Luminescence properties and optimized structural conformations of the S₀, S₁ and T₁ states of a tetra­nuclear formamidinate complex based on Au^I and Ag^I metal ions

N,N′-Bis­(pyridin-4-yl)formamidine (4-pyfH) was reacted with Au^I and Ag^I metal salts to form a novel tetra­nuclear complex, tetra­kis­[μ-N,N′-bis­(pyridin-4-yl)formamidinato]digold(I)disilver(I), [Ag₂Au₂(C₁₁H₉N₄)₂] or [Au_xAg_4–x(4-pyf)₄] (x = 0–4), 1, which is supported by its metallophilicity. Due to the potential permutation of the coordinated metal ions, six different canonical structures of 1 can be obtained. Complex 1 shows an emission at 501 nm upon excitation at 375 nm in the solid state and an emission at 438 nm upon excitation at 304 nm when dispersed in methanol. Time-dependent density functional theory (TD-DFT) calculations confirmed that these emissions can be ascribed to metal-to-ligand charge transfer (MLCT) processes. Moreover, the calculations of the optimized structural conformations of the S₀ ground state, and the S₁ and T₁ excited states are discussed and suggest a distorted planar conformation for the tetra­nuclear Au₂Ag₂ complex.

Computing details

Data collection: APEX2 (Bruker, 2008); cell refinement: SAINT (Bruker, 2008); data reduction: SAINT (Bruker, 2008); program(s) used to solve structure: olex2.solve (Bourhis et al., 2015); program(s) used to refine structure: SHELXL2018 (Sheldrick, 2015); molecular graphics: OLEX2 (Dolomanov et al., 2009); software used to prepare material for publication: OLEX2 (Dolomanov et al., 2009).

Tetrakis[µ-N,N'-bis(pyridin-4-yl)formamidinato]digold(I)disilver(I)

Crystal data

[AgAu(C11H9N4)2]	Dx = 1.876 Mg m^−3
Mr = 699.28	Mo Kα radiation, λ = 0.71073 Å
Tetragonal, P4n2	Cell parameters from 9407 reflections
a = 16.5350 (4) Å	θ = 2.9–28.3°
c = 18.1127 (4) Å	µ = 6.73 mm^−1
V = 4952.1 (3) Å^3	T = 296 K
Z = 8	Plate, colourless
F(000) = 2656	0.35 × 0.25 × 0.2 mm

Data collection

Bruker APEXII CCD diffractometer	4918 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.049
φ and ω scans	θmax = 28.3°, θmin = 1.7°
Absorption correction: multi-scan (SADABS; Bruker, 2008)	h = −16→21
Tmin = 0.385, Tmax = 0.746	k = −22→21
23337 measured reflections	l = −24→23
5627 independent reflections

Refinement

Refinement on F^2	Hydrogen site location: inferred from neighbouring sites
Least-squares matrix: full	H-atom parameters constrained
R[F^2 > 2σ(F^2)] = 0.032	w = 1/[σ^2(Fo^2) + (0.0347P)^2 + 5.3324P] where P = (Fo^2 + 2Fc^2)/3
wR(F^2) = 0.080	(Δ/σ)max < 0.001
S = 1.05	Δρmax = 1.22 e Å^−3
5627 reflections	Δρmin = −0.76 e Å^−3
299 parameters	Absolute structure: Flack x determined using 1780 quotients [(I+)-(I-)]/[(I+)+(I-)] (Parsons et al., 2013)
0 restraints	Absolute structure parameter: −0.070 (14)
Primary atom site location: iterative

Special details

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

Refinement. The diffraction data of this complex was collected on a Bruker SMART APEXII diffractometer equipped with a graphite-monochromatic Mo Kα (λ_α = 0.71073 Å) radiation at 296.15 K. Data reduction carried by standard methods with use of well-established computational procedures (Bruker & SHELXTL V6.14; Sheldrick, 2008). The structure factors were obtained after Lorentz and polarization correction.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Ų)

	x	y	z	Uiso*/Ueq	Occ. (<1)
Au1	0.3983 (2)	0.4864 (3)	0.24374 (17)	0.0202 (7)	0.5
Au2	0.500000	0.500000	0.37619 (3)	0.01540 (15)	0.5
Au3	0.500000	0.500000	0.11049 (3)	0.01605 (16)	0.5
Ag1	0.3991 (4)	0.4910 (5)	0.2442 (2)	0.0098 (10)	0.5
Ag2	0.500000	0.500000	0.37619 (3)	0.01540 (15)	0.5
Ag3	0.500000	0.500000	0.11049 (3)	0.01605 (16)	0.5
N1	0.2597 (9)	0.7481 (8)	0.3844 (6)	0.082 (4)
N2	0.3841 (5)	0.6071 (5)	0.2241 (4)	0.037 (2)
N3	0.4581 (6)	0.6156 (5)	0.1116 (4)	0.035 (2)
N4	0.5262 (8)	0.7869 (7)	−0.0518 (7)	0.061 (3)
N5	0.2953 (9)	0.2021 (6)	0.1164 (5)	0.066 (3)
N6	0.4058 (5)	0.3680 (5)	0.2659 (5)	0.037 (2)
N7	0.4811 (5)	0.3776 (5)	0.3785 (5)	0.034 (2)
N8	0.5755 (8)	0.2375 (6)	0.5546 (7)	0.063 (3)
C1	0.2402 (11)	0.6697 (10)	0.3687 (10)	0.100 (7)
H1	0.197200	0.646704	0.394262	0.120*
C2	0.2800 (9)	0.6221 (8)	0.3171 (9)	0.078 (5)
H2	0.263822	0.568785	0.309901	0.093*
C3	0.3433 (7)	0.6532 (7)	0.2765 (7)	0.051 (3)
C4	0.3689 (8)	0.7351 (8)	0.2945 (6)	0.050 (3)
H4	0.412216	0.759669	0.270723	0.060*
C5	0.3242 (9)	0.7751 (8)	0.3500 (7)	0.061 (4)
H5	0.342498	0.826086	0.363770	0.073*
C6	0.4131 (7)	0.6464 (6)	0.1658 (6)	0.036 (2)
H6	0.400631	0.701102	0.162478	0.044*
C7	0.5748 (9)	0.7292 (8)	−0.0293 (8)	0.063 (4)
H7	0.626603	0.728107	−0.049169	0.075*
C8	0.5551 (7)	0.6690 (7)	0.0224 (6)	0.043 (3)
H8	0.592408	0.629170	0.035005	0.051*
C9	0.4761 (8)	0.6703 (8)	0.0554 (6)	0.037 (3)
C10	0.4234 (8)	0.7308 (7)	0.0302 (6)	0.045 (3)
H10	0.370778	0.732982	0.048301	0.054*
C11	0.4487 (9)	0.7877 (8)	−0.0215 (7)	0.047 (3)
H11	0.412627	0.827633	−0.036408	0.057*
C12	0.2673 (9)	0.2792 (8)	0.1298 (8)	0.072 (5)
H12	0.220664	0.294951	0.104969	0.087*
C13	0.3025 (8)	0.3359 (9)	0.1773 (7)	0.062 (4)
H13	0.279966	0.387029	0.183072	0.074*
C14	0.3720 (7)	0.3138 (7)	0.2156 (6)	0.041 (3)
C15	0.4068 (7)	0.2360 (7)	0.2012 (6)	0.042 (3)
H15	0.454340	0.220553	0.224675	0.050*
C16	0.3690 (9)	0.1838 (8)	0.1520 (7)	0.059 (4)
H16	0.393541	0.134369	0.141969	0.071*
C17	0.4425 (6)	0.3366 (7)	0.3256 (6)	0.037 (3)
H17	0.440952	0.280653	0.330536	0.044*
C18	0.5081 (8)	0.2154 (9)	0.5179 (7)	0.048 (4)
H18	0.483215	0.167427	0.532046	0.057*
C19	0.4734 (7)	0.2584 (7)	0.4612 (6)	0.040 (3)
H19	0.426165	0.239928	0.439004	0.048*
C20	0.5088 (7)	0.3286 (8)	0.4378 (7)	0.034 (3)
C21	0.5815 (8)	0.3526 (7)	0.4742 (6)	0.048 (3)
H21	0.608530	0.399481	0.460039	0.057*
C22	0.6108 (9)	0.3055 (8)	0.5303 (7)	0.060 (4)
H22	0.658488	0.321707	0.553144	0.072*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Au1	0.0131 (12)	0.0101 (8)	0.0372 (13)	0.0016 (7)	0.0029 (10)	0.0014 (10)
Au2	0.0128 (4)	0.0094 (4)	0.0241 (3)	−0.0002 (3)	0.000	0.000
Au3	0.0133 (5)	0.0102 (4)	0.0246 (3)	0.0027 (3)	0.000	0.000
Ag1	0.010 (2)	0.0118 (19)	0.0072 (15)	0.0004 (14)	−0.0050 (14)	0.0039 (15)
Ag2	0.0128 (4)	0.0094 (4)	0.0241 (3)	−0.0002 (3)	0.000	0.000
Ag3	0.0133 (5)	0.0102 (4)	0.0246 (3)	0.0027 (3)	0.000	0.000
N1	0.121 (14)	0.043 (8)	0.080 (8)	0.021 (7)	0.059 (8)	0.003 (6)
N2	0.030 (5)	0.038 (5)	0.044 (5)	0.002 (4)	0.005 (4)	0.000 (4)
N3	0.041 (6)	0.032 (5)	0.031 (4)	0.008 (4)	0.004 (4)	0.003 (4)
N4	0.062 (8)	0.037 (7)	0.084 (9)	0.001 (6)	0.007 (7)	0.016 (6)
N5	0.123 (13)	0.015 (6)	0.061 (7)	−0.016 (5)	−0.037 (7)	−0.001 (5)
N6	0.035 (4)	0.025 (4)	0.051 (6)	−0.003 (3)	−0.013 (4)	0.007 (4)
N7	0.027 (5)	0.031 (5)	0.044 (5)	0.001 (4)	−0.010 (4)	−0.005 (4)
N8	0.083 (10)	0.032 (6)	0.073 (8)	−0.012 (6)	−0.028 (7)	0.002 (6)
C1	0.096 (14)	0.062 (11)	0.141 (16)	0.037 (9)	0.077 (12)	0.022 (11)
C2	0.066 (10)	0.040 (8)	0.127 (14)	0.013 (7)	0.054 (10)	0.009 (8)
C3	0.052 (7)	0.036 (7)	0.065 (8)	0.024 (5)	0.008 (6)	0.008 (6)
C4	0.049 (8)	0.060 (9)	0.041 (6)	0.026 (6)	−0.004 (6)	−0.005 (6)
C5	0.080 (11)	0.057 (9)	0.046 (7)	0.039 (7)	−0.008 (7)	−0.006 (6)
C6	0.038 (6)	0.028 (6)	0.044 (6)	0.005 (5)	−0.004 (5)	0.005 (5)
C7	0.073 (10)	0.036 (7)	0.078 (10)	0.006 (7)	0.026 (8)	0.010 (7)
C8	0.038 (7)	0.038 (7)	0.052 (7)	0.008 (5)	0.009 (5)	0.003 (5)
C9	0.039 (8)	0.028 (7)	0.042 (6)	0.006 (5)	0.001 (5)	−0.007 (5)
C10	0.042 (7)	0.037 (7)	0.057 (8)	0.004 (5)	0.005 (6)	0.000 (6)
C11	0.052 (9)	0.030 (7)	0.060 (8)	0.010 (6)	−0.008 (6)	0.006 (6)
C12	0.081 (11)	0.044 (8)	0.092 (10)	−0.019 (7)	−0.050 (9)	0.004 (8)
C13	0.059 (9)	0.049 (8)	0.078 (10)	−0.014 (7)	−0.033 (7)	0.004 (7)
C14	0.036 (6)	0.037 (6)	0.050 (7)	−0.010 (5)	−0.008 (5)	−0.007 (5)
C15	0.036 (6)	0.041 (7)	0.049 (7)	−0.008 (5)	−0.003 (5)	−0.002 (5)
C16	0.072 (10)	0.049 (8)	0.058 (8)	−0.010 (7)	0.006 (7)	−0.004 (6)
C17	0.030 (6)	0.034 (6)	0.048 (7)	−0.003 (4)	0.001 (5)	0.001 (5)
C18	0.042 (8)	0.043 (8)	0.057 (8)	0.006 (6)	−0.002 (6)	0.012 (6)
C19	0.041 (7)	0.034 (7)	0.045 (6)	−0.007 (5)	−0.002 (5)	−0.001 (5)
C20	0.031 (7)	0.025 (7)	0.046 (6)	−0.001 (5)	0.003 (5)	−0.003 (5)
C21	0.058 (9)	0.030 (6)	0.055 (7)	−0.008 (6)	−0.019 (6)	0.004 (5)
C22	0.074 (10)	0.047 (8)	0.058 (8)	0.005 (7)	−0.019 (7)	−0.005 (7)

Geometric parameters (Å, º)

Au1—Au2	2.938 (3)	C1—C2	1.388 (18)
Au1—Au3	2.950 (4)	C2—H2	0.9300
Au1—N2	2.041 (9)	C2—C3	1.379 (17)
Au1—N6	2.001 (9)	C3—C4	1.455 (17)
Au2—N7	2.048 (9)	C4—H4	0.9300
Au2—N7^i	2.048 (9)	C4—C5	1.413 (16)
Au3—N3	2.033 (8)	C5—H5	0.9300
Au3—N3^i	2.033 (8)	C6—H6	0.9300
Ag1—Ag2	2.920 (5)	C7—H7	0.9300
Ag1—Ag3	2.944 (6)	C7—C8	1.405 (16)
Ag1—N2	1.969 (11)	C8—H8	0.9300
Ag1—N6	2.074 (11)	C8—C9	1.437 (16)
Ag2—N7^i	2.048 (9)	C9—C10	1.405 (16)
Ag2—N7	2.048 (9)	C10—H10	0.9300
Ag3—N3	2.033 (8)	C10—C11	1.391 (16)
Ag3—N3^i	2.033 (8)	C11—H11	0.9300
N1—C1	1.37 (2)	C12—H12	0.9300
N1—C5	1.313 (17)	C12—C13	1.399 (16)
N2—C3	1.393 (13)	C13—H13	0.9300
N2—C6	1.329 (12)	C13—C14	1.391 (16)
N3—C6	1.334 (12)	C14—C15	1.433 (16)
N3—C9	1.393 (15)	C15—H15	0.9300
N4—C7	1.312 (16)	C15—C16	1.389 (16)
N4—C11	1.394 (18)	C16—H16	0.9300
N5—C12	1.377 (16)	C17—H17	0.9300
N5—C16	1.412 (17)	C18—H18	0.9300
N6—C14	1.396 (12)	C18—C19	1.375 (17)
N6—C17	1.345 (12)	C19—H19	0.9300
N7—C17	1.336 (12)	C19—C20	1.368 (17)
N7—C20	1.420 (15)	C20—C21	1.428 (16)
N8—C18	1.348 (16)	C21—H21	0.9300
N8—C22	1.340 (17)	C21—C22	1.370 (16)
C1—H1	0.9300	C22—H22	0.9300
Au2—Au1—Au3	109.63 (13)	N2—C3—C4	121.4 (11)
N2—Au1—Au2	97.7 (3)	C2—C3—N2	121.8 (12)
N2—Au1—Au3	81.3 (3)	C2—C3—C4	116.7 (11)
N6—Au1—Au2	82.9 (3)	C3—C4—H4	121.9
N6—Au1—Au3	101.7 (3)	C5—C4—C3	116.3 (13)
N6—Au1—N2	176.6 (4)	C5—C4—H4	121.9
Au1^i—Au2—Au1	70.54 (15)	N1—C5—C4	127.1 (14)
N7^i—Au2—Au1^i	81.6 (3)	N1—C5—H5	116.4
N7—Au2—Au1^i	100.4 (3)	C4—C5—H5	116.4
N7—Au2—Au1	81.6 (3)	N2—C6—N3	126.9 (10)
N7^i—Au2—Au1	100.4 (3)	N2—C6—H6	116.6
N7^i—Au2—N7	177.7 (5)	N3—C6—H6	116.6
Au1—Au3—Au1^i	70.21 (14)	N4—C7—H7	117.2
N3—Au3—Au1	82.5 (2)	N4—C7—C8	125.5 (14)
N3—Au3—Au1^i	96.6 (3)	C8—C7—H7	117.2
N3^i—Au3—Au1^i	82.5 (2)	C7—C8—H8	120.8
N3^i—Au3—Au1	96.6 (3)	C7—C8—C9	118.5 (12)
N3—Au3—N3^i	178.9 (4)	C9—C8—H8	120.8
Ag2—Ag1—Ag3	110.3 (2)	N3—C9—C8	119.2 (11)
N2—Ag1—Ag2	100.0 (4)	N3—C9—C10	124.6 (11)
N2—Ag1—Ag3	82.5 (3)	C10—C9—C8	116.1 (11)
N2—Ag1—N6	175.8 (5)	C9—C10—H10	119.5
N6—Ag1—Ag2	82.2 (3)	C11—C10—C9	120.9 (12)
N6—Ag1—Ag3	100.1 (3)	C11—C10—H10	119.5
N7—Ag2—Ag1	83.1 (3)	N4—C11—H11	118.8
N7^i—Ag2—Ag1	98.9 (3)	C10—C11—N4	122.4 (12)
N7^i—Ag2—N7	177.7 (5)	C10—C11—H11	118.8
N3—Ag3—Ag1	81.2 (3)	N5—C12—H12	117.0
N3^i—Ag3—Ag1	97.9 (3)	N5—C12—C13	126.1 (13)
N3—Ag3—N3^i	178.9 (4)	C13—C12—H12	117.0
C5—N1—C1	114.5 (12)	C12—C13—H13	120.8
C3—N2—Au1	118.2 (7)	C14—C13—C12	118.3 (13)
C3—N2—Ag1	117.9 (7)	C14—C13—H13	120.8
C6—N2—Au1	125.1 (7)	N6—C14—C15	122.3 (10)
C6—N2—Ag1	125.3 (7)	C13—C14—N6	119.2 (10)
C6—N2—C3	116.7 (9)	C13—C14—C15	118.4 (10)
C6—N3—Au3	123.8 (7)	C14—C15—H15	120.2
C6—N3—Ag3	123.8 (7)	C16—C15—C14	119.6 (11)
C6—N3—C9	114.1 (9)	C16—C15—H15	120.2
C9—N3—Au3	122.1 (7)	N5—C16—H16	118.4
C9—N3—Ag3	122.1 (7)	C15—C16—N5	123.2 (12)
C7—N4—C11	116.6 (12)	C15—C16—H16	118.4
C12—N5—C16	114.1 (10)	N6—C17—H17	116.7
C14—N6—Au1	118.2 (7)	N7—C17—N6	126.6 (10)
C14—N6—Ag1	119.0 (7)	N7—C17—H17	116.7
C17—N6—Au1	124.5 (7)	N8—C18—H18	117.5
C17—N6—Ag1	123.8 (7)	N8—C18—C19	125.0 (13)
C17—N6—C14	117.3 (8)	C19—C18—H18	117.5
C17—N7—Au2	124.0 (7)	C18—C19—H19	120.3
C17—N7—Ag2	124.0 (7)	C20—C19—C18	119.5 (12)
C17—N7—C20	114.0 (9)	C20—C19—H19	120.3
C20—N7—Au2	122.0 (7)	N7—C20—C21	117.5 (11)
C20—N7—Ag2	122.0 (7)	C19—C20—N7	125.5 (11)
C22—N8—C18	115.1 (12)	C19—C20—C21	116.9 (11)
N1—C1—H1	117.7	C20—C21—H21	120.6
N1—C1—C2	124.6 (15)	C22—C21—C20	118.8 (12)
C2—C1—H1	117.7	C22—C21—H21	120.6
C1—C2—H2	119.8	N8—C22—C21	124.6 (13)
C3—C2—C1	120.5 (14)	N8—C22—H22	117.7
C3—C2—H2	119.8	C21—C22—H22	117.7

Symmetry code: (i) −x+1, −y+1, z.