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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$_{2}$., Comment: 11 pages, 4 figures

We report the preparation of Mg1-xLixB2 compounds. Nearly single phased samples were obtained for x<0.3. The in-plane lattice parameter a decreases with Li doping, while the lattice parameter c does not show obvious change. The superconducting transition temperature of Mg1-xLixB2 decreases with Li doping and loss of superconductivity occurs for x=0.5 sample. The results of our work are consistent with the prediction of the hole superconductivity mechanism., Comment: 5 pages, 4 figures