The title compound, [Cu4Cl6O(C5H9N3)3(NH3)], is a neutral conformationally chiral cluster which crystallizes under the conditions described in this paper as a racemic conglomerate. It contains four CuII atoms in a tetrahedral coordination with a central O atom lying on a crystallographic threefold axis. Six chloride anions bridge the four CuII atoms. Three CuII atoms are bound by an N atom of a monodentate 1,4,6-triazabicyclo[3.3.0]oct-4-ene (Htbo) ligand and the remaining CuII atom is bound by a terminal ammine ligand. The geometry at each copper center is trigonal bipyramidal, produced by the bound N atom of Htbo or ammonia, the O atom in the axial position, and three chloride ions in the equatorial plane. The chloride anions form an octahedron about the oxygen center. The copper–ammonia bond lies along the crystallographic threefold axis, along which the molecules are packed in a polar head-to-tail fashion.
Supporting information
CCDC reference: 742165
The Htbo ligand was prepared by the procedure described by Cotton et al.
(2006). A solution of 0.057 g (0.51 mmol) of Htbo in 20 ml of
tetrahydrofuran
(THF) was placed in a 100 ml round-bottomed flask. Solid anhydrous copper(I)
chloride (0.05 g, 0.51 mmol) was added. A condenser was fitted with a fritted
drying tube containing magnesium carbonate and mounted on the reaction flask.
The reaction mixture was refluxed for 48 h. After removing the condenser, the
solution was evaporated to dryness by keeping the flask open and heated. After
cooling, the solid product was extracted with THF and then the remaining solid
was extracted with acetonitrile. The THF solution was layered with ether,
rendering after one week deep-orange block-shaped crystals. The crystal used
for data collection was mounted on a loop with Paratone oil. The THF fraction
gave 0.050 g of product (0.060 mmol), a yield of 47%. The acetonitrile
fraction was layered with ether but gave poor quality crystals of
(µ4-O)(µ2-Cl)6(CuHtbo)4 (structure not reported) in 20% yield. The
remaining solid contained decomposition products.
Since the crystal has a polar space group with a floating origin on c,
SHELXL97 (Sheldrick, 2008) automatically generated the
appropriate
restraint (Flack & Schwarzenbach, 1988). All H atoms were placed in
calculated
positions and refined using a riding model. The C—H disatances were fixed at
0.97 Å and the N—H distances at 0.86–0.89 Å. The Uiso(H)
parameters were fixed at 1.2Ueq(N,C). The H atoms of the ammonia
ligand are related to each other by the threefold axis; their positions were
first established using a local difference map and rotating rigid group
constraint (AFIX 137), and for the final refinement these H atoms were treated
as riding (AFIX 3). Their final positions were checked with an omit map, using
PLATON (Spek, 2009).
Data collection: APEX2 (Bruker–Nonius, 2008); cell refinement: APEX2 (Bruker–Nonius, 2008); data reduction: APEX2 (Bruker–Nonius, 2008); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXS97 (Sheldrick, 2008); molecular graphics: X-SEED (Barbour, 2001); software used to prepare material for publication: SHELXTL (Sheldrick, 2008).
amminehexa-µ
2-chlorido-µ
4-oxido-tris(1,4,6-triazabicyclo[3.3.0]oct-4-
ene)tetracopper(II)
top
Crystal data top
[Cu4Cl6O(C5H9N3)3(NH3)] | Dx = 1.971 Mg m−3 |
Mr = 833.35 | Mo Kα radiation, λ = 0.71073 Å |
Trigonal, R3 | Cell parameters from 2221 reflections |
Hall symbol: R3 | θ = 2.3–25.0° |
a = 17.548 (9) Å | µ = 3.59 mm−1 |
c = 7.898 (4) Å | T = 110 K |
V = 2106.2 (17) Å3 | Block, orange |
Z = 3 | 0.11 × 0.08 × 0.06 mm |
F(000) = 1248 | |
Data collection top
Bruker APEXII diffractometer | 1972 independent reflections |
Radiation source: fine-focus sealed tube | 1772 reflections with I > 2σ(I) |
Graphite monochromator | Rint = 0.061 |
ω scans | θmax = 26.7°, θmin = 2.3° |
Absorption correction: multi-scan (SADABS; Sheldrick, 2006) | h = −21→22 |
Tmin = 0.696, Tmax = 0.811 | k = −21→21 |
6295 measured reflections | l = −9→9 |
Refinement top
Refinement on F2 | Secondary atom site location: difference Fourier map |
Least-squares matrix: full | Hydrogen site location: inferred from neighbouring sites |
R[F2 > 2σ(F2)] = 0.033 | H-atom parameters constrained |
wR(F2) = 0.063 | w = 1/[σ2(Fo2) + (0.0255P)2] where P = (Fo2 + 2Fc2)/3 |
S = 0.94 | (Δ/σ)max < 0.001 |
1972 reflections | Δρmax = 0.42 e Å−3 |
109 parameters | Δρmin = −0.31 e Å−3 |
1 restraint | Absolute structure: Flack (1983), 983 Friedel pairs |
Primary atom site location: structure-invariant direct methods | Absolute structure parameter: −0.019 (19) |
Crystal data top
[Cu4Cl6O(C5H9N3)3(NH3)] | Z = 3 |
Mr = 833.35 | Mo Kα radiation |
Trigonal, R3 | µ = 3.59 mm−1 |
a = 17.548 (9) Å | T = 110 K |
c = 7.898 (4) Å | 0.11 × 0.08 × 0.06 mm |
V = 2106.2 (17) Å3 | |
Data collection top
Bruker APEXII diffractometer | 1972 independent reflections |
Absorption correction: multi-scan (SADABS; Sheldrick, 2006) | 1772 reflections with I > 2σ(I) |
Tmin = 0.696, Tmax = 0.811 | Rint = 0.061 |
6295 measured reflections | |
Refinement top
R[F2 > 2σ(F2)] = 0.033 | H-atom parameters constrained |
wR(F2) = 0.063 | Δρmax = 0.42 e Å−3 |
S = 0.94 | Δρmin = −0.31 e Å−3 |
1972 reflections | Absolute structure: Flack (1983), 983 Friedel pairs |
109 parameters | Absolute structure parameter: −0.019 (19) |
1 restraint | |
Special details top
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 | Uiso*/Ueq | Occ. (<1) |
Cu1 | 0.72127 (3) | 0.26784 (3) | 0.35495 (6) | 0.01685 (14) | |
Cu2 | 0.6667 | 0.3333 | 0.04015 (11) | 0.0178 (2) | |
Cl1 | 0.58657 (7) | 0.17217 (7) | 0.49138 (13) | 0.0202 (2) | |
Cl2 | 0.75559 (8) | 0.26465 (8) | 0.06120 (13) | 0.0223 (3) | |
O1 | 0.6667 | 0.3333 | 0.2827 (6) | 0.0133 (11) | |
N1 | 0.7872 (2) | 0.2140 (2) | 0.4352 (5) | 0.0205 (9) | |
N2 | 0.8474 (3) | 0.1481 (3) | 0.5876 (5) | 0.0217 (9) | |
N3 | 0.7198 (3) | 0.1269 (3) | 0.6852 (5) | 0.0275 (10) | |
H3 | 0.6700 | 0.1251 | 0.6886 | 0.033* | |
N4 | 0.6667 | 0.3333 | −0.2058 (9) | 0.0301 (17) | |
H4A | 0.6356 | 0.3575 | −0.2434 | 0.036* | 0.33333 |
H4B | 0.6427 | 0.2784 | −0.2434 | 0.036* | 0.33333 |
H4C | 0.7217 | 0.3645 | −0.2434 | 0.036* | 0.33333 |
C1 | 0.7794 (3) | 0.1647 (3) | 0.5622 (6) | 0.0192 (10) | |
C2 | 0.8745 (3) | 0.2400 (3) | 0.3603 (6) | 0.0244 (11) | |
H2A | 0.9063 | 0.3024 | 0.3339 | 0.029* | |
H2B | 0.8681 | 0.2070 | 0.2577 | 0.029* | |
C3 | 0.9227 (3) | 0.2181 (3) | 0.4981 (6) | 0.0244 (11) | |
H3A | 0.9599 | 0.1973 | 0.4497 | 0.029* | |
H3B | 0.9577 | 0.2681 | 0.5711 | 0.029* | |
C4 | 0.8473 (3) | 0.1284 (4) | 0.7683 (6) | 0.0296 (12) | |
H4D | 0.8839 | 0.1813 | 0.8332 | 0.035* | |
H4E | 0.8673 | 0.0865 | 0.7866 | 0.035* | |
C5 | 0.7509 (3) | 0.0892 (3) | 0.8126 (6) | 0.0295 (12) | |
H5A | 0.7200 | 0.0255 | 0.8049 | 0.035* | |
H5B | 0.7436 | 0.1061 | 0.9257 | 0.035* | |
Atomic displacement parameters (Å2) top | U11 | U22 | U33 | U12 | U13 | U23 |
Cu1 | 0.0177 (3) | 0.0186 (3) | 0.0170 (3) | 0.0112 (3) | 0.0020 (2) | 0.0030 (2) |
Cu2 | 0.0204 (4) | 0.0204 (4) | 0.0125 (5) | 0.01021 (18) | 0.000 | 0.000 |
Cl1 | 0.0175 (6) | 0.0194 (6) | 0.0221 (6) | 0.0081 (5) | 0.0028 (4) | 0.0062 (5) |
Cl2 | 0.0267 (6) | 0.0278 (7) | 0.0176 (6) | 0.0175 (6) | 0.0027 (5) | −0.0010 (5) |
O1 | 0.0143 (16) | 0.0143 (16) | 0.011 (3) | 0.0071 (8) | 0.000 | 0.000 |
N1 | 0.023 (2) | 0.021 (2) | 0.022 (2) | 0.0147 (19) | 0.0050 (17) | 0.0057 (17) |
N2 | 0.030 (2) | 0.026 (2) | 0.018 (2) | 0.021 (2) | −0.0005 (17) | 0.0023 (17) |
N3 | 0.028 (2) | 0.037 (3) | 0.024 (2) | 0.021 (2) | 0.0066 (17) | 0.0115 (18) |
N4 | 0.033 (3) | 0.033 (3) | 0.024 (4) | 0.0167 (13) | 0.000 | 0.000 |
C1 | 0.026 (3) | 0.017 (3) | 0.019 (2) | 0.014 (2) | 0.000 (2) | −0.0025 (19) |
C2 | 0.029 (3) | 0.025 (3) | 0.027 (3) | 0.020 (2) | 0.005 (2) | 0.006 (2) |
C3 | 0.022 (3) | 0.024 (3) | 0.031 (3) | 0.014 (2) | −0.003 (2) | −0.002 (2) |
C4 | 0.036 (3) | 0.035 (3) | 0.024 (3) | 0.023 (3) | −0.004 (2) | 0.000 (2) |
C5 | 0.041 (3) | 0.029 (3) | 0.025 (3) | 0.022 (3) | 0.003 (2) | 0.004 (2) |
Geometric parameters (Å, º) top
Cu1—O1 | 1.9146 (18) | N3—H3 | 0.8600 |
Cu1—N1 | 1.930 (4) | N4—H4A | 0.8913 |
Cu1—Cl1 | 2.3660 (15) | N4—H4B | 0.8885 |
Cu1—Cl2 | 2.4046 (16) | N4—H4C | 0.8902 |
Cu1—Cl1i | 2.5423 (16) | C2—C3 | 1.540 (6) |
Cu2—O1 | 1.916 (5) | C2—H2A | 0.9700 |
Cu2—N4 | 1.943 (7) | C2—H2B | 0.9700 |
Cu2—Cl2 | 2.4075 (16) | C3—H3A | 0.9700 |
N1—C1 | 1.286 (6) | C3—H3B | 0.9700 |
N1—C2 | 1.486 (6) | C4—C5 | 1.516 (7) |
N2—C1 | 1.377 (6) | C4—H4D | 0.9700 |
N2—C3 | 1.460 (6) | C4—H4E | 0.9700 |
N2—C4 | 1.468 (6) | C5—H5A | 0.9700 |
N3—C1 | 1.336 (6) | C5—H5B | 0.9700 |
N3—C5 | 1.452 (6) | | |
| | | |
O1—Cu1—N1 | 173.71 (13) | Cu2—N4—H4C | 109.5 |
O1—Cu1—Cl1 | 86.53 (8) | H4A—N4—H4C | 109.3 |
N1—Cu1—Cl1 | 97.69 (11) | H4B—N4—H4C | 109.6 |
O1—Cu1—Cl2 | 86.14 (15) | N1—C1—N3 | 134.0 (4) |
N1—Cu1—Cl2 | 95.00 (12) | N1—C1—N2 | 116.4 (4) |
Cl1—Cu1—Cl2 | 126.57 (5) | N3—C1—N2 | 109.5 (4) |
O1—Cu1—Cl1i | 81.65 (8) | N1—C2—C3 | 104.6 (4) |
N1—Cu1—Cl1i | 92.19 (12) | N1—C2—H2A | 110.8 |
Cl1—Cu1—Cl1i | 119.56 (6) | C3—C2—H2A | 110.8 |
Cl2—Cu1—Cl1i | 111.49 (5) | N1—C2—H2B | 110.8 |
O1—Cu2—N4 | 180.000 (1) | C3—C2—H2B | 110.8 |
O1—Cu2—Cl2 | 86.04 (3) | H2A—C2—H2B | 108.9 |
N4—Cu2—Cl2 | 93.96 (3) | N2—C3—C2 | 100.0 (4) |
Cl2—Cu2—Cl2i | 119.528 (8) | N2—C3—H3A | 111.8 |
Cu1—Cl1—Cu1ii | 80.23 (4) | C2—C3—H3A | 111.8 |
Cu1—Cl2—Cu2 | 79.77 (4) | N2—C3—H3B | 111.8 |
Cu1—O1—Cu1i | 111.51 (14) | C2—C3—H3B | 111.8 |
Cu1—O1—Cu2 | 107.34 (15) | H3A—C3—H3B | 109.5 |
C1—N1—C2 | 105.3 (4) | N2—C4—C5 | 101.6 (4) |
C1—N1—Cu1 | 134.2 (3) | N2—C4—H4D | 111.5 |
C2—N1—Cu1 | 119.8 (3) | C5—C4—H4D | 111.5 |
C1—N2—C3 | 105.5 (3) | N2—C4—H4E | 111.5 |
C1—N2—C4 | 107.0 (4) | C5—C4—H4E | 111.5 |
C3—N2—C4 | 124.2 (4) | H4D—C4—H4E | 109.3 |
C1—N3—C5 | 110.6 (4) | N3—C5—C4 | 102.8 (4) |
C1—N3—H3 | 124.7 | N3—C5—H5A | 111.2 |
C5—N3—H3 | 124.7 | C4—C5—H5A | 111.2 |
Cu2—N4—H4A | 109.4 | N3—C5—H5B | 111.2 |
Cu2—N4—H4B | 109.5 | C4—C5—H5B | 111.2 |
H4A—N4—H4B | 109.5 | H5A—C5—H5B | 109.1 |
| | | |
O1—Cu1—Cl1—Cu1ii | 1.77 (13) | Cl2ii—Cu2—O1—Cu1ii | −7.24 (3) |
N1—Cu1—Cl1—Cu1ii | 177.07 (12) | Cl2i—Cu2—O1—Cu1ii | 112.76 (3) |
Cl2—Cu1—Cl1—Cu1ii | −80.82 (6) | Cl1—Cu1—N1—C1 | −22.1 (5) |
Cl1i—Cu1—Cl1—Cu1ii | 80.14 (5) | Cl2—Cu1—N1—C1 | −150.1 (5) |
O1—Cu1—Cl2—Cu2 | −5.58 (3) | Cl1i—Cu1—N1—C1 | 98.1 (5) |
N1—Cu1—Cl2—Cu2 | −179.38 (11) | Cl1—Cu1—N1—C2 | 169.0 (3) |
Cl1—Cu1—Cl2—Cu2 | 77.20 (5) | Cl2—Cu1—N1—C2 | 41.0 (3) |
Cl1i—Cu1—Cl2—Cu2 | −85.04 (4) | Cl1i—Cu1—N1—C2 | −70.8 (3) |
O1—Cu2—Cl2—Cu1 | 5.58 (3) | C2—N1—C1—N3 | 174.2 (5) |
N4—Cu2—Cl2—Cu1 | −174.42 (3) | Cu1—N1—C1—N3 | 4.2 (9) |
Cl2ii—Cu2—Cl2—Cu1 | −77.60 (6) | C2—N1—C1—N2 | −2.3 (6) |
Cl2i—Cu2—Cl2—Cu1 | 88.76 (6) | Cu1—N1—C1—N2 | −172.3 (3) |
Cl1—Cu1—O1—Cu1i | 122.9 (2) | C5—N3—C1—N1 | −170.8 (5) |
Cl2—Cu1—O1—Cu1i | −110.1 (2) | C5—N3—C1—N2 | 5.9 (5) |
Cl1i—Cu1—O1—Cu1i | 2.34 (18) | C3—N2—C1—N1 | 20.5 (6) |
Cl1—Cu1—O1—Cu1ii | −2.49 (19) | C4—N2—C1—N1 | 154.5 (4) |
Cl2—Cu1—O1—Cu1ii | 124.55 (19) | C3—N2—C1—N3 | −156.9 (4) |
Cl1i—Cu1—O1—Cu1ii | −123.0 (2) | C4—N2—C1—N3 | −22.8 (5) |
Cl1—Cu1—O1—Cu2 | −119.80 (3) | C1—N1—C2—C3 | −15.7 (5) |
Cl2—Cu1—O1—Cu2 | 7.24 (3) | Cu1—N1—C2—C3 | 156.0 (3) |
Cl1i—Cu1—O1—Cu2 | 119.64 (4) | C1—N2—C3—C2 | −27.2 (5) |
Cl2—Cu2—O1—Cu1 | −7.24 (3) | C4—N2—C3—C2 | −151.0 (4) |
Cl2ii—Cu2—O1—Cu1 | 112.76 (3) | N1—C2—C3—N2 | 26.1 (5) |
Cl2i—Cu2—O1—Cu1 | −127.24 (3) | C1—N2—C4—C5 | 29.1 (5) |
Cl2—Cu2—O1—Cu1i | 112.76 (3) | C3—N2—C4—C5 | 152.2 (4) |
Cl2ii—Cu2—O1—Cu1i | −127.24 (3) | C1—N3—C5—C4 | 12.6 (5) |
Cl2i—Cu2—O1—Cu1i | −7.24 (3) | N2—C4—C5—N3 | −24.5 (5) |
Cl2—Cu2—O1—Cu1ii | −127.24 (3) | | |
Symmetry codes: (i) −y+1, x−y, z; (ii) −x+y+1, −x+1, z. |
Hydrogen-bond geometry (Å, º) top
D—H···A | D—H | H···A | D···A | D—H···A |
N3—H3···Cl1 | 0.86 | 2.54 | 3.210 (4) | 135 |
N4—H4B···Cl1iii | 0.89 | 2.64 | 3.423 (5) | 147 |
Symmetry code: (iii) x, y, z−1. |
Experimental details
Crystal data |
Chemical formula | [Cu4Cl6O(C5H9N3)3(NH3)] |
Mr | 833.35 |
Crystal system, space group | Trigonal, R3 |
Temperature (K) | 110 |
a, c (Å) | 17.548 (9), 7.898 (4) |
V (Å3) | 2106.2 (17) |
Z | 3 |
Radiation type | Mo Kα |
µ (mm−1) | 3.59 |
Crystal size (mm) | 0.11 × 0.08 × 0.06 |
|
Data collection |
Diffractometer | Bruker APEXII diffractometer |
Absorption correction | Multi-scan (SADABS; Sheldrick, 2006) |
Tmin, Tmax | 0.696, 0.811 |
No. of measured, independent and observed [I > 2σ(I)] reflections | 6295, 1972, 1772 |
Rint | 0.061 |
(sin θ/λ)max (Å−1) | 0.632 |
|
Refinement |
R[F2 > 2σ(F2)], wR(F2), S | 0.033, 0.063, 0.94 |
No. of reflections | 1972 |
No. of parameters | 109 |
No. of restraints | 1 |
H-atom treatment | H-atom parameters constrained |
Δρmax, Δρmin (e Å−3) | 0.42, −0.31 |
Absolute structure | Flack (1983), 983 Friedel pairs |
Absolute structure parameter | −0.019 (19) |
Selected geometric parameters (Å, º) topCu1—O1 | 1.9146 (18) | Cu1—Cl1i | 2.5423 (16) |
Cu1—N1 | 1.930 (4) | Cu2—O1 | 1.916 (5) |
Cu1—Cl1 | 2.3660 (15) | Cu2—N4 | 1.943 (7) |
Cu1—Cl2 | 2.4046 (16) | Cu2—Cl2 | 2.4075 (16) |
| | | |
Cl1—Cu1—Cl2 | 126.57 (5) | Cl2—Cu1—Cl1i | 111.49 (5) |
Cl1—Cu1—Cl1i | 119.56 (6) | Cl2—Cu2—Cl2i | 119.528 (8) |
Symmetry code: (i) −y+1, x−y, z. |
Hydrogen-bond geometry (Å, º) top
D—H···A | D—H | H···A | D···A | D—H···A |
N3—H3···Cl1 | 0.86 | 2.54 | 3.210 (4) | 135.3 |
N4—H4B···Cl1ii | 0.89 | 2.64 | 3.423 (5) | 146.8 |
Symmetry code: (ii) x, y, z−1. |
Table 1. Comparison of C—N distances and the N1—C1—N3 angle in isolated
Htbo and in Htbo acting as bridging and terminal ligands topCompound Ref. | C1—N1 (Å) | C1—N3 (Å) | C1—N2 (Å) | N1—C1—N3 (°) |
Neutral ligand alone | | | | |
Htbob | 1.2971 (18) | 1.3455 (18) | 1.3914 (16) | 132.44 (13) |
| | | | |
Bridging ligand | | | | |
Mo2(tbo)4b | 1.318 (5) | 1.322 (4) | 1.394 (4) | 128.0 (3) |
| 1.328 (4) | 1.314 (5) | 1.393 (4) | 128.0 (3) |
Mo2 (tbo)4Cl2b | 1.315 (4) | 1.312 (4) | 1.374 (4) | 128.0 (3) |
| 1.313 (4) | 1.310 (4) | 1.386 (4) | 127.7 (3) |
| | | | |
Terminal ligand | | | | |
{[Li(tbo)(VIII)(tboH)]2}∞c | 1.286 (3) | 1.344 (3) | 1.381 (2) | 132.40 (18) |
Li6(tbo)6(Htbo)3c | 1.291 (3) | 1.340 (3) | 1.388 (3) | 132.49 (19) |
| 1.276 (3) | 1.342 (3) | 1.438 (4) | 133.6 (2) |
| 1.308 (2)a | 1.337 (2) | 1.370 (2) | 132.37 (17) |
This work | 1.286 (6) | 1.336 (6) | 1.377 (6) | 134.0 (4) |
Note: (a) Nitrogen bridges two Li atoms.
References: (b) Cotton et al. (2006);
(c) Khalaf et al. (2008). |
Clusters with four copper(II) atoms arranged tetrahedrally around oxygen(II) have been studied for several years for their magnetic properties in materials science (Atria et al., 1999; Reim et al., 1995; Dickinson et al., 1977), as well as in bioinorganic chemistry (El-Sayed et al., 1992) and in anticorrosion studies (Skorda et al., 2005). They have been reported to be good catalysts in the oxidation of aromatic compounds and in some biological systems (Sun et al., 2004; Weinberger et al., 1998).
Other non-bridging ligands may be attached to copper(II), such as halides (Jackson et al., 1996; Belford et al., 1972; Fu & Chivers, 2007; Harlow Simonsen, 1977), oxygen-bonded ligands (Churchill & Rotella, 1979; Bertrand & Kelley, 1966), nicotine (Haendler, 1990), oxoamines (Weinberger et al., 1998), pyridine (Näther & Jeß, 2002; Gill & Sterns, 1970; Duncan et al., 1996; Kilbourn & Dunitz, 1967), imidazole (Zhang et al., 2003; Norman et al., 1989; Erdonmez et al., 1990; Clegg et al., 1988; Cortés et al., 2006), pyrazole (Keij et al., 1991; Liu et al., 2003), triazole (Skorda et al., 2005), tetrazole (Lyakhov et al., 2004), azaindole (Poitras & Beauchamp, 1992), phosphine (Bertrand, 1967), thiazole (Bolos & Christidis, 2002), sulfimide (Kelly et al., 1999), phosphite (Churchill et al., 1975) or sulfoxide (Brownstein et al., 1989; Guy et al., 1988).
We report here an example of an oxo-centered cluster with guanidinate (1,4,6-triazabicyclo[3.3.0]oct-4-ene; Htbo) and ammonia ligands. Although guanidinates are commonly found as deprotonated (anionic) bidentate ligands, in this cluster Htbo behaves as a terminal neutral ligand (see scheme). Only two other reported compounds have this terminal ligand feature (Khalaf et al., 2008), both with the metal lithium. This is the first structure in which a transition metal atom is coordinated by a terminal Htbo ligand. Table 3 presents the C—N distances and N—C—N angles for Htbo in the present compound, in neutral, unligated Htbo, and in previously reported bridging and terminal Htbo ligands.
When Htbo is a terminal ligand there is a significant difference between the C1—N1 and C1—N3 bond lengths. This difference has been interpreted as localization of the electron density from the double bond over the non-protonated N1 (Khalaf et al., 2008). The bond angle N1—C1—N3 is also noticeably larger for terminal Htbo, similar to the angle found in the free ligand.
In the cluster reported here, three copper(II) ions are bound by as many terminal Htbo ligands, with the fourth Cu atom bonded to ammonia. The result is a conformationally chiral compound which crystallizes in space group R3 (Fig. 1). This can be contrasted with the formation of racemic crystals, which contain equal numbers of both enantiomers in the same unit cell and usually crystallize in a centrosymmetric group (Li et al., 2008). Since the preparation and crystallization of this compound involve no factor that would favor one conformational chirality sense, and since our refinement gave a clear indication of the absolute structure, we conclude that the bulk sample is a racemic conglomerate (Flack & Bernardinelli, 1999).
The structure contains intramolecular non-covalent interactions that could be described as hydrogen bonds. The contact N3—H3···Cl1 (Table 2) stabilizes the tilt of the Htbo ligand, which is ultimately responsible for the conformational chirality of the molecule. There are no intermolecular hydrogen bonds, but there are some short contacts between H atoms and chloride anions (Table 2; vide infra).
The central oxo atom has a slightly distorted tetrahedral coordination geometry [with unique Cu—O—Cu angles 111.51 (14) and 107.34 (15)°]. The three Cl—Cu2—Cl angles, identical by symmetry, reveal only the slightest distortion from ideality in the equatorial plane of the trigonal–bipyramidal coordination about this metal (Table 1). The Cl—Cu—Cl angles at Cu1, however, reveal a degree of distortion. The Cu1—Cl distances also present significant differences (Table 1), varying over a range of about 0.18 Å. The unique Cu2—Cl2 distance is within the range presented by the Cu1—Cl distances. The Cu1 units are positioned out of the Cl2/Cl1/Cl1i plane by 0.216 Å toward the Htbo ligand [symmetry code: (i) -y + 1, x - y, z], while atom Cu2 is 0.166 Å out of the (Cl2)3 plane toward the ammonia ligand.
The space group R3 not only accommodates an enantiopure molecular conformation, but being polar also hosts a purely head-to-tail packing arrangement (Fig. 2). All of the Cu2→N4 vectors point toward the negative c direction (the polar axis direction is established by the absolute structure parameter). Three very well defined intermolecular N—H··· Cl interactions, from the three symmetry related N—H bonds of the ammonia ligand to the three Cl1 congeners of the molecule at (x, y, z - 1), mediate the polar organization of the structure. Thus, both the chirality and the polarity of space group R3 play a role in enabling important features of this structure.