A trinuclear oximato complex, [(NiHL1)(3)( y(3)-O)]CIO4 (1), with inverse metallacrown 9-MC-3 topology has been synthesized using a Schiff-base ligand (H2L1) formed by condensation of ethanolamine (Hee) and diacetylmonoxime (Hdamo). The diamagnetic compound has been diaracterized by electrospray ionization mass spectrometry as well as by single-crystal X-ray diffraction analysis. In the solid state., the alcoholic OH group in this molecule stays away from coordination. Surprisingly in a similar chemical reaction, when intact Hea and Hdamo have been used as ligands instead of their Schiff-base forms, the product obtained is a 12-MC-4-type metallEcrown, (Et3NH)[Ni-4(damo)(4)(Hea)(2)(ea)(2)](CIO4)(3) (2), with a larger cavity size needed to accommodate a pair of hydrogen-bonded (O-H center dot center dot center dot O)- anions. Unlike in 1, the alcoholic OH groups in 2 take part in metal coordination. Compound 2 on being refluxed with lithium hydroxide in methanol is converted to 1 in almost quantitative yield. This appears to be a novel reaction type, leading to contraction of a metallacrown ring size. A family of 12-MC-4 Ni-4 metallacrowns in inverse topology, viz., [Ni4(damo).](H(2)dea)2(Hdea)2](CIO4)(2)center dot 2H(2)O (3), [Ni-4(dpko)(4)(Hea)(2)(ea)(2)](CIO4)(2)center dot 4H(2)O (4), and [Ni-4(mpko)(4)(Hmea)(2)(mea)(2)](CIO4)(2) (5), have been synthesized following a methodology similar to that adopted for 2, using different combinations of free oximes [viz., dipyridylketonoxime (Hdpko) and methylpyridylketonoxime (Hmpko)] and amino alcohols [viz., diethanolamine (H(2)dea), and N-methylethanolamine (Hmea)]. Crystal and molecular structures of 3-5 have been reported, each involving either a quasi (in 3) or a perfect (in 4 and 5) square plane (S-4 symmetry) with four octahedral Ni centers occupying the comers, and,serve as a backbone of puckered metallacrown rings that accommodate a pair of hydrogenbonded (O-H center dot center dot center dot O)- anions. Antiferromagnetic interactions within the [Ni-4] core kikB -20 to -27 K based on the following spin Hamiltonian: H. -21,S-1.S-2 + S-2.S-3 + S-3.S-4 + S-4.S-1)] lead to an ST=0 ground state for these complexes.