Laura Scaccianoce

Design of organometallic molecular and ionic materials

Abstract Organometallic crystal engineering is the modeling, synthesis, characterization and evaluation of crystalline materials constituted by organometallic molecules and ions. The properties of solids containing transition metal complexes are distinct and diverse from those of purely organic systems as well as from those of inorganic materials. In particular, while the periphery of (most) organometallic molecules are ‘organic’ in nature, since the outer atoms are usually those of the ligands, the ‘cores’ are formed by transition metal atoms in their (often variable) spin and charge states. These characteristics can be exploited to make crystalline materials with predefined physical properties as well as to organize organometallic molecules in complex supramolecular structures for absorption and desorption of solvent molecules. The possibility of utilizing the same building blocks in different ionic conditions (including neutral, e.g. in molecular crystals) permits tuning of the intermolecular bonding capacity via acid-base reactions. Organometallic polymorphism is discussed as a possibility for preparing and interconverting crystalline isomers. Pseudo-polymorphism is shown to be advantageous for the preparation of elusive crystal forms.

Crystal engineering of chiral superstructures based on (R)-(+)-1,1'-bi-2-naphthol and the alkali derivatives of racemic (R,S)-1,1'-bi-2-naphthol

(R)-(+)-1,1′-Bi-2-naphthol [(R)-(+)-(HOC10H6C10H6OH)] has been used as a chiral building block in the construction of chiral organo-organometallic crystals. The reaction of the neutral molecule with [Co(η5-C5H5)2] in diethyl ether yields the supramolecular salts [CoIII(η5-C5H5)2][(R)-(+)-(HOC10H6C10H6O)]·[(R)-(+)-(HOC10H6C10H6OH)] (1) and [CoIII(η5-C5H5)2][(R)-(+)-(HOC10H6C10H6O)]·[(R)-(+)-(HOC10H6C10H6OH)]0.5 (2), depending on the stoichiometric ratios between the binaphthol and the organometallic sandwich compound. Molecular aggregation is achieved ia a combination of neutral and charge-assisted O–H···O bonds between the binaphthol and binaphtholate components and ia weaker interactions of the C–H···O and C–H···π types involving the [CoIII(η5-C5H5)2]+ cation. The same reaction with racemic 1,1′-bi-2-naphthol in diethyl ether, followed by recrystallisation from nitromethane, yields the solvate species [CoIII(η5-C5H5)2][(R,S)-(HOC10H6C10H6O)]·[(R,S)-(HOC10H6C10H6OH)][MeNO2]1.5 (3). For comparison, the alkali salts Cs[(R,S)-(HOC10H6C10H6O)]·[(R,S)-(HOC10H6C10H6OH)] (4) and Rb[(R,S)-(HOC10H6C10H6O)]· [(R,S)-(HOC10H6C10H6OH)] (5) have also been prepared by treating [(R,S)-(HOC10H6C10H6OH)] with the Cs and Rb hydroxides. Both organometallic and alkali salts show how the cations tend to be encapsulated within a niche formed by the folding of hydrogen-bonded naphthol–naphtholate chains.

Organometallic polymorphism. Synthesis and structural characterization of two forms of [Ru(η6-C6H6)(η6-C6H4(CH3)COOCH3)][BF4]2 and the phase transition in [Ru(η5-C5H5)(η6-C6H5OH)][PF6]

Abstract The synthesis and structural characterization of the complex [Ru(η6-C6H6)(η6-C6H4(CH3)COOCH3)] [BF4]2 (2) and of its precursor [Ru(η6-C6H4(CH3)COOCH3)Cl2]2 (1) are reported. Compound (2) has been characterized in two polymorphic modifications (2a and 2b) and the molecular organization in the solid state has been investigated. The complex [Ru(η5-C5H5)(η6-C6H5OH)][PF6] (3) has also been investigated; it has been shown to possess a disorder similar to that observed in the high temperature phase of related systems such as [Ru(η5-C5H5)(η6-C6H6)][PF6].

Making and converting organometallic pseudo-polymorphs via non-solution methods

The organometallic pseudo-polymorphism that arises from cocrystallisation of organometallic molecules or ions with solvent molecules is discussed, together with the possibility of interconversion between polymorphs and pseudo-polymorphs. Three cases have been investigated: (i) the quantitative preparation of a monohydrated pseudo-polymorph of the supramolecular salt [CoIII(η5-C5H5)2]+[Fe(η5-C5H4CO2H)(η5-C5H4CO2)]−1 by grinding the powder material and subsequently nucleating and crystallising the hydrated form [CoIII(η5-C5H5)2]+[Fe(η5-C5H4CO2H)(η5-C5H4CO2)]−·H2O 2, (ii) the quantitative preparation, nucleation and crystallisation of the elusive anhydrous form of the neutral zwitterion [CoIII(η5-C5H4CO2H)(η5-C5H4CO2)] 4 by thermal dehydration of the hydrated species [CoIII(η5-C5H4CO2H)(η5-C5H4CO2)]·3H2O 3, and (iii) the formation of the salt [RuII(η6-C6H6)2][BF4]25 either by direct crystallisation from water or by desolvation of the pseudo-polymorph [RuII(η6-C6H6)2][BF4]2·MeNO26 obtained from nitromethane. In order to investigate the processes, single crystal and powder X-ray diffraction measurements as well as thermogravimetry and differential scanning calorimetry have been carried out. These results show, inter alia, how elusive polymorphic or pseudo-polymorphic modifications of a given substance can be obtained by non-solution methods.

SYNTHESIS AND CHARACTERISATION OF RU6C(CO)14 CLUSTER COMPLEXES OF SOME 2.2- AND 2.2.2-CYCLOPHANE LIGANDS

Some [Ru6C(CO)14] cluster complexes bearing the [2.2]ortho-, anti-[2.2]meta- and [2.2.2]para-cyclophane ligands have been prepared, isolated and characterised. The molecular structure of two new compounds [Ru6C(CO)14(meta-C16H16)] 2 and [Ru6C(CO)14(para-C24H24)] 4 have been established by X-ray diffraction studies which show that the cyclophane ligands are bound in an apical η6 mode in both cases. This is at variance with the face-capping µ3-η2∶η2∶η2 mode observed in the previously reported structure of [Ru6C(CO)14(para-C16H16)] 1. Spectroscopic evidence obtained for [Ru6C(CO)14(ortho-C16H16)] 3 suggests that the cyclophane ligand is bound in an apical η6 mode too. The synthesis of 1 via the redox coupling of [Ru5C(CO)14]2– with [Ru(η6-C16H16)(NCMe)3]2+ is presented as an alternative to the thermolysis of [Ru3(CO)12] with [2.2]paracyclophane in heptane.

A tetranuclear cluster sandwiched between edge-bridgingcycloheptatrienyl rings: the synthesis and characterisation of[Ru4(CO)7(µ-C7H7)2]

The reaction of [Ru 3 (CO) 12 ] with cycloheptatriene affords [Ru 4 (CO) 7 (µ-C 7 H 7 ) 2 ] an example of a new class of sandwich cluster which is characterised in the solid-state by single-crystal X-ray diffraction and shown to contain an unusual arrangement of two parallel edge-bridging organic rings.