Tungsten cycloheptatriene tricarbonyl W(η6-C7H8)(CO)3 (M=360.01, sum formula C10H8O3W) is solid with melting point 102 °C (with decomposition).[]
W(η6-C7H8)(CO)3 was synthesized by adding cycloheptatriene to tungsten tricarbonyl tris(acetonitrile) adduct in boiling n-hexane (at 69°C):
W(CO)3(CH3CN)3 + C7H8 → W(C7H8)(CO)3
W(η6-C7H8)(CO)3 was applied as W precursor, for example for the deposition of W-C films by cold-wall ultra-high vacuum (1 – 2 mTorr) MOCVD. The source compound W(η6-C7H8)(CO)3 was evaporated at 100 – 120 °C. Reflective, adherent layers were obtained
at 350 – 700 °C temperatures. Films deposited at 540 °C contained 40 at. % W, 60 at. % C, < 1 at. % O and had resistivity 300 – 1500 μWcm.[i]
[i] Prof. Dr. Heinrich Lang, The Chemistry of Metal CVD, International Research Training Group, “Materials and Concepts for Advanced Interconnects”
Tungsten (cycloheptatriene) tris(carbonyl) W(cycloheptatriene)(CO)3 (or W(cht)(CO)3) (and for comparison WH(L)(CO)3 (L=Cp, Me5Cp), W(cod)(CO)4 and W(toluene)(CO)3 ) were tested as precursor for the growth of thin tungsten carbide layers by cold-wall low pressure (LP) CVD. The deposited coatings were analyzed by XRD, AES, SEM and electrical resistivity measurements. Tungsten carbide layers could be deposited from W(cht)(CO)3 at temperature as low as 350°C. Layer obtained from W(cycloheptatriene)(CO)3 at 540°C (as well as from WH(L)(CO)3 (L=Cp, Me5Cp)) (were amorphous WC (incorporating graphitic C and <1 at.% O contaminant), whereas crystalline textured WC1-x and a-W2C layers were obtained using W(cod)(CO)4 and W(toluene)(CO)3 as precursors). [i]
[i] K.K. Lai, H.H. Lamb, Chem. Mater. 1995, 7, 12, 2284–2292, « Precursors for Organometallic Chemical Vapor Deposition of Tungsten Carbide Films », https://doi.org/10.1021/cm00060a016 , https://pubs.acs.org/doi/pdf/10.1021/cm00060a016