  We report muSR experiments on Mg{x}Cu{4-x}(OH)6Cl2 with x \sim 1, a new
material isostructural to Herbertsmithite exhibiting regular kagome planes of
spin 1/2 (Cu^{2+}), and therefore a candidate for a spin liquid ground state.
We evidence the absence of any magnetic ordering down to 20 mK (\sim J/10^4).
We investigate in detail the spin dynamics on well characterized samples in
zero and applied longitudinal fields and propose a low T defect based
interpretation to explain the unconventional dynamics observed in the quantum
spin liquid phase.
