# Urea adducts

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. T

## List

| name | formula | ratio urea: solute | crystal system | space group | unit cell | volume | density | comment |
| hydrogen peroxide; urea (1:1) | HOOH•CH$_4$N$_2$O | 1:1 | orthorhombic | Pnca | a 6.732 b 4.8207 c 12.873 Z=4 | | | decomposes slowly at room temperature |
| urea; acetic acid (1:2) | 2CH$_3$COOH•CH$_4$N$_2$O | 1:2 | monoclinic | P2$_1$/n | a 7.6549 b 10.1351 c 11.5219 β 99.570° Z=4 | 881.47 | 1.358 | unstable in air |
| oxalic acid; urea (1:1) | C$_2$H$_2$O$_4$•CH$_4$N$_2$O | 1:1 | monoclinic | C2/c | a 13.0625 b 6.6437 c 6.8478 β 92.474° | | | |
| oxalic acid; urea (1:2) | C$_2$H$_2$O$_4$•2CH$_4$N$_2$O | 2:1 | monoclinic | P2/c | a 5.058 b 12.400 c 6.964 β 98.13° | | | |
| Urea - N,N-dimethylformamide (3:1) | 3CH$_4$N$_2$O·C$_3$H$_7$NO | 3:1 | triclinic | P1 | 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 |
| N,N-dimethylacetamide; urea (1:1) | C$_4$H$_9$NO·CH$_4$N$_2$O | 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 |
| Urea malonic acid | | 1:1 | monoclinic | P2/c | a 13.091 b 5.455 c 9.933 β 104.39° | | | |
| Maleic acid; urea (1:1) | | 1:1 | monoclinic | Cc | a 5.144 b 9.999 c 14.80 β 95.1° | | | |
| Succinic acid bis urea | | 2:1 | monoclinic | P2$_1$/c | a 5.637 b 8.243 c 12.262 β 96.75° Z=2 | 565.81 | 1.41 | |
| Maleic acid; urea (2:1) | | 2:1 | monoclinic | P2$_1$/n | a 5.661 b 11.754 c 19.173 β 91.56° | | | |
| Fumaric acid; urea (1:2) | | 1:2 | monoclinic | P2$_1$/c | a 5.540 b 8.227 c 12.426 β 97.22° | | | |
| D-Tartaric | | 1:1 | orthorhombic | P2$_1$2$_1$2$_1$ | a 17.229 b 9.824 c 5.056 Z=4 | | 1.63 | transparent 255 to 1370 nm; SHG 3×KDP |
| DL-Tartaric | | 1:1 | monoclinic | P2$_1$ | a 7.6973 b 23.3310 c 4.8727 β 100.82° | | | NLO; transparent from 240 to 1950 nm |
| Gluatric acid bis urea | | 2:1 | monoclinic | C2/c | a 11.954 b 10.932 c 9.078 β 97.86° Z=4 | | | |
| Itaconic acid | | 1:1 | monoclinic | P2$_1$/c | a 12.71 b 5.2695 c 13.833β 104.78° | | | |
| 2-bromotetradecane urea | | | hexagonal | P6$_1$22 | a=8.2582 c=10.9937 | | | 298K |
| 2-bromotetradecane urea | | | orthorhombic | C222$_1$ | | | | 207K |
| 2-bromotetradecane urea | | | monoclinic | P2$_1$ | 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) | (C$_7$H$_7$NO$_2$)$_2$(CH$_4$N$_2$O) | 1:2 | orthorhombic | Pnab | a=7.4159 b=11.870 c=18.750 | | | |
| 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 | |
| 5-nitro salicylic acid; urea (2:1) | (C$_7$H$_5$NO$_5$)$_2$(CH$_4$N$_2$O) | 1:2 | triclinic | P1 | 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) | (C$_7$H$_4$N$_2$O$_7$)(CH$_4$N$_2$O) | 1:1 | monoclinic | P2$_1$/c | a=4.942 b=22.337 c=10.389 β=100.92° | | | |
| o-phthalic acid; urea (1:1) | | 1:1 | triclinic | P1 | a=7.422 b=7.662 c=10.088 α=85.95° β=82.01° γ=65.14° | | | |
| urea : 1,4-dioxane (1 : 1) | C$_4$H$_8$O$_2$•C$_3$H$_6$O | 1:1 | monoclinic | P2/c | a=6.7949 b=4.5234 c=12.2711 β=95.701° Z=2 | | | |
| urea : morpholine (1 : 1) | C$_4$H$_8$ON•C$_3$H$_6$O | 1:1 | orthorhombic | Pbcm | a=4.5847 b=19.131 c=8.9047 Z=4 | | | |
| 3,5-dimethylpyridine bis(urea) | (CH$_3$)$_2$C$_5$H$_3$N•2C$_3$H$_6$O | 2:1 | orthorhombic | Abm2 | a=21.737 b=7.2102 c=15.590 Z=8 | 2443.4 | 1.236 | at 173K |
| 3,5-dimethylpyridine bis(urea) | (CH$_3$)$_2$C$_5$H$_3$N•2C$_3$H$_6$O | 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 | (CH$_3$)$_2$C$_5$H$_3$N•C$_3$H$_6$O | 1:1 | triclinic | P1 | 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 | (CH$_3$)$_2$C$_5$H$_3$N•C$_3$H$_6$O | 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) | (CH$_3$)$_2$C$_5$H$_3$N•2C$_3$H$_6$O | 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) | (CH$_3$)$_2$C$_5$H$_3$N•2C$_3$H$_6$O | 2:1 | monoclinic | C2/c | a=11.160 b=11.5421 c=10.910 β=116.12° | | | |
| 2-picoline; urea (1:1) | C$_6$H$_7$N·CH$_4$N$_2$O | 1:1 | orthorhombic | Pbca | a = 7.471 b = 14.916 c = 15.338 Z = 8 | 1709.2 | | |
| Urea pyrazine-2,3-dicarboxylic acid | | 1:1 | monoclinic | P2$_1$/n | a=7.725 b=10.2530 c=12.612 β=97.997° | | | |
| bipyridine urea | | | triclinic | P1 | a=7.200 b=8.297 c=9.835 α=75.849° β=70.744° γ =73.045° | | | |
| bipyridine urea | | | triclinic | P1 | 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·CH$_4$N$_2$O·H$_2$O | 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 |
| 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$_2$(C$_{10}$H$_{11}$O$_2$)$_4$]·6CH$_4$N$_2$O·2C$_3$H$_6$O | 5:1 | monoclinic | P2$_1$/c | a 17.0125 b 11.0470 c 17.2731 β 110.385° Z=2 | 3042.95 | 1.371 | green |
| aqua(N-salicylidene-rac-alaninato- O,N,O')copper(II)-urea (1/1) | | 1:1 | triclinic | P1 | a = 7.637, b = 8.509 c = 10.716 α = 93.10° β = 97.97° γ= 106.37° Z= 2, | 658.5 | | blue |
| Aqua[9-(1,8-diazafluoren-9-ylidene)amino-1,8-diazafluorenato]hydroxo(urea)zinc(II) urea solvate | [Zn(C$_{22}$H$_{12}$N$_5$)(OH)(CH$_4$N$_2$O)(H$_2$O)]•C$_4$N$_2$O | 1:1 | monoclinic | P2$_1$/c | a 7.8637 b 16.0133 c 17.9513 β 101.358° Z=4 | 2216.2 | 1.687 | purple |
| Pentakis(carbamide)dioxoneptunium(V) nitrate | [NpO$_2${OC(NH$_2$)$_2$}$_5$](NO$_3$) | | monoclinic | P2$_1$ | a = 11.142, b = 7.6379 c = 11.143 β = 108.9° Z = 2 | 897.1 | | |
| Bis[(isothiocyanato)tetraureadioxoneptunium(V)] urea | {NpO$_2$(NCS)[OC(NH$_2$)$_2$]$_4$}$_2$ · OC(NH$_2$)$_2$ | | tetragonal | P4$_3$2$_1$2 | a=7.851 c=56.84 Z=4 | 3504 | 2.265 | light green |