Cu₃(CN)₄(NH₃)₂Hg(CN)₂: a novel inter­penetrating framework formed from Cu^I, Cu^II, Hg^II and cyanide bridges

The title compound, poly[diammine­hexa-[mu]-cyano-di­copper(I)­copper(II)­mercury(II)], [Cu₃Hg(CN)₆(NH₃)₂]_n, has a novel threefold-inter­penetrating structure of three-dimensional frameworks. This three-dimensional framework consists of two-dimensional network Cu₃(CN)₄(NH₃)₂ complexes and rod-like Hg(CN)₂ complexes. The two-dimensional network complex contains trigonal-planar Cu^I (site symmetry m) and octa­hedral Cu^II (site symmetry 2/m) in a 2:1 ratio. Two types of cyanide group form bridges between three coordination sites of Cu^I and two equatorial sites of Cu^II to form a two-dimensional structure with large hexa­gonal windows. One type of CN^- group is disordered across a center of inversion, while the other resides on the mirror plane. Two NH₃ mol­ecules (site symmetry 2) are located in the hexa­gonal windows and coordinate to the remaining equatorial sites of Cu^II. Both N atoms of the rod-like Hg(CN)₂ group (Hg site symmetry 2/m and CN^- site symmetry m) coordinate to the axial sites of Cu^II. This linkage completes the three-dimensional framework and penetrates two hexa­gonal windows of two two-dimensional network complexes to form the threefold-inter­penetrating structure.

S1. Comment

The concept of supramolecular chemistry (Lehn, 1985) stimulated many chemists to create compounds having a multidimensional and interpenetrating structure. These attempts have typically involved the use of coordination bonds between metal ions and bridging ligands (Robson, 1996; Bowes & Ozin, 1996; Iwamoto, 1996a,b; Batten & Robson, 1998; Černák et al., 2002). In this method, an important key is a bridging ligand. Many useful bridging ligands have been developed and used so far. Among those ligands, the classic example cyanide is one of the most simple. Before the birth of supramolecular chemistry, cyanide had been often used as a bridging unit for preparing metal complex compounds with a multi-dimensional framework structure (Iwamoto, 1984, 1991, 1996a,b). Although many structural variations of this type of compound have already been reported, more possibilities undoubtedly remain to be discovered. We present here a new simple compound having a novel interpenetrating framework formed with Cu^I, Cu^II, Hg^II and cyanide bridges.

The crystal structure of the title compound, (I), is a threefold interpenetrating structure of three-dimensional Cu₃(CN)₄(NH₃)₂Hg(CN)₂ frameworks. The three-dimensional framework is formed from a two-dimensional network copper–cyanide complex, Cu₃(CN)₄(NH₃)₂, and a rod-like Hg(CN)₂ group connecting two two-dimensional Cu₃(CN)₄(NH₃)₂ complexes. Figs. 1, 2 and 3 show the two-dimensional Cu₃(CN)₄(NH₃)₂ complex, the rod-like Hg (CN)₂ as a bridging unit and the resulting interpenetrating structure, respectively.

The two-dimensional network complex contains Cu^I and Cu^II in a ratio of 2:1, denoted by Cu1 and Cu2, respectively. Atom Cu1 has a trigonal–planar coordination, with its three coordination sites occupied by cyanide bridges. The cyanide bridges are classified into two groups. One links Cu1 to a crystallographically equivalent Cu1 atom. This cyanide ligand, which is denoted by X1/X1ⁱ here, is in a structurally disordered state because its mid-point sits on an inversion center of the crystal [symmetry code: (i) 1/2 − x, y − 1/2,1 − z]. The Cu1ⁱ—X1ⁱ—X1—Cu1 bridge is repeated along a twofold screw axis parallel to the b axis to form a zigzag Cu1ⁱ—X1ⁱ—X1—Cu—X1ⁱⁱ—X1^iv—Cu^iv linkage [symmetry code: (ii) x, −y, z; (iv) 1/2 − x, y − 1/2, 1 − z]. At the remaining coordination site of Cu1 another cyanide group, C2/N2, is bound by its C atom, while the N atom is coordinated to atom Cu2 to from a Cu1—C2—N2—Cu2 bridge parallel to the [102] direction. Atom Cu2 sits on a 2/m symmetry site, whose twofold rotation axis is parallel to the b axis, so that another C2ⁱⁱⁱ/N2ⁱⁱⁱ cyanide is coordinated at the trans site of Cu2 to form a Cu1—C2—N2—Cu2—N2ⁱⁱⁱ—C2ⁱⁱⁱ—Cu1ⁱⁱⁱ linkage [symmetry code: (iii) 1 − x, −y, −z]. These two kinds of cyanide linkages form the two-dimensional network structure spreading over the (201) plane. The two-dimensional network has hexagonal windows elongated toward the [102] direction. The NH₃ molecules are located in these windows on twofold rotation axes and are coordinated to Cu2 in a trans fashion (Fig. 1).

As shown in Fig. 2, atom Hg1, which sits on a 2/m symmetry site, has a linear coordination geometry to give a rod-like Hg(CN)₂ complex. Both N ends of the Hg(CN)₂ complex are coordinated to the axial sites of Cu2 atoms to form a linkage of {something is missing here} along the [101] direction [symmetry code: (v) 2 − x, y, 1 − z]. This linkage completes the three-dimensional framework structure of this compound. Moreover, the linkage runs through two hexagonal windows of the two two-dimensional Cu₃(CN)₄(NH₃)₂ complexes, which are stacked along the [101] direction. Therefore, the whole crystal structure is a threefold interpenetrating framework, as shown in Fig. 3.

The Cu2—N4 bond length of 2.657 (9) Å is noticeably longer than the other two bond lengths of 1.975 (7) Å for Cu2—N2 and 2.034 (7) Å for Cu2—N3. This large structural deviation from the ideal octahedron comes from the Jahn–Teller effect, which often appears in Cu^II complexes, and our case is within the expected range of 2.11–3.28 Å for Cu^IIN₆-type complexes in a solid phase (Gažo et al., 1976). An example that is close to our case is an elongated Cu^II—N bond length of 2.583 (13) Å found in a Cu^II—N—C—Hg—C—N—Cu^II linkage in the complex [(tmeda)Cu{Hg(CN)₂}₂][HgCl₄] (Draper et al., 2003). The Cu2—N4—C4 bond angle of 125.0 (7)° is also far from the ideal value of 180° for such an M—N—C bond angle. This angular distortion is often observed in analogous compounds. In [(tmeda)Cu[Hg(CN)₂]₂][HgCl₄], 134.6 (7)° was reported for the Cu^II—N—C bond angle at the elongated Cu^II—N bond (Draper et al., 2003). In [Cu(en)₂][Ni(CN)₄], 123.6 (4)° was reported for the corresponding angle (Lokaj et al., 1991). Our case is not far from these examples. However, these geometric parameters and the large displacement parameter of atom N4 suggest that the connection between atoms Cu2 and N4 is considerably weakened. As another view, it might be possible that this compound is a clathrate compound in which the Cu₃(CN)₄(NH₃)₂ host includes Hg(CN)₂ complex guests.

There is astonishing progress in structural development of multidimensional structures of complexes using bridging ligands. In those studies, ligands with a large size and a complicated structure are often used. Such approaches are reasonable and important for creating new structures. However, unknown and interesting topology is still buried even in simple systems. Our compound is a good example.

S2. Experimental

K₂[Hg(CN)₄] (1.8 mmol) and an equimolar amount of CuCN were dissolved in water (25 ml). The solution was poured into a 50 ml vial and the vial was sealed. The air in the vial was not replaced with inert gas. After 17 months, dark-blue crystals of the title compound were found in the solution, whose color was pale blue at that time. Although the details of its formation reaction are unknown, the crystals contained NH₃ and Cu^II ions, which were not added in the solution at the initial stage. The presence of NH₃ was supported by elemental analysis and IR spectrum. That of Cu^II was confirmed from the crystal color and the electric charge balance of the compound. Elemental analysis: found C 12.20, H 1.15, N 19.25%; calculated for C₆H₆Cu₃HgN₈: C 12.40, H 1.04, N 19.27%.

S3. Refinement

X1, which is an atom of the disordered cyanide X1/X1ⁱ, was treated as a hybrid atom of 50% N and 50% C in the structure refinement. H atoms were placed at idealized positions and refined as riding, with N—H distances of 1.01 Å and U_iso(H) = 1.5 U_eq(N3).

Computing details

Data collection: PROCESS-AUTO (Rigaku, 1998); cell refinement: PROCESS-AUTO; data reduction: PROCESS-AUTO; program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: ORTEP-3 for Windows (Farrugia, 1997); software used to prepare material for publication: SHELXL97 and PLATON (Spek, 2003).

Figures

	Fig. 1. The structure of the two-dimensional network Cu3(CN)4(NH3)2 complex in the (201) plane. Displacement ellipsoids are drawn at the 50% probability level. [Symmetry codes: (i) 1/2 − x, 1/2 − y, 1 − z; (ii) x, −y, z; (iii) 1 − x, −y, −z; (iv) 1/2 − x, y − 1/2, 1 − z.]
	Fig. 2. The structure of the —Cu2—N4—C4—Hg1—C4—N4—Cu2— linkage penetrating two two-dimensional network complexes. Displacement ellipsoids are drawn at the 50% probability level. [Symmetry codes: (v) 2 − x, y, 1 − z; (vi) 1/2 + x, y − 1/2, z; (vii) 1/2 + x, 1/2 + y, z; (viii) 1 − x, y, 1 − z; (ix) 3/2 − x, y − 1/2, 1 − z; (x) 3/2 − x, y + 1/2, 1 − z; (xi) 1 + x, y, z.]
	Fig. 3. A view of (I). The two-dimensional network Cu3(CN)4(NH3)2 complexes are stacked along the [101] direction. The —Cu2—N4—C4—Hg1—C4— N4—Cu2— linkage runs along the same direction and penetrates two Cu3(CN)4(NH3)2 complexes to form a threefold interpenetrating structure. Cu and Hg atoms are highlighted with shading.

poly[diamminehexa-µ-cyano-dicopper(I)copper(II)mercury(II)]

Crystal data

[Cu3Hg(CN)6(NH3)2]	F(000) = 530
Mr = 581.40	Dx = 2.814 Mg m^−3
Monoclinic, C2/m	Mo Kα radiation, λ = 0.71075 Å
Hall symbol: -C 2y	Cell parameters from 3838 reflections
a = 8.915 (5) Å	θ = 4.3–30.0°
b = 8.095 (4) Å	µ = 15.73 mm^−1
c = 10.572 (6) Å	T = 153 K
β = 116.00 (2)°	Block, dark blue
V = 685.7 (7) Å^3	0.19 × 0.16 × 0.11 mm
Z = 2

Data collection

Rigaku R-AXIS RAPID imaging-plate diffractometer	1071 independent reflections
Radiation source: fine-focus sealed X-ray tube	1071 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.052
Detector resolution: 10.0 pixels mm^-1	θmax = 30.0°, θmin = 3.6°
ω scans	h = 0→12
Absorption correction: numerical (NUMABS; Higashi, 1999)	k = 0→11
Tmin = 0.088, Tmax = 0.177	l = −14→13
3830 measured reflections

Refinement

Refinement on F^2	Secondary atom site location: difference Fourier map
Least-squares matrix: full	Hydrogen site location: inferred from neighbouring sites
R[F^2 > 2σ(F^2)] = 0.030	H-atom parameters constrained
wR(F^2) = 0.085	w = 1/[σ^2(Fo^2) + (0.0272P)^2 + 0.6087P] where P = (Fo^2 + 2Fc^2)/3
S = 1.12	(Δ/σ)max < 0.001
1071 reflections	Δρmax = 3.21 e Å^−3
55 parameters	Δρmin = −2.02 e Å^−3
0 restraints	Extinction correction: SHELXL97, Fc^*=kFc[1+0.001xFc^2λ^3/sin(2θ)]^-1/4
Primary atom site location: structure-invariant direct methods	Extinction coefficient: 0.0103 (9)

Special details

Geometry. Bond distances, angles etc. have been calculated using the rounded fractional coordinates. All su's are estimated from the variances of the (full) variance-covariance matrix. The cell e.s.d.'s are taken into account in the estimation of distances, angles and torsion angles

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.

X1 is an atom of a disordered cyanide(CN) whose mid-point sits on an inversion center. X1 was treated as an hybrid atom of 50% C and 50% N in the refinement. X11 is a dummy atom for calculating X1 as the hybrid atom.

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

	x	y	z	Uiso*/Ueq	Occ. (<1)
Hg1	1.0000	0.0000	0.5000	0.01986 (17)
Cu1	0.32327 (10)	0.0000	0.39352 (8)	0.0240 (2)
Cu2	0.5000	0.0000	0.0000	0.0236 (2)
X1	0.2688 (6)	0.1954 (6)	0.4734 (5)	0.0264 (8)	0.50
X11	0.2688 (6)	0.1954 (6)	0.4734 (5)	0.0264 (8)	0.50
C2	0.3934 (9)	0.0000	0.2459 (7)	0.0249 (12)
N2	0.4355 (8)	0.0000	0.1565 (6)	0.0292 (12)
N3	0.5000	0.2513 (9)	0.0000	0.0384 (15)
H1	0.6040	0.2929	−0.0051	0.058*	0.50
H2	0.4978	0.2929	0.0892	0.058*	0.50
H3	0.3982	0.2929	−0.0841	0.058*	0.50
C4	0.8857 (8)	0.0000	0.2844 (7)	0.0252 (12)
N4	0.8263 (10)	0.0000	0.1651 (7)	0.0414 (17)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Hg1	0.0184 (2)	0.0222 (2)	0.0185 (2)	0.000	0.00768 (13)	0.000
Cu1	0.0247 (4)	0.0270 (4)	0.0216 (4)	0.000	0.0114 (3)	0.000
Cu2	0.0309 (6)	0.0228 (5)	0.0204 (5)	0.000	0.0143 (4)	0.000
X1	0.0293 (19)	0.0198 (17)	0.036 (2)	−0.0040 (15)	0.0196 (17)	−0.0020 (16)
X11	0.0293 (19)	0.0198 (17)	0.036 (2)	−0.0040 (15)	0.0196 (17)	−0.0020 (16)
C2	0.028 (3)	0.024 (3)	0.026 (3)	0.000	0.014 (2)	0.000
N2	0.034 (3)	0.031 (3)	0.023 (3)	0.000	0.013 (2)	0.000
N3	0.049 (4)	0.030 (3)	0.051 (4)	0.000	0.035 (3)	0.000
C4	0.019 (3)	0.030 (3)	0.022 (3)	0.000	0.006 (2)	0.000
N4	0.044 (4)	0.052 (4)	0.021 (3)	0.000	0.008 (3)	0.000

Geometric parameters (Å, º)

Hg1—C4	2.049 (7)	X1—X1^i	1.172 (9)
Cu1—X1	1.952 (5)	N2—C2	1.160 (10)
Cu1—C2	1.919 (8)	N4—C4	1.134 (9)
Cu2—N2	1.975 (7)	N3—H1	1.01
Cu2—N3	2.034 (7)	N3—H2	1.01
Cu2—N4	2.657 (9)	N3—H3	1.01
Cu1—X1—X1^i	174.8 (6)	N3—Cu2—N4	90.00 (2)
Cu1—C2—N2	179.9 (7)	Hg1—C4—N4	178.3 (8)
X1^ii—Cu1—X1	108.3 (2)	Cu2—N3—H1	109.0
X1—Cu1—C2	125.69 (15)	Cu2—N3—H2	109.0
Cu2—N2—C2	178.3 (7)	Cu2—N3—H3	109.0
Cu2—N4—C4	125.0 (7)	H1—N3—H2	109.0
N2—Cu2—N3	90.00 (2)	H1—N3—H3	109.0
N2—Cu2—N4	95.0 (3)	H2—N3—H3	109.0
N2—Cu2—N4^iii	85.0 (3)

Symmetry codes: (i) −x+1/2, −y+1/2, −z+1; (ii) x, −y, z; (iii) −x+1, −y, −z.