Carboxylic acid-tuned nickel(ii) clusters: syntheses, structures, solution behaviours and magnetic properties.

Three novel cicada-like nickel(ii) clusters, formulated as [Ni(bdped)(mba)(Hdmpz)(NO)(HO)]·4MeCN (SD/Ni6b), [Ni(bdped)(tca)(Hdmpz)(MeOH)(HO)]·MeOH (SD/Ni5a) and [Ni(Hbdped)(ba)(Hdmpz)]·2NO·2MeCN (SD/Ni4a), were obtained by tuning the auxiliary carboxylic acids, where Hbdped = 1,2-bis-(3,5-dimethylpyrazol-1-yl)-ethane-1,2-diol; Hmba = 2-methylbenzoic acid; Hdmpz = 3,5-dimethyl-1H-pyrazole; Htca = 3-thiophenecarboxylic acid; and Hba = benzoic acid. The structures of SD/Ni6b, SD/Ni5a and SD/Ni4a are built from a central NiO opened cube, appending two to zero NiNO octahedra. The solution behaviours of SD/Ni6b, SD/Ni5a and SD/Ni4a were studied in detail via an ESI-MS technique and their solution stabilities were confirmed. Magnetic analysis indicated the presence of Ising-type anisotropy: D = -13, -10, and -11 cm for SD/Ni6b, SD/Ni5a, and SD/Ni4a, respectively; moreover, dominantly ferromagnetic interactions were found between magnetic centers: J = 6.5 cm, J = -0.44 cm and J = 5.9 cm, J = 2.6 cm for SD/Ni5a and SD/Ni4a, respectively. Besides, the photocurrent signals were observed and they reached the maximum very quickly for these three nickel(ii) clusters and then their current intensities remained almost constant, which provide a possibility to be used for light-harvesting and photo-related catalysis.