New hydrophobic, tetradentate nitrogen heterocyclic reagents, 6,6′-bis-(5,6-dialkyl-1,2,4-triazin-3-yl)-2,2′-bipyridines (BTBPs) have been synthesised. These reagents form complexes with lanthanides and crystal structures with 11 different lanthanides have been determined. The majority of the structures show the lanthanide to be 10-coordinate with stoichiometry [Ln(BTBP)(NO₃)₃] although Yb and Lu are 9-coordinate in complexes with stoichiometry [Ln(BTBP)(NO₃)₂(H₂O)](NO₃). In these complexes the BTBP ligands are tetradentate and planar with donor nitrogens mutually cisi.e. in the cis, cis, cis conformation. Crystal structures of two free molecules, namely C2-BTBP and CyMe₄-BTBP have also been determined and show different conformations described as cis, trans, cis and trans, trans, trans respectively. A NMR titration between lanthanum nitrate and C5-BTBP showed that two different complexes are to be found in solution, namely [La(C5-BTBP)₂]³⁺ and [La(C5-BTBP)(NO₃)₃]. The BTBPs dissolved in octanol were able to extract Am(III) and Eu(III) from 1 M nitric acid with large separation factors.

Phenyl-substituted derivatives of 2,2′∶6′,2′′-terpyridine and a corresponding bipyridine–pyrazine derivative have been shown to have metal extraction properties and separation factors for americium(III) over europium(III) which are comparable to those previously obtained for 2,2′∶6′,2′′-terpyridine (L¹). The extracting agents in either tert-butylbenzene (TBB) or hydrogenated tetrapropene (TPH) gave D_Am/D_Eu separation factors (SFs) between 7 and 9 when used to extract the metal ions from 0.01–0.1 M nitric acid solution in synergistic combination with 2-bromodecanoic acid. In contrast to L¹, the new hydrophobic ligands have little or no solubility in the aqueous phase. In an effort to better understand the nature of the species which may be involved in the extraction process, a series of metal–L¹ complexes which cover the lanthanides have been prepared. Five different structural types have been established for the lanthanide coordination complexes. In type 1, [M(NO₃)₃(L¹)(H₂O)] (M = Nd), the metal is 10-coordinate being bonded to one terdentate L¹ ligand, three bidentate nitrates and a water molecule. In type 2, [M(NO₃)₂(L¹)₂]⁺[M(NO₃)₄(L¹)]⁻ (M = Nd, Sm, Tb, Dy and Ho), the metal atom in the cation is 10-coordinate, being bonded to two terdentate L¹ ligands and two bidentate nitrates; in the anion the metal is also 10-coordinate, being bonded to one terdentate L¹ ligand and four nitrates, of which three are bidentate and one unidentate. In type 3, [M(NO₃)₃(L¹)(H₂O)]·L¹ (M = Ho, Er, Tm and Yb), the metal is 10-coordinate, being bonded to three bidentate nitrates, one terdentate L¹ and a water molecule. In addition, an L¹ ligand is found in the asymmetric unit which is hydrogen-bonded to the coordinated water molecule. In type 4, [M(NO₃)₃(L¹)(H₂O)] (M = Tm), the metal is 9-coordinate, being bonded to two bidentate nitrates, one unidentate nitrate, one terdentate L¹ ligand and a water molecule. In type 5, [M(NO₃)₃(L¹)] (M = Yb), the metal is 9-coordinate, being bonded to three bidentate nitrates and one terdentate L¹ ligand. A sixth structural type was observed for M = La in the crystal structure [(H₂L¹)(NO₃)]⁺[(H₂L¹)]²⁺[La(NO₃)₆]³⁻. The metal is not bound to L¹ but instead forms the well-known hexanitrate anion. This complex may give some indication of the type of species which could be formed at higher acid concentrations in the aqueous phase, where protonation of L¹ can occur.

Three new heteronuclear nickel(II)/cadmium(II) complexes, [(SCN)(Cl)Cd(L)Ni(DMF)₂] (1), [(SCN)(CH₃CO₂)Cd(L)Ni(CH₃OH)₂] (2) and [(SCN)(Cl)Cd(L)Ni(NH₂CH₂CH₂CH₂NH₂)]_n (3) {where H₂L = N,N′-bis(3-ethoxy-salicylidene)propane-1,3-diamine is a N₂O₄ compartmental Schiff base}, have been synthesized and characterized. The structures of the complexes have been confirmed by single crystal X-ray diffraction studies. In each complex, nickel(II) is placed in the inner N₂O₂ environment and cadmium(II) is placed in the outer O₄ compartment of the compartmental Schiff base. Furthermore, the importance of unconventional C–H⋯π (chelate) interactions in the solid state of both complexes and C–H⋯π (thiocyanate) interaction in complex 2 has been described by means of DFT and MEP calculations and characterized using NCI plots. All complexes show photoluminescence at room temperature upon irradiation by ultraviolet light. The lifetimes of excited states are in the range of 2–6 ns.

The terdentate ligand 4-amino-bis(2,6-(2-pyridyl))-1,3,5-triazine L⁴ has been shown to have useful actinide(III)/lanthanide(III) separation properties relevant to nuclear reprocessing. The complexation of this ligand with the lanthanides has been investigated. Crystallographic analyses show the formation of five structural types. In the first part of the lanthanide series, (La–Sm), these structural types are (1) [LnL⁴(NO₃)₃(H₂O)₂], 11-coordinate, only for Ln = La; (2) [LnL⁴(NO₃)₃(H₂O)], 10-coordinate, for Ln = La, Pr, Nd, Sm; (3) [LnL⁴(NO₃)₂(H₂O)₃][NO₃] 10-coordinate for Ln = Nd, Sm. In the second part of the series from Eu to Lu the structures are all 9-coordinate but have two different stoichiometries; (4) [LnL⁴(NO₃)₂(H₂O)₂][NO₃] for Ln = Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu; (5) [LnL⁴(NO₃)₃(H₂O)] unusually with one unidentate nitrate for Ln = Yb, and Y. With M = Sc the structure obtained is [ScL⁴(NO₃)₃] which is 8-coordinate with one unidentate nitrate. The structure types found for particular lanthanides can be correlated with the size of the ion, although several of the lanthanides form two structure types. Particularly noticeable is the alternative pairing of one bidentate nitrate ion or two water molecules in the coordination sphere with a concomitant free nitrate anion in the latter case. Type 5 includes the relatively rare sighting of a unidentate nitrate anion. Extensive intermolecular hydrogen bonding involving the free amine group is found in all the structures.

Reflection loss is usually calculated and reported as a function of the thickness of microwave absorption material. However, misleading results are often obtained since the principles imbedded in the popular methods contradict the fundamental facts that electromagnetic waves cannot be reflected in a uniform material except when there is an interface and that there are important differences between the concepts of characteristic impedance and input impedance. In this paper, these inconsistencies have been analyzed theoretically and corrections provided. The problems with the calculations indicate a gap between the background knowledge of material scientists and microwave engineers and for that reason a concise review of transmission line theory is provided along with the mathematical background needed for a deeper understanding of the theory of reflection loss. The expressions of gradient, divergence, Laplacian, and curl operators in a general orthogonal coordinate system have been presented including the concept of reciprocal vectors. Gauss’s and Stokes’s theorems have been related to Green’s theorem in a novel way.