Bis(4-methyl­benzyl­ammonium) tetra­chloridozincate: a new noncentrosymmetric structure characterized by ¹³C CP-MAS NMR spectroscopy

A new noncentrosymmetric organic-inorganic hybrid material, (C₈H₁₂N)₂[ZnCl₄], has been synthesized as single crystals at room temperature and characterized by X-ray diffraction and solid-state NMR spectroscopy. Its novel structure consists of two 4-methyl­benzyl­ammonium cations and one [ZnCl₄]^2- anion connected by N-H...Cl and C-H...Cl hydrogen bonds, two of which are three-centre inter­actions. The Zn^II metal centre has a slightly distorted tetra­hedral coordination geometry. Results from ¹³C CP-MAS NMR spectroscopy are in good agreement with the X-ray structure. Density functional theory calculations allow the assignment of the carbon peaks to the independent crystallographic sites.

S1. Comment

Organic–inorganic hybrid materials having a noncentrosymmetric structure are interesting for their applications in various fields such as quadratic nonlinear optical materials research (Masse et al., 1993). Structural investigation of the tetrahalometallate anions of the metals of the first transition series with different countercations is of interest because of their large structural variabilities (Smith, 1976). Hybrid d₁₀-metal halides have been found to exhibit important structural properties because of their wide range of stereochemical features, such as distorted tetrahedral (Bhattacharya et al., 2002), square-pyramidal (Antolini et al., 1980) and trigonal–bipyramidal (Raymond et al., 1968) geometries. As a contribution to the investigation of the above materials, we report here the crystal structure of one such compound, (C₈H₁₁N)₂[ZnCl₄], (I), formed from the reaction of 4-methylbenzylamine and zinc chloride.

The asymmetric unit of (I) comprises two 4-methylbenzylammonium cations and a [ZnCl₄]^2- anion (Fig. 1). The crystal structure of this material consists of a network of the constituent 4-methylbenzylammonium cations and [ZnCl₄]^2- anions connected by N—H···Cl hydrogen bonds, two of which are three-centre interactions, N15—H152···(Cl2,Cl5) and N15—H153···(Cl2,Cl5) (Table 1). Multiple hydrogen bonds connect the different entities of (I) to form layers, built up from the [ZnCl₄]^2- anions and the ammonium groups, parallel to the ac plane (Fig. 2). Fig 3 shows that two such layers cross the unit cell at z = 0 and z = 1/2, and the bodies of the organic groups are located between these layers and connect them via weak C—H···Cl hydrogen bonds. The organic molecule exhibits a regular spatial configuration with normal C—C and C—N distances and C—C—C and C—C—N angles [Standard reference?]. No π–π stacking interactions between the phenylene rings or C—H···π interactions towards them are observed.

Previous studies [References?] showed that, in the [ZnCl₄]^2- anion, the Zn—Cl bond lengths and Cl—Zn—Cl bond angles are not equal, but vary with the environment around the Cl atom. In complex (I), the Zn—Cl bond lengths vary between 2.2568 (18) and 2.2842 (14) Å, and the Cl—Zn—Cl angles range from 104.28 (7) to 115.71 (7)°. Owing to these differences in the geometric parameters, the [ZnCl₄]^2- anion has a slightly distorted tetrahedral stereochemistry (as in Guo et al., 2007). In (I), since atom Cl4 is involved in a strong N—H···Cl hydrogen bond (H···Cl = 2.30 Å), the Zn—Cl4 bond is obviously longer than Zn—Cl2, Zn—Cl3 and Zn—Cl4 (Table 1).

Refining the structure in the noncentrosymmetric space group gives a value of 0.00 (2) for the Flack parameter (Flack & Bernardinelli, 1999). This value confirms that the direction of the polar axis is correctly determined.

The ¹³C CP–MAS NMR spectrum of crystalline (I) is shown in Fig. 4. In the aliphatic resonance domain, the spectrum displays four resonances corresponding to two methyl and two methylene C atoms. This result is consistent with the presence of two organic moieties in the asymmetric unit of the compound, in agreement with the X-ray diffraction data. Density functional theory (DFT) calculations were undertaken in order to assign the NMR resonances to the different crystallographically non-quivalent C atoms of the unit cell. These calculations were made at the B3LYP/6-31+G* level using the GAUSSIAN98 software (Frisch et al., 1998). Three different calculations were made on the two non-equivalent organic cations in the unit cell and in all cases the theoretical chemical shifts were subtracted from those of the reference (tetramethylsilane) calculated at the same level of theory. (1) Calculation of the NMR chemical shifts (with the GIAO method [define acronym?]) by taking the geometry obtained from X-ray diffraction. (2) Optimization of the positions of the H atoms in the molecule and calculation of the NMR chemical shifts in this semi-optimized geometry. (X-ray diffraction always leads to underestimated X—H bond lengths, due to the fact that it is sensitive to the electron cloud and does not see the nuclei.) (3) Full optimization of all atoms and calculation of NMR chemical shifts. This calculation, compared with that above, will give indications of the steric hindrance around the organic cation and the positions where it is the strongest. The results are listed in Table 2. Clearly, there is a very good agreement between the experimental and theoretical values calculated after optimization of the H-atom positions, allowing the unambiguous assignment of the different NMR signals to the various C atoms of the structure.

In conclusion, compound (I) was prepared as single crystals at room temperature and characterized by two physicochemical methods. On the structural level, the atomic arrangement of this material consists of a network of 4-methylbenzylyammonium cations and tetrachloridozincate anions connected by N—H···Cl and C—H···Cl hydrogen bonds. The number of ¹³C CP–MAS NMR components is in full agreement with those of the crystallographically independent sites.

Related literature

For related literature, see: Antolini et al. (1980); Bhattacharya et al. (2002); Flack & Bernardinelli (1999); Frisch (1998); Guo et al. (2007); Larson (1970); Masse et al. (1993); Prince (1982); Raymond et al. (1968); Smith (1976); Watkin (1994).

S2. Experimental

A mixture of 2-amino-5-chloropyridine (3 mmol, 0.385 g), zinc chloride (1.5 mmol, 0.297 g) and HCl (10 ml, 0.3 M) in water (Volume?) was placed in a Petri dish and allowed to evaporate slowly at room temperature. Colourless single crystals of the title compound, (I), were isolated after several days (yield 54%). The ¹³C CP–MAS NMR spectrum was recorded on a solid-state high-resolution Bruker DSX300 spectrometer operating at 75.49 MHz for ¹³C, with a classical 4 mm probe head allowing spinning rates up to 10 kHz. The chemical shifts are given relative to tetramethylsilane (external reference, precision 0.5 p.p.m.). The spectrum was recorded by use of cross-polarization (CP) from protons (contact time 5 ms) and MAS. It was checked that there was a sufficient delay between scans to allow full relaxation of the nuclei.

S3. Refinement

All H atoms were located in a difference map. They were initially refined with soft restraints on the bond lengths and angles to regularize their geometry, with C—H = 0.93–0.98 and N—H = 0.86–0.89 Å, and with U_iso(H) = 1.2–1.5U_eq(parent atom), after which the positions were refined with riding constraints. Software and methods used for extinction correction and weighting scheme: Larson (1970); Prince (1982); Watkin (1994).

Computing details

Data collection: CrysAlis PRO (Agilent Technologies, 2010); cell refinement: CrysAlis PRO (Agilent Technologies, 2010); data reduction: CrysAlis PRO (Agilent Technologies, 2010); program(s) used to solve structure: SIR97 (Altomare et al., 1999); program(s) used to refine structure: CRYSTALS (Betteridge et al., 2003); molecular graphics: CAMERON (Watkin et al., 1996); software used to prepare material for publication: CRYSTALS (Betteridge et al., 2003).

Figures

	Fig. 1. A view of (I), showing the atomic numbering scheme. Displacement ellipsoids are drawn at 50% probability level.
	Fig. 2. A projection, along the b axis, of a layer in the structure of (I), showing the N—H···Cl hydrogen-bonding interactions (dashed lines). Only the ammonium and tetrachloridozincate sections are shown, for clarity.
	Fig. 3. A projection of the structure of (I) along the c axis. Hydrogen bonds are denoted as dashed lines.
	Fig. 4. ^13C CP–MAS NMR spectrum of (C8H11N)2[ZnCl4].

Bis(4-methylbenzylammonium) tetrachloridozincate

Crystal data

(C8H12N)2[ZnCl4]	F(000) = 928
Mr = 451.57	Dx = 1.493 Mg m^−3
Orthorhombic, Pna21	Mo Kα radiation, λ = 0.7107 Å
Hall symbol: P 2c -2n	Cell parameters from 11472 reflections
a = 10.6623 (8) Å	θ = 3.3–29.6°
b = 25.395 (2) Å	µ = 1.76 mm^−1
c = 7.4167 (5) Å	T = 110 K
V = 2008.2 (3) Å^3	Needle, colourless
Z = 4	0.26 × 0.17 × 0.09 mm

Data collection

Make? Model? CCD area-detector diffractometer	5120 independent reflections
Radiation source: Enhance (Mo) X-ray source	4699 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.061
Detector resolution: 10.4685 pixels mm^-1	θmax = 29.6°, θmin = 3.4°
ω scans	h = −14→14
Absorption correction: analytical [CrysAlis PRO (Agilent Technologies, 2010), based on expressions derived by Clark & Reid (1995)]	k = −34→33
Tmin = 0.692, Tmax = 0.866	l = −10→10
26378 measured reflections

Refinement

Refinement on F^2	H-atom parameters constrained
Least-squares matrix: full	Method, part 1, Chebychev polynomial, (Watkin, 1994, Prince, 1982) [weight] = 1.0/[A0*T0(x) + A1*T1(x) ··· + An-1]*Tn-1(x)] where Ai are the Chebychev coefficients listed below and x = F /Fmax Method = Robust Weighting (Prince, 1982) W = [weight] * [1-(deltaF/6*sigmaF)^2]^2 Ai are: 0.168E + 04 0.269E + 04 0.142E + 04 428.
R[F^2 > 2σ(F^2)] = 0.066	(Δ/σ)max = 0.001
wR(F^2) = 0.143	Δρmax = 1.10 e Å^−3
S = 0.92	Δρmin = −1.36 e Å^−3
5120 reflections	Extinction correction: Larson (1970), Equation 22
210 parameters	Extinction coefficient: 40 (5)
1 restraint	Absolute structure: Flack & Bernardinelli (1999), with 2877 Friedel pairs
Primary atom site location: structure-invariant direct methods	Absolute structure parameter: 0.00 (2)
Hydrogen site location: inferred from neighbouring sites

Special details

Experimental. CrysAlisPro, Agilent Technologies, Version 1.171.34.46 (release 25-11-2010 CrysAlis171 .NET) (compiled Nov 25 2010,17:55:46) Analytical numeric absorption correction using a multifaceted crystal model based on expressions derived by Clark & Reid (1995).

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

	x	y	z	Uiso*/Ueq
Zn1	−0.25524 (5)	0.52545 (2)	0.28711 (18)	0.0233
Cl2	−0.16343 (13)	0.55061 (5)	0.5498 (2)	0.0288
Cl3	−0.24612 (14)	0.43815 (6)	0.2302 (3)	0.0313
Cl4	−0.46200 (12)	0.54629 (5)	0.3245 (2)	0.0310
Cl5	−0.15744 (14)	0.56572 (5)	0.0552 (2)	0.0315
N6	0.0648 (6)	0.9308 (2)	0.7572 (8)	0.0401
C7	0.0290 (6)	0.8918 (2)	0.8942 (9)	0.0340
C8	0.0207 (5)	0.8370 (2)	0.8228 (7)	0.0244
C9	0.1178 (5)	0.8148 (2)	0.7239 (8)	0.0294
C10	0.1116 (6)	0.7629 (3)	0.6722 (8)	0.0304
C11	0.0101 (5)	0.7312 (2)	0.7181 (8)	0.0263
C12	0.0092 (8)	0.6739 (2)	0.6660 (9)	0.0401
H122	−0.0572	0.6561	0.7281	0.0621*
H121	−0.0030	0.6707	0.5383	0.0622*
H123	0.0878	0.6581	0.6990	0.0620*
C13	−0.0867 (5)	0.7542 (2)	0.8144 (8)	0.0262
C14	−0.0829 (5)	0.8066 (2)	0.8660 (7)	0.0233
H141	−0.1503	0.8212	0.9288	0.0290*
H131	−0.1564	0.7337	0.8452	0.0321*
H101	0.1778	0.7487	0.6052	0.0372*
H91	0.1875	0.8350	0.6925	0.0359*
H72	−0.0522	0.9018	0.9414	0.0400*
H71	0.0905	0.8929	0.9905	0.0401*
H63	0.0470	0.9633	0.7957	0.0609*
H62	0.1469	0.9285	0.7363	0.0612*
H61	0.0231	0.9243	0.6560	0.0611*
N15	0.1067 (4)	0.55183 (18)	0.3432 (7)	0.0282
C16	0.1947 (7)	0.5751 (2)	0.2126 (10)	0.0378
C17	0.2060 (6)	0.6339 (2)	0.2313 (8)	0.0268
C18	0.3089 (5)	0.6559 (2)	0.3199 (8)	0.0258
C19	0.3232 (5)	0.7100 (2)	0.3265 (8)	0.0298
C20	0.2379 (5)	0.7433 (2)	0.2461 (8)	0.0255
C21	0.1342 (6)	0.7213 (2)	0.1611 (8)	0.0287
C22	0.1191 (6)	0.6673 (2)	0.1521 (8)	0.0256
H221	0.0499	0.6532	0.0915	0.0322*
H211	0.0739	0.7435	0.1089	0.0350*
C23	0.2526 (7)	0.8027 (2)	0.2487 (10)	0.0385
H231	0.1728	0.8192	0.2716	0.0582*
H233	0.2840	0.8147	0.1346	0.0582*
H232	0.3110	0.8124	0.3427	0.0581*
H191	0.3920	0.7242	0.3862	0.0360*
H181	0.3684	0.6342	0.3737	0.0318*
H162	0.1657	0.5664	0.0923	0.0452*
H161	0.2769	0.5594	0.2313	0.0451*
H153	0.1110	0.5168	0.3358	0.0430*
H152	0.0288	0.5619	0.3163	0.0430*
H151	0.1258	0.5620	0.4552	0.0433*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Zn1	0.0235 (3)	0.0192 (3)	0.0272 (3)	0.00026 (18)	−0.0020 (2)	−0.0006 (3)
Cl2	0.0302 (6)	0.0279 (6)	0.0284 (6)	−0.0023 (5)	−0.0017 (5)	−0.0056 (6)
Cl3	0.0433 (8)	0.0205 (6)	0.0300 (7)	0.0022 (5)	0.0012 (5)	−0.0019 (5)
Cl4	0.0246 (6)	0.0285 (6)	0.0399 (8)	0.0028 (4)	0.0000 (6)	0.0034 (5)
Cl5	0.0350 (7)	0.0233 (6)	0.0362 (7)	−0.0021 (5)	0.0085 (6)	0.0013 (6)
N6	0.051 (3)	0.026 (2)	0.043 (3)	−0.002 (2)	0.017 (3)	0.005 (2)
C7	0.035 (3)	0.032 (3)	0.035 (3)	0.003 (2)	0.000 (3)	−0.004 (2)
C8	0.026 (2)	0.024 (2)	0.024 (2)	0.0008 (18)	0.001 (2)	−0.003 (2)
C9	0.023 (2)	0.032 (3)	0.033 (3)	0.000 (2)	0.006 (2)	−0.006 (2)
C10	0.025 (3)	0.041 (3)	0.025 (2)	0.004 (2)	0.003 (2)	−0.007 (2)
C11	0.030 (2)	0.023 (2)	0.026 (2)	0.004 (2)	−0.006 (2)	0.000 (2)
C12	0.057 (4)	0.024 (3)	0.039 (3)	0.003 (3)	−0.004 (3)	−0.009 (2)
C13	0.025 (2)	0.026 (2)	0.028 (3)	0.0008 (19)	−0.003 (2)	0.000 (2)
C14	0.027 (2)	0.023 (2)	0.019 (2)	0.003 (2)	0.0000 (18)	−0.0012 (19)
N15	0.031 (2)	0.021 (2)	0.033 (3)	0.0001 (17)	0.005 (2)	0.0017 (18)
C16	0.045 (3)	0.027 (3)	0.041 (3)	−0.004 (3)	0.017 (3)	0.000 (3)
C17	0.033 (3)	0.024 (2)	0.024 (2)	−0.001 (2)	0.008 (2)	−0.001 (2)
C18	0.031 (2)	0.021 (2)	0.025 (2)	0.0031 (19)	0.000 (2)	0.000 (2)
C19	0.027 (2)	0.035 (3)	0.027 (3)	−0.005 (2)	0.003 (2)	−0.005 (2)
C20	0.029 (2)	0.020 (2)	0.028 (3)	−0.0006 (18)	0.002 (2)	0.001 (2)
C21	0.034 (3)	0.024 (2)	0.029 (3)	0.002 (2)	−0.001 (2)	0.004 (2)
C22	0.030 (2)	0.021 (2)	0.026 (2)	−0.004 (2)	0.003 (2)	−0.0010 (19)
C23	0.053 (4)	0.022 (3)	0.040 (4)	0.003 (2)	0.002 (3)	−0.001 (3)

Geometric parameters (Å, º)

Zn1—Cl2	2.2720 (17)	C13—H131	0.935
Zn1—Cl3	2.2591 (15)	C14—H141	0.932
Zn1—Cl4	2.2841 (14)	N15—C16	1.472 (7)
Zn1—Cl5	2.2564 (17)	N15—H153	0.893
N6—C7	1.469 (8)	N15—H152	0.891
N6—H63	0.894	N15—H151	0.894
N6—H62	0.890	C16—C17	1.506 (8)
N6—H61	0.888	C16—H162	0.970
C7—C8	1.491 (8)	C16—H161	0.972
C7—H72	0.967	C17—C18	1.395 (8)
C7—H71	0.970	C17—C22	1.387 (8)
C8—C9	1.389 (7)	C18—C19	1.383 (7)
C8—C14	1.385 (7)	C18—H181	0.930
C9—C10	1.375 (8)	C19—C20	1.378 (8)
C9—H91	0.932	C19—H191	0.930
C10—C11	1.392 (8)	C20—C21	1.391 (8)
C10—H101	0.935	C20—C23	1.517 (8)
C11—C12	1.505 (8)	C21—C22	1.380 (7)
C11—C13	1.384 (8)	C21—H211	0.940
C12—H122	0.959	C22—H221	0.936
C12—H121	0.959	C23—H231	0.964
C12—H123	0.961	C23—H233	0.959
C13—C14	1.387 (7)	C23—H232	0.966
Cl2—Zn1—Cl3	114.69 (6)	C13—C14—C8	119.7 (5)
Cl2—Zn1—Cl4	104.28 (6)	C13—C14—H141	119.7
Cl3—Zn1—Cl4	106.95 (6)	C8—C14—H141	120.7
Cl2—Zn1—Cl5	109.09 (6)	C16—N15—H153	109.0
Cl3—Zn1—Cl5	106.40 (6)	C16—N15—H152	109.4
Cl4—Zn1—Cl5	115.70 (6)	H153—N15—H152	108.7
C7—N6—H63	110.3	C16—N15—H151	110.5
C7—N6—H62	109.4	H153—N15—H151	109.5
H63—N6—H62	108.9	H152—N15—H151	109.8
C7—N6—H61	109.3	N15—C16—C17	112.8 (5)
H63—N6—H61	109.5	N15—C16—H162	108.1
H62—N6—H61	109.4	C17—C16—H162	109.6
N6—C7—C8	113.5 (5)	N15—C16—H161	108.5
N6—C7—H72	107.8	C17—C16—H161	108.7
C8—C7—H72	108.7	H162—C16—H161	109.0
N6—C7—H71	108.3	C16—C17—C18	120.2 (6)
C8—C7—H71	109.2	C16—C17—C22	121.0 (6)
H72—C7—H71	109.4	C18—C17—C22	118.7 (5)
C7—C8—C9	121.5 (5)	C17—C18—C19	120.1 (5)
C7—C8—C14	119.0 (5)	C17—C18—H181	120.1
C9—C8—C14	119.4 (5)	C19—C18—H181	119.8
C8—C9—C10	120.1 (5)	C18—C19—C20	121.5 (5)
C8—C9—H91	120.2	C18—C19—H191	119.3
C10—C9—H91	119.8	C20—C19—H191	119.2
C9—C10—C11	121.6 (5)	C19—C20—C21	118.2 (5)
C9—C10—H101	118.8	C19—C20—C23	122.5 (5)
C11—C10—H101	119.6	C21—C20—C23	119.2 (5)
C10—C11—C12	120.0 (6)	C20—C21—C22	120.9 (6)
C10—C11—C13	117.6 (5)	C20—C21—H211	119.2
C12—C11—C13	122.4 (6)	C22—C21—H211	119.8
C11—C12—H122	109.7	C17—C22—C21	120.6 (6)
C11—C12—H121	109.7	C17—C22—H221	119.6
H122—C12—H121	109.5	C21—C22—H221	119.8
C11—C12—H123	109.5	C20—C23—H231	110.1
H122—C12—H123	108.9	C20—C23—H233	109.8
H121—C12—H123	109.5	H231—C23—H233	109.0
C11—C13—C14	121.7 (5)	C20—C23—H232	109.2
C11—C13—H131	119.0	H231—C23—H232	109.3
C14—C13—H131	119.3	H233—C23—H232	109.4

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
N15—H153···Cl5^i	0.89	2.69	3.417 (5)	138
N15—H153···Cl2^ii	0.89	2.78	3.445 (5)	132
N15—H152···Cl2	0.89	2.69	3.262 (5)	122
N15—H152···Cl5	0.89	2.77	3.552 (5)	146
N15—H151···Cl3^i	0.89	2.40	3.242 (5)	155
N6—H61···Cl4^iii	0.88	2.57	3.274 (6)	136
N6—H62···Cl2^iii	0.89	2.50	3.315 (6)	151
N6—H63···Cl4^iv	0.89	2.30	3.171 (5)	163
C7—H72···Cl3^iv	0.96	2.81	3.459 (7)	125
C7—H71···Cl5^v	0.97	2.92	3.711 (6)	139
C16—H161···Cl4^vi	0.97	2.88	3.824 (8)	162
C16—H162···Cl3^ii	0.97	2.82	3.636 (8)	142

Symmetry codes: (i) −x, −y+1, z+1/2; (ii) −x, −y+1, z−1/2; (iii) x+1/2, −y+3/2, z; (iv) −x−1/2, y+1/2, z+1/2; (v) x+1/2, −y+3/2, z+1; (vi) x+1, y, z.