Tris(dithiolene) Complexes of Neodymium and Cerium: Mononuclear Species, Chains, and Honeycomb Networks

Reactions of Ln(BH4)3(THF)3 (Ln = Nd, Ce) and M2dddt (M = Na, K; dddt = 5,6-dihydro-1,4-dithiine-2,3-dithiolate)
in THF or pyridine gave, after addition of 18c6 (18-crown-6), several crystalline compounds which all contain the
tris(dithiolene) Ln(dddt)3 unit. Crystals of [Na(18c6)(py)2]2[Na(18c6)(py)][Nd(dddt)3(py)]·3py (1·3py) are built up from
discrete mononuclear cationic and anionic species whereas crystals of {[Na(18c6)(py)2]0.5[Na(18c6)(py)1.5][Na1.5Nd(dddt)3]}∞ (2) are composed of discrete [Na(18c6)(py)x]+ cations and polymeric anionic two-dimensional layers
in which the Nd(dddt)3 units are linked to three neighbors by sodium atoms to form a honeycomb network. Analysis
of the temperature dependence of the molar magnetic susceptibility of 2 shows that χMT decreases from 1.63 cm3
K mol-1 at 300 K down to 0.6 cm3 K mol-1 at 5 K, due to the crystal-field splitting of the 4I9/2 free-ion state.
Complexes {[Na3(18c6)1.5Nd(dddt)3(THF)]·3THF}∞ (3·3THF) and {[K3(18c6)1.5Nd(dddt)3(py)]·3py}∞ (4·3py) exhibit
neutral polymeric layers with the Nd(dddt)3 units linked by M2(18c6) fragments. In the cerium compound
{[Na2(18c6)Na(py)2Ce(dddt)3(py)]·3py}∞ (5·3py), each Ce(dddt)3 unit is linked to two neighbors only by Na2(18c6)
moieties, giving infinite zigzag chains.