ربيطة
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الربيطة بالإنجليزية: Ligand في الكيمياء عبارة عن ذرة أو أيون (شاردة) أو جزيء مرتبط بذرة الفلز المركزية في المعقدات التساندية.
تتشكل الرابطة بين الفلز والربيطة عادة بأن تقوم الربيطة بمنح زوج أو أكثر من الإلكترونات إلى ذرة الفلز، أي تنشأ رابطة تساندية بين الربيطة والفلز.
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أمثلة لربيطات شائعة (حسب قوة المجال)
In the following table the ligands are sorted by field strength (weak field ligands first):
| الربيطة | الصيغة (الذرة الرابطة بخط عريض) | الشحنة | Most common denticity | تعليق |
|---|---|---|---|---|
| يوديد (iodo) | I− | monoanionic | monodentate | |
| بروميد (bromo) | Br− | monoanionic | monodentate | |
| Sulfide (thio or less commonly "bridging thiolate") | S2− | dianionic | monodentate (M=S), or bidentate bridging (M-S-M') | |
| Thiocyanate (S-thiocyanato) | S-CN− | monoanionic | monodentate | ambidentate (see also isothiocyanate, below) |
| كلوريد (كلورو) | Cl− | monoanionic | monodentate | also found bridging |
| نيترات (نيتراتو) | O-NO2− | monoanionic | monodentate | |
| أزيد (azido) | N-N2− | monoanionic | monodentate | |
| فلوريد (فلوريدو) | F− | monoanionic | monodentate | |
| هيدروكسيد (hydroxo) | O-H− | monoanionic | monodentate | often found as a bridging ligand |
| اوكسالات (oxalato) | [O-C(=O)-C(=O)-O]2− | dianionic | bidentate | |
| ماء (aqua) | H-O-H | neutral | monodentate | monodentate |
| نيتريت (nitrito) | O-N-O− | monoanionic | monodentate | ambidentate (see also nitro) |
| Isothiocyanate (isothiocyanato) | N=C=S− | monoanionic | monodentate | ambidentate (see also thiocyanate, above) |
| Acetonitrile (acetonitrilo) | CH3CN | neutral | monodentate | |
| Pyridine (pyridino) | C5H5N | neutral | monodentate | |
| أمونيا (ammine or less commonly "ammino") | NH3 | neutral | monodentate | |
| Ethylenediamine | en | neutral | bidentate | |
| 2,2'-Bipyridine | bipy | neutral | bidentate | easily reduced to its (radical) anion or even to its dianion |
| 1,10-Phenanthroline | phen | neutral | bidentate | |
| Nitrite (nitro) | N-O2− | monoanionic | monodentate | ambidentate (see also nitrito) |
| Triphenylphosphine | PPh3 | neutral | monodentate | |
| سيانيد (cyano) | CN− | monoanionic | monodentate | can bridge between metals (both metals bound to C, or one to C and one to N) |
| أول أكسيد الكربون (carbonyl) | CO | neutral | monodentate | can bridge between metals (both metals bound to C) |
ربيطات أخرى عامة (أبجدياً)
In this table other common ligands are listed in alphabetical order.
| الربيطة | الصيغة (الذرة الرابطة بخط عريض) | الشحنة | Most common denticity | تعليق |
|---|---|---|---|---|
| Acetonitrile | MeCN | neutral | monodentate | |
| Acetylacetonate (Acac) | CH3-C(O)-CH-C(O)-CH3 | monoanionic | bidentate | In general bidentate, bound through both oxygens, but sometimes bound through the central carbon only, see also analogous ketimine analogues |
| ألكينs | R2C=CR2 | neutral | compounds with a C-C double bond | |
| بنزين | C6H6 | neutral | and other arenes | |
| 1,2-Bis(diphenylphosphino)ethane (dppe) | Ph2PC2H4PPh2 | neutral | bidentate | |
| 1,1-Bis(diphenylphosphino)methane (dppm) | C25H22P2 | neutral | Can bond to 2 metal atoms at once, forming dimers | |
| Corroles | tetradentate | |||
| Crown ethers | neutral | primarily for alkali and alkaline earth metal cations | ||
| 2,2,2-crypt | hexadentate | primarily for alkali and alkaline earth metal cations | ||
| Cryptates | neutral | |||
| Cyclopentadienyl (Cp) | [C5H5]− | monoanionic | ||
| Diethylenetriamine (dien) | C4H13N3 | neutral | tridentate | related to TACN, but not constrained to facial complexation |
| Dimethylglyoximate (dmgH−) | monoanionic | |||
| Ethylenediaminetetraacetate (EDTA) | tetra-anionic | hexadentate | actual ligand is the tetra-anion | |
| Ethylenediaminetriacetate | trianionic | pentadentate | actual ligand is the trianion | |
| glycinate (Glycinato) | monoanionic | bidentate | other α-amino acid anions are comparable (but chiral) | |
| Heme | dianionic | tetradentate | macrocyclic ligand | |
| Nitrosyl | NO+ | cationic | bent (1e) and linear (3e) bonding mode | |
| Pyrazine | N2C4H4 | neutral | ditopic | sometimes bridging |
| Scorpionate ligand | tridentate | |||
| Sulfite | monoanionic | monodentate | ambidentate | |
| 2,2',5',2-Terpyridine (terpy) | neutral | tridentate | meridional bonding only | |
| Triazacyclononane (tacn) | (C2H4)3(NR)3 | neutral | tridentate | macrocyclic ligand see also the N,N',N"-trimethylated analogue |
| Tricyclohexylphosphine | (C6H11)3P or (PCy3) | neutral | monodentate | |
| Triethylenetetramine (trien) | neutral | tetradentate | ||
| Trimethylphosphine | PMe3 | neutral | monodentate | |
| Tri(o-tolyl)phosphine | P(o-tolyl)3 | neutral | monodentate | |
| Tris(2-aminoethyl)amine (tren) | (NH2CH2CH2)3N | neutral | tetradentate | |
| Tris(2-diphenylphosphineethyl)amine (np3) | neutral | tetradentate | ||
| Terpyridine | C15H11N3 | neutral | tridentate | |
| Tropylium | C7H7+ | cationic |
تبادل الربيطات
Ligand exchange (also ligand substitution) is a type of chemical reaction in which one ligand in a chemical compound is replaced by another ligand. In organometallic chemistry this can take place by associative substitution or by dissociative substitution.
انظر أيضاً
- Crystal field theory
- Ligand field theory
- كيمياء المعقدات
- كيمياء غير عضوية
- Tanabe-Sugano diagram
- Spectrochemical series
