The geometrically frustrated diamond spin chain system has yielded materials with a diversity of interesting magnetic properties but is predominantly limited to compounds with single-spin components. Here, we report the compound [(CH3)(2)NH2](6)[(Fe4Fe2II)-Fe-III(mu(3)-O)(2)(mu(3)-OH)(2)(mu(3)-SO4)(8)] (1), which features the mixed-valent iron(II/III) diamond chain: infinity[Fe-III- (FeIII)(2)-Fe-III((FeI2))-I-I](.) Fe-57 Mossbauer spectroscopy shows that two-thirds of the total spins in the infinity[(Fe4Fe2II)-Fe-III] diamond chain are spin-5/2 (high-spin Fe) while the remaining one-third are spin-2 (high-spin Fe-II). To date, 1 is the only diamond-chain compound composed of more than one type of dimer, namely, (Fe-III)(2), and (Fe-II)(2). On the basis of temperature-dependent Fe-57 Mossbauer spectroscopy data, an alternating noncollinear 90 degrees magnetic structure is proposed. Both the (Fe-III)(2) and (Fe-II)(2) dimers are antiferromagnetically coupled and align in the direction along the chain axis approximate to[010], whereas the moments of the bridging Fe-III monomers are oriented orthogonally. The spin canting, arising from the anisotropy of the Fe-II ions, leads to ferrimagnetic ordering at low temperatures.