A. S. Antsyshkina

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.

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.

Interaction of Heteronuclear chromium-containing clusters with carboxalic acids. Molecular structure of the paramagnetic tetrahedral cluster Cp3Cr3(μ3-S)4Fe(OOCCMe3)

Abstract The reaction of (CpCrSCMe 3 ) 2 S and the adducts (CpCrSCMe 3 ) 2 S·ML (ML = Cr(CO) 5 , Mn 2 (CO) 9 and cluster (CpCrS) 2 (SCMe 3 )·Fe(CO) 3 (I) (containing CrCrFe metal chain) with benzoic acid gives the respective antiferromagnetic μ 3 -thio-bridged carboxylates Cr 2 MS(OOCPh) 6 (M = Cr(II), Mn(II), Fe(II)) (II–IV). On the other hand the reaction of I with the weaker trimethylacetic acid yields the tetrahedral cluster Cp 3 Cr 3 (μ 3 -S) 4 Fe(OOCCMe 3 ) (V) containing two unpaired electrons (μ eff = 2.81 BM). Crystal structure of V was solved by means of X-ray analysis (sp. gr. C2)c, a = 28.905(2), b = 9.563(2), c = 23.789(2) A, β = 131.84(3)°, V = 4902.8(4) A 3 Z = 4). In the metal tetrahedral skeleton Cr 3 Fe the average bond lengths CrCr and FeCr are 2.838(3) and 2.759(3) A respectively. The μ 3 -bridged sulfur atom locates over each tetrahedron face (the average CrS and FeS distances are 2.258(4) and 2.218(4) A respectively). Each chromium atom is combined to η 5 -C 5 H 5 ligand (the average CrC and CC distances are 2.224(20) and 1.391(30) A). The iron atom is bound to a terminal trimethylacetate group (FeO 1.896(10), O(1)C(1) 1.318(13), O(2)C(1) 1.252(21) A).

Antiferromagnetic complexes with the metalmetal bond: XVI. Synthesis and molecular structure of binuclear dihalogenide cyclopentadienly-t-butylate chromium(III) complexes

Abstract Reactions of (CpCrOR) 2 (I) (R = CME 3 ) with CH 2 X 2 in toluene and benzene at room temperature yield the binuclear complexes Cp 2 Cr 2 (μ-OR) 2 X 2 (X = Cl (II); Br (III); I (IV)) with the X ligands in the cis -position with respect to the CPCrCrCp moiety. The X-ray structural study of complexes II–Iv showed that the CrX distances (2.28(1), 2.29(1); 2.478(2); 2.716(2)m 2.711(2) A in II–IV) are markedly shortened compared with the sums of the corresponding covalent radii, owing to additional XCr π-bonding which involves the half-filled orbitals of the Cr atoms. This shortening is accompanied by the elongation of the CrCr bonds from 2.635 A in I up to 2.917(7), 2.971(2) and 2.967(2) A in II–IV and the weakening of the antiferromagnetic exchange interactions (−2 J = 150, 168 and 148 cm−1 for II–IV respectively as compared with −2 J = 246 cm−1 for I). The similarity between the ligand environment of the chromium atom in I and the vanadium atom in Cp 2 V is described.

Synthesis and molecular structure of a pentanuclear complex with niobium-indium bonds observed for the first time

The reaction of InCl~ with (MeC~H~)=NbBH~, which is activated by treatment with BuLi in the presence of Et~N, has been studied by us. The reaction occurs in tetrahydrofuran (THF) with the formation of the complex [(MeC~H~)NbH]~In=CI= (I) which was isolated as orange-yellow crystals by recrystallization from toluene and THF (48% yield). Complex (I) was diamagnetic. Found: C 39.70; H 4.76; C1 6.03%. C~H~Nb~In=CI~. Calculated: C 40.87; H 4.25; C1 6.71%. The structure of (I) was established by x-ray structural analysis of crystals of (I). THF solvate was obtained by the slow crystallization of (I) from THF (see Fig~ I)~