The synthesis and structure of an 8-coordinate Fe(ii) compound [Fe^II(L1)₂](ClO₄)₂ (1) with a [FeN₄O₄] core are reported. It is the first example of an 8-coordinate Fe(ii) complex exhibiting field-induced single-molecule magnet (SMM) behaviour.

A series of lanthanide (Ln) compounds, [Eu^III(L)₂(MeOH)(H₂O)](ClO₄)₃ (1), [Tb^III(L)₂(H₂O)](Cl₃) (2) and [M^III(L)₂(NO₃)](ClO₄)₂ (M = Eu (3); Sm (4); Tb (5); Dy (6)), have been prepared by the treatment of a neutral tetra-dentate ligand (N²,N⁹-dibutyl-1,10-phenanthroline-2,9-dicarboxamide, L) with various Ln(III) salts in MeOH. All of the compounds have been structurally characterized by X-ray crystallography. It is noted that the anions of the Ln(III) salts play crucial roles in the solid-state structures and the properties of the resulting complexes. In compounds 1 and 2, the metal centres are 10- and 9-coordinated, respectively, which are surrounded by two L ligands and solvent molecules. When the nitrate salts are used instead, four isostructural 10-coordinate Ln(III) compounds are obtained. The photophysical properties show that most of the compounds exhibit the characteristic emission peaks of Ln(III). Ligand L acts as a very good ‘antenna’ to sensitize the Eu(III) emission, but not for other Ln(III) emissions. The quantum yield of 3 is 75.4%, which is much higher than that of 1 (17.6%) due to the –OH oscillators of the coordinated H₂O and MeOH molecules in 1. The magnetic properties of the Tb(III) compounds 2 and 5 and the Dy(III) compound 6 were investigated in detail as a natural extension of our previous study of the effect of high-coordination number on the single-ion magnet (SIM) behaviour of 3d compounds. The results show that subtle changes in the coordination environment have significant effects on the magnetic behaviour. The 9-coordinate compound 2 is not a single ion magnet (SIM), but both 10-coordinate compounds 5 and 6 exhibit field-induced SIM behaviour. It is also interesting to note that, upon the application of a small dc field, 5 exhibits two distinct relaxation processes, which is uncommon in Ln-based SIMs.

A new series of luminescent phosphine copper(I) complexes with cyano- and hydroxyl-substituted 2,2′-bipyridine ligands [Cu^I(bpy(CN)₂)(P(PhX)₃)₂](ClO₄) [X = H (1); Me (2); Cl (3)], [Cu^I(bpy(CN)₂)(POP)](ClO₄) (4), [Cu^I(bpy(OH)₂)(PPh₃)₂](ClO₄) (5) and [Cu^I(bpy(OH)₂)(POP)](ClO₄) (6) have been synthesized and characterized. Three of these complexes have been structurally characterized by using X-ray crystallography. The effect of the attaching –CN and –OH groups at the ortho-positions of bpy ligand was investigated. In CH₂Cl₂ solution, these complexes show yellow to orange phosphorescence, with the emission maxima not only sensitive to the electronic nature of the bipyridine ligands, but also considerably varied with the modification of phosphine ligands. In addition, these complexes show intense tunable green to yellow emissions in their solid state. To elucidate the electronic structures and transitions of these complexes, density functional theory (DFT) calculations on representative examples revealed that the lowest energy electronic transition associated with these complexes predominantly originates from metal-to-ligand charge transfer transitions (MLCT).

Photochemical reactions of (PPh₄)[Os^VI(N)(L)(CN)₃] (NO₂-OsN) with piperidine and pyrrolidine afforded two osmium(V) hydrazido compounds, (PPh₄)[Os^V(L)(CN)₃(NNC₅H₁₀)] ([PPh₄]1) and (PPh₄)[Os^V(L)(CN)₃(NNC₄H₈)] ([PPh₄]2), respectively. Their structures consist of isolated, mononuclear distorted octahedral osmium anions that are well-separated from each other by PPh₄ ⁺. Their low spin S = 1/2 and L = 1 ground state was confirmed by magnetometry and DFT calculations. Interestingly, both compounds exhibit slow magnetic relaxation under a bias dc-field. These osmium(V) complexes are potentially useful building-blocks for the construction of molecule-based architectures with interesting magnetic properties. In contrast, the structurally related (PPh₄)[Os^III(L)(CN)₃(NH₃)] ([PPh₄]3), which also has a low-spin S = 1/2 ground state but with a different electronic configuration (5d⁵), does not exhibit slow magnetic relaxation, due to the absence of any orbital moment (L = 0). Furthermore, the structurally different osmium(V) hydrazido compound reported by Meyer, [Os^V(tpy)(Cl)₂(NNC₅H₁₀)](PF₆) (4[PF₆]), also does not exhibit slow magnetic relaxation due possibly to a change in magnetic anisotropy from axial for [PPh₄]1 and [PPh₄]2 to planar.