Structural and spectropscopic studies of a three-dimensional hydrogen-bonded copper(II) complex: aqua­[bis­(pyridin-2-ylcarbon­yl)amidato]­cyanido­copper(II)

The preparation and X-ray and spectroscopic studies of the title copper(II) complex, [Cu(C₁₂H₈N₃O₂)(CN)(H₂O)], are reported. The Cu^II cation is five-coordinated, forming a distorted square-planar pyramid with an Addison τ parameter of 0.14. The UV–vis spectrum shows a d–d transition of the Cu^II centre at 638 nm, and the electron paramagnetic resonance (EPR) spectrum confirms that the Cu^II cation has an axial symmetry coordination and that the unpaired electrons occupy the d_x²–y² orbital. Cyclic voltammetric studies show two irreversible oxidation and reduction peaks.

S1. Introduction

In recent years, the design and synthesis of copper complexes have attracted increasing attention for their fascinating structural diversities and potential applications in many fields, such as metal-ion drugs, protein–metal binding sites and magnetic-exchange models (Duraisamy et al., 2011; Dey et al., 2002). For metal–organic hybrid complexes, non-covalent inter­actions, including classical hydrogen bonds and π–π stacking, may play an important role in the construction of intriguing topologies (Ramírez de Arellano et al., 2013; Bianketti et al., 2009). [Bis(2-aryl­carbonyl)­amido]­copper(II) species, [Cu(bpca)]⁺, can be exploited as building blocks for self-assembly, with bpca acting as a tridentate ligand towards the Cu^II cation through its amidate and two pyridyl N atoms (Casellas et al., 2005; Cangussu et al., 2005). For example, mono- and polynuclear bpca-containing copper(II) complexes have been obtained and reported, such as [Cu(bpca)(X)] (X = Cl, Br or CH₃COO) and [Cu₂(bpca)₂(L)(H₂O)₂] (L = oxalate, succinate or other bridging ligands). Among those complexes, hydrogen-bonding and π–π stacking inter­actions play important roles in the design of their supra­molecular structures (Simões et al., 2013; Calatayud et al., 2000; Xu et al., 2013).

S2. Experimental

CHN elemental analyses were carried out with a Perkin–Elmer analyser, model 240. Electronic spectra were recorded with a Shimadzu UV-2101PC spectrophotometer in the 200–2000 nm range at room temperature. The FT–IR spectra were recorded with KBr pellets in the range 4000–400cm^-1 with a Bio-Rad FTS 135 spectrometer.

S2.1. Synthesis and crystallization

[Cu(bpca)(H₂O)(NO₃)]·H₂O and K₂[Ni(CN)₄] were synthesized according to the literature methods of Folgado et al. (1989) and Cao (1988). An aqueous solution (10 ml) of [Cu(bpca)(H₂O)(NO₃)]·H₂O (0.4 mmol) was added to one arm of an H-tube and an aqueous solution (10 ml) of K₂[Ni(CN)₄] (0.1 mmol) was added to the other arm. Propan-2-ol was added to the top of the tube as the diffusing agent. Deep-blue single crystals of (I) suitable for X-ray diffraction were obtained after one month by slow diffusion. Elemental analysis, calculated for C₁₃H₁₀CuN₄O₃: C 57.91, H 3.61, N 20.60%; found: C 57.78, H 3.73, N 20.73%. IR (KBr disc, ν, cm^-1): 3428 (s), 1702 (m), 2171 (s).

S2.2. Refinement

Crystal data, data collection and structure refinement details are summarized in Table 1. All H atoms were placed in geometrically idealized positions, with C—H = 0.93 Å for aromatic H atoms. Water H atoms were located in a difference Fourier map, and were refined with an O—H distance restraint of 0.85 (1) Å and an H···H distance restraint of 1.39 (1) Å, and with additional contraints U_iso(H) = 1.5U_eq(O).

S3. Results and discussion

The molecular structure of [Cu(CN)(bpca)(H₂O)], (I), is shown in Fig. 1 and selected bond lengths and angles are listed in Table 2. The Cu^II cation is five-coordinated by three N atoms from the bpca group (N1, N2 and N3), one O atom from the water molecule (O3) and one C atom from the cyanide group (C13). Atoms N1, N2, N3 and C13 form the basal plane and atom O3 occupies the apical position. The bond lengths in the basal plane range from 1.9525 (19) to 2.030 (2) Å, which are shorter than the bond length at the vertex [2.373 (2) Å]. The Cu^II cation is in a distorted square-pyramidal environment and is displaced by 0.1461 (4) Å from the mean basal plane towards atom O3. The two five-membered chelate rings formed by the bpca ligands and the central Cu^II cation are almost planar, with a dihedral angle of 3.61 (12)°. The two pyridine rings of the bpca ligand are planar and the dihedral angle between them is 4.96 (17)°. The values of the bond angles at the carbonyl C atoms [111.1 (2)° for C5—C6—N2 and 110.8 (2)° for C8—C7—N2] exhibit significant deviations from the expected value of 120° for sp² hybridization. The Addison τ parameter (Addison et al., 1984) for the CuN₃OC group has a value of 0.14, where the two largest basal angles are N2—Cu1—C13 = 169.60 (11) and N3—Cu1—N1 = 161.22 (8)°; the τ value indicates that the coordination is closer to square-pyramidal geometry (τ = 0) than to trigonal–bipyramidal geometry (τ = 1).

As shown in Fig. 2 and Table 3, inter­molecular hydrogen bonds between the coordinated water molecule (O3) and the three carbonyl O atoms (O1ⁱ, O2ⁱ and O2ⁱⁱ; all symmetry codes as in Table 3) of adjacent bpca groups afford a supra­molecular two-dimensional layered structure. There are three kinds of hydrogen-bonded ring in the structure. The first is described by the graph set (Etter, 1990) R₂⁴(8) and is formed by two O3—H3B···O2ⁱ and two O3—H3A···O2ⁱⁱ hydrogen bonds. The second kind of ring, graph set R₂¹(6), is completed by one O3—H3B···O1ⁱ and one O3—H3B···O2ⁱ hydrogen bond. The third type of ring, graph set R₂²(12), has three examples, i.e. one formed by two O3—H3B···O1ⁱ hydrogen bonds, another by two O3—H3B···O2ⁱ hydrogen bonds and the third by a combination of one O3—H3B···O1ⁱ and one O3—H3B···O2ⁱⁱ hydrogen bond. Furthermore, there are hydrogen-bonding chains in the structure, graph set C(6), formed by O3—H3A···O2ⁱⁱ hydrogen bonds. Additional weak π–π stacking between pyridine rings of adjacent bpca ligands (symmetry code: -x + 1, -y + 1, -z + 2), with a centroid-to-centroid distance of 3.872 (2) Å, stabilizes the whole structure.

As reported previously, the similar copper complex [Cu(bpca)(CN)] has been synthesized by the reaction of Cu(bpca)₂·H₂O and NaCN (Casellas et al., 2005). For this complex, the Cu^II centre is coordinated by three N atoms of the bpca ligand and by one C atom of the cyanide group, similar to the situation in complex (I), but the fifth coordinated position is occupied by the N atom of a cyanide group from a neighbouring [Cu(bpca)(CN)] unit, instead of water as in (I), and so a one-dimensional zigzag chain is formed along the (001) direction. In other words, the cyanide group acts as a µ₂-bridging ligand towards the Cu^II centre for [Cu(bpca)(CN)] but as a terminal ligand in (I). Such a difference may suggest that the rea­ctant [reaction conditions?] may greatly affect the coordination mode of a cyanide group.

The UV–vis spectrum of (I) in di­methyl sulfoxide (DMSO) was measured at room temperature and the spectrum shows a weak absorption band at 638 nm (Fig. 3), which can presumably be assigned to the d–d transition of Cu^II. The UV–vis spectra also shows two weakly resolved bands (582 and 663 nm), which may correspond to ²B₁²B₂ and ²B₁²A₁ transitions (Ballhausen, 1962).

The electron paramagnetic resonance (EPR) spectrum of (I) at X-band microwave frequencies at room temperature in DMSO is shown in Fig. 4. The values of the g tensor, g_x = 2.08, g_y = 2.08 and g_z = 2.20, suggest that the Cu^II cation is in an axial-symmetry coordinated environment and the unpaired electrons occupy the d_x²–_y² orbital (Athappan & Rajagopal, 1996).

A cyclic voltammogram of (I) (0.001 M) in DMSO was carried out at a platinum disc working electrode, using [Bu₄N][ClO₄] (TBAP, 0.1 M) as supporting electrolyte (NB perchlorate salts are explosives and should be used with caution) and Ag/AgCl as reference electrode (Fig. 5). The scanning range was from -2 to 2 V at a rate of 0.1 V s^-1. The results show that there are two irreversible oxidation peaks corresponding to the oxidizing steps of the bpca ligand and Cu^I/Cu^II (Epa₁ = -67 mV, Epa₂ = -334 mV), and two irreversible reduction peaks corresponding to the reductive steps of the bpca ligand and Cu^I/Cu^II (Epc₁ = -261 mV, Epc₂ = -769 mV).

Computing details

Data collection: SMART (Bruker, 2000); cell refinement: SMART (Bruker, 2000); data reduction: SMART (Bruker, 2000); program(s) used to solve structure: SIR2004 (Burla et al., 2007); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: OLEX2 (Dolomanov et al., 2009); software used to prepare material for publication: OLEX2 (Dolomanov et al., 2009).

Figures

	Fig. 1. The molecular structure of complex (I). Displacement ellipsoids are drawn at the ??% probability level. [Please complete]
	Fig. 2. The O—H···O hydrogen bonding in the two-dimensional structure of complex (I). Hydrogen bonds are drawn as dashed lines and three of the graph sets are indicated.
	Fig. 3. The UV–vis experimental spectrum (E) and Gauss-simulated spectrum (S) of complex (I). [Meaning of S1 and S2?]
	Fig. 4. The experimental EPR spectrum of (I) at 298 K.
	Fig. 5. A cyclic voltammogram (CV) of (I) in dimethyl sulfoxide (DMSO).

Aqua[bis(pyridin-2-ylcarbonyl)amidato]cyanidocopper(II)

Crystal data

[Cu(C12H8N3O2)(CN)(H2O)]	Z = 2
Mr = 333.79	F(000) = 338
Triclinic, P1	Dx = 1.710 Mg m^−3
a = 7.3171 (13) Å	Mo Kα radiation, λ = 0.71073 Å
b = 9.8692 (18) Å	Cell parameters from 1997 reflections
c = 10.2416 (18) Å	θ = 2.4–26.4°
α = 68.401 (3)°	µ = 1.70 mm^−1
β = 84.964 (3)°	T = 294 K
γ = 70.617 (3)°	Prism, blue
V = 648.2 (2) Å^3	0.3 × 0.18 × 0.16 mm

Data collection

Bruker APEXII CCD area-detector diffractometer	2231 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.017
ϕ and ω scans	θmax = 26.4°, θmin = 2.1°
Absorption correction: multi-scan (SADABS; Bruker, 2000)	h = −7→9
Tmin = 0.582, Tmax = 1.000	k = −11→12
3682 measured reflections	l = −8→12
2605 independent reflections

Refinement

Refinement on F^2	Primary atom site location: structure-invariant direct methods
Least-squares matrix: full	Hydrogen site location: other
R[F^2 > 2σ(F^2)] = 0.032	H atoms treated by a mixture of independent and constrained refinement
wR(F^2) = 0.081	w = 1/[σ^2(Fo^2) + (0.0405P)^2 + 0.2346P] where P = (Fo^2 + 2Fc^2)/3
S = 1.04	(Δ/σ)max = 0.001
2605 reflections	Δρmax = 0.31 e Å^−3
196 parameters	Δρmin = −0.29 e Å^−3
3 restraints

Special details

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.

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

	x	y	z	Uiso*/Ueq
Cu1	0.60371 (4)	0.76908 (4)	0.59014 (3)	0.02966 (12)
O1	0.3725 (3)	0.6810 (2)	0.29753 (19)	0.0406 (5)
O2	0.1901 (3)	0.5917 (2)	0.55606 (19)	0.0368 (4)
O3	0.8448 (3)	0.5231 (2)	0.6740 (2)	0.0345 (4)
H3A	0.949 (3)	0.533 (4)	0.636 (3)	0.052*
H3B	0.814 (4)	0.458 (3)	0.653 (3)	0.052*
C13	0.7333 (4)	0.8695 (3)	0.6675 (3)	0.0403 (7)
N1	0.7051 (3)	0.8215 (3)	0.3929 (2)	0.0317 (5)
N2	0.4349 (3)	0.7034 (2)	0.5062 (2)	0.0276 (5)
N3	0.4310 (3)	0.7145 (3)	0.7534 (2)	0.0307 (5)
N4	0.8022 (5)	0.9232 (4)	0.7220 (4)	0.0681 (9)
C1	0.8486 (4)	0.8816 (3)	0.3425 (3)	0.0389 (6)
H1	0.9105	0.9066	0.4017	0.047*
C2	0.9067 (4)	0.9073 (4)	0.2063 (3)	0.0469 (7)
H2	1.0081	0.9469	0.1749	0.056*
C3	0.8137 (5)	0.8740 (4)	0.1178 (3)	0.0482 (8)
H3	0.8497	0.8921	0.0252	0.058*
C4	0.6647 (4)	0.8127 (4)	0.1683 (3)	0.0412 (7)
H4	0.5993	0.7893	0.1099	0.049*
C5	0.6154 (4)	0.7873 (3)	0.3057 (3)	0.0292 (5)
C6	0.4578 (4)	0.7179 (3)	0.3682 (3)	0.0290 (5)
C7	0.3023 (3)	0.6442 (3)	0.5876 (2)	0.0272 (5)
C8	0.3054 (3)	0.6505 (3)	0.7324 (3)	0.0282 (5)
C9	0.1851 (4)	0.5971 (4)	0.8342 (3)	0.0393 (7)
H9	0.0998	0.5531	0.8169	0.047*
C10	0.1937 (5)	0.6103 (4)	0.9639 (3)	0.0472 (8)
H10	0.1146	0.5743	1.0351	0.057*
C11	0.3190 (5)	0.6764 (4)	0.9862 (3)	0.0464 (7)
H11	0.3251	0.6872	1.0720	0.056*
C12	0.4364 (4)	0.7267 (4)	0.8794 (3)	0.0406 (7)
H12	0.5226	0.7708	0.8951	0.049*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Cu1	0.03311 (19)	0.0386 (2)	0.02796 (18)	−0.02132 (14)	0.00155 (12)	−0.01537 (14)
O1	0.0497 (12)	0.0635 (14)	0.0279 (9)	−0.0377 (11)	0.0067 (8)	−0.0220 (9)
O2	0.0373 (10)	0.0574 (13)	0.0318 (10)	−0.0322 (9)	0.0083 (8)	−0.0207 (9)
O3	0.0336 (10)	0.0439 (11)	0.0385 (10)	−0.0230 (9)	0.0060 (8)	−0.0205 (9)
C13	0.0397 (15)	0.0413 (17)	0.0487 (17)	−0.0184 (13)	−0.0020 (13)	−0.0207 (14)
N1	0.0321 (11)	0.0361 (12)	0.0316 (11)	−0.0191 (10)	0.0009 (9)	−0.0102 (10)
N2	0.0299 (11)	0.0395 (13)	0.0217 (10)	−0.0211 (10)	0.0038 (8)	−0.0121 (9)
N3	0.0343 (11)	0.0398 (13)	0.0252 (10)	−0.0168 (10)	0.0006 (9)	−0.0151 (10)
N4	0.0671 (19)	0.064 (2)	0.095 (2)	−0.0273 (16)	−0.0186 (17)	−0.0428 (19)
C1	0.0366 (15)	0.0388 (16)	0.0443 (16)	−0.0236 (13)	−0.0006 (12)	−0.0076 (13)
C2	0.0427 (17)	0.0489 (19)	0.0485 (18)	−0.0282 (15)	0.0094 (14)	−0.0066 (15)
C3	0.0539 (19)	0.058 (2)	0.0387 (16)	−0.0326 (16)	0.0184 (14)	−0.0150 (15)
C4	0.0509 (17)	0.0522 (18)	0.0311 (14)	−0.0301 (15)	0.0103 (13)	−0.0169 (13)
C5	0.0308 (13)	0.0333 (14)	0.0272 (12)	−0.0169 (11)	0.0026 (10)	−0.0096 (11)
C6	0.0325 (13)	0.0367 (14)	0.0247 (12)	−0.0187 (11)	0.0016 (10)	−0.0120 (11)
C7	0.0264 (12)	0.0361 (14)	0.0249 (12)	−0.0140 (11)	0.0019 (10)	−0.0140 (11)
C8	0.0279 (12)	0.0351 (14)	0.0250 (12)	−0.0119 (11)	0.0007 (10)	−0.0128 (11)
C9	0.0381 (15)	0.0572 (19)	0.0308 (14)	−0.0264 (14)	0.0064 (11)	−0.0163 (13)
C10	0.0485 (18)	0.070 (2)	0.0284 (14)	−0.0267 (16)	0.0130 (13)	−0.0200 (15)
C11	0.0535 (18)	0.063 (2)	0.0285 (14)	−0.0193 (16)	0.0020 (13)	−0.0232 (14)
C12	0.0460 (16)	0.0561 (19)	0.0347 (14)	−0.0224 (14)	0.0028 (12)	−0.0280 (14)

Geometric parameters (Å, º)

Cu1—O3	2.373 (2)	C1—C2	1.378 (4)
Cu1—C13	1.960 (3)	C2—H2	0.9300
Cu1—N1	2.030 (2)	C2—C3	1.367 (4)
Cu1—N2	1.9525 (19)	C3—H3	0.9300
Cu1—N3	2.025 (2)	C3—C4	1.389 (4)
O1—C6	1.212 (3)	C4—H4	0.9300
O2—C7	1.225 (3)	C4—C5	1.374 (4)
O3—H3A	0.842 (10)	C5—C6	1.510 (3)
O3—H3B	0.844 (10)	C7—C8	1.509 (3)
C13—N4	1.136 (4)	C8—C9	1.372 (4)
N1—C1	1.347 (3)	C9—H9	0.9300
N1—C5	1.347 (3)	C9—C10	1.390 (4)
N2—C6	1.368 (3)	C10—H10	0.9300
N2—C7	1.362 (3)	C10—C11	1.364 (4)
N3—C8	1.346 (3)	C11—H11	0.9300
N3—C12	1.344 (3)	C11—C12	1.378 (4)
C1—H1	0.9300	C12—H12	0.9300
C13—Cu1—O3	95.40 (10)	C2—C3—C4	119.1 (3)
C13—Cu1—N1	99.84 (11)	C4—C3—H3	120.4
C13—Cu1—N3	97.04 (10)	C3—C4—H4	120.5
N1—Cu1—O3	93.16 (8)	C5—C4—C3	118.9 (3)
N2—Cu1—O3	94.84 (8)	C5—C4—H4	120.5
N2—Cu1—C13	169.60 (11)	N1—C5—C4	122.2 (2)
N2—Cu1—N1	81.37 (8)	N1—C5—C6	116.1 (2)
N2—Cu1—N3	80.55 (8)	C4—C5—C6	121.7 (2)
N3—Cu1—O3	93.37 (8)	O1—C6—N2	128.6 (2)
N3—Cu1—N1	161.22 (8)	O1—C6—C5	120.2 (2)
Cu1—O3—H3A	107 (2)	N2—C6—C5	111.1 (2)
Cu1—O3—H3B	111 (2)	O2—C7—N2	128.3 (2)
H3A—O3—H3B	110.3 (16)	O2—C7—C8	120.9 (2)
N4—C13—Cu1	174.7 (3)	N2—C7—C8	110.8 (2)
C1—N1—Cu1	128.32 (19)	N3—C8—C7	115.4 (2)
C5—N1—Cu1	113.39 (16)	N3—C8—C9	122.6 (2)
C5—N1—C1	118.3 (2)	C9—C8—C7	122.0 (2)
C6—N2—Cu1	117.99 (16)	C8—C9—H9	120.8
C7—N2—Cu1	118.71 (15)	C8—C9—C10	118.4 (3)
C7—N2—C6	123.3 (2)	C10—C9—H9	120.8
C8—N3—Cu1	114.11 (15)	C9—C10—H10	120.2
C12—N3—Cu1	127.77 (19)	C11—C10—C9	119.6 (3)
C12—N3—C8	118.0 (2)	C11—C10—H10	120.2
N1—C1—H1	118.9	C10—C11—H11	120.6
N1—C1—C2	122.2 (3)	C10—C11—C12	118.9 (3)
C2—C1—H1	118.9	C12—C11—H11	120.6
C1—C2—H2	120.4	N3—C12—C11	122.5 (3)
C3—C2—C1	119.3 (3)	N3—C12—H12	118.7
C3—C2—H2	120.4	C11—C12—H12	118.7
C2—C3—H3	120.4
Cu1—N1—C1—C2	178.0 (2)	C1—N1—C5—C6	179.1 (2)
Cu1—N1—C5—C4	−179.3 (2)	C1—C2—C3—C4	−1.0 (5)
Cu1—N1—C5—C6	0.2 (3)	C2—C3—C4—C5	−0.1 (5)
Cu1—N2—C6—O1	178.0 (2)	C3—C4—C5—N1	0.8 (5)
Cu1—N2—C6—C5	−0.8 (3)	C3—C4—C5—C6	−178.7 (3)
Cu1—N2—C7—O2	−176.8 (2)	C4—C5—C6—O1	1.0 (4)
Cu1—N2—C7—C8	3.5 (3)	C4—C5—C6—N2	179.9 (3)
Cu1—N3—C8—C7	−5.4 (3)	C5—N1—C1—C2	−0.7 (4)
Cu1—N3—C8—C9	175.8 (2)	C6—N2—C7—O2	2.4 (4)
Cu1—N3—C12—C11	−175.7 (2)	C6—N2—C7—C8	−177.2 (2)
O2—C7—C8—N3	−178.2 (2)	C7—N2—C6—O1	−1.3 (4)
O2—C7—C8—C9	0.5 (4)	C7—N2—C6—C5	179.9 (2)
N1—C1—C2—C3	1.4 (5)	C7—C8—C9—C10	−178.5 (3)
N1—C5—C6—O1	−178.5 (2)	C8—N3—C12—C11	0.0 (4)
N1—C5—C6—N2	0.4 (3)	C8—C9—C10—C11	0.5 (5)
N2—C7—C8—N3	1.4 (3)	C9—C10—C11—C12	−0.9 (5)
N2—C7—C8—C9	−179.8 (2)	C10—C11—C12—N3	0.6 (5)
N3—C8—C9—C10	0.1 (4)	C12—N3—C8—C7	178.3 (2)
C1—N1—C5—C4	−0.4 (4)	C12—N3—C8—C9	−0.4 (4)

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
O3—H3B···O1^i	0.85 (3)	2.15 (3)	2.878 (3)	144 (3)
O3—H3B···O2^i	0.85 (3)	2.37 (3)	3.027 (3)	135 (3)
O3—H3A···O2^ii	0.84 (3)	2.05 (3)	2.881 (3)	169 (3)

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