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The reactions of Ni2+, edt2– and PR3(R = Ph or Et) in MeOH gave the complexes [Ni(tpdt)(PPh3)]1, [Ni2(edt)2(PPh3)2]2, [Ni2(edt)2(Pet3)2]3 and [Ni2(tpdt)2]4(edt = ethane-1,2-dithiolate, tpdt = 3-thiapentane-1,5-dithiolate). Complex 3 is orthorhombic and crystallizes in space group Pbca with a= 14.086(4), b= 25.569(11), c= 13.768(4)A, Z= 8, R= 0.060. Complex 4 also crystallizes in the orthorhombic space group Pbca with a= 10.935(8), b= 28.826(15), c= 9.437(4)A, Z= 8, R= 0.047. All the nickel atoms are four-co-ordinated with distorted square-planar geometies of phosphorus and/or sulfur atoms. In the reaction system condensation of edt2– occurs through a C–S bond disruption to form tpdt2–, which co-ordinates to the nickel atoms to give complexes 1 and 4.

The complexes [Co(dppp)(SPh)2][dppp = 1,3-bis(diphenylphosphino)propane] and [Co(bdpp)(SPh)2][bdpp = bis(2-diphenylphosphinoethyl)phenylphosphine] were prepared in good yields by treating Co(dppp)Cl2 with NaSPh and elemental selenium in dimethylformamide and by treating CoCl2·6H2O and bdpp in acetonitrile with NaSPh, respectively. The complex [Co(dppp)(SPh)2] crystallizes in the triclinic space group P, with a= 9.665(2), b= 10.075(1), c= 18.288(2)A, α= 102.41(1), β= 93.89(1), γ= 92.40(1)° and Z= 2, whereas the complex [Co(bdpp)(SPh)2] is monoclinic, space group Cc, with a= 16.374(2), b= 26.033(3), c= 10.873(5)A, β= 117.49(2)° and Z= 4.

The complex [Co3(bdt)3(PBun3)3]1(H2bdt = benzene-1,2-dithiol) was obtained by the reaction of CoCl2, Na2bdt and PBun3 in 1:1:2 molar ratio in methanol. It crystallizes in triclinic space group P with a= 13.694(4), b= 18.460(4), c= 13.656(4)A, α= 100.69(2), β= 108.68(2), γ= 85.06(2)°, Z= 2, from 6366 reflections with I > 3σ(I), final R(R′)= 0.059 (0.066). The Co3 atoms form an isosceles triangle with rather short Co-Co bonds. The bdt ligands either bridge between two Co atoms or strongly chelate terminally to one Co atom and simultaneously bridge weakly to the others. Restricted air oxidation of 1 results in the isolation of [PHBun3][Co(bdt)2(PBun3)]2, which crystallizes in triclinic space group P with a= 10.800(3), b= 13.533(4), c= 15.342(2)A, α= 96.37(2), β= 108.57(2), γ= 97.02(2)°, Z= 2, from 3801 reflections with I > 3σ(I), R(R′)= 0.086 (0.088). The Co atom is in a square-pyramidal co-ordination environment with P in the axial position. The PBun3 group dissociates easily in dimethyl sulphoxide yielding paramagnetic [Co(bdt)2]–3 with square-planar cobalt co-ordination. Proton NMR data are discussed and cyclic voltammetry data reported.

Dicubane cluster compounds (Et4N)4[Mo2Fe7S8(SR)12] (2A) (R=Ph,a;o-tolyl,b;m-tolyl,c;p-tolyl,d) were made by reaction of (Et4N)2[Fe4(SR)10] (1) with (Et4N)2MoS4 in MeCN at room temperature. The structure,1Hn.m.r.,57Fe Mossbauer spectrum, magnetic susceptibility and cyclic voltammogram are described. (Et4N)3[Mo2Fe6S8Cl6(SR)3] (3) (R=Ph,a;m-tolyl,b) was obtained from the reaction of (2Aa) or (2Ac) with acetyl chloride in MeCN. This is the first time that compound of structural type (2) is transformed into that of structural type (3) by chemical conversion. Compound (2Aa) crystallizes in the triclinic space group P $$\bar 1$$ with Z=1 and unit cell dimensionsa=12.775(4),b=13.076(3), andc=20.576(4) A; the structure was refined to R=7.7% using 4031 unique data with I>3ϖ(Io). Compound (2Ac) 2THF crystallizes in the monoclinic space group P21/n with Z=2 and unit cell dimensionsa=18.022(2),b=18.375(2) andc=22.254(3) A; the structure was refined to R=6.4% using 5173 unique data with I>3ϖ(Io). Compound (3b) crystallizes in the hexagonal space groupP63/m with Z=2 and unit cell dimensionsa=b=16.827(3) andc=15.951(16) A; the structure was refined to R=4.9% using 1296 unique data with I>3ϖ(Io). Its characteristics are discussed and compared with those of known compounds. The ratios of core volumes S4/M4 are within the 2.34–2.40 range for core oxidation level [MoFe3S4]3+ indicating that distortion of the cubane core is a general phenomenon. Different thiolato ligands induce significant changes of structural parameters only at the Fe(SR)6 region for compound (2A) while terminal chlorides induce changes over the whole molecule of (3b) with the latter structure more comparable to [Mo2Fe6S8(SPh)9]5− (3f) with [MoFe3S4]2+ core than to [Mo2Fe6S8(SPh)9]3− (3d). The isotropic shifts of (2A) originate mainly from π-contact interaction. Both1H n.m.r. spectra and magnetic susceptibility measurements indicate practically no magnetic interaction among the three magnetic centres,i.e. a Fe(SR)6 bridge and two [MoFe3S4(SR)3] units. CV studies showed that the reduction of cubane unit having aromatic thiolates is easier than that having aliphatic thiolates as the aliphatic group is electron-donating. In addition, the very similar differences of Ep,c for first and second cubane units in compounds (2A) and in (3d) and (3e) imply that the effect of the first reduced unit [MoFe3S4]2+ upon the second unit [MoFe3S4]3+ is very similar in the two types of dicubane cluster compounds. Synergism in Mo−Fe−S cluster compounds is thus proposed to play an important role in their structural correlation with reactivities and must function in nitrogenase.

The cyclic voltammogram of sodium molybdate in weak acid solution exhibits two main reduction waves, one at −0.8 V (SCE) from the [Mo7O24]6− anion and the other at −1.3 V (SCE) from [MoO4]2−. The former is quasi-reversible and relates to three oxidation waves. The thiomolybdates give only one irreversible reduction wave at about −1.1 V (SCE). The reduction mechanism has also been discussed.

A new dinuclear pentacoordinate ironsulfur compound (Et 4 N) 2 [Fe 2 (1,2-OSC 6 H 4 ] ( 1 was synthesized and the structure of 1·2CH 3 CN was determined to be monoclinic, P 2 1 / n , M r = 950.97, with crystal data a = 11.580(2), b = 16.731(6), c = 12.869(2) A ; β = 98.07(2)°, V = 2468.6 A 3 , Z = 2, D x = 1.279 g cm −3 . From the 2242 independent reflections with I ⩾ 3σ( I o ), the final R converged to 0.069. The centrosymmetric anion of 1 is a dimer of [Fe(mp) 2 ] − bridged by the alkoxy groups of the two bridging mp 2− . The atom Fe(III) is in distorted trigonal bipyramidal environment with O(1) and O(2) as the two apical atoms and O(1′)S(1)S(2) forming the equatorial plane. Both 1 H NMR and CV measurements in DMSO and CH 3 CN showed the existence of species D (CH 3 CN) or M (DMSO), respectively, from the equilibrium (1). The dissociation of 1 into M in strongly polar solvent is further evidenced by 1 H NMR in DMF of intermediate polarity, which gave a ratio of D:M = 8:1. Mossbauer effect measured at 77 K indicated that the ground state spin of Fe(III) in 1 ·2CH 3 CN is .

The reaction of [Ag(dppm) (NO 3 )] 2 ( 1 ) with potassim i-mnt  2,2-dicyano-1,1-ethylenediothiolate; dppm  bis (diphenylphosphino)methane) in DMF at room temperature gave rise to the complex [Ag 4 ( μ -dppm) 4 ( μ 4 -S 2 C=C(CN) 2 ) 2 ] ( 2 ). The crystal structure of 2 has been determined by single crystal X-ray diffraction analysis. 2 is a tetranuclear complex with a silver-silver separation of 3.376(2) A and the four silver atoms form a distorted square plane bridged by four dppm and two i-mnt ligands. Each silver atom is coordinated by two phosphorus and two sulfur atoms in a distorted tetrahedral environment. The IR, 1 H and 31 P NMR spectroscopic properties of 2 have also been investigated.

The reaction of Et 2 NCS 2 Ag with [Et 4 N] 2 MoSe 4 or Na 2 Se in DMF/CH 3 CN gave rise to a polynuclear silver cluster compound Ag 11 ( μ 5 -Se)( μ 4 -Et 2 NCS 2 ) 3 ( μ 3 -Et 2 NCS 2 ) 6 , which crystallized in trigonal space group R 3 c with a = 18.633(6), c = 43.032(12) A , and Z = 6 . The molecule possesses a crystallographic C 3 symmetry axis and three equivalent units of Ag 3 (Et 2 NCS 2 ) 3 . The average AgAg and AgSe distances are 3.004(3) and 2.801(4) A, respectively. The structure is discussed together with its IR, UV-Vis and 1 H NMR spectra. The compound shows an intense emission with λ max at 565 nm in the solid state. Cyclic voltammetry and thermal gravimetric analysis of the title compound are also reported.

An asymmetrical dinuclear cobalt complex Co2(dppe)(µ-SPh)3SPh (dppe = Ph2PCH2CH2PPh2) has been prepared and characterized by X-ray diffraction showing the entirely different geometrical environments of the two cobalt(II) atoms.