Discrete versus Chain Assembly: Hexacyanometallate Linkers and Macrocyclic {3d-4f} Single-Molecule Magnet Building Blocks.

Abstract

The self-assembly of macrocyclic tetranuclear 3d-4f single-molecule magnet (SMM) building blocks, [CuII3TbIII(LPr)(NO3)2(H2O)]NO3 (1), with K3[MIII(CN)6] linkers, where M = Fe, Cr, or Co, results in a range of discrete (monomer and dimer) and one-dimensional (1D) chain (coordination polymer) supramolecular architectures, which have been structurally and magnetically characterized. The outcome of reactions of 1 with an excess of K3[Fe(CN)6] has been probed in detail. It was found to be dependent on several factors, resulting in five distinctly different compounds, all of which have the same 1:1 ratio of [Cu3Tb(LPr)]3+ to [Fe(CN)6]3-, but which differ in structural type, solvent content, and magnetic behavior. Three are discrete complexes: monomeric {[Cu3Tb(LPr)(H2O)5][Fe(CN)6]·(H2O)3·(MeCN)]} (2) and [Cu3Tb(LPr)Fe(CN)6(H2O)4(MeCN)]·(H2O)2·(MeCN) (3) plus dimeric {[Cu3Tb(LPr)Fe(CN)6(H2O)4]·(H2O)6.75}2 (4), while two are 1D chains (coordination polymers): {[Cu3Tb(LPr) cis-Fe(CN)6(H2O)3(MeOH)]·(H2O)3.75·(MeOH)0.75} n (5) and {[Cu3Tb(LPr) trans-Fe(CN)6(H2O)4]·(H2O)5·(DMF)5]} n (6). When K3[Cr(CN)6] or K3[Co(CN)6] are used in place of K3[Fe(CN)6], a discrete dimer {[Cu3Tb(LPr)Cr(CN)6(H2O)4]·(H2O)2.75}2 (7) and a 1D chain coordination polymer {[Cu3Tb(LPr)Co(CN)6(H2O)3(MeOH)]·(H2O)4·(MeOH)} n (8) are obtained, respectively, which are isomorphous with 4 and 5, respectively. Magnetic studies reveal the paramagnetism of these compounds down to 1.8 K, except for 7, which displays an ordered antiferromagnetic ground state with metamagnetic behavior. The 1D-coordination polymers (5, 6, and 8) do not exhibit single-chain magnet properties, because of the very weak interbuilding block magnetic interactions. For chain 8, below 2.8 K, a clear nonzero out-of-phase signal is seen, similar to that seen for the building block 1, so the magnetism of 8 is governed by that of these SMM building blocks (1).