We report the preparation of Mg$_{1-x}$B$_{2}$ (0$le$x$le$0.5) compounds with the nominal compositions. Single phase MgB$_{2}$ was obtained for x=0 sample. For 0$<$x$le$0.5, MgB$_{4}$ coexists with MgB$_{2}$ and the amount of MgB$_{4}$ increases with x. With the increase of x, the lattice parameter ${it c}$ of MgB$_{2}$ increases and the lattice parameter ${it a}$ decreases, correspondingly T$_{c}$ of Mg$_{1-x}$B$_{2}$ decreases. The results were discussed in terms of the presence of Mg vacancies or B interstitials in the MgB$_{2}$ structure. This work is helpful to the understanding of the MgB$_{2}$ films with different T$_{c}$, as well as the Mg site doping effect for MgB$_{2}$.
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