Uncompensated Spin Magnetic Moment and Properties of Coordination Bond M ← OH2 in Isostructural Nitrilo-tris-Methylenephosphonate Complexes [MII(H2O)3μ-NH(CH2PO3H)3] (MII = Cr–Zn)

Abstract

The parameters of coordination bonds M ← OH₂ (the magnetic moments of transition metals, interatomic distances, force constants, and break energies) in isostructural nitrilo-tris-methylenephosphonate complexes of transition metals of 3d-series [M^II(H₂O)₃μ–NH(CH₂PO₃H)₃] (M^II = Cr–Zn) are analyzed. It is shown that the correlation of force constants with interatomic distances is in good agreement with the Badger rule, and the break energy of bond M ← OH₂ deviates strongly from the empirical Poling dependence. It is shown that deviations of the break energy of bond M ← OH₂ from the Poling rule are due to the presence of an uncompensated spin density at the central atom. This explains the stability of Fe-containing heterometallic coordination polymers [(Fe,M)(H₂O)₃μ–NH(CH₂PO₃H)₃], which determines the high efficiency of nitrilo-tris-methylenephosphonate complexes as inhibitors of the corrosion of steel in aqueous media.