Yu. V. Rakitin

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.

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.

Structure and magnetic properties of iron(II) chloride tetrahydrofuranate (2FeCl2·3THF)2

Abstract On interacting FeCl3 with Cp2ReH in THF at room temperature while single crystals of the complex (2FeCl2·3THF)2 (I) were obtained. The structure of (I) was established by total X-ray analysis. Crystals of the complex are (space group P 1 ) with the unit cell parameters: a = 10.027(4), b = 10.983(6), c = 10.589(6) A; α = 116.86(4)°, β = 98.23(4)°, γ = 68.09(4)°, Z = 1, V = 964.7 A3. Four Fe(II) atoms in the molecule are bonded through the μ3-bridging Cl atoms (Fe-Clav = 2.46 A), with the coordination sphere of each metal atom being supplemented by the bonding with two or one THF molecule (FeOav = 2.12 A). All the Fe⋯Fe distances in the molecule were non-bonding. The unique magnetic properties of (I) are shown to be specified by the co-existence of ferro- and antiferromagnetic exchange interactions.

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 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.

Antiferromagnetic complexes involving metalmetal bonds III. Synthesis, structure and magnetic properties of heterotrinuclear complexes of the type M(CO)5L (M Cr, Mo and w) containing [(C5H5CrSCMe3)2S] as unusual antiferromagnetic ligand L

Isostructural heterotrinuclear complexes (C 5 H 5 CrSCMe 3 ) 2 S · M(CO) 5 (II–IV) were isolated from photochemical reactions between the antiferromagnetic complex (C 5 H 5 CrSCMe 3 ) 2 S (I) (with the CrCr bond 2.689 A long and with the exchange parameter −2 J = 430 cm −1 ) and metal hexacarbonyls, M(CO) 6 , where M is Cr, Mo, or W. According to the X-ray structural data on III and IV, complex I plays the role of an unusual antiferromagnetic ligand L bound to M through the sulphide bridge (M–S 2.58(2) A). Its geometry remains practically unaffected by the complex formation (the CrCr bond length in III and IV is 2.73(1) A). The exchange parameter, −2 J (410, 440 and 440 cm −1 in II to IV, respectively), also shifts only insignificantly from that of I, which probably means that indirect exchange via the sulphide bridge in I is of minor importance compared with the direct CrCr exchange. The CrCr bond length may thus be correlated with the observed overall exchange coupling.

Synthesis, molecular structure, and magnetic properties of bis(3,6-di-tert-butyl-o-benzosemiquinone)nickel(II) and -copper(II)

The title complexes of Ni and Cu with symmetrical 3,6-di-tert-butyl-o-benzosemiquinone are synthesized. Their EPR spectra and magnetic properties are investigated. The x-ray structure studies [Siemens R3/PC diffractometer, λ MoKα, ϑ/20-scanning in the rang 2 ≤ 2ϑ ≤ 54°, 2084 reflections withF > 4σ(F),R = 0.034,Rw = 0.039, monoclinic crystals,a = 9.982(2),b = 11.548(2),c = 12.145(2) Å, β = 95.05(3)°,Z = 2,dcalc = 1.19 g/cm−3, space groupP2l/c) demonstrated that the complex is monomeric with square-planar coordination for the Ni with theo-semiquinone ligands. The Cu complex is isostructural with the Ni (a = 9.88,b = 11.60,c = 12.15 Å, β = 95°]. The dependence of the magnetic moment of the Cu complex on temperature is consistent with the presence in it of two pathways for exchange interaction. These are antiferromagnetic ligand-ligandJ12 = −179 cm−1 and ferromagnetic metal-ligandJ13 = 100 cm−1 (mean-square deviation 2%). The Ni complex is diamagnetic over the whole studied temperature range despite the fact that it contains free-radicalo-semiquinone ligands. Such an effect involving electrons belonging to the free-radical ligands is observed for the first time in the magnetochemistry ofd8- andd9-transition-metal complexes. It is explained by incorporation of vacantpz- and/or occupieddxz- anddyz-orbitals of Ni in molecular orbitals containing the π-MO of the semiquinone ligands.

Antiferromagnetic complexes with metal-metal bonds. X: Synthesis and molecular structure of an antiferromagnetic bis [cyclopentadienyl(t-butoxy)-chromium] iron tetracarbonyl cluster containing a Cr2Fe metallacycle

Abstract Photochemical reaction of Fe(CO)5 with the Cp2Cr2(OR)2 (I) complex (Cp = π-C5H5, R = CMe3) in toluene gives brown-black prisms of the CpCr(μ-OR)2CrCp · Fe(CO)4 (II) cluster. An X-ray analysis of II shows that the metal atoms form an almost equilateral Cr2Fe triangle with normal CrFe bonds (2.707(1) and 2.691(1) A) and the short CrCr bond (2.635(1) A) supplemented by two bridged OR groups. Each Cr atom is coordinated by a planar π-C5H5 ligand while the Fe atom coordinates four terminal CO groups. A qualitative MO diagram gives an explanation of the CrCr bond length in II which is the same as in the starting complex I, although the antiferromagnetic exchange parameter −2J is simultaneously increased from 246 cm− in I to 304 cm− in II.