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Evidence for prehistoric salt production in Britain has been confined to the Bronze and Iron Ages. This article presents new evidence for Early Neolithic (3800–3700 BC) salt-working at Street House, Loftus, in north-east England. This deeply stratified coastal site has yielded the remains of a brine-storage pit and a saltern with at least three associated hearths, together with an assemblage of flint and stone tools, ceramic vessel sherds and briquetage. A process of production is suggested and parallels are drawn from contemporaneous European and later British sites. This discovery has the potential to influence future Neolithic studies considering subsistence, early technologies and exchange mechanisms.

A series of binuclear ruthenium(I) complexes, [Ru2(CO)4(μ-XY)2(PPh3)2], have been prepared by two closely related routes. Complexes 2 (XY− = S2NC3H4−) and 3 (XY− = NC5H4O−) have been prepared by the reaction of [Ru2(CO)4(O2-CCH3)2(PPh3)2] with sodium 2-mercaptothiazolinate and sodium 2-oxypyridinate, respectively. The related pyrazolate-bridged complex 4 (XY−=N2C3H3−) was prepared by the reaction of sodium pyrazolate with [Ru2(CO)4(O2CCH3)(NCMe)2] followed by addition of PPh3. The X-ray structures of compounds 3 and 4 have been determined. Compound 3 crystallizes in the triclinic space group P1 with a 14.766(2), b 15.821(2), c 10.745(3) A, α 98.28(2)°, β 110.99(2)°, γ 103.29(1)°, V 2209.1 A3, Z = 2. On the basis of 5521 unique observations (tNO) and 379 parameters varied (NV) the structure has been refined to R = 0.042 and Rw = 0.054. Compound 4 crystallizes in the orthorhombic space group P212121 with a 13.220(2), b 14.846(4), c 21.403(3) A, V 4200.7 A3 and Z = 4. This structure has been refined to R = 0.041 and Rw = 0.023 for NO = 3915 and NV = 546. Both structures display the sawhorse arrangement of carbonyl groups and have the phosphine ligands in the axial positions opposite the RuRu bonds. For 3 the oxypyridinate groups are bound in a head-to-tail arrangement. The two-atom pyrazolate bridge imparts more strain than the three-atom oxypyridinate bridge and as a result the equatorial planes of the Ru centers are tipped by only 16.2(4)° in 3 but by 35.4(1)° in 4. The RuRu distances (2.7108(4) A (3); 2.732(1) A (4)) correspond to normal single bonds.

The alkyne-bridged “A-Frame” complex, [Rh2Cl2(μ-CF3C2CF3(DPM)2] (DPM  Ph2PCH2PPh2), reacts with diazomethane to give the unusual species, [Rh2Cl2(μ-CH2(μ-CF3C2CF3)(DPM)2] (2) in which the two DPM ligands, the methylene and the hexafluoro-2-butyne groups bridge the metals with no accompanying RhRh bond. Attempts to produce a methylene-bridged complex from the analogous carbonyl-bridged “A-frame”, [Rh2Cl2(μ-CO)(DPM)2], were unsuccessful as this species did not react with diazomethane. An X-ray structure determination has been carried out on compound 2. This complex crystallizes in the tetragonal space group P41 with a 21.334(3), c 14.574(2) A, V=6633.2 A3 and Z = 4. On the basis of 3669 unique observations and 291 parameters varied the structure has converged to R = 0.034 and Rw = 0.039. The RhRh separation of 3.466(1) A indicates that there is no RhRh bond and the wide RhCRh angle at the bridged methylene group (119.5(5)°) is also consistent with the absence of metalmetal bonding. The methylene group in compound 2 is found to be unreactive towards CO, H2 and protic acids, probably in part because it is protected in the pocket between the two metals, however compound 2 did react with PMe3 to yield a complex mix of products, from which [Rh2Cl(μ-Cl)(μ-CH2)(μ-CF3C2CF3)(PMe3)5] (3) crystallized in low yield. This complex crystallizes with two molar equivalents of CH2Cl2 in the monoclinic space group P21/n with a 11.519(2), b 14.689(7), c 25.250(5) A, β 93.00(2)°. V 4266.7 A3 and Z = 4. Based on 4614 unique observations and 396 parameters varied the structure has converged to R = 0.063 and Rw = 0.095. Compound 3 is unusual in that it has resulted from the replacement of the two bridging bidentate DPM groups in 2 by five monodentate PMe3 ligands. Both rhodium atoms have octahedral geometries in which they share a common face, bridged by the methylene, the alkyne and one chloro group. The RhRh separation of 3.1338(7) A is consistent with the absence of metalmetal bonding, which is substantiated by the relatively large RhCH2Rh angle of 100.1(3)°.