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

Kaska, W.C.; Mayer, H.A.; Elsegood, M.R.J.; Horton, P.N.; Hursthouse, M.B.; Redshaw, C.; Humphrey, S.M.

doi:10.1107/S1600536804008098

metal-organic compounds

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Volume 60| Part 5| May 2004| Pages m563-m565

https://doi.org/10.1107/S1600536804008098

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

William C. Kaska,^a Hermann A. Mayer,^b Mark R. J. Elsegood,^c Peter N. Horton,^d Michael B. Hursthouse,^d Carl Redshaw ^e and Simon M. Humphrey ^f ^*

^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: smh49@cam.ac.uk

(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.

Comment

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 , 2000 ; Mathieson et al., 2000 ). 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 ) (see scheme). The substitution reaction of [LAuCl], whereby chloride is replaced with iodide, has yielded (I), whose structure shows clear evidence for aurophilic effects directing the appearance of its extended structure.

Compound (I) 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). 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). 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). 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).

A perfectly linear infinite chain of gold atoms is thus formed, aligned parallel to the crystallographic a axis (Fig. 2). 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). A network of classical (van der Waals) intermolecular interactions is formed primarily between methyl H atoms and adjacent I⁻ atoms (Fig. 3).

Figure 1
Part of the polymeric structure of (I

), 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
View of (I

), showing the chains of aurophilically bound gold centres running parallel to the crystallographic a axis. Aurophilic type bonds are drawn in red.

Figure 3
Projection of (I

) on the bc plane, detailing the approximately orthogonal arrangement of the iodide and isocyanoborane substituents.

Experimental

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 ).

Crystal data

[Au(C₄H₁₁BN₂)₂][AuI₂]
M_r = 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
D_x = 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 ) T_min = 0.267, T_max = 0.689
7106 measured reflections
2174 independent reflections
2033 reflections with I > 2σ(I)
R_int = 0.066
θ_max = 27.5°
h = −7 → 7
k = −12 → 12
l = −12 → 12

Refinement

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(F_o²) + (0.0926P)²] where P = (F_o² + 2F_c²)/3
(Δ/σ)_max < 0.001
Δρ_max = 6.24 e Å⁻³
Δρ_min = −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. U_iso values were set to 1.2U_eq of the parent atom for BH (1.5U_eq 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 ) and COLLECT (Nonius, 1998 ); cell refinement: DENZO and COLLECT; data reduction: DENZO and COLLECT; program(s) used to solve structure: SHELXS97 (Sheldrick, 1997 ); program(s) used to refine structure: SHELXTL (Sheldrick, 1997); molecular graphics: DIAMOND (Crystal Impact, 2001 ); software used to prepare material for publication: PLATON (Spek, 2003 ).

Supporting information

Crystal structure: contains datablocks I, global. DOI: https://doi.org/10.1107/S1600536804008098/hb6029sup1.cif

Structure factors: contains datablock I. DOI: https://doi.org/10.1107/S1600536804008098/hb6029Isup2.hkl

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
M_r = 421.82	F(000) = 372
Triclinic, P1	D_x = 2.927 Mg m⁻³
Hall symbol: -P 1	Melting point: 417-419 K K
a = 6.0875 (1) Å	Mo Kα radiation, λ = 0.71073 Å
b = 9.3080 (2) Å	Cell parameters from 2009 reflections
c = 9.6876 (2) Å	θ = 2.9–27.5°
α = 115.970 (1)°	µ = 18.52 mm⁻¹
β = 91.039 (1)°	T = 120 K
γ = 102.127 (2)°	Shard, light green
V = 478.68 (2) Å³	0.10 × 0.06 × 0.02 mm

Data collection top

Nonius KappaCCD area-detector diffractometer	2174 independent reflections
Radiation source: Nonius FR591 rotating anode	2033 reflections with I > 2σ(I)
Graphite monochromator	R_int = 0.066
Detector resolution: 9.091 pixels mm^-1	θ_max = 27.5°, θ_min = 3.5°
φ and ω scans to fill Ewald Sphere	h = −7→7
Absorption correction: multi-scan (SORTAV; Blessing, 1997)	k = −12→12
T_min = 0.267, T_max = 0.689	l = −12→12
7106 measured reflections

Refinement top

Refinement on F²	Primary atom site location: structure-invariant direct methods
Least-squares matrix: full	Secondary atom site location: difference Fourier map
R[F² > 2σ(F²)] = 0.049	Hydrogen site location: inferred from neighbouring sites
wR(F²) = 0.125	H-atom parameters constrained
S = 1.06	w = 1/[σ²(F_o²) + (0.0926P)²] where P = (F_o² + 2F_c²)/3
2174 reflections	(Δ/σ)_max < 0.001
88 parameters	Δρ_max = 6.24 e Å⁻³
0 restraints	Δρ_min = −4.28 e Å⁻³

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

	x	y	z	U_iso*/U_eq
Au1	0.0000	0.0000	0.5000	0.02402 (17)
Au2	−0.5000	0.0000	0.5000	0.02413 (17)
I1	−0.01262 (8)	−0.04700 (6)	0.21874 (5)	0.03220 (19)
N2	−0.3642 (10)	−0.6158 (7)	0.1986 (7)	0.0241 (12)
C1	−0.5406 (12)	−0.2415 (10)	0.3899 (9)	0.0281 (15)
C4	−0.4108 (14)	−0.8005 (9)	0.1236 (10)	0.0313 (16)
H4A	−0.2715	−0.8344	0.0892	0.047*
H4B	−0.5274	−0.8471	0.0343	0.047*
H4C	−0.4638	−0.8403	0.1984	0.047*
C2	−0.1955 (14)	−0.5474 (12)	0.3387 (10)	0.0372 (18)
H2A	−0.0579	−0.5864	0.3091	0.056*
H2B	−0.2595	−0.5840	0.4133	0.056*
H2C	−0.1581	−0.4268	0.3858	0.056*
C3	−0.2679 (15)	−0.5580 (11)	0.0871 (10)	0.0359 (18)
H3A	−0.2440	−0.4381	0.1321	0.054*
H3B	−0.3732	−0.6101	−0.0087	0.054*
H3C	−0.1229	−0.5876	0.0641	0.054*
N1	−0.5586 (10)	−0.3820 (7)	0.3243 (7)	0.0245 (12)
B1	−0.5989 (14)	−0.5722 (9)	0.2423 (10)	0.0257 (16)
H1A	−0.7086	−0.6197	0.1477	0.031*
H1B	−0.6613	−0.6184	0.3119	0.031*

Atomic displacement parameters (Å²) top

	U¹¹	U²²	U³³	U¹²	U¹³	U²³
Au1	0.0190 (3)	0.0229 (3)	0.0262 (3)	0.00771 (17)	0.00457 (17)	0.00637 (19)
Au2	0.0205 (3)	0.0164 (2)	0.0295 (3)	0.00851 (17)	0.00569 (17)	0.00314 (18)
I1	0.0319 (3)	0.0359 (3)	0.0273 (3)	0.0120 (2)	0.0062 (2)	0.0113 (2)
N2	0.022 (3)	0.024 (3)	0.028 (3)	0.013 (2)	0.008 (2)	0.010 (2)
C1	0.018 (3)	0.034 (4)	0.029 (4)	0.010 (3)	0.006 (3)	0.010 (3)
C4	0.036 (4)	0.018 (3)	0.039 (4)	0.017 (3)	0.011 (3)	0.007 (3)
C2	0.025 (4)	0.047 (5)	0.034 (4)	0.016 (3)	0.005 (3)	0.010 (3)
C3	0.040 (5)	0.037 (4)	0.038 (4)	0.019 (4)	0.016 (4)	0.019 (4)
N1	0.019 (3)	0.019 (3)	0.029 (3)	0.009 (2)	0.007 (2)	0.003 (2)
B1	0.020 (4)	0.016 (3)	0.032 (4)	0.008 (3)	0.009 (3)	0.002 (3)

Geometric parameters (Å, º) top

Au1—I1	2.5604 (5)	C4—H4A	0.9800
Au1—I1ⁱ	2.5604 (5)	C4—H4B	0.9800
Au1—Au2	3.0438 (1)	C4—H4C	0.9800
Au1—Au2ⁱⁱ	3.0438 (1)	C2—H2A	0.9800
Au2—C1	1.977 (8)	C2—H2B	0.9800
Au2—C1ⁱⁱⁱ	1.977 (8)	C2—H2C	0.9800
Au2—Au1^iv	3.0438 (1)	C3—H3A	0.9800
N2—C3	1.484 (10)	C3—H3B	0.9800
N2—C2	1.490 (10)	C3—H3C	0.9800
N2—C4	1.502 (9)	N1—B1	1.550 (9)
N2—B1	1.581 (9)	B1—H1A	0.9900
C1—N1	1.156 (10)	B1—H1B	0.9900

I1—Au1—I1ⁱ	180	N2—C4—H4C	109.5
I1—Au1—Au2	91.443 (11)	H4A—C4—H4C	109.5
I1ⁱ—Au1—Au2	88.557 (11)	H4B—C4—H4C	109.5
I1—Au1—Au2ⁱⁱ	88.557 (11)	N2—C2—H2A	109.5
I1ⁱ—Au1—Au2ⁱⁱ	91.443 (11)	N2—C2—H2B	109.5
Au2—Au1—Au2ⁱⁱ	180	H2A—C2—H2B	109.5
C1—Au2—C1ⁱⁱⁱ	180	N2—C2—H2C	109.5
C1—Au2—Au1	82.9 (2)	H2A—C2—H2C	109.5
C1ⁱⁱⁱ—Au2—Au1	97.1 (2)	H2B—C2—H2C	109.5
C1—Au2—Au1^iv	97.1 (2)	N2—C3—H3A	109.5
C1ⁱⁱⁱ—Au2—Au1^iv	82.9 (2)	N2—C3—H3B	109.5
Au1—Au2—Au1^iv	180	H3A—C3—H3B	109.5
C3—N2—C2	109.3 (7)	N2—C3—H3C	109.5
C3—N2—C4	108.4 (6)	H3A—C3—H3C	109.5
C2—N2—C4	108.7 (6)	H3B—C3—H3C	109.5
C3—N2—B1	112.7 (6)	C1—N1—B1	175.7 (7)
C2—N2—B1	111.5 (6)	N1—B1—N2	108.2 (6)
C4—N2—B1	106.2 (6)	N1—B1—H1A	110.1
N1—C1—Au2	178.1 (7)	N2—B1—H1A	110.1
N2—C4—H4A	109.5	N1—B1—H1B	110.1
N2—C4—H4B	109.5	N2—B1—H1B	110.1
H4A—C4—H4B	109.5	H1A—B1—H1B	108.4

Symmetry codes: (i) −x, −y, −z+1; (ii) x+1, y, z; (iii) −x−1, −y, −z+1; (iv) x−1, y, z.

Acknowledgements

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

References

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