{NiLn} (Ln = Gd, Dy) rod-like nano-sized heteronuclear coordination clusters with a double carbonate bridge skeleton and remarkable MCE behaviour.

The newly obtained complexes [NiLn(Piv)16(teaH)6(OCH3)2(CO3)2(H2O)2] Ln = Gd, Dy, show a remarkable μ5-carbonate bridged octanuclear planar {Ni4Ln4} core further capped with embedded {Ni3Ln} cubane motifs to afford a rod shaped nano-sized molecule of about 1.2 × 2.8 nm. Unusual MCE behaviour has been found due to multiple low lying excited states arising from competing ferromagnetic and anti-ferromagnetic Ni-Ni and Ni-Ln exchange interactions.