Lanthanoid Template Isolation of the α‑1,5 Isomer of Dicobalt(II)-Substituted Keggin Type Phosphotungstates: Syntheses, Characterization, and Magnetic Properties

A new
series of heterometallic 3d–4f sandwich type phosphotungstates,
[Ln­{PCo2W10O38(H2O)2}2]11– (Ln = SmIII, EuIII, GdIII, TbIII, DyIII, HoIII, ErIII, TmIII, YbIII, and LuIII, denoted 1a–10a, respectively),
have been synthesized by a one-pot reaction
procedure on reacting the dilacunary K14[P2W19O69(H2O)]·24H2O precursor
with Ln­(NO3)3·nH2O and Co­(NO3)2·6H2O in an aqueous
potassium chloride solution. All the compounds
were isolated as potassium salts and further characterized with different
analytical techniques such as single-crystal X-ray diffraction, Fourier
transform infrared spectroscopy, high-resolution electrospray ionization
mass spectrometry, elemental analysis by inductively coupled plasma
atomic emission spectroscopy, magnetic measurement, and thermogravimetric
analysis. Single-crystal X-ray diffraction analysis of the compounds
reveals that all these compounds are isostructural and crystallized
in the orthorhombic crystal system in space group Iba2. The polyanions contain the α-1,5 isomer of dicobalt-substituted
α-Keggin phosphotungstate, which sandwiched lanthanoid
cation and formed novel heterometallic dimer species. The temperature-dependent
magnetic susceptibilities of 1a, 2a, 4a, and 7a–10a indicate the dominant contribution
of the ferromagnetic interaction between CoII and CoII within the cluster, while the antiferromagnetic interaction
between CoII and LnIII dominates for 3a, 5a, and 6a. The isothermal magnetizations
of 1a–10a show a gradual increase in magnetization
at low fields
and do not reach saturation even at 50 kOe.