V.T. Kalinnikov

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.

The structure and formation of niobocene carbonyl heteronuclear derivatives. The molecular structures of Cp2Nb(CO)(μ-CO)Mn(CO)4, Cp2Nb(CO)(μ-H)Ni(CO)3 and [Cp2Nb(CO)(μ-H)]2Mo(CO)4

Abstract The heteronuclear Cp 2 Nb(CO)(μ-CO)Mn(CO) 4 (I), Cp 2 Nb(CO)(μ-H)Ni(CO) 3 (II) and [Cp 2 Nb(CO)(μ-H)] 2 M(CO) 4 (III, M = Mo;IV, M = W) complexes were prepared by reaction of Cp 2 NbBH 4 /Et 3 N with Mn 2 (CO) 10 in refluxing toluene, direct reaction of Cp 2 NbBH 4 with Ni(CO) 4 in ether, and reaction of Cp 2 NbBH 4 /Et 3 N with M(CO) 5 . THF complexes (M = Mo or W) in THF/benzene mixture. An X-ray investigation of compounds I–III was performed. It is established that in I the bonding between Mn(CO) 5 and Cp 2 Nb(CO) (with the angle (α) between the ring planes being 44.2(5)°) fragments takes place via a direct NbMn bond (3.176(1) A) and a highly asymmetric carbonyl bridge (MnC co 1.837(5) A, NbC co 2.781(5) A). On the other hand, in complex II the sandwich Cp 2 Nb(CO)H molecule (angle α = 37.8°) is combined with the Ni(CO) 3 group generally via a hydride bridge (NbH 1.83 A, NiH 1.68 A, NbHNi angle 132.7°) whereas the large Nb⋯Ni distance, 3.218(1) A, shows the weakening or even absence of the direct NbNi bond. Similarly, in complex III two Cp 2 Nb(CO)H molecules (with α angles equal to 41.4 and 43.0°, respectively) are joined to the Mo(CO) 4 group via the hydride bridges (NbH 1.83 and 1.75 A and MoH 2.04 and 2.06 A) producing a cis -form. The direct NbMo bonds are probably absent, since the Nb⋯Mo distances are rather long (3.579 and 3.565 A). The effect of electronic and steric factors on the structure of heteronuclear niobocene carbonyl derivatives 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.

Steric effects of nonbonded interligand interactions in dimeric adducts, Ni(II) quinaldimetrimethylacetate and Cu(II) acridinetrimethylacetate

Abstract The structures of two dimeric complexes of the type [LM(OOCR)2]2, QNi(OOCCMe3)4NiQ(I) where Q is quinaldine, and ACu(OOCCMe3)4CuA(II) where A is acridine, have been studied by X-ray diffraction (an automatic diffractometer,anisotropic LS treatment, γ-Cu for I and γ-Mo for II). Our purpose was to determine structural consequences of the combined action by steric hindrances due to α-substituted pyridine ligands and electronic effects of tertbutyl substituents in the carboxylate bridges. The crystals I are triclynic P 1 , a = 11.168(2), b = 18.334(2) c = 11.452(3) A, α = 90.037(4), β = 119.01(1). γ = 89.06(4)°, Z = 2. The Ni⋯Ni distance of 2.754(3) A is considerably larger than it is in low-spin clusters containing Ni. The Ni atoms are displaced by 0.23 A from the plane containing four oxygen atoms towards the ligands Q. The NiN bond has the usual length, 2.07 A, and makes an angle of 10° with the NiNi axis. The crystals II are triclynic, P 1 , a = 9.448(4), b = 11.463(5), c = 11.963(4) A, α = 105.61(3), β = 103.40(3), γ = 105.92(3)°, Z =1. The Cu⋯Cu distance is of 2.702(1) A. The Cu atoms are displaced by 0.24 A from the oxygen plane towards A. The normal intramolecular contacts are maintained owing to CuN bond elongation to 2.371 A.

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.

Antiferromagnetic complexes involving metalmetal bonds IV. Synthesis, molecular structure and magnetic properties of the heterotrinuclear cluster, (C5H5Cr)2(μ2-SCMe3)(μ3-S)2Fe(CO)3, with direct and indirect exchange between CrIII and FeI centers ☆

Abstract The photochemical reaction between the antiferromagnetic complex (C5H5-CrSCMe3)2S (I) (containing a CrCr bond 2.689 A long) and Fe(CO)5 results in the elimination of two carbonyl groups and one tert-butyl radical to give (C5H5Cr)2(μ2-SCMe3)(μ3-S)2 · Fe(CO)3 (III). As determined by X-ray diffraction, III contains a CrCr bond of almost the same length as in I (2.707 A), together with one thiolate and two sulphide bridges. The latter are also linked with the Fe atom of the Fe(CO)3 moiety (average FeS bond length 2.300 A). Fe also forms a direct bond, 2.726 A long, with one of the Cr atoms, whereas its distance from the other Cr atom (3.110 A) is characteristic for non-bonded interactions. Complex III is antiferromagnetic, the exchange parameter, −2J, values for CrCr, Cr(1)Fe and Cr(2)…Fe are 380, 2600 and 170 cm−1, respectively. The magnetic properties of III are discussed in terms of the “exchange channel model”. The contributions from indirect interactions through bridging ligands are shown to be insignificant compared with direct exchange involving metalmetal bonds. The effects of steric factors and of the nature of the M(CO)n fragments on the chemical transformations of (C5H5CrSCMe3)2S · M(CO)n are discussed.

Nitrosylation of dicyclopentadienyldi(μ-tert-butylthiolato)(μ-sulfido)dichromium giving tert-butylsulfanic group. Molecular structures of the binuclear complex Cp(NO)(NO)Cp and monomer CpCr(NO)2(ONO)

Reaction of CpCp (I) with NO in THF led to the binuclear complex Cp(NO)(NO)Cp (II) and monomer CpCr(NO)2(ONO) (III). The X-ray study demonstrates that the complex II has an ordinary CrCr bond (2.906(3) A) supported by the bridged SCMe3 (CrS 2.295(4) A) and (SSCMe3 (CrS 2.296(4) A), (SS 2.076(4) A) groups. In the monomeric complex III the Cr atom is surrounded by π-C5H5 (CrC 2.24(3) A), two terminal NO groups (CrN 1.71(1) A) and terminal ONO group (CrO 1.982(4) A, ONO 115(2)°).