Hydrothermal syntheses, crystal structures and physicochemical properties of 2-D and 3-D inorganic coordination cobalt(ii)-sulfitepolymers

Abstract

The hydrothermal reaction of [Co^III(NH₃)₆]Cl₃ with Na₂SO₃ yields, depending on the concentration of Na₂SO₃, compounds {Na[Co^II₂(SO₃)₂(μ₃-OH)(H₂O)]}_∞ (1) and {Na₄[Co^II₂(SO₃)₄]}_∞ (2). When (NH₄)₂SO₃·H₂O was substituted for Na₂SO₃, the trinuclear mixed valence cobalt(II/III) complex (NH₄)₄{Co^II[Co^III(SO₃)₃(NH₃)₃]₂}·2H₂O (3·2H₂O) was isolated. The cobalt-sulfites 1–3·2H₂O were structurally characterized. In 1, the 1-D chains along the a-axis of the subunit [Co^II(2)Co^II(3)(OH)₂(SO₃)₂] are cross-linked with Co^II(1) atoms via Co–O_sulfite and Co–O_hydroxide bonds in 2-D sheets, that are further stacked through interlayer hydrogen bonds. In 2, the [Co^II₂(SO₃)₂]_∞ chains along the b-axis are cross-linked with tetrahedral cobalts via Co^II–O_sulfite bonds in 2-D sheets parallel to the ab-plane and the sheets are further bound to sodium atoms via Na⁺–O_sulfite bonds to form a 3-D structure. The 3-D inorganic coordination polymer, 2, crystallizes in the non-centrosymmetric space group P2₁2₁2₁. In addition, in compound 2 octahedral and tetrahedral cobalt atoms coexist, which is rather unusual for cobalt clusters. Compound 3·2H₂O is a 0-D mixed-valence {[(NH₃)₃Co^III(μ-SO₃)₃]Co^II[(μ-SO₃)₃Co^III(NH₃)₃]}⁴⁻ trinuclear cluster and can be considered as an octahedral {Co^IIO₆} complex ligated to two tridentate [(NH₃)₃Co^III(SO₃)₃]³⁻ ligands. The trinuclear clusters are stacked through an extended network of hydrogen bonding into a 3-D structure. Variable temperature magnetic susceptibility studies for 1–3·2H₂O revealed that 1 and 2 are 2-D magnetic systems with strong antiferromagnetic interaction between the Co^II atoms leading to an S = 0 ground state for 1, while in compound 2 there is an almost zero interaction between the cobalt(II) atoms leading to a non-zero ground state. The trinuclear compound 3·2H₂O has two diamagnetic Co^III atoms and a high-spin Co^II atom with D = 84(1) cm⁻¹, E = 6(1) cm⁻¹ and g = 2.56(1). The IR, the solid-state UV-vis spectra and the thermogravimetric analyses of compounds 1–3·2H₂O are also reported.