Anionic Amidinourea–Metal(II) Tautomers: MN2O2 or MN4?

Abstract

Structures of amidinourea–metal complexes have been obscured by subtle tautomerism and crystal waters. To clarify the most stable form of the tautomers, bis(amidinourea)copper(II) anhydride and the alkyl derivatives were synthesized under basic conditions, and the stability of the CuN2O2 chromophore was suggested. From substituent effects of chelations, UV–vis spectra, IR/Raman spectra, and DFT calculations, it was suggested that the bis(amidinourea)copper(II) has a CuN2O2 chromophore, not CuN4 chromophore. The mutual exclusion rule of IR/Raman spectra supported the trans-CuN2O2 chromophore. Systematic calculations on bis(amidinourea)–Cu(II), –Ni(II), –Pd(II), –Zn(II), and –Cd(II) chelates revealed that the robust stability of CuN2O2 chromophores originates from quasi aromaticity in the six-membered chelate rings. cis- or trans-CuN4 stability reported in the early references is suspicious.

The Theoretical and Experimental Investigation of the Fluorinated Palladium β-Diketonate Derivatives: Structure and Physicochemical Properties

“…The use of theoretical approaches based on DFT calculations in combination with single-crystal X-ray diffraction (SXRD) and IR and NMR spectroscopies provides additional opportunities for studying the energies of crystal lattices and individual molecules of the complexes [ 25 , 26 ], for estimation of the strength of metal–ligand bonds [ 27 , 28 ] and the distribution of tautomeric forms [ 29 ]. From a practical point of view, spectral methods, together with DFT, are widely used to estimate kinetic parameters and probabilities of the cleavage of bonds in the precursor molecules [ 30 ] and to predict the decomposition pathway of the precursor vapors on various substrates during the MOCVD/ALD process [ 31 ].…”