Long-Range Magnetic Ordering at 5.5 K for Cobalt(II)–Hydroxide Diamond Chains Isolated by 17 Å with α-Phenylcinnamate

Abstract

[Co(4)(phcina)(6)(OH)(2)(H(2)O)(4)]·2H(2)O (1) (phcina = α-phenylcinnamate), obtained as pink needles by hydrothermal technique, consists of two edge-sharing pairs of octahedral CoO(6) connected by their apexes to form diamond-chains. The magnetic chains are isolated from one another without chemical bond at 17 Å by the nonmagnetic bulky organic ligand. It exhibits hidden canting below the long-range antiferromagnetic (AF) ordering at 5.5 K. A metamagnetic critical field of only 30 Oe at 2 K suffices to overcome the weak through space magnetic interaction between chains and reverse the moments within the chains to give a canted AF reaching only (1)/(4) of the required moment for all parallel moment alignment. The anisotropy measured on aligned crystals, using dc and ac modes, estimates g(||b) = 6.5 and g(⊥b) = 3.25, thus eliminating an Ising or a Heisenberg magnetic dimensionality while suggesting an easy-plane AF. Weak frequency dependence of the ac-susceptibilities below the transition temperature is associated with domain structure in the ordered state, and absence of it well above T(N) eliminates single-chain magnetism. It is inferred that the competition between the strong AF coupling between the edge-sharing pairs, which dominates the high temperature susceptibility, and the ferromagnetic coupling within the pairs, results in a canting of the moments within each chain, where the moments are out of the ac-plane by an estimated 13°. In zero-field the moments of adjacent chains are antiparallel resulting in a compensated system, i.e., hidden canting.