A combination of organic and inorganic cations in the synthesis of transition metal nitrates: preparation and characterization of canted rectangular Ising antiferromagnet (PyH)CsCo 2 (NO 3 ) 6 .

Pyridinium cesium cobalt nitrate, (PyH)CsCo 2 (NO 3 ) 6 , obtained from a nitric acid solution crystallizes in the orthorhombic space group Pnma with unit cell parameters a = 8.6905(14) Å, b = 11.9599(18) Å, c = 18.386(3) Å, V = 1911.0(5) Å 3 , and Z = 4. It consists of [Co(NO 3 ) 3 ] - layers, in which each Co 2+ ion is connected with four monodentate bridging NO 3 -groups and one bidentate terminal NO 3 -group, forming a corrugated rectangular net. Magnetization and specific heat measurements show that (PyH)CsCo 2 (NO 3 ) 6 undergoes a long-range canted antiferromagnetic ordering in two steps at T C1 = 5.0 K and T C2 = 2.6 K. The temperature dependence of the magnetic susceptibility and the field dependence of the magnetization measured for (PyH)CsCo 2 (NO 3 ) 6 show that it is an Ising antiferromagnet. In support of these observations, our DFT + U + SOC calculations show that the Co 2+ ions of (PyH)CsCo 2 (NO 3 ) 6 have an easy-axis magnetic anisotropy with preferred spin orientation along the b -axis. To a first approximation, the spin lattice of (PyH)CsCo 2 (NO 3 ) 6 is a weakly alternating Ising antiferromagnetic chain ( J 1 / J 2 ∼ 0.85), and these chains interact weakly ( J 3 / J 2 ∼ 0.07) to form a rectangular Ising antiferromagnetic lattice. In agreement with the prediction for a rectangular Ising antiferromagnet by Onsager, (PyH)CsCo 2 (NO 3 ) 6 undergoes a long-range antiferromagnetic ordering.