The two title CuII complexes, [Cu2(NCO)4(tmeda)2] (tmeda is tetramethylethylenediamine, C6H16N2), (I), and [Cu(NCO)2(pn)]n (pn is 1,3-diaminopropane, C3H10N2), (II), have been synthesized and their crystal structures determined. In (I), which lies about an inversion centre, each Cu centre possesses a distorted tetragonal–pyramidal geometry with four basal N atoms from two cyanate anions [Cu—N = 1.945 (2) and 1.948 (3) Å] and one tmeda molecule [Cu—N = 2.053 (2) and 2.071 (2) Å], and one axial O atom [Cu—O = 2.737 (3) Å] from another cyanate anion. The two neighbouring Cu atoms in (I) are joined by a pair of cyanates in an end-to-end fashion, forming a dimer. In (II), each Cu centre adopts a distorted square-bipyramidal geometry, with four equatorial N atoms from two cyanates [Cu—N = 1.988 (2) and 2.007 (3) Å] and a pn ligand [Cu—N = 1.996 (3) and 2.011 (3) Å], and one apical N atom [Cu—N = 2.437 (3) Å] and an apical O atom [Cu—O = 2.900 (3) Å] from two cyanates. In contrast with (I), the two neighbouring Cu atoms in (II) are bridged by two cyanates in an end-on fashion, to form a centrosymmetric dimeric unit. These units are further crosslinked, forming a two-dimensional network structure, via weak interactions between the bridging cyanate O atom and a neighbouring Cu atom, plus interactions of the amine H atoms with the cyanate O atoms and the terminal cyanate N atom.