Low Valent Magnesium Compounds

Two low valent magnesium compounds have been discovered that are the first examples of stable magnesium(I) compounds. Both examples have the formula L2Mg2, where L represents a bulky anionic ligand. X-ray crystallographic studies show an Mg-Mg bond length of 285.1 pm and 284.6 pm. Theoretical studies indicate an essentially ionic formulation Mg22+(Lāˆ’)2. The Mg22+ ion is the group 2 analogue of the group 12 Hg22+ (present in e.g. mercury(I) chloride) and Cd22+ ions (present in cadmium(I) tetrachloroaluminate). The preparation involved the reduction of MgII iodine complexes with potassium metal and the bulky ligands were:

  • a guanidinate, "priso", ā€“ where Ar = 2,6-diisopropylphenyl and Pri = iso-propyl
  • a ketiminate, "nacnac", {2CH}āˆ’,- where Ar = 2,6-diisopropylphenyl and Me = methyl

The chemistry of Mg is dominated by the +2 oxidation state and up to this point the ternary metal hydrides Mg2RuH4, Mg3RuH3, and Mg4IrH5 and magnesium diboride, MgB2 with short Mg-Mg bonds (293 pm, 303 pm, 275 pm, 308pm respectively) had been assumed to contain an Mg2 unit. Calculations had also indicated the stability of the Mg22+ cation

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