Synthesis, Structure Determination, and Magnetic Properties of [Cr3(dpa)4Cl2][CuCl2], a Compound Comprising a Trinuclear Chain Cation

The new compound [Cr-3(dpa)(4)Cl-2][CuCl2] (1) (dpa = di-2,2'-pyridylamido) was synthesized by reacting Cr-2(dpa)(4) and anhydrous CuCl2 in dry tetrahydrofuran. Partial oxidation of Cr-2(dpa)(4) by Cu(II) forms Cr3+ ions, which coordinate to the free N donor atoms of the dpa ligands, and led to the formation of a trinuclear chain cation [Cr-3(dpa)(4)Cl-2](+). Recrystallization from CH2/Cl-2/ethyl ether yielded dark-brown, block-shaped crystals suitable for X-ray structure determination (Pccn (no. 56), a = 1246.8(5), b = 1487.3 (3), c = 2184..8 (1) pm, V = 4051.6(8). 10(6) pm(3), Z = 4). The crystal structure is composed of discrete [Cr-3(dpa)(4)Cl-2](+) cations and [CuCl2](-) anions. The Cr-3 chain comprises quadruply-bonded diamagnetic (Cr-2)(4+) dimers and a pseudo-octahedrally coordinated, paramagnetic Cr3+ ion, manifesting itself in the effective magnetic moment mu(eff) of 3.54 mu(B) (d(3), S = 3/2) and the almost ideal Curie-paramagnetic behavior observed between 2 and 300 K with a Weiss constant theta = -0.25(4) K and chi o = 4.9(7) x 10(-4) emu mol(-1).