Compounds in the 3d transition metals and 3-hydroxypyridine (HL) system were synthesized from ammoniacal aqueous or ethanolic solutions. The synthesized compounds were identified as [Mn(L)2(HL)2]n 1, Co(L)2(HL)2 2, Ni(L)2(HL)2(H2O)2 3, {[Cu(L)2(HL)(H2O)](H2O)2}n 4 and 5. Compounds 1 and 4 had been previously reported, and their crystal structures had already been determined. 3-Hydroxypyridine is present in both, its neutral (HL) and anionic (L⁻) form, in all these compounds. The anionic form enables charge balance with the M²⁺ cations (Mn2+, Fe2+, Co2+, Ni2+, Cu2+, Zn2+) and the assembly of the mononuclear formula units into one-dimensional (1D) chains or two-dimensional (2D) networks. The IR spectra of all compounds are very similar and exhibit characteristic bands of 3-hydroxypyridine (HL). The molecular formulas of the compounds were determined from the experimentally obtained elemental mass fractions, which were compared with the corresponding calculated values. The powder X-ray diffraction (XRD) patterns were also compared with the calculated patterns. The data required for the calculation of powder X-ray diffraction patterns of the determined crystal structures were obtained from the Cambridge Structural Database (CSD). The electronic spectra of the compounds are found to be consistent with the corresponding metal ions and the characteristic colours of such compounds.
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