Structure and magnetism of novel mixed-anionic-group compounds M2(SeO3)(Te3O7) (M = Co2+, Ni2+)

Novel mixed-anionic-group compounds M 2 (SeO 3 )(Te 3 O 7 ) (M = Co 2+ , Ni 2+ ) are successfully synthesized by a conventional hydrothermal method. Two compounds are isostructural which crystallize in the orthorhombic system of a space group Pnma . The framework shows a (MO 6 ) ∞ chain structure along the b -axis, while SeO 3 groups are isolated and Te 3 O 7 groups form the (Te 3 O 7 ) ∞ chains running along the a -axis. This is the first time to realize transition-metal compounds coexisting with Se 4+ and Te 4+ anionic groups. Magnetic measurements show that Co 2 (SeO 3 )(Te 3 O 7 ) possesses an antiferromagnetic ordering at ∼11 K, while Ni 2 (SeO 3 )(Te 3 O 7 ) exhibits a similar antiferromagnetic ordering at ∼31 K. Also, the fitting of magnetic susceptibility using a spin-chain model gives the exchange coupling J /k B = −1.515 K for Co 2 (SeO 3 )(Te 3 O 7 ) and J /k B = −8.963 K for Ni 2 (SeO 3 )(Te 3 O 7 ), respectively.