Magnetic, optical and phonon properties of novel heterometallic formates [NH3CH2CH2OH][MIIIMII(HCOO6](MIII = Fe, Cr; MII = Mn, Ni, Co)

Four novel compounds, [NH3CH2CH2OH][(MMII)-M-III(HCOO)(6)] with M-III = Fe and M-II = Mn (HEAFeMn), M-III = Fe and M-II = Ni (HEAFeNi), M-III = Cr and M-II = Mn (HEACrMn) and M-III = Cr and M-II = Co (HEACrCo), have been synthesized. They crystallize in the trigonal niccolite-type structure (space group P (3) over bar 1c). Magnetic studies revealed that HEAFeNi, HEAFeMn and HEACrCo are weak ferromagnets with the ordering temperature of 43, 27 and 11 K, respectively, whereas HEACrMn does not order magnetically at least down to 2 K. A source of the ferromagnetic component is most likely a canting of the antiferromagnetically ordered moments by a small angle resulting from antisymmetric exchange or single-ion anisotropy. Raman and IR data confirm that all obtained samples are isostructural. Optical studies of HEACrMn show that local crystal field around Cr3+ ion is of intermediate strength with the Dq/B value of 2.57. Luminescence studies indicate that HEACrMn exhibits efficient Cr3+-based emission. Below 200 K, the E-2-(4)A(2) phosphorescence observed as two bands at 686 and 696 nm becomes predominate.