Formation of dimethylnickelate(I) and dimethylsilverate(I) anions in the gas phase from nickel(II) acetate and silver(I) acetate by laser desorption/ionisation Species containing methylmetal moiety (H 3 C-metal bond) can be regarded as the simplest organometallic species. In nature, there are only two examples; the first well-known compound containing H 3 C-Co bond is methylcobalamin [1] and the second, definitely less known, is methylnickel. [2] Methylmercury cation (H 3 C-Hg + ) can be produced by some organisms, [3] but its presence in the environment in the past was related with several industrial processes. Obviously, there are a vast number of examples of compounds containing H 3 C-metal bond(s) prepared in the lab. It is also obvious that the higher the oxidation state of the metal, the more the methyl groups can be attached to it. Therefore, such metals like Pb(IV) or Pt(IV) are able to attach even four methyl groups, the respective compounds were already known in the first half of the 20th century. [4,5] The trimethylcopper(III), copper at rather rare oxidation state, is also worth mentioning. [6] Metals that are prone to form anions (metalates), e.g. Mn, Al, Cu, Pt, can attach more methyl groups than the actual oxidation state of the metal, and the respective 'pure' organometallic anions are formed. ] − , can be generated in the gas phase from nickel(II) acetate, silver(I) acetate and copper(II) acetate, by laser desorption/ionisation (LDI). Gas-phase studies belong to the fundamental studies. [14] It is reasonable to expect that the gas-phase ion chemistry will have great impact on the 21st century development of physical and organic chemistry. [15] Figure 1 shows the LDI mass spectra of nickel(II) acetate, silver(I) acetate and copper(II) acetate obtained in the negative ion mode. In each mass spectrum, there are ions consisting of metal and acetate groups (i), metal, acetate group(s) and methyl group (ii), metal and methyl groups (iii). It can be assumed that the ions containing methyl groups are formed from the ions containing acetate groups by the loss of CO 2 molecule(s).In the mass spectrum of nickel (II) − . The full-scan mass spectra (Fig. 1) concern the complicated processes that occurred in the expanding plume (e.g. ion-molecule reactions) which contained ions, neutrals and free electrons. Strictly, gas-phase decompositions are observed in the CID MS/MS experiments. Figure 2( CO] − , were also observed. The latter ion was not observed in full-scan mass spectrum but it is the most abundant in CID MS/MS spectrum at higher collision energy (CE, Fig. 2(b)). The [NiCH 3 (CH 3 COO)] − ion, which can be regarded as a direct precursor of [Ni(CH 3 ) 2 ] − ion, is also observed. However, the [Ni(CH 3 ) 2 ] − ion was not detected, even at higher CE (Fig. 2(b)). The CID MS/MS spectra of [Ni(CH 3 COO) 2 ] − and [NiCH 3 (CH 3 COO)] − ions (Fig. 2(c and d)) show that [Ni(CH 3 ) 2 ] − is formed from them.Full-scan mass spectra of silver(I) acetate and copper(II) acetate are less complicated than the above-d...