The mixed-metal ferromagnet {[P(Ph)4][MnCr(ox)3]}n, where Ph is phenyl and ox is oxalate, has been prepared and a two-dimensional network structure, extended by Mn(II)-ox-Cr(III) bridges, has been determined from single crystal X-ray data. Crystal data: space group R3c, a=b=18.783(3), c=57.283(24) Å, α=β=90, γ=120°, Z=24 (C30H20O12PCrMn). The magnetic susceptibility data obey the Curie-Weiss law in the temperature range 260–20 K with a positive Weiss constant of 10.5 K. The temperature dependence of the molar magnetization exhibits a magnetic phase transition at Tc=5.9 K. The structure is discussed in relation to the strategy for preparing molecular based ferromagnets and, in addition, it is a solution to the question of the dimensionality of the [MM'(ox)3]n network, which in principle can extend two- or three-dimensionally to the crystal lattice. The optical absorption spectra of the single crystals are assigned to the ‘CrO6' chromophores. Their polarization patterns reflect the electric dipole selection rules for D3 symmetry. A strong site selective luminescence from the chromium(III) 2E states is observed at low temperature and the system may be suitable for studying energy transfer mechanisms.