A copper(I) coordination polymer incorporation the corrosion inhibitor 1H-benzotriazole: poly[μ₃-benzotriazolato-κ³N¹:N²:N³-copper(I)]

The title complex, [Cu(C₆H₄N₃)]_n, was synthesized by the reaction of cupric nitrate, 1H-benzotriazole (BTAH) and aqueous ammonia under hydro­thermal conditions. The asymmetric unit contains three crystallographically independent Cu^I cations and two 1H-benzotriazolate ligands. Two of the Cu^I cations, one with a linear two-coordinated geometry and one with a four-coordinated tetra­hedral geometry, are located on sites with crystallographically imposed twofold symmetry. The third Cu^I cation, with a planar three-coordinated geometry, is on a general position. Two Cu^I cations are doubly bridged by two BTA⁻ ligands to afford a noncentrosymmetric planar [Cu₂(BTA)₂] subunit, and two [Cu₂(BTA)₂] subunits are arranged in an anti­parallel manner to form a centrosymmetric [Cu₂(BTA)₂]₂ secondary building unit (SBU). The SBUs are connected in a crosswise manner via the sharing of four-coordinated Cu^I cations, Cu—N bonding and bridging by two-coordinate Cu^I cations, resulting in a one-dimensional chain along the c axis. These one-dimensional chains are further linked by C—H...π and weak van der Waals inter­actions to form a three-dimensional supra­molecular architecture.

S1. Introduction

Copper is one of the most essential metals owing to its many industrial applications, such as electronics, the production of wires, sheets, tubes, and also the ability form alloys. It is generally a relatively noble metal, however, it is susceptible to corrosion by acids and strong alkaline solutions, especially in the presence of oxygen or oxidants.

It has been known since 1947 (Procter et al., 1947) that 1H-benzotriazole (BTAH) is an effective corrosion inhibitor for copper and its alloys by preventing undesirable surface reactions. Since then, BTAH has been included in a number of patents (Walker, 1970, 1973). BTAH prevents discolouration of copper surfaces under atmospheric and immersed conditions. It has been used to protect artefacts of archaeological and historical importance (Brinch & Madsen, 1971; Walker, 1980). In the past five decades, various coordination modes between Cu and BTAH have been proposed (Cotton & Scholes, 1967; Morito & Suëtaka, 1973; Roberts, 1974; Fang et al., 1986; Xue & Ding, 1990; Xue et al., 1991; Ling et al., 1995; Finšgar et al., 2010). Cotton and his co-workers proposed the linear polymeric CuIBTA structure and stated more decisively that this structure contains Cu^I ions (Cotton & Scholes, 1967). The formation of Cu^IBTA was not limited to a monolayer, but could grow further to form films up to several thousand Angstroms thick. Later, this mode was confirmed by experiment (Poling, 1970), but no crystal structure has been reported for Cu^I complexes derived from the BTAH ligand. In this work, we use BTAH as a ligand to construct a new coordination polymer and report the synthesis and crystal structure of [Cu(BTA)]_n, (I). To the best of our knowledge, (I) is the first example of a Cu^I complex incoporating BTAH as a ligand. The crystal structure of (I) is much more complex than the hypothetical model proposed by Cotton. The first example of a Cu^I complex with BTAH could shed some light on how BTAH prevents copper from corrosion and could be beneficial in developing more effective corrosion inhibitors for copper.

S2. Experimental

S2.1. Synthesis and crystallization

The title compound was prepared under hydro­thermal conditions. A mixture of Cu(NO₃)₂.H₂O (1.0 mmol, 0.241 g), 1<H-benzotriazole (1.0 mmol, 0.118 g) and aqueous ammonia (25%, 6.0 ml) was stirred for 15 min in air, then transferred and sealed in a 23 ml Teflon-lined autoclave, which was heated in an oven to 433 K for 80 h, and then cooled to room temperature at a rate of 5 K h^-1. Yellow needle-like crystals of (I) suitable for X-ray analysis were obtained in 35% yield (based on Cu). The powder X-ray diffraction (PXRD) patterns was recorded on a Rigaku MiniFlex-II X-Ray diffractometer with Cu Kα radiation (λ = 1.54178 Å) at room temperature.

S2.2. Refinement

Crystal data, data collection and structure refinement details are summarized in Table 1. H atoms bonded to C atoms were refined in idealized positions using the riding-model approximation, with C—H = 0.93 Å and U_iso(H) = 1.2U_eq(C).

S3. Results and discussion

The asymmetric unit of [Cu(BTA)]_n, (I), contains three crystallographically independent Cu^I atoms and two BTA^- ligands. As shown in Fig. 1, the linear two-coordinated Cu1 atom and the four-coordinated Cu3 atom are located on sites with crystallographically imposed twofold symmetry, while the three-coordinated Cu2 atom is on a general position. Cu2 and Cu3 are doubly bridged by a pair of BTA^- ligands. Cu1 is two-coordinated by two triazole N atoms of two BTA^- ligands [N4 and N4ⁱ; symmetry code: (i) -x, y, -z-1/2]. The Cu1—N4 bond length (Table 2) is within the normal range (Xiao et al., 2011) and the N4ⁱ—Cu1—N4 angle displays a nearly linear geometry. The Cu2 atom is three-coordinated by three N atoms [N1ⁱⁱ, N3 and N5; symmetry code: (ii) x, -y, z-1/2] from three BTA^- ligands, giving a distorted T-shape geometry. Atoms N1ⁱⁱ, N3, N5 and Cu2 exhibits coplanar ring characteristics, the maximum deviation from the least-squares plane being 0.2476 (5) Å (for atom Cu2). The Cu2—N1ⁱⁱ/N3/N5 bond lengths (Table 2) fall within the typical range for three-coordinated Cu^I—N bond distances according to the Cambridge Structural Database (Allen, 2002). The Cu3 cation is four-coordinated by fourN atoms of four BTA^- ligands [N2, N2ⁱⁱⁱ, N6ⁱⁱⁱ and N6; symmetry code: (iii) -x, -y, -z+1/2], displaying a distorted tetra­hedral geometry. The Cu3—N bond lengths are similar to values reported previously for four-coordinated Cu^I complexes (Barclay et al., 2001; Chowdhury et al., 2003; Huang & Hartwig, 2012). The N—N bond lengths vary from 1.332 (5) to 1.346 (4) Å, indicating the strong delocalization within the triazole group is predominant in the structure of(I).

As shown in Fig. 2, two BTA^- ligands link two Cu^I cations to form a [Cu₂(BTA)₂] subunit and the [Cu₂(BTA)₂] subunits then form a [Cu₂(BTA)₂]₂ SBU (secondary building unit) in an anti­parallel fashion, which is further linked by the sharing a four-coordinated Cu^I atom, a bridging Cu^I atom and a Cu—N bond, resulting in a one-dimensional chain structure along the c axis. In the tetra­nuclear [Cu₂(BTA)₂]₂ SBU, atoms C8/C9/C10 and C2^v/C3^v/C4^v [symmetry code: (v) -x, -y, -z] define the upper and lower faces; the dihedral angle between these two faces is 0.81 (1)°, indicating that the two faces are nearly parallel. In the SBU, two Cu^I ions and two BTA^- ligands form a six-membered ring (Cu2/N5/N6/Cu3/N2/N3), the Cu2···Cu3 distance being 3.6532 (9) Å, which is slightly longer than in previously reported Cu^I complexes (Li et al., 2001; Wang et al., 2002).

There are strong π–π stacking inter­actions in the [Cu₂(BTA)₂]₂ SBU, with a Cg1···Cg2^v separation of 3.827 (8) Å [Cg1 and Cg2 are the centroids of the C7–C12 and C1–C6 rings, respectively]. It is noted that there are no hydrogen-bonding inter­actions in the structure; the chains inter­act through C—H···π inter­actions [H9···Cg2^vi = 3.202 Å, C9···Cg2^vi = 4.023 Å and C9—H9···Cg1^vi = 149.5°; symmetry code: (vi) x-1/2, -y+1/2, z-1/2] and weak van der Waals inter­actions connect the chains into a three-dimensional supra­molecular architecture (Fig. 3).

Powder X-ray diffraction (PXRD) experiments were carried out on (I) in order to establish the crystalline phase purity. As shown in Fig. 4, the major peak positions of the PXRD pattern of the bulk solid of (I) match those of the simulated pattern obtained from the single-crystal data, indicating the presence of mainly one crystalline phase in the coordination polymer.

Related literature

For related literature, see: Procter Gamble Ltd (1947); Allen (2002); Barclay et al. (2001); Brinch & Madsen (1971); Chowdhury et al. (2003); Cotton & Scholes (1967); Fang et al. (1986); Finšgar et al. (2010); Huang & Hartwig (2012); Li et al. (2001); Ling et al. (1995); Morito & Suëtaka (1973); Poling (1970); Roberts (1974); Walker (1970, 1973, 1980); Wang et al. (2002); Xiao et al. (2011); Xue & Ding (1990); Xue et al. (1991).

Computing details

Data collection: CrystalClear (Rigaku, 2002); cell refinement: CrystalClear (Rigaku, 2002); data reduction: CrystalClear (Rigaku, 2002); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: DIAMOND (Brandenburg, 2004); software used to prepare material for publication: SHELXL97 (Sheldrick, 2008) and publCIF (Westrip, 2010).

Figures

The coordination environment of the Cu^I ions in (I), showing the atom-labelling scheme and 50% probability displacement ellipsoids. H atoms have been omitted for clarity. [Symmetry codes: (i) -x, y, -z-1/2; (ii) x, -y, z-1/2; (iii) -x, -y, -z+1/2; (iv) x, -y, z+1/2.]

A view of the one-dimensional chain in (I). All H atoms have been omitted for clarity. [Symmetry codes: (v) -x, -y, -z.]

A packing diagram for (I), showing the C—H···π interactions (yellow dashed lines). All H atoms, except for those involved in the weak interactions, have been omitted. All atoms are shown as wires or sticks.

Simulated (bottom) and experimental (top) powder X-ray diffraction patterns of (I).

Poly[µ₃-benzotriazolato-κ³N¹:N²:N³-copper(I)]

Crystal data

[Cu(C6H4N3)]	Z = 16
Mr = 181.66	F(000) = 1440
Monoclinic, C2/c	Dx = 1.988 Mg m^−3
Hall symbol: -C 2yc	Mo Kα radiation, λ = 0.71073 Å
a = 19.116 (4) Å	µ = 3.50 mm^−1
b = 11.968 (2) Å	T = 173 K
c = 11.139 (2) Å	Needle, yellow
β = 107.70 (3)°	0.38 × 0.05 × 0.04 mm
V = 2427.9 (8) Å^3

Data collection

Rigaku Saturn 724 CCD area-detector diffractometer	2779 independent reflections
Radiation source: fine-focus sealed tube	1716 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.075
ω scans	θmax = 27.5°, θmin = 3.0°
Absorption correction: numerical (RAPID-AUTO; Rigaku, 1998)	h = −24→24
Tmin = 0.808, Tmax = 0.883	k = −15→15
11673 measured reflections	l = −14→12

Refinement

Refinement on F^2	Primary atom site location: structure-invariant direct methods
Least-squares matrix: full	Secondary atom site location: difference Fourier map
R[F^2 > 2σ(F^2)] = 0.044	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.092	H-atom parameters constrained
S = 1.05	w = 1/[σ^2(Fo^2) + (0.0301P)^2 + 1.9944P] where P = (Fo^2 + 2Fc^2)/3
2779 reflections	(Δ/σ)max < 0.001
182 parameters	Δρmax = 0.42 e Å^−3
0 restraints	Δρmin = −0.50 e Å^−3

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.

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 (Ų)

	x	y	z	Uiso*/Ueq
Cu1	0.0000	0.26811 (6)	−0.2500	0.0366 (2)
Cu2	0.07719 (3)	0.07190 (5)	−0.00732 (4)	0.03519 (17)
Cu3	0.0000	0.12080 (6)	0.2500	0.0359 (2)
N1	0.10524 (19)	−0.0660 (3)	0.3385 (3)	0.0307 (8)
N2	0.08148 (19)	0.0124 (3)	0.2480 (3)	0.0320 (8)
N3	0.1104 (2)	−0.0043 (3)	0.1541 (3)	0.0327 (8)
N4	−0.0115 (2)	0.2774 (3)	−0.0899 (3)	0.0318 (8)
N5	0.00901 (19)	0.1970 (3)	−0.0001 (3)	0.0314 (8)
N6	−0.0185 (2)	0.2180 (3)	0.0939 (3)	0.0325 (8)
C1	0.1516 (2)	−0.1352 (3)	0.3008 (3)	0.0294 (9)
C2	0.1897 (3)	−0.2319 (4)	0.3569 (4)	0.0381 (11)
H2	0.1863	−0.2600	0.4348	0.046*
C3	0.2311 (3)	−0.2826 (4)	0.2943 (4)	0.0463 (12)
H3	0.2578	−0.3479	0.3294	0.056*
C4	0.2360 (3)	−0.2417 (4)	0.1779 (4)	0.0486 (13)
H4	0.2665	−0.2797	0.1379	0.058*
C5	0.1987 (3)	−0.1505 (4)	0.1221 (4)	0.0434 (12)
H5	0.2021	−0.1240	0.0436	0.052*
C6	0.1545 (2)	−0.0959 (3)	0.1849 (3)	0.0313 (10)
C7	−0.0539 (3)	0.3511 (3)	−0.0513 (3)	0.0329 (10)
C8	−0.0887 (3)	0.4494 (4)	−0.1066 (4)	0.0455 (12)
H8	−0.0834	0.4770	−0.1833	0.055*
C9	−0.1307 (3)	0.5040 (4)	−0.0457 (4)	0.0545 (14)
H9	−0.1565	0.5697	−0.0817	0.065*
C10	−0.1363 (3)	0.4639 (4)	0.0700 (4)	0.0515 (13)
H10	−0.1658	0.5042	0.1099	0.062*
C11	−0.1013 (3)	0.3702 (4)	0.1274 (4)	0.0419 (11)
H11	−0.1053	0.3449	0.2059	0.050*
C12	−0.0592 (2)	0.3137 (3)	0.0641 (3)	0.0309 (10)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Cu1	0.0547 (5)	0.0418 (4)	0.0185 (3)	0.000	0.0189 (4)	0.000
Cu2	0.0542 (4)	0.0367 (3)	0.0217 (3)	−0.0037 (3)	0.0220 (3)	−0.0014 (2)
Cu3	0.0576 (6)	0.0324 (4)	0.0269 (4)	0.000	0.0265 (4)	0.000
N1	0.042 (2)	0.0341 (19)	0.0213 (15)	−0.0002 (18)	0.0173 (15)	0.0036 (15)
N2	0.045 (2)	0.037 (2)	0.0199 (16)	0.0024 (17)	0.0186 (17)	0.0020 (15)
N3	0.047 (2)	0.037 (2)	0.0227 (16)	0.0024 (17)	0.0232 (17)	0.0001 (15)
N4	0.045 (2)	0.0331 (19)	0.0194 (15)	0.0018 (18)	0.0127 (16)	0.0042 (14)
N5	0.047 (2)	0.033 (2)	0.0185 (16)	−0.0004 (17)	0.0157 (16)	−0.0009 (14)
N6	0.050 (2)	0.0348 (19)	0.0192 (15)	0.0014 (18)	0.0203 (17)	−0.0014 (15)
C1	0.033 (2)	0.036 (2)	0.0210 (18)	−0.003 (2)	0.0109 (18)	−0.0035 (17)
C2	0.047 (3)	0.038 (2)	0.031 (2)	0.003 (2)	0.014 (2)	0.0059 (19)
C3	0.045 (3)	0.047 (3)	0.044 (3)	0.009 (2)	0.011 (2)	−0.001 (2)
C4	0.052 (3)	0.050 (3)	0.052 (3)	0.008 (2)	0.029 (3)	−0.012 (2)
C5	0.056 (3)	0.047 (3)	0.035 (2)	0.001 (2)	0.027 (2)	−0.003 (2)
C6	0.039 (3)	0.036 (2)	0.0223 (19)	0.000 (2)	0.0153 (19)	−0.0009 (17)
C7	0.048 (3)	0.031 (2)	0.0213 (19)	−0.001 (2)	0.012 (2)	−0.0020 (17)
C8	0.065 (3)	0.040 (3)	0.031 (2)	0.003 (2)	0.015 (2)	0.008 (2)
C9	0.069 (4)	0.045 (3)	0.042 (3)	0.019 (3)	0.006 (3)	0.001 (2)
C10	0.064 (4)	0.047 (3)	0.044 (3)	0.017 (3)	0.017 (3)	−0.007 (2)
C11	0.056 (3)	0.045 (3)	0.029 (2)	0.006 (2)	0.020 (2)	−0.005 (2)
C12	0.042 (3)	0.030 (2)	0.025 (2)	−0.001 (2)	0.016 (2)	−0.0036 (17)

Geometric parameters (Å, º)

Cu1—N4	1.865 (3)	C1—C2	1.409 (6)
Cu1—N4^i	1.865 (3)	C2—C3	1.348 (6)
Cu2—N3	1.942 (3)	C2—H2	0.9500
Cu2—N1^ii	1.949 (3)	C3—C4	1.416 (6)
Cu2—N5	2.003 (3)	C3—H3	0.9500
Cu3—N6	2.032 (3)	C4—C5	1.348 (6)
Cu3—N6^iii	2.032 (3)	C4—H4	0.9500
Cu3—N2^iii	2.032 (3)	C5—C6	1.411 (6)
Cu3—N2	2.032 (3)	C5—H5	0.9500
N1—N2	1.351 (4)	C7—C12	1.394 (5)
N1—C1	1.369 (5)	C7—C8	1.399 (6)
N1—Cu2^iv	1.949 (3)	C8—C9	1.364 (6)
N2—N3	1.339 (4)	C8—H8	0.9500
N3—C6	1.361 (5)	C9—C10	1.409 (6)
N4—C7	1.354 (5)	C9—H9	0.9500
N4—N5	1.357 (4)	C10—C11	1.361 (6)
N5—N6	1.330 (4)	C10—H10	0.9500
N6—C12	1.367 (5)	C11—C12	1.396 (6)
C1—C6	1.391 (5)	C11—H11	0.9500
N4—Cu1—N4^i	173.2 (2)	C3—C2—H2	121.8
N3—Cu2—N1^ii	134.28 (14)	C1—C2—H2	121.8
N3—Cu2—N5	110.33 (13)	C2—C3—C4	122.1 (4)
N1^ii—Cu2—N5	114.77 (13)	C2—C3—H3	118.9
N6—Cu3—N6^iii	110.13 (18)	C4—C3—H3	118.9
N6—Cu3—N2^iii	116.14 (14)	C5—C4—C3	121.9 (4)
N6^iii—Cu3—N2^iii	106.89 (12)	C5—C4—H4	119.1
N6—Cu3—N2	106.89 (12)	C3—C4—H4	119.1
N6^iii—Cu3—N2	116.14 (14)	C4—C5—C6	117.4 (4)
N2^iii—Cu3—N2	100.67 (19)	C4—C5—H5	121.3
N2—N1—C1	107.0 (3)	C6—C5—H5	121.3
N2—N1—Cu2^iv	124.2 (2)	N3—C6—C1	108.1 (3)
C1—N1—Cu2^iv	128.7 (3)	N3—C6—C5	131.8 (4)
N3—N2—N1	110.8 (3)	C1—C6—C5	120.2 (4)
N3—N2—Cu3	127.1 (3)	N4—C7—C12	107.6 (3)
N1—N2—Cu3	121.3 (2)	N4—C7—C8	131.2 (4)
N2—N3—C6	107.1 (3)	C12—C7—C8	121.2 (4)
N2—N3—Cu2	123.8 (3)	C9—C8—C7	117.2 (4)
C6—N3—Cu2	127.9 (2)	C9—C8—H8	121.4
C7—N4—N5	107.1 (3)	C7—C8—H8	121.4
C7—N4—Cu1	126.8 (3)	C8—C9—C10	120.8 (4)
N5—N4—Cu1	124.8 (3)	C8—C9—H9	119.6
N6—N5—N4	110.6 (3)	C10—C9—H9	119.6
N6—N5—Cu2	126.2 (2)	C11—C10—C9	123.2 (5)
N4—N5—Cu2	123.1 (2)	C11—C10—H10	118.4
N5—N6—C12	107.4 (3)	C9—C10—H10	118.4
N5—N6—Cu3	123.9 (3)	C10—C11—C12	116.0 (4)
C12—N6—Cu3	128.7 (2)	C10—C11—H11	122.0
N1—C1—C6	107.0 (3)	C12—C11—H11	122.0
N1—C1—C2	131.0 (4)	N6—C12—C7	107.3 (3)
C6—C1—C2	121.9 (4)	N6—C12—C11	131.1 (4)
C3—C2—C1	116.5 (4)	C7—C12—C11	121.6 (4)

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