Complexes of Group V and VI metals with soft donor ligands - towards reagents for early metal chalcogenide thin films

Abstract

Preparations of NbX4 (X = Cl, Br) have been developed in good yield, leading to the formation of a series of 2:1 and 1:1 adducts upon reaction with neutral diphosphine ligands. The 2:1 ligand:metal complexes [NbX4(P–P)2] (X = Cl, Br; P–P = Me2P(CH2)2PMe2, Et2(CH2)2PEt2, o-C6H4(PMe2)2) were characterised by IR and UV-visible spectroscopies, their purities determined by microanalysis and the solid-state structures confirmed by X-ray crystallography to be that of eight coordinate dodecahedra or square antiprisms. The dimeric 1:1 complexes [Nb2X4(P–P)2(μ-X)4] (P–P = Me2P(CH2)2PMe2, Et2P(CH2)2PEt2, Ph2P(CH2)3PPh2, Cy2P(CH2)2PCy2, o-C6H4(PPh2)2) were also characterised by 1H and 31P{1H} NMR spectroscopy.

A series of six-coordinate monomeric complexes, [NbCl4(L–L)] (L–L = MeS(CH2)2SMe, iPrS(CH2)2SiPr, MeS(CH2)3SMe, o-C6H4(CH2SEt)2, MeSe(CH2)2SeMe, MeSe(CH2)3SeMe and nBuSe(CH2)3SenBu) and [NbCl4(ER2)2] (ER2 = SMe2, SeMe2, SenBu2 and TeMe2) were prepared from NbCl4 and the ligand in CH2Cl2 solution. X-ray structures show that most of them form six-coordinate octahedral complexes, whereas [NbCl4(SeMe2)2] and [NbCl4(TeMe2)2] are thought to be dimeric from X-ray crystallography of the latter. The Nb(IV) complexes were unsuitable as CVD precursors.

Monomeric [NbSCl3(L–L)] (L–L = MeS(CH2)2SMe, iPrS(CH2)2SiPr, MeS(CH2)3SMe, nBuS(CH2)3SnBu and MeSe(CH2)3SeMe) and dimeric [NbSCl3(SR2)] (R = Me and nBu) were prepared from reaction of [NbSCl3(NCCH3)2] with the ligand in CH2Cl2 solution or reaction of [NbCl5(SR2)] with S(SiMe3)2 in CH2Cl2 solution and characterised by IR, 1H NMR and 93Nb NMR spectroscopies, X-ray crystallography and microanalysis. Isolated complexes [NbSenCl3(L)] (n = 1, L = CH3CN; n = 2, L = nBu2Se) were identified by IR spectroscopy and microanalysis. [NbSCl3(SnBu2)], [NbSCl3(nBuS(CH2)3SnBu)] and [NbSe2Cl3(SenBu2)] were used as single source precursors in LPCVD. The resulting NbS2 and NbSe2 thin films were characterised via X-ray diffraction, SEM and EDX spectroscopy.

Isolated complexes of the form, [MBr5(EnBu2)] (M = Nb, Ta; E = S, Se), were identified via IR and multinuclear NMR spectroscopies and the Nb complexes were used as single source precursors in LPCVD to deposit NbS2 and NbSe2 thin films. The growth of 2H-/3R-NbSe2 thin films was controlled by varying the temperature used in LPCVD. All NbS2 and 2H-/3R-NbSe2 thin films were characterised using X-ray diffraction, SEM and EDX spectroscopies.

A series of new MoCl4 complexes, [MoCl4(ER2)2] (ER2 = Me2S, Me2Se, nBu2S, nBu2Se) and [MoCl4(L–L)] (L–L = MeS(CH2)2SMe, iPrS(CH2)2SiPr, MeS(CH2)3SMe, and MeSe(CH2)3SeMe), were made using MoCl5 or [MoCl4(NCCH3)2] as the Mo source and characterised using IR and UV-visible spectroscopies, X-ray crystallography and microanalysis. Single source LPCVD precursors, [MoCl4(SnBu2)2] and [MoCl4(SenBu2)2], deposited MoS2 or MoSe2 thin films which were characterised via X-ray diffraction, SEM and EDX spectroscopy.

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ORCID for Gillian Reid: orcid.org/0000-0001-5349-3468

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