Urea adducts explained

Urea can crystallise with other compounds. These can be called urea adducts or if a solvent is involved, a urea solvate, and the process is called urea extraction crystallization. Urea can also be a neutral ligand if it is coordinated to a central metal atom. Urea can form hydrogen bonds to other oxygen and nitrogen atoms in the substance it crystallises with. This stiffens the solid and raises the melting point.^[1] T

List

name	formula	ratiourea:solute	crystal system	space group	unit cell	volume	density	comment	reference
hydrogen peroxide; urea (1:1)	HOOH•CH4N2O	1:1	orthorhombic	Pnca	a 6.732 b 4.8207 c 12.873 Z=4			decomposes slowly at room temperature	^[2]
urea; acetic acid (1:2)	2CH3COOH•CH4N2O	1:2	monoclinic	P21/n	a 7.6549 b 10.1351 c 11.5219 β 99.570° Z=4	881.47	1.358	unstable in air	^[3]
oxalic acid; urea (1:1)	C2H2O4•CH4N2O	1:1	monoclinic	C2/c	a 13.0625 b 6.6437 c 6.8478 β 92.474°				^[4]
oxalic acid; urea (1:2)	C2H2O4•2CH4N2O	2:1	monoclinic	P2/c	a 5.058 b 12.400 c 6.964 β 98.13°				^[5]
Urea - N,N-dimethylformamide (3:1)	3CH4N2O·C3H7NO	3:1	triclinic	P	a = 7.525 b = 9.866 c = 10.821 α = 65.61° β = 79.43° γ = 70.76° Z=2	689.7	1.219	colourless @150K	^[6]
N,N-dimethylacetamide; urea (1:1)	C4H9NO·CH4N2O	1:1	monoclinic	C2/c	a = 7.2770 b = 17.5394 c = 7.3789 β = 119.450° Z=4	820.11	1.192	colourless @120K	^[7]
Urea malonic acid		1:1	monoclinic	P2/c	a 13.091 b 5.455 c 9.933 β 104.39°				^[8]
Maleic acid; urea (1:1)		1:1	monoclinic	Cc	a 5.144 b 9.999 c 14.80 β 95.1°				^[9]
Succinic acid bis urea		2:1	monoclinic	P21/c	a 5.637 b 8.243 c 12.262 β 96.75° Z=2	565.81	1.41		^[10]
Maleic acid; urea (2:1)		2:1	monoclinic	P21/n	a 5.661 b 11.754 c 19.173 β 91.56°
Fumaric acid; urea (1:2)		1:2	monoclinic	P21/c	a 5.540 b 8.227 c 12.426 β 97.22°				^[11]
D-Tartaric		1:1	orthorhombic	P212121	a 17.229 b 9.824 c 5.056 Z=4		1.63	transparent 255 to 1370 nm; SHG 3×KDP	^[12]
DL-Tartaric		1:1	monoclinic	P21	a 7.6973 b 23.3310 c 4.8727 β 100.82°			NLO; transparent from 240 to 1950 nm	^[13]
Gluatric acid bis urea		2:1	monoclinic	C2/c	a 11.954 b 10.932 c 9.078 β 97.86° Z=4				^[14]
Itaconic acid		1:1	monoclinic	P21/c	a 12.71 b 5.2695 c 13.833β 104.78°				^[15]
2-bromotetradecane urea			hexagonal	P6122	a=8.2582 c=10.9937			298K	^[16]
2-bromotetradecane urea			orthorhombic	C2221				207K
2-bromotetradecane urea			monoclinic	P21	a 16.338(1)Å b 10.9665(8)Å c 16.338(1)Å, α 90° β 60.00°
4-amino benzoic acid; urea (2:1)	(C7H7NO2)2(CH4N2O)	1:2	orthorhombic	Pnab	a=7.4159 b=11.870 c=18.750				^[17]
salicylic acid; urea (1:1)		1:1	monoclinic	C2/c	a=22.206 b=5.108 c=17.177 β=106.18 Z=8°		1.407		^[18]
5-nitro salicylic acid; urea (2:1)	(C7H5NO5)2(CH4N2O)	1:2	triclinic	P	a=6.9889 b=12.1968 c=12.3622 α=60.923° β=81.169° γ=76.938°
3,5-dinitro salicylic acid; urea (1:1)	(C7H4N2O7)(CH4N2O)	1:1	monoclinic	P21/c	a=4.942 b=22.337 c=10.389 β=100.92°
o-phthalic acid; urea (1:1)		1:1	triclinic	P	a=7.422 b=7.662 c=10.088 α=85.95° β=82.01° γ=65.14°
urea : 1,4-dioxane (1 : 1)	C4H8O2•C3H6O	1:1	monoclinic	P2/c	a=6.7949 b=4.5234 c=12.2711 β=95.701° Z=2
urea : morpholine (1 : 1)	C4H8ON•C3H6O	1:1	orthorhombic	Pbcm	a=4.5847 b=19.131 c=8.9047 Z=4
3,5-dimethylpyridine bis(urea)	(CH3)2C5H3N•2C3H6O	2:1	orthorhombic	Abm2	a=21.737 b=7.2102 c=15.590 Z=8	2443.4	1.236	at 173K	^[19]
3,5-dimethylpyridine bis(urea)	(CH3)2C5H3N•2C3H6O	2:1	monoclinic	Cc	a=8.5829 b=21.4843 c=7.2050 β=114.405° Z=4	1209.87	1.248	at 100K
2,6-dimethylpyridine urea	(CH3)2C5H3N•C3H6O	1:1	triclinic	P	a=7.4126 b=7.6720 c=8.1731 α=88.391° β=83.564° γ=80.059° Z=2	454.92	1.221	at 100K
urea 2,6-dimethylpyridine	(CH3)2C5H3N•C3H6O	1:1	monoclinic	C2/c	a=1.426 b=11.1168 c=7.4318 β=101.23° Z=4	925.9	1.200	at 200K
2,6-dimethylpyridine bis(urea)	(CH3)2C5H3N•2C3H6O	2:1	orthorhombic	Pnma	a=8.0772 b=7.2986 c=20.4169 Z=4	1203.64	1.254	at 100K
2,6-dimethylpyridine bis(urea)	(CH3)2C5H3N•2C3H6O	2:1	monoclinic	C2/c	a=11.160 b=11.5421 c=10.910 β=116.12°
2-picoline; urea (1:1)	C6H7N·CH4N2O	1:1	orthorhombic	Pbca	a = 7.471 b = 14.916 c = 15.338 Z = 8	1709.2			^[20]
Urea pyrazine-2,3-dicarboxylic acid		1:1	monoclinic	P21/n	a=7.725 b=10.2530 c=12.612 β=97.997°
bipyridine urea			triclinic	P	a=7.200 b=8.297 c=9.835 α=75.849° β=70.744° γ =73.045°				^[21]
bipyridine urea			triclinic	P	a=7.2862 b=8.3747 c=9.8647 α=76.061° β=72.789° γ=74.121°
1,10-Phenanthroline urea		1:1	monoclinic	C2/c	a=14.342 b=12.002 c=7.3724 β 116.743°
2,9-Dimethyl-1,10-phenanthroline urea		1:1	orthorhombic	Cmcm	a=11.370 b=17.351 c=7.3593
sodium chloride; urea; water (1:1:1)	NaCl·CH4N2O·H2O	1:1	triclinic		a = 6.44 Å, b = 5.245Å, c = 17.312 Å, and a=90°, β=90.15°, γ=90°	588.76		SHG 1.53 × KDP, birefringence 0.084@1064 nm UV edge 209 nm	^[22] ^[23]
Bis(2-3-isopropyl-7-oxocyclohepta-1,3,5-trien-1-olato)bis[(3-isopropyl-7-oxocyclohepta-1,3,5-trien-1-olato)copper(II)]-urea-acetone (1/6/2)	[Cu<sub>2</sub>(C<sub>10</sub>H<sub>11</sub>O<sub>2</sub>)<sub>4</sub>]·6CH4N2O·2C3H6O	5:1	monoclinic	P21/c	a 17.0125 b 11.0470 c 17.2731 β 110.385° Z=2	3042.95	1.371	green	^[24]
aqua(N-salicylidene-rac-alaninato- O,N,O')copper(II)-urea (1/1)		1:1	triclinic	P	a = 7.637, b = 8.509 c = 10.716 α = 93.10° β = 97.97° γ= 106.37° Z= 2,	658.5		blue	^[25]
Aqua[9-(1,8-diazafluoren-9-ylidene)amino-1,8-diazafluorenato]hydroxo(urea)zinc(II) urea solvate	[Zn(C<sub>22</sub>H<sub>12</sub>N<sub>5</sub>)(OH)(CH<sub>4</sub>N<sub>2</sub>O)(H<sub>2</sub>O)]•C4N2O	1:1	monoclinic	P21/c	a 7.8637 b 16.0133 c 17.9513 β 101.358° Z=4	2216.2	1.687	purple	^[26]
Pentakis(carbamide)dioxoneptunium(V) nitrate	[NpO<sub>2</sub>{OC(NH<sub>2</sub>)<sub>2</sub>}<sub>5</sub>](NO3)		monoclinic	P21	a = 11.142, b = 7.6379 c = 11.143 β = 108.9° Z = 2	897.1			^[27]
Bis[(isothiocyanato)tetraureadioxoneptunium(V)] urea	2 · OC(NH2)2		tetragonal	P43212	a=7.851 c=56.84 Z=4	3504	2.265	light green	^[28]

Notes and References

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