Synthesis, Structural and Magnetic Characterization of Ni(II) 3,4;9,10- Perylenediimide bis-phosphonate: a layered organic-inorganic hybrid ferromagnetic dye.

A new organic-inorganic hybrid nickel(II) bis-phosphonate has been prepared by a chemical reaction of a functional organic ligand with Ni(II)chloride.1 The ligand is 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 reaction of PDI-BP ligand with Ni(II) ions resulted in the isolation of the scarcely crystalline red solid of formula Ni2[(PDI-BP)(H2O)2]×3H2O (1). Due to poor crystallinity of (1) EDXD technique was applied in an attempt of determining the local structure. Magnetic measurements of (1) were performed in both DC and AC modes as a function of temperature and magnetic field. The experiments in the high temperature region confirms the electronic spin configuration (S = 1) for Ni(II) ion. cM -1 vs. T plot is linear above 100 K, and the estimated value of the Curie constant C of 3.49 emu.K.mol-1 confirms for the two Ni(II) ions per formula unit the electronic spin configurations d8 (S = 1). The Weiss constant is positive of +9.7 K and is an indication of exchange ferromagnetic interactions between nearest neighbour Ni(II) ions. Below 30 K the magnetic behaviour of Ni2[(PDIBP)( H2O)2]·3H2O is different when the sample is field (FC) and zero-field cooled (ZFC). The two M vs. T plots do not overlap below T = 20 K and the bifurcation point is localized at T ~ 20 K. The difference between the fc and zfc magnetizations, i.e. the irreversible magnetization, DMfc-zfc, becomes almost zero at the critical temperature Tc, which is found to be ~21 K. AC susceptibility measurement vs. T shows a peak located at ca. 20 K, in both, the in-phase c’ and outof phase c’’ components of the AC susceptibility (see Figure). The signals are slightly frequency dependent, and probably associated to disorder in the Ni(II) layer. Isothermal hysteresis loops recorded at several temperatures below 20 K are the signature of ferromagnetic order. The title compound is a rare example of ferromagnetic metal organophosphonate.