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

[Co4(phcina)6(OH)2(H2O)4]·2H2O (1) (phcina
= α-phenylcinnamate), obtained as pink needles by hydrothermal
technique, consists of two edge-sharing pairs of octahedral CoO6 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 TN 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.