Dipotassium di-μ-iso­thio­cyanato-κ⁴N:S-bis­[(N-salicyl­idene-DL-valinato-κ³O,N,O′)­cuprate(II)]

The title compound, K₂[Cu₂(NCS)₂(C₁₂H₁₃NO₃)₂], consists of two K⁺ cations and (N-salicyl­idene-D-valinato)­cop­per(II) and (N-salicyl­idene-L-valinato)cop­per(II) coordination units con­nected through three-atom thio­cyanate (μ-NCS) bridges into a centrosymmetric dianion. The Cu^II atom adopts a square-pyramidal coordination, with three donor atoms of the tridentate Schiff base and one N atom of the bridging ligand (μ-NCS) in the basal plane. The axial position is occupied by the thio­cyanate S atom of a symmetry-related ligand at an apical distance of 2.9332 (10) Å. Coulombic interactions between six-coordinated K⁺ ions and the heteroatoms of neighbouring dimeric anions leads to the formation of one-dimensional chains of mol­ecules parallel to [010]. The superposition of the normals of the pyramidal base planes in a direction close to [001] indicates possible π–π interactions between neighbouring units.

S1. Comment

Copper(II) complexes of tridentate Schiff bases (TSB) derived from salicylaldehyde and amino acids are of interest not only as simple structural models of more complicated bioinorganic systems, such as SOD-mimic activity (Bergendi et al., 1991; Valentová et al., 1995) or vitamin B6-mimic activities (Metzler et al., 1954; Koh et al., 1996), but also for their antimicrobial (Sokolík et al., 1997), antifungal (Švajlenová et al., 2002), antipyretic and immunoprotective activities. Another interesting feature of Cu–TSB complexes is the coordination geometry around the metal ion. If an additional ligand is present, square-pyramidal(4 + 1) complexes with an elongated bond distance (bond lengths up to 3 Å) between the central atom and the donor atom situated at the apex of pyramid (Friebel et al., 1997) are usually formed, and resulting units can be further involved in the formation of dimeric (Pavelčík et al., 1981; Werner et al., 1983; Warda, 1997, 1998a) or even polymeric (Warda, 1998b) structures. The impulse for studying the title derivative of the (N-salicylidene-DL-valinato-O,N,O')copper(II) complex was not only the difference between the magnetic and spectral (UV-VIS, ESR) properties of Cu(sal-DL-val) (Švajlenová et al., 1978) and dimeric Cu(sal-L-val)(H₂O) (Korhonen et al., 1979), but also the proposed significant biological activities discovered in other Cu–TSB complexes.

The title dimeric µ-isothiocyanato copper(II) complex, (I), was prepared by reaction of Cu(sal-DL-val) with thiocyanate anions in an ethanol/aqueous solution. The spectral and ESR properties of this type of compound indicate a square-pyramidal environment around the Cu^II atom (Kettmann et al., 1989, 1992; Sivý et al., 1990). As a direct proof of this assumption, we report here the crystal structure of (I).

The dimer (I) consists of [Cu(sal-D-val)(NCS)] and [Cu(sal-L-val)(NCS)] coordination units. The copper ions adopt 4 + 1 square-pyramidal geometry defined by the tridentate N-salicylidene-D-valinato-O,N,O' (or –L-valinato-) dianions and the N atom of of the NCS⁻ ligand in the basal plane. The apical position is occupied by the Sⁱ atom from a neighbouring molecule, with a Cu–S distance of 2.9332 (10) Å [symmetry code: (i) −x, 1 − y, 1 − z]. This length is comparable to the average length 2.88 Å of this bond in related complexes in the Cambridge Structural Database (Version 5.24.1; Allen, 2002).

The mean plane through Cu and the four basal atoms shows that the N atom of the NCS⁻ ligand is significantly [with deviation 0.532 (3) Å] shifted. The five-membered chelate and phenyl rings of the (sal-val) moiety are nearly planar (the average deviations of contributing atoms from the least-squares planes are 0.013 and 0.002 Å, respectively). The six-membered chelate ring is more deformed; atom N11 is displaced by 0.120 (3) Å from the mean plane through the five remaining atoms (their average deviation from the plane is 0.006 Å; the Cremer & Pople (1975) puckering parameters for the ring are Q = 0.083 (3) Å, Θ = 51 (2)°, ϕ₂ =46 (3)°]. The angles between the planes of the phenyl and six-membered chelate rings and between the planes of the six-membered and five-membered chelate rings are 1.46 (7)° and 4.40 (7)°, respectively.

The crystal packing is dominated by Coulomb interactions between the K⁺ ions and the heteroatoms of the neighbouring dimeric anions, which leads to the formation of one-dimensional chains of molecules through the crystal in the [010] direction. The coordination number of the K⁺ ion is 6.

The chelate ring system resulting from the TSB coordination could show metaloaromaticity (Masui, 2001) and related interactions. In crystals of (I), we observed the superposition of normals of pyramidal base planes, with possible π–π interactions in a direction close to [001].

S2. Experimental

The title compound was prepared according to published patented procedures (Krätsmár-Šmogrovič et al., 1989, 1991). The reaction mixture, consituted of Cu(sal-DL-val) (10 mmol, 2.8 g) and KSCN (30 mmol, 2.9 g) resolved in ethanol/water (2:1 v/v, 50 ml) was heated and mixed vigorously for 20 min until the solid phase disappeared. The solution was filtered and left to cool to room temperature. Dark-green well developed crystals were isolated and analyzed. Analysis (Carlo-Erba 1180 instrument) calculated for C₁₃H₁₃CuKN₂O₃S: C 41.09, H 3.45, N 7.37%; found: C 40.71, H 3.40, N 7.38%.

S3. Refinement

All H atoms were fixed geometrically and refined isotropically. Three free variables were used for describing the U_eq values of H atoms during refinement, viz. two for H atoms attached to the methyl C11 and C12 atoms and one for H atoms at the aromatic C4, C5, C6 and C7 atoms.

Computing details

Data collection: CrysAlis (Oxford Diffraction, 2002); cell refinement: CrysRed (Oxford Diffraction, 2002); data reduction: CrysRed; program(s) used to solve structure: SHELXS97 (Sheldrick, 1990); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: ORTEPIII (Johnson & Burnett, 1996); software used to prepare material for publication: SHELXL97, PARST (Nardelli, 1995).

Figures

	Fig. 1. : ORTEP plot of the title dimer. Non-H atoms are shown as displacement ellipsoids at the 50% probability level and H atoms as small spheres of arbitrary radii. The dependent part of the dimer is at the symmetry position −x, 1 − y, 1 − z.
	Fig. 2. : Part of the crystal structure of (I), showing the formation of a molecular chain between K^+ cations and dimeric dianions. [Symmetry codes: (i) −x, 1 − y, 1 − z; (ii) x, y − 1, z.]

Dipotassium Bis[(µ-isothiocyanato-N,S) (N-salicylidene-DL-valinato-O,N,O')cuprate(II)]

Crystal data

2K^+·2C13H13CuN2O3S^+	F(000) = 386
Mr = 759.0	Dx = 1.753 Mg m^−3
Triclinic, P1	Melting point: 510 K
a = 8.4753 (8) Å	Mo Kα radiation, λ = 0.71073 Å
b = 9.5364 (8) Å	Cell parameters from 1760 reflections
c = 10.1210 (11) Å	θ = 2.9–27.4°
α = 76.128 (8)°	µ = 1.95 mm^−1
β = 72.381 (9)°	T = 120 K
γ = 69.917 (8)°	Prism, dark green
V = 723.76 (12) Å^3	0.50 × 0.20 × 0.20 mm
Z = 1

Data collection

Kuma KM-4-Plus CCD diffractometer	2335 reflections with I > 2σ(I)
Radiation source: fine-focus sealed tube	Rint = 0.050
Enhance (Oxford Diffraction) monochromator	θmax = 25.0°, θmin = 2.6°
Detector resolution: 16.3 pixels mm^-1	h = −7→10
rotation method, ω–scan	k = −10→11
4202 measured reflections	l = −12→11
2479 independent reflections

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)] = 0.030	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.112	H-atom parameters constrained
S = 0.98	w = 1/[σ^2(Fo^2) + (0.075P)^2 + 1.75P] where P = (Fo^2 + 2Fc^2)/3
2479 reflections	(Δ/σ)max < 0.001
197 parameters	Δρmax = 0.65 e Å^−3
0 restraints	Δρmin = −0.82 e Å^−3

Special details

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
Cu	0.32825 (4)	0.45525 (4)	0.41296 (4)	0.01254 (17)
K	0.12073 (9)	0.17080 (8)	0.43660 (8)	0.0181 (2)
S	−0.12495 (11)	0.50485 (10)	0.78906 (9)	0.0194 (2)
O4	0.2126 (3)	0.6614 (3)	0.4483 (2)	0.0160 (5)
O5	0.4450 (3)	0.2515 (3)	0.3862 (3)	0.0176 (5)
N1	0.1572 (3)	0.3884 (3)	0.5766 (3)	0.0158 (6)
O10	0.2324 (3)	0.8947 (3)	0.3921 (3)	0.0195 (5)
N11	0.5134 (3)	0.5361 (3)	0.2967 (3)	0.0119 (5)
C1	0.6663 (4)	0.4535 (4)	0.2458 (3)	0.0132 (6)
H1	0.7536	0.5029	0.2036	0.011 (9)*
C2	0.7169 (4)	0.2933 (4)	0.2471 (3)	0.0125 (6)
C3	0.6061 (4)	0.2007 (4)	0.3159 (3)	0.0136 (6)
C4	0.6756 (4)	0.0447 (4)	0.3091 (4)	0.0171 (7)
H4	0.6049	−0.0200	0.3550	0.020 (5)*
C5	0.8434 (4)	−0.0161 (4)	0.2375 (4)	0.0182 (7)
H5	0.8863	−0.1217	0.2345	0.020 (5)*
C6	0.9515 (4)	0.0753 (4)	0.1693 (4)	0.0190 (7)
H6	1.0672	0.0329	0.1201	0.020 (5)*
C7	0.8873 (4)	0.2273 (4)	0.1749 (4)	0.0170 (7)
H7	0.9602	0.2899	0.1285	0.020 (5)*
C8	0.2932 (4)	0.7593 (4)	0.3832 (3)	0.0139 (7)
C9	0.4761 (4)	0.7006 (4)	0.2892 (3)	0.0125 (6)
H9	0.5613	0.7176	0.3293	0.020*
C10	0.4862 (4)	0.7923 (4)	0.1400 (3)	0.0151 (7)
H10	0.4341	0.9011	0.1519	0.020*
C11	0.3783 (5)	0.7592 (4)	0.0611 (4)	0.0234 (8)
H11A	0.3731	0.8316	−0.0256	0.031 (7)*
H11B	0.2609	0.7684	0.1201	0.031 (7)*
H11C	0.4318	0.6564	0.0382	0.031 (7)*
C12	0.6704 (5)	0.7757 (4)	0.0509 (4)	0.0235 (8)
H12A	0.7203	0.6749	0.0231	0.032 (7)*
H12B	0.7406	0.7890	0.1055	0.032 (7)*
H12C	0.6687	0.8525	−0.0330	0.032 (7)*
C13	0.0398 (4)	0.4373 (3)	0.6654 (3)	0.0128 (7)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Cu	0.0085 (2)	0.0095 (3)	0.0170 (3)	−0.00110 (16)	−0.00037 (16)	−0.00301 (16)
K	0.0155 (4)	0.0111 (4)	0.0252 (4)	−0.0020 (3)	−0.0010 (3)	−0.0063 (3)
S	0.0145 (4)	0.0239 (5)	0.0189 (4)	−0.0056 (3)	0.0013 (3)	−0.0085 (3)
O4	0.0108 (11)	0.0132 (12)	0.0214 (12)	−0.0012 (9)	−0.0004 (9)	−0.0059 (9)
O5	0.0120 (11)	0.0119 (12)	0.0241 (13)	−0.0023 (9)	0.0027 (10)	−0.0050 (9)
N1	0.0129 (13)	0.0144 (14)	0.0192 (15)	−0.0039 (11)	−0.0031 (12)	−0.0022 (11)
O10	0.0197 (12)	0.0116 (13)	0.0234 (13)	0.0010 (10)	−0.0035 (10)	−0.0060 (10)
N11	0.0099 (12)	0.0083 (13)	0.0162 (14)	0.0001 (10)	−0.0045 (11)	−0.0021 (10)
C1	0.0108 (14)	0.0165 (17)	0.0138 (16)	−0.0046 (13)	−0.0047 (12)	−0.0022 (12)
C2	0.0113 (15)	0.0126 (16)	0.0133 (16)	0.0000 (12)	−0.0052 (12)	−0.0033 (12)
C3	0.0129 (15)	0.0129 (16)	0.0134 (16)	0.0000 (12)	−0.0052 (12)	−0.0022 (12)
C4	0.0202 (17)	0.0133 (17)	0.0168 (17)	−0.0051 (13)	−0.0036 (14)	−0.0013 (13)
C5	0.0201 (17)	0.0094 (16)	0.0218 (18)	0.0036 (13)	−0.0072 (14)	−0.0053 (13)
C6	0.0123 (15)	0.0167 (17)	0.0231 (18)	0.0030 (13)	−0.0036 (13)	−0.0058 (14)
C7	0.0111 (15)	0.0165 (17)	0.0223 (18)	−0.0028 (13)	−0.0032 (13)	−0.0042 (13)
C8	0.0121 (15)	0.0133 (17)	0.0162 (16)	0.0005 (13)	−0.0064 (13)	−0.0043 (12)
C9	0.0112 (15)	0.0084 (16)	0.0182 (17)	−0.0013 (12)	−0.0044 (12)	−0.0037 (12)
C10	0.0162 (16)	0.0090 (16)	0.0169 (17)	−0.0016 (12)	−0.0027 (13)	−0.0007 (12)
C11	0.0261 (19)	0.0230 (19)	0.0223 (19)	−0.0063 (15)	−0.0114 (15)	0.0004 (14)
C12	0.0195 (18)	0.0229 (19)	0.0219 (18)	−0.0064 (15)	0.0009 (14)	0.0007 (14)
C13	0.0130 (15)	0.0110 (16)	0.0170 (17)	−0.0055 (12)	−0.0081 (14)	0.0020 (12)

Geometric parameters (Å, º)

Cu—O5	1.897 (2)	N11—C9	1.478 (4)
Cu—N11	1.929 (3)	C1—C2	1.436 (5)
Cu—O4	1.938 (2)	C1—H1	0.9500
Cu—N1	1.982 (3)	C2—C7	1.405 (5)
Cu—S^i	2.9332 (10)	C2—C3	1.423 (5)
Cu—N11^ii	3.608 (3)	C3—C4	1.410 (5)
Cu—Cu^ii	4.2238 (8)	C4—C5	1.377 (5)
Cu—Cu^i	5.1300 (9)	C4—K^iv	3.398 (3)
Cu—K	3.6359 (8)	C4—H4	0.9500
K—O10^iii	2.575 (2)	C5—C6	1.398 (5)
K—O4^i	2.774 (2)	C5—K^iv	3.333 (4)
K—N1	2.920 (3)	C5—H5	0.9500
K—O5	2.970 (2)	C6—C7	1.371 (5)
K—O10^i	3.159 (3)	C6—H6	0.9500
K—C5^iv	3.333 (4)	C7—H7	0.9500
K—C8^i	3.344 (3)	C8—C9	1.545 (4)
K—S^i	3.3800 (12)	C8—K^i	3.344 (3)
K—C4^iv	3.398 (3)	C9—C10	1.546 (4)
K—C13^i	3.520 (3)	C9—H9	1.0000
K—K^v	4.1750 (14)	C10—C12	1.524 (5)
S—C13	1.625 (3)	C10—C11	1.527 (5)
S—K^i	3.3800 (12)	C10—H10	1.0000
O4—C8	1.281 (4)	C11—H11A	0.9800
O4—K^i	2.774 (2)	C11—H11B	0.9800
O5—C3	1.314 (4)	C11—H11C	0.9800
N1—C13	1.164 (4)	C12—H12A	0.9800
O10—C8	1.230 (4)	C12—H12B	0.9800
O10—K^vi	2.575 (2)	C12—H12C	0.9800
O10—K^i	3.159 (3)	C13—K^i	3.520 (3)
N11—C1	1.286 (4)
O5—Cu—N11	96.19 (11)	C13^i—K—K^v	131.58 (6)
O5—Cu—O4	177.31 (10)	Cu—K—K^v	166.55 (3)
N11—Cu—O4	84.05 (10)	C13—S—K^i	81.25 (11)
O5—Cu—N1	90.14 (11)	C8—O4—Cu	116.7 (2)
N11—Cu—N1	162.93 (12)	C8—O4—K^i	105.04 (19)
O4—Cu—N1	88.90 (11)	Cu—O4—K^i	136.82 (11)
O5—Cu—S^i	91.61 (8)	C3—O5—Cu	125.5 (2)
N11—Cu—S^i	101.21 (8)	C3—O5—K	135.2 (2)
O4—Cu—S^i	90.97 (7)	Cu—O5—K	94.07 (9)
N1—Cu—S^i	94.41 (8)	C13—N1—Cu	140.3 (3)
O5—Cu—K	54.57 (7)	C13—N1—K	116.8 (2)
N11—Cu—K	141.81 (8)	Cu—N1—K	93.79 (10)
O4—Cu—K	126.38 (7)	C8—O10—K^vi	173.1 (2)
N1—Cu—K	53.26 (8)	C8—O10—K^i	87.74 (19)
S^i—Cu—K	60.82 (2)	K^vi—O10—K^i	92.90 (7)
O10^iii—K—O4^i	129.32 (8)	C1—N11—C9	121.1 (3)
O10^iii—K—N1	145.14 (8)	C1—N11—Cu	123.6 (2)
O4^i—K—N1	73.68 (7)	C9—N11—Cu	114.6 (2)
O10^iii—K—O5	102.93 (7)	N11—C1—C2	125.8 (3)
O4^i—K—O5	126.84 (7)	N11—C1—H1	117.1
N1—K—O5	55.58 (7)	C2—C1—H1	117.1
O10^iii—K—O10^i	87.10 (7)	C7—C2—C3	119.4 (3)
O4^i—K—O10^i	43.17 (6)	C7—C2—C1	116.4 (3)
N1—K—O10^i	105.31 (7)	C3—C2—C1	124.2 (3)
O5—K—O10^i	157.55 (7)	O5—C3—C4	118.5 (3)
O10^iii—K—C5^iv	83.89 (8)	O5—C3—C2	124.1 (3)
O4^i—K—C5^iv	87.75 (8)	C4—C3—C2	117.4 (3)
N1—K—C5^iv	69.90 (8)	C5—C4—C3	121.6 (3)
O5—K—C5^iv	88.88 (8)	C5—C4—K^iv	75.6 (2)
O10^i—K—C5^iv	72.06 (8)	C3—C4—K^iv	116.5 (2)
O10^iii—K—C8^i	108.50 (8)	C5—C4—H4	119.2
O4^i—K—C8^i	21.72 (8)	C3—C4—H4	119.2
N1—K—C8^i	88.51 (8)	K^iv—C4—H4	78.3
O5—K—C8^i	144.08 (8)	C4—C5—C6	120.9 (3)
O10^i—K—C8^i	21.56 (7)	C4—C5—K^iv	80.8 (2)
C5^iv—K—C8^i	77.79 (8)	C6—C5—K^iv	113.7 (2)
O10^iii—K—S^i	130.57 (6)	C4—C5—H5	119.6
O4^i—K—S^i	82.90 (5)	C6—C5—H5	119.6
N1—K—S^i	70.69 (6)	K^iv—C5—H5	75.8
O5—K—S^i	67.35 (5)	C7—C6—C5	118.7 (3)
O10^i—K—S^i	120.82 (5)	C7—C6—H6	120.6
C5^iv—K—S^i	140.55 (7)	C5—C6—H6	120.6
C8^i—K—S^i	102.85 (6)	C6—C7—C2	122.0 (3)
O10^iii—K—C4^iv	71.63 (8)	C6—C7—H7	119.0
O4^i—K—C4^iv	111.16 (8)	C2—C7—H7	119.0
N1—K—C4^iv	75.46 (8)	O10—C8—O4	123.5 (3)
O5—K—C4^iv	72.89 (8)	O10—C8—C9	119.5 (3)
O10^i—K—C4^iv	91.85 (7)	O4—C8—C9	117.0 (3)
C5^iv—K—C4^iv	23.58 (8)	O10—C8—K^i	70.70 (18)
C8^i—K—C4^iv	100.81 (8)	O4—C8—K^i	53.24 (15)
S^i—K—C4^iv	137.72 (6)	C9—C8—K^i	167.7 (2)
O10^iii—K—C13^i	153.06 (8)	N11—C9—C8	107.6 (2)
O4^i—K—C13^i	57.15 (7)	N11—C9—C10	115.1 (3)
N1—K—C13^i	58.47 (8)	C8—C9—C10	109.5 (3)
O5—K—C13^i	81.56 (7)	N11—C9—H9	108.1
O10^i—K—C13^i	98.66 (7)	C8—C9—H9	108.1
C5^iv—K—C13^i	122.96 (8)	C10—C9—H9	108.1
C8^i—K—C13^i	78.33 (8)	C12—C10—C11	110.3 (3)
S^i—K—C13^i	27.15 (5)	C12—C10—C9	113.8 (3)
C4^iv—K—C13^i	133.91 (8)	C11—C10—C9	112.7 (3)
O10^iii—K—Cu	134.21 (6)	C12—C10—H10	106.5
O4^i—K—Cu	96.16 (5)	C11—C10—H10	106.5
N1—K—Cu	32.94 (6)	C9—C10—H10	106.5
O5—K—Cu	31.36 (5)	C10—C11—H11A	109.5
O10^i—K—Cu	135.82 (5)	C10—C11—H11B	109.5
C5^iv—K—Cu	94.26 (6)	H11A—C11—H11B	109.5
C8^i—K—Cu	115.80 (6)	C10—C11—H11C	109.5
S^i—K—Cu	49.262 (19)	H11A—C11—H11C	109.5
C4^iv—K—Cu	88.84 (6)	H11B—C11—H11C	109.5
C13^i—K—Cu	53.32 (5)	C10—C12—H12A	109.5
O10^iii—K—K^v	49.08 (6)	C10—C12—H12B	109.5
O4^i—K—K^v	80.74 (5)	H12A—C12—H12B	109.5
N1—K—K^v	134.89 (6)	C10—C12—H12C	109.5
O5—K—K^v	146.84 (6)	H12A—C12—H12C	109.5
O10^i—K—K^v	38.02 (4)	H12B—C12—H12C	109.5
C5^iv—K—K^v	72.62 (6)	N1—C13—S	179.6 (3)
C8^i—K—K^v	59.47 (6)	N1—C13—K^i	108.5 (2)
S^i—K—K^v	142.07 (3)	S—C13—K^i	71.61 (11)
C4^iv—K—K^v	80.21 (6)

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