Comparing models for S = 1/2 Heisenberg antiferromagnetic chains: The validity of different approaches for describing a one-dimensional coordination polymer, [Cu^II(HL)₂(4,4′-bpy)]_n· 2nH₂O (H₂L = 3-nitrophthalic acid, bpy = bipyridine)

We have synthesized a new one-dimensional coordination polymer, [Cu ^II(HL)₂(4,4′-bpy)]_n·2nH ₂O (1), (HL^- = monodeprotonated 3-nitrophthalic acid, 4,4′-bpy = 4,4′-bipyridine) consisting of infinite chains of [Cu^II(HL)₂(4,4′-bpy)]_n and have investigated its structure and magnetic properties. Compound 1 crystallizes in the monoclinic C2/c space group with the [Cu^II(HL) ₂(4,4′-bpy)]_n chains running parallel to the b axis. The chains are linked together by hydrogen bonding between the HL^- groups and water molecules to form the three-dimensional crystal structure. The magnetic susceptibility of 1 can be well described using an antiferromagnetic S = 1/2 chain model with g = 2.11(1) and 2J = -0.61(1) cm^-1. Several techniques for describing the susceptibility of S = 1/2 chains are examined to compare their validity at low values of kT/|2J|, including exact numerical full-matrix diagonalization techniques, from which the magnetization curve of 1 could be calculated. The calculation fits well with the measured magnetization data.