Crystalline adducts of urea with magnesium iodide

The crystal structures of newly obtained [Mg(OC(NH2)(2))(2)(H2O)(4)]I-2 (tetraaqua bis (urea-O) magnesium diiodide), [Mg(OC(NH2)(2))(4)(H2O)(2)]I-2 (diaqua tetra(urea-O) magnesium diiodide) and [Mg(OC(NH2)(2))(6)]I-2 . 4OC(NH2)(2) (hexa(urea-O) magnesium diiodide tetraureate) are reported. It is found that the studied compounds crystalize in one and the same space group P2(1)/c and exhibit structure isotypical with the corresponding chlorides and bromides. The complexes were characterized by experimental IR spectroscopic and DTA-TG analyses, and DFT/B3LYP free energy and vibrational calculations at molecular level. The observed trans-conformation in the crystaline (MgX6)(2+)units was supported by calculated larger thermodynamic stability of trans conformers as compared to cis ones. The inclusion of Urea in Mg2+ complexes was preferred over water in agreement with the calculated exothermic exchange reactions. The comparative IR spectroscopic analysis of urea and the three Mg2+ complexes studied revealed that nu(C = O)(U) band shift could be an indication of Mg - O-U bond formation and its relative strength. The thermal analyses and calculated exchange reaction energies predicted larger stability of the Mg2+ complexes with an increase of the number of the urea (respectively a decrease of water's number in the first coordinating shell) due to formation of specific network of hydrogen bonds. (C) 2020 Elsevier B.V. All rights reserved.

Automated summary

The crystal structures of newly obtained magnesium complexes are reported to crystallize in the same space group, exhibiting isotypical structures with corresponding chlorides and bromides. Experimental and computational analyses characterized the complexes' properties and stability, showing that urea plays a more crucial role in magnesium coordination compared to water.