Novel Heterobimetallic Neodymium/Calcium 8‐Quinolinolate Complexes Prepared Directly From the Metals

Abstract

Reaction of 8-hydroxyquinoline (HOQ) with calcium and neodymium metal (mole ratio 1.6:0.72:1.1) in the presence of mercury at 110°C under vacuum in a durene flux yielded bis(8-quinolinolato-κ:N,O(Nd))hexakis(µ-(O)-8-quinolinolato-κ:N(Nd),O-(Nd,Ca))calcium(II) dineodymium(III) (NdCaNd) (1) (P1, a ϭ 11.305 (2), b ϭ 12.468(3), c ϭ 13.918(3) Å , Ͱ ϭ 116.62(3), β ϭ 95.46(3), γ ϭ 109.59(3)°, V ϭ 1580.6(6) Å 3 , R1 ϭ 0.0718). The trimetallic was again obtained but as the solvate 1. (HOQ) from Although 8-hydroxyquinoline (HOQ) and its derivatives have long been used in the quantitative determination (gravimetric, colourimetric, volumetric) of lanthanoids [1], little is known of their structures, particularly the Ln(OQ) 3 species implicated in analytical determinations. Recently, two oxyquinolinelanthanoid heteroleptic complexes were isolated as the trinuclear species [Yb 3 (OQ) 8 (OOCCH 3 )]·3CHCl 3 and [Er 3 (ClOQ) 8 (OOCCH 3 )] (ClOQ ϭ 5-chloro-8-quinolinolate) [2,3]. As a new approach to preparing Ln(OQ) 3 complexes, we have examined the direct synthesis from lanthanoid metals and 8-hydroxyquinoline at elevated temperatures either solvent free or in an inert flux.This method has been recently developed for lanthanoid complexes from weak acids [4], e.g. giving phenolates [5,6] and derivatives of nitrogen heterocycles including pyrazolates [7Ϫ10]. Following the fortuitous formation (see below) of a heterobimetallic complex, we have developed this synthesis to give the homoleptic bimetallic complexes [Nd 2 Ca(OQ) 8 ] (1) and [Nd 2 Ca(OQ) 8 ].(HOQ) (1·HOQ) from a mixture of calcium and neodymium metals. Preparation of several yellow crystals of 1 was initially a fortuitous result arising from a trace calcium contaminant in an aged sample of 8-hydroxyquinoline. In a deliberate synthesis, neodymium filings were treated with pieces of calcium and 8-hydroxyquinoline in the presence of an inert flux of 1,3,5-tri-tert-butylbenzene (tBuB) yielding 1·HOQ (Equation (1)). Although a monosolvate, it has the same morphology as 1. Repetition of this reaction but with a different flux (1,2,4,5-tetramethylbenzene (durene)) and a larger excess of metals (Nd:Ca:HOQ 1.0:0.72:1.1) afforded many yellow crystals of 1 (identified by unit cell data) rather than 1·HOQ. In 1 and 1·HOQ, the two eight coordinate neodymium atoms (Figure 1a) have a distorted dodecahedral geometry [11] and are symmetry related with the calcium atom positioned on a centre of inversion. The Nd atoms have one terminal chelating (O, N) oxyquinoline ligand and three chelating (O, N) ligands that are also bridged through their oxygens to calcium (Equation (1)).The four nitrogen * Prof. Glen. B. Deacon 1541 reaction between HOQ, Nd and Ca, (mole ratio 2.8:2:1) in a 1,3,5tri-tert-butylbenzene flux P1, a ϭ 10.206 (2), b ϭ 12.256(3), c ϭ 13.819(3) Å , Ͱ ϭ 85.93(3), β ϭ 89.94(3), γ ϭ 81.36(3)°, V ϭ 1704.5(6) Å 3 , R1 ϭ 0.0592).

Syntheses at Elevated Temperature and Structures of Lanthanoid/Alkaline Earth Heterobimetallic Derivatives of 2‐Methyl‐8‐hydroxyquinoline

“…The hexacoordinate alkaline earth metal is surrounded by the oxygen atoms in a distorted octahedral arrangement ( Figure S1). This motif (Scheme 1) has previously been observed in [Ln 2 Ca(OQ) 8 ] (Ln = Nd, Eu) complexes, [12,14] and the connectivity is the same in molecule Mg(2) (Figure 1). Bond length data (Table 1) show a somewhat variable response to the decrease in ionic radii (0.062 Å) [16] (Figure 2, vide infra), which is possibly attributable to greater crowding in the heterobimetallics.…”

“…Solubility problems also make it a challenge to prepare homoleptic f-element/ d-or alkaline earth element heterobimetallics of the parent HOQ and to obtain crystalline products for X-ray crystallography. We have presented preliminary accounts of three pseudo-solid-state synthetic approaches to crystalline Ln/M heterobimetallic 8-quinolinolates, namely by: (i) reaction of a mixture of calcium and neodymium metals with 8-hydroxyquinoline at elevated temperatures to afford [Nd 2 Ca(OQ) 8 ] as single crystals in low yield together with bulk red amorphous glass, [12] (ii) reaction of HOQ with a LaNi 5 alloy at elevated temperatures giving [LaNi 2 (OQ) 7 ] [13] and (iii) rearrangement of a mixture of Ln(OQ) 3 and either Ca(OQ) 2 7 ], respectively. [14] 8-Hydroxyquinaldine (HMQ) is also a gravimetric reagent with a similar solubility profile for metal complexes, thereby posing similar problems for the synthesis of f-element/d-or alkaline earth element heterobimetallics.…”

Two allotropic forms of 2-quinolinecarboxaldehyde

“…One compound, with two polymorphs (A and B) is 5,11-bis-(4-tert-butyl-phenyl)-6,12-diphenyl-naphthacene, a derivate of rubrene where t-butyl sidegroups are added. The electric transport properties of the two polymorphs are completely different: in polymorph B the in-plane hole mobility of 12 cm 2 /Vs measured on single crystal FETs is just as high as in rubrene crystals, whereas polymorph A does not show any measurable field-effect [2]. The crystal structure of polymorph A is monoclinic, with space group P2 1 /c.…”

“…The structure of polymorph B could not be solved so far, as the material seems to exclusively grow as ultrathin platelets. From measurements of the d-spacing perpendicular to the extended crystal surface [2], a structure closely related to the one found for a constitutional isomer, 5,12-bis-(4-tertbutyl-phenyl)-6,11-diphenyl-naphthacene [4] was assumed for polymorph B. The crystal structure of the second compound, 5,12-bis-(4-tert-butyl-phenyl)-6,11-diphenyl-naphthacene is orthorombic, with space group Pnma.…”

“…Keywords; DFT calculations, allotropes, structure determination 2,2′-Bipyridine has been used for over a century as the classical N,N′-bidentate ligand in coordination, organometallic and analytical chemistry. N,O-chelating ligands are somewhat less common but for instance 8-hydroxyquinoline and 8-methoxyquinoline has been used as versatile bidentate ligands [1][2][3]. We present here two distinct crystal structures of 2-quinolinecarboxaldehyde, a compound that we are starting to use as a ligand in metal complexation.…”