Cuthbert J. Wilkins

Cadmium halide complexes with pyridine-N-oxide, and their crystal structures

Abstract Cadmium chloride and bromide form crystalline pyridine-N-oxide (pyo) complexes [{(CdCl 2 ) 3 (pyo) 2 } n ] ( 1 ) and an isomorphous pair [{CdX 2 (pyo)} n ], X = Cl ( 2A ), Br ( 2B ). X-ray analysis of their structures shows them to have layer lattices arising from removal of a proportion of CdX 2 units from the cadmium halide structures. There is retention of six-coordination through insertion of pyo bridges. The pyo rings overlie the voids created by removal of the cadmium centres. Complexes 2A and 2B have the chromium chloride connectivity. The cadmium iodide lattice is more readily degraded and a series of compounds having increasing pyo content is formed; viz [{CdI 2 (pyo)} n ] ( 3 ) (an already known chain polymer), [{(CdI 2 ) 2 (pyo) 3 } n ] ( 4 ), [{CdI 2 (pyo) 2 } 2 ] ( 5 ), and [Cd(pyo) 6 ] 2+ [CdI 4 ] 2− ( 6 ). Compound 4 is a chain polymer with mixed iodo- and oxo-bridges, and alternating five- and six-coordinated cadmium centres. Compound 5 is a pyo-bridged dimer with five-coordinate cadmium. In both 4 and 5 pyo plays both bridging and terminal roles. There is a methanolate derivative of 5 , [{CdI 2 (pyo) 2 (MeOH)} 2 ] ( 5A ), with six-coordinate cadmium. The structures show the ease with which cadmium moves between five- and six-coordination, as well as the breaking of the Cd I bond. In these structures cadmium shows no evidence of any disposition towards the strong digonal bonding characteristic of mercury(II).

Molybdenum(VI) complexes with malic acid: their inter-relationships, and the crystal structure of dicaesium bis[(S)-malato(2–)]-cis-dioxomolybdate(VI)–water (1/1)

The complex anions obtainable in salts crystallising from aqueous solutions of molybdate and malic acid (H3mal) are of the types (i)[MoO2(Hmal)2]2–, (ia)[MoO2(mal)2]4–, and (ii)[Mo4O11(mal)2]4– The formation of each type is dependent primarily upon the reactant ratio, M+ : Mo : H3mal. With the structure of the type (ii) anion already known, the structure of the (simpler) anion (i) was determined by X-ray analysis of its salt, Cs2[MoO2(Hmal)2]·H2O. The complex is mononuclear, with each malato-ligand co-ordinated through the deprotonated hydroxy group and the vicinal carboxy group to form a five-membered chelate ring. The second carboxylate group is not co-ordinated, but there is inter-anion H-bonding between the two carboxy functions. The structural features of class (i) and (ii) anions show the importance of ligand characteristics in determining the type of molybdenum-oxygen core which forms. Compositional and i.r. evidence relating to class (ia) indicates it to be derived from (i) through proton replacement.

Structures of indium trihalide complexes with phosphine oxides and dimethyl sulphoxide, with comments on the metal–oxygen bonding

The crystal structures of several phosphine oxide and dimethyl sulphoxide complexes of indium trihalides have been determined. The compounds [InCl3(Me3PO)2(MeOH)], [InCl3-(Me3PO)2(H2O)]·H2O, [InCl3(PhMe2PO)3]·H2O, [InCl3(Me2SO)3], and [InBr3(Me2SO)3] are all fac octahedral, but [InCl3(Me3PO)3] has the mer configuration. Triphenylphosphine oxide yields ionic derivatives of the type [InX2(Ph3PO)4]+[InX4]–(X = Cl or Br). Methyldiphenylphosphine oxide gives covalent [InCl3(Ph2MePO)3], but ionic [InBr2(Ph2MePO)4]+[InBr4]–. The general development of six-co-ordination is possible through enlargement of the In–O–P bond angles, with individual values (range 135–160°) dependent upon steric interactions. The behaviour is consistent with a predominantly electrostatic metal–oxygen bonding. For the methanol and aqua complexes, determination of the positions of the hydroxylic protons established the ligand orientation with respect to the In–O vector. A quasi-ionic metal–ligand interaction is again in evidence.

Spectroscopic and related evidence on the coloring and constitution of New Zealand jade

Abstract Infrared, optical absorption spectroscopy, and Mössbauer spectroscopy were used to investigate the color of jade from New Zealand. Spectroscopic results were supplemented by chemical analyses and petrological examination. Infrared spectra gave a quick identification of the matrix, optical absorption spectra gave information on color in relation to observed absorption bands, and Mössbauer spectra gave the distribution of Fe2+ and Fe3+ at the cation sites and also show how the Fe3+/Fe2+ ratio increases due to oxidative weathering. The development of the attractive flecking in the gem-quality jade is due to agglomerations of colloidally dispersed magnetite or chromite that can also lead to the formation of black spots. Darker samples are generally high in total iron, although not all lightly colored (or pale) samples are low in iron-cream or white unweathered nephrite can also contain high iron concentrations. Weathering under the climatic conditions where the samples occur can produce either a brown, hydrated iron oxide, or a whitish outer rind if the acidity is high enough to remove the oxide. In either case the nephrite matrix is unaltered. Two quite rare variations were found and ascribed to: (1) incomplete nephrite formation in samples developed in association with an unusual ultramafic protolithology and (2) the formation of chromian margarite giving rise to a bluish-green (pseudo) jade

The crystal structure of a Di(tetramethylammonium)-bis[R,R-tartrato(2-)]-cis-dioxomolybdate(VI), (NMe4)2[MoO2(C4H4O6)2] · EtOH · 1.5 H2O, with comments on tartrate coordination

SummaryIn the salt (NMe4[MoO2(H2tart)2] · EtOH · 1.5 H2O (H4tart = R,R-(+)-tartaric acid) the tartrato-ligands are linked to molybdenum through a carboxyl oxygen and the vicinal deprotonated hydroxyl oxygen atom, with carboxyl oxygentrans to terminal oxygen of the MoO2cis-dioxo core. The configuration about Mo is A. The C-C-C-C torsion angles of the ligands are almost 180°. This enables inter-ligand H-bonding from the uncoordinated hydroxyl groups. The five skeletal atoms from the uncoordinated section of a ligand are nearly co-planar. The probable strong preference fortrans coordination of carboxyl must limit the range of dissolved molybdenum(VI)-tartrate species.

Evidence on ligand strengths from the crystal structures of [InCl3(dmf)3], [InCl3(dma)3], [{InCl3(PhCHO)3}2]·PhCHO and [InCl3(PhCOMe)2] from dimethylformamide (dmf), dimethylacetamide (dma), benzaldehyde and acetophenone

X-Ray crystal structure determinations have been made for the fac octahedral complexes [InCl3(dmf)3]1, [InCl3(dma)3]2 and [{InCl3(PhCHO)3}2]·PhCHO 3, from dimethylformamide (dmf), dimethyl-acetamide and benzaldehyde and the trigonal-bipyramidal complex [InCl3(PhCOMe)2]4 from acetophenone. The average In–O bond length for 3 is ca. 0.07 A greater than for 1 or 2. In 4, In–O is 0.07 A longer than that known for [InCl3(tmu)2] from tetramethylurea (tmu). An extension of the comparison to structures involving other ligands shows there to be a general correspondence between In–O bond lengths and ligand donor values. By contrast with the weak co-ordination of aldehydes and ketones, co-ordination of an amide is enhanced through polarisation. In the crystal of 3, individual [InCl3(PhCHO)3] molecules are paired, almost centrosymmetrically, with intermeshing of their PhCHO ligands.

The chain-polymeric structure of the cobalt chloride pyridine-N-oxide complex [CoCl2(pyo)(H2O)]n

Abstract An X-ray determination of the crystal structure of the cobalt chloride pyridine-N-oxide complex CoCl2(pyo)(H2O) shows it to have a polymeric chain structure with mixed bridging by pyo and one chlorine atom. Octahedral coordination of cobalt is completed by the second chlorine atom and the water molecule. These latter two ligands show interchange of positions.

Molybdenum(VI) complexes from diols and aminoalchols: the occurrence of MoO2, Mo2O3, and Mo2O5 core structures

The co-ordination behaviour of molybdenum(VI) towards diols and aminoalcohols is discussed, particularly in relation to newly determined reference structures. A pinacol (H2pin) complex, typical of the yellow vicinal diol derivatives, is constituted [MoO(pin)(Hpin)]2O, with an Mo2O3 core. An Mo2O5 core is present in the anion [{MoO2(Hnta)}2O]2–, formed by nitrilotriacetic acid (H3nta) at low pH. Several new complexes in which ligand bridging is inferred have been prepared. One of these, [{MoO2(Hpin)(OMe)}2]·2MeOH, which is derived from the yellow pinacolate, is shown by X-ray analysis to have methoxy-bridging. The bridge vibration from an Mo2O3 core is close to 750 cm–1, but the pattern of bands from an Mo2O5 core is variable. The MoO1bMo vibration involving an oxygen bridge provided by a chelating ligand gives an i.r. band in the region 625–650 cm–1.

Some binuclear molybdenum(VI) complexes obtained from condensation reactions: their crystal and molecular structures

Molybdenum(VI) complexes of three new structural types have been obtained from ethanol solution through use of triethoxymethane as condensing agent. The complex MoO3(dmso)1.33(dmso = dimethyl sulphoxide) alone yields [{MoO2(OEt)2(dmso)}2](1), MoO3(dmso)1.33 with 2-amino-1,3-dihydroxy-2-methylpropane (H2amp) gives [{MoO2(amp)}2]·2dmso (2), and two isomeric compounds [{MoO(hmmp)(OEt)}2], (3a) and (3b), are obtained from [MoO2(Hhmmp)](H3hmmp = 1,3-dihydroxy-2-hydroxymethyl-2-methylpropane). The crystal structures of these compounds have been determined and show that all four contain coplanar di-µ-OIb bridges (OIb= deprotonated ligand-bridging O). The molecules of (1), (2), and (3b) have Ci symmetry, while (3a) has C2 symmetry. The OIb–Mo–OIb angles are 69–72°, the low values being imposed by the bridging ligands. For [{MoO2(amp)}2] there is the unusual feature that each bridging atom belongs to a five-membered ring, and there is evidence of consequent ligand strain.

A Reversible Non-disruptive Phase Transition Shown by the Zinc Iodide Dimethylformamide Complex ZnI2(dmf)2

At 228 K crystals of ZnI 2 (dmf) 2 show a reversible phase transition which does not disrupt the lattice. Above the transition temperature the space group is C2/c and the cell contains eight symmetrically equivalent molecules. Cooling to below the transition temperature has little effect on the cell parameters or on the Zn- and I-atom positions, but the space group is now P2 1 /n and the asymmetric unit comprises two conformationally different molecules. These arise from cooperative rotations of either ca +25 or -43° about the Zn-O bond of one of the dmf ligands in the high-temperature form. This displacive transition involves large movements of some atoms. The corresponding chloride and bromide are isomorphous with the higher temperature C2/c form, but it is only with the iodide that the weaker intermolecular forces permit the unusual phase change. The transition has been followed by differential scanning calorimetry, which gives an enthalpy change of 1.44 (5) kJ mol -1 .