Low-temperature redetermination of hexa­kis(μ-chloro­acetato-κ2O:O′)-μ3-oxido-tris[aquachromium(III)] nitrate 3.5-hydrate

Ng, S.W.

doi:10.1107/S1600536808023805

metal-organic compounds

CRYSTALLOGRAPHIC
COMMUNICATIONS

ISSN: 2056-9890

Volume 64| Part 8| August 2008| Page m1102

doi:10.1107/S1600536808023805

Open

access

Low-temperature redetermination of hexakis(μ-chloroacetato-κ²O:O′)-μ₃-oxido-tris[aquachromium(III)] nitrate 3.5-hydrate

Seik Weng Ng ^a ^*

^aDepartment of Chemistry, University of Malaya, 50603 Kuala Lumpur, Malaysia
^*Correspondence e-mail: seikweng@um.edu.my

(Received 17 July 2008; accepted 28 July 2008; online 31 July 2008)

A low-temperature redetermination of the trinuclear cluster compound described as [Cr₃(C₂H₂ClO₂)₆O(H₂O)₃]NO₃·3H₂O [Glowiak, Kubiak & Jezowska-Trzebiatowska (1977 ). Bull. Acad. Pol. Sci. Ser. Sci. Chim. 25, 359–371] shows that the salt is a 3.5-hydrate, [Cr₃(C₂H₂ClO₂)₆O(H₂O)₃]NO₃·3.5H₂O. The trinuclear cluster cation is disordered in four of the six monochloroacetate groups. One is disordered over two positions in respect of the chloromethyl atoms (occupancy ratio 0.50:0.50); another is disordered over three positions in respect of the chloromethyl atoms (occupancy ratio 0.50:0.37:0.13) whereas two are disordered over two positions in respect of the Cl atoms only (occupancy ratios 0.84:0.16 and 0.60:0.40). Of the four independent uncoordinated water molecules, one has an occupancy factor of 0.5. The trinuclear cation has an oxido O atom that is connected to three water-coordinated Cr^III atoms, the three metal atoms forming the points of an equilateral triangle. Six carboxylate groups each chelate a Cr—O—Cr fragment. The cations, anions and uncoordinated water molecules are linked by hydrogen bonds.

Related literature

For the room-temperature study, see: Glowiak et al. (1977).

Experimental

Crystal data

[Cr₃(C₂H₂ClO₂)₆O(H₂O)₃]NO₃·3.5H₂O
M_r = 912.03
Monoclinic, P 2₁ /c
a = 12.4938 (2) Å
b = 14.7622 (2) Å
c = 17.2687 (3) Å
β = 96.293 (1)°
V = 3165.78 (9) Å³
Z = 4
Mo Kα radiation
μ = 1.61 mm⁻¹
T = 100 (2) K
0.12 × 0.06 × 0.03 mm

Data collection

Bruker SMART APEX CCD area-detector diffractometer
Absorption correction: multi-scan (SADABS; Sheldrick, 1996 ) T_min = 0.820, T_max = 0.953
39914 measured reflections
7271 independent reflections
5349 reflections with I > 2σ(I)
R_int = 0.053

Refinement

R[F² > 2σ(F²)] = 0.040
wR(F²) = 0.112
S = 1.03
7271 reflections
500 parameters
119 restraints
H atoms treated by a mixture of independent and constrained refinement
Δρ_max = 0.99 e Å⁻³
Δρ_min = −0.34 e Å⁻³

Table 1
Hydrogen-bond geometry (Å, °)

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
O1w—H11⋯O5wⁱ	0.84 (4)	1.83 (2)	2.616 (6)	157 (5)
O1w—H12⋯O6wⁱⁱ	0.84 (3)	1.99 (3)	2.816 (4)	169 (5)
O2w—H21⋯O15ⁱⁱⁱ	0.84 (3)	1.90 (3)	2.732 (4)	170 (4)
O2w—H22⋯Cl5′^iv	0.84 (3)	2.75 (3)	3.295 (6)	124 (6)
O3w—H31⋯O4w	0.844 (14)	1.84 (2)	2.669 (4)	168 (5)
O3w—H32⋯O6w	0.84 (3)	1.88 (3)	2.711 (4)	171 (4)
O4w—H41⋯O7^v	0.85 (5)	2.20 (5)	3.046 (4)	175 (5)
O4w—H42⋯O16ⁱⁱ	0.83 (4)	2.27 (4)	2.976 (5)	142 (6)
O5w—H51⋯O7w	0.85 (4)	2.06 (7)	2.79 (1)	144 (11)
O5w—H52⋯O12	0.85 (7)	2.47 (7)	3.27 (1)	156 (10)
O6w—H61⋯O14	0.83 (4)	2.31 (2)	3.093 (6)	158 (5)
O6w—H62⋯O7w	0.85 (4)	2.15 (3)	2.86 (1)	141 (4)
Symmetry codes: (i) $[x, -y+{\script{3\over 2}}, z+{\script{1\over 2}}]$ ; (ii) $[-x+1, y+{\script{1\over 2}}, -z+{\script{1\over 2}}]$ ; (iii) $[-x+2, y+{\script{1\over 2}}, -z+{\script{1\over 2}}]$ ; (iv) -x+2, -y+1, -z+1; (v) $[-x+1, y-{\script{1\over 2}}, -z+{\script{1\over 2}}]$ .

Data collection: APEX2 (Bruker, 2007 ); cell refinement: SAINT (Bruker, 2007); data reduction: SAINT; program(s) used to solve structure: SHELXS97 (Sheldrick, 2008 ); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: X-SEED (Barbour, 2001 ); software used to prepare material for publication: publCIF (Westrip, 2008 ).

Supporting information

Crystal structure: contains datablocks global, I. DOI: 10.1107/S1600536808023805/hy2147sup1.cif

Structure factors: contains datablock I. DOI: 10.1107/S1600536808023805/hy2147Isup2.hkl

checkCIF report

Comment top

The low-temperature redetermination of the trinuclear cluster compound described as [Cr₃O(C₂H₂ClO₂)₆(H₂O)₃](NO₃).3H₂O by Glowiak et al. (1977) shows that the salt is a 3.5-hydrate, [Cr₃O(C₂H₂ClO₂)₆(H₂O)₃](NO₃).3.5H₂O (Scheme1; Fig. 1). The trinuclear cluster cation is disordered in four of the six monochloroacetate groups. One is disordered over two positions in respect of the chloromethyl atoms (occupancy ratio 0.50:0.50); another is disordered over three positions in respect of the chloromethyl atoms (occupancy ratio 0.50:0.37:0.13) whereas two are disordered over two positions in respect of the Cl atoms only (occupancy ratios 0.84:0.16 and 0.60:0.40). Of the four independent lattice water molecules, one has an occupancy factor of 0.50. The trinuclear cation has an oxido O atom that is connected to three water-coordinated Cr^III atoms, the three metal atoms forming the points of an equilateral triangle. Six carboxylate groups each chelates a Cr–O–Cr fragment. The cations, anions and lattice water molecules are linked by hydrogen bonds (Table 1).

Related literature top

For the room-temperature study, see: Glowiak et al. (1977).

Experimental top

Crystals of the title compound obtained by the method of Glowiak et al. (1977) were supplied by Dr Rosiyah Yahya.

Computing details top

Data collection: APEX2 (Bruker, 2007); cell refinement: SAINT (Bruker, 2007); data reduction: SAINT; program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: X-SEED (Barbour, 2001); software used to prepare material for publication: publCIF (Westrip, 2008).

Figures top

Fig. 1. Molecular structure of the title compound. Displacement ellipsoids are drawn at the 50% probability level. The minor disorder components are not shown. The water molecule O7w has 0.5 occupancy.

hexakis(µ-chloroacetato-κ²O:O')-µ₃-oxido- tris[aquachromium(III)] nitrate 3.5-hydrate top

Crystal data top

[Cr₃(C₂H₂ClO₂)₆O(H₂O)₃]NO₃·3.5H₂O	F(000) = 1832
M_r = 912.03	D_x = 1.914 Mg m⁻³
Monoclinic, P2₁/c	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2ybc	Cell parameters from 7530 reflections
a = 12.4938 (2) Å	θ = 2.4–25.8°
b = 14.7622 (2) Å	µ = 1.61 mm⁻¹
c = 17.2687 (3) Å	T = 100 K
β = 96.293 (1)°	Irregular chip, green
V = 3165.78 (9) Å³	0.12 × 0.06 × 0.03 mm
Z = 4

Data collection top

Bruker SMART APEX CCD area-detector diffractometer	7271 independent reflections
Radiation source: fine-focus sealed tube	5349 reflections with I > 2σ(I)
Graphite monochromator	R_int = 0.053
ϕ and ω scans	θ_max = 27.5°, θ_min = 1.8°
Absorption correction: multi-scan (SADABS; Sheldrick, 1996)	h = −16→16
T_min = 0.820, T_max = 0.953	k = −19→19
39914 measured reflections	l = −21→22

Refinement top

Refinement on F²	Primary atom site location: structure-invariant direct methods
Least-squares matrix: full	Secondary atom site location: difference Fourier map
R[F² > 2σ(F²)] = 0.040	Hydrogen site location: inferred from neighbouring sites
wR(F²) = 0.112	H atoms treated by a mixture of independent and constrained refinement
S = 1.03	w = 1/[σ²(F_o²) + (0.0523P)² + 3.1321P] where P = (F_o² + 2F_c²)/3
7271 reflections	(Δ/σ)_max = 0.001
500 parameters	Δρ_max = 0.99 e Å⁻³
119 restraints	Δρ_min = −0.34 e Å⁻³

Crystal data top

[Cr₃(C₂H₂ClO₂)₆O(H₂O)₃]NO₃·3.5H₂O	V = 3165.78 (9) Å³
M_r = 912.03	Z = 4
Monoclinic, P2₁/c	Mo Kα radiation
a = 12.4938 (2) Å	µ = 1.61 mm⁻¹
b = 14.7622 (2) Å	T = 100 K
c = 17.2687 (3) Å	0.12 × 0.06 × 0.03 mm
β = 96.293 (1)°

Data collection top

Bruker SMART APEX CCD area-detector diffractometer	7271 independent reflections
Absorption correction: multi-scan (SADABS; Sheldrick, 1996)	5349 reflections with I > 2σ(I)
T_min = 0.820, T_max = 0.953	R_int = 0.053
39914 measured reflections

Refinement top

R[F² > 2σ(F²)] = 0.040	119 restraints
wR(F²) = 0.112	H atoms treated by a mixture of independent and constrained refinement
S = 1.03	Δρ_max = 0.99 e Å⁻³
7271 reflections	Δρ_min = −0.34 e Å⁻³
500 parameters

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å²) top

	x	y	z	U_iso*/U_eq	Occ. (<1)
Cr1	0.65855 (4)	0.69687 (3)	0.39526 (3)	0.02667 (13)
Cr2	0.88330 (4)	0.58714 (3)	0.37503 (3)	0.02515 (13)
Cr3	0.66063 (4)	0.53305 (3)	0.26482 (3)	0.02583 (13)
Cl1	0.4146 (3)	0.7073 (3)	0.09142 (17)	0.0663 (8)	0.50
Cl1'	0.4626 (3)	0.7531 (2)	0.09294 (17)	0.0689 (8)	0.50
Cl2	0.33828 (7)	0.56139 (6)	0.47320 (6)	0.0418 (2)
Cl3	0.77180 (9)	0.70060 (7)	0.66950 (6)	0.0518 (3)
Cl4	1.0378 (4)	0.86104 (15)	0.3111 (5)	0.0628 (13)	0.836 (19)
Cl5	0.9066 (6)	0.2693 (5)	0.4493 (4)	0.0461 (19)	0.60 (6)
Cl4'	1.0551 (6)	0.8685 (10)	0.352 (2)	0.057 (4)	0.164 (19)
Cl5'	0.882 (3)	0.2778 (14)	0.4609 (12)	0.076 (4)	0.40 (6)
Cl6	0.8796 (3)	0.5426 (4)	0.0487 (2)	0.1104 (14)	0.50
Cl6'	0.8604 (3)	0.6140 (3)	0.0492 (2)	0.0697 (12)	0.365 (3)
Cl6"	1.0377 (7)	0.6016 (6)	0.1326 (6)	0.059 (3)	0.135 (3)
O1	0.5781 (2)	0.63301 (17)	0.21039 (15)	0.0379 (6)
O2	0.5744 (2)	0.74057 (16)	0.30038 (17)	0.0423 (6)
O3	0.54075 (18)	0.61446 (15)	0.41606 (15)	0.0340 (6)
O4	0.54119 (19)	0.50527 (16)	0.32604 (15)	0.0345 (6)
O5	0.72939 (19)	0.67414 (15)	0.50140 (15)	0.0339 (5)
O6	0.87725 (18)	0.59321 (17)	0.48763 (15)	0.0351 (6)
O7	0.76364 (18)	0.79443 (14)	0.37780 (15)	0.0331 (6)
O8	0.91622 (18)	0.71719 (15)	0.37064 (16)	0.0370 (6)
O9	0.87243 (19)	0.45427 (15)	0.38598 (16)	0.0362 (6)
O10	0.7303 (2)	0.41852 (15)	0.30173 (15)	0.0357 (6)
O11	0.9199 (2)	0.57897 (18)	0.26822 (16)	0.0411 (6)
O12	0.7686 (2)	0.55303 (18)	0.19041 (15)	0.0381 (6)
O13	0.73395 (16)	0.60570 (13)	0.34506 (13)	0.0254 (5)
O14	0.6731 (3)	0.1472 (3)	0.2318 (3)	0.0833 (13)
O15	0.8166 (3)	0.1658 (2)	0.1787 (2)	0.0597 (9)
O16	0.7875 (3)	0.0391 (2)	0.2332 (2)	0.0697 (10)
O1w	0.5730 (2)	0.79263 (18)	0.4438 (2)	0.0475 (7)
H11	0.592 (3)	0.829 (3)	0.480 (2)	0.071*
H12	0.5059 (10)	0.795 (3)	0.433 (3)	0.071*
O2w	1.04519 (18)	0.57105 (16)	0.40302 (16)	0.0341 (6)
H21	1.092 (2)	0.595 (3)	0.3781 (17)	0.051*
H22	1.069 (3)	0.570 (3)	0.4506 (7)	0.051*
O3w	0.5804 (2)	0.45767 (17)	0.18032 (16)	0.0387 (6)
H31	0.5132 (10)	0.459 (3)	0.182 (3)	0.058*
H32	0.598 (3)	0.4075 (16)	0.163 (3)	0.058*
O4w	0.3657 (3)	0.4663 (2)	0.1620 (2)	0.0705 (10)
H41	0.328 (4)	0.419 (3)	0.154 (3)	0.106*
H42	0.352 (5)	0.489 (4)	0.204 (2)	0.106*
O5w	0.6040 (6)	0.5620 (5)	0.0300 (4)	0.141 (2)
H51	0.613 (9)	0.506 (2)	0.021 (6)	0.211*
H52	0.635 (9)	0.574 (7)	0.075 (3)	0.211*
O6w	0.6466 (3)	0.3047 (2)	0.1130 (2)	0.0585 (8)
H61	0.672 (4)	0.265 (3)	0.144 (2)	0.088*
H62	0.691 (3)	0.316 (3)	0.080 (2)	0.088*
O7w	0.7204 (12)	0.4105 (8)	−0.0095 (8)	0.157 (5)	0.50
H71	0.7843	0.4292	−0.0046	0.235*	0.50
H72	0.7038	0.3898	−0.0545	0.235*	0.50
N1	0.7603 (2)	0.1175 (2)	0.2160 (2)	0.0417 (8)
C1	0.5514 (3)	0.7089 (2)	0.2344 (2)	0.0349 (8)
C2	0.4863 (12)	0.7624 (7)	0.1699 (5)	0.0362 (18)	0.50
H2A	0.5367	0.8047	0.1481	0.043*	0.50
H2B	0.4341	0.7998	0.1949	0.043*	0.50
C2'	0.4833 (12)	0.7822 (7)	0.1910 (5)	0.0362 (18)	0.50
H2C	0.5208	0.8413	0.1972	0.043*	0.50
H2D	0.4133	0.7876	0.2125	0.043*	0.50
C3	0.5051 (3)	0.5443 (2)	0.3823 (2)	0.0281 (7)
C4	0.4108 (3)	0.4957 (2)	0.4107 (2)	0.0328 (8)
H4A	0.4373	0.4402	0.4387	0.039*
H4B	0.3609	0.4768	0.3650	0.039*
C5	0.8135 (3)	0.6338 (2)	0.5270 (2)	0.0294 (7)
C6	0.8464 (3)	0.6291 (3)	0.6136 (2)	0.0370 (8)
H6A	0.9235	0.6454	0.6239	0.044*
H6B	0.8384	0.5659	0.6312	0.044*
C7	0.8616 (3)	0.7876 (2)	0.3679 (2)	0.0270 (7)
C8	0.9157 (3)	0.8759 (2)	0.3518 (2)	0.0352 (8)
H8A	0.9299	0.9101	0.4012	0.042*	0.836 (19)
H8B	0.8661	0.9124	0.3156	0.042*	0.836 (19)
H8C	0.8920	0.9223	0.3881	0.042*	0.164 (19)
H8D	0.8904	0.8956	0.2974	0.042*	0.164 (19)
C9	0.8080 (3)	0.4002 (2)	0.3506 (2)	0.0308 (7)
C10	0.8248 (4)	0.2993 (2)	0.3643 (3)	0.0511 (11)
H10A	0.8731	0.2754	0.3273	0.061*	0.60 (6)
H10B	0.7549	0.2676	0.3545	0.061*	0.60 (6)
H10C	0.8613	0.2754	0.3200	0.061*	0.40 (6)
H10D	0.7536	0.2688	0.3624	0.061*	0.40 (6)
C11	0.8661 (3)	0.5728 (2)	0.2035 (2)	0.0348 (8)
C12	0.9326 (13)	0.591 (2)	0.1367 (4)	0.050 (3)	0.50
H12A	1.0062	0.5668	0.1508	0.060*	0.50
H12B	0.9386	0.6571	0.1296	0.060*	0.50
C12'	0.9334 (16)	0.606 (3)	0.1410 (5)	0.050 (3)	0.365 (3)
H12C	0.9942	0.5631	0.1379	0.060*	0.365 (3)
H12D	0.9639	0.6656	0.1562	0.060*	0.365 (3)
C12"	0.9007 (16)	0.576 (4)	0.1220 (7)	0.050 (3)	0.135 (3)
H12E	0.8598	0.6235	0.0906	0.060*	0.135 (3)
H12F	0.8877	0.5172	0.0955	0.060*	0.135 (3)

Atomic displacement parameters (Å²) top

	U¹¹	U²²	U³³	U¹²	U¹³	U²³
Cr1	0.0183 (2)	0.0182 (2)	0.0442 (3)	0.00070 (18)	0.0065 (2)	0.0001 (2)
Cr2	0.0173 (2)	0.0190 (2)	0.0398 (3)	0.00040 (18)	0.0064 (2)	0.0012 (2)
Cr3	0.0225 (3)	0.0238 (2)	0.0313 (3)	0.00189 (19)	0.0034 (2)	0.0028 (2)
Cl1	0.0588 (17)	0.096 (2)	0.0418 (14)	0.0318 (15)	−0.0030 (12)	−0.0015 (16)
Cl1'	0.091 (2)	0.0727 (19)	0.0409 (14)	0.0348 (16)	−0.0019 (15)	0.0023 (14)
Cl2	0.0289 (4)	0.0431 (5)	0.0559 (6)	−0.0019 (4)	0.0155 (4)	−0.0009 (4)
Cl3	0.0521 (6)	0.0564 (6)	0.0475 (6)	0.0105 (5)	0.0077 (5)	−0.0128 (5)
Cl4	0.0508 (13)	0.0436 (8)	0.101 (3)	−0.0061 (8)	0.0421 (16)	0.0069 (12)
Cl5	0.042 (2)	0.0331 (15)	0.060 (3)	0.0081 (11)	−0.0086 (13)	0.0093 (12)
Cl4'	0.033 (4)	0.041 (4)	0.097 (11)	−0.005 (3)	0.006 (5)	0.017 (6)
Cl5'	0.084 (8)	0.044 (3)	0.093 (4)	0.001 (5)	−0.023 (5)	0.019 (3)
Cl6	0.086 (2)	0.203 (4)	0.0466 (17)	0.021 (3)	0.0250 (15)	0.020 (3)
Cl6'	0.065 (2)	0.111 (3)	0.0340 (17)	−0.020 (2)	0.0111 (15)	0.015 (2)
Cl6"	0.054 (5)	0.058 (5)	0.069 (5)	−0.015 (4)	0.026 (4)	0.000 (4)
O1	0.0346 (13)	0.0363 (13)	0.0418 (15)	0.0098 (11)	0.0000 (11)	0.0077 (11)
O2	0.0364 (15)	0.0282 (13)	0.0600 (19)	0.0087 (11)	−0.0049 (13)	0.0009 (12)
O3	0.0239 (12)	0.0266 (12)	0.0536 (16)	−0.0047 (9)	0.0137 (11)	−0.0050 (11)
O4	0.0295 (13)	0.0355 (13)	0.0396 (15)	−0.0089 (10)	0.0082 (11)	−0.0029 (11)
O5	0.0271 (12)	0.0320 (12)	0.0426 (15)	0.0046 (10)	0.0039 (11)	−0.0025 (11)
O6	0.0234 (12)	0.0420 (14)	0.0406 (15)	0.0044 (10)	0.0068 (11)	0.0003 (11)
O7	0.0251 (12)	0.0233 (11)	0.0525 (16)	−0.0022 (9)	0.0112 (11)	−0.0006 (10)
O8	0.0235 (12)	0.0221 (11)	0.0656 (18)	−0.0021 (9)	0.0055 (12)	0.0051 (11)
O9	0.0259 (12)	0.0196 (11)	0.0616 (17)	−0.0004 (9)	−0.0022 (11)	0.0013 (11)
O10	0.0379 (14)	0.0222 (11)	0.0450 (15)	0.0031 (10)	−0.0050 (12)	0.0023 (10)
O11	0.0291 (13)	0.0504 (16)	0.0457 (17)	0.0016 (11)	0.0128 (12)	−0.0018 (13)
O12	0.0319 (14)	0.0483 (15)	0.0353 (14)	0.0032 (11)	0.0088 (11)	0.0026 (11)
O13	0.0193 (10)	0.0199 (10)	0.0373 (13)	0.0011 (8)	0.0049 (9)	0.0019 (9)
O14	0.0467 (19)	0.085 (3)	0.125 (4)	0.0030 (18)	0.041 (2)	−0.029 (2)
O15	0.0555 (19)	0.0463 (16)	0.081 (2)	−0.0064 (14)	0.0256 (18)	0.0027 (16)
O16	0.078 (2)	0.0499 (19)	0.082 (3)	0.0108 (17)	0.011 (2)	0.0139 (17)
O1w	0.0254 (13)	0.0346 (14)	0.083 (2)	0.0047 (11)	0.0088 (14)	−0.0190 (14)
O2w	0.0197 (11)	0.0342 (13)	0.0490 (16)	0.0008 (10)	0.0070 (11)	0.0052 (12)
O3w	0.0338 (14)	0.0371 (14)	0.0442 (16)	0.0008 (11)	−0.0010 (12)	−0.0075 (12)
O4w	0.0472 (19)	0.065 (2)	0.101 (3)	−0.0105 (16)	0.0167 (19)	−0.037 (2)
O5w	0.142 (5)	0.157 (5)	0.128 (4)	0.046 (4)	0.031 (4)	0.086 (4)
O6w	0.0514 (19)	0.0529 (19)	0.070 (2)	0.0062 (15)	−0.0006 (16)	−0.0111 (16)
O7w	0.181 (9)	0.119 (7)	0.173 (9)	0.006 (7)	0.029 (7)	−0.008 (7)
N1	0.0307 (17)	0.0429 (18)	0.052 (2)	−0.0041 (14)	0.0080 (15)	−0.0089 (15)
C1	0.0211 (16)	0.0286 (17)	0.056 (3)	0.0036 (13)	0.0075 (16)	0.0165 (17)
C2	0.040 (2)	0.026 (4)	0.042 (5)	0.013 (3)	−0.001 (4)	−0.001 (3)
C2'	0.040 (2)	0.026 (4)	0.042 (5)	0.013 (3)	−0.001 (4)	−0.001 (3)
C3	0.0207 (15)	0.0246 (15)	0.038 (2)	0.0001 (12)	0.0006 (14)	0.0055 (14)
C4	0.0259 (17)	0.0333 (17)	0.040 (2)	−0.0053 (14)	0.0072 (15)	−0.0007 (15)
C5	0.0236 (16)	0.0226 (15)	0.043 (2)	−0.0060 (13)	0.0081 (15)	0.0004 (14)
C6	0.0333 (19)	0.0398 (19)	0.038 (2)	0.0028 (15)	0.0062 (16)	−0.0014 (16)
C7	0.0262 (17)	0.0215 (15)	0.0333 (18)	−0.0035 (12)	0.0038 (14)	0.0015 (13)
C8	0.0314 (18)	0.0248 (16)	0.051 (2)	−0.0052 (14)	0.0128 (17)	0.0002 (15)
C9	0.0266 (17)	0.0247 (16)	0.042 (2)	0.0009 (13)	0.0080 (15)	0.0027 (14)
C10	0.047 (2)	0.0234 (18)	0.077 (3)	−0.0011 (16)	−0.019 (2)	0.0082 (18)
C11	0.0323 (19)	0.0287 (17)	0.046 (2)	0.0068 (14)	0.0173 (17)	0.0071 (16)
C12	0.046 (3)	0.054 (9)	0.053 (3)	0.005 (3)	0.025 (3)	0.014 (3)
C12'	0.046 (3)	0.054 (9)	0.053 (3)	0.005 (3)	0.025 (3)	0.014 (3)
C12"	0.046 (3)	0.054 (9)	0.053 (3)	0.005 (3)	0.025 (3)	0.014 (3)

Geometric parameters (Å, º) top

Cr1—O13	1.905 (2)	O1w—H12	0.84 (3)
Cr1—O2	1.957 (3)	O2w—H21	0.84 (3)
Cr1—O3	1.973 (2)	O2w—H22	0.84 (3)
Cr1—O5	1.975 (3)	O3w—H31	0.844 (14)
Cr1—O7	1.994 (2)	O3w—H32	0.84 (3)
Cr1—O1w	2.010 (2)	O4w—H41	0.85 (5)
Cr2—O13	1.901 (2)	O4w—H42	0.83 (4)
Cr2—O11	1.952 (3)	O5w—H51	0.85 (4)
Cr2—O6	1.956 (3)	O5w—H52	0.85 (7)
Cr2—O8	1.967 (2)	O6w—H61	0.83 (4)
Cr2—O9	1.977 (2)	O6w—H62	0.85 (4)
Cr2—O2w	2.041 (2)	O7w—H71	0.84
Cr3—O13	1.906 (2)	O7w—H72	0.84
Cr3—O4	1.964 (2)	C1—C2'	1.522 (7)
Cr3—O10	1.975 (2)	C1—C2	1.525 (7)
Cr3—O1	1.978 (2)	C2—H2A	0.9900
Cr3—O12	1.984 (2)	C2—H2B	0.9900
Cr3—O3w	2.013 (3)	C2'—H2C	0.9900
Cl1—C2	1.741 (8)	C2'—H2D	0.9900
Cl1'—C2'	1.738 (8)	C3—C4	1.507 (4)
Cl2—C4	1.772 (3)	C4—H4A	0.9900
Cl3—C6	1.763 (4)	C4—H4B	0.9900
Cl4—C8	1.762 (4)	C5—C6	1.508 (5)
Cl4'—C8	1.745 (8)	C6—H6A	0.9900
Cl5'—C10	1.770 (8)	C6—H6B	0.9900
Cl6—C12	1.742 (11)	C7—C8	1.507 (4)
Cl6'—C12'	1.744 (12)	C8—H8A	0.9900
Cl6"—C12"	1.741 (13)	C8—H8B	0.9900
O1—C1	1.252 (4)	C8—H8C	0.9900
O2—C1	1.236 (5)	C8—H8D	0.9900
O3—C3	1.247 (4)	C9—C10	1.518 (4)
O4—C3	1.254 (4)	C10—H10A	0.9900
O5—C5	1.247 (4)	C10—H10B	0.9900
O6—C5	1.255 (4)	C10—H10C	0.9900
O7—C7	1.258 (4)	C10—H10D	0.9900
O8—C7	1.242 (4)	C11—C12	1.517 (7)
O9—C9	1.246 (4)	C11—C12'	1.518 (8)
O10—C9	1.244 (4)	C11—C12"	1.518 (10)
O11—C11	1.243 (5)	C12—H12A	0.9900
O12—C11	1.249 (4)	C12—H12B	0.9900
O14—N1	1.233 (4)	C12'—H12C	0.9900
O15—N1	1.230 (4)	C12'—H12D	0.9900
O16—N1	1.234 (4)	C12"—H12E	0.9900
O1w—H11	0.84 (4)	C12"—H12F	0.9900

O13—Cr1—O2	95.69 (10)	C1—C2—Cl1	121.0 (6)
O13—Cr1—O3	93.62 (9)	C1—C2—H2A	107.1
O2—Cr1—O3	90.71 (11)	Cl1—C2—H2A	107.1
O13—Cr1—O5	96.24 (10)	C1—C2—H2B	107.1
O2—Cr1—O5	168.02 (10)	Cl1—C2—H2B	107.1
O3—Cr1—O5	89.64 (11)	H2A—C2—H2B	106.8
O13—Cr1—O7	94.29 (9)	C1—C2'—Cl1'	108.6 (5)
O2—Cr1—O7	86.43 (11)	C1—C2'—H2C	110.0
O3—Cr1—O7	171.82 (9)	Cl1'—C2'—H2C	110.0
O5—Cr1—O7	91.58 (11)	C1—C2'—H2D	110.0
O13—Cr1—O1w	177.12 (12)	Cl1'—C2'—H2D	110.0
O2—Cr1—O1w	81.71 (13)	H2C—C2'—H2D	108.3
O3—Cr1—O1w	85.20 (10)	O3—C3—O4	127.1 (3)
O5—Cr1—O1w	86.39 (12)	O3—C3—C4	119.6 (3)
O7—Cr1—O1w	86.81 (10)	O4—C3—C4	113.2 (3)
O13—Cr2—O11	94.36 (11)	C3—C4—Cl2	114.1 (2)
O13—Cr2—O6	96.91 (10)	C3—C4—H4A	108.7
O11—Cr2—O6	168.71 (11)	Cl2—C4—H4A	108.7
O13—Cr2—O8	92.98 (9)	C3—C4—H4B	108.7
O11—Cr2—O8	87.27 (11)	Cl2—C4—H4B	108.7
O6—Cr2—O8	91.41 (11)	H4A—C4—H4B	107.6
O13—Cr2—O9	95.36 (9)	O5—C5—O6	126.6 (3)
O11—Cr2—O9	93.14 (11)	O5—C5—C6	120.1 (3)
O6—Cr2—O9	86.55 (11)	O6—C5—C6	113.3 (3)
O8—Cr2—O9	171.60 (10)	C5—C6—Cl3	114.4 (3)
O13—Cr2—O2w	177.32 (10)	C5—C6—H6A	108.7
O11—Cr2—O2w	83.58 (11)	Cl3—C6—H6A	108.7
O6—Cr2—O2w	85.14 (10)	C5—C6—H6B	108.7
O8—Cr2—O2w	85.22 (10)	Cl3—C6—H6B	108.7
O9—Cr2—O2w	86.48 (10)	H6A—C6—H6B	107.6
O13—Cr3—O4	93.39 (10)	O8—C7—O7	126.9 (3)
O13—Cr3—O10	95.01 (10)	O8—C7—C8	118.4 (3)
O4—Cr3—O10	88.96 (11)	O7—C7—C8	114.7 (3)
O13—Cr3—O1	96.30 (10)	C7—C8—Cl4'	114.3 (4)
O4—Cr3—O1	91.39 (11)	C7—C8—Cl4	113.0 (2)
O10—Cr3—O1	168.65 (11)	C7—C8—H8A	109.0
O13—Cr3—O12	94.62 (10)	Cl4—C8—H8A	109.0
O4—Cr3—O12	171.88 (11)	C7—C8—H8B	109.0
O10—Cr3—O12	91.67 (11)	Cl4—C8—H8B	109.0
O1—Cr3—O12	86.40 (10)	H8A—C8—H8B	107.8
O13—Cr3—O3w	178.83 (10)	C7—C8—H8C	108.0
O4—Cr3—O3w	85.83 (11)	C7—C8—H8D	108.8
O10—Cr3—O3w	85.86 (11)	H8C—C8—H8D	107.8
O1—Cr3—O3w	82.86 (11)	O10—C9—O9	127.4 (3)
O12—Cr3—O3w	86.14 (11)	O10—C9—C10	113.8 (3)
C1—O1—Cr3	130.9 (3)	O9—C9—C10	118.8 (3)
C1—O2—Cr1	134.1 (2)	C9—C10—Cl5'	110.9 (8)
C3—O3—Cr1	131.5 (2)	C9—C10—H10A	109.4
C3—O4—Cr3	132.8 (2)	Cl5'—C10—H10A	109.5
C5—O5—Cr1	133.3 (2)	C9—C10—H10B	109.4
C5—O6—Cr2	131.1 (2)	Cl5'—C10—H10B	109.4
C7—O7—Cr1	129.0 (2)	H10A—C10—H10B	108.0
C7—O8—Cr2	134.6 (2)	C9—C10—H10C	107.1
C9—O9—Cr2	129.6 (2)	C9—C10—H10D	109.3
C9—O10—Cr3	133.6 (2)	H10C—C10—H10D	107.3
C11—O11—Cr2	134.1 (2)	O11—C11—O12	126.9 (3)
C11—O12—Cr3	129.5 (3)	O11—C11—C12	112.6 (5)
Cr2—O13—Cr1	119.84 (12)	O12—C11—C12	120.5 (5)
Cr2—O13—Cr3	119.75 (11)	O11—C11—C12'	109.3 (5)
Cr1—O13—Cr3	120.41 (11)	O12—C11—C12'	123.4 (6)
Cr1—O1w—H11	130 (3)	O11—C11—C12"	130.6 (7)
Cr1—O1w—H12	120 (3)	O12—C11—C12"	102.2 (7)
H11—O1w—H12	110 (4)	C11—C12—Cl6	113.9 (6)
Cr2—O2w—H21	124 (3)	C11—C12—H12A	108.8
Cr2—O2w—H22	118 (3)	Cl6—C12—H12A	108.8
H21—O2w—H22	108 (4)	C11—C12—H12B	108.8
Cr3—O3w—H31	113 (3)	Cl6—C12—H12B	108.8
Cr3—O3w—H32	128 (3)	H12A—C12—H12B	107.7
H31—O3w—H32	110 (4)	C11—C12'—Cl6'	113.2 (7)
H41—O4w—H42	108 (5)	C11—C12'—H12C	108.9
H51—O5w—H52	108 (6)	Cl6'—C12'—H12C	108.9
H61—O6w—H62	110 (4)	C11—C12'—H12D	108.9
H71—O7w—H72	110	Cl6'—C12'—H12D	108.9
O15—N1—O14	118.7 (4)	H12C—C12'—H12D	107.8
O15—N1—O16	120.7 (3)	C11—C12"—Cl6"	106.6 (8)
O14—N1—O16	120.5 (4)	C11—C12"—H12E	110.4
O2—C1—O1	126.9 (3)	Cl6"—C12"—H12E	110.4
O2—C1—C2'	104.2 (4)	C11—C12"—H12F	110.4
O1—C1—C2'	128.9 (5)	Cl6"—C12"—H12F	110.4
O2—C1—C2	121.9 (4)	H12E—C12"—H12F	108.6
O1—C1—C2	111.2 (5)

O13—Cr3—O1—C1	−23.1 (3)	O5—Cr1—O13—Cr3	139.83 (13)
O4—Cr3—O1—C1	70.4 (3)	O7—Cr1—O13—Cr3	−128.11 (13)
O10—Cr3—O1—C1	162.1 (5)	O4—Cr3—O13—Cr2	131.56 (13)
O12—Cr3—O1—C1	−117.4 (3)	O10—Cr3—O13—Cr2	42.31 (14)
O3w—Cr3—O1—C1	156.1 (3)	O1—Cr3—O13—Cr2	−136.66 (13)
O13—Cr1—O2—C1	18.0 (3)	O12—Cr3—O13—Cr2	−49.78 (14)
O3—Cr1—O2—C1	−75.8 (3)	O4—Cr3—O13—Cr1	−48.53 (14)
O5—Cr1—O2—C1	−167.4 (4)	O10—Cr3—O13—Cr1	−137.78 (13)
O7—Cr1—O2—C1	111.9 (3)	O1—Cr3—O13—Cr1	43.25 (14)
O1w—Cr1—O2—C1	−160.8 (4)	O12—Cr3—O13—Cr1	130.13 (13)
O13—Cr1—O3—C3	−25.9 (3)	Cr1—O2—C1—O1	1.1 (6)
O2—Cr1—O3—C3	69.9 (3)	Cr1—O2—C1—C2'	−179.6 (7)
O5—Cr1—O3—C3	−122.1 (3)	Cr1—O2—C1—C2	−177.3 (8)
O1w—Cr1—O3—C3	151.5 (3)	Cr3—O1—C1—O2	2.1 (5)
O13—Cr3—O4—C3	22.5 (3)	Cr3—O1—C1—C2'	−177.0 (9)
O10—Cr3—O4—C3	117.5 (3)	Cr3—O1—C1—C2	−179.3 (7)
O1—Cr3—O4—C3	−73.9 (3)	O2—C1—C2—Cl1	−156.9 (7)
O3w—Cr3—O4—C3	−156.6 (3)	O1—C1—C2—Cl1	24.5 (13)
O13—Cr1—O5—C5	17.5 (3)	C2'—C1—C2—Cl1	−150 (5)
O2—Cr1—O5—C5	−157.2 (5)	O2—C1—C2'—Cl1'	171.1 (7)
O3—Cr1—O5—C5	111.1 (3)	O1—C1—C2'—Cl1'	−9.6 (14)
O7—Cr1—O5—C5	−77.0 (3)	C2—C1—C2'—Cl1'	−2 (3)
O1w—Cr1—O5—C5	−163.7 (3)	Cr1—O3—C3—O4	3.7 (5)
O13—Cr2—O6—C5	−27.7 (3)	Cr1—O3—C3—C4	−178.5 (2)
O11—Cr2—O6—C5	148.5 (5)	Cr3—O4—C3—O3	−1.6 (6)
O8—Cr2—O6—C5	65.4 (3)	Cr3—O4—C3—C4	−179.5 (2)
O9—Cr2—O6—C5	−122.7 (3)	O3—C3—C4—Cl2	16.3 (4)
O2w—Cr2—O6—C5	150.5 (3)	O4—C3—C4—Cl2	−165.7 (3)
O13—Cr1—O7—C7	−25.0 (3)	Cr1—O5—C5—O6	−1.5 (5)
O2—Cr1—O7—C7	−120.4 (3)	Cr1—O5—C5—C6	179.5 (2)
O5—Cr1—O7—C7	71.4 (3)	Cr2—O6—C5—O5	7.9 (5)
O1w—Cr1—O7—C7	157.7 (3)	Cr2—O6—C5—C6	−173.1 (2)
O13—Cr2—O8—C7	14.9 (4)	O5—C5—C6—Cl3	−10.9 (4)
O11—Cr2—O8—C7	109.2 (4)	O6—C5—C6—Cl3	170.0 (2)
O6—Cr2—O8—C7	−82.1 (4)	Cr2—O8—C7—O7	10.5 (6)
O2w—Cr2—O8—C7	−167.1 (4)	Cr2—O8—C7—C8	−170.1 (3)
O13—Cr2—O9—C9	30.3 (3)	Cr1—O7—C7—O8	−3.9 (6)
O11—Cr2—O9—C9	−64.4 (3)	Cr1—O7—C7—C8	176.8 (2)
O6—Cr2—O9—C9	126.9 (3)	O8—C7—C8—Cl4'	−8.4 (14)
O2w—Cr2—O9—C9	−147.8 (3)	O7—C7—C8—Cl4'	171.0 (14)
O13—Cr3—O10—C9	−11.4 (3)	O8—C7—C8—Cl4	17.8 (6)
O4—Cr3—O10—C9	−104.7 (3)	O7—C7—C8—Cl4	−162.8 (4)
O1—Cr3—O10—C9	163.4 (5)	Cr3—O10—C9—O9	−7.9 (6)
O12—Cr3—O10—C9	83.4 (3)	Cr3—O10—C9—C10	174.4 (3)
O3w—Cr3—O10—C9	169.4 (3)	Cr2—O9—C9—O10	−4.0 (5)
O13—Cr2—O11—C11	−10.5 (3)	Cr2—O9—C9—C10	173.5 (3)
O6—Cr2—O11—C11	173.2 (5)	O10—C9—C10—Cl5'	−149.7 (16)
O8—Cr2—O11—C11	−103.3 (3)	O9—C9—C10—Cl5'	32.4 (16)
O9—Cr2—O11—C11	85.1 (3)	Cr2—O11—C11—O12	−14.5 (6)
O2w—Cr2—O11—C11	171.2 (3)	Cr2—O11—C11—C12	166.4 (14)
O13—Cr3—O12—C11	25.2 (3)	Cr2—O11—C11—C12'	158 (2)
O10—Cr3—O12—C11	−70.0 (3)	Cr2—O11—C11—C12"	173 (3)
O1—Cr3—O12—C11	121.2 (3)	Cr3—O12—C11—O11	4.9 (5)
O3w—Cr3—O12—C11	−155.7 (3)	Cr3—O12—C11—C12	−176.1 (15)
O11—Cr2—O13—Cr1	−135.27 (13)	Cr3—O12—C11—C12'	−166 (2)
O6—Cr2—O13—Cr1	44.00 (14)	Cr3—O12—C11—C12"	179 (2)
O8—Cr2—O13—Cr1	−47.79 (14)	O11—C11—C12—Cl6	156.8 (13)
O9—Cr2—O13—Cr1	131.16 (13)	O12—C11—C12—Cl6	−22 (2)
O11—Cr2—O13—Cr3	44.64 (14)	C12'—C11—C12—Cl6	−134 (12)
O6—Cr2—O13—Cr3	−136.09 (13)	C12"—C11—C12—Cl6	−8 (7)
O8—Cr2—O13—Cr3	132.12 (14)	O11—C11—C12'—Cl6'	−172 (2)
O9—Cr2—O13—Cr3	−48.93 (14)	O12—C11—C12'—Cl6'	1 (4)
O2—Cr1—O13—Cr2	138.63 (13)	C12—C11—C12'—Cl6'	74 (8)
O3—Cr1—O13—Cr2	−130.29 (13)	C12"—C11—C12'—Cl6'	36 (5)
O5—Cr1—O13—Cr2	−40.26 (14)	O11—C11—C12"—Cl6"	−5 (4)
O7—Cr1—O13—Cr2	51.80 (14)	O12—C11—C12"—Cl6"	−179 (2)
O2—Cr1—O13—Cr3	−41.28 (14)	C12—C11—C12"—Cl6"	14 (6)
O3—Cr1—O13—Cr3	49.80 (14)	C12'—C11—C12"—Cl6"	31 (5)

Hydrogen-bond geometry (Å, º) top

D—H···A	D—H	H···A	D···A	D—H···A
O1w—H11···O5wⁱ	0.84 (4)	1.83 (2)	2.616 (6)	157 (5)
O1w—H12···O6wⁱⁱ	0.84 (3)	1.99 (3)	2.816 (4)	169 (5)
O2w—H21···O15ⁱⁱⁱ	0.84 (3)	1.90 (3)	2.732 (4)	170 (4)
O2w—H22···CL5′^iv	0.84 (3)	2.75 (3)	3.295 (6)	124 (6)
O3w—H31···O4w	0.84 (1)	1.84 (2)	2.669 (4)	168 (5)
O3w—H32···O6w	0.84 (3)	1.88 (3)	2.711 (4)	171 (4)
O4w—H41···O7^v	0.85 (5)	2.20 (5)	3.046 (4)	175 (5)
O4w—H42···O16ⁱⁱ	0.83 (4)	2.27 (4)	2.976 (5)	142 (6)
O5w—H51···O7w	0.85 (4)	2.06 (7)	2.79 (1)	144 (11)
O5w—H52···O12	0.85 (7)	2.47 (7)	3.27 (1)	156 (10)
O6w—H61···O14	0.83 (4)	2.31 (2)	3.093 (6)	158 (5)
O6w—H62···O7w	0.85 (4)	2.15 (3)	2.86 (1)	141 (4)

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

Experimental details

Crystal data
Chemical formula	[Cr₃(C₂H₂ClO₂)₆O(H₂O)₃]NO₃·3.5H₂O
M_r	912.03
Crystal system, space group	Monoclinic, P2₁/c
Temperature (K)	100
a, b, c (Å)	12.4938 (2), 14.7622 (2), 17.2687 (3)
β (°)	96.293 (1)
V (Å³)	3165.78 (9)
Z	4
Radiation type	Mo Kα
µ (mm⁻¹)	1.61
Crystal size (mm)	0.12 × 0.06 × 0.03

Data collection
Diffractometer	Bruker SMART APEX CCD area-detector diffractometer
Absorption correction	Multi-scan (SADABS; Sheldrick, 1996)
T_min, T_max	0.820, 0.953
No. of measured, independent and observed [I > 2σ(I)] reflections	39914, 7271, 5349
R_int	0.053
(sin θ/λ)_max (Å⁻¹)	0.650

Refinement
R[F² > 2σ(F²)], wR(F²), S	0.040, 0.112, 1.03
No. of reflections	7271
No. of parameters	500
No. of restraints	119
H-atom treatment	H atoms treated by a mixture of independent and constrained refinement
Δρ_max, Δρ_min (e Å⁻³)	0.99, −0.34

Computer programs: APEX2 (Bruker, 2007), SAINT (Bruker, 2007), SAINT, SHELXS97 (Sheldrick, 2008), SHELXL97 (Sheldrick, 2008), X-SEED (Barbour, 2001), publCIF (Westrip, 2008).

Hydrogen-bond geometry (Å, º) top

D—H···A	D—H	H···A	D···A	D—H···A
O1w—H11···O5wⁱ	0.84 (4)	1.83 (2)	2.616 (6)	157 (5)
O1w—H12···O6wⁱⁱ	0.84 (3)	1.99 (3)	2.816 (4)	169 (5)
O2w—H21···O15ⁱⁱⁱ	0.84 (3)	1.90 (3)	2.732 (4)	170 (4)
O2w—H22···CL5'^iv	0.84 (3)	2.75 (3)	3.295 (6)	124 (6)
O3w—H31···O4w	0.844 (14)	1.84 (2)	2.669 (4)	168 (5)
O3w—H32···O6w	0.84 (3)	1.88 (3)	2.711 (4)	171 (4)
O4w—H41···O7^v	0.85 (5)	2.20 (5)	3.046 (4)	175 (5)
O4w—H42···O16ⁱⁱ	0.83 (4)	2.27 (4)	2.976 (5)	142 (6)
O5w—H51···O7w	0.85 (4)	2.06 (7)	2.79 (1)	144 (11)
O5w—H52···O12	0.85 (7)	2.47 (7)	3.27 (1)	156 (10)
O6w—H61···O14	0.83 (4)	2.31 (2)	3.093 (6)	158 (5)
O6w—H62···O7w	0.85 (4)	2.15 (3)	2.86 (1)	141 (4)

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

Acknowledgements

I thank the University of Malaya for supporting this study through the purchase of the diffractometer.

References

Barbour, L. J. (2001). J. Supramol. Chem. 1, 189–191. CrossRef CAS Google Scholar
Bruker (2007). APEX2 and SAINT. Bruker AXS Inc., Madison, Wisconsin, USA. Google Scholar
Glowiak, T., Kubiak, M. & Jezowska-Trzebiatowska, B. (1977). Bull. Acad. Pol. Sci. Ser. Sci. Chim. 25, 359–371. CAS Google Scholar
Sheldrick, G. M. (1996). SADABS. University of Göttingen, Germany. Google Scholar
Sheldrick, G. M. (2008). Acta Cryst. A64, 112–122. Web of Science CrossRef CAS IUCr Journals Google Scholar
Westrip, S. P. (2008). publCIF. In preparation. Google Scholar

This is an open-access article distributed under the terms of the Creative Commons Attribution (CC-BY) Licence, which permits unrestricted use, distribution, and reproduction in any medium, provided the original authors and source are cited.