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, [Cu II3 Tb III (L Pr )(NO 3 ) 2 (H 2 O)]NO 3 (1), with K 3 [M III (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 K 3 [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 [Cu 3 Tb(L Pr )] 3+ to [Fe(CN) 6 ] 3- , but which differ in structural type, solvent content, and magnetic behavior. Three are discrete complexes: monomeric {[Cu 3 Tb(L Pr )(H 2 O) 5 ][Fe(CN) 6 ]·(H 2 O) 3 ·(MeCN)]} (2) and [Cu 3 Tb(L Pr )Fe(CN) 6 (H 2 O) 4 (MeCN)]·(H 2 O) 2 ·(MeCN) (3) plus dimeric {[Cu 3 Tb(L Pr )Fe(CN) 6 (H 2 O) 4 ]·(H 2 O) 6.75 } 2 (4), while two are 1D chains (coordination polymers): {[Cu 3 Tb(L Pr )cis-Fe(CN) 6 (H 2 O) 3 (MeOH)]·(H 2 O) 3.75 ·(MeOH) 0.75 } n (5) and {[Cu 3 Tb(L Pr )trans-Fe(CN) 6 (H 2 O) 4 ]·(H 2 O) 5 ·(DMF) 5 ]} n (6). When K 3 [Cr(CN) 6 ] or K 3 [Co(CN) 6 ] are used in place of K 3 [Fe(CN) 6 ], a discrete dimer {[Cu 3 Tb(L Pr )Cr(CN) 6 (H 2 O) 4 ]·(H 2 O) 2.75 } 2 (7) and a 1D chain coordination polymer {[Cu 3 Tb(L Pr )Co(CN) 6 (H 2 O) 3 (MeOH)]·(H 2 O) 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). ©