ni, Cu, Zn), 1–6, were characterized by single crystal X-ray structural studies revealing complexes with pentacoordinate distorted square pyramidal coordination environments. This assembly of complexes provided a unique array for examining the relationship between experimental structure and computed electronic structure. While experimental structural features basically correlated with the Irving–Williams series, some clear deviations were rationalized through the computational analysis. A balance of bis(imino)pyridine/metal with bonding/antibonding π interactions was used to explain the divergent directions of Fe(II)–N and Co(II)–N bond lengths. Similarly, orbital details were used to justify the opposing change in Cu–Br_ap and Cu–Br_bas bond lengths. Furthermore, computational analysis provided a unique method to document a surprising low bond order for the M–N bonds of bis(imino)pyridine ligand in this series.