Synthetic ability of dinuclear mesocates containing 1,3-bis(diazinecarboxamide)benzene bridging ligands to form complexes of increased nuclearity. Crystal structures, magnetic properties and theoretical studies.

Triple stranded Ni-metallacyclic complexes Na[Ni(bpcb)]·0.5OH·18.5HO (1) and Na[Ni(bpzcb)]·16HO (2), and double stranded Cu-metallacyclic complexes [Cu(bpcb)(HO)]·8HO (3) and [Cu(bpzcb)(HO)]·4HO (4) have been assembled from the tailored bisbidentate bridging ligands, 1,3-bis(pyrimidine-2-carboxamide)benzene (Hbpcb) and 1,3-bis(pyrazine-2-carboxamide)benzene (Hbpzcb), and the corresponding nitrate salts of the metal ions. Following the "complex as ligand" strategy, 1 can be assembled with either Ni, Co ions or the [Mn(acen)Cl] complex to afford unique, neutral, bent trinuclear molecules [MNi(bpcb)]·xHO (5 and 6) and the 2D honeycomb-like complex (PPh){[Ni(bpcb)][Mn(acen)]} (7), respectively. In these cases, the Ni units are linked to the corresponding metal ions through amidate oxygen atoms and the outward nitrogen atom of one of the pyrimidine rings of the bcpb ligand. The assembly of 2 with Ln ions (Ln = Tb, Gd) leads to one dimensional complexes of formula [{[Ni(bpzcb)]Tb(HO)}(CFSO)·THF·5HO] (8) and [{[Ni(bpzcb)]Ln(HO)(NO)}·2THF·nHO] (9 and 10) (Ln = Gd and Tb), where the dinuclear Ni units are joined to two Ln ions exclusively through amidate oxygen atoms of two different ligands. The analyses of the magnetic data indicate that 1-4 exhibit intradinuclear ferromagnetic interactions between the metal ions through a spin polarisation mechanism, as supported by DFT calculations. Trinuclear complexes 5 and 6 show predominant antiferromagnetic coupling, which is a result of an antiferromagnetic interaction between one of the Ni ions of the Ni unit and the M ion through the pyrimidine bridging fragment that is stronger than the polarised ferromagnetic interaction between the Ni ions through the bpcb ligand in the dinuclear [Ni(bpcb)] moiety. Complex 7 shows a dominant antiferromagnetic interaction between the Ni and Mn, whereas the NiLn (Ln = Gd, Tb) chain complexes present ferromagnetic interactions inside the Ni mesocate unit as well as between the Ni ions of the Ni unit and the Ln ions. The magnetic exchange interactions in these new materials have been experimentally analysed and supported by theoretical DFT studies.