The synthesis and magnetic properties of a series of layered compounds, where the interlayer separation has been tuned from 9 to 28 Angstrom, are reported. it is shown that the Brucite-type layered compounds of cobalt having octahedral sites only, Co-2(OH)(3)X, are metamagnets, while those adopting the triple-deck structure, Co-5(OH)(8)(X)(2). xsolvent, containing both octahedral and tetrahedral sites are two-sublattice ferrimagnets. The long range ordering (LRO), T-C up to 60 K or T-N of 38 K, in both structural types is brought about by dipolar interaction between layers and super-exchange interactions between nearest neighbors within a layer. The exceptional hardness of these two structural types, coercive field of 20,000 Oe for the ferrimagnets and greater than 50,000 Oe for the metamagnet, is due to the synergy of single-ion and crystalline shape anisotropies and, most importantly, the alignment of the moments perpendicular to the layer.