Multifunctional Magnetic Molecular {[MII(urea)2(H2O)]2[NbIV(CN)8]}n System: Magnetization-Induced SHG in the Chiral Polymorph

Incorporation of urea molecules into the magnetic system Mn-II-[Nb-IV(CN)(8)] results in formation of two magnetic polymorphs {[Mn-II(H2O)(urea)(2)](2)[Nb-IV(CN)(8)]}(n), chiral a and centric beta crystallizing in space groups P4(1) and (1) over bar, respectively. Both polymorphs exhibit extremely similar structures and are soft ferrimagnets with critical temperatures of 43 and 42 K, respectively. The presence of coordinated urea in the noncentrosymmetric alpha produces NLO functionality, second harmonic generation (SHG), whereas centric beta is just another molecular magnet. As a result of interaction of both functionalities below magnetic ordering temperature, the magnetization-induced SHG (MSHG) is observed for polymorph alpha. The observed MSHG/SHG signal ratio was the largest among molecule-based noncentrosymmetric magnets. The presence of urea molecules in both polymorphs gives also rise to their interesting topotactic reactivity. Both polymorphs can be easily transformed into a new entity {[Mn-II(H2O)](2)[Nb-IV(CN)(8)]center dot 2.5MeOH}(n) 2b with significant shift of critical temperature T-c to 70 K. Subsequent hydration of 2b leads to {[Mn-II(H2O)(2)](2)[Nb-IV(CM8]center dot 4H(2)O}(n) 3 with T-c, of 47 K.