A POLYMERIC 2-DIMENSIONAL MIXED-METAL NETWORK - CRYSTAL-STRUCTURE ANDMAGNETIC-PROPERTIES OF ([P(PH)4][MNCR(OX)3])N

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 st ructure, extended by Mn(II)-ox-Cr(III) bridges, has been determined fr om single crystal X-ray data. Crystal data: space group R3c, a = b = 1 8.783(3), c = 57.283(24) angstrom, alpha = beta = 90, gamma = 120-degr ees, Z=24 (C30H20O12PCrMn). The magnetic susceptibility data obey the Curie-Weiss law in the temperature range 260-20 K with a positive Weis s constant of 10.5 K. The temperature dependence of the molar magnetiz ation exhibits a magnetic phase transition at T(c) = 5.9 K. The struct ure is discussed in relation to the strategy for preparing molecular b ased ferromagnets and, in addition, it is a solution to the question o f the dimensionality of the [MM'(ox)3]n network, which in principle ca n extend two- or three-dimensionally to the crystal lattice. The optic al absorption spectra of the single crystals are assigned to the 'CrO6 ' chromophores. Their polarization patterns reflect the electric dipol e selection rules for D3 symmetry. A strong site selective luminescenc e from the chromium(III) 2E states is observed at low temperature and the system may be suitable for studying energy transfer mechanisms.