Monomeric two-coordinate gold(I) complexes,
[Au(P(mes)3)X] (P(mes)3
= tris(2,4,6-trimethylphenyl)phosphine, X = Cl, Br and I), have
been prepared and characterized by single-crystal X-ray structure
determinations, far-infrared spectroscopy and solution and solid-state CPMAS
31 P n.m.r. spectroscopy. X-Ray structure determinations
show that crystals obtained from solutions of
[NBu4] [AuX2]
and P(mes)3 in acetonitrile for X = Cl, Br and I
and in dimethylformamide (dmf) for X = Br and I form an isomorphous
series of complexes, crystallizing in space group
P21/c
with a ª 8, b ª 22,
c ª 13 Å, b ª 98˚ (a form).
Crystallization of the chloride from dimethylformamide yields the solvated
complex [Au(P(mes)3)X]·(dmf) in space
group P2/a with a 15.224(2),
b 10.070(1), c 18.210(4) Å,
b 100.42(2)˚. Electrochemical synthesis of the complexes for X =
Cl and Br yield two new crystalline phases; the chloride in space group
P21/c
with a 10.249(2), b 8.189(2),
c 31.844(3) Å, b 91.68(1)˚ (b form) and the
bromide in space group Pbca with a
19.208(4), b 15.586(3), c
16.962(4) Å ( g form). The Au–P bond lengths increase in the order
Cl < Br < I with distances c. 0.02–0.03
Å longer than average values for other
[Au(PR3)X] complexes, reflecting steric
congestion by the P(mes)3 ligand. For the unsolvated
complexes, the Au–X distances are c. 0.02 Å
shorter than average values. For the Cl/dmf solvate, both Au–P and
Au–X bond lengths increase. For the a complexes, far-infrared spectra
show n(Au 35,37 Cl) 336, 329 cm
–1 , n(AuBr) 234 cm –1
and n(AuI) 195 cm –1 and solid-state
31 P CPMAS n.m.r. spectra yield broad peaks with
d–3.9 (Cl), –0.6 (Br) and +6.0 I). For the Cl/dmf
solvate, n(Au 35,37 Cl) are 334, 327 cm
–1 and d is –4.4. Solution
31 P n.m.r. spectra in CDCl3 give
sharp single peaks at d –5.0 (Cl), –1.4 (Br) and +5.5 (I)
with the similarity of the values with those for the solid-state spectra
consistent with similar conformational structures for the
[Au(P(mes)3)X] molecules in the two states.
Synchrotron-Based High Resolution Far-Infrared Spectroscopy of trans-Butadiene
