Electrospray mass spectrometric (ESMS) studies have been made on some representative examples of the trinuclear complexes [M30(RC00),;(H20)3]+ (M = Cr, Fe; R = H, CH3, CH3CH2, (CH3)3C) in methanol and pyridine/ methanol solutions. The nonbridging water ligands in the Cr(III) complexes partially exchange with the solvent molecules and ions containing the central Cr30(RCOO)6 core, and various combinations of terminal ligand are observed. At low first skimmer voltages, intact ions with three terminal ligands are detected, but as the skimmer voltage is increased, interaction with solvent molecules within the ion source causes collisionally activated decompositions to occur, leading to progressive loss of the labile terminal groups. The ES mass spectra of [Fe30(CH3C00)6-(H20)3]+ in MeOH or pyridine/MeOH show that the water molecules exchange completely with the solvent, and for other iron derivatives the core carboxylate ligands exchange completely with the acetate in the mobile phase used in the spectrometer. Collisionally activated decomposition (CAD) mass spectra (argon, 200 V) have been observed for some of the core ions [M30(CH3C00)6]+.

Complexes of manganese(111) and S-substituted salicylaldimines have been prepared of general formulae Nn(sa1-NR), and Nn(sa1-SR),X ( X = C1, Br, OAc).$ The complexes show high-spin magnetic behaviour with small deviations of the susceptibilities from the Curie law. Complexes of the type Mn(sa1en)X ( X = Br, I) have also been studied and these show somewhat larger deviations from Curie behaviour. I t is difficult to interpret this Curie-Weiss behaviour with certainty, but it can be explained for the salen derivatives, in particular, in terms of very weak antiferromagnetic interactions. The visible and near-infrared spectra fbr all the complexes are assigned. A Sahn-Teller splitting of the d-d transition is observed. Comparison of the i.r. spectra of the M(sal), derivatives (M = CrlI1, &1nI1I, and FeI1I) in the region 500-250 cm-l has enabled assignments of the v(R9-0) modes to be made. The spectra suggest that a Jahn-Teller distortion is operative in the Mn(sal), complex.

Organotin(1V) chelates with a quadridentate Schiff base of the type R,Sn(salen) (R = Me or Ph) have been synthesised by use of the recently reported Tl,(salen) complex. The n.m.r. spectra of the chelates suggest that the R groups are cis to each other with the salen ligand in the unusual twisted configuration. A number of tin(1v) Schiff-base complexes of the types SnCI4,2(salH-N-p-MeC8H4) ; SnCl,,(salenH,) ; Sn(salen)CI, and SnCI,-(salH-N-(2-OC8H,)),Et,N are also described. l.r., l H n.m.r., and mass spectra and conductance measurements have been used where possible to suggest possible structures for the complexes. IN a recent attempt to synthesise organotin(1v) chelates of dibasic quadridentate Schiff bases, Barbieri and his co-workers1 obtained adducts of the type R2SnC1,,LH, rather than the desired R,SnL (LH, = quadridentate Schiff base)." We report here the synthesis of this type of compound, R,Sn(salen) (R = Me or Ph), starting from the thallium(1) compound,2 Tl,(salen). Though there are numerous examples of TABLE 1 Abbreviations used for ligands salenH, salophenH, acacenH, salH-N-( 2-HO.C,H4) salH-NR salH oxH acacH NN'-Ethylenebis( salicylaldiniine) NN'-Phen ylenebis (salic ylaldimine) NN'-Ethylenebis(acety1acetone imine) N-(2-Hydroxyphenyl) salicylaldimine N-Substituted salicylaldimine Salicylaldehyde 8-H ydroxyquinoline Acetylacetone bidentate derivatives of the type R,Sn(chelate), these are the first examples with a quadridentate chelate ligand. The lH n.m.r. spectra of the complexes have been studied. Some new ' simple ' complexes of tin(1v) with neutral and deprotonated bi-, ter-, and quadridentate Schiff-base ligands are also described. Related compounds with other monobasic bidentate ligands have recently been the subject of i.r.,394 MGssba~er,~-~ and structural studies .lo R,Sn(salen) (R = Me OY Ph), R'le2Sn[sal-~V-(2-0*C6H,)].-The yellow crystalline R,Sn(salen) compounds are prepared by heating a methanolic solution of R2SnC1, and Tl,(salen) under reflux. Precipitated thallium(1) chloride is filtered off and the product obtained on concentration of the solution is recrystallised from methanol. Of the various procedures used by Barbieri and his co-workers it is surprising that the sodium salt of the Schiff base did not produce this type of chelate.

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The electrochemical oxidation of an extensive series of cis,mer-M(CO) 2 (κ 1 -dpm)(κ 2 -P-P)X (M ) Mn, Re; dpm ) Ph 2 PCH 2 PPh 2 ; P-P ) dpm, Ph 2 PCH 2 CH 2 PPh 2 (dpe), o-(Ph 2 P) 2 C 6 H 4 -(dpbz); X ) Cl, Br) complexes has been investigated on both the voltammetric and bulk electrolysis time scales. At short time domains or low temperatures, the manganese complexes undergo a reversible one-electron oxidation to cis,mer-[Mn(CO) 2 (κ 1 -dpm)(κ 2 -P-P)X] + . These compounds isomerize under slow scan rate voltammetric conditions at room temperature to give trans-[Mn(CO) 2 (κ 1 -dpm)(κ 2 -P-P)X] + , which on even longer bulk electrolysis time scales slowly lose Xto form a reactive trans-[Mn(CO) 2 (κ 2 -dpm)(κ 2 -P-P)] 2+ intermediate. In turn, this complex is reduced either at the electrode surface (X ) Cl) or in a homogeneous chemical reaction (X ) Br) to form trans-[Mn(CO) 2 (κ 2 -dpm)(κ 2 -P-P)] + , which is the final product observed under conditions of bulk electrolysis. In contrast, the first oxidation step for the corresponding rhenium complexes involves oxidation of the pendant phosphorus atom and reaction with traces of water to give cis,mer-Re(CO) 2 (κ 1 -dpmO)(κ 2dpm)X and then cis-[Re(CO) 2 (κ 2 -dpmO) 2 ] + , with the rhenium center subsequently being oxidized at more positive potentials. Methylation of the pendant phosphorus of cis,mer-Re-(CO) 2 (κ 1 -dpm)(κ 2 -dpm)X gives cis,mer-[Re(CO) 2 (κ 1 -dpmMe)(κ 2 -dpm)X] + . The ligand-based oxidation pathway is blocked by the methylation, so that only the usual metal-centered Re-(I)/Re(II)-based oxidation processes are observed in the voltammetry of these compounds. The compounds cis,mer-Re(CO) 2 (κ 1 -ape)(κ 2 -ape)X and cis,mer-[Re(CO) 2 (κ 1 -apeMe)(κ 2 -ape)X] + (ape ) Ph 2 AsCH 2 CH 2 PPh 2 ) exhibit electrochemistry similar to that of the dpm analogues. The major products of the interaction of dpe with the metal pentacarbonyl halides (2:1) are the new binuclear species {M(CO) 2 (κ 2 -dpe)X} 2 (µ-dpe), whose structures have been determined by IR and 31 P NMR spectroscopy and electrospray mass spectrometry (ESMS). The stereochemistry of the manganese complexes is cis,fac, and upon voltammetric oxidation, first one and then the second manganese atom are oxidized. Bulk oxidative electrolysis at low temperature leads to the generation of cis,fac-[{Mn(CO) 2 (κ 2 -dpe)X} 2 (µ-dpe)] + and cis,fac-[{Mn(CO) 2 (κ 2 -dpe)X} 2 (µ-dpe)] 2+ . The stereochemistry of the oxidized metal centers isomerizes to trans + at room temperature, but the binuclear structure is retained. Bulk reductive electrolysis at low temperature after bulk oxidative electrolysis at room temperature leads to the characterization of trans-{Mn(CO) 2 (κ 2 -dpe)X} 2 (µ-dpe). The binuclear rhenium complexes cis,mer-{Re(CO) 2 (κ 2 -P-P)X} 2 (µ-P-P) (P-P ) dpe, Ph 2 P(CH 2 ) 3 PPh 2 (dpp)) were isolated, and they each undergo two successive one-electron oxidations to generate the monoand dications without any isomerization on the voltammetric time scale. ESMS provides independent proof of the bin...