Basal Ligands Research Articles

Pentagonal pyramidal lead coordination in the crystal structure of dimeric diaquopyridine-2,6-dicarboxylatolead(II) pyridine-2,6-dicarboxylic acid monohydrate

The crystal structure of dimeric diaquopyridine-2,6-dicarboxylatolead(II) pyridine-2,6-dicarboxylic acid monohydrate, empirical formula and asymmetric unit C14H14N2O11Pb, has been solved and refined to R = 0.081, Rw = 0.100. The space group was [Formula: see text] with a = 1073.8(3), b = 1123.2(5), c = 705.0(3) pm, α = 101.28(8)°, β = 95.42(6)°, γ = 92.80(7)°, ρ = 2.37 g cm−3 (meas.). Measurements were done on an automatic 4-circle diffractometer ([Formula: see text], λ = 71.069 pm), and corrected for absorption. The lead complex is dinuclear with an inversion point at the centre of the double bridging. Each lead atom has distorted pentagonal pyramidal coordination with a water molecule at the apex. The basal ligands are water and terdentate pyridine-2,6-dicarboxylate. The double bridging is by one of the coordinated carboxylic oxygen atoms and its inverse. The electron pair geometry is assumed to be pentagonal bipyramidal with a stereochemically active lone pair occupying considerable solid angle in an axial position. Bond lengths (±2 pm) are: Pb—OH2 (apex), 259; Pb—OH2 (basal), 273; Pb—O, 251, 258, 273; Pb—N, 259. The mean of the bond angles at Pb involving the apical oxygen is 77°. The unit cell contains two water and two dicarboxylic acid molecules of crystallisation which are involved in an H-bonding network with one bond for each hydrogen attached to oxygen in the structure.

The absolute configuration of organometallic compounds : VII. An x-ray structural study of (−) 579436-(η 5-C 5H 5)Mo(CO) 2[(C 5H 5N)C(=S)NR] prepared from H 2NR = ( S)-(−)-α-phenylethylamine

The reaction of (η 5-C 5H 5)Mo(CO) 3Cl with pyridine-2-carboxylic acid [( S)-1-phenylethylthioamide] yields two diastereoisomers having composition (η 5-C 5H 5)Mo(CO) 2(thioamide) which are in equilibrium with one another in the ratio of 58/42 (toluene; 90°C). The diastereoisomers are separable by chromatography, and that (V; see text) whose CD spectrum shows (−) and (+)-bands, respectively, at 579 and 436 nm was used in the current crystallographic study. The space group is P2 12 12 1 and the cell parameters are: a 6.950(4), b 14.038(4) and c 20.709(8) Å; V 2020.4 Å 3; d(obs; flotation in aqueous ZnBr 2) 1.51 g cm −3; d(calc; Z = 4) 1.507 g cm −3. A total of 3321 data were recorded in one octant of reciprocal space (2θ max 60.0°) of which 2134 were considered observed ( I > 2σ( I)) and used in the solution of the structure and in the least-squares refinement. The molecules consist of a central Mo atom surrounded by an approximately square-pyramidal array of five ligands: the bidentate thioamide, two carbonyls and the Cp ring. The binding points of the thioamide are the nitrogen of the pyridine and the sulfur of the thioamide moiety. Thus, unlike previous examples of CpMo(CO) 2(thioamides) studied here, the nitrogen of the thioamide is not part of the chelate ring; instead, it is part of an unusual, three atom, conjugated system (SCN) never observed before in thioamide-metal chelates. The SMoN, SMoC(O), NMoC(O) and (O)MoC(O) angles are 76.9(2), 75.2(3), 81.4(4) and 75.6(5)°, values which are typical of square-pyramidal compounds in which the metal is above the plane defined by the basal ligands. The bonds to the carbons of the C 5H 5 ring are normal but the two MoC(O) and the two CO distances are slightly different, and the differences make sense if we attribute them to inequalities in trans effect between S and N ligands opposite the carbonyls. The MoN(pyridine) bond (2.233(8) Å) is a little longer than those observed in thioamides but nearly the same as that observed in Schiff base derivatives of related CpMo(CO) 2 compounds studied here earlier. Concomitantly, in V there is a shorter MoS bond than those observed in the thioamides containing normal, four-membered (MoSCN) chelate rings. Parallel with this, V contains longer SC bonds showing that an increase in the MoS bond order leads to a reduction of the SC π-bond order, which in this case is estimated to be only 0.47. Finally, the plane of the chelate ring (MoSCCN) and that of the pyridine ring make an angle of 8.7°, even though the two are fused to each other. The absolute configuration at the Mo site of the [(−) 579, (+) 436] diastereoisomer has been established as ( S).

Absolute configurations of organometallic compounds : V. X-ray study of (−) 578-(η 5-C 5H 5)Mo(CO) 2SC(CH 3NR′ with R′ = ( S-CH(CH 3)(C 6H 5)

The structure and absolute configuration of the thioamido complex (−) 578-(η 5-C 5H 5Mo(DO) 2SC(CH 3NR′ with R′ = ( S)CH(CH 3)(C 6H 5) have been determined by single-crystal X-ray diffraction. The substance crystallizes in the orthorhombic system; space group P2 12 12 1 with cell constants of a = 8.314(1), b = 9.020(1), and c = 22.352(2) Å, and Z = 4 molecules/unit cell. The absolute configuration was determined using Bijvoet's method. Refinement of the data using the anomalous scattering contributions of Mo and S yields a final R( F = 0.036 for 2715 independent reflections having I > 3σ( I). The distorted square pyramidal coordination of the Mo atom is defined by two carbonyl carbons and the S and N atoms of the thioamido ligand occupying the four basal plane sites and the five carbons of the η 5-C 5C 5 ligand in the axial position. The Mo—ligand distances and most of the bond lengths and angles within the ligands are normal and compare closely with those of recent structure determinations. However, the distances and angles within the thioacetamide ligand show, distinctly, the effect of chelate binding to the Mo atom. In particular, the angles at the central thioacetamide carbon differ markedly from those of free thioacetamide and monodentate, S-bound metal thioacetamido complexes. The Mo atom is 1.041 Å above the plane formed by the four basal ligands. The conformation of the ( S)-α-phenylethyl group with respect to the ligand plane, defined by the thioamido system and the Mo atom, is discussed. The configuration at the metal atom in the (−) 578-isomer of (η 5-C 5H 5)Mo(CO) 2SC(CH 3)NR′ is specified as ( S).

Structure and stability of carboxylate complexes. Part XIII. Crystal and molecular structure of aquobis(NN′-dimethylglycinato)copper(II) dihydrate

The crystal and molecular structure of the title compound (orthorhombic, a= 7·05 ± 0·01, b= 31·7 ± 0·05, c= 6·51 ± 0·01 Å, space group P212121 visual data, 1111 independent reflections) has been determined by three-dimensional X-ray methods and refined by least squares to R 0·12. The copper atom is five-co-ordinate; a square-based pyramid with the ligand water molecule at the apex (mean Cu–N 2·05, Cu–O 1·97; Cu–OH2 2·28 Å) and the basal ligands in the trans-configuration. The structural relationship between this and similar simple copper aminocarboxylate complexes is discussed.