A series of trigonal bipyramidal pentanuclear complexes involving the alkoxo-diazine ligands poap and p3oap, containing the M-5[mu -O](6) core is described, which form by a strict self-assembly process. [Co-5(poap-H)(6)](ClO4)(4). 3H(2)O (1), [Mn-5(poap-H)(6)](ClO4)(4).3.5CH(3)OH .H2O (2), [Mn-5(p3oap-H)(6)](ClO4)(4). CH3CH2OH . 3H(2)0 (3), and [Zn-5-(poap-H)(6)](ClO4)(4).2.5H(2)O (4) are homoleptic pentanuclear complexes, where there is an exact match between the coordination requirements of the five metal ions in the cluster, and the available coordination pockets in the polytopic ligand. [Zn-4(poap)(poap-H)(3)(H2O)(4)] (NO3)(5).1.5H(2)O (5) is a square [2 x 2] grid with a Zn-4[mu -O](4) core, and appears to result from the presence of NO3, Which is thought to be a competing ligand in the self-assembly. X-ray structures are,reported for 1, 4, and 5. 1 crystallized in the monoclinic system, space group P2(1)/n with a = 13.385(l) Angstrom, b = 25.797(2) Angstrom, c = 28.513(3) Angstrom, beta= 98.704(2)degrees, and Z = 4. 4 crystallized in the triclinic system, space group P1 with a = 13.0897(9) Angstrom, b = 18.889(1) Angstrom, c = 20.506(2) Angstrom, alpha = 87.116(1)degrees, beta =74.280(2)degrees, gamma = 75.809(2)degrees, and Z = 2. 5 crystallized in the monoclinic system, space group P2(1)/n with a = 14.8222(7) Angstrom, b = 21.408(1) Angstrom, c = 21.6197(9) Angstrom, beta =90.698(1)degrees, and Z = 4. Compounds 1-3 exhibit intramolecular antiferromagnetic coupling.