The foreword to this special issue of the Journal dedicated to Professor Allan White gives an overview of his work and his legacy.

The simple formulae presented for main-group metal complexes of oligopyridines (typically 2,2-bipyridine, 1,10-phenanthroline, and 2,2′:6′,2″-terpyridine) hide a wide variety of polymeric solid-state structures.

Fifteen years of intense collaboration with Professor Allan White is narrated in this article. The most important results in coordination and organometallic chemistry are described. These results will be of help for those who want to venture into the chemistry of scorpionates and phosphines towards coinage and transition metals.

Co-ligand binding in a sequence of calixarene complexes changes as a function of lanthanoid cation size.

Allan White’s almost heroic dedication to systematic structural studies of all areas of coordination chemistry is exemplified in his numerous studies concerning the lanthanide elements. The present work is a meticulous investigation of lanthanide halide complexes with polypyridines considerably extending knowledge in this particular area.

Structural characterisation of adducts of lanthanide picrates with dimethylsulfoxide has provided evidence that the 9-coordinate, tricapped trigonal-prismatic, mer-[Ln(pic)₃(dmso)₃] form with chelating picrate ligands may extend through the full series. Partial aquation of the tris(dmso) complexes to [Ln(pic)₃(dmso)₂(OH₂)] provides three examples of an otherwise similar but facial isomer.

Structural studies of crystalline adducts of [Eu(dipivaloylmethanato)₃] with dmso, dma, tmp, hmpa, and ompa have shown all to contain seven-coordinate Eu^III. This low coordination number appears to be a consequence of partial coordination sphere interpenetration in the solid state.

Trimethylphosphate (tmp) is the first of a series of related O-donor solvates of lanthanide(III) picrates to give isomeric mer- and fac-[Ln(pic)₃(tmp)₃] complexes.

Six-coordination of Sc^III is observed throughout in crystalline adducts of scandium picrate with dmso, dma, nmp, tmp, hmpa, and ompa, although with variations in the adduct stoichiometry and the coordination mode of picrate.

Structural studies of adducts of the lanthanide picrates with hexamethylphosphoramide (hmpa) and octamethylpyrophosphoramide (ompa) provide significant contrasts with those of analogous adducts with dimethylsulfoxide and trimethylphosphate. Adducts of hmpa show a transition from 9-coordinate (hmpa)₃ to 8-coordinate (hmpa)₂ species, while ompa displaces one picrate from the primary coordination sphere.

Structural studies of the adducts of lanthanide picrates with dimethylacetamide (dma) and N-methylpyrrolidinone (nmp) add further variety to the nature of simple O-donor ligand complexes of these picrates. Polymorphism is readily detected in the dma complexes, while, with the heavier lanthanides, nmp causes partial detachment of the picrate ligands.

Comparison of the bond lengths in [(Ph₃As)₂AuI] and [(Ph₃As)₃AuI] and related complexes show that they are generally consistent with the ‘gold is smaller than silver’ phenomenon caused by relativistic orbital contraction effects in gold, but the results also show that the magnitude of this effect is dependent on the nature of the metal–ligand bonds involved.

A series of organoamidoantimony(III) complexes of the general type [SbL^Me_3 − nCl_n] (n = 2, 1, 0) incorporating a bulky amido fluorine ligand tethered with an amino pendant arm, HL^Me = p-HC₆F₄NH(CH₂)₂NMe₂ have been successfully gained and fully characterised as monomers in the solid state highlighting a variety of coordination modes.

Single crystal X-ray structure determinations have been executed for several mononuclear Zn halide, sulphate, and nitrate complexes with 2,2′-bipyridyl and 1,10-phenanthroline ligands.

Various 3,5-disubstituted pyrazoles were treated with nBuLi in Et₂O or tmeda/hexane, leading to the formation of three structurally diverse lithium pyrazolates while a mononuclear zinc complex [Zn(tBu₂pz)₂(tBu₂pzH)₂].1/2THF and a dinuclear complex ([AlMe₂(Ph₂pz)]₂.1/2THF) were isolated by treating the pyrazole with ZnEt₂ or AlMe₃.

Structure determinations on complexes of lanthanide(III) picrates with aza-aromatic ligands provide examples of various stacking arrays. The chain of [La(terpy)₂(pic)₂]⁺ cations (shown in space-filling mode) present in the lattice of [La(terpy)₂(pic)₂](pic)·CH₃CN involves both intra- and intermolecular heterogeneous stacks.

Structural studies of the products of reaction of different lanthanide(III) salts with trimethylphosphate show them to contain dimethylphosphate as a bridging bidentate rather than a chelate ligand across the lanthanide series.

The reaction of 4,4′-(2,5-dimethyl-1,4-phenylene)dipyridine (L) with cobalt(II) acetate tetrahydrate in mixed methanol/DMF solvent produces a two-dimensional coordination polymer [Co₂L₂(OAc)₄(H₂O)₂]_n.

The dark blue complex [{Cp(dppe)Ru(C≡C)}₃C]PF₆ 1 was obtained in 46 % yield by treatment of Ru(C≡CH)(dppe)Cp with CuCl/TMEDA, followed by KOH and [NH₄]PF₆ in acetone; it was accompanied by known complexes {Cp(dppe)Ru}C≡CC≡C{Ru(dppe)Cp} 2 (22 %) and yellow [1,3-{Cp(dppe)Ru}₂C₄H₃]PF₆ 3 (2.6 %).

Silver(I) carboxylates and nitrates are investigated for their coordination modes by application of a combination of solid-state NMR, single-crystal X-ray diffraction, and quantum-chemical methods. Bending potentials in the coordination sphere of the silver(I) atoms are shallow, so that intermolecular interactions can cause conformational polymorphism in the crystalline forms. The different crystal packing modes in the polymorphic forms are understood in terms of Hirshfeld Surface Analysis.

Bilayers are created when cone-shaped p-sulfonatocalix[4]arene forms complexes with La³⁺ and Er³⁺, whereas with Yb³⁺ overall assembly deviates from the bilayer arrangement. With conformational flexible p-sulfonatocalix[6]arene, this results in a hydrogen bonded network with alternating hydrophobic-hydrophilic layers associated with primary coordination of Yb³⁺, with the calixarene crystallised in a partial cone conformation.

The stepwise synthesis of two palladium(II) complexes containing an N-heterocyclic carbene ligand substituted by the bulky 9-propyl-9-fluorenyl group is described. In both complexes, two methylenic H atoms of the propyl group interact with the metal atom in an anagostic manner.