metal-organic compounds\(\def\hfill{\hskip 5em}\def\hfil{\hskip 3em}\def\eqno#1{\hfil {#1}}\)

ISSN: 2056-9890

[{(H3C)3NB(H)2NC}2Au][AuI2]: a linear chain polymer of gold(I) iodide with an unusual iso­cyano­borane ligand showing aurophilic behaviour


aDepartment of Chemistry and Biochemistry, University of California, Santa Barbara, CA 93106-9510, USA, bUniversität Tübingen, Institut für Anorganische Chemie, Auf der Morgenstelle 18, D-72076 Tübingen, Germany, cChemistry Department, Loughborough University, Loughborough, Leicestershire LE11 3TU, England, dSchool of Chemistry, University of Southampton, Southampton SO17 1BJ, England, eWolfson Materials and Catalysis Centre, School of Chemical Sciences and Pharmacy, University of East Anglia, Norwich NR4 7TJ, England, and fUniversity Chemical Laboratory, University of Cambridge, Lensfield Road, Cambridge CB2 1EW, England
*Correspondence e-mail:

(Received 29 March 2004; accepted 2 April 2004; online 17 April 2004)

Treatment of the (iso­cyano­borane)gold(I) chloride adduct [LAuCl] [L = (H3C)3NB(H)2NC] with KI at room temperature yields the unusal title compound, bis­[iso­cyano­(tri­methyl­amino)­borane]­gold(I) di­iodoaurate(I), [Au(C4H11BN2)2][AuI2], which forms via an in situ rearrangement of iso­cyano­borane and halide ligands. The structure consists of alternating [L2Au]+ and [AuI2] ions, which form an infinite linear one-dimensional chain due to aurophilic Au⋯Au interactions. Both Au atoms occupy inversion centres.


We have recently been interested in the formation of (isocyanide)gold(I) halide adducts, because of their propensity to interact aurophilically. The term aurophilicity is used to describe observed Au⋯Au interactions. These intermolecular contacts have been shown to have bond energies and distances similar to those observed for classical hydrogen-bonding interactions (7.5–12.5 kcal mol−1 and 2.7–3.5 Å, respectively) (Schmidbaur, 1990[Schmidbaur, H. (1990). Gold Bull. 23, 11-21.], 2000[Schmidbaur, H. (2000). Gold Bull. 33, 3-9.]; Mathieson et al., 2000[Mathieson, T., Schier, A. & Schmidbaur, H. (2000). J. Chem. Soc. Dalton Trans. pp. 3881-3884.]). Hence, aurophilic behaviour is considered to be a major factor in determining the particular supramolecular motif which a series of monomers is observed to adopt. Our recent synthetic studies have involved the use of an unusual zwitterionic iso­cyano­borane species (L) (Andersen et al., 2001[Andersen, W. C., Mitchell, D. R., Young, K. J. H., Bu, X., Lynch, V. M., Mayer, H. A. & Kaska, W. C. (1999). Inorg. Chem. 38, 1024-1027.]) (see scheme). The substitution reaction of [LAuCl], whereby chloride is replaced with iodide, has yielded (I[link]), whose structure shows clear evidence for aurophilic effects directing the appearance of its extended structure.[link]

[Scheme 1]

Compound (I[link]) crystallizes in the triclinic space group P[\overline 1] (Z = 2). The asymmetric unit comprises one equivalent of the iso­cyano­borane donor species and a single iodide, each coord­inated to crystallographically distinct gold cations Au1 and Au2, both of which are located on inversion centres (Fig. 1[link]). Both Au1 and Au2 exhibit pseudo-square-planar coordination geometry, with bonding angles of 91.443 (11) (I1—Au1⋯Au2) and 97.1 (2)° (C1—Au2⋯Au1i; symmetry code as in Table 1[link]). Au1 is trans-coordinated by two equivalents of iodide; Au2 is also trans-coordinated, by isocyanide moieties. The coordination of each gold ion is completed by Au⋯Au contacts with adjacent Au centres, where Au1⋯Au2 is a mere 3.0438 (7) Å, suggesting that significant aurophilic character is present in (I[link]). Literature values for observed Au⋯Au contact distances suggest an approximate range of 4.1 Å (as often associated with the inter–dimer bonding in chains of dimers) to 2.9 Å for complexes similar in topology to (I[link]).

A perfectly linear infinite chain of gold atoms is thus formed, aligned parallel to the crystallographic a axis (Fig. 2[link]). It can be seen that adjacent chains are displaced from each other along the b axis, thus forming a two-dimensional grid-like array of sheets. The B1—N1—C1 angle is 175.7 (7)°, this portion of the coordinated iso­cyano­borane being almost linear. Adjacent iodide and isocyanide substituents are aligned approximately orthogonally to one another (Fig. 3[link]). A network of classical (van der Waals) intermolecular interactions is formed primarily between methyl H atoms and adjacent I atoms (Fig. 3[link]).

[Figure 1]
Figure 1
Part of the polymeric structure of (I[link]), showing two asymmetric units and two additional Au atoms, with displacement ellipsoids drawn at the 50% probability level. Coordination environments of all unique atoms are drawn completed. [Symmetry codes: (i) −x, −y, 1 − z; (ii) 1 + x, y, z; (iii) −1 − x, −y, 1 − z.]
[Figure 2]
Figure 2
View of (I[link]), showing the chains of aurophilically bound gold centres running parallel to the crystallographic a axis. Aurophilic type bonds are drawn in red.
[Figure 3]
Figure 3
Projection of (I[link]) on the bc plane, detailing the approximately orthogonal arrangement of the iodide and iso­cyano­borane substituents.


A solution of [LAuCl] (42 mg, 0.202 mmol) in di­chloro­methane (10 ml) was stirred vigorously with KI (51 mg, 0.307 mmol) in H2O (10 ml) over a period of 18 h. After removal of all solvent, the yellow–green residual solid was dissolved in di­chloro­methane (5 ml). Small light green shard-like crystals of (I) were grown from the solution by layering with heptane (1:1) and allowing slow evaporation of the solvent. For full experimental details and characterization data, see Humphrey et al. (2004[Humphrey, S. M., Mack, H. G., Redshaw, C., Elsegood, M. R. J., Young, K. J. H., Mayer, H. A. & Kaska, W. C. (2004). Chem. Eur. J. In preparation.]).

Crystal data
  • [Au(C4H11BN2)2][AuI2]

  • Mr = 421.82

  • Triclinic, [P\overline 1]

  • a = 6.0875 (1) Å

  • b = 9.3080 (2) Å

  • c = 9.6876 (2) Å

  • α = 115.970 (1)°

  • β = 91.039 (1)°

  • γ = 102.127 (2)°

  • V = 478.680 (16) Å3

  • Z = 2

  • Dx = 2.927 Mg m−3

  • Mo Kα radiation

  • Cell parameters from 2009 reflections

  • θ = 2.9–27.5°

  • μ = 18.52 mm−1

  • T = 120 (2) K

  • Shard, light green

  • 0.10 × 0.06 × 0.02 mm

Data collection
  • Nonius KappaCCD area-detector diffractometer

  • φ and ω scans

  • Absorption correction: multi-scan (SORTAV; Blessing, 1995[Blessing, R. H. (1995). Acta Cryst. A51, 33-38.]) Tmin = 0.267, Tmax = 0.689

  • 7106 measured reflections

  • 2174 independent reflections

  • 2033 reflections with I > 2σ(I)

  • Rint = 0.066

  • θmax = 27.5°

  • h = −7 → 7

  • k = −12 → 12

  • l = −12 → 12

  • Refinement on F2

  • R[F2 > 2σ(F2)] = 0.049

  • wR(F2) = 0.125

  • S = 1.06

  • 2174 reflections

  • 88 parameters

  • H-atom parameters constrained

  • w = 1/[σ2(Fo2) + (0.0926P)2] where P = (Fo2 + 2Fc2)/3

  • (Δ/σ)max < 0.001

  • Δρmax = 6.24 e Å−3

  • Δρmin = −4.28 e Å−3

Table 1
Selected geometric parameters (Å, °)

Au1—I1 2.5604 (5)
Au1⋯Au2 3.0438 (1)
Au2—C1 1.977 (8)
C1—N1 1.156 (10)
N1—B1 1.550 (9)
I1—Au1—I1i 180
I1—Au1⋯Au2 91.443 (11)
I1i—Au1⋯Au2 88.557 (11)
Au2⋯Au1⋯Au2ii 180
C1—Au2—C1iii 180
C1—Au2⋯Au1 82.9 (2)
C1iii—Au2⋯Au1 97.1 (2)
N1—C1—Au2 178.1 (7)
C1—N1—B1 175.7 (7)
N1—B1—N2 108.2 (6)
Symmetry codes: (i) -x,-y,1-z; (ii) 1+x,y,z; (iii) -1-x,-y,1-z.

Methyl H (C—H distance = 0.98 Å) and BH2 (B—H distance = 0.99 Å) atoms were placed in calculated positions using a riding model. Uiso values were set to 1.2Ueq of the parent atom for BH (1.5Ueq for methyl H). The maximum and minimum difference map features were located 0.94 Å from Au1 and 0.81 Å from Au2, respectively.

Data collection: DENZO (Otwinowski & Minor, 1997[Otwinowski, Z. & Minor, W. (1997). Methods in Enzymology, Vol. 276, Macromolecular Crystallography, Part A, edited by C. W. Carter Jr and R. M. Sweet, pp. 307-326. New York: Academic Press.]) and COLLECT (Nonius, 1998[Nonius (1998). COLLECT. Nonius BV, Delft, The Netherlands.]); cell refinement: DENZO and COLLECT; data reduction: DENZO and COLLECT; program(s) used to solve structure: SHELXS97 (Sheldrick, 1997[Sheldrick, G. M. (1997). SHELXTL. Version 6.10. Bruker AXS Inc., Madison, Wisconsin, USA.]); program(s) used to refine structure: SHELXTL (Sheldrick, 1997[Sheldrick, G. M. (1997). SHELXTL. Version 6.10. Bruker AXS Inc., Madison, Wisconsin, USA.]); molecular graphics: DIAMOND (Crystal Impact, 2001[Crystal Impact (2001). DIAMOND. Crystal Impact GbR, Bonn, Germany.]); software used to prepare material for publication: PLATON (Spek, 2003[Spek, A. L. (2003). J. Appl. Cryst. 36, 7-13.]).

Supporting information

Computing details top

Data collection: DENZO (Otwinowski and Minor, 1997); cell refinement: DENZO and COLLECT (Hooft, 1998); data reduction: DENZO and COLLECT; program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: PLATON (Spek, 1990); software used to prepare material for publication: DIAMOND (Crystal Impact, 2001).

(I) top
Crystal data top
[Au(C4H11BN2)2][AuI2]Z = 2
Mr = 421.82F(000) = 372
Triclinic, P1Dx = 2.927 Mg m3
Hall symbol: -P 1Melting point: 417-419 K K
a = 6.0875 (1) ÅMo Kα radiation, λ = 0.71073 Å
b = 9.3080 (2) ÅCell parameters from 2009 reflections
c = 9.6876 (2) Åθ = 2.9–27.5°
α = 115.970 (1)°µ = 18.52 mm1
β = 91.039 (1)°T = 120 K
γ = 102.127 (2)°Shard, light green
V = 478.68 (2) Å30.10 × 0.06 × 0.02 mm
Data collection top
Nonius KappaCCD area-detector
2174 independent reflections
Radiation source: Nonius FR591 rotating anode2033 reflections with I > 2σ(I)
Graphite monochromatorRint = 0.066
Detector resolution: 9.091 pixels mm-1θmax = 27.5°, θmin = 3.5°
φ and ω scans to fill Ewald Sphereh = 77
Absorption correction: multi-scan
(SORTAV; Blessing, 1997)
k = 1212
Tmin = 0.267, Tmax = 0.689l = 1212
7106 measured reflections
Refinement top
Refinement on F2Primary atom site location: structure-invariant direct methods
Least-squares matrix: fullSecondary atom site location: difference Fourier map
R[F2 > 2σ(F2)] = 0.049Hydrogen site location: inferred from neighbouring sites
wR(F2) = 0.125H-atom parameters constrained
S = 1.06 w = 1/[σ2(Fo2) + (0.0926P)2]
where P = (Fo2 + 2Fc2)/3
2174 reflections(Δ/σ)max < 0.001
88 parametersΔρmax = 6.24 e Å3
0 restraintsΔρmin = 4.28 e Å3
Special details top

Experimental. PLEASE NOTE cell_measurement_ fields are not relevant to area detector data, the entire data set is used to refine the cell, which is indexed from all observed reflections in a 10 degree phi range.

Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s. planes.

Refinement. Refinement of F2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F2, conventional R-factors R are based on F, with F set to zero for negative F2. The threshold expression of F2 > σ(F2) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F2 are statistically about twice as large as those based on F, and R- factors based on ALL data will be even larger.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2) top
Au10.00000.00000.50000.02402 (17)
Au20.50000.00000.50000.02413 (17)
I10.01262 (8)0.04700 (6)0.21874 (5)0.03220 (19)
N20.3642 (10)0.6158 (7)0.1986 (7)0.0241 (12)
C10.5406 (12)0.2415 (10)0.3899 (9)0.0281 (15)
C40.4108 (14)0.8005 (9)0.1236 (10)0.0313 (16)
C20.1955 (14)0.5474 (12)0.3387 (10)0.0372 (18)
C30.2679 (15)0.5580 (11)0.0871 (10)0.0359 (18)
N10.5586 (10)0.3820 (7)0.3243 (7)0.0245 (12)
B10.5989 (14)0.5722 (9)0.2423 (10)0.0257 (16)
Atomic displacement parameters (Å2) top
Au10.0190 (3)0.0229 (3)0.0262 (3)0.00771 (17)0.00457 (17)0.00637 (19)
Au20.0205 (3)0.0164 (2)0.0295 (3)0.00851 (17)0.00569 (17)0.00314 (18)
I10.0319 (3)0.0359 (3)0.0273 (3)0.0120 (2)0.0062 (2)0.0113 (2)
N20.022 (3)0.024 (3)0.028 (3)0.013 (2)0.008 (2)0.010 (2)
C10.018 (3)0.034 (4)0.029 (4)0.010 (3)0.006 (3)0.010 (3)
C40.036 (4)0.018 (3)0.039 (4)0.017 (3)0.011 (3)0.007 (3)
C20.025 (4)0.047 (5)0.034 (4)0.016 (3)0.005 (3)0.010 (3)
C30.040 (5)0.037 (4)0.038 (4)0.019 (4)0.016 (4)0.019 (4)
N10.019 (3)0.019 (3)0.029 (3)0.009 (2)0.007 (2)0.003 (2)
B10.020 (4)0.016 (3)0.032 (4)0.008 (3)0.009 (3)0.002 (3)
Geometric parameters (Å, º) top
Au1—I12.5604 (5)C4—H4A0.9800
Au1—I1i2.5604 (5)C4—H4B0.9800
Au1—Au23.0438 (1)C4—H4C0.9800
Au1—Au2ii3.0438 (1)C2—H2A0.9800
Au2—C11.977 (8)C2—H2B0.9800
Au2—C1iii1.977 (8)C2—H2C0.9800
Au2—Au1iv3.0438 (1)C3—H3A0.9800
N2—C31.484 (10)C3—H3B0.9800
N2—C21.490 (10)C3—H3C0.9800
N2—C41.502 (9)N1—B11.550 (9)
N2—B11.581 (9)B1—H1A0.9900
C1—N11.156 (10)B1—H1B0.9900
I1—Au1—Au291.443 (11)H4A—C4—H4C109.5
I1i—Au1—Au288.557 (11)H4B—C4—H4C109.5
I1—Au1—Au2ii88.557 (11)N2—C2—H2A109.5
I1i—Au1—Au2ii91.443 (11)N2—C2—H2B109.5
C1—Au2—Au182.9 (2)H2A—C2—H2C109.5
C1iii—Au2—Au197.1 (2)H2B—C2—H2C109.5
C1—Au2—Au1iv97.1 (2)N2—C3—H3A109.5
C1iii—Au2—Au1iv82.9 (2)N2—C3—H3B109.5
C3—N2—C2109.3 (7)N2—C3—H3C109.5
C3—N2—C4108.4 (6)H3A—C3—H3C109.5
C2—N2—C4108.7 (6)H3B—C3—H3C109.5
C3—N2—B1112.7 (6)C1—N1—B1175.7 (7)
C2—N2—B1111.5 (6)N1—B1—N2108.2 (6)
C4—N2—B1106.2 (6)N1—B1—H1A110.1
N1—C1—Au2178.1 (7)N2—B1—H1A110.1
Symmetry codes: (i) x, y, z+1; (ii) x+1, y, z; (iii) x1, y, z+1; (iv) x1, y, z.


We thank the University of East Anglia and EPSRC for funding (SMH and CR).


First citationAndersen, W. C., Mitchell, D. R., Young, K. J. H., Bu, X., Lynch, V. M., Mayer, H. A. & Kaska, W. C. (1999). Inorg. Chem. 38, 1024–1027.  Web of Science CSD CrossRef PubMed CAS Google Scholar
First citationBlessing, R. H. (1995). Acta Cryst. A51, 33–38.  CrossRef CAS Web of Science IUCr Journals Google Scholar
First citationCrystal Impact (2001). DIAMOND. Crystal Impact GbR, Bonn, Germany.  Google Scholar
First citationHumphrey, S. M., Mack, H. G., Redshaw, C., Elsegood, M. R. J., Young, K. J. H., Mayer, H. A. & Kaska, W. C. (2004). Chem. Eur. J. In preparation.  Google Scholar
First citationMathieson, T., Schier, A. & Schmidbaur, H. (2000). J. Chem. Soc. Dalton Trans. pp. 3881–3884.  Web of Science CSD CrossRef Google Scholar
First citationNonius (1998). COLLECT. Nonius BV, Delft, The Netherlands.  Google Scholar
First citationOtwinowski, Z. & Minor, W. (1997). Methods in Enzymology, Vol. 276, Macromolecular Crystallography, Part A, edited by C. W. Carter Jr and R. M. Sweet, pp. 307–326. New York: Academic Press.  Google Scholar
First citationSchmidbaur, H. (1990). Gold Bull. 23, 11–21.  CrossRef CAS Google Scholar
First citationSchmidbaur, H. (2000). Gold Bull. 33, 3–9.  CrossRef CAS Google Scholar
First citationSheldrick, G. M. (1997). SHELXTL. Version 6.10. Bruker AXS Inc., Madison, Wisconsin, USA.  Google Scholar
First citationSpek, A. L. (2003). J. Appl. Cryst. 36, 7–13.  Web of Science CrossRef CAS IUCr Journals Google Scholar

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