Crystal structure of ammonium/potassium trans-bis-(N-methyl-iminodi-acetato-κ(3) O,N,O')chromate(III) from synchrotron data.

The structure of the title compound, [(NH4)0.8K0.2][Cr(C5H7NO4)2] (C5H7NO4 is methyl-iminodi-acetate; mida), has been determined from synchrotron data. The Cr(III) atom is located on a centre of symmetry and is coordinated by two N atoms and four O atoms of two facially arranged tridentate mida ligands, displaying a slightly distorted octa-hedral coordination environment. The Cr-N and mean Cr-O bond lengths are 2.0792 (14) and 1.958 (14) Å, respectively. The cation site is located on a twofold rotation axis and shows occupational disorder, being occupied by ammonium and potassium cations in a 0.8:0.2 ratio. In the crystal, inter-molecular hydrogen bonds involving the N-H groups of the ammonium cation as donor and the two non-coordinating O atoms of the carboxyl-ate group as acceptor groups consolidate the three-dimensional packing.

Chemical context

Methyl­iminodi­acetate (abbreviated here as mida; n class="Chemical">C5H7NO4) can coordinate to a central metal ion as a tridentate ligand through one N atom and two O atoms. The mida ligand differs from iminodi­acetate (ida) in the substitution of the imino hydrogen with a methyl group. This change has significant consequences with respect to the configuration of the bis-chromate(III) complexes with these ligands. Two facial configurations in cis or trans mode relative to the two N atoms have been observed: for example K[Cr(ida)2]·3H2O (Mootz & Wunderlich, 1980 ▸) and Na[Cr(ida)2]·1.5H2O (Li et al., 2003 ▸) are cis-fac structures whereas Na[Cr(mida)2] is a trans-fac structure (Suh et al., 1997 ▸). However, the trans meridional isomer of octa­hedrally coordinated chromium(III) with ida or mida ligands has not yet been identified. In order to confirm the bonding mode of the methyl­iminodi­acetato ligand and its structural arrangement, we report herein on the crystal structure of the title salt, [(NH4)0.8K0.2][Cr(C5H7NO4)2], (I).

Structural commentary

Counter-ionic species play important roles in crystal packings and hydrogen-bonding patterns. The structure reported here is another example of a [n class="Chemical">Cr(mida)2]− salt but with a different cation (Suh et al., 1996 ▸, 1997 ▸). The structural analysis shows that the two tridentate mida dianions octa­hedrally coordinate to the CrIII metal atom through one N atom and two carboxyl­ate O atoms in a facial configuration. The coordinating N atoms are mutually trans due to point group for the entire anionic complex. The asymmetric unit of (I) comprises one half of the CrIII complex anion and one occupationally disordered ammonium/potassium cation (situated on a twofold rotation axis), respectively. An ellipsoid plot of title compound together with the atomic numbering is illustrated in Fig. 1 ▸.

Figure 1

The structures of the mol­ecular entities of (I), showing the atom-numbering scheme. Non-H atoms are shown as displacement ellipsoids at the 50% probability level. The primed atoms are related by symmetry code (−x + 1, −y + 1, −z + 1). Dashed lines represent hydrogen-bonding inter­actions.

The facial configuration of the complex anion in (I) can be compared with that of NH4[Cr(pydc)2] (pydc = pyridine-2,6-di­carboxyl­ate; Moon & Choi, 2015 ▸) where it displays a trans meridional configuration. The Cr—N and mean Cr—O bond lengths involving the n class="Gene">mida ligands are 2.0792 (14) and 1.958 (14) Å, respectively, in good agreement with the values observed for Na[Cr(mida)2] (Suh et al., 1997 ▸). Bond angles about the central chromium atom are 90.23 (6) for O1—Cr1—O3, 84.66 (6) for O1—Cr1—N1 and 82.62 (5)° for N1—Cr1—O3 indicating a distorted octa­hedral coordination environment. The C–O bond lengths within the carboxyl­ate group of the mida ligand range from 1.219 (2) to 1.296 (2) Å and can be compared with values of 1.225 (15) and 1.294 (15) Å for NH4[Cr(pydc)2] (Moon & Choi, 2015 ▸). The slightly longer C—O bond length (C1—O2 and C3—O4) and smaller O—C—O bond angles of the carboxyl­ate groups in the mida ligand of (I) compared to the ligand in Na[Cr(mida)2] (Suh et al., 1997 ▸) may be attributed to the involvement of the two non-coordinating O atoms in hydrogen bonds with the N—H groups of the ammonium cation. The N—C and C—C distances in the mida moieties are close to those found in the free H2mida mol­ecule (Shkol’nikova et al., 1986 ▸) and are equal to 1.479 (2)–1.494 (2) and 1.508 (3)–1.512 (2) Å, respectively.

Supra­molecular features

The pattern of hydrogen bonding around the cation is different from the crystal packing network in the related n class="Chemical">sodium salt (Suh et al., 1996 ▸, 1997 ▸). The cation is linked to four non-coordinating O atoms of carboxyl­ate groups from four neighboring mida ligands through classical N—H⋯O hydrogen bonds (Table 1 ▸). An array of these inter­actions generate a three-dimensional network of mol­ecules whereby individual mol­ecules are stacked along the b-axis direction (Fig. 2 ▸).

Table 1

Hydrogen-bond geometry (Å, °)

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
N1S—H1NS⋯O3i	0.92 (1)	2.07 (1)	2.9658 (16)	166 (3)
N1S—H2NS⋯O2	0.90 (1)	1.95 (1)	2.8485 (17)	175 (3)

Symmetry code: (i) .

Figure 2

A packing diagram of (I), viewed perpendicular to the ac plane. Dashed lines represent hydrogen-bonding inter­actions N—H⋯O (cyan).

Database survey

A search of the Cambridge Structural Database (Version 5.37, Feb. 2016 with two updates; Groom et al., 2016 ▸) gave just two hits for a complex anion [Cr(C5H7NO4)2]− unit. The crystal structures of Na[n class="Chemical">Cr(mida)2] with three different space groups have been reported and compared previously (Suh et al., 1996 ▸, 1997 ▸).

Synthesis and crystallization

All chemicals were reagent-grade materials and were used without further purification. The starting material, K[Cr(mida)2] was prepared by a method similar to that outlined previously (Wernicke et al., 1977 ▸; Uehara et al., 1970 ▸). The n class="Chemical">potassium salt (0.25 g) was dissolved in 15 mL of water at 343 K and added to 5 mL of water containing 0.50 g of NH4Cl. The resulting solution was filtered to remove any impurities and allowed to stand at room temperature for several days to give pale pink plate-like crystals of the mixed-occupancy ammonium/potassium salt, (I), suitable for X-ray diffraction analysis.

Refinement

Crystal data, data collection and structure refinement details are summarized in Table 2 ▸. All H atoms of the complex were placed in geometrically idealized positions and constrained to ride on their parent atoms, with C—H distances of 0.97–0.98 Å and with U iso(H) values of 1.5 (meth­yl) and 1.2 times U n class="Chemical">eq (all others) of the parent atoms. The H atoms of the cation were located from difference Fourier maps and refined with DFIX and DANG restraints and fixed N—H distances of 0.855 (9) and 0.869 (9) Å, with U iso(H) values of 1.2U eq(N). The occupancy of mixed-occupied (NH4/K) first was refined and then fixed at a ratio of 0.8:0.2. The corresponding (NH4/K) sites was refined using EXYZ/EADP commands for the two atom types.

Table 2

Experimental details

Crystal data
Chemical formula	[(NH4)0.8K0.2][Cr(C5H7NO4)2]
M r	364.48
Crystal system, space group	Monoclinic, C2/c
Temperature (K)	243
a, b, c (Å)	16.786 (3), 6.5240 (13), 13.925 (3)
β (°)	113.19 (3)
V (Å3)	1401.8 (6)
Z	4
Radiation type	Synchrotron, λ = 0.610 Å
μ (mm−1)	0.61
Crystal size (mm)	0.02 × 0.02 × 0.01
Data collection
Diffractometer	ADSC Q210 CCD area-detector
Absorption correction	Empirical (using intensity measurements) (HKL3000sm SCALEPACK; Otwinowski & Minor, 1997 ▸)
T min, T max	0.989, 0.995
No. of measured, independent and observed [I > 2σ(I)] reflections	6984, 1833, 1519
R int	0.028
(sin θ/λ)max (Å−1)	0.693
Refinement
R[F 2 > 2σ(F 2)], wR(F 2), S	0.035, 0.100, 1.05
No. of reflections	1833
No. of parameters	110
No. of restraints	3
H-atom treatment	H atoms treated by a mixture of independent and constrained refinement
Δρmax, Δρmin (e Å−3)	0.40, −0.69

Computer programs: PAL BL2D-SMDC (Shin et al., 2016 ▸), HKL3000sm (Otwinowski & Minor, 1997 ▸), SHELXT2014 (Sheldrick, 2015a ▸), SHELXL2014 (Sheldrick, 2015b ▸), DIAMOND (Putz & Brandenburg, 2014 ▸) and publCIF (Westrip, 2010 ▸).

Crystal structure: contains datablock(s) I. DOI: 10.1107/S2056989016011804/wm5304sup1.cif

Structure factors: contains datablock(s) I. DOI: 10.1107/S2056989016011804/wm5304Isup2.hkl

CCDC reference: 1494843

Additional supporting information: crystallographic information; 3D view; checkCIF report

[(NH4)0.8K0.2][Cr(C5H7NO4)2]	F(000) = 754
Mr = 364.48	Dx = 1.727 Mg m−3
Monoclinic, C2/c	Synchrotron radiation, λ = 0.610 Å
a = 16.786 (3) Å	Cell parameters from 23758 reflections
b = 6.5240 (13) Å	θ = 0.4–33.7°
c = 13.925 (3) Å	µ = 0.61 mm−1
β = 113.19 (3)°	T = 243 K
V = 1401.8 (6) Å3	Plate, pale pink
Z = 4	0.02 × 0.02 × 0.01 mm

ADSC Q210 CCD area-detector diffractometer	1519 reflections with I > 2σ(I)
Radiation source: PLSII 2D bending magnet	Rint = 0.028
ω scan	θmax = 25.0°, θmin = 2.7°
Absorption correction: empirical (using intensity measurements) (HKL3000sm SCALEPACK; Otwinowski & Minor, 1997)	h = −23→23
Tmin = 0.989, Tmax = 0.995	k = −9→9
6984 measured reflections	l = −17→17
1833 independent reflections

Refinement on F2	Hydrogen site location: mixed
Least-squares matrix: full	H atoms treated by a mixture of independent and constrained refinement
R[F2 > 2σ(F2)] = 0.035	w = 1/[σ2(Fo2) + (0.0702P)2] where P = (Fo2 + 2Fc2)/3
wR(F2) = 0.100	(Δ/σ)max < 0.001
S = 1.05	Δρmax = 0.40 e Å−3
1833 reflections	Δρmin = −0.69 e Å−3
110 parameters	Extinction correction: SHELXL2014 (Sheldrick, 2015b), Fc*=kFc[1+0.001xFc2λ3/sin(2θ)]-1/4
3 restraints	Extinction coefficient: 0.0118 (19)

Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes.

	x	y	z	Uiso*/Ueq	Occ. (<1)
Cr1	0.5000	0.5000	0.5000	0.01108 (14)
O1	0.53582 (8)	0.3160 (2)	0.61977 (10)	0.0228 (3)
O2	0.64463 (9)	0.2272 (2)	0.76630 (10)	0.0267 (3)
O3	0.54917 (8)	0.3115 (2)	0.42746 (10)	0.0228 (3)
O4	0.65906 (10)	0.2681 (2)	0.37913 (13)	0.0361 (4)
N1	0.62700 (8)	0.6057 (2)	0.56638 (10)	0.0129 (3)
C1	0.61393 (11)	0.3333 (3)	0.68756 (13)	0.0175 (3)
C2	0.67027 (13)	0.4929 (3)	0.66707 (15)	0.0326 (5)
H2A	0.6886	0.5922	0.7245	0.039*
H2B	0.7225	0.4260	0.6668	0.039*
C3	0.62435 (11)	0.3600 (3)	0.42841 (13)	0.0196 (4)
C4	0.66622 (12)	0.5484 (3)	0.49128 (15)	0.0232 (4)
H4A	0.7283	0.5226	0.5297	0.028*
H4B	0.6601	0.6633	0.4435	0.028*
C5	0.63441 (13)	0.8296 (3)	0.58441 (19)	0.0333 (5)
H5A	0.6948	0.8699	0.6086	0.050*
H5B	0.6121	0.8653	0.6368	0.050*
H5C	0.6012	0.9003	0.5197	0.050*
K1S	0.5000	−0.0201 (2)	0.7500	0.0275 (3)	0.2
N1S	0.5000	−0.0201 (2)	0.7500	0.0275 (3)	0.8
H1NS	0.5139 (17)	−0.091 (4)	0.8115 (14)	0.033*	0.8
H2NS	0.5476 (13)	0.052 (4)	0.757 (2)	0.033*	0.8

	U11	U22	U33	U12	U13	U23
Cr1	0.00847 (19)	0.01210 (19)	0.0120 (2)	−0.00089 (12)	0.00332 (13)	−0.00138 (12)
O1	0.0173 (6)	0.0248 (6)	0.0209 (6)	−0.0064 (5)	0.0018 (5)	0.0078 (5)
O2	0.0231 (7)	0.0300 (7)	0.0217 (7)	0.0003 (5)	0.0030 (5)	0.0107 (5)
O3	0.0201 (6)	0.0223 (6)	0.0290 (7)	−0.0052 (5)	0.0130 (5)	−0.0119 (5)
O4	0.0328 (8)	0.0430 (9)	0.0416 (9)	−0.0005 (7)	0.0243 (7)	−0.0173 (7)
N1	0.0110 (6)	0.0145 (6)	0.0134 (6)	−0.0023 (5)	0.0050 (5)	−0.0013 (5)
C1	0.0174 (8)	0.0198 (8)	0.0152 (8)	−0.0010 (6)	0.0063 (6)	0.0000 (6)
C2	0.0205 (9)	0.0530 (14)	0.0160 (9)	−0.0150 (8)	−0.0018 (7)	0.0125 (8)
C3	0.0201 (8)	0.0219 (8)	0.0185 (9)	0.0005 (6)	0.0094 (6)	−0.0027 (6)
C4	0.0203 (8)	0.0327 (9)	0.0226 (10)	−0.0081 (7)	0.0148 (7)	−0.0083 (7)
C5	0.0221 (9)	0.0186 (9)	0.0574 (14)	−0.0070 (7)	0.0137 (9)	−0.0129 (8)
K1S	0.0277 (7)	0.0278 (8)	0.0270 (8)	0.000	0.0107 (6)	0.000
N1S	0.0277 (7)	0.0278 (8)	0.0270 (8)	0.000	0.0107 (6)	0.000

Cr1—O1	1.9479 (13)	C2—H2B	0.9800
Cr1—O1i	1.9479 (13)	C3—C4	1.512 (2)
Cr1—O3	1.9673 (12)	C3—K1Sii	3.371 (2)
Cr1—O3i	1.9673 (12)	C4—H4A	0.9800
Cr1—N1	2.0792 (14)	C4—H4B	0.9800
Cr1—N1i	2.0792 (14)	C5—H5A	0.9700
O1—C1	1.284 (2)	C5—H5B	0.9700
O1—K1S	3.0524 (17)	C5—H5C	0.9700
O2—C1	1.226 (2)	K1S—O2iii	2.8484 (16)
O2—K1S	2.8485 (17)	K1S—O3iv	2.9658 (16)
O3—C3	1.296 (2)	K1S—O3ii	2.9658 (16)
O3—K1Sii	2.9658 (16)	K1S—O4iv	3.033 (2)
O4—C3	1.219 (2)	K1S—O4ii	3.033 (2)
O4—K1Sii	3.033 (2)	K1S—O1iii	3.0524 (17)
N1—C5	1.479 (2)	K1S—C1iii	3.322 (2)
N1—C4	1.486 (2)	K1S—C3ii	3.371 (2)
N1—C2	1.494 (2)	K1S—C3iv	3.371 (2)
C1—C2	1.508 (3)	N1S—H1NS	0.920 (10)
C1—K1S	3.322 (2)	N1S—H2NS	0.899 (10)
C2—H2A	0.9800
O1—Cr1—O1i	180.00 (5)	O2—K1S—O3ii	112.23 (4)
O1—Cr1—O3	90.23 (6)	O3iv—K1S—O3ii	100.26 (7)
O1i—Cr1—O3	89.77 (6)	O2iii—K1S—O4iv	150.81 (4)
O1—Cr1—O3i	89.77 (6)	O2—K1S—O4iv	74.40 (4)
O1i—Cr1—O3i	90.23 (6)	O3iv—K1S—O4iv	43.35 (4)
O3—Cr1—O3i	180.0	O3ii—K1S—O4iv	92.48 (6)
O1—Cr1—N1	84.66 (6)	O2iii—K1S—O4ii	74.40 (4)
O1i—Cr1—N1	95.34 (6)	O2—K1S—O4ii	150.82 (4)
O3—Cr1—N1	82.62 (5)	O3iv—K1S—O4ii	92.48 (6)
O3i—Cr1—N1	97.38 (5)	O3ii—K1S—O4ii	43.36 (4)
O1—Cr1—N1i	95.34 (6)	O4iv—K1S—O4ii	115.53 (8)
O1i—Cr1—N1i	84.66 (6)	O2iii—K1S—O1iii	43.90 (4)
O3—Cr1—N1i	97.38 (5)	O2—K1S—O1iii	84.65 (6)
O3i—Cr1—N1i	82.62 (5)	O3iv—K1S—O1iii	91.19 (4)
N1—Cr1—N1i	180.00 (7)	O3ii—K1S—O1iii	154.19 (4)
C1—O1—Cr1	117.20 (11)	O4iv—K1S—O1iii	111.36 (5)
C1—O1—K1S	90.53 (10)	O4ii—K1S—O1iii	113.71 (4)
Cr1—O1—K1S	152.23 (6)	O2iii—K1S—O1	84.65 (6)
C1—O2—K1S	101.75 (11)	O2—K1S—O1	43.90 (4)
C3—O3—Cr1	116.48 (11)	O3iv—K1S—O1	154.19 (4)
C3—O3—K1Sii	96.63 (10)	O3ii—K1S—O1	91.19 (4)
Cr1—O3—K1Sii	142.48 (6)	O4iv—K1S—O1	113.71 (4)
C3—O4—K1Sii	95.27 (12)	O4ii—K1S—O1	111.36 (5)
C5—N1—C4	109.69 (15)	O1iii—K1S—O1	88.15 (7)
C5—N1—C2	110.46 (15)	O2iii—K1S—C1iii	21.17 (4)
C4—N1—C2	110.50 (15)	O2—K1S—C1iii	98.43 (6)
C5—N1—Cr1	113.95 (11)	O3iv—K1S—C1iii	103.11 (4)
C4—N1—Cr1	105.34 (10)	O3ii—K1S—C1iii	131.52 (4)
C2—N1—Cr1	106.75 (10)	O4iv—K1S—C1iii	132.69 (5)
O2—C1—O1	123.79 (16)	O4ii—K1S—C1iii	93.56 (4)
O2—C1—C2	119.04 (16)	O1iii—K1S—C1iii	22.73 (4)
O1—C1—C2	117.17 (15)	O1—K1S—C1iii	85.72 (6)
O2—C1—K1S	57.08 (10)	O2iii—K1S—C1	98.43 (6)
O1—C1—K1S	66.74 (9)	O2—K1S—C1	21.17 (4)
C2—C1—K1S	175.95 (12)	O3iv—K1S—C1	131.52 (4)
N1—C2—C1	114.11 (15)	O3ii—K1S—C1	103.11 (4)
N1—C2—H2A	108.7	O4iv—K1S—C1	93.56 (4)
C1—C2—H2A	108.7	O4ii—K1S—C1	132.69 (5)
N1—C2—H2B	108.7	O1iii—K1S—C1	85.72 (6)
C1—C2—H2B	108.7	O1—K1S—C1	22.73 (4)
H2A—C2—H2B	107.6	C1iii—K1S—C1	92.12 (7)
O4—C3—O3	123.62 (17)	O2iii—K1S—C3ii	93.03 (5)
O4—C3—C4	120.65 (16)	O2—K1S—C3ii	133.81 (4)
O3—C3—C4	115.66 (15)	O3iv—K1S—C3ii	94.64 (6)
O4—C3—K1Sii	63.63 (11)	O3ii—K1S—C3ii	22.45 (4)
O3—C3—K1Sii	60.92 (9)	O4iv—K1S—C3ii	103.37 (7)
C4—C3—K1Sii	166.70 (13)	O4ii—K1S—C3ii	21.10 (4)
N1—C4—C3	112.21 (14)	O1iii—K1S—C3ii	134.49 (4)
N1—C4—H4A	109.2	O1—K1S—C3ii	104.15 (4)
C3—C4—H4A	109.2	C1iii—K1S—C3ii	113.34 (5)
N1—C4—H4B	109.2	C1—K1S—C3ii	121.12 (4)
C3—C4—H4B	109.2	O2iii—K1S—C3iv	133.81 (4)
H4A—C4—H4B	107.9	O2—K1S—C3iv	93.03 (5)
N1—C5—H5A	109.5	O3iv—K1S—C3iv	22.45 (4)
N1—C5—H5B	109.5	O3ii—K1S—C3iv	94.64 (6)
H5A—C5—H5B	109.5	O4iv—K1S—C3iv	21.10 (4)
N1—C5—H5C	109.5	O4ii—K1S—C3iv	103.37 (7)
H5A—C5—H5C	109.5	O1iii—K1S—C3iv	104.15 (4)
H5B—C5—H5C	109.5	O1—K1S—C3iv	134.49 (4)
O2iii—K1S—O2	111.01 (8)	C1iii—K1S—C3iv	121.12 (4)
O2iii—K1S—O3iv	112.23 (4)	C1—K1S—C3iv	113.34 (5)
O2—K1S—O3iv	110.35 (4)	C3ii—K1S—C3iv	97.73 (8)
O2iii—K1S—O3ii	110.35 (4)	H1NS—N1S—H2NS	105.9 (19)
K1S—O2—C1—O1	−1.9 (2)	K1Sii—O4—C3—C4	−165.65 (16)
K1S—O2—C1—C2	178.67 (16)	Cr1—O3—C3—O4	−173.25 (15)
Cr1—O1—C1—O2	−179.97 (14)	K1Sii—O3—C3—O4	−11.5 (2)
K1S—O1—C1—O2	1.73 (19)	Cr1—O3—C3—C4	3.7 (2)
Cr1—O1—C1—C2	−0.5 (2)	K1Sii—O3—C3—C4	165.51 (14)
K1S—O1—C1—C2	−178.83 (16)	Cr1—O3—C3—K1Sii	−161.79 (12)
Cr1—O1—C1—K1S	178.30 (12)	C5—N1—C4—C3	−151.02 (16)
C5—N1—C2—C1	127.82 (19)	C2—N1—C4—C3	86.96 (18)
C4—N1—C2—C1	−110.61 (19)	Cr1—N1—C4—C3	−27.99 (18)
Cr1—N1—C2—C1	3.4 (2)	O4—C3—C4—N1	−165.12 (17)
O2—C1—C2—N1	177.29 (16)	O3—C3—C4—N1	17.8 (2)
O1—C1—C2—N1	−2.2 (3)	K1Sii—C3—C4—N1	89.7 (5)
K1Sii—O4—C3—O3	11.2 (2)

D—H···A	D—H	H···A	D···A	D—H···A
N1S—H1NS···O3iv	0.92 (1)	2.07 (1)	2.9658 (16)	166 (3)
N1S—H2NS···O2	0.90 (1)	1.95 (1)	2.8485 (17)	175 (3)