reveal, however, t hat , contrary to MP2 results, the strength of metallophilic interaction in t hese systems increases negligibly from Cu to Ag, but decreases from Ag to Rg. Thus st ating that metallophilicity does decrease down group 1 1 .
Since t here are no pairs of analogous free dimers for this series of compounds, K alt soyannis' results cannot be tested experimentally easily. For this purpose, Pyykkb probed comparative calculations for t he A-frame molecules [S(MPH3 ) 2J [326] , applying full ge ometry optimization at the MP2-MP4, CCSD and CCSD(T) level, and concluded t hat t he oscillations of t he met al-met al d ist ance, as a function of t heoretical level, are large
and in the fol lowing order: Cu > Au > Ag. Thus, qualitat ively agreeing wit h Kaltsoyan
nis, t hat MP2 may not be the appropriate method for investigating the metallophilicity.
By performing local 1'vIP2 and CCSD calculations, he ascertained that dispersion terms dominate t he silver and gold systems, while the ionic terms dominate the Cu compound . Furthermore, he stated t hat there is st ill a too large discrepancy between t he optimized and experimental geometric data even at t he CCSD (T) level.
The motivation of t his work was to further probe t he performance of DFT 111 the field of met allophilicity, to invest igate a greater range of ligands t han Kaltsoyannis [325J
and t o include for the first t ime also t he t rimers of t he [X-M-P H3Jn=1-3 systems ( X=Cl, Br, I ; M=Cu, Ag, Au) . More extensive basis sets were employed and in cont rast to Kaltsoyannis' study, all monomer, dimer and trimer struct ures were fully optimized at t he D FT level3
8 . 2 Methods
When investigat ing metallophilicity, t he choice of basis set is particularly important due to a combinat ion of basis set superposition error (BSSE) [327J and t he inherent weakness of t he effect itself. Furt hermore, it is imperative to treat t he coinage metals and t he bromine and iodine atoms relat ivistically and on t he same footing. It has been shown that relativis t ic effects cannot be neglected in accurate calculations of bond lengths and energies in cop per compounds [332, 333J . Therefore, t he extensive and well proven STUTTGART valence basis s ts and energy-consistent small-core pseudopotentials4 , where scalar-relativistic ef fects are implicitly included, were used for Cu, Ag, Au, Br and I [337, 338J .
3Van del' Waals-like interactions are not reliably described by the current DFT schemes [210, 324]
however, DFT has a reputation for producing the correct answer for unreliable reasons.
CHA PTER 8. MET A L L OPHIL ICITY, THE PERFORMANCE OF DFT 153
The heteroatoms of all compounds, i .e. H, P and Cl, were t r ated with all-electron
aug-cc-pVDZ5 basis set s as implemented in t he GAUSSIAN03 program package [33 1 ] . All
calculat ions were performed with the GAUSS I AN 03 program package [33 1 ] .
A s i n all other related t heoretical studies cited here, the P R3 (R =alkyl, aryl)
which are present in t he experimental compounds, wer replaced by PH3 in order to sim
plify t he calculat ions. Tab I (8. 1 ) shows, that PH3 is a good model for t he larger PR3
ligands, as far as struct ural properties are concerned. The struct ures of all monomeric,
dimeric and trimeric compounds of t he type [X-M-PH3] n=1-3 ( M=Cu, Ag, Au; X=CI, Br,
I ) were fully opt imized at the DFT level, only constraining the dihedral angle (dx!If!lf x ) to 900 , according to figure (8.1 (b) and (c) ) (see t able (8.2) for geometric d at a ) . The latter restriction was made to reduce electrostat ic interact ions between t he monomers by minimizing the leading dipole-dipole term, and hence to allow more unencumbered focus on the metallophilicity. It has been shown that by lifting this restrict ion, signifi cantly bigger interaction energies and in almost all cases smaller metal-metal distances
are obtained [325] , hence illustrating the need for t he 900 restriction when invest igating
metallophilicity in t hese systems.
For t he exchange-correlat ion potent ial, t he generalized gradient approximat ion, ac
cording to t he parameterization suggested by Becke [ 1 1 1] and Perdew [1 1 2] (bp86) , was
applied in a self-consistent fashion.
The BSSEs were accounted for using t he counterpoise correction according to [10] ,
!::::. Ecomplex = EAB [ab] - EA [a] - EB [b] !::::.Ecp = EA [ab] + E8 [ab] - EA [a] - EB [b]
Ecpc = !::::.Ecomplex - !::::.Ecp,
(8. 1 )
where !::::.Ecomplex denotes t he complexation energy, !::::.Ecp t he counterpoise correction
energy and Ecpc t he counterpoise corrected complexation energy of t he dimer [X-M
PH3b respectively.
A
and B represent t he monomers,AB
the dimer complex, a and bthe basis set s of t he respective monomers and * t he opt imized complex geomet ry.
CHAP TER 8. METALL OPHILICITY, THE PERFORMANCE OF DFT
Cl-Au-Au-Cl = const. = 96'
Figure 8 . 1 : Opt imized st ruct ures of [CI-Au-PH3] n=1-3; bond lengths in A.
8 . 3 Results and D iscussion
1 54
A wide range of t heoretical and experimental geometric data of the monomers of [X-M PH3] are compared in t able (8. 1 ) . Clearly, t he simplification of the r nt alkyl and aryl phosphine groups, which are present in t he experimental st udies, to the phosphane (PH3) group is j ustified6 , as t he discrepancies betw en t he calculated and experimental bond lengths rAI-X and rAI_p for t he monomers come to less t han 3 % for all t he st udied
compounds. It furt her becomes evident , when comparing the available theoret ical work with t he experimental, t hat bot h MP2 and DFT perform very satisfyingly. However, no clear conclusion can be drawn as to which method performs best , as there is no experimental data available for the optimized compounds.
The isostructural series of phosphine substituted compounds [X-M-(TMPP)]
CHA PTER 8. METALL OPHILICITY, THE PER PO R MANCE OF DFT 1 55
Table 8 . 1 : Comparison of geometric data of [X- M-P H3J (M=Cu, Ag, Au; X= Cl , Br,
I); angles in deg and bond lengt hs in A.
Molecule Method rf\/ - x rA/ - p L- X - M - P Ref.
[ClCuPH3] bp86 2.084 2. 1 43 1 80.0 thi work
[ClCuPH3] bp86 2.094 2 . 1 43 [325]
[ lCuPH3] b31yp 2 . 1 06 2. 1 75 [325]
[ClCuPH3] b31yp 2. 1 23 2.207 [324]
[ClCuPH3] M P 2 2.097 2 1 59 1 80.0 [3 1 7] [C1Cu (TI', I PP)] exp 2. 1 1 8 2. 1 1 7 1 73.0 [328]a
[BrCuP H3] bp86 2. 2 1 3 2. 1 5 1 1 80.0 this work [BrCu(TM PP)] exp 2. 259 2 . 1 97 1 72 . 0 [328]b
[ICuPH3] bp86 2. 393 2 . 1 63 1 80.0 this work
[ICu(TMPP)] exp 2 . 4 1 7 2. 1 88 1 7 1 . 0 [328]b
[ClAgPH3] bp86 2.283 2.3 1 2 this work
[ClAgPH3] bp86 2.294 2.3 1 9 [325] [C1AgPH3] bp86 2.299 2.333 [339] [ClAgPH3] b3lyp 2.3 1 0 2.364 [325] [ClAgPH3] MP2 2 . 306 2.372 1 80.0 [3 17] [C1Ag(Tt\1 PP)] exp 2 . 342 2.379 1 75.0 [329] [BrAgPH3] bp86 2 . 4 05 2.325 1 80.0 t h i s work [BrAg(T1Vl PP)] exp 2.440 2 370 1 74 . 4 [329]
[ IAgPH3] bp86 2.579 2.342 1 0.0 this work
[ I Ag(TMPP)] exp [Cl AuP H3] bp86 2 . 2 72 2.242 1 80 . 0 this work [ClAuPH3] bp86 2 . 2 89 2.24 1 [325] [ClAuPH3] bp86 2.227 2.222 [339] [ClAuPH3] B3LYP 2 . 302 2.262 [325] [ClAuPH3] B3LYP 2 . 325 2 . 283 [341] [ClAuPH3] MP2 2 . 300 2.249 1 80 . 0 [3 1 7] [C1Au(TM PP)] exp 2.30 4 2.253 1 76 . 0 [330] [ClAuPPh3] exp 2.279 2 . 235 1 79 . 6 [342]
[ClAuPEt3] exp 2.305" 2.233a 1 78 . 7a [344]
[C1AuPMe3] exp 2 . 309b 2 . 234b 1 80 . 0b [343]
[BrAuPH3] bp86 2.395 2 . 253 1 80 . 0 this work
[BrAu(TMPP)] exp 2 . 4 1 3 2 . 255 1 75.9 [330] [ IAuPH3] bp86 2.56 2 2 . 269 1 80.0 this work
[ I A u (TMPP)] exp 2.586 2 . 240 1 77 . 7 [330]
a Average for two crystallographically inequivalent molecules
CHA P T ER 8. META L L OPHILICITY, THE PERFORMA NCE OF DFT 1 56
(M
= Cu(1 ) , Ag(1) , Au (1) ; X= Cl, Br, 1)7 , with the exception of the Ag1 complex, all form isomorphous solids in which the metals display t he linear P-M-X tructure, which is normally only characteristic to the gold(1) complexes [328-330]. The crystallographic data on the Chloro (triphenyl- , triethyl- R,nd trimethylpho phin ) gold(1) complexes all show t he l inear P-M-X struct ure as well and negligible deviat ions in t heir bond lengt hs rp.1-X and ri\I_p, respectively.On t he basis of the SIze of the phosphine ligands, t he
Chloro( trimethylphosphine)gold(1) complex IS t he most clos st related to t he
Chloro(phosphane)gold (1) complex i nvest igated in this work. This is reflected by
t he fact that , while t he monomers of [CIAuPMe3] are aggregated to form a helical chain t hrough fairly short alternat ing Au . . . Au contacts of 3.27 1 , 3.356, and 3.386 A [343] ,
the dos st Au . . . Au cont acts in the cryst al lattice of [CIAuPEt 3] is 3 . 6 1 5 A [344]. Such Au . . . Au contacts are not present in the Chloro(tripropylphosphine)gold(1) complex at all [343] . The calculated Au-Au dist ances for the dimers and trimers of [ClAuPH3] are
3 . 1 90 and 3 . 1 46 A, respectively, and resemble the ones of t he [CIAuPMe3] nicely.
The Lrends in geometric data, going from t he monomers to t he trimers, can be sum marized as follows: While t he r p- H bond lengths are rat her const ant at l .43 A in all compounds, t he metal- halide and metal-phosphorus bond lengths, ril/-X and rill- p , in crease slight ly when comparing the monomers of a respective metal complex with its dimers and trimers. Within the halide series, both ril/-X and rM _p increase almost lin early t owards the softest halide. The gold complexes show t he highest tendency towards
linearity for t he L.x _ill _p angle, which decreases slightly going from the h arder halides to the softer ones (see t able (8.2) ) .
The rill-X and ri\I-p bond dist ances within all calculated compounds increase from
copper to silver and decrease from silver to gold (see figures (8. 2 and 8 . 3) ) . ote, t hat
t he rill-X distances are quite similar for t he silver and gold complexes, but the ri\I-p
distances in t he gold complexes are significantly shorter than t hose of the silver com
pounds. This contraction is due to t he large relat ivistic effects at gold [23] and is confirmed
by comparison of relativistic and non-relativistic calculations for these and similar com
pounds [3 1 7 , 339] . Bowmaker et al. give two possible reasons, why the decrease in rM-p
bond lengths is more pronounced than t hat of the ri\I-X bond lengths [339] . The first one
7TMPP [tris(2,4,6)methoxyphenylphosphine] is a strongly sterically hindered phosphine ligand t hat allows for overcoming the preferred tetrahedral four-coordination for copper(I) and silver(I) compounds.
CHA P TER 8. ME TA LL OPHILICITY, THE PER FORMA NCE OF DF T 157
Table 8.2: Opt imized geometric data for [X-M-PH31n [lVI=Cu, Ag, Au and X=Cl, Br, IJ ,
angles in deg and dist ances in A .
Monomers rAl - X rAl _ p rp- f/ LX - Al - p
Iv I =Cu; X=CI 2 . 084 2. 1 4 3 1 . 436 1 80 . 0 Iv I =Cu; X=Br 2 . 2 1 3 2. 1 5 1 1 .436 1 80.0 M =Cu; X=! 2 . 393 2 . 1 6 3 1 . 436 1 80.0 Iv l =Ag; X=CI 2. 283 2 .3 1 2 1 . 434 1 80 . 0 M =Ag; X=Br 2. 405 2.325 1 . 434 1 80 . 0 M =Ag; X = l 2 . 579 2.342 1 . 434 1 80 . 0 I\ I =A u ; X=Cl 2 . 272 2 . 24 2 1 . 434 1 80 . 0 1\ ! = Au; X= Br 2 . 395 2.253 1 . 434 1 80 . 0 Iv I =Au; X=l 2 . 562 2 . 269 1 . 414 1 80 . 0
D i mers" rAl-AI rA/ - X fAl_ P fP- f/ LX -Al-p 1\ 1 =Cll; X=Cl 2 . 6 1 6 2. 100 2 . 1 6 7 1 . 435 1 67 . 2 M =Cu; X=Br 2 . 596 2 . 2 3 1 2 . 1 76 1 . 435 1 66 . 5 M =Cu; X = l 2 . 572 2 . 4 1 2 2. 1 89 1 .435 lti5.4 M =Ag; X=CI 2.970 2 . 297 2.328 1 .434 1 7 1 . 7 M =Ag; X=Br 2 . 952 2 .4 2 1 2.343 1 . 434 1 7 1 . 1 M =Ag; X = l 2 . 940 2 . 588 2 . 362 1 . 434 1 70 . 2 M =A u ; X=CI 3 . 190 2 . 283 2 . 254 1 . 434 1 74 . 3 1\ ! =Au; X=Br 3 . 1 54 2 . 407 2 . 26 5 1 . 434 1 73 . 7 I\ I =Au; X=! 3. 1 24 2 . 574 2 . 283 1 . 434 1 72 . 6
Tr i mersa r hi - hI rA/ - X rA/ - p rp - f/ Lx - A/ - P
Iv I =Cll; X=CI 2 . 634 2 . 1 1 4 2 . 1 76 1 . 435 1 70.3 2 . 6 1 7 M =Cll; X=Br 2 . 607 2 . 249 2 . 1 83 1 . 435 1 68 . 5 2.589 M =Cu; X=I 2 . 578 2. 430 2 . 200 1 . 435 1 66 . 4 2 . 564 !\1 =Ag; X=CI 2.957 2 . 308 2 . 337 1 .434 1 73.2 2.943 M=Ag; X=Br 2.950 2 435 2 . 3fi1 1 .434 1 7 1 . 7 2.920 M =Ag; X = ! 2.943 2. 607 2 . 374 1 . 43 4 1 69.8 2.903 M =Au; X=CI 3 . 1 5 1 2 . 291 2 . 256 1 . 43 4 1 75 . 6 3 . 140 M =A u ; X=Br 3 . 1 27 2 . 4 1 7 2 .269 1 . 434 1 75.0 3 . 1 10 M = A u ; X=I 3. 1 07 2 . 586 2 . 287 1 . 434 1 74 . 4 3.093
CHAPTER 8. METAL L OPHILICITY, THE PERFORMANCE OF DFT