The X-ray crystal structure of (CH3NH3)(4)[(Mg(H2O)(5))(2)(H6W12O42)]Br(2 center dot)8H(2)O (1) obtained by a reaction of Li2WO4 center dot H2O and Mg(NO3)(2)center dot 6H(2)O in the presence of MeNH3Br is reported. Crystallographic parameters are: triclinic, space group P-1, a = 10.8280(4) angstrom, b = 12.4866(5) angstrom, c = 12.6201(5) angstrom, alpha = 108.501(1)degrees, beta = 111.542(1)degrees, gamma = 91.139(1)degrees, V = 1486.98(10) angstrom(3), Z = 1, C4H66Br2Mg2N4O60W12, d(x) = 3.959 g/cm(3), T = 150 K, R-1 = 0.030 for 9914 F-o > 4 delta(F) until 2 theta(max) = 66.6 degrees The structure contains tetraprotonated [H2W12O42](10-) anions coordinated with {Mg(H2O)(5)}(2+) cations as ditopic ligands via terminal oxygen atoms. The crystal structure also incorporates outer-sphere CH3NH3+ and Br- ions. The Mg2+ cations are in the octahedral environment, Mg-O(H2O) and Mg-O(W) bond lengths being 2.102(5)divided by 2.044(5) angstrom and 2.071(5) angstrom, respectively.