Synthesis and magnetic characterization of two layered organic-inorganic hybrid Ni(II) and Mn(II) 3,4;9,10-perylenediimide bisphosphonates.

Two new layered metal(II) bis-phosphonates have been prepared by chemical assembling of a functional organic ligand with paramagnetic transition metal ions. The ligand is represented by the bifunctional R(PO3H2)2 molecule where R is the N,N'-bis(2-phosphonoethyl)perylene-3,4;9,10-tetracarboximide (hereafter PDI-BP). The latter features an extended ?- electron system, which is responsible of interesting optical properties. The PDI-BP ligand reacts with Mn(II) and Ni(II) ions to give the new metal(II) bisphosphonates of formula Mn2[(PDI-BP)(H2O)2]·0.5H2O (1) and Ni2[(PDIBP)( H2O)2]·3H2O (2). The compounds were characterized by several techniques and resulted to be scarcely crystalline red solids. The magnetic properties of both the compounds have been explored by a SQUID magnetometer in the temperature range from r. t. down to 2 K. Magnetic measurements were performed in the DC and AC modes as a function of temperature and magnetic field. The experiments in the high temperature region confirm the electronic spin configurations (d5(S = 5/2) for Mn(II) ion and d8(S = 1) for Ni(II) ion), respectively. At low temperatures, DC susceptibility vs. T measurements on compound (1) indicate the presence of antiferromagnetic coupling and AC susceptibility experiments show two peaks in the in-phase and out-of-phase signals located at 2.5 K and 25 K. The slightly frequency dependent signal at lower temperatures might be attributed to domain wall movements in the ordered state, while the frequency dependent peak at higher temperatures may be due to disorder in the Mn(II) layer. Hysteresis cycles performed below 30 K indicate the presence of spin canting below that temperature.The magnetic behavior of compound (2) is similar to the previous one. AC susceptibility measurement vs. T shows a peak located at ca. 20 K, in both, the in-phase ?' and out-of phase ?'' components of the AC susceptibility. The signals are sligthly frequency dependent, and probably associated to disorder in the Ni(II) layer. Hysteresis loops recorded at several temperatures below 20 K together with the previous data are the signature of magnetic order.