I. L. Eremenko

Antiferromagnetic complexes involving metalmetal bonds : I. Synthesis and molecular structure of an antiferromagnetic dimer with a CrCr bond

The binuclear complex (C5H5)2Cr2(S)(SCMe3)2 was prepared by refluxing a solution of chromocene and t-butylmercaptane in heptane. The structure of the product was determined by single crystal X-ray diffraction. The chronium atoms are linked by a sulphide bridge (SCr 2.24 A;, <CrSCr 74.1° and two SCMe3 bridges (CrS 2.38 A;, <CrSCr 68.3–69.3°). The two cyclopentadienyl ligands (CC 1.41 A;, CrC 2.23 A;) are in apical positions, their ring planes being parallel to each other. The complex is an antiferromagnet (−2J cm−1) despite the small CrSCr angles and short chromiumchromium distance (2.689 A;) indicative of strong CrCr bonding.

Synthesis and molecular structure of niobocene(tricarbonyl)(π-cyclopentadienyl)molybdenum with metalmetal bond and unusual coordination of carbonyl groups

Abstract (C5H5)2NbBH4 reacts with C5H5M(CO)3Me in toluene solution in the presence of Et3N to give binuclear complexes (C5H5)2NbM(CO)3C5H5 where M is Mo or W (IV and V, respectively). The structure of IV has been studied by X-ray diffraction (the crystals are orthorhombic, a 12.748(5), b 16.745(6), c 14.314 A/ac> ;; Z = 8, space group of Pbca, automatic difractometer Syntex P2I, λ(Mo-Kα, 1382 reflections, R = 0.056, Rw = 0.058). Molecule IV contains a wedge-like sandwich (π-C5H5)2Nb (NbC 2.37–2.48, CC (av) 1.42 A/ac> ;, angle between ring planes 49°) linked with the (π-C5H5)Mo(CO) fragment by a direct NbMo bond (3.073 A/ac> ;) and two bridging CO groups, one nonsymmetrically bonded through the carbon atom only (CO 1.17, NbC 2.53, MoC 2.02 A/ac> ;) and the other σ-bonded to Mo (MoC 1.944 A/ac> ;) and π-bonded to Nb (CO 1.22, NbC 2.22, NbO 2.26 A/ac> ;). Three types of carbonyl groups present in IV give rise to strong IR bands at 1870, 1700 and 1560 cm−1 assigned to the terminal, μ-bridging and σ, π-bridging CO groups respectively. Complex IV has a similar structure. The electronic structure of IV and its dissociation across the NbMo bond are discussed.

Antiferromagnetic complexes with metal-metal bonds: IX. Synthesis and molecular structures of methylcyclopentadienylchromium(III) sulfide diamagnetic tetramer and the antiferromagnetic copper(II) bromide adduct of the tetranuclear cluster (MeC5H4)4Cr4(μ3-O)(μ3-S)3

Abstract Reaction of (MeC5H4)2Cr with HSCMe3 gave (MeC5H4)2Cr2S(SCMe3)2 (I) in the form of violet antiferromagnetic crystals ( − 2J = 478 cm−1). Pyrolysis of I in xylene and its reaction with a CuBr2 solution in THF/Et3N (1/1) leads to readily-soluble black diamagnetic crystals of (MeC5H4)4Cr4S4(II). An oxygen-containing antiferromagnetic analog of complex II, (MeC5H4)4Cr4O4(III) was isolated on oxidation of (MeC5H4)2Cr with traces of oxygen in the presence of Ar. The reaction of I with CuBr2 in the absence of Et3N yielded black-green needle-like crystals of the antiferromagnetic adduct (MeC5H4)4Cr4S3O · CuBr2(IV) (μeff at room temperature is 3.91 BM). The structures of II and IV were established by X-ray crystallography. The molecule of II contains a metallotetrahedral Cr4 skeleton (CrCr 2.822(2) A) with faces centered at the μ3-bridged S atoms (CrS 2.248(2) A). Each Cr atom is bonded to a η5-MeC5H4 (CrCaver. 2.241(9) A). In IV the tetrahedral Cr4 skeleton is distorted owing to the μ3-O bridging ligand (CrCr 2.70(1)–2.78(1) A, CrSaver. 2.25(2) A, CrO 2.07(2)–2.12(2) A) and to CuBr2 coordination to a sulfur atom (CuBr 2.23(2) A, BrCuBr 163.9(8)°, Cu···S 320 A).

Antiferromagnetic complexes involving metal—metal bonds: V &. Synthesis, molecular structures and magnetic properties of an adduct, (CpCrSCMe3)2S·Mn2(CO)9, and a cluster, (CpCr)2(μ2-SCMe3)(μ3-S)2Co(CO)2, containing the CrCrCo metallocycle*

Summary The photochemical reaction of the antiferromagnetic binuclear complex (CpCrSCMe 3 ) 2 S (I, Cp=cyclopentadienyl) with Mn 2 (CO) 10 in THF yields the adduct (CpCrSCMe 3 ) 2 S·Mn 2 (CO) 9 (IV). According to X-ray diffraction data, the fragments in IV are linked through an Mn−S bond (2.448(2) A), and the geometry of I changes only insignificantly upon the addition of Mn 2 (CO) 9 : the Cr−Cr bond distance changes from 2.689(8) A in I to 2.740(8) A in IV, the Cr−S( sulphide ) bond length increases from 2.24(1) A (I) to 2.31(1) A (IV), whereas the Cr−S (thiolate) bond and CrSCr angles (72.7(3) and 71.4(3)°) remain almost unaffected. Accordingly, formation of the adduct has little affect on the magnetic properties of I (the exchange parameter, −2 J , value is equal to 440 cm −1 for IV and 430 cm −1 for I). Compound I reacts with Co 2 (CO) 8 in THF at 20°C without UV irradiation to give the trinuclear cluster, (Cp 2 Cr 2 SCMe 3 )-(μ 3 -S) 2 Co(CO) 2 (V). Compound V is antiferromagnetic (−2 J 530 cm −1 , the Co atom is diamagnetic) and, according to the X-ray structural data, contains the CrCrCo metallacycle (the bond lengths are: Cr−Cr, 2.617(1); Cr−Co, 2.579(1) and 2.592(1) A) and sulphide bridges above and below the metallacycle plane. The effect of the coordination number of M on the transformations of the adducts of the type (CpCrSCMe 3 ) 2 S·M 2 (CO) n is discussed.

Antiferrogmagnetic complexes with metal/3- metal bonds : VII. Synthesis and molecular structure of (CpCrSCMe3)2S Mn(CO)2Cp and formation of the tetranuclear clusters CP4Cr3MS4 (M Cr, V, Nb)

Abstract Photochemical reaction of (CpCrCSMe3)2S (I) with CpMn(CO)3 gave the complex (CpCrSCMe3)2S - Mn(CO)2CP(II). According to X-ray analysis its fragments are joined by an MnS (sulfide) bond (2.334A) with almost no change in geometry of complex I upon coordination (CrCr 2.704, CrS (sulfide) 2.29, CrS (thiolate) 2.35, CrC(Cp) 2.256 A, CrS(sulfide)Cr 72.2°, CrS(thiolate)Cr 70.0°). However, the reaction of I with CPM(CO)4 (M  V, Nb) under the same conditions yielded the corresponding paramagnetic heteronuelear complexes [Cp3Cr3(μ3-S)4]MCP (III and IV, respectively) probably containing a tetrahedral metallic skeleton. The reason for the rearrangement of I in the latter reactions may be a greater steric hindrance in the intermediate complexes (CpCrSCMe3)2S - M(CO)3CP with respect to II. The known diamagnetic tetrahedral analog of III and IV, Cp4Cr4S4 was obtained by pyrolysis of I.

Antiferromagnetic complexes involving metalmetal bonds. II. The conditions for observation and means of intented variation of antiferromagnetic properties of binuclear complexes involving CrCr and VV bonds

Abstract The complex (CpCrSCMe 3 ) 2 S (I), contains a CrCr bond (2.689 A) and at the same time shows antiferromagnetic properties (−2J = 430 cm −1 ). It reacts with PhEH (E is S, Se) or MeI to give binuclear complexes (CpCrEPh) 2 S or [(CpCrSCMe 3 ) 2 SMe] + I − characterized by exchange parameter, −2J, values of 496, 398, and 350 cm −1 , respectively. Reaction between Cp 2 Cr and PhEH yields the antiferromagnetic trimer [CpCr(SPh) 2 ] 3 (−2J = 194 cm −1 ) and dimer [CpCr(SePh) 2 ] 2 (−2J = 208 cm −1 ). CpV(CO) 4 reacts with PhEH to give dimeric complexes [CpV(EPh) 2 ] 2 one of which shows antiferromagnetic behaviour (E = Se, −2J = 700 cm −1 ) and the other one is a diamagnetic substance (E = S, −2J>> 1000 cm −1 ). The magnetic properties of the complexes are treated in terms of the exchange channel model. It is shown that antiferromagnetic behaviour (magnetic moment decreases with temperature) of binuclear complexes involving direct metalmetal bonds may be expected when the paramagnetic ions are in high-spin states (S ⩾ 1). In such complexes, variations in metalmetal bond strength caused by ligand substitution may be studied by the methods of magnetochemistry.

Pentanuclear pivalate Ni(II) and Co(II) clusters: modulation of molecular structures and magnetic properties

Abstract Reaction of nickel cluster Ni9(HOOCCMe3)4(μ4-OH)3(μ3-OH)3(μn-OOCCMe3)12 (1) or cobalt pivalate polymer [Co(OH)n(OOCCMe3)2−n]x (7) with bis[3,5-(dimethylpyrazolyl)]-1,2,4,5-tetrazine (3) in MeCN solution was found as a result in the formation of isostructural pentanuclear clusters of composition M5(μ3-OH)2(μ-OOCCMe3)4(μ-N,N′,N″-3,5-Me2C3HN2C2(O)N4)4(MeCN)2 (M=Ni (4), Co (8)) with a planar spirane metal core. Reaction of cobalt complex 7 with 3 in benzene gives rise to a pentanuclear cluster Co5(μ3-OH)2(μ-OOCCMe3)4(μ-N,N′,N″-3,5-Me2C3HN2C2(O)N4)4(C5N2H8)2 (9), containing coordinated pyrazole molecules as terminating ligands instead of labile MeCN ligands in 8. The reaction of cluster 8 with 2,6-diaminopyridine (T=85 ° C ) in MeCN results in the substitution of MeCN ligands and formation of a new cluster Co5(μ3-OH)2(μ-OOCCMe3)4(μ-N,N′,N″-3,5-Me2C3HN2C2(O)N4)4(C5H7N3)2 (10) with two 2,6-diaminopyridine ligands instead of MeCN molecules. The reactions of 4 and 8 with NiCl2·6H2O in MeCN/EtOH solution (3:1) give rise to isostructural ferromagnetic pentanuclear chloro-bridged clusters M5(μ3-OH)2(μ-CI)2(μ-OOCCMe3)2(μ-N,N′,N″-3,5-Me2C3HN2C2(O)N4)2(μ-N,N′,N″,O-3,5-Me2C3HN2C2(O)N4)2(MeCN)2 (M=Co (11), Ni (12)).The reaction of 8 with solid CoCl2·6H2O in MeCN results in new seven-nuclear ferromagnetic cluster Co5(μ3-OH)2(μ-CI)2(μ-OOCCMe3)2(μ-N,N′,N″-3,5-Me2C3HN2C2(O)N4)2(μ-N,N′,N″,O-3,5-Me2C3HN2C2(O)N4)2(MeCN)2[Co(CH3CN)CI2]2 (13). The molecular structures of 4, 8, 9, 10, 12 and 13 established by X-ray diffraction studies and magnetic behavior of new nickel and cobalt pivalate clusters are discussed.

Antiferromagnetic complexes with a metal—metal bond: XII. Synthesis, molecular structures, and magnetic properties of the clusters (MeC5H4)2Cr2(μ-SCMe3)(μ3-S)2Co(CO)2 and (C5H5)2Cr2(μ-SCMe3)(μ3-S)2Mn(CO)3 with triangular Cr2M metal frames☆

Abstract The triangular cluster (MeC5H4)2Cr2(μ-SCMe3)(μ3-S)2Co(CO)2 V was obtained by reaction of the binuclear complex (MeC5H4)2Cr2(μ-SCMe3)2(μ3-S) (IV) with Co2(CO)8 in heptane. The structure of V was solved by an X-ray structural study. Crystals of V are monoclinic, space group P21, a 9.437(1), b 15.9460(8), c 7.2540(8) A, β 109.399(9), V 1029.6 A3, Z = 4, R = 0.047, Rw = 0.052. The main geometric parameters of V are close to those of its previously described cyclopentadienyl analogue (C5H5)2Cr2(μ-SCMe3)(μ3-S)2Co(CO)2 (III), however, the CrCr bonds in V are somewhat shorter (by 0.02–0.04 A) and the methylcyclopentadienyl rings are in a staggered conformation in contrast to the eclipsed conformation of the C5H5 ligands in III. A photochemical reaction of (C5H5)2Cr2(μ-SCMe3)2(μ3-S) (I) with Mn2(CO)10 with a reagent ratio of 2 1 in boiling benzene (3 h) yielded the heteronuclear cluster (C5H5)2Cr2(μ-SCMe3)(μ3-S)2Mn(CO)3 (VI), characterized by an X-ray study (space group C2, a 18.709(7), b 9.883(4), c 11.470(5) A, β 109.65(2)°, V 1997.3 A3 Z = 4). VI has a triangular metal frame Cr2Mn (CrCr 2.646(2), CrMn 2.828(2) and 2.716(2) A). The electronic and steric factors governing the formation of III, V and VI are discussed. I, III–VI exhibit antiferromagnetic properties with the exchange parameter (−2J) increasing on introduction of a methyl group into the cyclopentadienyl ligand, as well as with the formation of metal cycle Cr2M (−2J(CrCr) 430, 530, 478, 556, 654 cm−1, respectively).

Synthesis and molecular structure of lanthanum tris[cyclopentadienylmolybdenotricarbonylate] tetrahydrofuranate, (THF)5La[CpMo(CO)3]3•THF

Abstract The interaction of activated La powder with [CpMo(CO) 3 ] 2 or Hg[CpMo(CO) 3 ] 2 in THF resulted in the formation of crystalline (THF) 5 La[CpMo(CO) 3 ] 3 · THF (I), which oxidized readily on exposure to air with cleavage of [CpMo(CO) 3 ) 2 . Complex I was characterized by X-ray structural analysis. The La atom is bound to three equivalent CpMo(CO) 3 fragments via almost linear carbonyl bridges, MoCOLa (MoCO 177.9(7)°). The coordination of La with the terminal CO group (LaO av 2.444(5) A) leads to elongation of the CO bond from an average value of 1.16(1) to 1.21(1) A, and to shortening of the MoC bond from an average value of 1.943(9) to 1.874(9) A, compared with the unbridged CO. The coordination of La is complemented to CN = 8 at the expense of binding of five THF molecules (LaO(THF) av = 2.580(6) A; the sixth THF molecule is crystallizable).

Synthesis and molecular structure of the niobocene sulphide dimer

Abstract The reaction of Cp 2 NbBH 4 in benzene in the presence of Et 3 N and PhSH results in a green, crystalline, diamagnetic complex, [Cp 2 NbSPh] n (I), which probably has a polymer structure. The reaction of Cp 2 NbBH 4 under the same conditions with t-BuSH or (CpCrSCMe 3 ) 2 S yields a red, crystalline, diamagnetic complex, [Cp 2 NbS] 2 (II), whose structure was established by X-ray analysis. In II, the Nb atom belongs to the niobocene fragment, whose inclined rings (dihedral angle 47.25°) are in a staggered conformation (NbC Cp(av.) 2.452(7), CC Cp(av.) 1.40(1) A). Moreover, each Nb atom forms two equivalent short bonds, NbS (2.429(2) and 2.427(2) A), and the angles NbSNb (83.51(5)°) are coequal, as are the SNbS angles (96.49(6)°). The NbNb distance (3.2343(8) A) is evidently bond-forming. The molecule on the whole resembles C 2ν in symmetry.