Bis{μ-2-[(1,5-diaza-1-cyclooctyl)methyl]phenolato-N,N′,O:O}bis[chlorozinc(II)] diacetone solvate: design of a square-pyramidal ZnN₂O₂Cl complex

The title complex, [Zn₂(C₁₃H₁₉N₂O)₂Cl₂]·2C₃H₆O, resides on a crystallographic inversion center. The two Zn^II centers bridged by the phenoxo groups are in pentacoordinated distorted square-pyramidal coordination environments with an intramolecular Zn...Zn distance of 3.175 (3) Å. The mesocyclic ligand takes a boat–chair conformation and an H atom from the 1,5-di­aza­cyclo­octane ring effectively blocks the axial coordination site opposite the Cl ligand to form the ZnN₂O₂Cl geometry. The crystal structure is stabilized by a N—H...O hydrogen bond between the amino group and an acetone mol­ecule.

S1. Comment

Zinc, the second most abundant transition metal in biology, functions as the active site of hydrolytic enzymes, such as carboxypetidase and carbonic anhydrase where it is in a hard donor coordination environment of nitrogen and oxygen (Lipscomb & Strater, 1996). There are numerous structural studies on zinc-containing complexes in which the zinc atom generally is found to assume a tetrahedral geometry. Corresponding studies on the less common pentacoordinated zinc complexes are relatively less explored (Yam et al., 2000). Geometries other than that of four coordinate are interesting in view of the possibility of the zinc adopting a as penta-, tri- or perhaps even hexacoordinated structures in the functional states of the biological system (Brand et al., 1996). As most of the zinc complexes with unusual coordination numbers were discovered more by accident than by design or with special ligand systems. The factors governing pentacoordination are still largely unknown (Zhang et al., 1991). \sch

1,5-Diazacyclooctane (DACO) is a typical example of diazamesocycles, which usually shows an interesting `boat/chair' conformation when binding to metal ions, and such a conformation blocks the sixth coordination from the apical site to form a pentacoordination complex (Musker, 1992; Grapperhaus & Darensbourg, 1998). In our ongoing studies of 1,5-diazacyclooctane ligands we have obtained a series of pentacoordinate complexes with a variety of metals: Cu^II (Bu et al., 2000), Co^II (Du, Shang et al., 2000), Ni^II (Bu et al., 2001) and Cd^II (Du, Weng et al., 2000). However, the crystal structure of the zinc(II) complexes of DACO ligands are still undetermined. In this paper, we report the crystal structure of a novel phenoxo-bridged binuclear zinc(II) complex with a distorted square-pyramidal ZnN₂O₂Cl geometry of 1-(2-hydroxybenzyl)-1,5-diazacyclooctane, (I) (Chart I). \sch

The structure of (I) comprises a neutral binuclear entity and an uncoordinated acetone molecule (Fig. 1). Each molecule results from the pairing of two mononuclear units related by a crystallographic center of symmetry. Each Zn^II center in this complex is bound by five donor atoms occupying the vertices of a distorted square-pyramidal coordination environment with τ = 0.27 (Addison et al., 1984), which is used to describe the degree of distortion for pentacoordinated complexes (τ = 0 for an ideal square-pyramid, and τ = 1 for an ideal trigonal bipyramid). Two bridging oxygen atoms of the deprotonated pendant phenol groups and two nitrogen donors of the DACO ring of the ligand comprise the basal plane, and each axial coordination site is occupied by a chloride anion. The Zn^II ion deviates from the basal mean equatorial plane of the square-pyramid towards the apical Cl1 by ca 0.61 Å.

The two Zn^II centers are equivalently bridged by two phenoxo oxygen anions of the parallel phenol rings, which are bound asymmetrically to Zn^II at slightly different distances of 2.0056 (15) versus 2.1109 (16) Å, respectively (Table 1). The Zn—O—Zn bridging angle is 100.80 (12)° and the two Zn^II centers are separated by 3.175 (3) Å.

The ligand adopts a `boat/chair' conformation and gives rise with each Zn^II center to two five-membered chelate rings, which enhance the coordination ability to Zn^II. The central methylene C—H group of the boat form in DACO shields the Zn^II center with an H2b—Zn1 distance of 2.749 (3) Å, which effectively blocks the sixth coordination position to give this novel pentacoordinated Zn^II complex.

In this structure, each amino group of the ligand forms an N—H···O hydrogen bond with an acetone molecule. The N···O separation is 3.038 (3) Å with an H···O separation 2.278 of Å and bond angle of 141°, which are in the normal range of weak interactions (Sasada, 1984).

Related literature

For related literature, see: Addison et al. (1984); Brand et al. (1996); Bu et al. (2000, 2001); Du, Shang, Xu, Zhang, Leng & Bu (2000); Du, Weng, Leng, Bu & Zhang (2000); Grapperhaus & Darensbourg (1998); Lipscomb & Strater (1996); Musker (1992); Sasada (1984); Yam et al. (2000); Zhang et al. (1991).

S2. Experimental

The title complex was synthesized by mixing ZnCl₂ (27 mg, 0.2 mmol) and HL (44 mg, 0.2 mmol) in acetone-water. The reaction mixture was filtered, and then colorless single crystals suitable for X-ray diffraction analysis were obtained by slow evaporation of the solvent [yield 49 mg (65%)]. FT—IR data (KBr pellet, cm^-1): 3439(b), 3290(m), 2923(w), 2843(w), 1705(s), 1593(s), 1568(m), 1484(versus), 1453(s), 1280(versus), 1271(versus), 1127(m), 1016(s), 881(s), 755(s). Analysis calculated for the title complex: C 50.81, H 6.66, N 7.41%. Found: C 50.68, H 6.81, N 7.22%.

S3. Refinement

Hydrogen atoms were placed at idealized positions and were allowed to ride on the parent atom. The U_iso for the hydrogen atoms were set to be 1.2U_eq for the parent atom.

Computing details

Data collection: SMART (Bruker, 1998); cell refinement: SMART; data reduction: SAINT (Bruker, 1998); program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: XP (Bruker, 1998).

Figures

Fig. 1. An ORTEPII (Johnson, 1976) view of the title complex with 30% probability ellipsoids (the acetone molecules and H atoms have been omitted for clarity).

Bis[chloro(1-(2-hydroxybenzyl)-1,5-diazacyclooctane) zinc(II) acetone]

Crystal data

[Zn2(C13H19N2O)2Cl2]·2C3H6O	Z = 1
Mr = 756.40	F(000) = 396
Triclinic, P1	Dx = 1.414 Mg m^−3
a = 8.8173 (14) Å	Mo Kα radiation, λ = 0.71073 Å
b = 10.8916 (17) Å	Cell parameters from 3683 reflections
c = 11.2986 (17) Å	θ = 2.1–25.0°
α = 115.254 (3)°	µ = 1.54 mm^−1
β = 99.964 (3)°	T = 293 K
γ = 106.135 (3)°	Prism, colorless
V = 888.0 (2) Å^3	0.30 × 0.15 × 0.10 mm

Data collection

BRUKER SMART 1000 diffractometer	2718 reflections with I > 2.0σ(I)
ω scans	Rint = 0.017
Absorption correction: multi-scan SAINT (Bruker, 1998) and SADABS (Sheldrick, 1996)	θmax = 25.0°
Tmin = 0.655, Tmax = 0.861	h = −10→10
3735 measured reflections	k = −12→12
3129 independent reflections	l = −11→13

Refinement

Refinement on F^2	w = 1/[σ^2(Fo^2) + (0.0494P)^2 + 0.0111P] where P = (Fo^2 + 2Fc^2)/3
R[F^2 > 2σ(F^2)] = 0.030	(Δ/σ)max = 0.005
wR(F^2) = 0.075	Δρmax = 0.27 e Å^−3
S = 1.02	Δρmin = −0.29 e Å^−3
3129 reflections	Extinction correction: SHELXL
199 parameters	Extinction coefficient: none
H-atom parameters constrained

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. Full-MATRIX

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

	x	y	z	Uiso*/Ueq
Zn1	0.00206 (3)	0.53107 (3)	0.15105 (3)	0.03281 (11)
Cl1	0.18300 (9)	0.45530 (9)	0.24277 (8)	0.0604 (2)
N1	0.0064 (2)	0.7367 (2)	0.28977 (19)	0.0358 (4)
H1C	0.0909	0.8064	0.2887	0.043*
N2	−0.2151 (2)	0.4500 (2)	0.21253 (19)	0.0338 (4)
O1	0.13497 (19)	0.61957 (17)	0.04810 (16)	0.0385 (4)
C1	−0.1490 (3)	0.7601 (3)	0.2500 (3)	0.0452 (6)
H1A	−0.1276	0.8249	0.2114	0.054*
H1B	−0.1756	0.8097	0.3331	0.054*
C2	−0.3007 (3)	0.6176 (3)	0.1446 (3)	0.0431 (6)
H2A	−0.3957	0.6431	0.1258	0.052*
H2B	−0.2776	0.5744	0.0585	0.052*
C3	−0.3514 (3)	0.5010 (3)	0.1859 (2)	0.0400 (6)
H3A	−0.3811	0.5409	0.2690	0.048*
H3B	−0.4498	0.4169	0.1124	0.048*
C4	−0.1454 (3)	0.4987 (3)	0.3624 (2)	0.0448 (6)
H4A	−0.0529	0.4688	0.3757	0.054*
H4B	−0.2312	0.4486	0.3883	0.054*
C5	−0.0839 (3)	0.6646 (3)	0.4583 (2)	0.0471 (6)
H5A	−0.1790	0.6922	0.4496	0.056*
H5B	−0.0429	0.6861	0.5533	0.056*
C6	0.0531 (3)	0.7618 (3)	0.4340 (2)	0.0447 (6)
H6A	0.0794	0.8646	0.4988	0.054*
H6B	0.1534	0.7432	0.4532	0.054*
C7	−0.2738 (3)	0.2861 (3)	0.1307 (2)	0.0405 (6)
H7A	−0.3500	0.2426	0.1677	0.049*
H7B	−0.1781	0.2597	0.1422	0.049*
C8	0.2884 (3)	0.7278 (2)	0.1034 (2)	0.0335 (5)
C9	0.3813 (3)	0.7947 (3)	0.2442 (2)	0.0398 (6)
H9A	0.3370	0.7600	0.2982	0.048*
C10	0.5366 (3)	0.9104 (3)	0.3058 (3)	0.0439 (6)
H10A	0.5937	0.9541	0.4002	0.053*
C11	0.6063 (3)	0.9608 (3)	0.2262 (3)	0.0451 (6)
H11A	0.7103	1.0391	0.2664	0.054*
C12	0.5194 (3)	0.8930 (3)	0.0862 (3)	0.0433 (6)
H12A	0.5684	0.9251	0.0325	0.052*
C13	0.3613 (3)	0.7787 (2)	0.0223 (2)	0.0351 (5)
C14	0.4178 (5)	0.2542 (4)	0.3898 (5)	0.1026 (15)
H14A	0.4629	0.2777	0.4841	0.154*
H14B	0.3936	0.3346	0.3891	0.154*
H14C	0.4982	0.2382	0.3438	0.154*
C15	0.2624 (5)	0.1190 (3)	0.3168 (4)	0.0653 (9)
C16	0.1757 (7)	0.0649 (5)	0.1698 (5)	0.1132 (16)
H16A	0.0775	−0.0234	0.1339	0.170*
H16B	0.2494	0.0437	0.1178	0.170*
H16C	0.1435	0.1391	0.1619	0.170*
O2	0.2075 (3)	0.0548 (2)	0.3747 (3)	0.0780 (7)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Zn1	0.03135 (16)	0.03404 (17)	0.02656 (16)	0.01193 (12)	0.00601 (11)	0.01181 (12)
Cl1	0.0504 (4)	0.0661 (5)	0.0723 (5)	0.0329 (4)	0.0110 (3)	0.0386 (4)
N1	0.0335 (11)	0.0322 (10)	0.0322 (10)	0.0095 (9)	0.0055 (8)	0.0124 (9)
N2	0.0381 (11)	0.0306 (10)	0.0266 (10)	0.0106 (9)	0.0077 (8)	0.0124 (8)
O1	0.0312 (9)	0.0386 (9)	0.0284 (9)	0.0032 (7)	0.0061 (7)	0.0103 (7)
C1	0.0467 (15)	0.0364 (13)	0.0475 (15)	0.0201 (12)	0.0089 (12)	0.0171 (12)
C2	0.0397 (14)	0.0427 (14)	0.0409 (14)	0.0218 (12)	0.0045 (11)	0.0160 (12)
C3	0.0311 (12)	0.0407 (13)	0.0344 (13)	0.0111 (11)	0.0071 (10)	0.0107 (11)
C4	0.0485 (16)	0.0497 (15)	0.0318 (13)	0.0127 (13)	0.0108 (11)	0.0219 (12)
C5	0.0524 (16)	0.0514 (16)	0.0239 (12)	0.0150 (13)	0.0086 (11)	0.0127 (12)
C6	0.0439 (15)	0.0404 (14)	0.0295 (13)	0.0125 (12)	0.0029 (11)	0.0067 (11)
C7	0.0438 (14)	0.0335 (13)	0.0369 (14)	0.0076 (11)	0.0079 (11)	0.0183 (11)
C8	0.0301 (12)	0.0289 (11)	0.0325 (12)	0.0102 (10)	0.0084 (9)	0.0097 (10)
C9	0.0359 (13)	0.0418 (14)	0.0324 (13)	0.0125 (11)	0.0106 (10)	0.0131 (11)
C10	0.0362 (14)	0.0418 (14)	0.0359 (14)	0.0125 (11)	0.0041 (11)	0.0095 (11)
C11	0.0344 (14)	0.0329 (13)	0.0470 (16)	0.0039 (11)	0.0020 (11)	0.0126 (12)
C12	0.0424 (15)	0.0337 (13)	0.0470 (15)	0.0084 (11)	0.0115 (12)	0.0199 (12)
C13	0.0365 (13)	0.0274 (11)	0.0354 (13)	0.0108 (10)	0.0075 (10)	0.0136 (10)
C14	0.083 (3)	0.080 (3)	0.153 (4)	0.028 (2)	0.064 (3)	0.058 (3)
C15	0.081 (2)	0.0511 (18)	0.087 (2)	0.0413 (18)	0.051 (2)	0.0363 (18)
C16	0.168 (5)	0.105 (3)	0.093 (3)	0.071 (4)	0.057 (3)	0.056 (3)
O2	0.0965 (19)	0.0525 (13)	0.0791 (16)	0.0185 (13)	0.0360 (14)	0.0324 (13)

Geometric parameters (Å, º)

Zn1—O1^i	2.0056 (15)	C4—C5	1.522 (4)
Zn1—N1	2.0998 (19)	C5—C6	1.519 (4)
Zn1—O1	2.1109 (16)	C7—C13^i	1.509 (3)
Zn1—N2	2.2298 (19)	C8—C9	1.400 (3)
Zn1—Cl1	2.2781 (7)	C8—C13	1.414 (3)
N1—C6	1.491 (3)	C9—C10	1.381 (3)
N1—C1	1.492 (3)	C10—C11	1.384 (4)
N2—C7	1.491 (3)	C11—C12	1.380 (4)
N2—C4	1.489 (3)	C12—C13	1.391 (3)
N2—C3	1.494 (3)	C13—C7^i	1.509 (3)
O1—C8	1.343 (3)	C14—C15	1.476 (5)
O1—Zn1^i	2.0056 (15)	C15—O2	1.210 (4)
C1—C2	1.528 (3)	C15—C16	1.471 (5)
C2—C3	1.514 (3)
O1^i—Zn1—N1	133.30 (7)	Zn1^i—O1—Zn1	100.92 (7)
O1^i—Zn1—O1	79.08 (7)	N1—C1—C2	113.82 (19)
N1—Zn1—O1	92.62 (7)	C3—C2—C1	116.4 (2)
O1^i—Zn1—N2	89.13 (7)	N2—C3—C2	112.45 (19)
N1—Zn1—N2	81.63 (7)	N2—C4—C5	113.8 (2)
O1—Zn1—N2	157.62 (7)	C6—C5—C4	116.3 (2)
O1^i—Zn1—Cl1	111.63 (5)	N1—C6—C5	113.4 (2)
N1—Zn1—Cl1	115.04 (6)	N2—C7—C13^i	113.62 (19)
O1—Zn1—Cl1	102.18 (5)	O1—C8—C9	120.9 (2)
N2—Zn1—Cl1	99.84 (5)	O1—C8—C13	121.4 (2)
C6—N1—C1	112.69 (19)	C9—C8—C13	117.8 (2)
C6—N1—Zn1	109.81 (14)	C10—C9—C8	122.4 (2)
C1—N1—Zn1	114.51 (14)	C11—C10—C9	119.5 (2)
C7—N2—C4	108.39 (18)	C12—C11—C10	119.0 (2)
C7—N2—C3	112.05 (18)	C11—C12—C13	122.6 (2)
C4—N2—C3	111.66 (18)	C12—C13—C8	118.7 (2)
C7—N2—Zn1	103.64 (14)	C12—C13—C7^i	118.9 (2)
C4—N2—Zn1	106.29 (14)	C8—C13—C7^i	122.5 (2)
C3—N2—Zn1	114.28 (14)	O2—C15—C16	121.0 (4)
C8—O1—Zn1^i	130.14 (14)	O2—C15—C14	121.7 (4)
C8—O1—Zn1	127.40 (14)	C16—C15—C14	117.3 (4)

Symmetry code: (i) −x, −y+1, −z.

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
N1—H1C···O2^ii	0.91	2.28	3.038 (3)	141

Symmetry code: (ii) x, y+1, z.