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Figure 1. Mg(thd)2(en) (1) |
Figure 2. Mg(thd)2(etOH)2 (2) |
VOLATILE Mg(thd)2ETHYLENEDIAMINE AND Mg(thd)2DIETHANOL AT 193 K
Jarno Kansikas, Timo Hatanpää, Ilpo Mutikainen and Markku Leskelä
Department of Chemistry, Laboratory of Inorganic Chemistry, University of Helsinki, POBox 55, FIN-00014 University of Helsinki, Finland, E-mail: kansikas@penger.helsinki.fi
Keywords: volatile, b-diketonate,
precursor, ALE
b-Diketonates and especially thd (thd=2,2,6,6-tetramethyl-3,5-heptanedione) complexes are the most important precursors of alkaline earth metals needed in chemical vapor deposition (CVD) or atomic layer epitaxy (ALE) method of growing thin films. Thd complexes have been stabilized by adduct molecules such as amines, polyethers and alcohols.[1] Two Mg-complexes will be presented here, [Mg(thd)2ethylenediamine] (1) and [Mg(thd)2diethanol] (2). These complexes were prepared by dissolving [Mg2(thd)2]2 synthesized by previously reported method to ethanol and adding the adduct ligand to the solution.[2]
Compound (1) crystallizes in a space group P(-1) with two molecules and (2) in P21/n with one molecule in an asymmetric unit. Cell dimensions are a=10.372(2), b=14.790(3), c=19.588(4) A, a=93.08(3), b=91.45(3) and g=107.44(3)° for (1) and a=16.725(5), b=10.461(5), c=18.801(5) A and b=110.63(1)° for (2).
The structure of (1) is presented in Fig. 1 and for (2) in Fig. 2. Only one molecule of (1) is shown. Both compouds are monomeric and coordination of Mg is distorted octahedral. Bond lengths with the e.s.d.s of 0.004 A for (1) are 2.033, 2.034, 2.054, 2.018, 2.015, 2.055, 2.019 and 2.047 A for Mg(1,2)-O(11-42), respectively. Mg(1,2)-N(1-4) distances are 2.246, 2.207, 2.252 and 2.200 A for molecules 1 and 2, respectively. In (2) the distances with the e.s.d.s of 0.003 A, for Mg-O(11-22) are 2.063, 2.026, 2.006 and 2.004 A, respectively. Mg-O(ethanol) distances are 2.113 and 2.163 A.
In (1) the practically planar thd molecules are tilted so that Mg1 deviates 0.59 A from the thd-1 plane while the deviation of Mg1 from thd-2 is 0.01 A. The interplanar angle is 78.1°. The respective deviations of Mg2 from thd-3 and thd-4 planes are 0.29 and -0.59 A, respectively, and the interplanar angle is 88.2°. In (2) Mg deviates -0.69 and 0.32 A from thd-1 and thd-2 planes, respectively. Their interplanar angle is 64.1°.
TG measurements reveal that 99% volatility is achieved below 580 K under nitrogen atmosphere with both complexes at the heating rate of 10°/min. Both complexes also dissociate during heating.
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Figure 1. Mg(thd)2(en) (1) |
Figure 2. Mg(thd)2(etOH)2 (2) |
